Journal articles on the topic 'Petroleum exploration; Petrophysics; Lithology'

China has vast reserves of shale gas. Currently, shale gas is one of the focuses of the unconventional reservoir. Well logs play an import role in shale gas production, and it is the bridge connecting geology, geophysics and petroleum engineering. In the exploration stage, well logs are used to identify lithology, evaluate the parameters of mineral types and compositions, total organic carbon (TOC), porosity, permeability, gas content, and the potential resources quantity. In the development stage, well logs offer various parameters of geological and engineering for horizontal drilling and production, evaluate the mechanical properties and calculate the magnitude and orientation of the in-situ stress for hydraulic fracturing stimulation. We reviewed current well logs for shale gas in China and discussed the development trend in the paper. A case history in Sichuan Basin presented to analyze the logs response characteristics and parameters calculation for a shale gas well. The difficulty and the future attention focus are also discussed.

To date, most of the oil and gas production in Cuu Long Basin (CLB) is contributed from structural traps, making them more and more depleted after years of exploitation. Exploration activities in CLB, therefore, are shifting towards other traps, including stratigraphic and/or combination ones. The results of exploration and appraisal activities in recent years have increasingly discovered more hydrocarbons in the Oligocene section; some of them were discovered in combination/ stratigraphic traps. Many studies on Oligocene targets in Southeast CLB have been carried out but only a few mention nonstructural traps. This leads to uncertainty about the forming mechanisms and distribution, as well as unevaluated hydrocarbon potential of these traps. An integrated approach- utilizing methods of seismic sequence stratigraphy, seismic attribute interpretation, and petrophysical/ petrographical analysis- was applied in this research to identify the forming mechanisms of Oligocene combination/ stratigraphic traps in southeast area of CLB and to evaluate their reservoir quality. The research results show that the key forming factor for stratigraphic traps of sand body is lithology change and the one for pinch-out stratigraphic traps is tapering off of sand layers landward or toward the horsts. The reservoir quality of these traps ranges from moderate to good. By integratedly applying the methods, the forming mechanisms and reservoir quality of Oligocene stratigraphic traps could be delineated. In order to optimize the next-stage exploration strategy in CLB, detailed studies on petroleum system, especially top and bottom seals, and the hydrocarbon potential of these stratigraphic traps, need to be carried out.

The need to extract more information about the subsurface from geophysical and petrophysical measurements has led to a great interest in the study of the effect of rock and fluid properties on geophysical and petrophysical measurements. Rock physics research in the last few years has been concerned with studying the effect of lithology, fluids, pore geometry, and fractures on velocity; the mechanisms of attenuation of seismic waves; the effect of anisotropy; and the electrical and dielectric properties of rocks. Understanding the interrelationships between rock properties and their expression in geophysical and petrophysical data is necessary to integrate geophysical, petrophysical, and engineering data for the enhanced exploration and characterization of petroleum reservoirs. The use of amplitude offsets, S‐wave seismic data, and full‐waveform sonic data will help in the discrimination of lithology. The effect of in situ temperatures and pressures must be taken into account, especially in fractured and unconsolidated reservoirs. Fluids have a strong effect on seismic velocities, through their compressibility, density, and chemical effects on grain and clay surfaces. S‐wave measurements should help in bright spot analysis for gas reservoirs, but theoretical considerations still show that a deep, consolidated reservoir will not have any appreciable impedance contrast due to gas. The attenuation of seismic waves has received a great deal of attention recently. The idea that Q is independent of frequency has been challenged by experimental and theoretical findings of large peaks in attenuation in the low kHz and hundreds of kHz regions. The attenuation is thought to be due to fluid‐flow mechanisms and theories suggest that there may be large attenuation due to small amounts of gas in the pore space even at seismic frequencies. Models of the effect of pores, cracks, and fractures on seismic velocity have also been studied. The thin‐crack velocity models appear to be better suited for representing fractures than pores. The anisotropy of seismic waves, especially the splitting of polarized S‐waves, may be diagnostic of sets of oriented fractures in the crust. The electrical properties of rocks are strongly dependent upon the frequency of the energy and logging is presently being done at various frequencies. The effects of frequency, fluid salinity, clays, and pore‐grain geometry on electrical properties have been studied. Models of porous media have been used extensively to study the electrical and elastic properties of rocks. There has been great interest in extracting geometrical parameters about the rock and pore space directly from microscopic observation. Other models have focused on modeling several different properties to find relationships between rock properties.

The Roebuck Basin and the adjoining Beagle and Barcoo sub-basins are underexplored areas on Australia’s North West Shelf that are undergoing renewed exploration interest since the discovery of oil at Phoenix South 1 in 2014 and subsequent hydrocarbon discoveries in the Bedout Sub-basin. A well folio of 24 offshore wells across the Beagle, Bedout, Rowley and Barcoo sub-basins has been compiled as part of Geoscience Australia’s hydrocarbon prospectivity assessment across the region. It consists of composite well log plots and well correlations that summarise lithology, lithostratigraphy, Geoscience Australia’s newly acquired biostratigraphic and geochemical data as well as results of petrophysical analysis. A revised sequence-stratigraphic interpretation, key petroleum system elements and drilling results are also documented. The wells dominantly target Triassic shoreward facies (Keraudren Formation) as the primary reservoir objective and Jurassic fluvial-deltaic (Depuch Formation) and/or Lower Cretaceous sandy deltaic facies as the secondary objective. The Keraudren Formation sandstones are sealed intra-formationally either by discontinuous units and/or by the regional Cossigny Member. The Jurassic Depuch Formation sandstones are sealed by regional Lower Cretaceous mudstones. Both charge and structure have been identified as critical issues in the Roebuck Basin. In the Beagle Sub-basin, seal integrity and migration pathways are also considered high risk. Well correlations have identified differences in the basin history and provide insights into the distribution of facies and other characteristics of the Jurassic and Triassic successions.

Reservoir pore space assessment is of great significance for petroleum exploration and production. However, it is difficult to describe the pore characteristics of deep-buried dolomite reservoirs with the traditional linear method because these rocks have undergone strong modification by tectonic activity and diagenesis and show significant pore space heterogeneity. In this study, 38 dolostone samples from 4 Cambrian formations of Tarim Basin in NW China were collected and 135 thin section images were analyzed. Multifractal theory was used for evaluation of pore space heterogeneity in deep-buried dolostone based on thin section image analysis. The physical parameters, pore structure parameters, and multifractal characteristic parameters were obtained from the digital images. Then, the relationships between lithology and these parameters were discussed. In addition, the pore structure was classified into four categories using K-means clustering analysis based on multifractal parameters. The results show that the multifractal phenomenon generally exists in the pore space of deep-buried dolomite and that multifractal analysis can be used to characterize the heterogeneity of pore space in deep-buried dolomite. For these samples, multifractal parameters, such as αmin, αmax, ΔαL, ΔαR, Δf, and AI, correlate strongly with porosity but only slightly with permeability. However, the parameter Δα, which is usually used to reveal heterogeneity, does not show an obvious link with petrophysical properties. Of dolomites with different fabrics, fine crystalline dolomite and medium crystalline dolomite show the best petrophysical properties and show significant differences in multifractal parameters compared to other dolomites. More accurate porosity estimations were obtained with the multifractal generalized fractal dimension, which provides a new method for porosity prediction. The various categories derived from the K-means clustering analysis of multifractal parameters show distinct differences in petrophysical properties. This proves that reservoir evaluation and pore structure classification can be accurately performed with the K-means clustering analysis method based on multifractal parameters of pore space in deep-buried dolomite reservoirs.

