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1
Cui, Xiaoqin, Edward S. Krebes, and Laurence R. Lines. "Seismic inversion for geologic fractures and fractured media." GEOPHYSICS 82, no. 5 (2017): C145—C161. http://dx.doi.org/10.1190/geo2016-0123.1.
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Amplitude variation with offset (AVO) inversion attempts to use the available surface seismic data to estimate the density, P-wave velocity, and S-wave velocity of the earth model. Under linear slip interface theory, synthetic seismograms for models with fractures prove that fractures are also reflection generators. Consequently, observed reflections are not necessarily due to lithologic variations only, but they could be due in part to the effect of fractures. To obtain approximate equations for AVO inversion for fractured media, denoted by AVO with fracture (AVOF), we derived new equations for PP-wave reflection and transmission coefficients that are based on nonwelded contact boundary conditions. In particular, along with the fracture compliances, azimuth has also been taken into account in the equations because the fractures can have any orientation. The new approximate AVOF equations for a horizontally fractured medium with impedance contrast are developed by simplifying the equations for the new PP-wave reflection and transmission coefficients. In the new approximate AVOF equations, the reflection coefficients are divided into a welded contact part (a conventional impedance contrast part) and a nonwelded contact part (a fracture part). This makes the equations flexible enough to separately invert for the rock properties of the fracture and the background medium in the case of a fractured medium with impedance contrast. The new approximate AVOF equations state that fractures could cause the seismic reflectivity to be frequency dependent, and that the fractures not only influence the wave amplitude but also change the wave phase. The linear least-squares and nonlinear conjugate gradient inversion algorithms are applied to estimate the elastic reflectivity using the new approximate AVOF equations. The inverted results for seismic data for a horizontally fractured medium with impedance contrast are evaluated to find a more accurate delineation of the subsurface rock properties.
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Tsoflias, Georgios P., Jean‐Paul Van Gestel, Paul L. Stoffa, Donald D. Blankenship, and Mrinal Sen. "Vertical fracture detection by exploiting the polarization properties of ground‐penetrating radar signals." GEOPHYSICS 69, no. 3 (2004): 803–10. http://dx.doi.org/10.1190/1.1759466.
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Vertically oriented thin fractures are not always detected by conventional single‐polarization reflection profiling ground‐penetrating radar (GPR) techniques. We study the polarization properties of EM wavefields and suggest multipolarization acquisition surveying to detect the location and azimuth of vertically oriented fractures. We employ analytical solutions, 3D finite‐difference time‐domain modeling, and field measurements of multipolarization GPR data to investigate EM wave transmission through fractured geologic formations. For surface‐based multipolarization GPR measurements across vertical fractures, we observe a phase lead when the incident electric‐field component is oriented perpendicular to the plane of the fracture. This observation is consistent for nonmagnetic geologic environments and allows the determination of vertical fracture location and azimuth based on the presence of a phase difference and a phase lead relationship between varying polarization GPR data.
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Choo, Jinhyun, and Fan Fei. "Phase-field modeling of geologic fracture incorporating pressure-dependence and frictional contact." E3S Web of Conferences 205 (2020): 03004. http://dx.doi.org/10.1051/e3sconf/202020503004.
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Geologic fractures such as joints and faults are central to many problems in energy geotechnics. Notable examples include hydraulic fracturing, injection-induced earthquakes, and geologic carbon storage. Nevertheless, our current capabilities for simulating the development and evolution of geologic fractures in these problems are still insufficient in terms of efficiency and accuracy. Recently, phase-field modeling has emerged as an efficient numerical method for fracture simulation which does not require any algorithm for tracking the geometry of fracture. However, existing phase-field models of fracture neglected two distinct characteristics of geologic fractures, namely, the pressure-dependence and frictional contact. To overcome these limitations, new phase-field models have been developed and described in this paper. The new phase-field models are demonstrably capable of simulating pressure-dependent, frictional fractures propagating in arbitrary directions, which is a notoriously challenging task.
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Sliz, Krzysztof (Kris), and Saleh Al-Dossary. "Seismic attributes and kinematic azimuthal analysis for fracture and stress detection in complex geologic settings." Interpretation 2, no. 1 (2014): SA67—SA75. http://dx.doi.org/10.1190/int-2013-0082.1.
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Fractured rocks can exhibit good reservoir properties and provide high-permeability passages for hydrocarbons. Understanding fracture and stress systems is a key element in successful horizontal drilling and fracking for unconventional reservoir exploration. As a result, there is growing interest in methods that can estimate fracture orientation, density, and style. However, fracture detection using surface seismic data is challenging, and the results are usually ambiguous. Each method has its own strengths and weaknesses and responds to fractures and compressional stress in different ways. A major uncertainty in fracture analysis based on azimuthally variant seismic velocities is caused by interference from structural effects, localized small-scale velocity anomalies, and directional stress. They can induce azimuthal variation in velocity, which can mask the influence on traveltimes caused by the fractures. To overcome these challenges, we focused on a fracture and compressional stress detection methodology using 3D scanning of azimuthally dependent residual moveout volumes constrained by fracture-sensitive seismic attributes. Our workflow was successfully applied to wide-azimuth, highfold land seismic data acquired over a fractured formation in the northern part of Saudi Arabia, where we were able to map 3D zones with a high probability of fractures and differentiate them from areas with higher compressional stress.
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Gardner, W. Payton, Stephen J. Bauer, and Scott Broome. "Investigating Fracture Network Deformation Using Noble Gas Release." Geofluids 2021 (May 19, 2021): 1–16. http://dx.doi.org/10.1155/2021/6697819.
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We investigate deformation mechanics of fracture networks in unsaturated fractured rocks from subsurface conventional detonation using dynamic noble gas measurements and changes in air permeability. We dynamically measured the noble gas isotopic composition and helium exhalation of downhole gas before and after a large subsurface conventional detonation. These noble gas measurements were combined with measurements of the subsurface permeability field from 64 discrete sampling intervals before and after the detonation and subsurface mapping of fractures in borehole walls before well completion. We saw no observable increase in radiogenic noble gas release from either an isotopic composition or a helium exhalation point of view. Large increases in permeability were observed in 13 of 64 discrete sampling intervals. Of the sampling intervals which saw large increases in flow, only two locations did not have preexisting fractures mapped at the site. Given the lack of noble gas release and a clear increase in permeability, we infer that most of the strain accommodation of the fractured media occurred along previously existing fractures, rather than the creation of new fractures, even for a high strain rate event. These results have significant implications for how we conceptualize the deformation of rocks with fracture networks above the percolation threshold, with application to a variety of geologic and geological engineering problems.
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Selvadurai, A. P. S., A. P. Suvorov, and P. A. Selvadurai. "Thermo-hydro-mechanical processes in fractured rock formations during a glacial advance." Geoscientific Model Development 8, no. 7 (2015): 2167–85. http://dx.doi.org/10.5194/gmd-8-2167-2015.
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Abstract. The paper examines the coupled thermo-hydro-mechanical (THM) processes that develop in a fractured rock region within a fluid-saturated rock mass due to loads imposed by an advancing glacier. This scenario needs to be examined in order to assess the suitability of potential sites for the location of deep geologic repositories for the storage of high-level nuclear waste. The THM processes are examined using a computational multiphysics approach that takes into account thermo-poroelasticity of the intact geological formation and the presence of a system of sessile but hydraulically interacting fractures (fracture zones). The modelling considers coupled thermo-hydro-mechanical effects in both the intact rock and the fracture zones due to contact normal stresses and fluid pressure at the base of the advancing glacier. Computational modelling provides an assessment of the role of fractures in modifying the pore pressure generation within the entire rock mass.
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Selvadurai, A. P. S., A. P. Suvorov, and P. A. Selvadurai. "Thermo-hydro-mechanical processes in fractured rock formations during glacial advance." Geoscientific Model Development Discussions 7, no. 6 (2014): 7351–94. http://dx.doi.org/10.5194/gmdd-7-7351-2014.
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Abstract. The paper examines the coupled thermo-hydro-mechanical (THM) processes that develop in a fractured rock region within a fluid-saturated rock mass due to loads imposed by an advancing glacier. This scenario needs to be examined in order to assess the suitability of potential sites for the location of deep geologic repositories for the storage of high-level nuclear waste. The THM processes are examined using a computational multiphysics approach that takes into account thermo-poroelasticity of the intact geological formation and the presence of a system of sessile but hydraulically interacting fractures (fracture zones). The modeling considers coupled thermo-hydro-mechanical effects in both the intact rock and the fracture zones due to contact normal stresses and fluid pressure at the base of the advancing glacier. Computational modelling provides an assessment of the role of fractures that can modify the pore pressure generation within the entire rock mass.
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Huang, Jixiang, Joseph P. Morris, Pengcheng Fu, Randolph R. Settgast, Christopher S. Sherman, and Frederick J. Ryerson. "Hydraulic-Fracture-Height Growth Under the Combined Influence of Stress Barriers and Natural Fractures." SPE Journal 24, no. 01 (2018): 302–18. http://dx.doi.org/10.2118/189861-pa.
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Summary A fully coupled finite-element/finite-volume code is used to model 3D hydraulically driven fractures under the influence of strong vertical variations in closure stress interacting with natural fractures. Previously unknown 3D interaction mechanisms on fracture-height growth are revealed. Slipping of a natural fracture, triggered by elevated fluid pressure from an intersecting hydraulic fracture, can induce both increases and decreases of normal stress in the minimum-horizontal-stress direction, toward the center and tip of the natural fracture, respectively. Consequently, natural fractures are expected to be able to both encourage and inhibit the progress of hydraulic fractures propagating through stress barriers, depending on the relative locations between the intersecting fractures. Once the hydraulic fracture propagates above the stress barrier through the weakened segment near a favorably located natural fracture, a configuration consisting of two opposing fractures cuts the stress barrier from above and below. The fluid pressure required to break the stress barrier under such opposing-fracture configurations is substantially lower than that required by a fracture penetrating the same barrier from one side. Sensitivity studies of geologic conditions and operational parameters have also been performed to explore the feasibility of controlled fracture height. The interactions between hydraulic fractures, natural fractures, and geologic factors such as stress barriers in three dimensions are shown to be much more complex than in two dimensions. Although it is impossible to exhaust all the possible configurations, the ability of a 3D, fully coupled numerical model to naturally capture these processes is well-demonstrated.
