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19 pages, 14233 KiB  
Article
Subsurface Characterization of the Merija Anticline’s Rooting Using Integrated Geophysical Techniques: Implications for Copper Exploration
by Mohammed Boumehdi, Hicham Khebbi, Doha Dchar, Lahsen Achkouch, Anwar Ain Tagzalt, Nour Eddine Berkat, Mohammed Magoua, Youssef Hahou and Othman Sadki
Geosciences 2025, 15(8), 305; https://doi.org/10.3390/geosciences15080305 - 6 Aug 2025
Abstract
This study investigates the subsurface rooting of the Merija anticline in the Missour Basin, Morocco, with a focus on copper mineralization exploration. A sequential geophysical workflow was implemented, combining gravity surveys, electrical resistivity (ER), and induced polarization (IP) methods. The gravity data, acquired [...] Read more.
This study investigates the subsurface rooting of the Merija anticline in the Missour Basin, Morocco, with a focus on copper mineralization exploration. A sequential geophysical workflow was implemented, combining gravity surveys, electrical resistivity (ER), and induced polarization (IP) methods. The gravity data, acquired along spaced profiles extending from outcropping areas to Quaternary-covered zones, clearly delineated the structural continuity of the anticline beneath the cover. The application of trend filtering in covered areas allowed the removal of regional effects, successfully isolating residual anomalies associated with the buried continuation of the anticline. Interpolated Bouguer anomaly maps highlighted a major regional fault, interpreted as controlling the deep rooting of the anticline. A resistivity profile was then deployed perpendicular to this fault, providing detailed imaging of the anticline’s geometry and lithological contrasts. Complementary IP profiles conducted near the mine site targeted the detection of chargeability anomalies associated with copper mineralization dominated by malachite, confirming the electrical signature of copper mineralization, particularly within the sandstone and conglomerate formations of the Lower Cretaceous. To validate the geophysical interpretations, a drilling campaign was conducted, which confirmed the presence of the identified lithological units and the anticline rooting, as revealed by geophysical data. This approach provides a robust framework for copper exploration in the Merija area and can be adapted to similar geological contexts elsewhere. Full article
(This article belongs to the Section Geophysics)
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22 pages, 30259 KiB  
Article
Controlling Effects of Complex Fault Systems on the Oil and Gas System of Buried Hills: A Case Study of Beibuwan Basin, China
by Anran Li, Fanghao Xu, Guosheng Xu, Caiwei Fan, Ming Li, Fan Jiang, Xiaojun Xiong, Xichun Zhang and Bing Xie
J. Mar. Sci. Eng. 2025, 13(8), 1472; https://doi.org/10.3390/jmse13081472 - 31 Jul 2025
Viewed by 176
Abstract
Traps are central to petroleum exploration, where hydrocarbons accumulate during migration. Reservoirs are likewise an essential petroleum system element and serve as the primary medium for hydrocarbon storage. The buried hill is a geological formation highly favorable for reservoir development. However, the factors [...] Read more.
Traps are central to petroleum exploration, where hydrocarbons accumulate during migration. Reservoirs are likewise an essential petroleum system element and serve as the primary medium for hydrocarbon storage. The buried hill is a geological formation highly favorable for reservoir development. However, the factors influencing hydrocarbon accumulation in buried hill reservoirs are highly diverse, especially in areas with complex, active fault systems. Fault systems play a dual role, both in the formation of reservoirs and in the migration of hydrocarbons. Therefore, understanding the impact of complex fault systems helps enhance the exploration success rate of buried hill traps and guide drilling deployment. In the Beibuwan Basin in the South China Sea, buried hill traps are key targets for deep-buried hydrocarbon exploration in this faulted basin. The low level of exploration and research in buried hills globally limits the understanding of hydrocarbon accumulation conditions, thereby hindering large-scale hydrocarbon exploration. By using drilling data, logging data, and seismic data, stress fields and tectonic faults were restored. There are two types of buried hills developed in the Beibuwan Basin, which were formed during the Late Ordovician-Silurian period and Permian-Triassic period, respectively. The tectonic genesis of the Late Ordovician-Silurian period buried hills belongs to magma diapirism activity, while the tectonic genesis of the Permian-Triassic period buried hills belongs to reverse thrust activity. The fault systems formed by two periods of tectonic activity were respectively altered into basement buried hills and limestone buried hills. The negative structural inversion controls the distribution and interior stratigraphic framework of the deformed Carboniferous strata in the limestone buried hill. The faults and derived fractures of the Late Ordovician-Silurian period and Permian-Triassic period promoted the diagenesis and erosion of these buried hills. The faults formed after the Permian-Triassic period are not conducive to calcite cementation, thus facilitating the preservation of the reservoir space formed earlier. The control of hydrocarbon accumulation by the fault system is reflected in two aspects: on the one hand, the early to mid-Eocene extensional faulting activity directly controlled the depositional process of lacustrine source rocks; on the other hand, the Late Eocene-Oligocene, which is closest to the hydrocarbon expulsion period, is the most effective fault activity period for connecting Eocene source rocks and buried hill reservoirs. This study contributes to understanding of the role of complex fault activity in the formation of buried hill traps within hydrocarbon-bearing basins. Full article
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26 pages, 21628 KiB  
Article
Key Controlling Factors of Deep Coalbed Methane Reservoir Characteristics in Yan’an Block, Ordos Basin: Based on Multi-Scale Pore Structure Characterization and Fluid Mobility Research
by Jianbo Sun, Sijie Han, Shiqi Liu, Jin Lin, Fukang Li, Gang Liu, Peng Shi and Hongbo Teng
Processes 2025, 13(8), 2382; https://doi.org/10.3390/pr13082382 - 27 Jul 2025
Viewed by 302
Abstract
The development of deep coalbed methane (buried depth > 2000 m) in the Yan’an block of Ordos Basin is limited by low permeability, the pore structure of the coal reservoir, and the gas–water occurrence relationship. It is urgent to clarify the key control [...] Read more.