Exploring for the Future (EFTF) is an Australian Government initiative focused on gathering new data and information about potential mineral, energy and groundwater resources across Australia. The energy component of EFTF, initially focussed on northern Australia, aims to improve our understanding of the petroleum potential of frontier Australian basins. Building an understanding of geomechanical rock properties is key to understanding both conventional and unconventional petroleum systems as well as carbon storage and sedimentary geothermal systems. Under EFTF, Geoscience Australia has undertaken geomechanical work including stress modelling, shale brittleness studies and the acquisition of new rock property data through extensive testing on samples from the Paleo- to Mesoproterozoic South Nicholson region of Queensland and the Northern Territory, and the Paleozoic Kidson Sub-basin of Western Australia. Work in these regions demonstrates regional stress orientations in broad agreement with previously modelled, continent-scale stress orientations and stress magnitudes that vary through the basin with depth and by lithology. Rock testing highlights potentially brittle shales and demonstrates variable rock properties in line with lithology. These analyses are summarised herein. Providing baseline geomechanical data in frontier basins is essential as legacy data coverage can often be inadequate for making investment decisions, particularly where unconventional plays are a primary exploration target. As EFTF increases in scope, Geoscience Australia anticipates expanding these studies to encompass further underexplored regions throughout Australia, lowering the barrier to entry and encouraging greenfield exploration.

Permeability is one of the most important property for reservoir characterization, and its prediction has been one of the fundamental challenges specially for a complex formation such as carbonate, due to this complexity, log analysis cannot be accurate enough if it’s not supported by core data, which is critically important for formation evaluation. In this paper, permeability is estimated by making both core and log analysis for five exploration wells of Yammama formation, Nasiriyah oil field. The available well logging recorders were interpreted using Interactive Petrophysics software (IP) which used to determine lithology, and the petrophysical properties. Nuclear Magnetic Resonance (NMR) Measurements is used for laboratory tests, which provide an accurate, porosity and permeability measurements. The results show that the main lithology in the reservoir is limestone, in which average permeability of the potential reservoir units’ values tend to range from 0.064275 in zone YA to 20.74 in zone YB3, and averaged porosity values tend to range from 0.059 in zone YA to 0.155 in zoneYB3. Zone YB3 is found to be the best zone in the Yammama formation according to its good petrophysical properties. The correlation of core-log for permeability and porosity produce an acceptable R^2 equal to 0.618, 0.585 respectively

As economics of the oil and gas industry become more restrictive, the need for new means of improving exploration risks and reducing expenses is becoming more acute. Partnerships between industry and academia are making significant improvements in four general areas: Seismic acquisition, reservoir characterization, quantitative structural modeling, and geochemical inversion. In marine seismic acquisition the vertical cable concept utilizes hydrophones suspended at fixed locations vertically within the water column by buoys. There are numerous advantages of vertical cable technology over conventional 3-D seismic acquisition. In a related methodology, ‘Borehole Seismic,’ seismic energy is passed between wells and valuable information on reservoir geometry, porosity, lithology, and oil saturation is extracted from the P-wave and S-wave data. In association with seismic methods of determining the external geometry and the internal properties of a reservoir, 3-dimensional sedimentation-simulation models, based on physical, hydrologic, erosional and transport processes, are being utilized for stratigraphic analysis. In addition, powerful, 1-D, coupled reaction-transport models are being used to simulate diagenesis processes in reservoir rocks. At the regional scale, the bridging of quantitative structural concepts with seismic interpretation has lead to breakthroughs in structural analysis, particularly in complex terrains. Such analyses are becoming more accurate and cost effective when tied to highly advanced, remote-sensing, multi-spectral data acquisition and image processing technology. Emerging technology in petroleum geochemistry enables geoscientists to infer the character, age, maturity, identity and location of source rocks from crude oil characteristics (‘Geochemical Inversion’) and to better estimate hydrocarbon-supply volumetrics, which can be invaluable in understanding petroleum systems and in reducing exploration risks and associated expenses.

Lithology identification based on conventional well-logging data is of great importance for geologic features characterization and reservoir quality evaluation in the exploration and production development of petroleum reservoirs. However, there are some limitations in the traditional lithology identification process: (1) It is very time consuming to build a model so that it cannot realize real-time lithology identification during well drilling, (2) it must be modeled by experienced geologists, which consumes a lot of manpower and material resources, and (3) the imbalance of labeled data in well-log data may reduce the classification performance of the model. We have developed a gradient boosting decision tree (GBDT) algorithm combining synthetic minority oversampling technique (SMOTE) to realize fast and automatic lithology identification. First, the raw well-log data are normalized by maximum and minimum normalization algorithm. Then, SMOTE is adopted to balance the number of samples in each class in training process. Next, a lithology identification model is built by GBDT to fit the preprocessed training data set. Finally, the built model is verified with the testing data set. The experimental results indicate that the proposed approach improves the lithology identification performance compared with other machine-learning approaches.

Offshore petroleum systems are often very complex and subtle because of a variety of depositional environments. Characterizing a reservoir based on conventional seismic and well-log stratigraphic analysis in intricate settings often leads to uncertainties. Drilling risks, as well as associated subsurface uncertainties can be minimized by accurate reservoir delineation. Moreover, a forecast can also be made about production and performance of a reservoir. This study is aimed to design a workflow in reservoir characterization by integrating seismic inversion, petrophysics and rock physics tools. Firstly, to define litho facies, rock physics modeling was carried out through well log analysis separately for each facies. Next, the available subsurface information is incorporated in a Bayesian engine which outputs several simulations of elastic reservoir properties, as well as their probabilities that were used for post-inversion analysis. Vast areal coverage of seismic and sparse vertical well log data was integrated by geostatistical inversion to produce acoustic impedance realizations of high-resolution. Porosity models were built later using the 3D impedance model. Lastly, reservoir bodies were identified and cross plot analysis discriminated the lithology and fluid within the bodies successfully.

In short, yes. This case study illustrates that the application of a thorough geotechnical workflow incorporating many new and advanced techniques can assist in exploration business case decision making. Is an exploration drilling decision made lightly? A workflow incorporating 3D seismic processing, AVO inversion and stratigraphic framework studies involving high-resolution biostratigraphic and chemostratigraphic analyses was used to assess the prospectivity of an exploration permit near giant gas fields in the offshore Northern Carnarvon Basin. The primary reservoir is the prolific Triassic Mungaroo Formation fluvio-deltaic sediments, and secondary reservoirs include mid-Jurassic marine sands. 3D seismic reprocessing xcombined a newly acquired broadband seismic dataset into a multi-survey multi-azimuth PSDM volume that conditioned data for input to an AVO inversion. New petrophysics and rock physics analysis and modelling on regional well data were then calibrated with the AVO inversion to statistically derive lithology and fluid prediction volumes. These data were used in conjunction with reservoir paleo-stratigraphy studies to derive a subsurface model for reservoir distribution and hydrocarbon prediction. A two-stage risking process was applied to each prospect that objectively applied risk based on the seismic amplitudes. This enabled a more accurate risked-volume assessment, combined with the ability to assess a prospect portfolio covering different plays. The resultant interpretation identified issues with interpretations made on vintage data that would not have been easily identified without undertaking these studies. The integration of these assessments resulted in an unfavourable exploration drilling business case and a decision not to renew the permit.

The Heazlewood-Luina-Waratah area is a prospective region for minerals in northwest Tasmania, Australia, associated with historically important ore deposits related to the emplacement of granite intrusions and/or ultramafic complexes. The geology of the area is poorly understood due to the difficult terrain and dense vegetation. We have constructed an initial high-resolution 3D geologic model of this area using constraints from geologic maps and geologic and geophysical cross sections. This initial model is improved upon by integrating results from 3D geometry and physical property inversion of potential field (gravity and magnetic) data, petrophysical measurements, and updated field mapping. Geometry inversion reveals that the Devonian granites in the south are thicker than previously thought, possibly connecting to deep sources of mineralization. In addition, we identified gravity anomalies to the northeast that could be caused by near-surface granite cupolas. A newly discovered ultramafic complex linking the Heazlewood and Mount Stewart Ultramafic Complexes in the southwest also has been modeled. This implies a greater volume of ultramafic material in the Cambrian successions and points to a larger obducted component than previously thought. The newly inferred granite cupolas and ultramafic complexes are targets for future mineral exploration. Petrophysical property inversion reveals a high degree of variation in these properties within the ultramafic complexes indicating a variable degree of serpentinization. Sensitivity tests suggest maximum depths of 2–3 km for the contact aureole that surrounds major granitic intrusions in the southeast, whereas the Heazlewood River complex is likely to have a deeper source up to 4 km. We have demonstrated the value of adding geologic and petrophysical constraints to 3D modeling for the purpose of guiding mineral exploration. This is particularly important for the refinement of geologic structures in tectonically complex areas that have lithology units with contrasting magnetic and density characteristics.

