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1
Hart, Bruce S. "Whither seismic stratigraphy?" Interpretation 1, no. 1 (2013): SA3—SA20. http://dx.doi.org/10.1190/int-2013-0049.1.
Texte intégralRésumé :
Here, I provide an historical summary of seismic stratigraphy and suggest some potential avenues for future collaborative work between sedimentary geologists and geophysicists. Stratigraphic interpretations based on reflection geometry- or shape-based approaches have been used to reconstruct depositional histories and to make qualitative and (sometimes) quantitative predictions of rock physical properties since at least the mid-1970s. This is the seismic stratigraphy that is usually practiced by geology-focused interpreters. First applied to 2D seismic data, interest in seismic stratigraphy was reinvigorated by the development of seismic geomorphology on 3D volumes. This type of reflection geometry/shape-based interpretation strategy is a fairly mature science that includes seismic sequence analysis, seismic facies analysis, reflection character analysis, and seismic geomorphology. Rock property predictions based on seismic stratigraphic interpretations usually are qualitative, and reflection geometries commonly may permit more than one interpretation. Two geophysics-based approaches, practiced for nearly the same length of time as seismic stratigraphy, have yet to gain widespread adoption by geologic interpreters even though they have much potential application. The first is the use of seismic attributes for “feature detection,” i.e., helping interpreters to identify stratigraphic bodies that are not readily detected in conventional amplitude displays. The second involves rock property (lithology, porosity, etc.) predictions from various inversion methods or seismic attribute analyses. Stratigraphers can help quality check the results and learn about relationships between depositional features and lithologic properties of interest. Stratigraphers also can contribute to a better seismic analysis by helping to define the effects of “stratigraphy” (e.g., laminations, porosity, bedding) on rock properties and seismic responses. These and other seismic-related pursuits would benefit from enhanced collaboration between sedimentary geologists and geophysicists.
2
Abdullah, Agus, and Waskito Pranowo. "Layer-steered filter for enhancing seismic reflection interpretability." Journal of Petroleum Exploration and Production Technology 10, no. 8 (2020): 3235–39. http://dx.doi.org/10.1007/s13202-020-00994-2.
Texte intégralRésumé :
Abstract Seismic artifacts due to random and linear noises, low fold coverage, statics, and spatial aliasing are frequently affecting uncertainties in seismic interpretation. Several conventional methods, such as median filter, have been implemented to reduce random noises. However, this method can not be utilized for the area in which rich with stratigraphic features such as clinoforms and in the area with strong dips. We implemented layer-steered filter in order to attenuate random noises in this kind of situation. Layer-steered filter has ability to attenuate random noises but still respects to local dip events; therefore, the method provides better preservation of events and stratigraphics compared to other conventional methods such as median filter and dip-steered filter.
3
Bugge, Aina Juell, Jan Erik Lie, Andreas K. Evensen, Espen H. Nilsen, Odd Kolbjørnsen, and Jan Inge Faleide. "Data-driven identification of stratigraphic units in 3D seismic data using hierarchical density-based clustering." GEOPHYSICS 85, no. 5 (2020): IM15—IM26. http://dx.doi.org/10.1190/geo2019-0413.1.
Texte intégralRésumé :
Seismic sequences are stratigraphic units of relatively conformable seismic reflections. These units are intervals of similar sedimentation conditions, governed by sediment supply and relative sea level, and they are key elements in understanding the evolution of sedimentary basins. Conventional seismic sequence analyses typically rely on human interpretation; consequently, they are time-consuming. We have developed a new data-driven method to identify first-order stratigraphic units based on the assumption that the seismic units honor a layer-cake earth model, with layers that can be discriminated by the differences in seismic reflection properties, such as amplitude, continuity, and density. To identify stratigraphic units in a seismic volume, we compute feature vectors that describe the distribution of amplitudes, texture, and two-way traveltime for small seismic subvolumes. Here, the seismic texture is described with a novel texture descriptor that quantifies a simplified 3D local binary pattern around each pixel in the seismic volume. The feature vectors are preprocessed and clustered using a hierarchical density-based cluster algorithm in which each cluster is assumed to represent one stratigraphic unit. Field examples from the Barents Sea and the North Sea demonstrate that the proposed data-driven method can identify major 3D stratigraphic units without the need for manual interpretation, labeling, or prior geologic knowledge.
4
Denelle, E. "TO TACKLE THE DECONVOLUTION PROBLEM — A POWERFUL METHOD BASED ON MORE GEOLOGICAL HYPOTHESES." APPEA Journal 26, no. 1 (1986): 192. http://dx.doi.org/10.1071/aj85019.
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The new rules of the game in hydrocarbon exploration demand an exact positioning of the seismic markers in order to define the geometry of the targets more than ever before. However, the degree of success will depend to a great extent on how accurately the amplitude of reflection coefficients can be estimated.These new requirements mean that all stages of traditional seismic processing have to be critically evaluated. It can be seen, in particular, when assessing existing deconvolution methods for seismic processing, that they are often ill-conditioned to problems posed by the targets of stratigraphic exploration or by reservoir seismic prospecting. The amplitude of the reflectivity function is often estimated inaccurately.The approach described in this paper abandons the usual hypothesis (white reflectivity spectra) made by deconvolution methods and employs as alternative information the lateral redundancies which are always present on a seismic section. Our method first estimates the location of high amplitude reflectors with good lateral continuity, by means of an elegant automatic picking program. Based on these locations, a generalized inversion can be used to yield the wavelet emitted by the source, and the amplitude of the main reflection coefficients simultaneously for each trace. All the reflection coefficients are then estimated using the amplitudes and the wavelets computed previously.The various stages of this method which is called Deconvolution-Inversion, developed by Total Compagnie Française des Pétroles, are illustrated in the paper by means of both synthetic and real examples. The ability of the method to preserve the amplitudes makes it a powerful tool for stratigraphic and reservoir seismic prospecting purposes.
5
Poulin, Andrew, Ron Weir, David Eaton, et al. "Focal-time analysis: A new method for stratigraphic depth control of microseismicity and induced seismic events." GEOPHYSICS 84, no. 6 (2019): KS173—KS182. http://dx.doi.org/10.1190/geo2019-0046.1.
Texte intégralRésumé :
Focal-time analysis is a straightforward data-driven method to obtain robust stratigraphic depth control for microseismicity or induced seismic events. The method eliminates the necessity to build an explicit, calibrated velocity model for hypocenter depth estimation, although it requires multicomponent 3D seismic data that are colocated with surface or near-surface microseismic observations. Event focal depths are initially expressed in terms of zero-offset focal time (two-way P-P reflection time) to facilitate registration and visualization with 3D seismic data. Application of the focal-time method requires (1) high-quality P- and S-wave time picks, which are extrapolated to zero offset and (2) registration of correlative P-P and P-S reflections to provide [Formula: see text] and [Formula: see text] time-depth control. We determine the utility of this method by applying it to a microseismic and induced-seismicity data set recorded with a shallow-borehole monitoring array in Alberta, Canada, combined with high-quality multicomponent surface seismic data. The calculated depth distribution of events is in good agreement with hypocenter locations obtained independently using a nonlinear global-search method. Our results reveal that individual event clusters have distinct depth distributions that can provide important clues about the mechanisms of fault activation.
6
Zhang, Rui, and John Castagna. "Seismic sparse-layer reflectivity inversion using basis pursuit decomposition." GEOPHYSICS 76, no. 6 (2011): R147—R158. http://dx.doi.org/10.1190/geo2011-0103.1.
Texte intégralRésumé :
A basis pursuit inversion of seismic reflection data for reflection coefficients is introduced as an alternative method of incorporating a priori information in the seismic inversion process. The inversion is accomplished by building a dictionary of functions representing reflectivity patterns and constituting the seismic trace as a superposition of these patterns. Basis pursuit decomposition finds a sparse number of reflection responses that sum to form the seismic trace. When the dictionary of functions is chosen to be a wedge-model of reflection coefficient pairs convolved with the seismic wavelet, the resulting reflectivity inversion is a sparse-layer inversion, rather than a sparse-spike inversion. Synthetic tests suggest that a sparse-layer inversion using basis pursuit can better resolve thin beds than a comparable sparse-spike inversion. Application to field data indicates that sparse-layer inversion results in the potentially improved detectability and resolution of some thin layers and reveals apparent stratigraphic features that are not readily seen on conventional seismic sections.
7
Stovas, Alexey, and Børge Arntsen. "Vertical propagation of low-frequency waves in finely layered media." GEOPHYSICS 71, no. 3 (2006): T87—T94. http://dx.doi.org/10.1190/1.2197488.
Texte intégralRésumé :
Multiple scattering in finely layered sediments is important for interpreting stratigraphic data, matching well-log data with seismic data, and seismic modeling. Two methods have been used to treat this problem in seismic applications: the O’Doherty-Anstey approximation and Backus averaging. The O’Doherty-Anstey approximation describes the stratigraphic-filtering effects, while Backus averaging defines the elastic properties for an effective medium from the stack of the layers. It is very important to know when the layered medium can be considered as an effective medium. In this paper, we only investigate vertical propagation. Therefore, no anisotropy effect is taken into consideration. Using the matrix-propagator method, we derive equations for transmission and reflection responses from the stack of horizontal layers. From the transmission response, we compute the phase velocity and compare the zero-frequency limit with the effective-medium velocity from Backus averaging. We also investigate how the transition from time-average medium to effective medium depends on contrast; i.e., strength of the reflection-coefficient series. Using numerical examples, we show that a transition zone exists between the effective medium (low-frequency limit) and the time-average medium (high-frequency limit), and that the width of this zone depends on the strength of the reflection-coefficient series.