The development of deep coalbed methane (buried depth > 2000 m) in the Yan’an block of Ordos Basin is limited by low permeability, the pore structure of the coal reservoir, and the gas–water occurrence relationship. It is urgent to clarify the key control mechanism of pore structure on gas migration. In this study, based on high-pressure mercury intrusion (pore size > 50 nm), low-temperature N2/CO2 adsorption (0.38–50 nm), low-field nuclear magnetic resonance technology, fractal theory and Pearson correlation coefficient analysis, quantitative characterization of multi-scale pore–fluid system was carried out. The results show that the multi-scale pore network in the study area jointly regulates the occurrence and migration process of deep coalbed methane in Yan’an through the ternary hierarchical gas control mechanism of ‘micropore adsorption dominant, mesopore diffusion connection and macroporous seepage bottleneck’. The fractal dimensions of micropores and seepage are between 2.17–2.29 and 2.46–2.58, respectively. The shape of micropores is relatively regular, the complexity of micropore structure is low, and the confined space is mainly slit-like or ink bottle-like. The pore-throat network structure is relatively homogeneous, the difference in pore throat size is reduced, and the seepage pore shape is simple. The bimodal structure of low-field nuclear magnetic resonance shows that the bound fluid is related to the development of micropores, and the fluid mobility mainly depends on the seepage pores. Pearson’s correlation coefficient showed that the specific surface area of micropores was strongly positively correlated with methane adsorption capacity, and the nanoscale pore-size dominated gas occurrence through van der Waals force physical adsorption. The specific surface area of mesopores is significantly positively correlated with the tortuosity. The roughness and branch structure of the inner surface of the channel lead to the extension of the migration path and the inhibition of methane diffusion efficiency. Seepage porosity is linearly correlated with gas permeability, and the scale of connected seepage pores dominates the seepage capacity of reservoirs. This study reveals the pore structure and ternary grading synergistic gas control mechanism of deep coal reservoirs in the Yan’an Block, which provides a theoretical basis for the development of deep coalbed methane. Full article
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31 pages, 14609 KiB  
Article
Reservoir Properties and Gas Potential of the Carboniferous Deep Coal Seam in the Yulin Area of Ordos Basin, North China
by Xianglong Fang, Feng Qiu, Longyong Shu, Zhonggang Huo, Zhentao Li and Yidong Cai
Energies 2025, 18(15), 3987; https://doi.org/10.3390/en18153987 - 25 Jul 2025
Viewed by 240
Abstract
In comparison to shallow coal seams, deep coal seams exhibit characteristics of high temperature, pressure, and in-situ stress, leading to significant differences in reservoir properties that constrain the effective development of deep coalbed methane (CBM). This study takes the Carboniferous deep 8# coal [...] Read more.
