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GEOPHYSICS (33 journals)

Showing 1 - 31 of 31 Journals sorted by number of followers
Geophysical Research Letters     Full-text available via subscription   (Followers: 200)
GIScience & Remote Sensing     Open Access   (Followers: 55)
Reviews of Geophysics     Full-text available via subscription   (Followers: 50)
Journal of Remote Sensing & GIS     Full-text available via subscription   (Followers: 36)
Physics and Chemistry of the Earth, Parts A/B/C     Hybrid Journal   (Followers: 9)
Journal of the Earth and Space Physics     Open Access   (Followers: 7)
Artificial Intelligence in Geosciences     Open Access   (Followers: 6)
New Zealand Journal of Geology and Geophysics     Hybrid Journal   (Followers: 6)
Research in Geophysics     Open Access   (Followers: 5)
Geothermal Energy     Open Access   (Followers: 5)
Eos, Transactions American Geophysical Union     Open Access   (Followers: 5)
Journal of Earth Sciences and Geotechnical Engineering     Open Access   (Followers: 4)
Greenhouse Gases : Science and Technology     Hybrid Journal   (Followers: 4)
NRIAG Journal of Astronomy and Geophysics     Open Access   (Followers: 4)
Journal of Environmental & Engineering Geophysics     Hybrid Journal   (Followers: 3)
Geodesy and Cartography     Open Access   (Followers: 2)
Geodesy and Cartography : The Journal of Committee on Geodesy of Polish Academy of Sciences     Open Access   (Followers: 2)
GEOMATICA     Hybrid Journal   (Followers: 1)
Geology, Geophysics and Environment     Open Access   (Followers: 1)
Interpretation     Hybrid Journal   (Followers: 1)
Contributions to Geophysics and Geodesy     Open Access   (Followers: 1)
Near Surface Geophysics     Open Access   (Followers: 1)
Chinese Journal of Geophysics     Full-text available via subscription   (Followers: 1)
Transportation Geotechnics     Full-text available via subscription   (Followers: 1)
Results in Geophysical Sciences     Open Access  
Energy Geoscience     Open Access  
Geomechanics and Geophysics for Geo-Energy and Geo-Resources     Hybrid Journal  
Geodesy and Geodynamics     Open Access  
Acta Geologica Polonica     Open Access  
Geofísica internacional     Open Access  
GeoScience Engineering     Open Access  
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Interpretation
Number of Followers: 1  
 
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 2324-8858 - ISSN (Online) 2324-8866
Published by Society of Exploration Geophysicists Homepage  [3 journals]
  • When the levee breaks: Visualization of a deepwater crevasse splay in Late
           Cretaceous in Exmouth Basin Offshore Western Australia

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      Abstract: Abstract“The present is the key to the past” is a foundational geologic concept that helps us contextualize buried subsurface features in current geologic analogs. As seismic interpreters, the generation of the geologic model should be unbiased, yet as humans our unconscious biases are expected, and we sometimes overlook anomalous reflection patterns in our seismic data that do not fit the model. As a result, we often disservice ourselves when we overlook these characteristics, potentially ignoring additional geologic context. These anomalous geoforms or funny-looking things (FLTs) may provide further geologic context and aid us in solving the geologic model if included. Crevasse splay on a continental slope marine environment is described and analyzed using attributes, seismic inversion, and voxel-based classification. We discuss possible causes that may have triggered the break of the levee on the Exmouth Basin during the Early Eocene and why a crevasse splay on a steep slope is an FLT. A possible explanation is that the presence of preexisting faults beneath said feature is the likely culprit for a levee break that created the crevasses splay. Thus, in contrast with the Led Zeppelin song about why the levee breaks, it is equally important to understand the preexisting faults when analyzing sediment supply. In addition, this highlights the importance of integral stratigraphic sequence interpretation — from deep to shallow — to understand geology in a full context.Geologic feature:Crevasse splays and distributary channelsSeismic appearance:Mounded high-amplitude reflection with hummocky low-amplitude internal reflection on vertical section, subparallel overlapping sinuous features on seismic attribute horizon sliceAlternative interpretation:Mass-transport deposit, avulsion node; channel overbankFormation:The Wilcox FormationAge:Early Eocene-Late PaleoceneLocation:Offshore Western AustraliaSeismic data:Stybarrow 2008 M4D MSS obtained by the Geoscience Department of AustraliaAnalysis tools:Coherence, multispectral coherency, principal curvature (K1 and K2), acoustic seismic inversion, flatness and curvedness, CNN automatic fault interpretation, and spectral decomposition
      PubDate: Thu, 20 Oct 2022 00:00:00 GMT
       
  • Pore structure and fractal characteristics of marine-continental
           transitional shales in the southern North China Basin

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      Abstract: AbstractResearch on marine-continental transitional shale in China is significant because this type of shale contains rich gas resources. The shale pore development, which is the key factor in determining the reservoir gas-bearing capacity, is complex. The organic matter (OM) content of the Shanxi and Taiyuan Formations shale in the southern North China Basin is medium to high, the mineral composition differs from that of other transitional shales, and the quartz content is higher than the clay content. The OM content and mineral composition exhibit a strong longitudinal heterogeneity. The pore types are mainly inorganic pores, and OM pores are less developed. The pore morphology is mainly parallel plate-like fissure pores, and there are a few ink-bottle-like pores composed of micro- and macropores. The specific surface area and total pore volume (TPV) of mesoporous-macropores are mainly controlled by mesoporous. The micropore volume is mainly controlled by micropores with sizes below 1.2 nm. Pore structure parameters and fractal dimension find that Shanxi and Taiyuan Formations shale has complex pore structure and rough pore surface. The fractal dimension D2 more accurately characterizes the roughness of the micropore surface. Compared with other shales, the micropore surface roughness of Shanxi and Taiyuan Formations shale is lower. The fractal dimensions and TPV do not correlate. The pore morphology and mineral characteristics of Shanxi and Taiyuan Formations shale leads to relatively low gas adsorption capacity and strong gas storage capacity, and is favorable for oil and gas migration. Due to the effects of compaction, macropores formed by quartz break and are filled with clay, resulting in a low daily gas production of the transitional shale in well MY1 after fracturing. The results provide references for the optimization of favorable reservoirs and the prediction of enrichment areas during transitional shale gas exploration.
      PubDate: Thu, 20 Oct 2022 00:00:00 GMT
       