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Maxime Abbey, Assa, Loukou Nicolas Kouame, Lacine Coulibaly, Simon Pierre Djroh, and Boko Celestin Sombo. "STUDY OF THE ARCHITECTURE OF SEDIMENTARY DEPOSITS IN THE IVORIAN ONSHORE BASIN THROUGH SEISMIC REFLECTION." International Journal of Advanced Research 8, no. 12 (2020): 575–84. http://dx.doi.org/10.21474/ijar01/12186.
Texte intégralRésumé :
The seismic profiles analysis of 4,533 km study area made it possible to study the sedimentary deposits in the Ivorian onshore basin. The method used consisted of manual plots of the seismic sections leading to the production of isochronos, iso-velocity, isobaths and isopac maps. As for the stratigraphic interpretation, it was used to develop a sedimentary model to extract information on the nature of sedimentary deposits and the mechanisms of their establishment based on the analysis of seismic facies. Examination of the different seismic profiles of the study area allowed the onshore sedimentary series to be subdivided into four main sequences which are: sequences I, II, III and IV. Thus, this analysis revealed two stages of sedimentary deposits linked to the behavior of the reflectors: 1. a syn-rift stage, characterized by significant fracturing in the sedimentation with faults and tilted blocks inthe Lower Cretaceous 2. a post-rift stage , corresponding to a less deformed sedimentation with parallel and continuous reflectors from the Upper Cretaceous to the present . These two phases allow us to understand the stratigraphic evolution of the onshore basin.
9
Mark, Norman. "Case history: Seismic exploration in Egypt’s Eastern Desert." GEOPHYSICS 57, no. 2 (1992): 296–305. http://dx.doi.org/10.1190/1.1443243.
Texte intégralRésumé :
Although oil exploration has been performed in the Eastern Desert of Egypt for over a century, seismic reflection techniques have only been in use for less than a fourth of that time. In an effort to improve seismic imaging of geologic targets, many styles of acquisition and processing have been tested, accepted, or discarded. Over the last twenty‐four years, seismic data acquisition has evolved from low‐channel analog to high‐channel digital recordings. The most difficult exploration problems encountered in these efforts have been the low‐frequency and high‐energy ground roll and depth of penetration when imaging the oil producing Pre‐Miocene sandy reservoirs below the highly reflective salt and evaporites. Efforts have been focused on developing seismic processing procedures to enhance the seismic data quality of recently acquired seismic data and developing new acquisition methods to improve seismic data through acquisition and processing. In older acquisition, the new processing has improved the seismic quality (vertical and lateral resolution), but it still retains a low‐frequency character. In the newly acquired seismic data, however, there is improved reflection continuity, depth of penetration, and resolution. We attribute this result to the change from low‐fold (6–24 fold), long receiver and source patterns (50 to 222 m) to high fold (96 fold) short receiver and source group (25 m), and spectral balancing in the processing. The most recent acquisition and processing have greatly improved the quality of the shallow seismic reflections and the deeper reflections that have helped unravel the structural and stratigraphic style of the deeper portions of the basin.
10
Qi, Chen, and Fred Hilterman. "Well ties for seismic with severe stratigraphic filtering." GEOPHYSICS 82, no. 5 (2017): IM31—IM39. http://dx.doi.org/10.1190/geo2016-0695.1.
Texte intégralRésumé :
Stratigraphic filtering (SF), or short-period multiples, is prominent in cyclically stratified sedimentation with large impedance contrasts that result in normal-incident reflection magnitudes greater than 0.5. Because SF attenuates and delays the propagating wavelet, similar to the effects of [Formula: see text] attenuation, the integrity of well ties is often jeopardized. A method is proposed to obtain better well ties in areas with severe SF. Starting with a well-log acoustic impedance curve, two-way transmitted wavefields and their equivalent inverse filters are generated at each time sample. Because a time-varying convolution of the transmitted wavefields with the primary-only reflectivity yields the multiple reflectivity, a time-varying deconvolution of the multiple synthetic with the inverse filters yields the primary-only reflectivity. In essence, when the multiple synthetic matches the near-angle stack at a well location, the near-angle stack is deconvolved in a time-varying fashion to match the primary-only synthetic, which then constitutes a correlation with the acoustic impedance yielding a good well tie. This new well-tie technique preserves the integrity of the lithologic interpretation because stretching and squeezing the time scale of the primary-only synthetic to force a seismic match are avoided. Our well-tie method is applied to the synthetic and field data from Cooper Basin, Australia, where more than 30 coal beds are observed within a 1000 ft (304 m) interval.
11
Johansen, Ståle, Espen Granberg, Donatella Mellere, Børge Arntsen, and Torben Olsen. "Decoupling of seismic reflectors and stratigraphic timelines: A modeling study of Tertiary strata from Svalbard." GEOPHYSICS 72, no. 5 (2007): SM273—SM280. http://dx.doi.org/10.1190/1.2759479.
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In sequence stratigraphic interpretations, the key premise is that stratal surfaces effectively represent geologic timelines. When applied to seismic sections, the fundamental assumption is that primary reflections generally mimic stratigraphic timelines. The main objective of this study was to test how well key reflectors in a seismic section couple to timelines. To achieve the high level of ground control needed for such testing, we combined photogrammetry and traditional sedimentologic fieldwork to optimize the geologic model. We relied further on petrophysical analysis to derive a numerical model suitable for the simulation of seismic data. In spite of laterally discontinuous vertical-impedance contrasts (VICs), false seismic continuity was created, and we observed frequent decoupling of seismic reflectors and stratigraphic timelines. These observations demonstrate how the low-frequency seismic method fails to image normal complexity in a stratigraphic unit. A seismic correlation test showed that the interpreters made numerous mistakes and that such mistakes are very difficult to avoid. The failure of a fundamental assumption, as illustrated here, creates serious problems for the sequence stratigraphic concept when applied to detailed correlation analysis on seismic sections.
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Gochioco, Lawrence M. "Modeling studies of interference reflections in thin‐layered media bounded by coal seams." GEOPHYSICS 57, no. 9 (1992): 1209–16. http://dx.doi.org/10.1190/1.1443336.
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High‐resolution seismic data collected over a major U.S. coal basin indicated potential complex problems associated with interference reflections. These problems differed from those normally encountered in the exploration of oil and gas because of differences in the geologic boundary conditions. Modeling studies were conducted to investigate the effects of overlapping primary reflections and the composite reflection that result from stacking individual wavelets. A modified empirical formula of Lindseth’s linear relationship between acoustic impedance and velocity is used to extrapolate velocity information from density logs to provide appropriate geophysical properties for modeling. The synthetic seismograms generated from density and synthetic sonic logs correlated well with the processed seismic data. A 150-Hz Ricker wavelet is used to convolve with the computer models, and the models showed that certain anomalous composite reflections result from the superposition of overlapping primary reflections. Depending on the traveltime delay of latter primary reflections, constructive or destructive interference could significantly alter the signature of the initial reflection associated with the bed of interest, which may lead to misinterpretations if not properly identified. The stratigraphic modeling technique further enhances the interpretation process and shows a close correlation with the seismic data, suggesting that more precise analytical methods need to be used to interpret, sometimes complex, high‐resolution seismic data.
13
Hubral, Peter, Jörg Schleicher, Martin Tygel, and Ch Hanitzsch. "Determination of Fresnel zones from traveltime measurements." GEOPHYSICS 58, no. 5 (1993): 703–12. http://dx.doi.org/10.1190/1.1443454.
Texte intégralRésumé :
For a horizontally stratified (isotropic) earth, the rms‐velocity of a primary reflection is a key parameter for common‐midpoint (CMP) stacking, interval‐velocity computation (by the Dix formula) and true‐amplitude processing (geometrical‐spreading compensation). As shown here, it is also a very desirable parameter to determine the Fresnel zone on the reflector from which the primary zero‐offset reflection results. Hence, the rms‐velocity can contribute to evaluating the resolution of the primary reflection. The situation that applies to a horizontally stratified earth model can be generalized to three‐dimensional (3-D) layered laterally inhomogeneous media. The theory by which Fresnel zones for zero‐offset primary reflections can then be determined purely from a traveltime analysis—without knowing the overburden above the considered reflector—is presented. The concept of a projected Fresnel zone is introduced and a simple method of its construction for zero‐offset primary reflections is described. The projected Fresnel zone provides the image on the earth’s surface (or on the traveltime surface of primary zero‐offset reflections) of that part of the subsurface reflector (i.e., the actual Fresnel zone) that influences the considered reflection. This image is often required for a seismic stratigraphic analysis. Our main aim is therefore to show the seismic interpreter how easy it is to find the projected Fresnel zone of a zero‐offset reflection using nothing more than a standard 3-D CMP traveltime analysis.
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Genau, Robert B., John A. Madsen, Susan McGeary, and John F. Wehmiller. "Seismic-Reflection Identification of Susquehanna River Paleochannels on the Mid-Atlantic Coastal Plain." Quaternary Research 42, no. 2 (1994): 166–75. http://dx.doi.org/10.1006/qres.1994.1066.
Texte intégralRésumé :
AbstractLand-based, high-resolution seismic-reflection methods were used to image Quaternary paleochannels of the Susquehanna River system. Using a portable, 12-channel signal-enhancing seismograph, 12 accelerometers as receivers, and a 4.54-kg sledge hammer struck against an aluminum plate as a source, a sixfold, multichannel seismic profile 2.5 km long was acquired at Taylors Island, Maryland. On the processed seismic profile, pronounced high-amplitude seismic reflections delineate the unconformity between Quaternary and underlying Tertiary sediments and the disconformable contact separating Miocene and Eocene deposits. Subsurface-seismic stratigraphic relationships that clearly indicate the presence of two paleochannels were observed, one believed to be the Exmore paleochannel, projected to underlie northern Taylors Island based on marine seismic data. An overlapping sequence of fill sediments was observed on the eastern margin of the Exmore paleochannel. The second paleochannel may be a tributary of the Exmore or possibly the western edge of the younger Eastville paleochannel. Results from this study indicate that land-based, shallow, high-resolution seismic-reflection data can be used to delineate subsurface geomorphology successfully in coastal plain environments. This technique of defining erosional surfaces and depositional units beneath present land areas, when integrated with chronostratigraphic data, is a powerful tool for developing a better understanding of the Quaternary record.