The identification of underground formation lithology can serve as a basis for petroleum exploration and development. This study integrates Extreme Gradient Boosting (XGBoost) with Bayesian Optimization (BO) for formation lithology identification and comprehensively evaluated the performance of the proposed classifier based on the metrics of the confusion matrix, precision, recall, F1-score and the area under the receiver operating characteristic curve (AUC). The data of this study are derived from Daniudui gas field and the Hangjinqi gas field, which includes 2153 samples with known lithology facies class with each sample having seven measured properties (well log curves), and corresponding depth. The results show that BO significantly improves parameter optimization efficiency. The AUC values of the test sets of the two gas fields are 0.968 and 0.987, respectively, indicating that the proposed method has very high generalization performance. Additionally, we compare the proposed algorithm with Gradient Tree Boosting-Differential Evolution (GTB-DE) using the same dataset. The results demonstrated that the average of precision, recall and F1 score of the proposed method are respectively 4.85%, 5.7%, 3.25% greater than GTB-ED. The proposed XGBoost-BO ensemble model can automate the procedure of lithology identification, and it may also be used in the prediction of other reservoir properties.

Formation lithology identification is of great importance for reservoir characterization and petroleum exploration. Previous methods are based on cutting logging and well-logging data and have a significant time lag. In recent years, many machine learning methods have been applied to lithology identification by utilizing well-logging data, which may be affected by drilling fluid. Drilling string vibration data is a high-density ancillary data, and it has the advantages of low-latency, which can be acquired in real-time. Drilling string vibration data is more accessible and available compared to well-logging data in ultra-deep well drilling. Machine learning algorithms enable us to develop new lithology identification models based on these vibration data. In this study, a vibration dataset is used as the signal source, and the original vibration signal is filtered by Butterworth (BHPF). Vibration time–frequency characteristics were extracted into time–frequency images with the application of short-time Fourier transform (STFT). This paper develops lithology classification models using new data sources based on a convolutional neural network (CNN) combined with Mobilenet and ResNet. This model is used for complex formation lithology, including fine gravel sandstone, fine sandstone, and mudstone. This study also carries out related model accuracy verification and model prediction results interpretation. In order to improve the trustworthiness of decision-making results, the gradient-weighted class-activated thermal localization map is applied to interpret the results of the model. The final verification test shows that the single-sample decision time of the model is 10 ms, the test macro precision rate is 90.0%, and the macro recall rate is 89.3%. The lithology identification model based on vibration data is more efficient and accessible than others. In conclusion, the CNN model using drill string vibration supplies a superior method of lithology identification. This study provides low-latency lithology classification methods to ensure safe and fast drilling.

Recon Exploration Pty. Ltd. has successfully completed initial testing of a new method for processing and interpretation of AGSO’s (Australian Geological Survey Organization, formerly Bureau of Mineral Resources) aerial gamma‐ray spectrometer data for petroleum exploration in the Canning Basin, Western Australia and the Otway Basin, Victoria. Count‐rate data for potassium and uranium were normalized to the thorium count rate for each sample to suppress unwanted effects of variations in surface lithology or soil type, soil moisture, vegetation cover, and counting geometry. The Canning Basin test area included five producing oil fields. All except one clearly exhibit significant and characteristic radiometric anomalies which include negative normalized potassium and more positive normalized uranium values. The Otway Basin test areas included PPL-1 commercial gas production which is associated with a group of significant radiometric anomalies similar to those in the Canning Basin. These results are similar to extensive ongoing tests in the U.S. and are explained in terms of well‐understood geological, geochemical, and geophysical models. Based on 69 wells in the three test areas, it is estimated that the chance of encountering hydrocarbons (economic production or shows) in wells within the radiometrically favorable zones is about 2.6 times greater than outside the favorable areas.

As economics of the oil and gas industry become more restrictive, the need for new means of improving exploration risks and reducing expenses is becoming more acute. Partnerships between industry and academia are making significant improvements in four general areas: Seismic acquisition, reservoir characterisation, quantitative structural modelling, and geochemical inversion.In marine seismic acquisition the vertical cable concept utilises hydrophones suspended at fixed locations vertically within the water column by buoys. There are numerous advantages of vertical cable technology over conventional 3-D seismic acquisition. In a related methodology, 'Borehole Seismic', seismic energy is passed between wells and valuable information on reservoir geometry, porosity, lithology, and oil saturation is extracted from the P-wave and S-wave data.In association with seismic methods of determining the external geometry and the internal properties of a reservoir, 3-dimensional sedimentation-simulation models, based on physical, hydrologic, erosional and transport processes, are being utilised for stratigraphic analysis. In addition, powerful, 1-D, coupled reaction-transport models are being used to simulate diagenesis processes in reservoir rocks.At the regional scale, the bridging of quantitative structural concepts with seismic interpretation has led to breakthroughs in structural analysis, particularly in complex terrains. Such analyses are becoming more accurate and cost effective when tied to highly advanced, remote-sensing, multi-spectral data acquisition and image processing technology. Emerging technology in petroleum geochemistry, enables geoscientists to infer the character, age, maturity, identity and location of source rocks from crude oil characteristics ('Geochemical Inversion') and to better estimate hydrocarbon-supply volumetrics. This can be invaluable in understanding petroleum systems and in reducing exploration risks and associated expenses.

Theia Energy Pty Ltd1 (Theia Energy) discovered a potential unconventional hydrocarbon resource in the Ordovician Lower Goldwyer (GIII) Formation shale located on the Broome Platform of the onshore Canning Basin. The collation, processing, analysis and interpretation of all available regional data culminated in a successful exploration well, Theia-1 (drilled in 2015), which, based upon petrophysical and core analyses, intersected a 70 m gross oil column at 1500–1570 m depth. Theia-1 recovered essential core and wireline log data required to analyse and assess the play elements and reservoir properties necessary for a viable shale oil and gas development. Utilisation of an ‘Unconventional Play Element’ methodology has proven the unconventional hydrocarbon potential of the GIII Formation, and preliminary modelling indicates that economic stimulated flow rates may be achieved. Further operations (a test well with multi-stage hydraulic fracture stimulation) are scheduled in the coming permit year to further quantify the presence of extractable organic matter in the GIII Formation, assess hydrocarbon flow rates, determine fluid composition and appraise commercial viability. This paper will discuss Theia Energy’s exploration campaign in the onshore Canning Basin starting with the regional evaluation, which encompassed all available geoscience data (offset wells, pre-existing seismic and potential analogue fields) and modern specialised shale analysis (sequence stratigraphy, paleogeography, geochemistry, unconventional petrophysics and petroleum systems modelling), to develop a robust regional geological model for the GIII Formation. Pre-drill analysis reduced exploration risk and successfully identified the key geological play elements essential for the successful Theia-1 exploration evaluation program.

Over the past four years Comalco in joint venture with Bridge Oil have undertaken extensive exploration within the Carpentaria Basin. Over 3000 km of multifold reflection seismic data has been acquired and four petroleum exploration wells were drilled. In addition, the Queensland Department of Mines (GSQ) has drilled four cored full-section stratigraphic wells in the deeper parts of the basin.Analysis of the work to date indicates that the basin is not as structurally simple as first thought. Four sub- basins are recognised based on the composition and timing of Mesozoic sedimentary fill. These are the Weipa, Western Gulf, Staaten and Boomarra sub-basins. The Boomarra Sub-basin contains a Middle Triassic red-bed sequence which is 250 m thick in drill hole GSQ Dobbyn- 1. Thick, Middle Jurassic-Lower Cretaceous, basal fluvial and marine sandstone sequences are restricted to the Weipa and Staaten sub-basins, where they are confined principally to the palaeotopographic valleys. The Western Gulf Sub-basin is believed to contain minimal basal Mesozoic sandstone.Although sedimentary depositional environments exhibit widespread continuity throughout the Carpentaria Basin, variations in lithology and provenance as well as diachronism can be demonstrated between the various sub-basins. Most notably the late Neocomian marine transgression began earlier at Weipa than in the southern sub-basins. A basin-wide stratigraphy has been developed from deep drill hole correlations and mapping of outcrop sections around the margin of the basin in the Olive River, Gregory Range and Melish Park areas thus enabling the petroleum reservoir character of the basin to be determined.