  • The characteristics of the tight gas reservoir with strong heterogeneity
           and its 3D recovery technology in Yan’an gas field, China

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      Abstract: AbstractThe Yan’an gas field is located in the southeastern part of the Ordos Basin of China. After years of research, we have clarified the characteristics of the upper Paleozoic tight sandstone reservoirs: four main sets of intervals, including the Carboniferous Benxi Formation, the Shan second and Shan first members of the Permian Shanxi Formation, and the He eighth member of the Permian Lower Shihezi Formation, are multilayer complex superposed tight sandstone reservoirs that developed under the control of multiple differential sedimentary systems. Compared with the northern gas field, the upper Paleozoic reservoir is characterized by the small-scale effective sand body and poor physical property in the Yan’an gas field; the heterogeneity of the upper Paleozoic tight reservoir varies greatly: the heterogeneity of the He eighth and the Shan first members was increasing from the north to the south of the research area, owing to the intersection of the north and south provenance. The Shan second member indicates an obviously opposite trend: the heterogeneity of the Benxi Formation weakened from the center to both sides; the Yan’an gas field developed four main superposed composite sand bodies types, including the vertical superposed, lateral migration, cut superposed, and isolated types. Due to the existence of the interlayers rich in mudstone and soft debris near the architectural boundary, the reservoir sand body has strong structural heterogeneity under the interaction of differential diagenesis and densification. Aiming at the strong heterogeneity and multilayer complex superposition characteristics of the Yan’an gas field, we have made clear the constraints and matching relationships between control factors and well-pattern elements on the basis of deep analysis. We have formed the hybrid well pattern for 3D recovery technology that unlocked multilayer complex superposed tight sandstone gas reservoirs with strong heterogeneity in the southeastern portion of the Ordos Basin.
      PubDate: Fri, 14 Oct 2022 00:00:00 GMT
       
  • Control of climate events caused by the volcano on organic matter
           enrichment in the lacustrine source rocks of the Ordos Basin, central
           China

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      Abstract: AbstractWe systematically analyze the geochemical characteristics of source rocks of the Yan Chang Formation in the Ordos Basin to reveal the influence mechanisms of the volcano on lacustrine organic matter enrichment. Organic matter enrichment is not synchronous with the volcanic eruption in time, but it has a “hysteresis” effect. The evidence of volcanic activity mainly includes two aspects: one is a large amount of volcanic ash in black shale, and the other is a negative shift of organic carbon isotopes of source rocks and finding that black shale was affected by climate events caused by the volcano. The climate event caused by the volcano has three effects on organic matter enrichment in black shale: (1) it brought nutrients for the growth of organisms and released a large amount of greenhouse gases, such as CO2, to accelerate photosynthesis and promote the growth of organisms; (2) a large amount of toxic gases, such as SO2 and H2S, were released and O2 was consumed and diluted in the air, forming a severe anoxic environment and accelerating the preservation of organic matter; and (3) it caused extremely hot weather, resulting in long-time surface runoff and other climate events, increasing input of terrestrial organic matter, and forming light components of hydrocarbons.
      PubDate: Fri, 14 Oct 2022 00:00:00 GMT
       
  • Elastic moduli parameterization and inversion considering nanopores
           effects in shale

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      Abstract: AbstractNanopores are widely developed in organic kerogen in shale. Due to the large surface-bulk ratio, nanopores cause significant surface effects that affect the overall elastic properties of shale. It is essential to consider the effects of nanopores when applying the prestack seismic inversion technique for shale reservoir prediction. Based on classical elastic theory, the technique of amplitude variation with offset (AVO) can usually extract velocity of the longitudinal wave and shear wave, elastic modulus, and density in shale reservoir from prestack seismic amplitudes but often ignores the surface effects of nanopores. For this reason, we have derived a new AVO parameterization combining the nanoporoelasticity theory and AVO technique. The newly derived parameterization contains four parameters (shear modulus of matrix, nanopores-related parameter, shear modulus of saturated rock, and density) which can be used to estimate the nanopore properties of shale. The model test and real seismic data examples verify the feasibility and suitability of the proposed method by applying the Bayesian inversion technique with smooth background constraint.
      PubDate: Tue, 11 Oct 2022 00:00:00 GMT
       
  • Prediction of petrophysical classes and reservoir beds through microfacies
           and pore types characterization, Tahe Ordovician naturally fractured vuggy
           carbonates