15
Li, Tonglin, and David W. Eaton. "Delineating the Tuwu porphyry copper deposit at Xinjiang, China, with seismic-reflection profiling." GEOPHYSICS 70, no. 6 (2005): B53—B60. http://dx.doi.org/10.1190/1.2122409.
Texte intégralRésumé :
The Tuwu deposit is one of a series of recently discovered porphyry copper deposits in the eastern Tian Shan range of Xinjiang, China. Since its discovery in 1997, more than ten boreholes have been drilled and a suite of geophysical surveys has been acquired to delineate the deposit. As part of the geophysical program, a set of eight seismic reflection profiles was acquired in 2000, followed by a physical rock-property study in 2001. The ores are characterized by slightly higher density (Δρ ∼ 0.1 g/cm[Formula: see text]) and significantly higher P-wave velocity ([Formula: see text] ∼ 1.0–1.5 km/s) than the dioritic host rocks. The seismic surveys used 0.6- to 0.9-kg shallow dynamite sources, with a 24-channel end-on spread and offsets up to 350 m. The orebody and associated igneous layers dip steeply (>45°) toward the south, so careful processing of the seismic data was required. Weak reflections from stratigraphic contacts are visible on most of the profiles, including the top of the intrusion and the base of the orebody. Since the observed reflections include a significant out-of-plane component, we developed a simple 2.5D migration procedure. This method was applied to line drawings of the seismic profiles, providing the basis for delineation of the orebody in three dimensions. Synthetic seismic sections computed using the inferred bounding surfaces of the ore deposit are in reasonable agreement with observed reflections, even for along-strike lines not used to build the model. The ability to verify interpreted reflections using line intersections was critical to the development of our model. The results of this work indicate that seismic methods may be useful as an aid for mapping the flanks of shallow, moderately dipping porphyry copper orebodies and associated strata, particularly for defining the structure of deeper sections of the mineralized zones in advance of drilling.
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Ziolkowski, Anton, John R. Underhill, and Rodney G. K. Johnston. "Wavelets, well ties, and the search for subtle stratigraphic traps." GEOPHYSICS 63, no. 1 (1998): 297–313. http://dx.doi.org/10.1190/1.1444324.
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We examine the conventional methodology for tying wells to processed seismic data and show why this methodology fails to allow for reliable interpretation of the seismic data for stratigraphy. We demonstrate an alternative methodology that makes the tie without the use of synthetic seismograms, but at the price of measuring the seismic source signature, the cost of such measurements being about 1% of data acquisition costs. The essence of the well tie is (1) to identify geological and seismic interfaces from the logs and core, (2) to measure the one‐way traveltime to these interfaces using downhole geophones, and (3) to use the polarity information from (1) and the timing information from (2) to identify the horizons on the zero‐phase processed seismic data. Conventional processing of seismic data usually causes the wavelet to vary from trace to trace, and conventional wavelet extraction at a well using the normal‐incidence reflection coefficients relies on a convolutional relationship between these coefficients and the processed data that has no basis in the physics of the problem. Each new well introduces a new wavelet and poses a new problem—how should the zero‐phasing filter be derived between wells? Our methodology consists of three steps: (1) determination of the wavelet consisting of all known convolutional effects before any processing using measurements of the source time function made during data acquisition, (2) compression of this wavelet to the shortest zero‐phase wavelet within the bandwidth available, and (3) elimination of uncontrolled distortions to the wavelet in subsequent processing. This method is illustrated with data from the prospective Jurassic succession in the Moray Firth rift arm of the North Sea in which we have identified, for the first time on seismic data, a major regional unconconformity that cuts out more than 20 Ma of geological time. This method offers two major benefits over the conventional approach. First, all lateral variations in the processed seismic data are caused by the geology. Second, events on the processed seismic data may be identified from well logs simply by their polarity and timing. It follows that events can then be followed on the seismic data from one well to another with confidence, the seismic data can be interpreted for stratigraphy, and subtle stratigraphic traps may be identified.
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Bradford, John H., Dale S. Sawyer, Colin A. Zelt, and John S. Oldow. "Imaging a shallow aquifer in temperate glacial sediments using seismic reflection profiling with DMO processing." GEOPHYSICS 63, no. 4 (1998): 1248–56. http://dx.doi.org/10.1190/1.1444426.
Texte intégralRésumé :
We acquired a seismic reflection profile to image a shallow (<100 m) aquifer system on a small island in Puget Sound, north of Seattle, Washington. The aquifer system is comprised of temperate glacial sedimentary strata, with the primary aquifer lying approximately 45 m below the surface. We chose the site because there are water‐well boring descriptions available and a sea cliff parallels the profile location, providing stratigraphic control. A 20-lb (9-kg) weight drop was used as an energy source to acquire a 30-fold common‐midpoint (CMP) reflection profile along a 400-m line. Analysis of the recorded wavefield was not straightforward because of complex stratigraphy and the presence of a laterally variable thin bed (∼5–15 m) of high‐impedance lodgement till within a few meters of the surface. We used finite‐difference modeling to determine that conventional CMP processing would provide a reasonable approximation for imaging strata in the primary target zone, roughly 20 m below the high velocity till. For CMP processing, we analyzed the velocity structure using iterative dip moveout (DMO) velocity analysis. Use of this method results in a velocity field that dramatically improves the poststack depth‐migrated section.
18
Arditto, P. A. "THE EASTERN OTWAY BASIN WANGERRIP GROUP REVISITED USING AN INTEGRATED SEQUENCE STRATIGRAPHIC METHODOLOGY." APPEA Journal 35, no. 1 (1995): 372. http://dx.doi.org/10.1071/aj94024.
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Recent exploration by BHP Petroleum in VIC/ P30 and VIC/P31, within the eastern Otway Basin, has contributed significantly to our understanding of the depositional history of the Paleocene to Eocene siliciclastic Wangerrip Group. The original lithostratigraphic definition of this group was based on outcrop description and subsequently applied to onshore and, more recently, offshore wells significantly basinward of the type sections. This resulted in confusing individual well lithostratigraphies which hampered traditional methods of subsurface correlation.A re-evaluation of the Wangerrip Group stratigraphy is presented based on the integration of outcrop, wireline well log, palynological and reflection seismic data. The Wangerrip Group can be divided into two distinct units based on seismic and well log character. A lower Paleocene succession rests conformably on the underlying Maastrichtian and older Sherbrook Group, and is separated from an overlying Late Paleocene to Eocene succession by a significant regional unconformity. This upper unit displays a highly progradational seismic character and is named here as the Wangerrip Megasequence.Regional seismic and well log correlation diagrams are used to illustrate a subdivision of the Wangerrip Megasequence into eight third-order sequences. This sequence stratigraphic subdivision of the Wangerrip Group is then used to construct a chronostratigraphic chart for the succession within this part of the Otway Basin.
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Xie, Qiu Hong, Bao Hua Liu, Xi Shuang Li, and Xiang Zhen Yan. "Stability Analysis of Shallow Stratum in Jiangshidi Nuclear Power Plant Site and its Surrounding Areas." Advanced Materials Research 433-440 (January 2012): 1162–68. http://dx.doi.org/10.4028/www.scientific.net/amr.433-440.1162.
Texte intégralRésumé :
The differential GPS navigation and positioning technique, multi-channel shallow seismic exploration and high resolution single channel seismic technique were used for the geophysical exploration of the shallow stratum in Jiangshidi nuclear power plant site and its surrounding areas. Based on seismic data post processing results, the seismic section interpretation was performed, combined with regional geological background, borehole data and shallow anatomy data. Five main seismic reflection surfaces were recognized by using seismic stratigraphic method, and eight breakpoints were found according to the active fault discrimination criteria. Then the distribution and activity characteristics of main faults were obtained. The results show that any fault and marked deformation in the quaternary sediments has not been observed in the range of 5 km away from Jiangshidi nuclear power plant site. So the stability analysis results of shallow stratum in target area can meet the requirement of nuclear power plant site selection code.
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Forte, Emanuele, Matteo Dossi, Michele Pipan, and Anna Del Ben. "Automated phase attribute-based picking applied to reflection seismics." GEOPHYSICS 81, no. 2 (2016): V141—V150. http://dx.doi.org/10.1190/geo2015-0333.1.
Texte intégralRésumé :
We have applied an attribute-based autopicking algorithm to reflection seismics with the aim of reducing the influence of the user’s subjectivity on the picking results and making the interpretation faster with respect to manual and semiautomated techniques. Our picking procedure uses the cosine of the instantaneous phase to automatically detect and mark as a horizon any recorded event characterized by lateral phase continuity. A patching procedure, which exploits horizon parallelism, can be used to connect consecutive horizons marking the same event but separated by noise-related gaps. The picking process marks all coherent events regardless of their reflection strength; therefore, a large number of independent horizons can be constructed. To facilitate interpretation, horizons marking different phases of the same reflection can be automatically grouped together and specific horizons from each reflection can be selected using different possible methods. In the phase method, the algorithm reconstructs the reflected wavelets by averaging the cosine of the instantaneous phase along each horizon. The resulting wavelets are then locally analyzed and confronted through crosscorrelation, allowing the recognition and selection of specific reflection phases. In case the reflected wavelets cannot be recovered due to shape-altering processing or a low signal-to-noise ratio, the energy method uses the reflection strength to group together subparallel horizons within the same energy package and to select those satisfying either energy or arrival time criteria. These methods can be applied automatically to all the picked horizons or to horizons individually selected by the interpreter for specific analysis. We show examples of application to 2D reflection seismic data sets in complex geologic and stratigraphic conditions, critically reviewing the performance of the whole process.