Because the high-precision calibration results of the petroleum underground layer are of great significance for oil production efficiency, research on the calibration method of the petroleum underground layer based on high precision gravity and magnetic exploration is researched. The gravity magnetic model is used to retrieve the bedrock depth, and the results of the basement structure and sedimentary rock distribution of the gravity and magnetic geology in the petroleum underground horizon of the Tongbai basin are obtained. On this basis, the geological data, logging data, seismic data, and VSP data are comprehensively used, and the layered calibration method is used to calibrate the petroleum underground layer of the Tongbai basin. Considering the seismic datum and the core elevation in the area, the rock formation is divided by various logging curves. The average time difference and density of the divided rock layers are interpolated at equal depth intervals to obtain velocity sequences and density sequences at equal time intervals and finally realize time-depth conversion. When the drilling geological horizon is unified, the synthetic record of the seismic reflection layer is compared with the geological horizon to realize the horizon calibration of the seismic reflection layer. When the local stratification is not uniform, the seismic reflection layer is calibrated by tracking the seismic reflection layer, high-precision velocity analysis, and various synthetic records to verify the reliability of the geological horizon. The results show that the proposed method can accurately survey the geological conditions of the Tongbai basin. It detected 14 basement faults, and the NW-trending and NE-trending faults controlled the basin, while the north-south faults controlled the later evolution of the basin. The method can be used for the horizon calibration of inclined wells, which is suitable not only for anisotropic media but also for formations with a less lateral variation of local formation lithology. Moreover, its usage is flexible, and it can be corrected by multiple speed data.

An important element of the geological modeling of oil reservoirs is represented by determining of the mineralogical composition and rock types as part of the reservoir characterization process. In the paper we provide a comprehensive mineralogo-petrographic study based on petrographic observations and X-rays diffraction investigations made on several Miocene rock samples collected in the wells spudded in an oil field belonging to the Getic Basin. Getic Basin is a prolific petroleum province in Romania and belongs to petroleum systems of the Carpathian Foredeep. The oil exploration in the Getic Basin started more than 100 years ago and resulted in thousands of wells drilled and tens of fields discovered. The oil field is located in the Gorj County, geologically belongs to the internal zone of the Getic Basin, and is a faulted anticline with hydrocarbon accumulations in Burdigalian and Sarmatian deposits. The petrographic study led to the interpreting of the rock samples analyzed as epiclastic sedimentary rocks represented by conglomerates, breccias, sands, sandstones, claystones and marlstones, and carbonate rocks (limestones). X-rays diffraction investigations indicated the phyllosilicates (smectite and illite) as main minerals in the Sarmatian samples, while in the Burdigalian samples were found as main minerals: quartz, feldspars and carbonate minerals. The paper provides detailed information (like petrographic types, composition and microtexture) on the Miocene reservoir rocks belonging to the Getic Basin. Also the data obtained may be used as basis for future reservoir modeling studies in the region.

The Barrow and Dampier Sub-basins of the Northern Carnarvon Basin developed by repeated reactivation of long-lived basement structures during Palaeozoic and Mesozoic tectonism. Inherited basement fabric specific to the terranes and mobile belts in the region comprise northwest, northeast, and north–south-trending Archaean and Proterozoic structures. Reactivation of these structures controlled the shape of the sub-basin depocentres and basement topography, and determined the orientation and style of structures in the sediments.The Lewis Trough is localised over a reactivated NEtrending former strike-slip zone, the North West Shelf (NWS) Megashear. The inboard Dampier Sub-basin reflects the influence of the fabric of the underlying Pilbara Craton. Proterozoic mobile belts underlie the Barrow Sub-basin where basement fabric is dominated by two structural trends, NE-trending Megashear structures offset sinistrally by NS-trending Pinjarra structures.The present-day geometry and basement topography of the basins is the result of accumulated deformation produced by three main tectonic phases. Regional NESW extension in the Devonian produced sinistral strikeslip on NE-trending Megashear structures. Large Devonian-Carboniferous pull-apart basins were introduced in the Barrow Sub-basin where Megashear structures stepped to the left and are responsible for the major structural differences between the Barrow and Dampier Sub-basins. Northwest extension in the Late Carboniferous to Early Permian marks the main extensional phase with extreme crustal attenuation. The majority of the Northern Carnarvon basin sediments were deposited during this extensional basin phase and the subsequent Triassic sag phase. Jurassic extension reactivated Permian faults during renewed NW extension. A change in extension direction occurred prior to Cretaceous sea floor spreading, manifest in basement block rotation concentrated in the Tithonian. This event changed the shape and size of basin compartments and altered fluid migration pathways.The currently mapped structural trends, compartment size and shape of the Barrow and Dampier Sub-basins of the Northern Carnarvon Basin reflect the “character” of the basement beneath and surrounding each of the subbasins.Basement character is defined by the composition, lithology, structure, grain, fabric, rheology and regolith of each basement terrane beneath or surrounding the target basins. Basement character can be discriminated and mapped with mineral exploration methods that use non-seismic data such as gravity, magnetics and bathymetry, and then calibrated with available seismic and well datasets. A range of remote sensing and geophysical datasets were systematically calibrated, integrated and interpreted starting at a scale of about 1:1.5 million (covering much of Western Australia) and progressing to scales of about 1:250,000 in the sub-basins. The interpretation produced a new view of the basement geology of the region and its influence on basin architecture and fill history. The bottom-up or basement-first interpretation process complements the more traditional top-down seismic and well-driven exploration methods, providing a consistent map-based regional structural model that constrains structural interpretation of seismic data.The combination of non-seismic and seismic data provides a powerful tool for mapping basement architecture (SEEBASE™: Structurally Enhanced view of Economic Basement); basement-involved faults (trap type and size); intra-sedimentary geology (igneous bodies, basement-detached faults, basin floor fans); primary fluid focussing and migration pathways and paleo-river drainage patterns, sediment composition and lithology.

The Great South Basin, off New Zealand’s southeast coast, has attracted renewed exploration interest from major petroleum companies since 2005. The distribution of the mid Cretaceous to Paleocene source rocks (coals and coaly mudstones) is a critical component in evaluating basin prospectivity. This paper delineates source rock distribution from seismic facies characterisation, and presents a series of updated paleogeographic maps over the initial (Cretaceous) phases of basin evolution. Basin evolution has been analysed from mapped sequence stratigraphic boundaries and isochron maps. Seismic facies were characterised based on the amplitude, continuity, and stacking pattern of the reflection packages. The identified facies were calibrated with well data for age, gross lithology, and gross depositional environment. Areas of source rock deposition were demarcated using seismic attribute interval maps, from which a series of updated paleogeographic maps was prepared. Four second-order sequences have been identified within the Cretaceous succession. The lower two sequences are mainly fault bounded and were deposited in a syn-rift phase. In contrast, the upper two sequences reflect a change in basin character from rifting to a post-rift thermal sag phase. Source facies within both the syn- and post-rift sequences were deposited in mainly non-marine to marginal marine settings, although there is also the possibility of lacustrine source rocks in isolated syn-rift depocentres. The wide geographic spread of source rock intervals within the Cretaceous sequences allows for a variety of petroleum generation and exploration play scenarios.