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      Abstract: AbstractCarbonates commonly present a stacking-pattern architecture determined by the depositional processes despite the diagenetic modifications. This study integrates spectral cyclostratigraphy and petrophysical analysis to locate prolific reservoir beds to optimize reservoir development. This involves subdividing the reservoir succession into different hierarchical units to understand the variation of microfacies and pore-structure types. The variation trends and discontinuity surfaces (chronostratigraphic and lithostratigraphic boundaries) are determined by conjointly interpreting the prediction error filter analysis (PEFA) and integrated PEFA (INPEFA) and synthetic seismic trace and seismogram. We define the rock texture types (microfacies) through self-consistent approximation based on the INPEFA log while considering the variation of depositional sequence and grain size, core/thin-section petrography, and borehole electrical image interpretation. We establish lithology-depth and petrophysical classes-depth profiles using largely well-log data and present new petrophysical classes for naturally fractured vuggy reservoirs. We predict porosity and permeability from the distribution of high-frequency cycles and lithofacies while considering the implications of diagenesis. The results indicate that the depositional processes and diagenesis largely control the quality of the reservoir beds in response to the relative sea-level variations. The reservoir beds comprise the reservoir units with connected-vugs- and fractures-dominated pore systems and the horizons with microporosity-dominated pore systems that are candidates for secondary recovery processes. The study proposes a total porosity variation model that describes an external cardiac compression-like depth profile, revealing alternation between low/tight and high-porosity horizons, with the highly porous intervals associated with the solution-enlarged porosity zones. Permeability varies with the pore type mixing and rock texture type rather than the total porosity. The method well applies to distinguish flow conduits from baffles and barriers in complex carbonate reservoirs.
      PubDate: Fri, 30 Sep 2022 00:00:00 GMT
       
  • Particle size distribution analysis of mudstone based on digital image
           processing

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      Abstract: AbstractMudstone is becoming increasingly important for unconventional oil and gas development. The morphological characteristics of clastic are not only contributions to the 3D framework of mudstone, but they can clearly affect the physical properties of a mudstone reservoir, including surface area, pore-size distribution, and porosity. However, it is very difficult and time-consuming to measure the particle size distribution (PSD) of mudstone because of its small particle size and strong cementation. However, because of the importance of oil and gas extraction, it is urgent to develop a fast, accurate, and objective analysis method to measure the PSD of mudstone. Based on a comparison of various PSD measurement methods commonly used in the energy industry and geology, the best PSD measurement method for mudstone should be digital image processing. Two imaging methods, trainable Weka segmentation (TWS) and black mudstone particle size measurement, were used to analyze sections of the early Silurian Longmaxi mudstone of China’s Sichuan Basin. The PSD data obtained by manual measurement, TWS, and the contribution method are compared. Image analysis finds that the particle sizes of all samples fall in the range of coarse silt to clay, and the average sizes fall in the range of coarse silt to fine silt. The skewness, kurtosis, standard deviation, and other distribution characteristics parameters find minor errors, and the relative error is less than 15%. The Pearson correlation coefficient of the 10th quantile of TWS, black mudstone particle size measure, and manual measurement were calculated, which found R2 values typically ranging between 0.64 and 0.87. Kolmogorov-Smirnov test results find that the data obtained by the three measurement methods are from the same distribution at the level of 0.05. Analytic results find that the method presented is effective, cost-efficient, and could avoid artificial errors.
      PubDate: Fri, 30 Sep 2022 00:00:00 GMT
       
  • Structural characteristics of shallow faults in the Delaware Basin

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      Abstract: AbstractThe Delaware Basin of Texas and New Mexico is experiencing elevated levels of seismicity. There have been more than 130 earthquakes with local magnitudes of at least 3.0 recorded between 2017 and 2021, with earthquakes occurring in spatiotemporally isolated and diffuse clusters. Many of these events have been linked to oilfield operations such as hydraulic fracturing and wastewater disposal at multiple subsurface levels; however, the identification and characterization of earthquake-hosting faults have remained elusive. There are two distinct levels of faulting in the central region of the basin where most earthquakes have been measured. These fault systems include a contractional basement-rooted fault system and a shallow extensional fault system. Shallow faults trend parallel to and rotate along with, the azimuth of SHMAX, are vertically decoupled from the basement-rooted faults, accommodate dominantly dip-slip motion, and are the product of more recent processes including regional exhumation and anthropogenic influences. The shallow fault system is composed of northwest–southeast-striking, high angle, and parallel trending faults which delineate a series of elongate, narrow, and extensional graben. Although most apparent in 3D seismic reflection data, these narrow elongate graben features also are observed from interferometric synthetic aperture radar (InSAR) surface deformation measurements and can be delineated using well-located earthquakes. In contrast to the basin-compartmentalizing basement-rooted fault system, shallow faults do not display any shear movement indicators, and they have small throw displacement given their mapped length, producing an anomalous mean throw-to-length ratio of 1:1000. These characteristics indicate that these features are more segmented than can be mapped with conventional subsurface data. Much of the recent seismicity in the south-central Delaware Basin is associated with these faults and InSAR surface deformation observations find that these faults also may be slipping aseismically.
      PubDate: Tue, 27 Sep 2022 00:00:00 GMT
       
  • Neural net detection of seismic features related to gas hydrates and free
           gas accumulations on the northern U.S. Atlantic margin

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      Abstract: AbstractBottom-simulating reflections (BSRs) that sometimes mark the base of the gas hydrate stability zone in marine sediments are often identified based on the reverse polarity reflections that cut across stratigraphic layering in seismic amplitude data. On the northern U.S. Atlantic margin (USAM) between Cape Hatteras and Hudson Canyon, legacy seismic data have revealed pronounced BSRs south of the deepwater extension of Hudson Canyon and more subtle ones from offshore Delaware south to Cape Hatteras, where the reflections sometimes follow stratigraphic layering. Using high-resolution seismic data acquired during the 2018 Mid-Atlantic Resource Imaging Experiment and a supervised neural net, we identify seismic features associated with gas hydrates and/or the top of gas between Hudson Canyon and Cape Hatteras. Using seismic attributes especially sensitive to the presence of gas, we train a neural network algorithm on seismic data from an area with strong BSRs and then apply the model to the rest of the data set. The results indicate that gas hydrate and/or shallow free gas are significantly more widespread on the northern part of the USAM than previously known. Seismic indicators of gas extend landward from the 2000 m isobath to the upper continental slope in sectors with (offshore Virginia) and, to a lesser extent, without (offshore New Jersey) pervasive upper slope methane seeps. Higher sand content and intermediate sediment thickness, factors related to the container size and gas charge in a petroleum systems framework, are associated with more robust gas indicators.
      PubDate: Tue, 27 Sep 2022 00:00:00 GMT
       