21
Liu, Guofeng, Xiaohong Meng, Jianhui Ni, Zhaoxi Chen, and Da Zhang. "Evaluation of the 2D reflection seismic method toward the exploration of thrust-controlled mineral deposits in southwestern Fujian Province, China." GEOPHYSICS 83, no. 4 (2018): B209—B220. http://dx.doi.org/10.1190/geo2017-0289.1.
Texte intégralRésumé :
The southwestern region of the Fujian Province is one of the major ore districts in China. The current model states that mineral deposition is highly controlled by thrust structure, which means that there may be concealed deposits located deep within overlapping thrust areas. Reflection seismology, which has great depth penetration and higher resolution than other geophysical methods, has great potential to delineate complex structures and give some clues to mineralization. In 2015, an experimental 2D reflection seismic survey called “Fujian 2D” was conducted in this region. Data were acquired along a 13.8 km length, with a source interval of 60 m, and 691 identical receivers with an equal spacing of 20 m were used to record data for each source. Due to topographical restrictions caused by the source environment, the mass or position of some shots was changed. Despite the restrictions, the average fold number reached 64 for a 10 km distance along the middle of the survey line. During the data processing procedure, conventional technologies involving static correction, noise elimination, deconvolution, and iterative velocity analyses were applied. After the prestack time migration failed to obtain a high-quality imaging result, rugged prestack depth migration (PSDM) was introduced that resulted in a better quality image of the subsurface structure and which included near-surface parts of the thrusts. In addition, P- and S-wave velocities and density data were determined from two borehole cores. Forward modeling and imaging found that the Permian marble hosting the mineral deposits has lower velocity than the surrounding rocks, where contacts give rise to strong reflections. The final rugged PSDM also clearly delineated the thrust bodies and magma intrusion zones. Combining this forward modeling with the known geology of the investigated site, the Fujian 2D reflection seismic experiment demonstrates great potential for unveiling the main elements controlling mineral deposition, such as tectonic structure, stratigraphic contacts, and lithology. Our experimental results demonstrate that reflection seismology has a wide range of applications for future mineral exploration at greater depths.
22
Mathisen, M. E., and M. Budny. "Seismic lithostratigraphy of deep subsalt Permo‐Carboniferous gas reservoirs, Northwest German Basin." GEOPHYSICS 55, no. 10 (1990): 1357–65. http://dx.doi.org/10.1190/1.1442783.
Texte intégralRésumé :
Recent improvements in land seismic data quality have made it possible to initiate lithostratigraphic interpretations of deep (4000–5500 m; 2.2–2.8 s) subsalt Permo‐Carboniferous gas reservoirs in the Northwest German Basin. The first modeling and interpretation results indicate that the reflection character of Permian reservoir dolomites and sandstones can be interpreted to predict lithology and porosity variations using reflection character analysis. These formations are commonly thick enough to be resolved (>20 m) and typically have velocities 1000 to 2000 m/s slower than overlying and underlying nonreservoir rocks. Deeper Upper Carboniferous reservoir sandstones occur within a discontinuous low‐amplitude seismic facies which can be clearly differentiated from a continuous high‐amplitude facies formed by the less prospective Upper Carboniferous coal measures. The accuracy of Permian reflection character interpretations is dependent on the availability of high‐frequency, zero‐phase, relative amplitude seismic data. New 3-D data are appropriate but of limited availability. To provide suitable 2-D data, wavelet processing of selected variable vintage lines was completed. More routine use of wavelet processing and lithostratigraphic interpretation methods should help to better define reservoir facies and stratigraphic traps, lower prospect risk, and increase success ratios.
23
Baker, Gregory S., Don W. Steeples, and Matt Drake. "Muting the noise cone in near‐surface reflection data: An example from southeastern Kansas." GEOPHYSICS 63, no. 4 (1998): 1332–38. http://dx.doi.org/10.1190/1.1444434.
Texte intégralRésumé :
A 300-m near‐surface seismic reflection profile was collected in southeastern Kansas to locate a fault(s) associated with a recognized stratigraphic offset on either side of a region of unexposed bedrock. A substantial increase in the S/N ratio of the final stacked section was achieved by muting all data arriving in time after the airwave. Methods of applying traditional seismic data processing techniques to near‐surface data (200 ms of data or less) often differ notably from hydrocarbon exploration‐scale processing (3–4 s of data or more). The example of noise cone muting used is contrary to normal exploration‐scale seismic data processing philosophy, which is to include all data containing signal. The noise cone mute applied to the data removed more than one‐third of the total data volume, some of which contains signal. In this case, however, the severe muting resulted in a higher S/N ratio in the final stacked section, even though some signal could be identified within the muted data. This example supports the suggestion that nontraditional techniques sometimes need to be considered when processing near‐surface seismic data.
24
Gao, Dengliang. "Volume texture extraction for 3D seismic visualization and interpretation." GEOPHYSICS 68, no. 4 (2003): 1294–302. http://dx.doi.org/10.1190/1.1598122.
Texte intégralRésumé :
Visual inspection of poststack seismic image patterns is effective in recognizing large‐scale seismic features; however, it is not effective in extracting quantitative information to visualize, detect, and map seismic features in an automatic and objective manner. Although conventional seismic attributes have significantly enhanced interpreters' ability to quantify seismic visualization and interpretation, very few attributes are published to characterize both intratrace and intertrace relationships of amplitudes from a three‐dimensional (3D) perspective. These relationships are fundamental to the characterization and identification of certain geological features. Here, I present a volume texture extraction method to overcome these limitations. In a two‐dimensional (2D) image domain where data samples are visualized by pixels (picture elements), a texture has been typically characterized based on a planar texel (textural element) using a gray level co‐occurrence matrix. I extend the concepts to a 3D seismic domain, where reflection amplitudes are visualized by voxels (volume picture elements). By evaluating a voxel co‐occurrence matrix (VCM) based on a cubic texel at each of the voxel locations, the algorithm extracts a plurality of volume textural attributes that are difficult to obtain using conventional seismic attribute extraction algorithms. Case studies indicate that the VCM texture extraction method helps visualize and detect major structural and stratigraphic features that are fundamental to robust seismic interpretation and successful hydrocarbon exploration.
25
Smithyman, B. R., R. M. Clowes, and E. Bordet. "New geophysical models for subsurface velocity structure in the Nechako–Chilcotin plateau from 2.5-D waveform tomography." Canadian Journal of Earth Sciences 51, no. 4 (2014): 373–92. http://dx.doi.org/10.1139/cjes-2013-0152.
Texte intégralRésumé :
Seismic inversion is applied to generate physical property models (P-wave velocity and numerical attenuation) for four profiles in the Nechako–Chilcotin plateau region of south-central British Columbia, Canada. A newly developed method that combines three-dimensional (3-D) travel-time inversion and 2.5-dimensional (2.5-D) viscoacoustic full-waveform inversion was applied to generate the geophysical models from vibroseis data acquired along the preexisting crooked roads. These models are useful for the characterization of rock types in terms of their positions and thicknesses, which may be used in conjunction with geological ground truth to infer the extent of lithostratigraphic units in the subsurface. The velocity structures also may be used for future reprocessing of the seismic reflection data to derive improved images based on the better near-surface velocity models. The subsurface geology of the Nechako–Chilcotin plateau region is complex, resulting from multiple stages of tectonic compression and extension, contemporaneous with the deposition of sediments and volcanic material. Several basin structures are identified from the joint interpretation of the waveform tomography velocity models and post-stack time migration images. The combination of these results enables the extrapolation and characterization of geological structures to ∼3 km depth, particularly within the Cenozoic volcanic units that dominate near-surface stratigraphy. Based on the seismic profiles, a fence-diagram geological interpretation that extends to ∼3 km depth illustrates the complex structure of the Jurassic to Neogene stratigraphic sequence.
26
Hunter, J. A., S. E. Pullan, R. A. Burns, et al. "Downhole seismic logging for high‐resolution reflection surveying in unconsolidated overburden." GEOPHYSICS 63, no. 4 (1998): 1371–84. http://dx.doi.org/10.1190/1.1444439.
Texte intégralRésumé :
Downhole seismic velocity logging techniques have been developed and applied in support of high‐resolution reflection seismic surveys. For shallow high‐resolution reflection surveying within unconsolidated overburden, velocity‐depth control can sometimes be difficult to achieve; as well, unambiguous correlation of reflections with overburden stratigraphy is often problematic. Data obtained from downhole seismic logging can provide accurate velocity‐depth functions and directly correlate seismic reflections to depth. The methodologies described in this paper are designed for slimhole applications in plastic‐cased boreholes (minimum ID of 50 mm) and with source and detector arrays that yield similar frequency ranges and vertical depth resolutions as the surface reflection surveys. Compressional- (P-) wave logging uses a multichannel hydrophone array with 0.5-m detector spacings in a fluid‐filled borehole and a high‐frequency, in‐hole shotgun source at the surface. Overlapping array positions downhole results in redundant first‐arrival data (picked using interactive computer techniques), which can be processed to provide accurate interval velocities. The data also can be displayed as a record suite, showing reflections and directly correlating reflection events with depths. Example applications include identification of gas zones, lithological boundaries within unconsolidated sediments, and the overburden‐bedrock interface. Shear- (S-) wave logging uses a slimhole, well‐locked, three‐component (3-C) geophone pod and a horizontally polarized, hammer‐and‐loaded‐plate source at ground surface. The pod is moved in successive 0.5- or 1-m intervals downhole with no redundancy of overlapping data as in the P-wave method. First‐arrival data can be obtained by picking the crossover onset of polarized energy or by closely examining particle‐motion plots using all three components of motion. In unconsolidated sediments, shear‐wave velocity contrasts can be associated with changes in material density or dynamic shear modulus, which in turn can be related to consolidation. Example applications include identification of a lithological boundary for earthquake hazard applications and mapping massive ice within permafrost materials.