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Theune, Ulrich, Dean Rokosh, Mauricio D. Sacchi, and Douglas R. Schmitt. "Mapping fractures with GPR: A case study from Turtle Mountain." GEOPHYSICS 71, no. 5 (2006): B139—B150. http://dx.doi.org/10.1190/1.2335515.
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Ground-penetrating radar (GPR) surveys were acquired of rocks on the highly fractured summit of Turtle Mountain in Canada. In 1903 a disastrous rock slide occurred at Turtle Mountain and it still poses a geologic hazard. Dips, shapes, and penetration depths of fractures are important parameters in slope-stability analysis. Determination of fracture orientation at Turtle Mountain has been based mostly on areal geologic mapping and, most recently, on data collected from boreholes. The purpose of GPR surveys was to test, confirm, and extend information about fractures and bedding planes. Data acquisition was complicated by the rough terrain; because slopes are steep and uneven. This also complicated analysis of the data. Measurement of in situ velocity — an important value for migration — was impossible. Instead, data were migrated with different velocities and data results were chosen that were considered to be reasonable. Analysis and interpretation of the data, resulted in confirmation and extension of the a priori information on orientations of fractures and bedding planes at Turtle Mountain. Despite the rough terrain and highly fractured rock mass, GPR surveys provide reliable information about the shapes and density of fractures — information important for slope-stability evaluation. The most reliable migration results obtained for velocities were considerably less than the standard velocities recorded for limestone, the dominant lithofacies at Turtle Mountain. We interpret this observation as an indicator of water within the rock. However, thorough investigation of this conclusion remains a project for future work.
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Whitaker, Amy, C. Shah Kabir, and Wayne Narr. "An Integrated Geologic and Engineering Assessment of Fracture-Flow Potential in the Ratawi Reservoir of the Wafra Field, Partitioned Neutral Zone." SPE Reservoir Evaluation & Engineering 11, no. 06 (2008): 1071–81. http://dx.doi.org/10.2118/106994-pa.
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Summary The extent to which fractures affect fluid pathways is a vital component of understanding and modeling fluid flow in any reservoir. We examined the Wafra Ratawi grainstone for which production extending for 50 years, including recent horizontal drilling, has provided some clues about fractures, but their exact locations, intensity, and overall effect have been elusive. In this study, we find that a limited number of total fractures affect production characteristics of the Ratawi reservoir. Although fractures occur throughout the Wafra field, fracture-influenced reservoir behavior is confined to the periphery of the field where the matrix permeability is low. This work suggests that for the largest part of the field, explicit fractures are not necessary in the next-generation Earth and flow-simulation models. The geologic fracture assessment included seismic fault mapping and fracture interpretation of image logs and cores. Fracture trends are in the northeast and southwest quadrants, and fractures are mineralized toward the south and west of the field. Pressure-falloff tests on some peripheral injectors indicate partial barriers, and most of these wells lie on seismic-scale faults in the reservoir, suggesting partial sealing. A few wells show fractured-reservoir production characteristics, and rate-transient analysis on a few producers indicates localized dual-porosity behavior. Producers proximal to dual-porosity wells display single-porosity behavior, however, to attest to the notion of localized fracture response. The spatially restricted fracture-flow characteristics appear to correlate with fracture or vug zones in a low-permeability reservoir. Presence of fracture-flow behavior was tested by constructing the so-called flow-capacity index (FCI), the ratio of khwell (well test-derived value) to khmatrix (core-derived property). Data from 80 wells showed khmatrix to be consistently higher than khwell, a relationship that suggests insignificant fracture production in these wells. Introduction The Wafra field is in the Partitioned Neutral Zone (PNZ) between Kuwait and Saudi Arabia, as shown in Fig. 1. The field has been producing since the 1950s and has seen renewed drilling activity since the late 1990s, including horizontal drilling and implementation of peripheral water injection (Davis and Habib 1999). The Lower Cretaceous Ratawi formation contains the most reserves of the producing intervals at Wafra. The Ratawi oolite (a misnomer--it is a grainstone) reservoir has variable porosity (5 to 35%) and permeability that ranges from tens to hundreds of md (Longacre and Ginger 1988). The main Wafra structure is a gentle (i.e., interlimb angle >170°), doubly plunging anticline trending north-northwest to south-southeast, which culminates near its northern end. The East Wafra spur is a north-trending branch that extends from the center of the main Wafra structure. As seen in Fig. 1, relief on the Main Wafra structure exceeds that on East Wafra. The Ratawi oolite in the Wafra field has been studied at length, and various authors have reported geologic and engineering elements, leading to reservoir characterization and understanding of reservoir performance. Geologic studies are those of Waite et al. (2000) and Sibley et al. (1997). In contrast, Davis and Habib (1999) presented implementation of peripheral water injection, whereas Chawathé et al. (2006) discussed realignment of injection pattern owing to lack of pressure support in the reservoir interior. Previous studies considered the reservoir to behave like a single-porosity system. But recent image-log fracture interpretations indicate high fracture densities, suggesting that the implementation of a dual-porosity model may be necessary because the high impact of fractures during field development has been recognized in some Middle East reservoirs for more than 50 years (Daniel 1954). Static and dynamic data are required to characterize fracture reservoir behavior accurately (Narr et al. 2006). Geologic description of the fracture system, by use of cores, borehole images, seismic data, and well logs, does not in itself determine whether fractures affect reservoir behavior. While seismic and some image logs were available to locate fractures in the Wafra Ratawi reservoir, no dynamic testing with the specific objective of understanding fracture impact has occurred. So, to determine whether fractures influence oil productivity significantly, we used diagnostic analyses of production data and well tests of available injectors. The assessment of fracture effects in the Ratawi reservoir will be used to guide the next generation of geologic and flow-simulation models. Dynamic data involving pressure and rate have the potential to reveal the influence of open fractures in production performance. Unfortunately, pressure-transient testing on single wells does not always provide conclusive evidence about the presence of fractures with the characteristic dual-porosity dip on the pressure-derivative signature (Bourdet et al. 1989). That is because a correct mixture of matrix/fracture storativity must be present for the characteristic signature to appear (Serra et al. 1983). In practice, interference testing (Beliveau 1989) between wells appears to provide more-definitive clues about interwell connectivity, leading to inference about fractures. In contrast to pressure-transient testing, rate-transient analysis offers the potential to provide the same information without dedicated testing. In this field, all wells are currently on submersible pumps. Consequently, the pump-intake pressure and measured rate provided the necessary data for pressure/rate convolution or rate-transient analysis. We provide the Ratawi-reservoir case study primarily as an example of the integration of diverse geologic and engineering data to develop an assessment of fracture influence on reservoir behavior. It illustrates the use of production-data diagnostic tests to determine fracture influence in the absence of targeted fracture-analysis testing. The workflow can be applied to similar static/dynamic problems, such as fault-transmissivity determination. Secondly, this analysis illustrates the process of deciding that fractures, although present throughout the reservoir, may not lead to widespread fractured-reservoir characteristics (e.g., Allan and Sun 2003).
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Han, Tongcheng, and Sam Yang. "Dielectric properties of fractured carbonate rocks from finite-difference modeling." GEOPHYSICS 84, no. 1 (2019): MR37—MR44. http://dx.doi.org/10.1190/geo2018-0003.1.
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Fractures are common features in virtually all types of geologic rocks and tend to dominate their mechanical and hydraulic properties. Detection and characterization of fractures in rocks are of interest to a variety of geophysical applications. We have investigated the frequency-dependent dielectric properties of fractured porous carbonate rocks in the frequency range [Formula: see text] and their relationships with different types of fluids filling the fractures, fracture connectivity, and directions of electrical field applied to the rocks using numerical simulation methods based on a 3D finite-difference model. We tested the validity of the modeling method on a spherical-shell model with the theoretical analytical solutions. The two fractures in the two digital carbonate rocks have the same length, but in one rock, they intersect and in the other sample they do not. The fractures in the brine-saturated digital rocks are filled either with oil or with the same brine as in the background rock. We found that although conductivity and relative permittivity are sensitive to the fracture-filling fluids, the dielectric loss factor is the best parameter discriminating the fluids. When filled with brine, the fracture connectivity does not affect the dielectric properties of the rocks. When filled with oil, the fracture connectivity can only be detected if the electrical field is parallel to the longer fracture orientation. The results provide new insights into the frequency-dependent dielectric responses of fractured sedimentary rocks and will help with the interpretation of the dielectric data acquired from rocks with fractures.
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Gao, Dengliang, and Haibin Di. "Extreme curvature and extreme flexure analysis for fracture characterization from 3D seismic data: New analytical algorithms and geologic implications." GEOPHYSICS 80, no. 2 (2015): IM11—IM20. http://dx.doi.org/10.1190/geo2014-0185.1.
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Fracture characterization is fundamental to the reliable prediction of fractured reservoirs; however, it is difficult and expensive to obtain detailed fracture information required for reservoir prediction due to the lack of direct observational data in the subsurface. Here we develop seismic analysis methods to characterize fractured reservoirs based on reflection geometry related to bending and shearing of reservoir formations. Among various geometric attributes, we focus on extreme curvature and extreme flexure that are considered effective at detecting fractures. Extreme curvature refers to the signed absolute maximum curvature at a specific azimuth where the curve shape is the tightest, whereas extreme flexure refers to the signed absolute maximum gradient of curvature at a specific azimuth where the curve shape changes the most. We implement new algorithms based on analytical equations to calculate extreme curvature and extreme flexure along with the corresponding azimuth from 3D seismic data. Results from 3D seismic surveys demonstrate that the new algorithms help resolve structural details that are otherwise not easily discernible from regular amplitude and conventional attributes. Most importantly, the algorithms hold the potential to volumetrically detect and visualize fractures in an automatic and quantitative manner. We conclude that extreme curvature and extreme flexure attributes have important geologic implications for predicting fundamental fracture properties that are critical to fractured reservoir characterization in the subsurface.