AbstractLow-frequency resistivity logging plays an important role in the field of petroleum exploration, but the complex resistivity spectrum of rock also contains a large amount of information about reservoir parameters. The complex resistivity spectra of 15 natural sandstone cores from western China, with different water saturations, were measured with an impedance analyzer. The pore space of each core was saturated with NaCl solution, and measurements were collected at a frequency range of 40–15 MHz. The results showed a linear relationship between the real resistivity at 1 kHz and the maximum values of imaginary resistivity for each core with different water saturations. The slopes of the linear best-fit lines had good linear relationships with the porosity and the permeability of cores. Based on this, a permeability estimation model was proposed and tested. In addition, the maxima of imaginary resistivity had power exponential relationships with the porosity and the water saturation of the cores. A saturation evaluation model based on the maxima of imaginary resistivity was established by imitating Archie’s formula. The new models were found to be feasible for determining the permeability and saturation of sandstone based on complex resistivity spectrum measurements. These models advance the application of complex resistivity spectrum in petrophysics.

In 2008, Central Petroleum was involved in an extended exploration campaign in the Pedirka Basin. The main targets were conventional oil and coal seam gas (CSG). A comprehensive logging program including nuclear magnetic resonance (NMR) measurements was acquired, with the scope of evaluating both targets in two wells. NMR tools measure the magnetisation of hydrogen protons present in the flushed-zone of the formation pore space. By calibrating this measurement in a water tank, NMR tools provide formation porosity independent of lithology, while classical methods for deriving porosity (density, neutron, etc.) are lithology dependent. While in conventional plays (clastics, carbonates) porosity is needed for evaluating the reservoir storage capacity, in coal beds porosity is needed for evaluating the surface areas of the pores. As methane in coal is bound to the coal surface, total pore surface affects the coal bed methane producing capacity. NMR measurements also provide information about porosity/grain size distribution, permeability and hydrocarbon saturation in conventional formations. This information can be very useful for evaluating coal seam gas, provided the conventional models can be converted and applied in coal beds. Evaluation of coal seam gas prospects using nuclear magnetic resonance is an industry first. This presentation highlights the benefits and difficulties of nuclear magnetic resonance evaluation of CSG prospects in these two wells.

Present simulation results based on two-dimensional basin cannot obtain accurate evaluations of petroleum resources because of not combining the thermal history in the Dongpu Depression. In this paper, Shahejie 3 Formation source rocks are evaluated using the geochemical data, and based on the thermal history, the thermal maturity evolution of typical wells and the top and bottom of the Shahejie 3 Formation source rocks are modeled using BasinMod software. Results show that source rocks are mainly distributed in the Haitongji-Liutun and Qianliyuan areas, and dominated by medium to high maturity source rocks. Organic matter types are primarily types II and III kerogen with a small amount of type I. The Shahejie 3 Formation source rocks in the Menggangji area experienced two stages of hydrocarbon generation: (1) during the Dongying Formation depositional period (33–17 Ma) and (2) from the Minghuazhen Formation depositional period to present (5.1–0 Ma). The source rocks are generally underdeveloped with low potential for hydrocarbon generation due to nonpoor and thin source rocks in this area. The two stages of hydrocarbon generation are not obvious for other areas. When the bottom of the source rocks reached overmature stage, the mid-lower Shahejie 3 Formation experienced the peak of hydrocarbon generation during the Dongying Formation depositional period. The thermal maturity evolution of the Shahejie 3 Formation source rocks revealed that the main hydrocarbon generation period was during the Dongying Formation depositional period. Therefore, petroleum exploration is suggested to be performed at the Shahejie 3 Formation source rocks in the Qianliyuan and Haitongji-Liutun areas to study the lithology and discover complex petroleum reservoirs in the Dongpu Depression.

Abstract. Joint marine electromagnetic (EM) and seismic interpretations are widely used for offshore gas hydrate and petroleum exploration to produce improved estimates of lithology and fluids and to decrease the risk of low gas saturation. However, joint data acquisition is not commonly employed. Current marine EM data acquisition depends on an ocean bottom electromagnetic receiver (OBEM), and current seismic exploration methods use seismometers. Joint simultaneous data acquisition can decrease costs and improve efficiency, but conventional independent data receivers have several drawbacks, including a large size, high costs, position errors, and low operational efficiencies. To address these limitations, we developed a compact ocean bottom electromagnetic receiver and seismometer (OBEMS). Based on existing ocean bottom E-field receiver (OBE) specifications, including low noise levels, low power consumption, and low time drift errors, we integrated two induction coils for the magnetic sensor and a three-axis omnidirectional geophone for the seismic sensor to assemble an ultra-short baseline (USBL) transponder as the position sensor, which improved position accuracy and operational efficiency while reducing field data acquisition costs. The resulting OBEMS has a noise level of 0.1 nV m−1 rt−1 (Hz) at 1 Hz in the E-field, 0.1 pT rt−1 (Hz) at 1 Hz in the B-field, and a 30 d battery lifetime. This device also supports a Wi-Fi interface for the configuration of data acquisition parameters and data download. Offshore acquisition was performed to evaluate the system's field performance during offshore gas hydrate exploration. The OBEMS operated effectively throughout the operation and field testing. Therefore, the OBEMS can function as a low-cost, compact, and highly efficient joint data acquisition method.

In recent years, petroleum geochemists have been re-focusing their efforts on developing practical means for inferring, from hydrocarbon chemistry and geologic constraints, the “provenance” of hydrocarbon accumulations, seeps or stains. This capability, referred to here as “Geochemical Inversion”, can be invaluable to the explorationist in deriving clues as to the character, age, identity, maturity and location of an accumulation's source rocks and evaluating a petroleum system's hydrocarbon supply volumetrics. Geochemical inversion is most useful where pertinent source-rock information may be absent because exploratory drilling focused strictly on structural highs and failed to penetrate the deeply buried, effective basinal source facies. Advances in chemical analysis technology over the last decade have facilitated the development of powerful geochemical methods for unravelling of complex chemistries of crude oil and natural gas at the molecular and subatomic levels to extract specific information on the hydrocarbons' source. Inferences on such factors as organic matter make-up, depositional environment, lithology, age and maturity of the source can frequently be drawn. These inferences, together with a sound analysis of the geologic and architectural constraints on the system, can supply clues as to the identity and location of the probable source sequence. This paper describes the principles underlying geochemical “inversion” and provides applications in exploration and exploitation settings. In addition, this paper demonstrates inversion of geochemical characteristics of migrated hydrocarbon fluids to specific attributes of the source. The paper also illustrates the use of systematic variations in fluid chemistry within a geologic setting to infer source location, degree of hydrocarbon mixing and relative migration distance.

In the Enping 17 sag within the Pearl River Mouth Basin in the South China Sea, one wildcat well has been drilled to the Lower Paleogene Enping Formation (FM EP) and partially into the Wenchang Formation (FM WC) for deep formation hydrocarbon exploration. However, no commercial play was discovered. The reasons for this are clear if the petroleum systems modeling is examined. In FM EP, the main reason for failure is due to poor sealing. In FM WC, the failure is due to the lack of a good reservoir for hydrocarbon accumulation. Encountering a 9 m thick reservoir at a depth of 4650 m indicates that braided fluvial delta and lowstand turbidite sandstone may develop in FM WC. With the objective of establishing cap rock in FM EP and reservoir rock in FM WC, and in the absence of sufficient well data, an integrated framework for 3D seismic reservoir characterization of offshore deep and thin layers was developed. The workflow includes seismic data reprocessing, well-log-based rock-physics analysis, seismic structure interpretation, simultaneous amplitude variation with offset (AVO) inversion, 3D lithology prediction, and geologic integrated analysis. We present four key solutions to address four specific challenges in this case study: (1) the application of adaptive deghosting techniques to remove the source and streamer depth-related ghost notches in the seismic data bandwidth and the relative amplitude-preserved bandwidth extension technique to improve the seismic data resolution; (2) a practical rock-physics modeling approach to consider the formation overpressure for pseudoshear sonic log prediction; (3) interactive and synchronized workflow between prestack 3D AVO inversion and seismic processing to predict a 9 m thick layer in FM WC through more than 60 rounds of cyclic tests; and (4) cross validation between seismic qualitative attributes and quantitative inversion results to verify the lithology prediction result under the condition of insufficient well data.