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Manzi, Musa S. D., Mark A. S. Gibson, Kim A. A. Hein, Nick King, and Raymond J. Durrheim. "Application of 3D seismic techniques to evaluate ore resources in the West Wits Line goldfield and portions of the West Rand goldfield, South Africa." GEOPHYSICS 77, no. 5 (2012): WC163—WC171. http://dx.doi.org/10.1190/geo2012-0133.1.
Texte intégralRésumé :
As expensive as 3D seismic reflection surveys are, their high cost is justified by improved imaging of certain ore horizons in some of the Witwatersrand basin gold mines. The merged historical 3D seismic reflection data acquired for Kloof and South Deep mines forms an integral part of their Ventersdorp Contact Reef mine planning and development programme. The recent advances in 3D seismic technology have motivated the reprocessing and reinterpretation of the old data sets using the latest algorithms, therefore significantly increasing the signal-to-noise ratio of the data. In particular, the prestack time migration technique has provided better stratigraphic and structural imaging in complex faulted areas, such as the Witwatersrand basin, relative to older poststack migration methods. Interpretation tools such as seismic attributes have been used to identify a number of subtle geologic structures that have direct impact on ore resource evaluation. Other improvements include more accurate mapping of the depths, dip, and strike of the key seismic horizons and auriferous reefs, yielding a better understanding of the interrelationship between fault activity and reef distribution, and the relative chronology of tectonic events. The 3D seismic data, when integrated with underground mapping and borehole data, provide better imaging and modeling of critical major fault systems and zones of reef loss. Many faults resolve as multifault segments that bound unmined blocks leading to the discovery and delineation of resources in faulted areas of the mines.
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Lou, Yihuai, Bo Zhang, Tengfei Lin, and Danping Cao. "Seismic horizon picking by integrating reflector dip and instantaneous phase attributes." GEOPHYSICS 85, no. 2 (2020): O37—O45. http://dx.doi.org/10.1190/geo2018-0303.1.
Texte intégralRésumé :
Seismic horizons are the compulsory inputs for seismic stratigraphy analysis and 3D reservoir modeling. Manually interpreting horizons on thousands of vertical seismic slices of 3D seismic survey is a time-consuming task. Automatic horizon interpreting algorithms are usually based on the seismic reflector dip. However, the estimated seismic reflector dip is usually inaccurate near and across geologic features such as unconformities. We are determined to improve the quality of picked horizons using multiple seismic attributes. We assume that seismic horizons follow the reflector dip and that the same horizons should have similar instantaneous phase values. We first generate horizon patches using a reflector dip attribute, which is similar to current methods. We use seismic coherence attribute as the stop criteria for tracking the horizon within each patch. Considering the inaccuracy of reflector dip estimates at and near the discontinuous structures such as fault and unconformities, we use the seismic instantaneous phase attribute to improve the quality of the generated horizon patches. We generate horizons by merging the residual horizon patches and only outputting the best horizon in each iteration. Our method is capable of generating a horizon for each reflection within the 3D seismic survey, and the generated horizons strictly follow the seismic reflections over the whole seismic survey. Finally, each time sample of seismic traces is assigned a chronostratigraphic relative geologic time value according to the tracked horizons.
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Riazi, Naimeh, David W. Eaton, Alemayehu Aklilu, and Andrew Poulin. "Application of focal-time analysis for improved induced seismicity depth control: A case study from the Montney Formation, British Columbia, Canada." GEOPHYSICS 85, no. 6 (2020): KS185—KS196. http://dx.doi.org/10.1190/geo2019-0833.1.
Texte intégralRésumé :
Characterization of induced seismicity and associated microseismicity is an important challenge for enhanced oil recovery and development of tight hydrocarbon reservoirs. In particular, accurately correlating hypocenters of induced events to stratigraphic layers plays an important role in understanding the mechanisms of fault activation. Existing methods for estimating focal depth, however, are prone to a high degree of uncertainty. A comprehensive analysis of inferred focal depths is applied to induced events that occurred during completions of horizontal wells targeting the Montney Formation in British Columbia, Canada. Our workflow includes a probabilistic, nonlinear global-search algorithm (NonLinLoc), a hierarchical clustering algorithm for relative relocation (GrowClust), and depth refinement using the recently developed focal-time method. The focal-time method leverages stratigraphic correlations between P-P and P-S reflections to eliminate the need for an explicit velocity model developed specifically for hypocenter depth estimation. We find that this approach is robust in the presence of noisy picks and location errors from epicenters obtained using a global-search algorithm, but it is limited to areas where multicomponent 3D seismic data are available. We have developed a novel method to determine statics corrections to ensure that the passive seismic observations and 3D seismic data share a common datum in areas of moderate to high topography. Our results highlight the importance of transverse faults, which appear to provide permeable pathways for activation of other faults at distances of up to 2 km from hydraulic fracturing operations.
30
Sullivan, Michael F., and Jack K. Cohen. "Prestack Kirchhoff inversion of common‐offset data." GEOPHYSICS 52, no. 6 (1987): 745–54. http://dx.doi.org/10.1190/1.1442341.
Texte intégralRésumé :
In trying to resolve complex geologic structures, the pitfalls in employing the CDP method become evident. Additionally, stacking multioffset traces corrupts the amplitudes necessary for stratigraphic analysis. In order to preserve whatever structural and amplitude information is in the data, prestack processing should be performed. Given common‐offset data and the velocity above a reflector, prestack acoustic Kirchhoff inversion resolves the location of the interface. When amplitude information has been preserved in the data, the method additionally calculates the reflection coefficient at each interface point. For band‐limited seismic data, the inversion operator produces a sinc‐like picture of the reflector, with the peak amplitude of this band‐limited singular function equal to the angularly dependent reflection coefficient. The inversion development is based upon high‐frequency Kirchhoff data which are inserted into a general 3-D inversion operator. Asymptotically evaluating the four resulting integrals by the method of four‐dimensional stationary phase permits an inversion amplitude function to be chosen so that the inversion operator produces a singular function of support on the reflector, weighted by the reflection coefficient. Specializing the three‐dimensional inversion operator to two and one‐half dimensions allows for processing of single lines of common‐offset data. Synthetic examples illustrate the accuracy of the method for constant‐velocity Kirchhoff data, as well as the problems in applying constant‐velocity data to multivelocity models.
31
Astawa, Nyoman, and Wayan Lugra. "GEOLOGI BAWAH PERMUKAAN DASAR LAUT BERDASARKAN PENAFSIRAN REKAMAN SEISMIK PANTUL DANGKAL SALURAN TUNGGAL DI PERAIRAN SELAT SUNDA." JURNAL GEOLOGI KELAUTAN 12, no. 2 (2016): 103. http://dx.doi.org/10.32693/jgk.12.2.2014.250.
Texte intégralRésumé :
Penelitian ini bertujuan untuk mengetahui kondisi geologi bawah permukaan dasar laut dengan metode seismik pantul dangkal saluran tunggal, dan pemeruman. Seismik stratigrafi daerah penelitian dapat dibedakan menjadi 3 (tiga) unit, yaitu Unit 1 diinterpretasikan sebagai batuan intrusi, Unit 2 yang dekat dengan Pulau Jawa sebagai batuan volkanik dan yang dekat dengan Pulau Sumatera diduga sebagai Formasi Lampung, dan batuan lava andesit, serta Unit 3 diinterpretasikan sebagai sedimen Kuarter. Kedalaman permukaan dasar yang dapat direkam berkisar antara -5 hingga -125 meter dengan perubahan yang terjadi secara bergradasi dari arah pantai ke laut. 
 
 Kata kunci : Morfologi permukaan dasar laut, seismik stratigrafi, geologi bawah permukaan, Selat Sunda
 
 
 The aims of study is to determine the subsurface geology condition of Sunda Strait by using single channel shallow seismic reflection, and the sounding method. Seismic stratigraphy of the study area can be divided into three (3) units, those are Unit 1, interpreted as intrusive rocks, Unit 2, which is close to Java be expected at volcanic rocks and the adjacent of Sumatera island interpreted Lampung Formation and andesitic lava rock, while Unit 3 as suspected Quaternary sediments. The sea floor depth that can be recorded ranging from -5 to -125 metres with the changes depth gradually from the shore to the sea.
 
 Keywords : Seafloor morphology, seismic stratigraphy, subsurface geology, Sunda Strait
32
Mariano, John, and William J. Hinze. "Gravity and magnetic models of the Midcontinent Rift in eastern Lake Superior." Canadian Journal of Earth Sciences 31, no. 4 (1994): 661–74. http://dx.doi.org/10.1139/e94-059.
Texte intégralRésumé :
Gravity and magnetic models of the Midcontinent Rift (MCR) in eastern Lake Superior supplement recent structural and stratigraphic interpretations based on the seismic reflection method. An algorithm developed to accommodate spatially varying direction and magnitude of magnetization within a magnetic source is used in both forward and inverse modeling procedures. Structural attitudes of rift-filling basalts derived from seismic reflection sections are used to rotate the Keweenawan remanent magnetization vectors in the direction of deformation. An iterative linear inversion routine calculates magnitudes of induced and remanent magnetizations, as well as normal and reversed polarity basalt flow distributions. The results indicate that the Koenigsberger ratios of these basalts generally range from 1 to 3, which is in agreement with values obtained from rock property measurements. The models also suggest that the greater volume of the Keweenawan basalt section in eastern Lake Superior is reversely polarized and that remanent magnetizations persist to depths of up to 20 km. Our results, supplemented by isotopic and paleomagnetic data, suggest that the vast majority of the basalts predate 1097 ± 1 Ma. A prominent positive magnetic anomaly and a corresponding gravity low strike west across the trend of the rift from the vicinity of Michipicoten Island. These anomalies may reflect a relatively strongly magnetized, felsic igneous body of late-middle to upper Keweenawan in age. Forward gravity models suggest clastic sedimentary rocks up to several kilometers thick overlay the volcanic rocks in localized depressions. Deep crustal seismic data used to constrain gravity models provide evidence of anomalously dense lower crust beneath the MCR.