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Grasmueck, Mark, Tijmen Jan Moser, Michael A. Pelissier, Jan Pajchel, and Kenri Pomar. "Diffraction signatures of fracture intersections." Interpretation 3, no. 1 (2015): SF55—SF68. http://dx.doi.org/10.1190/int-2014-0086.1.
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Fractured rock causes diffractions, which are often discarded as noise in ground-penetrating radar (GPR) and seismic data. Most fractures are too thin, too steep, and their displacement is too small to be imaged by reflections, and diffractions are the only detectable signal. To decipher the information about fracture geometry and distribution contained in diffractions, we compare 3D synthetic ray-Born modeling with high-density 3D GPR data and outcrop observations from the Cassis Quarry in Southern France. Our results reveal how the intersection between two fractures is the basic geologic element producing a recordable diffraction. In this new model, two intersecting fractures are represented by one finite-length line diffractor. The intersection of three fractures is a 3D cross composed of three line diffractors. Fractures extending over several meters in the outcrop display linear clusters of diffraction circles in unmigrated GPR time slices. Such large-scale fracture intersections are composed of many aligned short subwavelength line diffractors due to fracture roughness and variations of fracture opening. The shape irregularities and amplitude variations of composite diffraction signatures are a consequence of the geometry and spacing of the intersecting fractures generating them. With three simple base-type intersecting fracture models (horizontal dip, gentle dip, and steep dip), the fracture network geometry can be directly deciphered from the composite diffraction signatures visible on unmigrated time slices. The nonrandom distribution of diffractions is caused by fracture trends and patterns providing information about fracture dip, spacing, and continuity of fractured domains. With the similarity law, the diffraction phenomena observed in GPR data are very similar in character to those seen on the seismic scale with the wavelength as the scaling link. GPR data serve as a proxy to decipher seismic diffractions.
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Elkarmoty, Mohamed, Camilla Colla, Elena Gabrielli, Stefano Bonduà, and Roberto Bruno. "Deterministic Three-dimensional Rock Mass Fracture Modeling from Geo-radar Survey: a Case Study in a Sandstone Quarry in Italy." Environmental and Engineering Geoscience 23, no. 4 (2017): 314–31. http://dx.doi.org/10.2113/gseegeosci.23.4.314.
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Abstract Rock mass fractures adversely affect the production of ornamental stone quarries. Fractures cause natural rock blocks, which threaten extraction of the required commercial block size of ornamental stones. Accurate subsurface detection and modeling of fractures are required for pre-exploitation evaluation and planning. This paper introduces a new three-dimensional deterministic fracture modeling approach using ground penetrating radar (GPR) as a data acquisition tool. A case study was performed in a fractured bench of a sandstone quarry in Firenzuola, Italy, using a 400 MHz GPR antenna. To accurately detect fractures at true depth, an in situ calibration based on previous knowledge of the depth of a subsurface reference reflector allowed us to estimate a bulk dielectric constant of the rock mass during the time of data acquisition. A data interpretation tracing technique was developed to model fractures as 3-D surfaces in two forms, either irregular or planes. The modeled fractures were visualized through a multi-platform visualization software package (ParaView). A comparison between the orientations of the fractures measured by the traditional manual method and the orientations of the modeled fractures is presented as a possible geologic validation for the detection and interpretation of fractures. For the objective of pre-exploitation evaluation, a distribution analysis provided an evaluation-based fracture index for the bench in the case study.
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Zareidarmiyan, Ahmad, Hossein Salarirad, Victor Vilarrasa, Silvia De Simone, and Sebastia Olivella. "Geomechanical Response of Fractured Reservoirs." Fluids 3, no. 4 (2018): 70. http://dx.doi.org/10.3390/fluids3040070.
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Geologic carbon storage will most likely be feasible only if carbon dioxide (CO2) is utilized for improved oil recovery (IOR). The majority of carbonate reservoirs that bear hydrocarbons are fractured. Thus, the geomechanical response of the reservoir and caprock to IOR operations is controlled by pre-existing fractures. However, given the complexity of including fractures in numerical models, they are usually neglected and incorporated into an equivalent porous media. In this paper, we perform fully coupled thermo-hydro-mechanical numerical simulations of fluid injection and production into a naturally fractured carbonate reservoir. Simulation results show that fluid pressure propagates through the fractures much faster than the reservoir matrix as a result of their permeability contrast. Nevertheless, pressure diffusion propagates through the matrix blocks within days, reaching equilibrium with the fluid pressure in the fractures. In contrast, the cooling front remains within the fractures because it advances much faster by advection through the fractures than by conduction towards the matrix blocks. Moreover, the total stresses change proportionally to pressure changes and inversely proportional to temperature changes, with the maximum change occurring in the longitudinal direction of the fracture and the minimum in the direction normal to it. We find that shear failure is more likely to occur in the fractures and reservoir matrix that undergo cooling than in the region that is only affected by pressure changes. We also find that stability changes in the caprock are small and its integrity is maintained. We conclude that explicitly including fractures into numerical models permits identifying fracture instability that may be otherwise neglected.
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Wang, Kang, Suping Peng, Yongxu Lu, and Xiaoqin Cui. "The velocity-stress finite-difference method with a rotated staggered grid applied to seismic wave propagation in a fractured medium." GEOPHYSICS 85, no. 2 (2020): T89—T100. http://dx.doi.org/10.1190/geo2019-0186.1.
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To enable a mathematical description, geologic fractures are considered as infinitely thin planes embedded in a homogeneous medium. These fracture structures satisfy linear slip boundary conditions, namely, a discontinuous displacement and continuous stress. The general finite-difference (FD) method described by the elastic wave equations has challenges when attempting to simulate the propagation of waves at the fracture interface. The FD method expressed by velocity-stress variables with the explicit application of boundary conditions at the fracture interface facilitates the simulation of wave propagation in fractured discontinuous media that are described by elastic wave equations and linear slip interface conditions. We have developed a new FD scheme for horizontal and vertical fracture media. In this scheme, a fictitious grid is introduced to describe the discontinuous velocity at the fracture interface and a rotated staggered grid is used to accurately indicate the location of the fracture. The new FD scheme satisfies nonwelded contact boundary conditions, unlike traditional approaches. Numerical simulations in different fracture media indicate that our scheme is accurate. The results demonstrate that the reflection coefficient of the fractured interface varies with the incident angle, wavelet frequency, and normal and tangential fracture compliances. Our scheme and conclusions from this study will be useful in assessing the properties of fractures, enabling the proper delineation of fractured reservoirs.
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Xu, Meng Ya, Xin Wei Liao, and Xiao Liang Zhao. "Pressure Transient Modeling of Fractured Horizontal Wells in the Closed Tight Gas Reservoir." Advanced Materials Research 616-618 (December 2012): 749–52. http://dx.doi.org/10.4028/www.scientific.net/amr.616-618.749.
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Fractured horizontal well is the important means for the development of tight gas reservoirs. Based on the geologic characteristics of the tight gas reservoir, a pressure transient model for fractured horizontal wells is established by the Green functions and Newman product principle. The model considers the seepage resistances and the inferences from fractures each other. Practical application presents the pressure changes and flow rate distribution of fractures at non-steady state and quasi-steady state, and the suggestions for field operation are given as well.
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Beskardes, G. Didem, W. Anderson McAliley, Mohsen Ahmadian, David T. Chapman, Chester J. Weiss, and Jason E. Heath. "Power Density Distribution in Subsurface Fractures Due to an Energized Steel Well-casing Source." Journal of Environmental and Engineering Geophysics 24, no. 2 (2019): 285–97. http://dx.doi.org/10.2113/jeeg24.2.285.
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Robust in situ power harvesting underlies the realization of embedded wireless sensors for monitoring the physicochemical state of subsurface engineered structures and environments. The use of electromagnetic (EM) contrast agents in hydraulically fractured reservoirs, in coordination with completion design of wells, offers a way to transmit energy to remotely charge distributed sensors and interrogate fracture width, extent, and fracture-stage cross-communication. The quantification of available power in fracture networks due to energized steel-cased wells is crucial for such sensor designs; however, this has not been clarified via numerical modeling in the limit of Direct Current (DC). This paper presents a numerical modeling study to determine the EM characteristics of a subsurface system that is based on a highly instrumented field observatory. We use those realistic field scenarios incorporating geometry and material properties of contrast agents, the wellbore, and the surrounding geologic environment to estimate volumetric power density near the wellbore and within hydraulic fractures. The numerical modeling results indicate that the highest power densities are mainly focused around the wellbore excited by a point current source and the fracture boundary. Using DC excitation, the highest power density in the fracture is at the fracture tip. The relatively high-power density on the order of tens of mW/m 3 at the vicinity of the wellbore and at fracture tips suggests that remote charging of sensor devices may be readily possible. Simulation results also show that the region of the highest power density can be significantly increased when the EM source is located inside a conductive fracture, which may lead to a promising deployment strategy for embedded micro-sensors in geologic formations.
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Zhang, Tingting, Ruifeng Zhang, Jianzhang Tian, et al. "Two-parameter prestack seismic inversion of porosity and pore-structure parameter of fractured carbonate reservoirs: Part 2 — Applications." Interpretation 6, no. 4 (2018): SM9—SM17. http://dx.doi.org/10.1190/int-2018-0019.1.