In comparison to shallow coal seams, deep coal seams exhibit characteristics of high temperature, pressure, and in-situ stress, leading to significant differences in reservoir properties that constrain the effective development of deep coalbed methane (CBM). This study takes the Carboniferous deep 8# coal seam in the Yulin area of Ordos basin as the research subject. Based on the test results from core drilling wells, a comprehensive analysis of the characteristics and variation patterns of coal reservoir properties and a comparative analysis of the exploration and development potential of deep CBM are conducted, aiming to provide guidance for the development of deep CBM in the Ordos basin. The research results indicate that the coal seams are primarily composed of primary structure coal, with semi-bright to bright being the dominant macroscopic coal types. The maximum vitrinite reflectance (Ro,max) ranges between 1.99% and 2.24%, the organic is type III, and the high Vitrinite content provides a substantial material basis for the generation of CBM. Longitudinally, influenced by sedimentary environment and plant types, the lower part of the coal seam exhibits higher Vitrinite content and fixed carbon (FCad). The pore morphology is mainly characterized by wedge-shaped/parallel plate-shaped pores and open ventilation pores, with good connectivity, which is favorable for the storage and output of CBM. Micropores (<2 nm) have the highest volume proportion, showing an increasing trend with burial depth, and due to interlayer sliding and capillary condensation, the pore size (<2 nm) distribution follows an N shape. The full-scale pore heterogeneity (fractal dimension) gradually increases with increasing buried depth. Macroscopic fractures are mostly found in bright coal bands, while microscopic fractures are more developed in Vitrinite, showing a positive correlation between fracture density and Vitrinite content. The porosity and permeability conditions of reservoirs are comparable to the Daning–Jixian block, mostly constituting oversaturated gas reservoirs with a critical depth of 2400–2600 m and a high proportion of free gas, exhibiting promising development prospects, and the middle and upper coal seams are favorable intervals. In terms of resource conditions, preservation conditions, and reservoir alterability, the development potential of CBM from the Carboniferous deep 8# coal seam is comparable to the Linxing block but inferior to the Daning–Jixian block and Baijiahai uplift. Full article
(This article belongs to the Section H: Geo-Energy)
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21 pages, 7866 KiB  
Article
Asteroid and Meteorite Impacts as a Cause of Large Sedimentary Basins: A Case Study of the Transylvanian Depression
by Dumitru Ioane, Irina Stanciu and Mihaela Scradeanu
Geosciences 2025, 15(7), 267; https://doi.org/10.3390/geosciences15070267 - 9 Jul 2025
Viewed by 695
Abstract
Impact cratering determined by collisions with meteorites and asteroids is considered one of the main natural processes in the Solar System, modifying the planets and their satellites surface during time. The Earth includes in its impact record a small number of such events [...] Read more.
Impact cratering determined by collisions with meteorites and asteroids is considered one of the main natural processes in the Solar System, modifying the planets and their satellites surface during time. The Earth includes in its impact record a small number of such events due to active plate tectonics, sedimentation, and volcanism, with these geological processes destroying and burying their impact geomorphological signatures. To enlarge the Earth’s impacts database, new concepts and research methods are necessary, as well as the reinterpretation of old geological and geophysical models. Geomorphological, Geological, and Geophysical (3G) signatures in concealed impacted areas are discussed in this paper; the first offers the target characteristics, while the others give means for detecting their unseen remnants. The 3G signatures have been applied to the Transylvanian Depression, a fascinating geological structure, with difficulties in explaining the direct overlapping of regionally developed thick tuff and thick salt layers, and undecided interpretation of the regional magnetic anomaly. Large and deep sedimentary basins, such as the Precaspian, Alexandria and Transylvanian depressions, are interpreted to have started as impacted areas during the Permian or the Lower Neogene. Geophysical and geological existing information have been reinterpreted, offering a new way in understanding deeply located geological structures. Full article
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21 pages, 15682 KiB  
Article
Detection of Sedimentary Basins and Karstic Faults in the Yucatán Peninsula by Gravity Inversion and Euler Deconvolution
by José Carlos Ortiz-Alemán, Mauricio Nava-Flores, Jaime Humberto Urrutia-Fucugauchi, Sebastián Ortiz-Aguilar, Mauricio Gabriel Orozco-del-Castillo and Sebastian López-Juárez
Earth 2025, 6(2), 42; https://doi.org/10.3390/earth6020042 - 16 May 2025
Viewed by 1817
Abstract
The northern Yucatán Peninsula hosts a complex karstic environment shaped by carbonate platform development and the Chicxulub impact event, making subsurface characterization crucial for geological and hydrogeological studies. This work aimed to resolve the shallow crustal structure and identify major tectonic features that [...] Read more.