  • Fluid identification based on geophysical well logs in ultralow-porosity
           tight sandstone reservoirs

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      Abstract: AbstractDeep tight sandstone reservoirs typically exhibit ultralow porosity and permeability owing to their small pore size, narrow pore throats, and poor pore connectivity. In heterogeneous tight formations, well-log interpretation is uncertain, and it is difficult to identify fluid types using the classic picket-plot (resistivity versus porosity crossplot) method. To better identify and characterize gas-bearing zones in heterogeneous tight sandstone reservoirs, effective sensitivity factors for fluids need to be constructed. From the conventional logging principle, the acoustic neutron porosity difference, density-neutron porosity difference, and triple-porosity ratio are all sensitive parameters for gas-bearing layers. In addition, the density and nuclear magnetic resonance (NMR) porosity difference and T2 geometric mean of the movable fluid are sensitive to gas saturation. Based on these parameters, a series of fluid typing crossplots was constructed, and their effectiveness was compared. In contrast, the interpretation results from NMR logging are better, and the dual-porosity difference and triple-porosity ratio methods from conventional logs also are effective when NMR logging is not available. In practice, these methods are used to provide their results, and then they are combined using a voting strategy according to the performance of each crossplot. In two case studies of the Kuqa Depression of the Tarim Foreland Basin, China, the new fluid typing method proved effective, and it provides an alternative method for fluid identification using nonelectrical logs (when electrical logs are not available or applicable).
      PubDate: Tue, 27 Sep 2022 00:00:00 GMT
       
  • Deep carbonate reservoir and gas prediction based on multicomponent
           seismic amplitude attributes — A case study

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      Abstract: AbstractMulticomponent seismic exploration provides more valuable information for the prediction of underground structures, lithology, fluids, and fractures. Most studies on lithology estimation and fluid description using PP- and PS-wave seismic data mainly focus on relatively shallow targets with high porosity. Focusing on deep carbonate (dolomite) reservoirs with low porosity (generally less than 5%), we first analyze the characteristics of the seismic response difference between PP and PS waves, and then we combine logging data and seismic forward modeling to implement the identification of fluids using the amplitude difference between PP and PS waves. Data sets are acquired over grain beach dolomite reservoirs in the Cambrian Longwangmiao Formation, the central Sichuan Basin, Western China. The reservoirs are filled with different types of fluids (e.g., gas, water, bitumen, etc.). Based on comparisons between seismic responses of PP and PS waves, we observe that, at the location of the gas-bearing layer, PP-wave amplitude exhibits strong peaks and PS-wave amplitude finds relatively weak peaks, which is different from that obtained for the water-saturated layer. However, at the location of bitumen-filled reservoirs, PP- and PS-wave amplitudes exhibit strong peaks, and the reflection amplitude of PP waves is stronger than that of PS waves. Therefore, the amplitude difference of PP and PS waves provides valuable information and feasibility for fluid identification. We verify that the maximum peak amplitude attribute of PS waves may better characterize the distribution of porous dolomite reservoirs than that of PP waves, and using the attribute of maximum peak amplitude difference between PP and PS waves, we may distinguish gas-bearing and water-saturated layers. Comparing with actual drilling results, we conclude that our PP/PS interpretation technique is feasible for fluid identification in deep carbonate reservoirs.
      PubDate: Mon, 26 Sep 2022 00:00:00 GMT
       
  • Pore system characterization in diagenetically complex Mississippian-aged
           carbonate reservoirs (Kansas, USA)

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      Abstract: AbstractAdvanced petrophysical methods and detailed statistical analysis help to quantitatively and qualitatively characterize pore structure variations in carbonate rocks. Using a core from the Mississippian limestone play in south-central Kansas, we have investigated geologic constraints on reservoir properties using observations of the variability in pore architecture and measured petrophysical properties, i.e., porosity, permeability, and nuclear magnetic resonance (NMR) response. The sample set includes facies that retain their original depositional texture and rocks that have been subject to dolomitization, silicification, and dissolution to varying extents. The dominant macropore types include intercrystalline, moldic, and dissolution-enhanced vuggy porosity, whereas the dominant microporosity types are micritic and dolomitic intercrystalline micropores and nano-intercrystalline within silicified samples. The porosity-permeability relationships and T2 modal distribution of the carbonates that we investigated correlate with dominant pore types depending on the extent and type of diagenetic modification. The fractal nature of pore systems in dolograinstones is not apparent in partially dolomitized samples, and pore complexity significantly decreases with increasing dolomitization. T2cutoff and bound fluid volume estimates indicate that independent of geologic origin, small and intricate pore systems with microporosity are likely to host higher amounts of capillary-bound fluids. This relationship holds, especially among samples with nano-intercrystalline porosity. Correlation coefficients from predicting NMR-derived parameters with porosity improved from 0.1 to 0.78 by including pore architecture data and pore types in the multiple linear regression model. The results and observations presented here improve the current understanding and predictability of petrophysical parameters in carbonate rocks with complex pore systems.
      PubDate: Mon, 26 Sep 2022 00:00:00 GMT
       