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Fractures and fracture-related dissolution pores, as well as cavities, molds, and vugs, provide the major conduit and/or storage space for hydrocarbons in the deeply buried carbonate hill of Hexiwu field, Bohai Bay Basin. The fractured reservoir generally has lower porosity but better permeability than moldic/vuggy reservoir, and it consists of the major part of the buried-hill slope and buried-hill internal reservoirs. The conventional method of characterizing carbonate reservoirs, however, often mixes these two types of reservoirs together because they both have low acoustic impedance and low bulk modulus. The rock-physics analysis of two field wells indicates that a pore-structure parameter defined in a rock-physics model, the so-called Sun model, can help to distinguish the fractured reservoir zones together with porosity. Fractured zones usually have porosity of less than 5% and a pore-structure parameter of greater than six, whereas moldic/vuggy reservoirs of higher porosity have a pore-structure parameter of less than six. Field-scale application demonstrates that simultaneous prestack seismic inversion for the porosity and pore-structure parameter enables 3D mapping of fractured reservoir zones in the buried carbonate hills. It also provides an analog of detecting fractures and/or fracture-related pores in deeply buried carbonates in similar geologic settings.
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Busetti, Seth. "A method for modeling multiscale geomechanical effects in the stimulated rock volume." Interpretation 9, no. 1 (2021): T45—T61. http://dx.doi.org/10.1190/int-2020-0090.1.
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I have developed a workflow to efficiently simulate geomechanical effects in the stimulated rock volume (SRV) by including regional geologic structures such as faults and folds as well as high-resolution-oriented mechanical stratigraphy. The motivation is that the local model used for hydraulic fracture analysis should include macroscale 3D geomechanical effects derived from regional tectonic and seismic data. A practical computational strategy is developed to link multiple 3D geomechanical models derived at different scales and their associated stress effects. I apply the workflow to a synthetic reservoir problem composed of a tectonic-scale structural framework model with three embedded mechanical stratigraphic models representing three stimulated vertical wells. I first combine regional stresses solved with 3D finite-element analysis with perturbation stresses from elastic dislocation modeling using elastic superposition concepts. I then apply the macroscale stress effects as unique boundary conditions to an embedded finite-element submodel, a mesoscale stratigraphic model representing the SRV allowing for resolution of variable stress amplification, and stress rotation in geologic sublayers. Finally, I conduct hydraulic-fracture simulations within the SRV models. The simulated hydraulic fractures are controled by the structural position and mechanical stratigraphy. Closest to the back limb of the main structural anticline, hydraulic fractures tend to be height-restricted, and in some realizations, fractures propagate horizontally. Adjacent to the fold and a fault, where differential stresses are elevated, fracture growth is the most unconstrained in height and length. Results suggest that this multiscale approach can be applied to better predict and understand behaviors related to unconventional reservoir stimulation. The workflow could easily be modified for other operational problems and geologic settings.
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Ivanov, Yuriy, and Alexey Stovas. "Upscaling in orthorhombic media: Behavior of elastic parameters in heterogeneous fractured earth." GEOPHYSICS 81, no. 3 (2016): C113—C126. http://dx.doi.org/10.1190/geo2015-0392.1.
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A stack of horizontal homogeneous elastic arbitrary anisotropic layers in welded contact in the long-wavelength limit is equivalent to an elastic anisotropic homogeneous medium. Such a medium is characterized by an effective average description adhering to previously derived closed-form formalism. We have used this formalism to study three different inhomogeneous orthorhombic (ORT) models that could represent real geologic scenarios. We have determined that a stack of thin orthorhombic layers with arbitrary azimuths of vertical symmetry planes can be approximated by an effective orthorhombic medium. The most suitable approach for this is to minimize the misfit between the effective anisotropic medium, monoclinic in that case, and the desirable orthorhombic medium. The second model is an interbedding of VTI (transversely isotropic with a vertical symmetry axis) layers with the same layers containing vertical fractures (shales are intrinsically anisotropic and often fractured). We have derived a weak-anisotropy approximation for important P-wave processing parameters as a function of the relative amount of the fractured lithology. To accurately characterize fractures, inversion for the fracture parameters should use a priori information on the relative amount of a fractured medium. However, we have determined that the cracks’ fluid saturation can be estimated without prior knowledge of the relative amount of the fractured layer. We have used field well-log data to demonstrate how fractures can be included in the interval of interest during upscaling. Finally, the third model that we have considered is a useful representation of tilted orthorhombic medium in the case of two-way propagation of seismic waves through it. We have derived a weak anisotropy approximation for traveltime parameters of the reflected P-wave that propagates through a stack of thin beds of tilted orthorhombic symmetry. The tilt of symmetry planes in an orthorhombic medium significantly affects the kinematics of the reflected P-wave and should be properly accounted for to avoid mispositioning of geologic structures in seismic imaging.
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Blake, Oshaine Omar, Daniel Roy Faulkner, and Renelle Bascombe. "Using the Q factor to detect closed microfractures." GEOPHYSICS 85, no. 5 (2020): MR285—MR295. http://dx.doi.org/10.1190/geo2019-0093.1.
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Fractures are ubiquitous within the subsurface and play an important role in the fluid flow, elasticity, and strength of rocks. Because they are essential to geologic systems such as hydrocarbon and geothermal systems, they need to be properly imaged and monitored. We used the spectral-ratio technique to measure the P-wave Q factor ([Formula: see text]) and the S-wave Q factor ([Formula: see text]) of dry and water-saturated crystalline rock samples that were thermally fractured by heating to 250, 450, 650, and 850°C. Increasing the temperature during thermal treatment produces an increased fracture density that is isotropically distributed. The samples were subjected to hydrostatic pressures up to the pressure at which all fractures are closed, and they were axially loaded to 25% of the failure strength. Axial loading of the samples further closes fractures that are oriented perpendicular to the loading direction, but it opens those that are oriented parallel and oblique to the loading direction. Attenuation measurements were made in the frequency range of 0.8 to 1.7 MHz. At the fracture closure pressure, the sample with the highest fracture density showed a reduction in [Formula: see text] and [Formula: see text] when compared to the sample with the lowest fracture density of 84% and 24%, respectively, under dry conditions and by 33% and 5%, respectively, under saturated conditions. The [Formula: see text] and [Formula: see text] increase as the samples were axially loaded. The increase is more pronounced in [Formula: see text] because it is less influenced by the opening of parallel and obliquely oriented fractures. The opening of these fractures mostly affects the propagation of the S-wave and therefore reduces the increase in [Formula: see text]. The results suggest that [Formula: see text] is very sensitive to fracture closure at intermediate and high effective mean stresses. We determine that [Formula: see text] is a useful measure of the fracture density even at high pressures at which fractures might be expected to be fully closed.
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Costain, John K., G. A. Bollinger, and J. Alexander Speer. "Hydroselsmicity: A Hypothesis for The Role of Water in the Generation of Intraplate Seismicity." Seismological Research Letters 58, no. 3 (1987): 41–64. http://dx.doi.org/10.1785/gssrl.58.3.41.
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Abstract A new hypothesis termed Hydroseismicity that has hydrologic (diffusion of pore pressure transients from recharge areas of groundwater basins), geologic (rifted, fractured crust), and chemical (solubility of minerals) elements is proposed to explain the role of water in the generation of intraplate seismicity. Its basis is a spatial correlation in the southeastern U. S. between 1) seismogenic crustal volumes of high seismicity, 2) large gravity-driven river basins that can provide an adequate supply of water to the upper- and mid-crust, and 3) a permeable crust that is tectonically stressed close to failure. It is suggested that in crustal volumes with a combination of connected fractures and adequate groundwater, natural transient increases in hydraulic head in recharge areas of groundwater basins can be transmitted to depths of 10–20 km, and thereby trigger earthquakes, via a flow-path geometry that resembles except for scale the model familiar to groundwater hydrologists for near-surface flow. Possible trigger mechanisms for Hydroseismicity include small increases in fluid pressure at hypocentral depths caused by such transient increases, and hydrolytic weakening of minerals that leads to structural weakening. Implicit in the model is a diffuse distribution of epicenters (as is observed in the region) rather than concentrations along discrete geologie (faults) or geomorphic (rivers) elements. Open fractures imply fracture roughness, i.e., asperities under a higher stress that keep fractures open even in an ambient tectonic stress field. Intraplate earthquakes in a fractured crust prestressed to near-failure are thus postulated to be triggered by small transient increases in fluid pressure transmitted along preexisting fractures in a rock fabric weakened by stress corrosion of asperities. Abundant petrologic evidence is available to justify an assumption of fracture permeability to depths of 20 km near passive rifted margins. All four principal seismogenic volumes in the southeastern U. S. are within gravity-driven groundwater basins that can provide an abundant supply of water to the ernst, and that intersect known or suspected Eocambrian or Mesozoic rifted crust. The host basins have the largest surface recharge areas and contain rivers with the highest average stream gradients as measured from their headwaters to the Fall Line. Seismicity in the region is characterized by steeply dipping focal mechanism nodal planes and diffuse alignments and/or clusters of epicenters. These characteristics are compatible with a steep to vertical fracture fabric currently being reactivated by porc pressure diffusion from surface recharge of groundwater basins.
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He, Guan Hong, En Zhi Wang, and Xiao Li Liu. "Analysis on Seepage Field and Seepage Control Measure around Kunlong Hydropower Project." Applied Mechanics and Materials 438-439 (October 2013): 1314–19. http://dx.doi.org/10.4028/www.scientific.net/amm.438-439.1314.
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The Kunlong Hydropower has high water head and complex geologic environment. It is necessary to study the seepage field and the seepage control measure. In order to set up a three dimensional seepage numerical model around the dam site, double fracture seepage systems contained main fractures network and fractured rock masses is adopted. Pipe to represent a drain hole and fissure to represent a line of holes methods are used in simulation of drainage curtain. After setting boundary conditions and calculating parameter appropriately, the whole seepage field around the Kunlong Dam is calculated with the finite element method. The optimal depths of the impervious curtain and drainage curtain are determined by sensitive analysis. The implications of the analysis results on the design of the project are significant.
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Truche, Laurent, Thomas M. McCollom, and Isabelle Martinez. "Hydrogen and Abiotic Hydrocarbons: Molecules that Change the World." Elements 16, no. 1 (2020): 13–18. http://dx.doi.org/10.2138/gselements.16.1.13.