33
Zhu, Tieyuan, Jonathan Ajo-Franklin, Thomas M. Daley, and Chris Marone. "Dynamics of geologic CO2 storage and plume motion revealed by seismic coda waves." Proceedings of the National Academy of Sciences 116, no. 7 (2019): 2464–69. http://dx.doi.org/10.1073/pnas.1810903116.
Texte intégralRésumé :
Quantifying the dynamics of sequestered CO2 plumes is critical for safe long-term storage, providing guidance on plume extent, and detecting stratigraphic seal failure. However, existing seismic monitoring methods based on wave reflection or transmission probe a limited rock volume and their sensitivity decreases as CO2 saturation increases, decreasing their utility in quantitative plume mass estimation. Here we show that seismic scattering coda waves, acquired during continuous borehole monitoring, are able to illuminate details of the CO2 plume during a 74-h CO2 injection experiment at the Frio-II well Dayton, TX. Our study reveals a continuous velocity reduction during the dynamic injection of CO2, a result that augments and dramatically improves upon prior analyses based on P-wave arrival times. We show that velocity reduction is nonlinearly correlated with the injected cumulative CO2 mass and attribute this correlation to the fact that coda waves repeatedly sample the heterogeneous distribution of cumulative CO2 in the reservoir zone. Lastly, because our approach does not depend on P-wave arrival times or require well-constrained wave reflections it can be used with many source–receiver geometries including those external to the reservoir, which reduces the risk introduced by in-reservoir monitoring wells. Our results provide an approach for quantitative CO2 monitoring and plume evolution that increases safety and long-term planning for CO2 injection and storage.
34
Polom, Ulrich, Hussam Alrshdan, Djamil Al-Halbouni, et al. "Shear wave reflection seismic yields subsurface dissolution and subrosion patterns: application to the Ghor Al-Haditha sinkhole site, Dead Sea, Jordan." Solid Earth 9, no. 5 (2018): 1079–98. http://dx.doi.org/10.5194/se-9-1079-2018.
Texte intégralRésumé :
Abstract. Near-surface geophysical imaging of alluvial fan settings is a challenging task but crucial for understating geological processes in such settings. The alluvial fan of Ghor Al-Haditha at the southeast shore of the Dead Sea is strongly affected by localized subsidence and destructive sinkhole collapses, with a significantly increasing sinkhole formation rate since ca. 1983. A similar increase is observed also on the western shore of the Dead Sea, in correlation with an ongoing decline in the Dead Sea level. Since different structural models of the upper 50 m of the alluvial fan and varying hypothetical sinkhole processes have been suggested for the Ghor Al-Haditha area in the past, this study aimed to clarify the subsurface characteristics responsible for sinkhole development.For this purpose, high-frequency shear wave reflection vibratory seismic surveys were carried out in the Ghor Al-Haditha area along several crossing and parallel profiles with a total length of 1.8 and 2.1 km in 2013 and 2014, respectively. The sedimentary architecture of the alluvial fan at Ghor Al-Haditha is resolved down to a depth of nearly 200 m at a high resolution and is calibrated with the stratigraphic profiles of two boreholes located inside the survey area.The most surprising result of the survey is the absence of evidence of a thick (> 2–10 m) compacted salt layer formerly suggested to lie at ca. 35–40 m depth. Instead, seismic reflection amplitudes and velocities image with good continuity a complex interlocking of alluvial fan deposits and lacustrine sediments of the Dead Sea between 0 and 200 m depth. Furthermore, the underground section of areas affected by sinkholes is characterized by highly scattering wave fields and reduced seismic interval velocities. We propose that the Dead Sea mud layers, which comprise distributed inclusions or lenses of evaporitic chloride, sulfate, and carbonate minerals as well as clay silicates, become increasingly exposed to unsaturated water as the sea level declines and are consequently destabilized and mobilized by both dissolution and physical erosion in the subsurface. This new interpretation of the underlying cause of sinkhole development is supported by surface observations in nearby channel systems. Overall, this study shows that shear wave seismic reflection technique is a promising method for enhanced near-surface imaging in such challenging alluvial fan settings.
35
de Bruin, C. G. M., C. P. A. Wapenaar, and A. J. Berkhout. "Angle‐dependent reflectivity by means of prestack migration." GEOPHYSICS 55, no. 9 (1990): 1223–34. http://dx.doi.org/10.1190/1.1442938.
Texte intégralRésumé :
Most present day seismic migration schemes determine only the zero‐offset reflection coefficient for each grid point (depth point) in the subsurface. In matrix notation, the zero‐offset reflection coefficient is found on the diagonal of a reflectivity matrix operator that transforms the illuminating source‐wave field into a reflected‐wave field. However, angle dependent reflectivity information is contained in the full reflectivity matrix. Our objective is to obtain angle‐dependent reflection coefficients from seismic data by means of prestack migration (multisource, multioffset). After downward extrapolation of source and reflected wave fields to one depth level, the rows of the reflectivity matrix (representing angle‐dependent reflectivity information for each grid point at that depth level) are recovered by deconvolving the reflected wave fields with the related source wave fields. This process is carried out in the space‐frequency domain. In order to preserve the angle‐dependent reflectivity in the imaging we must not only add all frequency contributions but we should extend the imaging principle by adding along lines of constant angle in the wavenumber‐frequency domain. This procedure is carried out for each grid point. The resulting amplitude information provides a rigorous approach to amplitude‐versus‐offset related methods. The new imaging technique has been tested on media with horizontal layers. However, with our shot‐record oriented algorithm it is possible to handle any subsurface geometry. The first tests show excellent results up to high angles, both in the acoustic and in the elastic case. With angle‐dependent reflectivity information it becomes feasible to derive detailed velocity and density information in a subsequent stratigraphic inversion step.
36
Sinha, Ajit K. "Stratigraphic mapping of sedimentary formations in southern Ontario by ground electromagnetic methods." GEOPHYSICS 55, no. 9 (1990): 1148–57. http://dx.doi.org/10.1190/1.1442931.
Texte intégralRésumé :
Multifrequency and transient electromagnetic (EM) soundings were done at several locations in southern Ontario to evaluate the possibility of stratigraphic mapping of gently dipping sedimentary formations by ground EM techniques. The possibility of detecting structural features such as folds, faults, and grabens in the formations was also explored. The two EM techniques were used to map a buried river valley near the village of Copetown, about 75 km southwest of Toronto. The valley, buried under fairly resistive glacial till and dolomite formations was mapped at depths ranging from 100 to 200 m. The interpreted shape and depth of the valley agreed well with information from a high resolution seismic reflection survey and data from wells penetrating the bedrock. Transient EM (TEM) data, using square transmitter loops with side dimensions comparable to the transmitter‐receiver separation for the multifrequency system, was found to be less affected by the presence of shallow conductors and lateral inhomogeneities than the multifrequency data, and had greater depth of investigation. TEM soundings were made on five additional profiles in the area. Lithologic logs from old oil and gas wells located near the profiles provided information for comparison with EM sounding interpretations. The depths to various dolomite, shale, and limestone formations interpreted from EM data agreed well with drillhole information. The EM soundings also detected structures in the Paleozoic formations such as faults and folds that were not previously known. The soundings confirmed the existence of a graben at one site at a depth of 100 m, which was postulated from logs from a cluster of closely spaced drillholes by geologists. The survey results indicated that EM sounding methods can be used for stratigraphic mapping in areas where detailed geological information is unavailable either because the bedrock is concealed by overburden, or when drillholes are sparsely distributed.
37
Tsai, C. J. "Use of autoconvolution to suppress first‐order, long‐period multiples." GEOPHYSICS 50, no. 9 (1985): 1410–25. http://dx.doi.org/10.1190/1.1442010.
Texte intégralRésumé :
A common problem in interpreting marine seismic data is the interference of water‐bottom multiples with primary reflections containing the structural or stratigraphic information. In deep ‐water areas, where considerable primary energy arrives before the first simple water‐bottom multiple, weak and deep crustal reflections are often obscured by the first‐order water‐bottom multiples. In order to obtain a more interpretable section, a technique involving a two‐step process was developed to suppress the first‐order water‐bottom multiples. First, the relation between the zero‐order, water‐bottom primary and its first‐order, simple water‐bottom multiple is used to derive statistically an inverse of the seismic wavelet in order to remove its effect, i.e., to wavelet‐shape the data. This wavelet processing provides a band‐limited estimate of the subsurface impulse response. The second step consists of using the autoconvolution of the wavelet‐shaped primary energy to estimate deterministically and subtract the actual first‐order, water‐bottom multiples, The method was applied to field data from the deep Gulf of Mexico. Different incidence angles for the input primaries and multiples, as well as dipping reflecting interfaces, introduce uncompensated traveltime errors. These errors reduce the ability to suppress multiples, thus restricting the validity of the method to low frequencies where common‐depth‐point stacking is less effective. On the other hand, curved interfaces may also cause amplitude prediction problems. In spite of this, the first‐order, water‐bottom multiple energy is significantly reduced (by up to 18 dB) on dip‐filtered, single‐channel data.
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Arifin, Lukman, and Tommy Naibaho. "STRUKTUR GEOLOGI DI PERAIRAN PULAU BUTON SELATAN." JURNAL GEOLOGI KELAUTAN 13, no. 3 (2016): 143. http://dx.doi.org/10.32693/jgk.13.3.2015.269.