  • Seismic reservoir characterization of the Gassum Formation in the
           Stenlille aquifer gas storage, Denmark — Part 2: Unsupervised
           classification

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      Abstract: AbstractIdeally, a good static reservoir model provides an accurate estimate of the extent, porosity, permeability, and lithology of the container as well as the properties of the seal and any faults or fractures that may allow the reservoir to leak. The major pitfall of deterministic, statistical, or supervised learning workflows is that they estimate only the properties sampled by the wells or provided by empirical relations and may miss mapping heterogeneities in the reservoir and seal that can give rise to flow baffles and reservoir leakage. This shortcoming is exacerbated when the number of wells is small, the types of logs recorded are limited, and the migrated seismic gathers are absent or of limited quality. In contrast, unsupervised learning looks for patterns in the seismic amplitude and attribute volumes themselves. In this paper, we apply unsupervised learning algorithms to evaluate the natural gas storage Stenlille aquifer in Denmark and compare the results with a supervised multiattribute regression reservoir characterization described in a companion paper. Specifically, we apply principal component analysis, self-organizing mapping, and generative topographic mapping workflows to extract patterns across eight attribute volumes: relative acoustic impedance, energy, sweetness, gray level co-occurrence matrices (GLCM) entropy, curvedness, and three spectral magnitude volumes. We find that the large-scale patterns are similar, but that the unsupervised learning algorithms provide greater detail. Because our deterministic model was built on poststack data using the limited well-log data available, we believe that the heterogeneity mapped by the unsupervised learning workflows provides a relatively unbiased means of estimating risk in our reservoir model. Quantifying the importance of these anomalies will need to be reconciled with a dynamic reservoir model.
      PubDate: Mon, 26 Sep 2022 00:00:00 GMT
       
  • Characteristics and main controlling factors of dolomite reservoirs in the
           Upper Cambrian Sanshanzi Formation, eastern Ordos Basin, China

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      Abstract: AbstractThe Cambrian system in the Ordos Basin has a similar development degree of carbonate strata to that in the Sichuan and the Tarim Basins; however, no significant oil and gas breakthroughs similar to those in the latter two basins have been made in the Ordos Basin yet, and the characteristics, genesis, and differences in the reservoir need to be explored. Field outcrop observations reveal that the oil and gas shows are common in the Upper Cambrian Sanshanzi Formation in the eastern Ordos Basin, indicating important oil and gas exploration potential. Analysis of the characteristics and genesis of dolomite reservoirs can greatly support the exploration and development of the Cambrian carbonate oil reservoirs in the Ordos Basin. Based on the field outcrop observations and comprehensive laboratory tests and analyses, the reservoir characteristics and main control factors are systematically discussed. This study reveals that the reservoir lithology mainly comprises crystalline dolomite, from fine crystalline dolomite to coarse crystalline dolomite; this results in reservoirs with low porosity, extreme-low porosity, and ultralow permeability dominated by intergranular denudation, caves, and microfractures. They can be further divided into two types of reservoirs: type I reservoirs that have low porosity, ultralow permeability, and medium pore-throat radii, and type II reservoirs that have extreme-low porosity, ultralow permeability, and small pore-throat radii. The physical properties of fine-medium crystalline and medium crystalline dolomite reservoirs are slightly better, and the throats tend to be larger with increasing grain size. The reservoirs have not experienced deep burial processes; dolomitization mainly occurs in the marine-sourced fluid environment with weak oxidation and weak reduction, influenced by the atmospheric fresh water and thermal fluid transformation during the late period to some extent, whereas the hydrocarbons mainly charged during the late period. The crystalline dolomite in residual grains superimposes the denudation and cataclasis in the epigenetic karst stage that are the main controlling factors of the reservoirs. The crystalline cataclasis of dolomite can aid in the formation and reconstruction of the reservoirs. The spatial and temporal distribution laws of the reservoirs and key formation periods need to be studied further.
      PubDate: Mon, 26 Sep 2022 00:00:00 GMT
       
  • Prediction and research of fracture distribution characteristics of the
           Chang 8 reservoir in Zhenjing area, Ordos Basin

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      Abstract: AbstractThe Zhenjing area is on the southwestern margin of the Ordos Basin where the tectonic activity is strong, and natural fractures are widely developed. As the main seepage channels of the reservoir, fractures significantly affect the accumulation of oil and gas. Therefore, it is crucial to study the distribution of fractures in this area. This study comprehensively used cores, image logging, field outcrops, and geophysical data to study the genesis and distribution characteristics of these fractures. The results indicate that the Chang 8 reservoirs in the study area primarily developed high-angle structural fracture-oriented northwest-west and northeast-east. We used five methods to identify and predict the fractures of the Chang 8 reservoir in the Zhenjing area: coherent volume fracture detection, a high-precision curvature method, a maximum likelihood method, a structural restoration method, and ant-tracking technology. After comparing and analyzing the prediction results of the five methods, it was concluded that the structural restoration method performed relatively poorly, whereas the maximum likelihood method was more accurate and better at fracture detection. It was found that the distribution direction of the fractures of the Chang 8 reservoir was primarily northeast-east and northwest-west, showing a strip shape. Oil and gas enrichment is obviously dependent on faults and fractures. The degree of oil and gas enrichment in the northeast-east-oriented tension-torsional fractures was significantly higher than that of northwest-west directional compression-torsional fractures, and oil and gas were more likely to accumulate at the intersections and tails of these fractures.
      PubDate: Mon, 26 Sep 2022 00:00:00 GMT
       
  • Geochemical transformation of tuffaceous materials in tight sandstone and
           its significance for reservoir reconstruction: A case study from the
           Taiyuan and Shihezi Formation in Dingbei area, Ordos Basin