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Molecular hydrogen (H2), methane, and hydrocarbons with an apparent abiotic origin have been observed in a variety of geologic settings, including serpentinized ultramafic rocks, hydrothermal fluids, and deep fractures within ancient cratons. Molecular hydrogen is also observed in vapor plumes emanating from the icy crust of Saturn’s moon Enceladus, and methane has been detected in the atmosphere of Mars. Geologic production of these compounds has been the subject of increasing scientific attention due to their use by chemosynthetic biological communities. These compounds are also of interest as possible energy resources. This issue summarizes the geological sources of abiotic H2 and hydrocarbons on Earth and elsewhere and examines their impact on microbial life and energy resources.
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Idris, M. A., M. L. Garba, S. A. Kasim, I. M. Madabo, and K. A. Dandago. "The role of geological structures on groundwater occurrence and flow in crystalline basement aquifers: a status review." Bayero Journal of Pure and Applied Sciences 11, no. 1 (2018): 155–64. http://dx.doi.org/10.4314/bajopas.v11i1.27.
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The paper is review on the role of geological structures on groundwater occurrence and flow in Crystalline Basement aquifers. The aim was to study the existing available literatures in order to evaluate structural/lineaments (faults, joints/fractures, folds, shear zone etc.) their influences and controls of groundwater occurrence and flow of bedrock of crystalline rocks of igneous and/or metamorphic origin. Groundwater in the basement aquifers resides/occurs within the weathered overburden and fractured bedrocks which originate from rainfall through the process of hydrological cycle. Remote sensing technique uses satellite imagery or aerial photograph to identify linear features on the ground and attempts to relate these lines to geologic structures capable of transmitting and storing large quantities of groundwater. Faults, joints/fractures and folds act as conduit and make rocks excellent aquifers. These features also, served as channels for groundwater movement which may results to an increased in secondary porosity, permeability and therefore, can results as a groundwater prospective/promising zones in crystalline basement rocks. Keywords: Basement Terrain, Groundwater, Lineament, Movement, Occurrence
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Pan, Xinpeng, Lin Li, Guangzhi Zhang, and Yian Cui. "Elastic-Impedance-Based Fluid/Porosity Term and Fracture Weaknesses Inversion in Transversely Isotropic Media with a Tilted Axis of Symmetry." Geofluids 2020 (February 13, 2020): 1–17. http://dx.doi.org/10.1155/2020/7026408.
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The rock containing a set of tilted fractures is equivalent to a transversely isotropic (TTI) medium with a tilted axis of symmetry. To implement fluid identification and tilted fracture detection, we propose an inversion approach of utilizing seismic data to simultaneously estimate parameters that are sensitive to fluids and tilted fractures. We first derive a PP-wave reflection coefficient and elastic impedance (EI) in terms of the dip angle, fluid/porosity term, shear modulus, density, and fracture weaknesses, and we present numerical examples to demonstrate how the PP-wave reflection coefficient and EI vary with the dip angle. Based on the information of dip angle of fractures provided by geologic and well data, we propose a two-step inversion approach of utilizing azimuthal seismic data to estimate unknown parameters involving the fluid/porosity term and fracture weaknesses: (1) the constrained sparse spike inversion (CSSI) for azimuthally anisotropic EI data and (2) the estimation of unknown parameters with the low-frequency constrained regularization term. Synthetic and real data demonstrate that fluid and fracture parameters are reasonably estimated, which may help fluid identification and fracture characterization.
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Li, David, Xiao Tian, Hao Hu, Xiao-Ming Tang, Xinding Fang, and Yingcai Zheng. "Gaussian beam imaging of fractures near the wellbore using sonic logging tools after removing dispersive borehole waves." GEOPHYSICS 85, no. 4 (2020): D133—D143. http://dx.doi.org/10.1190/geo2019-0104.1.
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The ability to image near-wellbore fractures is critical for wellbore integrity monitoring as well as for energy production and waste disposal. Single-well imaging uses a sonic logging instrument consisting of a source and a receiver array to image geologic structures around a wellbore. We use cross-dipole sources because they can excite waves that can be used to image structures farther away from the wellbore than traditional monopole sources. However, the cross-dipole source also will excite large-amplitude, slowly propagating dispersive waves along the surface of the borehole. These waves will interfere with the formation reflection events. We have adopted a new fracture imaging procedure using sonic data. We first remove the strong amplitude borehole waves using a new nonlinear signal comparison method. We then apply Gaussian beam migration to obtain high-resolution images of the fractures. To verify our method, we first test our method on synthetic data sets modeled using a finite-difference approach. We then validate our method on a field data set collected from a fractured natural gas production well. We are able to obtain high-quality images of the fractures using Gaussian beam migration compared with Kirchhoff migration for the synthetic and field data sets. We also found that a low-frequency source (around 1 kHz) is needed to obtain a sharp image of the fracture because high-frequency wavefields can interact strongly with the fluid-filled borehole.
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Ramesh Babu, V., Subhash Ram, and N. Sundararajan. "Modeling and inversion of magnetic and VLF-EM data with an application to basement fractures: A case study from Raigarh, India." GEOPHYSICS 72, no. 5 (2007): B133—B140. http://dx.doi.org/10.1190/1.2759921.
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We present modeling of magnetic and very low frequency electromagnetic (VLF-EM) data to map the spatial distribution of basement fractures where uranium is reported in Sambalpur granitoids in the Raigarh district, Chhattisgarh, India. Radioactivity in the basement fractures is attributed to brannerite, [Formula: see text] complex, and uranium adsorbed on ferruginous matter. The amplitude of the 3D analytical signal of the observed magnetic data indicates the trend of fracture zones. Further, the application of Euler 3D deconvolution to magnetic data provides the spatial locations and depth of the source. Fraser-filtered VLF-EM data and current density pseudosections indicate the presence of shallow and deep conductive zones along the fractures. Modeling of VLF-EM data yields the subsurface resistivity distribution of the order of less than 100 ohm-m of the fractures. The interpreted results of both magnetic and VLF-EM data agree well with the geologic section obtained from drilling.
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Hayatudeen, Musa, Bello Rasaq, Raheem I. Onaolapo, and Ayoola Olumide Abe. "First horizontal and first vertical derivatives from high resolution aeromagnetic data over the Gongola basin upper Benue trough Northeastern Nigeria." Global Journal of Pure and Applied Sciences 27, no. 2 (2021): 181–92. http://dx.doi.org/10.4314/gjpas.v27i2.10.
Full textAbstract:
High-resolution aeromagnetic data investigation was carried out over the Gongola basin upper Benue trough northeastern Nigeria. Total intensity magnetic map were processed to get the residual map, reduction to equator, polynomial fitting, radially average power spectrum (RAPS) were done, subsequently the first horizontal and first vertical derivatives of the data was carried out in order to identify linear structures (faults and fractures). The outcomes from both the horizontal and vertical derivatives give contact locations that are continuous, thin and show major structures in the NE-SW direction both in the maps and in the rose diagrams. The study focused on delineation of geological structures such as rock contacts; rock boundaries, fractures and faulted zones from the maps, they are principally important in mineral resources studies because many of these resources are located along fracture zones. Linear structures perceived in this kind of studies are also reliable indicators for geologic structures. The result of this work is also significant in identifying areas to be avoided when constructing bridges, dams as well as siting nuclear power plants and delineation of potential risk areas of natural hazard.
 Keywords: Aeromagnetic Data, first Horizontal Derivative, first Vertical Derivatives, Gongola Basin, Linear Features.
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Nichols Jr., Thomas C., Kenneth W. King, Donley S. Collins, and Robert A. Williams. "Seismic-reflection technique used to verify shallow rebound fracture zones in the Pierre Shale of South Dakota." Canadian Geotechnical Journal 25, no. 2 (1988): 369–74. http://dx.doi.org/10.1139/t88-037.
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Shallow seismic-reflection data are presented to demonstrate their usefulness for locating and showing the continuity and lateral extent of rebound fracture zones in the Pierre Shale. Rebound fracture zones, identified in boreholes near Hayes, South Dakota, have variable depth, thickness, and character, thus making questionable the correlation of these zones between holes. Thus, the subsequent determination of dip and of continuity of the zones is somewhat tenuous, especially if the fracture characteristics change significantly between holes. Once rebound fracture zones have been identified and located by borehole geotechnical and geologic data, seismic profiles can reveal the extent and geometry of fractures in these zones, thus providing valuable preconstruction information without the cost of additional drilling. Key words: seismic reflection, fracture zones, fracture mapping, shale.
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Chen, Lei, Fengkai Zhang, Yuxiao Ren, Xinji Xu, Zhichao Yang, and Ming Li. "Tunnel Prospecting Based on Integrated Interpretation of Geophysical Data: Xiangyun Tunnel, Yunnan Province, China." Journal of Environmental and Engineering Geophysics 24, no. 1 (2019): 63–75. http://dx.doi.org/10.2113/jeeg24.1.63.
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With China's expanding economy, many tunnels are being designed and constructed. However, tunneling in hazardous geologic terrain, with faults, fractures, water-bearing openings, and other adverse geological conditions, construction safety is seriously endangered. To ensure the safety of tunnel construction, a tunnel geological prospecting method was proposed and applied at the Xiangyun Tunnel in Yunnan Province, China. In the investigation stage, the engineering geological and hydrogeological conditions were analyzed to recognize high-risk sections. In the construction stage, the “tunnel ahead” prospecting scheme was optimized based on the macroscopic geological conditions. Geological mapping of the tunnel, seismic ahead prospecting and transient electromagnetic soundings were employed as well as resistivity models to image potential adverse conditions. Horizontal drilling and tunnel excavation records verified the geophysical predictions and interpretations.
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Nelepov, Mikhail, Ruslan Gridin, Olesya Lutsenko, et al. "Fracture modeling of carbonate reservoirs of Low Triassic Neftekumsk formation of hydrocarbon field in Petrel software." E3S Web of Conferences 244 (2021): 03020. http://dx.doi.org/10.1051/e3sconf/202124403020.