The northern Yucatán Peninsula hosts a complex karstic environment shaped by carbonate platform development and the Chicxulub impact event, making subsurface characterization crucial for geological and hydrogeological studies. This work aimed to resolve the shallow crustal structure and identify major tectonic features that influence karst processes and groundwater dynamics. We applied a rapid 3D gravity inversion method, linear back projection (LBP), to Bouguer anomaly data, combined with Euler deconvolution to map shallow and deep fault systems. The inversion produced a high-resolution density model down to 12.8 km depth, revealing key geological structures. Multilevel thresholding delineated significant low-density basins, notably the Chicxulub crater, as well as buried sedimentary basins. Euler solutions identified fault networks that coincide with areas of intense karstification, particularly in the eastern peninsula. Results highlight the interplay between impact-related tectonics and karst evolution, influencing groundwater flow paths and recharge zones. This study demonstrates the effectiveness of gravity inversion and Euler deconvolution for regional crustal imaging in carbonate platforms and emphasizes the need for further local-scale surveys to investigate coastal aquifer vulnerability and saltwater intrusion processes. Full article
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15 pages, 8076 KiB  
Article
Applicability of Machine Learning and Mathematical Equations to the Prediction of Total Organic Carbon in Cambrian Shale, Sichuan Basin, China
by Majia Zheng, Meng Zhao, Ya Wu, Kangjun Chen, Jiwei Zheng, Xianglu Tang and Dadong Liu
Appl. Sci. 2025, 15(9), 4957; https://doi.org/10.3390/app15094957 - 30 Apr 2025
Viewed by 522
Abstract
Accurate Total Organic Carbon (TOC) prediction in the deeply buried Lower Cambrian Qiongzhusi Formation shale is constrained by extreme heterogeneity (TOC variability: 0.5–12 wt.%, mineral composition Coefficient of Variation > 40%) and ambiguous geophysical responses. This study introduces three key innovations to address [...] Read more.
Accurate Total Organic Carbon (TOC) prediction in the deeply buried Lower Cambrian Qiongzhusi Formation shale is constrained by extreme heterogeneity (TOC variability: 0.5–12 wt.%, mineral composition Coefficient of Variation > 40%) and ambiguous geophysical responses. This study introduces three key innovations to address these challenges: (1) A Dynamic Weighting–Calibrated Random Forest Regression (DW-RFR) model integrating high-resolution Gamma-Ray-guided dynamic time warping (±0.06 m depth alignment precision derived from 237 core-log calibration points using cross-validation), Principal Component Analysis-Deyang–Anyue Rift Trough Shapley Additive Explanations (PCA-SHAP) hybrid feature engineering (89.3% cumulative variance, VIF < 4), and Bayesian-optimized ensemble learning; (2) systematic benchmarking against conventional ΔlogR (R2 = 0.700, RMSE = 0.264) and multi-attribute joint inversion (R2 = 0.734, RMSE = 0.213) methods, demonstrating superior accuracy (R2 = 0.917, RMSE = 0.171); (3) identification of Gamma Ray (r = 0.82) and bulk density (r = −0.76) as principal TOC predictors, contrasted with resistivity’s thermal maturity-dependent signal attenuation (r = 0.32 at Ro > 3.0%). The methodology establishes a transferable framework for organic-rich shale evaluation, directly applicable to the Longmaxi Formation and global Precambrian–Cambrian transition sequences. Future directions emphasize real-time drilling data integration and quantum computing-enhanced modeling for ultra-deep shale systems, advancing predictive capabilities in tectonically complex basins. Full article
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17 pages, 6045 KiB  
Article
Formation Mechanism of Granitic Basement Reservoir Linked to Felsic Minerals and Tectonic Stress in the Qiongdongnan Basin, South China Sea
by Qianwei Hu, Tengfei Zhou, Xiaohu He, Zhihong Chen, Youyuan Que, Anqing Chen and Wenbo Wang
Minerals 2025, 15(5), 457; https://doi.org/10.3390/min15050457 - 28 Apr 2025
Viewed by 462
Abstract
Recent exploration efforts in the Qiongdongnan Basin have revealed hydrocarbon resources within granitic basement rocks in buried hill traps. However, the formation mechanisms and primary controlling factors of these reservoirs remain poorly understood. In this study, we utilized data from six wells in [...] Read more.