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      Abstract: AbstractCombined with thin sections and electronic probe microanalyzer (EPMA) analysis, we studied the effect of the chemical composition of tuffaceous materials on the quality of sandstone reservoir in the Dingbei area. Analysis of 100 thin sections from five drilled wells indicates that the tuffaceous materials in sandstones from the Taiyuan and Shihezi Formation are common due to the volcanic eruptions. There are three types of tuffaceous materials in the sandstone: intermediate-basic type, intermediate-acid type, and mixed type. Seven thin sections were selected to analyze the chemical elements of tuffaceous materials by EPMA, with 3–8 test points on each thin section. The results indicate a clear decline in most major elements except for SiO2 and Al2O3. The elemental differentiation of tuffaceous sandstone is largely controlled by the activity of the diagenetic system. Under the slow-moving fluid, the active elements such as K, Na, Ca, Mg, and Fe are lost, and Si and Al are enriched. The SiO2 contents of EPMA results are up to 42%. Under the strong-flow fluid, Si and Al can be transferred to precipitate the kaolinites. In the closed diagenetic system, the contents of active elements such as Na and K are high. Dissolution or alteration of tuffaceous materials with different types under the acid fluid is one of the reasons for the generation of heterogeneous reservoirs. The intermediate-acid tuffaceous materials with high SiO2 content experience transformation without dissolution. The mixed tuffaceous materials are mainly transformed into kaolinite to form intercrystalline pores. Due to a large number of soluble components in the intermediate-basic tuffaceous materials, a large number of secondary pores are developed.
      PubDate: Mon, 26 Sep 2022 00:00:00 GMT
       
  • Seismic reservoir characterization of the Gassum Formation in the
           Stenlille aquifer gas storage, Denmark — Part 1

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      Abstract: AbstractSeismic reservoir characterization plays an important role in carbon capture and storage analysis. The Havnsø anticlinal structure in Denmark is a prospective CO2 storage site due to its proximity to two large emission sources—a coal-fired power station and a nearby refinery. Although legacy 2D seismic lines over the area outline the anticlinal structure, their quality is insufficient for quantitative interpretation. Earlier studies have shown that the natural gas stored in the Stenlille aquifer exhibits a seismic response similar to the modeled CO2 fluid in the Havnsø structure. Thus, seismic reservoir characterization carried out on the Stenlille aquifer gas storage in terms of identifying spatial distribution of gas and outlining faults would provide insight regarding value addition that seismic data can bring into the proposed CO2 storage at Havnsø. Using the available poststack seismic data, we apply an integrated reservoir characterization analysis. After performing the adequate data conditioning, the impedance of the target Stenlille Formation is estimated through generation of an accurate low-frequency model. Thereafter, multiattribute analysis was used to generate volumetric estimates of porosity, gamma ray, and water saturation within the target formation so that the spatial distribution of gas can be mapped. The resulting porosity and gamma-ray volumes indicate encouraging results and were used for Bayesian classification to predict the probability of the more important lithofacies, namely, sand, shale, moderate-porosity sand, and moderate-porosity shaly sand, which enabled the mapping of high-porosity/facies zones in the two aquifer storage levels. Independently, we make use of unsupervised machine learning applications for seismic facies prediction and compare them at the two storage levels, which will be presented in the part 2 of this paper.
      PubDate: Thu, 08 Sep 2022 00:00:00 GMT
       
  • Seismic interpretation of sandstone-type uranium deposits in the Songliao
           Basin, Northeast China

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      Abstract: AbstractNuclear energy is a clean energy source that can replace fossil energy on a large scale, and the nuclear energy industry has great advantages in terms of its technical maturity, economic potential, and sustainability. The stable supply of uranium ore, a type of energy mineral, is an important factor for the sustainable development of the nuclear energy industry; as a result, uranium ore has increasingly become the focus of current mineral exploration. We have used seismic attribute analysis, stratal slicing, and seismic inversion to characterize the Sifangtai Formation’s sandstone-type uranium deposit in area A of the central Songliao Basin. We conclude that seismic attribute analysis and the stratal slicing method can predict the continuous reservoir sand body in the study area, and seismic inversion can describe the spatial features of the reservoir sand body in detail. Further analysis of uranium-bearing drilling finds that uranium ore is located in the middle sand body of the lower segment of the Sifangtai Formation, in the middle of the study area, and that the predicted reservoir sand body meets the high-precision requirements for exploration. We use the combination of seismic interpretation and drilling analysis of uranium-bearing ore bodies to effectively predict the size and shape of uranium-bearing ore bodies, and this combined approach can provide guidance for uranium exploration. Furthermore, the results of this study also are significant for the prediction of sand bodies in uranium reservoirs.
      PubDate: Mon, 05 Sep 2022 00:00:00 GMT
       
  • Pore structure analysis of tight reservoirs in the He-8 Member of Upper
           Paleozoic in the southwestern Ordos Basin, China

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      Abstract: AbstractQuantitative characterization of the pore structure in tight reservoir can provide basic parameters for the evaluation of the reservoir quality. By using the cast thin-section petrography, scanning electron microscopy, mercury injection capillary pressure, and constant-rate mercury injection, we have evaluated the distribution characteristics of pore throat and its contribution to permeability. In addition, we have established the relationship between different pore-throat structure parameters and reservoir physical, which provides theoretical support for reservoir evaluation of the He-8 Member in the study area. The results indicate that the pore structure exerts a great control on the quality of the reservoir. Large pore throats (>0.15 μm) are the main contributors to the high seepage capacity of the reservoir. Throat radius, throat distribution, and pore-throat ratio are the key factors controlling the quality of tight reservoir. The He-8 Member of the Upper Paleozoic in the study area is dominated by tight reservoirs, accompanied by a small number of conventional reservoirs.
      PubDate: Mon, 05 Sep 2022 00:00:00 GMT
       