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Construction of geologic and hydrodynamic models of carbonate reservoirs in the conditions of information lack about fracture parameters is always connected with the high degree of uncertainty. In the article the approach to the studying and the prediction of fracture of the carbonate reservoir based on the distribution and the trending of tectonic stress in the region of the researching object is presented. As illustrated by one of the field of the Eastern Caucasus the geotectonic description of the territory is listed, the fracture parameters on the indirect data were received, the zones of the increased productivity (fracturing) of reservoirs were highlighted and the modeling of fractures was held in Petrel software.
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Williams, Ryan Michael, Enric Pascual-Cebrian, Jon Charles Gutmanis, and Gaynor Suzanne Paton. "Closing the seismic resolution gap of fractures through seismic and image-log analysis, a North Sea case study." Interpretation 5, no. 3 (2017): SJ21—SJ30. http://dx.doi.org/10.1190/int-2016-0163.1.
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The “seismic resolution gap” has been an area of ambiguity ever since the results of 3D seismic interpretation have been used as inputs for modeling purposes because many important structural events such as fractures are at or below seismic resolution, which can impinge reservoir properties such as porosity and permeability. Having the means to accurately map these events with confidence has always been a challenge. More often than not, localized mapping of these features at borehole conditions can be achieved by core or image-log analysis. Seismic-derived attributes have assisted in improving the interwell geologic understanding in a lateral sense, but they are always hampered by vertical resolution. Enhanced imaging, such as cyan-magenta-yellow blending of attributes, has helped improve the lateral understanding of fracture patterns and networks, as shown in this workflow, but the challenge with vertical resolution still persists. However, by combining borehole and seismic data studies in a distinct workflow, it has become possible to identify overlaps and misalignments, which in turn has assisted in identification of discrete structural patterns not previously identified because of the seismic resolution gap. These results will then be used to improve the confidence of structural interpretation and static fracture models, which all go toward improving reservoir simulation models and geologic understanding.
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Yao, Yao, Kaimin Wang, Tao Zeng, and Leon M. Keer. "The effects of inclusions and heterogeneous stress field on hydraulic fracture." GEOPHYSICS 83, no. 3 (2018): MR153—MR166. http://dx.doi.org/10.1190/geo2016-0707.1.
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Hydraulic fracture technology has been widely applied to improve unconventional oil and gas production. The prevailing numerical analysis for hydraulic fracture technology is mainly based on the assumption of a homogeneous reservoir. However, unconventional reservoirs usually have complicated geologic conditions and the hypothesis of the homogeneous reservoir can strongly affect the accuracy of fracture simulation. To better understand the influence of heterogeneity to hydraulic fracture development, the effects of inclusions and heterogeneous stress fields are investigated by using the extended finite-element method. The heterogeneous stress field with fracture processing is developed, and the corresponding interaction between fracture and inclusion is investigated. The effects of different inclusions positions, opening and rotation angles, fractures lengths, and injected fluid viscosities to the hydraulic fracture development are studied based on the developed numerical model. Compared with the homogeneous stress field, numerical analysis indicates that the heterogeneous stress field could affect fracture behaviors and change the fracture energy distribution. In addition, the effects of inclusion can be restricted to some extent with higher injected fluid viscosity. The “stress shadow” effect with multiple fractures can weaken the influence of inclusions with properly designed perforation locations, which may be applied to optimize the hydraulic fracture development.
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Prioul, Romain, Adam Donald, Randy Koepsell, Zakariae El Marzouki, and Tom Bratton. "Forward modeling of fracture-induced sonic anisotropy using a combination of borehole image and sonic logs." GEOPHYSICS 72, no. 4 (2007): E135—E147. http://dx.doi.org/10.1190/1.2734546.
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We develop a methodology to model and interpret borehole dipole sonic anisotropy related to the effect of geologic fractures, using a forward-modeling approach. We use a classical excess-compliance fracture model that relies on the orientation of the individual fractures, the elastic properties of the host rock, and the normal and tangential fracture-compliance parameters. Orientations of individual fractures are extracted from borehole-image log analysis. The model is validated using borehole-resistivity image and sonic logs in a gas-sand reservoir over a [Formula: see text] (50 m) vertical interval of a well. Significant amounts of sonic anisotropy are observed at three zones, with a fast-shear azimuth (FSA) exhibiting 60° of variation and slowness difference between 2% and 16%. Numerous quasivertical fractures with varying dip azimuths are identified on the image log at the locations of strong sonic anisotropy. The maximum horizontal-stress direction, given by breakouts and drilling-induced fractures, is shown not to be aligned with the strike of natural fractures. We show that using just two adjustable fracture-compliance parameters, one fornatural fractures and one for drilling-induced fractures, is an excel-lent first-order approximation to explain the fracture-induced anisotropy response over a depth interval of [Formula: see text]. Given the presence of gas and the absence of clay filling within the fractures, we assumed equal normal and tangential compliances. The two inverted normal compliances are [Formula: see text] and [Formula: see text]. Predicted FSA matches measured FSA over [Formula: see text] (40 m) of the [Formula: see text] (50 m) studied interval. Predicted slowness anisotropy matches the overall variation and measured values of anisotropy for two of the three strong anisotropy zones. Analysis of the symmetries of the modeled anisotropic response shows that the medium is mostly a horizontal transverse isotropic medium, with small azimuthal variation of the symmetry axis. Analysis of each independent fracture type shows that the anisotropy is mainly driven by open or partially healed fractures, but also consistent with stress-related, drilling-induced fractures. Therefore, the measured sonic anisotropy is caused by the combination of stress and fracture effects where the predominance of one mechanism over the other is depth-dependent. This method provides a consistent approach to data interpretation by integrating borehole image and sonic logs that probe the formation at different depths of investigation around the borehole.
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Marrett, Randall, Stephen E. Laubach, and Jon E. Olson. "Anisotropy and beyond: Geologic perspectives on geophysical prospecting for natural fractures." Leading Edge 26, no. 9 (2007): 1106–11. http://dx.doi.org/10.1190/1.2780778.
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Lehman, R. Michael, Frederick S. Colwell, and Greg A. Bala. "Attached and Unattached Microbial Communities in a Simulated Basalt Aquifer under Fracture- and Porous-Flow Conditions." Applied and Environmental Microbiology 67, no. 6 (2001): 2799–809. http://dx.doi.org/10.1128/aem.67.6.2799-2809.2001.
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ABSTRACT Bench scale column studies were used to examine the partitioning of microorganisms between groundwater and a geologic medium and to examine the effect of hydrogeology (i.e., porous- versus fracture-flow) on organism partitioning. Replicated columns were constructed with intact basalt core segments that contained natural fractures and with the same basalt crushed into particles. The columns were perfused with groundwater, and upon reaching a steady state, the columns were sacrificed and the attached and unattached communities were analyzed by multiple approaches. The analyses included the total number of cells, the phylogenetic affiliation of the cells (i.e., the α, β, and γ subclasses of the class Proteobacteria and gram positives with high G+C DNA content) by fluorescent in situ hybridization (FISH), number and taxonomic affiliation by fatty acid methyl ester profiles of culturable heterotrophs, most-probable-number estimates of methanotrophs and phenol oxidizers, and whole-community sole carbon source utilization patterns from Biolog GN microplates. In the packed columns, about 99% of the total biomass (per cubic centimeter of porous medium) was attached to the geologic medium. Lack of equitable units precluded a comparison of attached and unattached biomasses in the fractured columns where the attached biomass was expressed per unit of surface area. Compositional differences in the attached and unattached communities were evidenced by (i) the recovery ofPseudomonas stutzeri, an Enterococcus sp., andBacillus psychrophilus from the groundwater and not from the basalt, (ii) differences between community carbon source utilization patterns, and (iii) the relative abundances of different phylogenetic groups estimated by FISH in both column types. In the packed columns, attached communities were depleted of members of the α- and β-Proteobacteria subclasses in comparison to those in the corresponding groundwater. In the fractured columns, attached communities were enriched in gram-positive Bacteriaand γ-Proteobacteria and depleted of β-Proteobacteria, in comparison to those in the corresponding groundwater. Segregation of populations and their activities, possibly modified by attachment to geologic media, may influence contaminant fate and transport in the subsurface and impact other in situ applications.
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Duan, Taizhong, Wenbiao Zhang, Xinbian Lu, Meng Li, Huawei Zhao, and Xiaofei Shang. "Architectural characterization of Ordovician fault-controlled paleokarst carbonate reservoirs, Tahe oilfield, China." Interpretation 8, no. 4 (2020): T953—T965. http://dx.doi.org/10.1190/int-2019-0012.1.
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Fault-controlled karst carbonate reservoirs are one of the most important reservoir types in the Tahe oilfield of the Tarim Basin. These reservoirs have a large oil reserve and belong to a strongly reconstructed reservoir type with a highly heterogeneous distribution of pores and fractures. This study characterizes a fault-controlled karst reservoir by using integrated methods, including outcrops, well logging, structure interpretation, seismic inversion, and statistical geomodeling. We have established a fault-/fracture-controlling karstic geologic model and classified the internal architectural elements so that we adopted an origin-controlled hierarchical geomodeling strategy based on the fault-controlling characteristics. The results determined that large strike-slip faults provide an important tectonic framework and that its derived fractures act as important channels and spaces for dissolution. Flower structure fault zones and the associated fractures are the main range of karst development, within which a high stress is concentrated during the strike-slip shear process with a high-density fracture development. This is the highly developed karst reservoir, which mainly is concentrated along large faults. The coexistence of fractures and karst dissolution has resulted in a complicated reservoir architecture (karst architecture), which can be classified into four types: (1) large caverns, (2) small caverns and vugs, (3) fractured zones, and (4) matrix (tight limestone). Controlled by the degree of dissolution, the karst architecture is quite different from the sedimentary facies. Large caverns are formed under the strongest degree of dissolution and are the most favorable reservoir type. Small caves and vugs are created under relatively strong dissolution; they are distributed outside large caves and also can act as favorable reservoirs. The fractured zones are not necessarily affected by strong dissolution but have high conductivity and act as important channels for fluid movement. The carbonate matrix is less reconstructed. The architecture development model of the fault-controlled karst carbonate reservoir presented a tree system, within which the karst reservoir caves are connected by the fractures and faults similar to fruits and trunks. The new geomodeling method revealed the constraining characteristics of faults, seismic attributes, and hierarchical architectural elements. Furthermore, we also have built a 3D model of the Tuoputai unit in the Tahe oilfield to show the robustness of this workflow. This research enables us to better understand the structure of fault-controlled karst reservoirs, and it could provide a specified characterization approach that is considered to be theoretically and practically useful.