Structural closures on the western flank of the Patchawarra Trough in the Cooper–Eromanga Basin are truly low relief; drilling opportunities regularly target hydrocarbon columns of similar magnitude to the uncertainty of depth prediction. Improving the accuracy and precision of depth prediction will reduce risk for drilling opportunities, and improve drilling success rates. A detailed study of the near surface geology (surface to ~500 m depth) of the western flank of the Patchawarra Trough has been undertaken to better understand the effect of observed geological variations of the near surface on depth prediction at deeper target levels. The stratigraphic interval investigated includes the top of the Eromanga Basin and the entire Lake Eyre Basin, which is sparingly studied and routinely overlooked in the statics and velocity modelling process. This study analysed recently acquired cased-hole sonic logs in conjunction with gamma logs and mudlog data to map out the observed geological variations, and construct a 3D velocity model of the near surface. Variations of layer thickness and seismic velocity were input into Monte Carlo simulations to investigate sensitivities of each formation on two-way travel time and depth prediction. This investigation has found that velocity variations of the Weathered Winton Formation, and thickness variations of the Namba Clastics have the greatest impact on imaging of structures at depth. Independently, these have the potential to completely conceal or create structures in the time domain. Continued efforts in improved understanding of the near surface will subsequently lead to enhanced imaging of structures, which can then be used in the mapping of structural closures in petroleum exploration and development.

Fault core accommodates intense deformation in the form of slip surfaces and fault rocks such as fault gouge, cataclasite, breccia, lenses, shale smear, and diagenetic features. The complexity and variation in fault core geometry and thickness affect fluid flow both along and across the fault. In this study, we have investigated a total of 99 faults in siliciclastic and carbonate rocks. This has resulted in two large datasets that include 871 fault core thickness measurements T in siliciclastic rocks and 693 measurements in carbonates, conducted at regular intervals along fault elevations (fault height) on the outcrop or photos of the outcrop. Many of these measurements have been analyzed with respect to fault displacement measurements D in order to study the relationship between displacement and fault core thickness and to further uncover the fault growth process. We found that the fault type and geometry, displacement, type of fault rocks, lithology, and competency contrasts between faulted layers lead to significant variations in the fault core internal structure and thickness. Analysis of average values of fault core thickness-displacement data of this study and of previously published studies shows that the core thickness-displacement relationship follows an overall power law, in which its exponent and intercept change depending on the lithology of the faulted rocks. In general, small faults in carbonate and siliciclastic rocks (D≤5 m) show comparable T/D ratios, with a slightly higher ratio in carbonate rocks. The outcomes of this study contribute to the understanding of the fault core internal structure and variation in fault core thickness as a result of the interplay between fault displacement and host rock in different lithologies. These outcomes have significant implication for characterizing the sealing and conductivity potential of faulted rocks, which is relevant to different applications such as petroleum exploration and development of existing fields, hydrogeology, geothermal energy storage and extraction, and CO2 sequestration.

The uniaxial compressive strength of rock ([Formula: see text]) is an important parameter for petroleum engineers, drilling operations, and all related activities from exploration through to production and abandonment. A thorough understanding of the parameters affecting [Formula: see text] is a basic prerequisite for accurate geomechanical modeling of the reservoir and overburden properties. Uniaxial compressive strength plays a significant role in mud weight determination while drilling, especially for a troublesome lithology such as shale. However, standard geomechanical practice requires well-preserved core samples for measurement of [Formula: see text] in the lab. Because core samples are not often available, there is a need for alternative methods to obtain fit-for-purpose values of [Formula: see text], based on other related rock parameters. Our primary objective was to identify a minimum set of related rock properties that could be used to predict [Formula: see text]. From a review of existing data in the literature, supplemented by laboratory measurements on Iranian samples, we established a database and accomplished extensive statistic analysis. Also, a normality test was executed to make sure a statistically acceptable set of data was collected. We suggested that two parameters of Young’s modulus ([Formula: see text]) and porosity ([Formula: see text]), which might be estimated from geophysical log data, were sufficient for a reliable prediction of [Formula: see text] in shale formations, and the overall contribution of [Formula: see text] was more than [Formula: see text]. We obtained a prediction equation with improved accuracy compared to previous investigations. Furthermore, we determined that the relative sensitivity of shale strength to porosity and Young’s modulus very much depended on the range of porosity.

Contemporaneous seismic data acquisition in the Santos and Campos Basins offshore Brazil have focused on image characterization of deepwater and ultra-deepwater reservoirs and their relationship with hydrocarbons originating from synrift source rocks. Our interpretation has mapped the stratigraphy of postsalt turbidite reservoirs, and, on the presalt lithology, it has uncovered the underlying synrift sequences that embrace oil-bearing source rocks and the prolific, recently discovered, microbialite carbonate reservoirs. The new phase in geophysical data acquisition and offshore drilling that started in 1999 bolstered the Brazilian offshore petroleum production to record levels. The new, massive, nonexclusive, speculative 2D and 3D data acquisition surveys conducted offshore the Brazilian coast far exceed the amount of all existing cumulative vintage data. Deepwater drilling programs probed the interpreted new prospects. As whole, the modern geophysics data libraries offshore Brazil brought in the technology era to seismic interpretation, reservoir characterization, and geosteering operations in deepwater development drilling. Still, regional interpretation mapping of the outer shelf, slope, deepwater and ultra-deepwater provinces of the Santos and Campos Basins indicates plenty of prospective future drilling in the salt locked minibasins of the ultra-deepwater provinces. Salt tectonics shapes the architecture of these basins; hence, postsalt deepwater turbidite plays were readily interpreted from seismic amplitudes of the modern data that also allow for resolution images of the synrift source rocks, salt architecture, migration paths through faulting and salt windows, reservoir characterization, and regional seal mapping. The new techniques of prestack depth migration have enabled uncovering the imaging structure of the synrift that led to characterization of the presalt carbonate reservoirs and discovery of giant accumulations. Future offshore exploration will continue aiming at postsalt deepwater and ultra-deepwater minibasins plus presalt plays under the massive salt walls, still an underexplored frontier.

A nanoscale pore throat system develops extensively in rocks of unconventional reservoirs serving as both source and reservoir rock. The nanoscale pores provide the main storage spaces, accounting for 70% to 80% of the total unconventional tight reservoirs in China. As one of most important unconventional petroleum accumulations, tight oil has accumulated in more than 20 lacustrine strata since the Permian in China. Three types of tight oil reservoirs were identified based on the lithology and provenance in the lacustrine basins, including terrigenous sandstone, endogenous carbonate rocks and mixed sedimentary rocks. The micro/nanopore structures of these tight rocks were investigated with the application of optical microscopy, scanning electron microscopy (SEM), mercury injection capillary pressure (MICP), gas adsorption (GA) and nuclear magnetic resonance (NMR). The results indicated that the pore systems were connected by nanoscale throats dominated the storage spaces of the lacustrine tight oil reservoirs, while there were obvious differences among these three tight rocks, including pore types, pore size and movable fluid distribution. (i) The terrigenous sandstones, which were represented by the Triassic Chang 7 tight sandstones in the Ordos Basin and Cretaceous Quantou tight sandstones in the Songliao Basin, were mainly arkoses, and their storage space was mainly composed of dissolution pores and intraclay mineral pores. Feldspar, rock fragments and carbonate cements were the majority of the dissolved components, and the diameter of dissolution pores ranged from 1 micron to 50 microns. Abundant intrakaolinite and illite/smectite mixed layers pores were developed, and the pore size was 10 nm to 500 nm. The MICP and GA data suggested that storage spaces were connected by throats with diameters of 10 nm˜300 nm. (ii) The endogenous carbonate rocks, which were represented by the Jurassic Da’anzhai limestones in the Sichuan Basin, were the tightest rocks with porosities of less than 5% and permeabilities of less than 0.01×10−3 μm2. The calcite dissolution pores and fractures with diameters of 10 nm˜500 nm were the most important storage spaces. The majority of pore systems were connected by throats with diameters of 6 nm˜100 nm based on the MICP and GA data. (iii) The tight mixed sedimentary rocks, which were represented by the Permian Lucaogou Formation in the Junggar Basin, were complex in lithologic composition, and dolostones and dolomite sandstones were the most important exploration targets. The interdolomite pores were the dominant storage spaces, in which abundant illite/smectite mixed layers were filled, and the pore size ranged from 50 nm to 50 microns. The MICP and GA data showed that the storage space was dominated by throats with diameters of 10 nm˜200 nm, and their volumetric contributions could reach over 70%. These results could provide a reference for future tight oil research and exploration in China.