Recent exploration efforts in the Qiongdongnan Basin have revealed hydrocarbon resources within granitic basement rocks in buried hill traps. However, the formation mechanisms and primary controlling factors of these reservoirs remain poorly understood. In this study, we utilized data from six wells in the Qiongdongnan Basin, including sidewall cores, thin sections, imaging logging, and seismic reflection profiles, to analyze the petrological characteristics, pore systems, and fracture networks of the deep basement reservoir. The aim of our study was to elucidate the reservoir formation mechanisms and identify the key controlling factors. The results indicate that the basement lithology is predominantly granitoid, intruded during the late Permian to Triassic. These rocks are characterized by high felsic mineral content (exceeding 90% on average), with them possessing favorable brittleness and solubility properties. Fractures identified from sidewall cores and interpreted from image logging can be categorized into two main groups: (1) NE-SW trending conjugate shear fractures with sharp dip angles and (2) NW-SE trending conjugate shear fractures with sharp angles. An integrated analysis of regional tectonic stress fields suggests that the NE-trending fractures and associated faults were formed by compressional stresses related to the Indosinian closure of the ancient Tethys Ocean. In contrast, the NW-trending fractures and related faults resulted from southeast-directed compressional stresses during the Yanshanian subduction event. During the subsequent Cenozoic extensional phase, these fractures were reactivated, creating effective storage spaces for hydrocarbons. The presence of calcite and siliceous veins within the reservoir indicates the influence of meteoric water and magmatic–hydrothermal fluid activities. Meteoric water weathering exerted a depth-dependent dissolution effect on feldspathoid minerals, leading to the formation of fracture-related pores near the top of the buried hill trap during the Mesozoic exposure period. Consequently, the combination of high-density fractures and dissolution pores forms a vertically layered reservoir within the buried hill trap. The distribution of potential hydrocarbon targets in the granitic basement is closely linked to the surrounding tectonic framework. Full article
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14 pages, 7040 KiB  
Article
Thermal Performance of Deep Borehole Heat Exchangers (DBHEs) Installed in a Groundwater-Filled Hot Dry Rock (HDR) Well in Qinghai, China
by Qixing Zhang, Feiyang Lu, Yong Huang, Liwei Tan, Jin Luo and Longcheng Duan
Energies 2025, 18(9), 2229; https://doi.org/10.3390/en18092229 - 27 Apr 2025
Viewed by 361
Abstract
Deep borehole heat exchangers (DBHEs) have been widely used for extracting geothermal energy in China. However, the application of this technology in an open well with high temperature remains unknown. In this paper, the thermal performance of a DBHE installed in a groundwater-filled [...] Read more.
Deep borehole heat exchangers (DBHEs) have been widely used for extracting geothermal energy in China. However, the application of this technology in an open well with high temperature remains unknown. In this paper, the thermal performance of a DBHE installed in a groundwater-filled hot dry rock (HDR) well in the Gonghe Basin of Qinghai Province in China was investigated. A U-shaped pipe subjected to a hydraulic pressure of 30 MPa and a temperature of 180 °C was tested successfully. Severe heat loss was detected during the test, which might have been due to the pipe not being well-insulated. To better understand the performance of DBHEs, a numerical model was developed. The results indicate that the pipe’s thermal performance increased by 247% using insulation with a 15 mm layer thickness and a thermal conductivity of 0.042 W/m·K. Thermal performance was significantly improved by increasing the fluid flow rate and pipe diameter. Among the different pipe configurations, double U-shaped buried pipes can achieve the highest performance. The heat-specific rate can reach up to 341.33 W/m with a double U-shaped pipe with a diameter of 63 mm. The second highest rate can be achieved with a coaxial pipe, while single U-shaped pipes have the lowest one. Full article
(This article belongs to the Section J1: Heat and Mass Transfer)
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19 pages, 4734 KiB  
Article
Fractal Analysis of Volcanic Rock Image Based on Difference Box-Counting Dimension and Gray-Level Co-Occurrence Matrix: A Case Study in the Liaohe Basin, China
by Sijia Li, Zhuwen Wang and Dan Mou
Fractal Fract. 2025, 9(2), 99; https://doi.org/10.3390/fractalfract9020099 - 4 Feb 2025
Viewed by 969
Abstract
Volcanic rocks, as a widely distributed rock type on the earth, are mostly buried deep within basins, and their internal structures possess characteristics by irregularity and self-similarity. In the study of volcanic rocks, accurately identifying the lithology of volcanic rocks is significant for [...] Read more.
Volcanic rocks, as a widely distributed rock type on the earth, are mostly buried deep within basins, and their internal structures possess characteristics by irregularity and self-similarity. In the study of volcanic rocks, accurately identifying the lithology of volcanic rocks is significant for reservoir description and reservoir evaluation. The accuracy of lithology identification can improve the success rate of petroleum exploration and development as well as the safety of engineering construction. In this study, we took the electron microscope images of four types of volcanic rocks in the Liaohe Basin as the research objects and comprehensively used the differential box-counting dimension (DBC) and the gray-level co-occurrence matrix (GLCM) to identify the lithology of volcanic rocks. Obtain the images of volcanic rocks in the research area and conduct preprocessing so that the images can meet the requirements of calculations. Firstly, calculate the different box-counting dimension. Divide the grayscale image into boxes of different scales and determine the differential box-counting dimension based on the variation of grayscale values within each box. The differential box-counting dimension of basalt ranges from 1.7 to 1.75, that of trachyte ranges from 1.82 to 1.87, that of gabbro ranges from 1.76 to 1.79, and that of diabase ranges from 1.78 to 1.82. Then, the gray-level co-occurrence matrix is utilized to extract four image texture features of volcanic rock images, namely contrast, energy, entropy, and variance. The recognition of four types of volcanic rock images is achieved by combining the different box-counting dimension and the gray-level co-occurrence matrix. This method has been experimentally verified by volcanic rock image samples. It has a relatively high accuracy in identifying the lithology of volcanic rocks and can effectively distinguish four different types of volcanic rocks. Compared with single-feature recognition methods, this approach significantly improves recognition accuracy, offers reliable technical support and a data basis for volcanic rock-related geological analyses, and drives the further development of volcanic rock research. Full article
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17 pages, 13142 KiB  
Article
Diagenetic Fluids and Multiphase Dolomitizations of Lower Paleozoic Carbonate Reservoirs, Offshore Bohai Bay Basin, Northern China
by Xuewei Zhou, Haiyang Cao, Jian Luo, Anqing Chen, Zeji Wang and Mingcai Hou
Minerals 2025, 15(1), 35; https://doi.org/10.3390/min15010035 - 30 Dec 2024
Viewed by 819
Abstract
Dolomitization is a critical diagenetic alteration that impacts the formation of carbonate hydrocarbon reservoirs. In the offshore Bohai Bay Basin, the Lower Paleozoic carbonate reservoirs in buried hill traps, and the basement highs unconformably overlain by younger rock units, are emerging as a [...] Read more.