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Sun, Xuekai, and Sam Zandong Sun. "Full-azimuth anisotropic prestack time migration in the local-angle domain and its applications on fracture detection." GEOPHYSICS 80, no. 2 (2015): C37—C47. http://dx.doi.org/10.1190/geo2014-0162.1.
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Considering that geologic structures disturb prestack amplitude relationships, anisotropic migration is thus advocated not only for extracting azimuth-preserved common image gathers (CIGs), but also for preserving fracture-induced amplitude responses. However, most conventional anisotropic migration methods are hindered by their inefficiency in either modeling azimuthal traveltime variations at large offsets or characterizing subsurface reflections. Given that prestack time migration is widely applied for most practical purposes, we began with reformulations on a quartic traveltime formula, through which a new set of anisotropic parameters was developed. Then, an anisotropic migration method was established in the local-angle domain (LAD) for more reasonable uses of subsurface wavefield information. We also used a traveltime inversion scheme to estimate those anisotropic parameters required by anisotropic migration. Using this methodology on a physical model with a fracture medium, we derived better focused CIGs by thoroughly correcting the anisotropic effects of overburden. As a result, predicted properties of the fracture medium showed fewer interventions of geologic impacts. In a field example, a comprehensive study was performed on a deep carbonate reservoir to examine influences of different anisotropic migration algorithms on ultimate fracture prediction. Comparisons of the signal-to-noise ratio and agreements with formation microimage information reconfirmed the superiority of LAD anisotropic migration in recovering true properties of subsurface fractures, relative to routine methods (i.e., azimuth-sectored migration and anisotropic migration in the surface-offset domain).
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Pérez Donoso, Patricio-Ignacio, Adrián-Enrique Ortiz Rojas, and Ernesto Meneses Rioseco. "Bilinear pressure diffusion and termination of bilinear flow in a vertically fractured well injecting at constant pressure." Solid Earth 11, no. 4 (2020): 1423–40. http://dx.doi.org/10.5194/se-11-1423-2020.
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Abstract. This work studies intensively the flow in fractures with finite hydraulic conductivity intersected by a well injecting or producing at constant pressure, either during an injection or production well test or the operation of a production well. Previous investigations showed that for a certain time the reciprocal of flow rate is proportional to the fourth root of time, which is characteristic of the flow regime known as bilinear flow. Using a 2D numerical model, we demonstrated that during the bilinear flow regime the transient propagation of isobars along the fracture is proportional to the fourth root of time. Moreover, we present relations to calculate the termination time of bilinear flow under constant injection or production well pressure as well as an expression for the bilinear hydraulic diffusivity of fractures with finite hydraulic conductivity. To determine the termination of bilinear flow regime, two different methods were used: (a) numerically measuring the transient flow rate in the well and (b) analyzing the propagation of isobars along the fracture. Numerical results show that for low dimensionless fracture conductivities the transition from bilinear flow to another flow regime (e.g., pseudo-radial flow) occurs before the pressure front reaches the fracture tip, and for high dimensionless fracture conductivities it occurs when the pressure front arrives at the fracture tip. Hence, this work complements and advances previous research on the interpretation and evaluation of well test analysis under different reservoir conditions. Our results aim to improve the understanding of the hydraulic diffusion in fractured geologic media, and as a result they can be utilized for the interpretation of hydraulic tests, for example to estimate the fracture length. Highlights. The reciprocal of flow rate is proportional to the fourth root of time. The migration of isobars in the fracture is proportional to the fourth root of time. For low dimensionless fracture conductivities, bilinear flow ends before the pressure front reaches the fracture tip. For high dimensionless fracture conductivities, bilinear flow ends when the pressure front reaches the fracture tip. Isobars accelerate when they approach the fracture tip.
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Shi, Hui, Xiaorong Luo, Hui Xu, et al. "Identification and distribution of fractures in the Zhangjiatan shale of the Mesozoic Yanchang Formation in Ordos Basin." Interpretation 5, no. 2 (2017): SF167—SF176. http://dx.doi.org/10.1190/int-2016-0123.1.
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The natural fractures in mud or shale directly affect the quality and efficiency of shale gas reservoirs, and fracture identification and prediction play an important role in drilling shale gas wells and making plans for reservoir stimulation. We adopted ant tracking technology for 3D poststack reflective seismic waves to identify the size and distribution of high-angle structural fractures in the Zhangjiatan shale of the Yanchang Formation in the Ordos Basin, which is a typical continental shale. The parameters for ant tracking fractures are extracted from the investigation on outcrop, cores, and image logs. The prestack seismic diffractive wave imaging technique for the super-resolution identification of mid- and small-scale breakpoints can be used as the constraint conditions for ant tracking. The identified result of high-angle fractures was validated by the image logging and drilling gas logging results. The geologic and logging data indicate that the Zhangjiatan shale is mainly characterized by high-angle fractures and a smaller number of low-angle fractures. The fractures mainly trend in the near east–west direction, followed by the near north–south direction, and a small amount of fractures in the north–northeast and northwest–west directions. The average density of structural fractures is relatively low, but the cemented rate is only 15.7%, and most structural fractures maintain an open state. The identified and predicted structural fractures are mainly distributed in the southeast of well LP180 and south of well LP179. The higher gas shows from actual well drilling in shale directly correspond to the density and intensity of high-angle fractures rather than the matrix gas abundance in shale, which indicates that the sweet spot of gas production in shale is clearly controlled by structural fractures.
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Assous, Said, Peter Elkington, Stuart Clark, and James Whetton. "Automated detection of planar geologic features in borehole images." GEOPHYSICS 79, no. 1 (2014): D11—D19. http://dx.doi.org/10.1190/geo2013-0189.1.
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The interpretation of borehole images begins with the detection and classification of features—a time-consuming manual process subject to variations between interpreters. In seeking to automate the detection part for the most frequently picked features (which in circumferential images from clastic rock environments are sinusoids corresponding to planar or subplanar bedding surfaces and fractures), it is not necessary to pick all instances, but it is necessary to pick sufficient representative instances to satisfy the interpretation objective, accounting for a broad range of apparent dips, and allowing for the likelihood of fractures crossing bedding surfaces. A key challenge in this context is the minimization of false picks, as manual corrections would potentially negate the principal benefit of automation. A fast nonsubjective method is described for the detection of prominent discontinuities and the calculation of associated dip angles. It combines a gradient based approach for edge detection with a phase congruency method for validation, followed by a robust sinusoid detection technique. It has been evaluated on microresistivity images from wireline and logging-while-drilling tools, these images having a wide range of features with varying degrees of geologic complexity; the proportion of false positives in the case of noisy data is less than 5%, improving to better than 2% in the case of good-quality data. In contrast to manual picking, the method is fast and gives reproducible results. With potentially thousands of sinusoids in a single image, the method dramatically improves efficiency.
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Michelena, Reinaldo J., James R. Gilman, and Christopher K. Zahm. "Seismic, geologic, geomechanics, and dynamic constraints in flow models of unconventional fractured reservoirs: Example from a south Texas field." Leading Edge 38, no. 2 (2019): 116–22. http://dx.doi.org/10.1190/tle38020116.1.
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We present a workflow to build permeability models for flow simulation in unconventional naturally fractured reservoirs constrained by 3D seismic, geologic data and concepts, geomechanics observations, and dynamic data. Joints and faults are modeled separately to account for their differences in scale and flow properties. Seismic-derived orientation statistics are compared against orientations from outcrops and microseismic data to assess their validity and consistency across multiple scales. We show the impact of natural fractures and stress orientation in the flow and variability of the pressure field around producing wells in an unconventional reservoir from south Texas. Such variability can have a significant impact on well interference and optimal well spacing.
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Ashraf, Umar, Hucai Zhang, Aqsa Anees, et al. "Application of Unconventional Seismic Attributes and Unsupervised Machine Learning for the Identification of Fault and Fracture Network." Applied Sciences 10, no. 11 (2020): 3864. http://dx.doi.org/10.3390/app10113864.
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The identification of small scale faults (SSFs) and fractures provides an improved understanding of geologic structural features and can be exploited for future drilling prospects. Conventional SSF and fracture characterization are challenging and time-consuming. Thus, the current study was conducted with the following aims: (a) to provide an effective way of utilizing the seismic data in the absence of image logs and cores for characterizing SSFs and fractures; (b) to present an unconventional way of data conditioning using geostatistical and structural filtering; (c) to provide an advanced workflow through multi-attributes, neural networks, and ant-colony optimization (ACO) for the recognition of fracture networks; and (d) to identify the fault and fracture orientation parameters within the study area. Initially, a steering cube was generated, and a dip-steered median filter (DSMF), a dip-steered diffusion filter (DSDF), and a fault enhancement filter (FEF) were applied to sharpen the discontinuities. Multiple structural attributes were applied and shortlisted, including dip and curvature attributes, filtered and unfiltered similarity attributes, thinned fault likelihood (TFL), fracture density, and fracture proximity. These shortlisted attributes were computed through unsupervised vector quantization (UVQ) neural networks. The results of the UVQ revealed the orientations, locations, and extensions of fractures in the study area. The ACO proved helpful in identifying the fracture parameters such as fracture length, dip angle, azimuth, and surface area. The adopted workflow also revealed a small scale fault which had an NNW–SSE orientation with minor heave and throw. The implemented workflow of structural interpretation is helpful for the field development of the study area and can be applied worldwide in carbonate, sand, coal, and shale gas fields.