The study of petroleum systems by using the PetroMoD 1D software is one of the most prominent ways to reduce risks in the exploration of oil and gas by ensuring the existence of hydrocarbons before drilling. The petroleum system model was designed for Dima-1 well by inserting several parameters into the software, which included the stratigraphic succession of the formations penetrating the well, the depths of the upper parts of these formations, and the thickness of each formation. In addition, other related parameters were investigated, such as lithology, geological age, periods of sedimentation, periods of erosion or non-deposition, nature of units (source or reservoir rocks), total organic carbon (TOC), hydrogen index (HI) ratio of source rock units, temperature of both surface and formations as they are available, and well-bottom temperature. Through analyzing the models by the evaluation of the source rock units, the petrophysical properties of reservoir rock units, and thermal gradation with the depth during the geological time, it became possible to clarify the elements and processes of the petroleum system of the field of Dima. It could be stated that Nahr Umr, Zubair, and Sulaiy formations represent the petroleum system elements of Dima-1 well.

Over the past 20 years, oil and gas companies have turned their attention to producing petroleum directly from organic-rich shale. Successful exploration, appraisal, and production strategies for source rocks critically depend on reliable identification of their organic components (kerogen, in particular) and generation potential. There is mounting demand to evaluate organic richness in terms of quantity (i.e. total organic carbon) and quality (i.e. hydrogen index) from seismic data, which is usually the only source of information in the early development period of emerging shale plays. We delineated major seismic lithofacies on the Alaska North Slope using elastic, seismic, and petrophysical properties. We performed a well-established quantitative seismic interpretation workflow to integrate geochemical data in the lithofacies definition. Rock physics templates of seismic parameters, Acoustic Impedance, (AI), versus P-wave to S-wave velocity ratio, (VP/VS), are constructed for each lithofacies to assess variations in pore fluid and lithology. We proposed correlations between source rock properties (hydrogen index, total organic carbon) and petrophysical properties (bulk density, porosity, sonic velocity ratio) of the major lithofacies. These correlations, together with facies-specific rock physics templates, can be utilized to predict organic richness and source rock properties away from drilled wells. The models are validated by training data from 2 regional wells to observe their applicability on the Alaska North Slope.