Texte intégralRésumé :
Penelitian geofisika dengan metode seismik pantul dangkal dilakukan di perairan Pulau Buton bagian selatan. Tujuan dari penelitian adalah untuk mengetahui kondisi geologi di bawah permukaan dasar laut. Dari data rekaman seismik diinterpretasikan bahwa stratigrafi seismik dibagi menjadi dua runtunan yaitu runtunan A dan B. Bila disebandingkan dengan geologi daratnya maka runtunan A termasuk dalam Formasi Wapulaka yang berumur Tersier dan runtunan B termasuk Formasi Sampolakosa yang berumur Kuater. Data rekaman tersebut juga menunjukkan adanya beberapa struktur geologi seperti sesar, lipatan, dan pengangkatan. Diduga struktur geologi tersebut berkembang dengan masih aktifnya proses tektonik hingga sekarang. Implikasi aktifnya tektonik ini dapat memperkaya dan meningkatkan potensi sumberdaya alam yang ada seperti migas dan aspal. Kata kunci seismik pantul dangkal, struktur geologi, tektonik, Perairan Pulau Buton. Geophysical research with shallow reflection seismic method carried out in the waters of the southern part of Buton Island. The aim of research is to determine the geological conditions under the sea floor. Data from seismic recordings interpreted that seismic stratigraphy is divided into two sequences, that are sequence A and B. Ifthe land geology to be compared then the sequence A is Wapulaka Formation which is Tertiary age and sequence B is Sampolakosa Formation which is Kuarter age. The recording data also indicated a number of geological structures such as faults, folds, and uplift. It was alleged that the geological structure is developing with tectonic processes are still active until now. The implications of the active tectonic can enrich and enhance the existing natural resources such as oil and gas, and bitumen. Keywords: shallow seismicreflection, geology structure, tectonic, Buton Island Waters.
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Henninges, Jan, Evgeniia Martuganova, Manfred Stiller, Ben Norden, and Charlotte M. Krawczyk. "Wireline distributed acoustic sensing allows 4.2 km deep vertical seismic profiling of the Rotliegend 150 °C geothermal reservoir in the North German Basin." Solid Earth 12, no. 2 (2021): 521–37. http://dx.doi.org/10.5194/se-12-521-2021.
Texte intégralRésumé :
Abstract. We performed so-far-unprecedented deep wireline vertical seismic profiling at the Groß Schönebeck site with the novel method of distributed acoustic sensing (DAS) to gain more detailed information on the structural setting and geometry of the geothermal reservoir, which is comprised of volcanic rocks and sediments of Lower Permian age. During the survey of 4 d only, we acquired data for 61 source positions using hybrid wireline fiber-optic sensor cables deployed in two 4.3 km deep, already existing wells. While most of the recorded data have a very good signal-to-noise ratio, individual sections of the profiles are affected by characteristic coherent noise patterns. This ringing noise results from incomplete coupling of the sensor cable to the borehole wall, and it can be suppressed to a large extent using suitable filtering methods. After conversion to strain rate, the DAS data exhibit a high similarity to the vertical component data of a conventional borehole geophone. We derived accurate time–depth relationships, interval velocities, and corridor stacks from the recorded data. Based on integration with other well data and geological information, we show that the top of a porous and permeable sandstone interval of the geothermal reservoir can be identified by a positive reflection event. Overall, the sequence of reflection events shows a different character for both wells explained by lateral changes in lithology. The top of the volcanic rocks has a somewhat different seismic response in both wells, and no clear reflection event is obvious at the postulated base of the volcanic rocks, so that their thickness cannot be inferred from individual reflection events in the seismic data alone. The DAS method enabled measurements at elevated temperatures up to 150 ∘C over extended periods and led to significant time and cost savings compared to deployment of a conventional borehole geophone string. This wireline approach finally suggests significant implications for observation options in old wells for a variety of purposes.
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Martinez, Ruben D., та George A. McMechan. "Analysis of absorption and dispersion effects in synthetic τ-p seismograms". GEOPHYSICS 52, № 8 (1987): 1033–47. http://dx.doi.org/10.1190/1.1442369.
Texte intégralRésumé :
Analysis of absorption and dispersion effects may be done in intercept time‐ray parameter (τ-p) synthetic seismograms calculated using the slowness formulation of the reflectivity method. Seismograms initially computed in the frequency‐ray parameter (ω-p) domain to incorporate absorption and dispersion effects are then Fourier transformed to the (τ-p) domain. Absorption and dispersion are functions of p. Modeling both simple and more realistic stratigraphic sequences shows the interaction of only velocity and density for infinite Q and the complicated effects added when Q is finite. The observed null reflection at p = 0 for infinite Q is no longer null when Q is finite. For p ≠ 0, the inclusion of absorption and dispersion effects complicates the amplitude and phase of the seismic response. Reflectivity due to Q alone (i.e., at an interface with no impedance contrast), as a function of Q contrast and p, contains interesting variations of amplitude and phase. The responses of three geologically realistic models (a brine sand, a partially saturated gas sand, and an ocean‐sediment interface) demonstrate the cumulative nature of the attenuation effect and how the Q contributions become dominant when the acoustic impedance contrast is small. For large acoustic impedance contrasts, the attenuation effect occurs as an amplitude decay and phase rotation for some (especially high) frequencies. The modeling results suggest that absorption and dispersion effects should be taken into account in seismic inversion. Q estimations (in addition to velocity and density) are particularly desirable in exploration for hydrocarbons because of the sensitivity of Q to lithology and fluid content. Q contributes to the reflectivity information inherent in the seismic data.
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Yang, Chun, Yun Wang, Shu Xiong, Zikun Li, and Hewei Han. "P-Wave Reflection Approximation of a Thin Bed and Its Application." Applied Sciences 10, no. 22 (2020): 8061. http://dx.doi.org/10.3390/app10228061.
Texte intégralRésumé :
“Thin-bed” reservoirs have become important targets of seismic exploration and exploitation. However, traditional amplitude versus offset/amplitude versus angle (AVO/AVA) technologies, for example, those based on Zoeppritz equations and their approximations for a single interface, are not sufficiently accurate for thin-bed stratigraphy. Analytic solutions of thin-bed reflectivity may become practical for thin-bed AVO analysis and inversion. Therefore, a linear analytic approximation of thin-bed P-wave reflectivity is developed under small-incidence and thin-bed assumptions. Numerical simulations show that the amplitude approximation errors are usually smaller than 10% for incidence angles less than 20 degrees, and the thin-bed thicknesses are less than one-tenth of the P-wave wavelength. Based on the least-squares approach, the inversion strategy is proposed using the approximate formula. A synthetic data test shows that the proposed inversion method can produce more accurate thin-bed properties than that based on the Zoeppritz equations, which reveals the potential of the inversion method based on the linear analytic approximate formula in the fine characterization of thin reservoirs.
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Wu, Xinming, and Sergey Fomel. "Automatic fault interpretation with optimal surface voting." GEOPHYSICS 83, no. 5 (2018): O67—O82. http://dx.doi.org/10.1190/geo2018-0115.1.
Texte intégralRésumé :
Numerous types of fault attributes have been proposed to detect faults by measuring reflection continuities or discontinuities. However, these attributes can be sensitive to other seismic discontinuities, such as noise and stratigraphic features. In addition, fault features within a fault attribute image often cannot be continuously tracked. We have developed an optimal surface-voting method to enhance a fault attribute image so that the noisy features (unrelated to faults) are suppressed whereas the fault features become cleaner and more continuous. In this method, we first automatically pick seed points from the input attribute image and use these seeds as control points to compute optimal surface patches that pass through the control points and follow globally maximum fault attribute values. Then, we consider all the computed surfaces as voters and define voting scores for each voter by using fault attribute values that are smoothed along the surface voter. We further collect voting scores of all the voters to compute a voting score map as a new fault attribute image, in which fault features (with high scores) are much cleaner, sharper, and more continuous than those in the input attribute image. With the optimal surface voters, we can also accurately estimate fault orientations (strikes and dips) by computing weighted averages of the surface voter orientations. From a voting score map with clean and continuous fault features, fault surfaces can be extracted by tacking the fault features along the estimated fault orientations. The computational cost of the method depends on the number of seed points, not the size of the seismic volume, which makes the method highly efficient. With an four-core computer, our parallel implementation can process more than 1000 seeds in 1 s to compute the corresponding optimal voting surfaces and a final voting score map.
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Gras, Clàudia, Daniel Dagnino, Clara Estela Jiménez-Tejero, Adrià Meléndez, Valentí Sallarès, and César R. Ranero. "Full-waveform inversion of short-offset, band-limited seismic data in the Alboran Basin (SE Iberia)." Solid Earth 10, no. 6 (2019): 1833–55. http://dx.doi.org/10.5194/se-10-1833-2019.
Texte intégralRésumé :
Abstract. We present a high-resolution P-wave velocity model of the sedimentary cover and the uppermost basement to ∼3 km depth obtained by full-waveform inversion of multichannel seismic data acquired with a 6 km long streamer in the Alboran Sea (SE Iberia). The inherent non-linearity of the method, especially for short-offset, band-limited seismic data as this one, is circumvented by applying a data processing or modelling sequence consisting of three steps: (1) data re-datuming by back-propagation of the recorded seismograms to the seafloor; (2) joint refraction and reflection travel-time tomography combining the original and the re-datumed shot gathers; and (3) full-waveform inversion of the original shot gathers using the model obtained by travel-time tomography as initial reference. The final velocity model shows a number of geological structures that cannot be identified in the travel-time tomography models or easily interpreted from seismic reflection images alone. A sharp strong velocity contrast accurately defines the geometry of the top of the basement. Several low-velocity zones that may correspond to the abrupt velocity change across steeply dipping normal faults are observed at the flanks of the basin. A 200–300 m thick, high-velocity layer embedded within lower-velocity sediment may correspond to evaporites deposited during the Messinian crisis. The results confirm that the combination of data re-datuming and joint refraction and reflection travel-time inversion provides reference models that are accurate enough to apply full-waveform inversion to relatively short offset streamer data in deep-water settings starting at a field-data standard low-frequency content of 6 Hz.
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Lyu, Bin, Jie Qi, Saurabh Sinha, Jianjun Li, and Kurt J. Marfurt. "Improving fault delineation using maximum entropy multispectral coherence." Interpretation 8, no. 4 (2020): T835—T850. http://dx.doi.org/10.1190/int-2020-0089.1.