Dolomitization is a critical diagenetic alteration that impacts the formation of carbonate hydrocarbon reservoirs. In the offshore Bohai Bay Basin, the Lower Paleozoic carbonate reservoirs in buried hill traps, and the basement highs unconformably overlain by younger rock units, are emerging as a prospective target and predominantly occur in dolomite layers. Meanwhile, the formation mechanisms of the dolomite are not clear, which affects the understanding of the occurrence of deep dolomite reservoirs and hinders oil and gas exploration. Based on comprehensive observations of the thin sections of the carbonate samples, the dolomite types were meticulously categorized into micritic dolostone, fine-crystalline dolostone, and saddle dolomite. Then, carbon, oxygen, and strontium isotope and trace elements were examined to elucidate the dolomitization fluids and propose diagenetic models for the three kinds of dolomite formation. The mineralogical and geochemical evidence reveals that there were two kinds of dolomitization fluids, including penecontemporaneous seawater, and hydrothermal fluid. The diagenetic fluid of the micritic dolostone and fine-crystalline dolostone both involved penecontemporaneous seawater, but fine-crystalline dolostone is also affected by later burial dolomitization processes. The saddle dolomite, filling in pre-existing fractures or dissolution pore cavities, is attributed to a hydrothermal fluid associated with magmatic activities. Notably, the extensive layered fine-crystalline dolostone was the predominant reservoir rock. The initial mechanism for its formation involves penecontemporaneous seepage reflux dolomitization, which is superimposed by later burial dolomitization. The burial dolomitization enhanced porosity, subsequently facilitating the formation of a fracture-related dissolution pore cavity system, and partly filled by saddle dolomite during the Cenozoic hydrothermal events. The findings highlight that the layered fine-crystalline dolostone that underwent multiphase dolomitization is the most potential target for hydrocarbon exploration. Full article
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18 pages, 4434 KiB  
Article
Fractal Characteristics of Pore Structure of Longmaxi Shales with Different Burial Depths in Southern Sichuan and Its Geological Significance
by Manping Yang, Yanyan Pan, Hongye Feng, Qiang Yan, Yanjun Lu, Wanxin Wang, Yu Qi and Hongjian Zhu
Fractal Fract. 2025, 9(1), 2; https://doi.org/10.3390/fractalfract9010002 - 24 Dec 2024
Cited by 3 | Viewed by 968
Abstract
Burial depth can significantly impact the pore structure characteristics of shale. The Lower Silurian Longmaxi Shale in the Weiyuan block of the Sichuan Basin is a marine formation that we studied for deep shale gas exploration. We used two groups of Longmaxi samples, [...] Read more.