Unconventional energy sources have become increasingly important to the global energy mix. These include coal seam gas, shale gas and shale oil. The unconventional gas industry was pioneered in the United States and embraced following the first oil shock in 1973 (Rogers). As has been the case with many global resources (Hiscock), many of the same companies that worked in the USA carried their experience in this industry to early Australian explorations. Recently the USA has secured significant energy security with the development of unconventional energy deposits such as the Marcellus shale gas and the Bakken shale oil (Dobb; McGraw). But this has not come without environmental impact, including contamination to underground water supply (Osborn, Vengosh, Warner, Jackson) and potential greenhouse gas contributions (Howarth, Santoro, Ingraffea; McKenna). The environmental impact of unconventional gas extraction has raised serious public concern about the introduction and growth of the industry in Australia. In coal rich Australia coal seam gas is currently the major source of unconventional gas. Large gas deposits have been found in prime agricultural land along eastern Australia, such as the Liverpool Plains in New South Wales and the Darling Downs in Queensland. Competing land-uses and a series of environmental incidents from the coal seam gas industry have warranted major protest from a coalition of environmentalists and farmers (Berry; McLeish). Conflict between energy companies wanting development and environmentalists warning precaution is an easy script to cast for frontline media coverage. But historical perspectives are often missing in these contemporary debates. While coal mining and natural gas have often received “boosting” historical coverage (Diamond; Wilkinson), and although historical themes of “development” and “rushes” remain predominant when observing the span of the industry (AGA; Blainey), the history of unconventional gas, particularly the history of its environmental impact, has been little studied. Few people are aware, for example, that the first shale gas exploratory well was completed in late 2010 in the Cooper Basin in Central Australia (Molan) and is considered as a “new” frontier in Australian unconventional gas. Moreover many people are unaware that the first coal seam gas wells were completed in 1976 in Queensland. The first four wells offer an important moment for reflection in light of the industry’s recent move into Central Australia. By locating and analysing the first four coal seam gas wells, this essay identifies the roots of the unconventional gas industry in Australia and explores the early environmental impact of these wells. By analysing exploration reports that have been placed online by the Queensland Department of Natural Resources and Mines through the lens of environmental history, the dominant developmental narrative of this industry can also be scrutinised. These narratives often place more significance on economic and national benefits while displacing the environmental and social impacts of the industry (Connor, Higginbotham, Freeman, Albrecht; Duus; McEachern; Trigger). This essay therefore seeks to bring an environmental insight into early unconventional gas mining in Australia. As the author, I am concerned that nearly four decades on and it seems that no one has heeded the warning gleaned from these early wells and early exploration reports, as gas exploration in Australia continues under little scrutiny. Arrival The first four unconventional gas wells in Australia appear at the beginning of the industry world-wide (Schraufnagel, McBane, and Kuuskraa; McClanahan). The wells were explored by Houston Oils and Minerals—a company that entered the Australian mining scene by sharing a mining prospect with International Australian Energy Company (Wiltshire). The International Australian Energy Company was owned by Black Giant Oil Company in the US, which in turn was owned by International Royalty and Oil Company also based in the US. The Texan oilman Robert Kanton held a sixteen percent share in the latter. Kanton had an idea that the Mimosa Syncline in the south-eastern Bowen Basin was a gas trap waiting to be exploited. To test the theory he needed capital. Kanton presented the idea to Houston Oil and Minerals which had the financial backing to take the risk. Shotover No. 1 was drilled by Houston Oil and Minerals thirty miles south-east of the coal mining town of Blackwater. By late August 1975 it was drilled to 2,717 metres, discovered to have little gas, spudded, and, after a spend of $610,000, abandoned. The data from the Shotover well showed that the porosity of the rocks in the area was not a trap, and the Mimosa Syncline was therefore downgraded as a possible hydrocarbon location. There was, however, a small amount of gas found in the coal seams (Benbow 16). The well had passed through the huge coal seams of both the Bowen and Surat basins—important basins for the future of both the coal and gas industries. Mining Concepts In 1975, while Houston Oil and Minerals was drilling the Shotover well, US Steel and the US Bureau of Mines used hydraulic fracture, a technique already used in the petroleum industry, to drill vertical surface wells to drain gas from a coal seam (Methane Drainage Taskforce 102). They were able to remove gas from the coal seam before it was mined and sold enough to make a profit. With the well data from the Shotover well in Australia compiled, Houston returned to the US to research the possibility of harvesting methane in Australia. As the company saw it, methane drainage was “a novel exploitation concept” and the methane in the Bowen Basin was an “enormous hydrocarbon resource” (Wiltshire 7). The Shotover well passed through a section of the German Creek Coal measures and this became their next target. In September 1976 the Shotover well was re-opened and plugged at 1499 meters to become Australia’s first exploratory unconventional gas well. By the end of the month the rig was released and gas production tested. At one point an employee on the drilling operation observed a gas flame “the size of a 44 gal drum” (HOMA, “Shotover # 1” 9). But apart from the brief show, no gas flowed. And yet, Houston Oil and Minerals was not deterred, as they had already taken out other leases for further prospecting (Wiltshire 4). Only a week after the Shotover well had failed, Houston moved the methane search south-east to an area five miles north of the Moura township. Houston Oil and Minerals had researched the coal exploration seismic surveys of the area that were conducted in 1969, 1972, and 1973 to choose the location. Over the next two months in late 1976, two new wells—Kinma No.1 and Carra No.1—were drilled within a mile from each other and completed as gas wells. Houston Oil and Minerals also purchased the old oil exploration well Moura No. 1 from the Queensland Government and completed it as a suspended gas well. The company must have mined the Department of Mines archive to find Moura No.1, as the previous exploration report from 1969 noted methane given off from the coal seams (Sell). By December 1976 Houston Oil and Minerals had three gas wells in the vicinity of each other and by early 1977 testing had occurred. The results were disappointing with minimal gas flow at Kinma and Carra, but Moura showed a little more promise. Here, the drillers were able to convert their Fairbanks-Morse engine driving the pump from an engine run on LPG to one run on methane produced from the well (Porter, “Moura # 1”). Drink This? Although there was not much gas to find in the test production phase, there was a lot of water. The exploration reports produced by the company are incomplete (indeed no report was available for the Shotover well), but the information available shows that a large amount of water was extracted before gas started to flow (Porter, “Carra # 1”; Porter, “Moura # 1”; Porter, “Kinma # 1”). As Porter’s reports outline, prior to gas flowing, the water produced at Carra, Kinma and Moura totalled 37,600 litres, 11,900 and 2,900 respectively. It should be noted that the method used to test the amount of water was not continuous and these amounts were not the full amount of water produced; also, upon gas coming to the surface some of the wells continued to produce water. In short, before any gas flowed at the first unconventional gas wells in Australia at least 50,000 litres of water were taken from underground. Results show that the water was not ready to drink (Mathers, “Moura # 1”; Mathers, “Appendix 1”; HOMA, “Miscellaneous Pages” 21-24). The water had total dissolved solids (minerals) well over the average set by the authorities (WHO; Apps Laboratories; NHMRC; QDAFF). The well at Kinma recorded the highest levels, almost two and a half times the unacceptable standard. On average the water from the Moura well was of reasonable standard, possibly because some water was extracted from the well when it was originally sunk in 1969; but the water from Kinma and Carra was very poor quality, not good enough for crops, stock or to be let run into creeks. The biggest issue was the sodium concentration; all wells had very high salt levels. Kinma and Carra were four and two times the maximum standard respectively. In short, there was a substantial amount of poor quality water produced from drilling and testing the three wells. Fracking Australia Hydraulic fracturing is an artificial process that can encourage more gas to flow to the surface (McGraw; Fischetti; Senate). Prior to the testing phase at the Moura field, well data was sent to the Chemical Research and Development Department at Halliburton in Oklahoma, to examine the ability to fracture the coal and shale in the Australian wells. Halliburton was the founding father of hydraulic fracture. In Oklahoma on 17 March 1949, operating under an exclusive license from Standard Oil, this company conducted the first ever hydraulic fracture of an oil well (Montgomery and Smith). To come up with a program of hydraulic fracturing for the Australian field, Halliburton went back to the laboratory. They bonded together small slabs of coal and shale similar to Australian samples, drilled one-inch holes into the sample, then pressurised the holes and completed a “hydro-frac” in miniature. “These samples were difficult to prepare,” they wrote in their report to Houston Oil and Minerals (HOMA, “Miscellaneous Pages” 10). Their program for fracturing was informed by a field of science that had been evolving since the first hydraulic fracture but had rapidly progressed since the first oil shock. Halliburton’s laboratory test had confirmed that the model of Perkins and Kern developed for widths of hydraulic fracture—in an article that defined the field—should also apply to Australian coals (Perkins and Kern). By late January 1977 Halliburton had issued Houston Oil and Minerals with a program of hydraulic fracture to use on the central Queensland wells. On the final page of their report they warned: “There are many unknowns in a vertical fracture design procedure” (HOMA, “Miscellaneous Pages” 17). In July 1977, Moura No. 1 became the first coal seam gas well hydraulically fractured in Australia. The exploration report states: “During July 1977 the well was killed with 1% KCL solution and the tubing and packer were pulled from the well … and pumping commenced” (Porter 2-3). The use of the word “kill” is interesting—potassium chloride (KCl) is the third and final drug administered in the lethal injection of humans on death row in the USA. Potassium chloride was used to minimise the effect on parts of the coal seam that were water-sensitive and was the recommended solution prior to adding other chemicals (Montgomery and Smith 28); but a word such as “kill” also implies that the well and the larger environment were alive before fracking commenced (Giblett; Trigger). Pumping recommenced after the fracturing fluid was unloaded. Initially gas supply was very good. It increased from an average estimate of 7,000 cubic feet per day to 30,000, but this only lasted two days before coal and sand started flowing back up to the surface. In effect, the cleats were propped open but the coal did not close and hold onto them which meant coal particles and sand flowed back up the pipe with diminishing amounts of gas (Walters 12). Although there were some interesting results, the program was considered a failure. In April 1978, Houston Oil and Minerals finally abandoned the methane concept. Following the failure, they reflected on the possibilities for a coal seam gas industry given the gas prices in Queensland: “Methane drainage wells appear to offer no economic potential” (Wooldridge 2). At the wells they let the tubing drop into the hole, put a fifteen foot cement plug at the top of the hole, covered it with a steel plate and by their own description restored the area to its “original state” (Wiltshire 8). Houston Oil and Minerals now turned to “conventional targets” which included coal exploration (Wiltshire 7). A Thousand Memories The first four wells show some of the critical environmental issues that were present from the outset of the industry in Australia. The process of hydraulic fracture was not just a failure, but conducted on a science that had never been tested in Australia, was ponderous at best, and by Halliburton’s own admission had “many unknowns”. There was also the role of large multinationals providing “experience” (Briody; Hiscock) and conducting these tests while having limited knowledge of the Australian landscape. Before any gas came to the surface, a large amount of water was produced that was loaded with a mixture of salt and other heavy minerals. The source of water for both the mud drilling of Carra and Kinma, as well as the hydraulic fracture job on Moura, was extracted from Kianga Creek three miles from the site (HOMA, “Carra # 1” 5; HOMA, “Kinma # 1” 5; Porter, “Moura # 1”). No location was listed for the disposal of the water from the wells, including the hydraulic fracture liquid. Considering the poor quality of water, if the water was disposed on site or let drain into a creek, this would have had significant environmental impact. Nobody has yet answered the question of where all this water went. The environmental issues of water extraction, saline water and hydraulic fracture were present at the first four wells. At the first four wells environmental concern was not a priority. The complexity of inter-company relations, as witnessed at the Shotover well, shows there was little time. The re-use of old wells, such as the Moura well, also shows that economic priorities were more important. Even if environmental information was considered important at the time, no one would have had access to it because, as handwritten notes on some of the reports show, many of the reports were “confidential” (Sell). Even though coal mines commenced filing Environmental Impact Statements in the early 1970s, there is no such documentation for gas exploration conducted by Houston Oil and Minerals. A lack of broader awareness for the surrounding environment, from floral and faunal health to the impact on habitat quality, can be gleaned when reading across all the exploration reports. Nearly four decades on and we now have thousands of wells throughout the world. Yet, the challenges of unconventional gas still persist. The implications of the environmental history of the first four wells in Australia for contemporary unconventional gas exploration and development in this country and beyond are significant. Many environmental issues were present from the beginning of the coal seam gas industry in Australia. Owning up to this history would place policy makers and regulators in a position to strengthen current regulation. The industry continues to face the same challenges today as it did at the start of development—including water extraction, hydraulic fracturing and problems associated with drilling through underground aquifers. Looking more broadly at the unconventional gas industry, shale gas has appeared as the next target for energy resources in Australia. Reflecting on the first exploratory shale gas wells drilled in Central Australia, the chief executive of the company responsible for the shale gas wells noted their deliberate decision to locate their activities in semi-desert country away from “an area of prime agricultural land” and conflict with environmentalists (quoted in Molan). Moreover, the journalist Paul Cleary recently complained about the coal seam gas industry polluting Australia’s food-bowl but concluded that the “next frontier” should be in “remote” Central Australia with shale gas (Cleary 195). It appears that preference is to move the industry to the arid centre of Australia, to the ecologically and culturally unique Lake Eyre Basin region (Robin and Smith). 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