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Huang, Jian, Reza Safari, Uno Mutlu, et al. "Natural-hydraulic fracture interaction: Microseismic observations and geomechanical predictions." Interpretation 3, no. 3 (2015): SU17—SU31. http://dx.doi.org/10.1190/int-2014-0233.1.
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Natural fractures can reactivate during hydraulic stimulation and interact with hydraulic fractures producing a complex and highly productive natural-hydraulic fracture network. This phenomenon and the quality of the resulting conductive reservoir area are primarily functions of the natural fracture network characteristics (e.g., spacing, height, length, number of fracture sets, orientation, and frictional properties); in situ stress state (e.g., stress anisotropy and magnitude); stimulation design parameters (e.g., pumping schedule, the type/volume of fluid[s], and proppant); well architecture (number and spacing of stages, perforation length, well orientation); and the physics of the natural-hydraulic fracture interaction (e.g., crossover, arrest, reactivation). Geomechanical models can quantify the impact of key parameters that control the extent and complexity of the conductive reservoir area, with implications to stimulation design and well optimization in the field. We have developed a series of geomechanical simulations to predict natural-hydraulic fracture interaction and the resulting fracture network in complex settings. A geomechanics-based sensitivity analysis was performed that integrated key reservoir-geomechanical parameters to forward model complex fracture network generation, synthetic microseismic (MS) response, and associated conductivity paths as they evolve during stimulation operations. The simulations tested two different natural-hydraulic fracture interaction scenarios and could generate synthetic MS events. The sensitivity analysis revealed that geomechanical models that involve complex fracture networks can be calibrated against MS data and can help to predict the reservoir response to stimulation and optimize the conductive reservoir area. We analyzed a field data set (obtained from two hydraulically fractured wells in the Barnett Formation, Tarrant County, Texas) and established a coupling between the geomechanics and MS within the framework of a 3D geologic model. This coupling provides a mechanics-based approach to (1) verify MS trends and anomalies in the field, (2) optimize conductive reservoir area for reservoir simulations, and (3) improve stimulation design on the current well in near-real-time and well design/stimulation for future wells.
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Scully, J. E. C., D. L. Buczkowski, N. Schmedemann, et al. "Evidence for the Interior Evolution of Ceres from Geologic Analysis of Fractures." Geophysical Research Letters 44, no. 19 (2017): 9564–72. http://dx.doi.org/10.1002/2017gl075086.
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Spikes, Kyle T. "Modeling elastic properties and assessing uncertainty of fracture parameters in the Middle Bakken Siltstone." GEOPHYSICS 76, no. 4 (2011): E117—E126. http://dx.doi.org/10.1190/1.3581129.
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A statistical rock-physics technique, based on well data that provides estimates and associated uncertainty of fracture density in the Middle Bakken Siltstone, is presented. Geologic and hydrocarbon-charging history of the Middle Bakken indicate multiple sets of fractures that justify treating this unit as elastically isotropic. The generalized n-phase self-consistent model relates the elastic properties to composition, matrix porosity, and fracture porosity, where an assigned aspect ratio and volumetric fraction corresponds to each input. The modeling of bulk density as a function of total porosity supplies deterministic estimates of the composition. Analysis of in situ stress and pore-stiffness calculations provide a range of fracture aspect ratios, corresponding to open fractures. Stochastic simulation of fracture porosity initiates the statistical nature of the technique. This treatment of fracture porosity enables the rock-physics model to be treated statistically through multiple realizations. Modeling results explain the measured bulk and shear moduli, with the bulk modulus more accurately described, and the results also provide statistical estimates of fracture porosity. Calculations using these estimates of fracture porosity, along with fracture aspect ratios, result in statistical estimates of fracture density for each depth value in the Middle Bakken unit. Values of fracture density fall within imposed limits (< 0.10). The results and technique demonstrated here could be applied to field seismic data to identify locations of increased fracture density. These locations might indicate areas of increased permeability in the Middle Bakken Siltstone.
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Li, Meng, Jixiong Zhang, Weiqing Zhang, Ailing Li, and Wei Yin. "Experimental Investigation of Water-Inrush Risk Based on Permeability Evolution in Coal Mine and Backfill Prevention Discussion." Geofluids 2019 (December 30, 2019): 1–9. http://dx.doi.org/10.1155/2019/3920414.
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Induced by coal mining, the fractures constantly occur in geologic strata until failure occurs, which provide channels for water flow. Therefore, it is essential to investigate the permeability evolution of rocks under load. Borehole sampling was conducted in a bedrock layer beneath an aquifer, and the permeability evolution of sandstone specimens under different confining pressures was tested in rock mechanics testing laboratories. The results indicated that the permeability gradually decreases with the increasing confining pressures, while the peak strength increases with the increase of confining pressures. The minimum and maximum permeabilities occurred in the sandstone specimens that were subjected to elastic deformation and strain-softening stages, respectively. The failure, and maximum permeability, of these sandstone specimens did not occur simultaneously. To prevent the flow channel being formed due to the development and failure of rock fractures, a method of backfill gob was proposed and also the influence of backfill on fracture development was discussed.
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Abbaszadeh, Maghsood, Chip Corbett, Rolf Broetz, et al. "Development of an Integrated Reservoir Model for a Naturally Fractured Volcanic Reservoir in China." SPE Reservoir Evaluation & Engineering 4, no. 05 (2001): 406–14. http://dx.doi.org/10.2118/74336-pa.
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Summary This paper presents the development of an integrated, multidiscipline reservoir model for dynamic flow simulation and performance prediction of a geologically complex, naturally fractured volcanic reservoir in the Shang 741 Block of the Shengli field in China. A static geological model integrates lithological information, petrophysics, fracture analysis, and stochastic fracture network modeling with Formation MicroImage (FMI) log data and advanced 3D seismic interpretations. Effective fracture permeability, fracture-matrix interaction, reservoir compartmentalization, and flow transmissibility of conductive faults are obtained by matching various dynamic data. As a result of synergy and multiple iterations among various disciplines, a history-matched dynamic reservoir-simulation model capable of future performance prediction for optimum asset management is constructed. Introduction The multidisciplinary approach of closely related teamwork across the disciplines of geology, geophysics, petrophysics, and reservoir engineering is now the accepted approach in the industry for reservoir management and field development.1–6Fig. 1 shows components of integrated reservoir characterization and the contribution of each discipline to the process. The strength of integrated reservoir modeling, however, can be particularly dramatized with some reservoirs that contain extreme forms of heterogeneity and unusual structural features. The Shang 741 Block of the Shengli fractured volcanic reservoirs is one such example. The Shang 741 Block contains a series of vertically separated fractured volcanic reservoirs with different characteristics. Matrix porosity and permeability are both low in most horizons; thus, natural fractures are the main flow pathways for fluids. FMI logs delineate the orientation and density of the fracture distribution. Lithology variations, extensive compartmentalization, and looping of reservoir body units are recognized from the geologic depositional model and seismic data. Tying acoustic well data to 3D seismic data through synthetic seismograms combined with FMI information controls time and depth structure maps for a reliable geological model. Reservoir modeling (RM) software provides a platform to integrate lithology correlations with seismically based structural features and petrophysical properties to yield a framework for a dual-porosity Eclipse** reservoir flow-simulation model. Fractures delineated and characterized from well data are stochastically distributed in the reservoir for each horizon with a fractal-based, fracture-mapping algorithm.7 Simulation of effective gridblock fracture permeability and matrix-fracture transfer function parameters are upscaled into coarse-scale simulation gridblocks. These upscaled values are verified and calibrated by available pressure-transient effective permeabilities for consistency. In this paper, a dual-porosity reservoir-simulation model is constructed from a static geological and geophysical (G&G) model in a stepwise fashion through successive incorporation of dynamic information from pressure-transient tests, static reservoir pressure, water breakthrough behavior, and well-production performance data. Compartmentalization incorporates effects of multiple oil/ water contacts (OWC) for proper modeling of regional pressure-trend behavior. Fault conductivity or thin channel transmissibility, verified by seismic and well tests, is augmented for better modeling of water movement in the reservoir. As a result of synergy among various G&G disciplines and incorporation of dynamic reservoir engineering data, a representative and production-data calibrated model is constructed for this reservoir. The paper shows that this is possible only through multiple iterations across the disciplines and through integrated project teams. The model also serves as a reservoir-management tool in production monitoring, in evaluating the effects of implementing pressure-maintenance injection programs, and in better understanding the impact of various uncertainties on the ultimate recovery of the field. Database The data sources available for this study include:Geological interpretations and geological framework model, including geological markers.Three-dimensional seismic survey data with 529 lines by 583 common depth points (CDPs) at 25-m bin size that covers a 200-km2 area.Three vertical seismic profile (VSP) surveys and their detailed interpretations.Petrophysical analysis on 13 nearly vertical wells that penetrate the reservoir horizons.FMI logs and analysis for fracture delineation.Pressure/volume/temperature (PVT) samples and analyses.Conventional and special core analysis for matrix and fracture relative permeability, matrix capillary-pressure characteristics, and rock compaction.Two single-well, pressure-buildup tests.Three interference tests.Spot static-pressure measurements.Production data, including flowing bottomhole and tubing pressure, oil, water, and gas flow rates.Extensive information from 13 drilled wells in the field. Reservoir Characterization Geology. Shang 741 fractured reservoirs are located within the large Shengli field in the Bohai basin, China (Fig. 2). These volcanic reservoirs, primarily of the Oligocene Shahejie and Dongying formations, are composed of fractured basalt, extrusive tuff, and fractured diabase of intrusive origin (Fig. 3). The Shang 741 consists of a stack of separated fractured reservoirs, which communicate with each other only through drilled wellbores. These are divided into the H1, H2, H3, Lower H3, H3 1, and H4 fractured reservoir units. Fig. 4 shows the stacking order of these reservoirs along with geological markers, lithology type, and facies relationships.