Texte intégralRésumé :
Knowledge of fault geometry plays an important role in reservoir modeling and characterization. Seismic attributes, such as volumetric dip, coherence, and curvature, provide an efficient and objective tool to extract fault geometry attributes. Traditionally, we use noise-attenuated full-bandwidth seismic data to compute coherence followed by smoothing, sharpening, and skeletonization. However, different stratigraphic reflectors with relatively similar waveforms and amplitudes juxtaposing across a fault will algorithmically appear to be continuous, with the resulting fault image being broken. This leads to pseudo fault breakpoints and challenges the accurate extraction of other fault geometric attributes. Because the phase of the similar reflections across the faults varies with different spectral components, such nonstratigraphic alignments occur for only a few spectral components such that a multispectral coherence algorithm produces more continuous fault images. We have evaluated the influence of spectral voice selection and spectral decomposition algorithm on the quality of fault imaging in multispectral coherence images using a 3D seismic survey acquired in the Taranaki Basin, New Zealand. Of the algorithms evaluated, we find that the high-resolution maximum-entropy-based multispectral coherence method provides better results than those based on other spectral decomposition algorithms, which especially improves the fault continuity. However, the lateral resolution of fault imaging in multispectral coherence is decreased compared to the full-bandwidth coherence, because the fault image is smeared when we combine the coherence volumes computed using different spectral voices. We perform a fault enhancement workflow on the maximum-entropy-based multispectral coherence volume to improve the lateral resolution of fault imaging, which helps delineate the minor faults.
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Adam, Erick, Bernd Milkereit, and Marianne Mareschal. "Seismic reflection and borehole geophysical investigations in the Matagami mining camp." Canadian Journal of Earth Sciences 35, no. 6 (1998): 686–95. http://dx.doi.org/10.1139/e98-022.
Texte intégralRésumé :
A high-frequency vibroseis seismic survey was conducted by Lithoprobe across a well-known section of the Matagami mining camp to assess the usefulness of seismic methods in lithological mapping. The data have been reprocessed to enhance shallow reflections. Critical processing steps for the preservation of the shallow features include refraction static corrections, cross-dip corrections, and first break mutes. The seismic data were calibrated using geophysical logs from two boreholes adjacent to the profile. Physical rock property measurements suggest that strong reflectivity within the volcanic sequence occurs at rhyolite-gabbro contacts. The Lower Wabassee Group, a sequence of gabbros and basalts with interlayered rhyolite horizons, has been identified as a seismic marker. This reflective package overlays the horizon where most sulphide deposits are known to be located. In the Matagami mining camp, seismic reflection methods can be used to map the deep volcanic stratigraphy and structures.
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Hardage, Bob, Mike Graul, Tim Hall, et al. "Determining fast-S and slow-S propagation directions with SV-P data produced by buried explosives and recorded with vertical geophones." Interpretation 9, no. 2 (2021): T599—T609. http://dx.doi.org/10.1190/int-2020-0226.1.
Texte intégralRésumé :
We have evaluated the concept of practicing S-wave reflection seismology with legacy 3D seismic data generated by a P-wave source and recorded with only vertical geophones. This type of S-wave imaging is based on the principle that seismic P-wave sources not only produce a downgoing illuminating P wavefield, but they also simultaneously produce a downgoing illuminating SV wavefield that, in almost all cases, is suitable for S-wave reflection imaging. The S-mode used in this study is the SV-P, or converted-P, mode. This mode involves a downgoing illuminating SV wavefield and an upgoing reflected P-mode that is recorded by vertical geophones. In flat-layered stratigraphy, the lengths of the SV and P raypaths in SV-P imaging are identical to the lengths of the SV and P raypaths in P-SV imaging with P-sources and 3C geophones. P-SV imaging of deep rocks has been practiced for more than two decades; SV-P imaging is a new concept. SV-P data should provide the same options for investigating deep rocks as do P-SV data. We have determined one of the equivalences between SV-P data extracted from vertical-geophone data and P-SV data extracted from horizontal geophones: that both modes react to azimuth-dependent variations in the S velocity in anisotropic rocks. Azimuthal variations in the SV-P traveltime can be used to define the polarization direction of the fast-S-wave mode, which is also the azimuth of the maximum horizontal stress (SHmax). Our investigation demonstrates a noninvasive method for monitoring changes in the SHmax azimuth across a CO2 storage reservoir, or any targeted porous rock, as fluids are cycled into, and then out of, that rock’s pore space.
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Wu, Xinming, and Zhenwei Guo. "Detecting faults and channels while enhancing seismic structural and stratigraphic features." Interpretation 7, no. 1 (2019): T155—T166. http://dx.doi.org/10.1190/int-2017-0174.1.
Texte intégralRésumé :
A 3D seismic image contains structural and stratigraphic features such as reflections, faults, and channels. When smoothing such an image, we want to enhance all of these features so that they are easier to interpret. Most smoothing methods aim to enhance reflections but may blur faults and channels in the image. A few methods smooth seismic reflections while preserving faults and channel boundaries. However, it has not well-discussed to smooth simultaneously along the seismic reflections and channels, which are linear features apparent within dipping reflections. In addition, to interpret faults and channels, extra steps are required to compute attributes or mappings of faults and channels from a seismic image. Such fault and channel attributes are often sensitive to noise because they are typically computed as discontinuities of seismic reflections. In this paper, we have developed methods to simultaneously enhance seismic reflections, faults, and channels while obtaining mappings of the faults and channels. In these methods, we first estimate the orientations of the reflections, faults, and channels directly in a seismic image. We then use the estimated orientations to control the smoothing directions in an efficient iterative diffusion scheme to smooth a seismic image along the reflections and channels. In this iterative scheme, we also efficiently compute mappings of faults and channels, which are used to control smoothing extents in the diffusion to stop smoothing across them. This diffusion scheme iteratively smooths a seismic image along reflections and channels while updating the mappings of faults and channels. By doing this, we will finally obtain an enhanced seismic image (with enhanced reflections and channels and sharpened faults) and cleaned mappings of faults and channels (discontinuities related to noise are cleaned up). We have examined the methods using 2D and 3D real seismic images.
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Adam, Erick, G. Perron, B. Milkereit, et al. "A review of high-resolution seismic profiling across the Sudbury, Selbaie, Noranda, and Matagami mining camps." Canadian Journal of Earth Sciences 37, no. 2-3 (2000): 503–16. http://dx.doi.org/10.1139/e99-064.
Texte intégralRésumé :
Lithoprobe high-resolution seismic surveys have provided the first systematic images of the deep stratigraphy in four major Canadian mining camps (Noranda, Matagami, Sudbury, and Selbaie). Systematic compressional wave velocity and density measurements in deep boreholes have established that lithological contacts were the main impedance contrast imaged, although reflections from faults and deformation zones have also been observed. The strongest reflections are attributed to mafic intrusions and some sulphides and oxides. Integrating seismic, physical rock property measurements, and geological data has resulted in the revision of several geological models with direct impact on local strategies for deep mineral exploration. Mining companies have shown an interest in seismic reflection methods and this has led to several follow-up studies. The application of seismic methods to the direct detection of massive sulphides, based on physical rock property measurements, has been studied through two-dimensional and three-dimensional (3D) seismic imaging and vertical seismic profiling technologies. The challenge will now be to optimize 3D seismic imaging for mineral exploration and to improve seismic data processing by enhancing the seismic response from deep, lenticular orebodies.
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Zeng, Hongliu. "What is seismic sedimentology? A tutorial." Interpretation 6, no. 2 (2018): SD1—SD12. http://dx.doi.org/10.1190/int-2017-0145.1.
Texte intégralRésumé :
I have developed an alternative narrative of seismic sedimentology from a geologist’s perspective. Seismic sedimentology is a high-resolution supplement for traditional, low-resolution seismic stratigraphy, reflecting the fact that seismic responds to sedimentary bodies differently at low and high resolution. Seismic stratigraphy is a model-driven method that follows the principles of field geology and the well-based study of subsurface sedimentology, and it assumes that seismic reflections can duplicate geologic correlations. Seismic sedimentology is a more data-driven approach based on the understanding of how a seismic signal responds to thin-bedded depositional elements in the context of stratigraphy, which is a function of thickness, lithology-impedance model, wavelet phase, and frequency. Seismic sedimentology is focused on mapping seismic litho-geomorphologic facies, by joint investigation of seismic lithology and seismic geomorphology. In such an investigation, seismic lithology and seismic geomorphology are complementary, making more complete use of seismic information, and they can be more powerful in determining the sedimentary environment and reservoir quality. To reduce the knowledge gap between sedimentary geologists and seismic geophysicists, sedimentologists have to learn and master geophysical principles and techniques. To begin with, a simplified four-step workflow is recommended, which can be summarized as select-adjust-decompose-blend.
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Haines, Seth S., and Karl J. Ellefsen. "Shear-wave seismic reflection studies of unconsolidated sediments in the near surface." GEOPHYSICS 75, no. 2 (2010): B59—B66. http://dx.doi.org/10.1190/1.3340969.
Texte intégralRésumé :
We have successfully applied of SH-wave seismic reflection methods to two different near-surface problems targeting unconsolidated sediments. At the former Fort Ord, where the water table is approximately [Formula: see text] deep, we imaged aeolian and marine aquifer and aquitard stratigraphy to a depth of approximately [Formula: see text]. We identified reflections from sand/clay and sand/silt interfaces and we mapped these interfaces along our transects. At an aggregate study site in Indiana, where the water table is at a depth of [Formula: see text], we imaged stratigraphy in alluvial sand and gravel, and observe a strong reflection from the [Formula: see text]-deep bedrock surface. In both cases, we exploited the high resolution potential of SH waves, their insensitivity to water content, and the possibility of reducing Love wave contamination by working along a roadway. We accomplished our results using only sledgehammer sources and simple data processing flows.