Burial depth can significantly impact the pore structure characteristics of shale. The Lower Silurian Longmaxi Shale in the Weiyuan block of the Sichuan Basin is a marine formation that we studied for deep shale gas exploration. We used two groups of Longmaxi samples, outcrop shale and middle-deep shale, to investigate the pore structure fractal features at varying burial depths using a combination of mineralogy, organic geochemistry, scanning electron microscopy (SEM), and low-temperature gas (CO2, N2) adsorption. The V-S fractal model was used to determine the fractal dimension (Dc) of micropores, and the FHH fractal model was used to determine the fractal dimension (DN) of mesopores. The findings indicate that the pore morphology of organic matter becomes irregular and more broken as the burial depth increases, as does the content and maturity of organic matter. The pore size of organic matter gradually decreases, the SSA (BET, DR) and PV (BJH, DA) of shale pores increase, the pore structure becomes more complex, and the average shale pore size decreases. According to this study, the organic matter content and its maturity show an increasing trend as burial depth increases. Meanwhile, the organic matter’s pore morphology tends to be irregular, and fracture rates rise, which causes the organic matter’s pore size to gradually decrease. In addition, the SSA (comprising the values assessed by BET and DR techniques) and PV (evaluated by BJH and DA methods) of shale pores grew, suggesting that the pore structure became more complex. Correspondingly, the average pore size of the shale decreased. The fractal dimensions of the micropores (DC), mesoporous surface (DN1), and mesoporous structure (DN2) of outcrop shale are 2.6728~2.7245, 2.5612~2.5838, and 2.7911~2.8042, respectively. The mean values are 2.6987, 2.5725, and 2.7977, respectively. The DC, DN1, and DN2 of middle-deep shale are 2.6221~2.7510, 2.6085~2.6390, and 2.8140~2.8357, respectively, and the mean values are 2.7050, 2.6243, and 2.8277, respectively. As the fractal dimension grows, the shale’s pore structure becomes more intricate, and the heterogeneity increases as the buried depth increases. The fractal dimension has a positive association with the pore structure parameters (SSA, PV), TOC, and Ro and a negative association with the mineral component (quartz, feldspar, clay mineral) contents. Minerals like quartz, feldspar, and clay will slow down the expansion of pores, but when SSA and PV increase, the pore heterogeneity will be greater and the pore structure more complex. Full article
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10 pages, 5198 KiB  
Article
A Study on the Application of a Deep Thermal Reservoir by Using a Magnetotelluric Sounding Method: Taking an Example of Geothermal Resources’ Exploration in the Western Taikang Uplift of the Southern North China Basin
by Bowen Xu, Huailiang Zhu, Min Zhang, Zhongyan Yang, Gaofeng Ye, Zhilong Liu, Zhiming Hu, Bingsong Shao and Yuqi Zhang
Processes 2024, 12(12), 2839; https://doi.org/10.3390/pr12122839 - 11 Dec 2024
Viewed by 771
Abstract
Geothermal resources are abundant in the Southern North China Basin, which is one of the prospective areas hosting low–medium-temperature geothermal resources in sedimentary basins in China. The purpose of this work is to reveal the formation and storage conditions of the geothermal resources [...] Read more.
Geothermal resources are abundant in the Southern North China Basin, which is one of the prospective areas hosting low–medium-temperature geothermal resources in sedimentary basins in China. The purpose of this work is to reveal the formation and storage conditions of the geothermal resources in the western margin of the Taikang Uplift and delineate the range of potential geothermal reservoirs. This paper uses five magnetotelluric sounding profiles for data processing and analysis, including the calculation of 2D skewness and electric strike. Data processing, analysis, and NLCG 2D inversion were performed on MT data, which consisted of 111 measurement points, and reliable two-dimensional resistivity models and resistivity planes were obtained. In combination with drilling verification and the analysis of geophysical logging data, the stratigraphic lithology and the range of potential geothermal reservoirs were largely clarified. The results show that using the magnetotelluric sounding method can well delineate the range of deep geothermal reservoirs in sedimentary basins and that the MT method is suitable for exploring buried geothermal resources in deep plains. The analytical results showed that the XZR-1 well yielded 1480 cubic meters of water per day, with the water temperature of the wellhead being approximately 78 °C, and combined with the results of this electromagnetic and drilling exploration, a geothermal geological model and genesis process of the west of the Taikang Uplift area was constructed. The water yield and temperature were higher than those of previous exploration results, which has important guiding significance for the future development and utilization of karst fissure heat reservoirs in the western Taikang Uplift. Full article
(This article belongs to the Special Issue Oil and Gas Drilling Processes: Control and Optimization)
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19 pages, 8323 KiB  
Article
Pore Types and Dolomite Reservoir Genesis of the Fifth Member of the Ordovician Majiagou Formation in the Central and Eastern Ordos Basin
by Shilei Chen, Rong Dai and Shunshe Luo
Appl. Sci. 2024, 14(23), 10976; https://doi.org/10.3390/app142310976 - 26 Nov 2024
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Abstract
The Ordovician dolomite in the Ordos Basin is an important natural gas reservoir. Exploring dolomite genesis and the factors influencing reservoir characteristics is essential for deep carbonate rock exploration. This study offers a comprehensive analysis of dolomite evolution using methods such as thin-section [...] Read more.