  • Multiscale fracture prediction technique via deep learning, seismic
           gradient disorder, and aberrance: Applied to tight sandstone reservoirs in
           the Hutubi block, southern Junggar Basin

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      Abstract: AbstractFracture prediction is an important and active area of research for oil and gas exploration in fractured unconventional reservoirs. Traditional seismic fracture prediction techniques come in one of two flavors, prestack anisotropy-based or poststack edge-enhancement attributes such as ant tracking and maximum likelihood. Inaccurate predictions may result from an apparent low signal-to-noise ratio in the prestack domain approaches or from cumulative effects that are misrepresented in poststack data; there also are shortcomings from using a single pre- or poststack domain. We propose a comprehensive multiscale prediction framework to delineate major faults (using deep learning), associated minor faults (using seismic gradient disorder), and fractures (using seismic aberrance). The principles of deep learning, seismic gradient disorder, and aberrance are introduced and their application effects are verified through the study of tight sandstone reservoir fractures in the Hutubi area, the southern margin of the Junggar Basin.
      PubDate: Thu, 11 Aug 2022 00:00:00 GMT
       
  • Exploring factors affecting the performance of deep learning in seismic
           fault attribute computation

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      Abstract: AbstractRecently, the computation of seismic fault attribute that may be significant in seismic interpretation is that seismic fault detection is treated as an image segmentation problem using different deep-learning (DL) architectures. To do this, researchers have concentrated on applying cutting-edge DL architectures in computing seismic fault attributes. To explore the factors that may affect the accuracy of seismic fault attribute, we compare the computed fault probability using DL architectures under different scenarios. The designed scenarios aim to highlight the leading factors that may affect the accuracy and resolution of seismic image segmentation. The discussed factors include the dimension and size of training data, training data preparation, ensemble learning, and batch size in DL. The proposed comparisons are applied to one marine seismic survey from New Zealand and one land seismic survey from China. The results demonstrate that properly preparing training data is far more important than choosing a cutting-edge DL architecture in computing seismic fault attribute. We also propose a practical workflow that can include real seismic data and corresponding interpreted fault sticks in training data for a specific seismic survey.
      PubDate: Mon, 08 Aug 2022 00:00:00 GMT
       
  • Gravity and magnetic field features and the prospects of iron deposits in
           the eastern Hebei province, China

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      Abstract: AbstractTo study the features of the gravity and magnetic anomalies and the prospects of iron deposits in the eastern Hebei province, we have collected and arranged gravity data at scales of 1:50,000 and 1:200,000 and aeromagnetic data at scales of 1:25,000 and 1:200,000. Then, we have separated the Bouguer gravity anomaly and the aeromagnetic anomaly by reduction to the pole (RTP) by the moving average method and processed these two anomalies using the total horizontal gradient method and the vertical second derivative method. Combined with existing geologic and geophysical research, we have studied the features of the gravity and magnetic anomalies and investigated the corresponding relationship between the distribution of iron deposits and these anomalies, and then we predicted the favorable areas for iron deposits in the eastern Hebei province. The results find that there is a good corresponding relationship between the distribution of iron deposits and the gravity and magnetic anomalies in the eastern Hebei province. Identification marks of the gravity and magnetic anomalies are determined to find the iron deposits in the eastern Hebei province, including the magnetic highs of the local magnetic anomaly and the vertical second derivative anomaly, the gravity highs of the local gravity anomaly and the vertical second derivative anomaly, the gradient belts of the Bouguer gravity anomaly, the high-value zones of the RTP aeromagnetic anomaly, and the extreme-value zones of the total horizontal gradient of the Bouguer gravity anomaly and the RTP aeromagnetic anomaly. There are 17 favorable areas for iron deposits in the eastern Hebei province, and these favorable areas display complex trends, including east–west-trending, north-northwest-trending, and northeast-east-trending features.
      PubDate: Mon, 08 Aug 2022 00:00:00 GMT
       
  • Undulating sediments of the Cape Fear submarine landslide system, offshore
           U.S. Atlantic margin: Sediment waves versus creep deformation

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      Abstract: AbstractWe interpret a region of undulatory sediments adjacent to a major headwall of the Cape Fear submarine landslide system offshore of North Carolina, USA, as sediment waves rather than creep or fault-related deformation. The wave package extends 19 km upslope from the S4 landslide headwall and thickens upslope from approximately 250 to 450 m. The field of undulating sediments displays the continuity of seismic horizons, upslope-migrating crests, downslope thinning, and wave heights and lengths of approximately 26 m and approximately 1 km, respectively, which are consistent with sediment wavefields. The Western Boundary Undercurrent formed contourites on the nearby Blake Ridge and it is possible that these sediment undulations were deposited via similar mechanisms. Ocean Drilling Program (ODP) cores near the sediment undulation field suggest that the turbidity currents also may have played a role in wave formation. Although most of the 19 km long field comprises unaltered sediment waves, we observe an approximately 5 km long zone adjacent to the landslide scarp that expresses evidence of faults that offset and deform the sediment wave strata. We interpret this deformation as the result of reduction in stress following the removal of the landslide mass. Given that the Cape Fear system has generated several episodes of potentially tsunamigenic slope failure, the future stability of the system is pertinent. Redefining these undulatory sediments as sediment waves eliminates a major slope instability mechanism of the system and is important for understanding the future slope stability hazards of Cape Fear. Our analysis highlights the importance of understanding sediment waves in hybrid submarine landslide-sediment wave systems.Geological feature:Cape Fear submarine landslide sediment wavesSeismic appearance:Continuous undulating horizonsAlternative interpretations:Downslope creep or faultsFeatures with similar appearance:Extensional slope failureFormation:Alongslope and downslope currentsAge:QuaternaryLocation:Cape Fear submarine landslide complex, offshore North CarolinaSeismic data:High resolution multichannel seismic dataAnalysis tools:Multichannel seismic data, multibeam bathymetry, sub-bottom Chirp
      PubDate: Fri, 05 Aug 2022 00:00:00 GMT
       