The Ordovician dolomite in the Ordos Basin is an important natural gas reservoir. Exploring dolomite genesis and the factors influencing reservoir characteristics is essential for deep carbonate rock exploration. This study offers a comprehensive analysis of dolomite evolution using methods such as thin-section petrography, isotope analysis, and trace and rare earth elements. The analysis shows that: Based on petrographic observations of the Majiagou Formation in the study area, the dolomite in the study area can be divided into residual oolitic dolomite of synsedimentary or metasomatic origin, micritic dolomite of secondary metasomatism or recrystallization origin, powder crystal dolomite, and fine crystal dolomite. Reservoir pores mainly develop intergranular pores, mold pores, dissolved pores, and fractures. Combined with the characteristics of major elements, trace elements, carbon and oxygen isotopes, rare earth elements, and inclusions in the study area, it can be concluded that the fifth member dolomite of the Majiagou Formation is of shallow–medium burial origin. The diagenetic evolution sequence from the penecontemporaneous period to the middle–deep burial period in the study area is penecontemporaneous dolomite, anhydrite dissolution → seepage silt filling, freshwater dolomite, calcite, and gypsum filling, pressure solution compaction, calcite partial dissolution → gypsum filling, karst cave, buried hydrothermal dolomite, dolomite partial dissolution → calcite complete dissolution, pore dissolution expansion, and quartz pyrite filling. In the early stage of compaction and pressure solution, the primary pores are rapidly reduced, and in the later stage, sutures are generated to provide channels for reservoir fluid migration. The recrystallization reduces the porosity during the middle–deep burial period. Full article
(This article belongs to the Section Earth Sciences)
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Article
Natural Gas Enrichment Processes and Differential Accumulation Models in the Central Anticline Belt of the Xihu Sag, East China Sea Shelf Basin
by Yinshan Chang, Yiming Jiang, Jun Qin, Wenqi Chang, Zhiwu Xiong, Fujia Ji, Ruoyu Zhang and Zhiwei Zeng
Appl. Sci. 2024, 14(22), 10242; https://doi.org/10.3390/app142210242 - 7 Nov 2024
Cited by 1 | Viewed by 1122
Abstract
The Central Anticline Belt of the Xihu Sag is one of the structural units with the most abundant natural gas in the East China Sea Shelf Basin. However, there are significant differences among the anticline units in terms of the scale of natural [...] Read more.
The Central Anticline Belt of the Xihu Sag is one of the structural units with the most abundant natural gas in the East China Sea Shelf Basin. However, there are significant differences among the anticline units in terms of the scale of natural gas enrichment, occurrence horizons, types of gas reservoirs, accumulation processes, and gas-bearing properties of different strata, which influence the optimization of exploration zones and the orientation of exploration in deep-buried areas. This study conducted a comprehensive analysis in terms of the structural evolution, fault activity, hydrocarbon charging stages, and process of hydrocarbon accumulation. It clarifies that (1) the preservation condition is one of the core factors for the differential enrichment of natural gas in the Central Anticline Belt. Under the background of differential compression of the Longjing Movement, late-stage and E-W-trending faults are commonly developed in the anticline cores of the strong compression area in the south, which damage the effectiveness of traps, resulting in a large amount of natural gas escaping and being locally adjusted and accumulated in shallow effective traps. The gas reservoirs show the characteristics of multiple accumulation horizons and a small scale. In the moderately strong compression area in the north, the E-W-trending faults have weak activities and shallow incision horizons. The original gas reservoirs are not damaged, and the structures are fully filled. (2) The coupling between faults and sand bodies determines the degree of oil and gas enrichment. In the weakly compressed area in the west, late-stage E-W-trending faults are not developed, and the preservation conditions are good. The main controlled faults on the flanks of the anticline are highly active, and the coupling degree between faults and sand bodies is good, resulting in a high gas saturation. However, the transport capacity in the anticline cores is relatively poor, with a low gas saturation. (3) The differences in the paleo-structural characteristics affect the degree of oil and gas enrichment. The paleo-structures formed before the Longjing Movement provided favorable conditions for the early convergence of oil and gas. Natural gas has the characteristics of multi-stage charging, and the deep gas reservoirs have higher gas saturation than the shallow ones. On this basis, this study proposed two natural gas accumulation processes developed in the Central Anticline Belt of the Xihu Sag under the background of differential compression. One is where the hydrocarbon convergence occurs first and then oil and gas transport and accumulate into the reservoirs; the other one is where the hydrocarbon convergence and accumulation occur simultaneously, followed by gas adjustment. This paper also concludes three differential accumulation models: the local enrichment and accumulation model of gas in the strongly compressed zone, the integrated enrichment and accumulation model in the medium-strongly compressed zone, and the fault–sand coupling accumulation model in the weakly compressed zone. The results of this research have great significance for the subsequent exploration, hydrocarbon enrichment style analysis, and further strategy in the deep-buried, tight to low-permeable reservoirs in ocean exploration areas. Full article
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