  • The Lower Devonian (Ovinparmian) reservoir: Prospects in the offshore part
           of the Timan-Pechora petroleum basin

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      Abstract: AbstractThe offshore part of the Timan-Pechora petroleum basin is one of the most promising areas to search for new petroleum accumulations. The commercial potential of the Carboniferous-Lower Permian play has already been proven by exploratory drilling in the Dolginskoye uplift, whereas the Prirazlomnoye field has been in production since 2013. However, significant petroleum resources in this area may be confined to the Ordovician-Lower Devonian play. The purpose of the study is to evaluate the potential of the Lower Devonian (Ovinparmian) reservoirs within the Pechora Sea shelf based on new geologic and geophysical data. We identified multiple prospects within the Dolginsko-Papaninskaya structural zone and estimated its resources. The potential of the Lower Devonian within the study area is comparable with that of the Carboniferous-Lower Permian play. Based on the new 3D seismic data performed in three offshore license blocks, we identified several unconformities, where the Timanian-Sargaevian regional seal onlaps carbonate rocks of the Ovinparmian horizon (Lochkovian stage, Lower Devonian). We hypothesize that due to the Middle Devonian structural deformations, the Lower Devonian carbonate deposits have been exposed to subaerial erosion and surface and subsurface karst. Diagenetic alterations of the Ovinparmian sediments (i.e., dolomitization, dissolution, and fracturing) are favorable for the development of high-porosity reservoirs. In our study, we consider some sedimentation, diagenesis, and catagenesis models of the Ovinparmian carbonates. Furthermore, we designed an exploration program with a view to further study the Lower Devonian reservoirs.
      PubDate: Fri, 05 Aug 2022 00:00:00 GMT
       
  • Study on the characteristics and influencing factors of Chang 7
           ultralow-porosity and low-permeability reservoirs in the Heshui area,
           Ordos Basin

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      Abstract: AbstractRecently, the exploration and development of the Chang 7 shale oil reserves and production have increased in the Ordos Basin. However, the characteristics of the Chang 7 reservoir vary greatly in different areas, which affect the exploration and development of shale oil. We used various analytical methods such as core observation, casting section, high-pressure mercury injection, nuclear magnetic resonance, X-ray diffraction (XRD), and logging interpretation to study characteristics of the reservoir in the Heshui area. The lithology of the Chang 7 member is mainly feldspathic quartz sandstone suggesting that the content of quartz is higher than that of feldspar, and it has relatively low carbonates. In addition, the kinds of feldspar are mainly plagioclase and potassium feldspar, and the concentration of clay minerals is 80%, mainly comprising illite and chlorite. The reservoir of the Chang 7 member is chiefly comprised of submicron pores, such as feldspar dissolved pores, intergranular pores, dissolved pores, microfractures, and intergranular pores. The porosity ranges from 6% to 12%, whereas permeability is less than 0.2 × 10−3 μm2. The Chang 7 reservoir has a strong heterogeneity. Specifically, the heterogeneity of Chang 71 is weaker than that of Chang 72. There is a complex diagenesis such as compaction, dissolution, and cementation, and the compaction and cementation are relatively more and the dissolution is dominated by constructive diagenesis of feldspar dissolution. Sedimentary microfacies are one of the main factors controlling reservoir development. The physical properties of the reservoir in the branch channel are better than the edges of the branch channel and the lacustrine. The diagenesis affects the development and distribution of good reservoirs, and destructive diagenesis such as compaction and cementation reduces porosity and permeability. Conversely, dissolution increases the physical properties of the reservoir. Tectonics has no obvious effects on reservoir but plays a positive role in the migration and accumulation of hydrocarbon when microfractures developed.
      PubDate: Fri, 05 Aug 2022 00:00:00 GMT
       
  • V P / V S ratio anomalies in fractured rocks and implication for dolomite
           gas reservoir identification in the northwest Sichuan Basin

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      Abstract: AbstractThe dolomite gas reservoir of the Permian Chihsia Formation has recently become the main target of hydrocarbon exploration in the northwest Sichuan Basin. Owing to its substantially low porosity and permeability, the dolomite gas reservoir has become a great challenge for geophysicists in terms of distinguishing gas-filled dolomite thin layers. We have used limestone and dolomite core samples from the Permian in the northwest Sichuan Basin to investigate the physical characteristics of the dolomite gas reservoir in a laboratory. Dolomite has a comparatively higher permeability than limestone due to its higher fracture development. X-ray CT scanning indicates that a few large pore spaces dominate the pore space in limestone that cannot provide good pore connections, whereas small pores and fractures dominate the pore spaces in dolomite. The fracture development in the dolomites provides insignificant porosity that substantially increases the permeability. The VP/VS ratio estimated from well-logging data in the northwest Sichuan Basin indicates significantly lower anomalies. These low VP/VS anomalies validate the rock-physics analysis from the laboratory data and indicate that the VP/VS ratio could be a good indicator of gas reservoirs in dolomite layers.
      PubDate: Fri, 05 Aug 2022 00:00:00 GMT
       
 
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