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Abstract: Abstract Correlations between material parameters are useful because they provide a first estimation of unknown parameters. Here, the correlation between the tensile strength and the mode I fracture toughness of rocks is studied. Some researchers have proposed empirical correlations based on a certain amount of empirical data and a fitting process. On the other hand, a few researchers have considered that the proportionality coefficient could be related to a rock property with units of length. Here, a linear relationship without an intercept at the origin between the tensile strength and the mode I fracture toughness of rocks is theoretically confirmed using the theory of critical distances (TCD). A comprehensive experimental database is presented and comparisons with this data from the literature (including tests at different temperatures) confirm the linear relationship and values of the critical distance of several millimeters (e.g., 3–15 mm). However, the scatter is large because there are different sources of uncertainty in the correlation, such as the testing method. Finally, the physical meaning of the critical distance is explored and its linear correlation with the grain size using the experimental database. PubDate: 2023-11-21
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Abstract: Abstract Geological facies evaluation is crucial for the exploration and development of hydrocarbon reservoirs. To achieve accurate predictions of litho-facies in wells, a multidisciplinary approach using well log analysis, machine learning, and statistical methods was proposed for the Lower Indus Basin. The study utilized five supervised machine learning techniques, including Random Forest (FR), Support Vector Machine (SVM), Artificial Neural Network (ANN), Extreme Gradient Boosting (XGB), and Multilayer Perceptron (MLP), to analyse gamma ray, resistivity, density, neutron porosity, acoustic, and photoelectric factor logs. The Concentration-Number (C-N) fractal model approach and log–log plots were also used to define geothermal features. In a study on machine learning models for classifying different rock types in the Sawan field of the Southern Indus Basin, it was discovered that sand (fine, medium and coarse) facies were most accurately classified (87–94%), followed by shale (70–85%) and siltstone facies (65–79%). The accuracy of the machine learning models was assessed using various statistical metrics, such as precision, recall, F1 score, and ROC curve. The study found that all five machine learning methods successfully predicted different litho-facies in the Lower Indus Basin. In particular, sand facies were most accurately classified, followed by shale and siltstone facies. The multilayer perceptron method performed the best overall. This multidisciplinary approach has the potential to save time and costs associated with traditional core analysis methods and enhance the efficiency of hydrocarbon exploration and development. PubDate: 2023-11-18
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Abstract: Abstract During the process of coal mining, there is a violent appearance of mining stress when the initial weighting occurs. To guarantee the safety of the gob-side entry formed automatically by roof-cutting (EFARC) in an inclined coal seam, a study was conducted on the initial weighting mechanism and appearance characteristics through field monitoring and theoretical analysis. The findings reveal that, upon the initial breaking of the main roof in the non-pillar mining stope of an inclined coal seam, the deflection of the thin plate structure exhibits asymmetric distribution, with the maximum position situated in the middle-upper part of the thin plate. As the main roof thin plate reaches its limit interval, the tensile fracture first occurs in the middle-upper part of the coal wall in front and back of the stope. Once broken, the thin plate changes to a simply supported state. The analysis of field data reveals that the mine pressure in the non-pillar stope of EFARC shows an asymmetric weighting phenomenon. The periodic weighting interval at the ends of the working face increases, and the weighting intensity decreases. These results can serve as theoretical support for controlling mine pressure in non-pillar mining through EFARC in inclined coal seams and can serve as a basis for further investigations in this area. PubDate: 2023-11-17
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Abstract: Abstract How to ensure the safety of abandoned mine resources, scientifically develop and utilize abandoned mine resources, and promote the transformation of resource-exhausted mining areas have become an important issue in the field of energy and environment in the world today. Aiming at the stability of the surrounding rock in deep closed/abandoned mine chamber, the mechanical model of the surrounding rock under the coupling effect of anchorage and seepage field was proposed. Considering the elastic brittleness degradation and plastic dilatancy effect of rock mass, the analytical solutions of stress and displacement of rockbolt-seepage-surrounding rock coupling system were respectively deduced, and the accuracy of the results were verified. Based on the analytical results, the evolution law of stress and displacement of the surrounding rock under the combined action of seepage field and anchorage effect were further revealed, and a new quantitative design method of rockbolt parameters was proposed. Results show that the influence of rockbolt spacing and rod diameter on the mechanical field is obvious, while the rockbolt length and pre-tension load is small. Dense, short rockbolt with larger diameter should be used in the surrounding rock of deep chamber. The influence of seepage on the displacement of the surrounding rock is very significant. The more serious the seepage is, the more obvious the control effect of rockbolt on the displacement is. Appropriately increasing the density and diameter of rockbolt can effectively reduce the displacement of the surrounding rock. PubDate: 2023-11-14
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Abstract: Abstract Fracture pressure is an important reference for wellbore stability analysis and hydraulic fracturing. Considering the low prediction accuracy, significant deviations, and limited applicability of traditional methods for predicting formation fracture pressure, this paper proposes an intelligent prediction method for fracture pressure using conventional well logging data based on the Stacking ensemble algorithm. The base learners of the model include RF, KNN, and LSTM algorithms with low correlation. The meta-learner adopts the XGBoost algorithm. The effectiveness of the model is validated using the fracture pressure data from Dagang Oilfield. The prediction results indicate that the stacking algorithm outperforms individual algorithms. After optimization with genetic algorithm, the R2 of the stacking model is 0.989, RMSE is 0.009%, and MAE is 0.32%. The global sensitivity analysis results show that AC and DEN in the well logging data have higher sensitivity to the fracture pressure. When using intelligent fracture pressure prediction methods, it is essential to ensure the accuracy of AC and DEN data. The work demonstrates the reliability and effectiveness of the method proposed for the intelligent prediction of fracturing pressure using conventional well logging data through Stacking ensemble algorithm to overcome the limitations of traditional methods. PubDate: 2023-11-14
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Abstract: Abstract The extensive thinning and destruction of North China Craton (NCC) during the Early Cretaceous led to the development of numerous rift basins and petroleum systems. However, the specific relationship between NCC evolution and hydrocarbon generation and accumulation in these sedimentary basins is still unclear. In this study organic geochemistry and oil-source correlation analyses were conducted to investigate the hydrocarbons generation potential and migration pathway in the representative Fuxin Basin. Results demonstrate that the semi-deep lacustrine source rocks were developed in the Jiufotang Formation (K1jf) in the west and the upper Shahai Formation (K1sh) in the east, both of which are enriched with organic matter content and hydrocarbon generation potential of kerogen Types II to III. Based on the hierarchical cluster analysis of crude oils biomarker fingerprints, two crude oil types (A and B) were deduced. The Type A crude oil is characterized by high gammacerane, low pristane/phytane, relatively high C29 regular sterane and methylphenanthrene index, which is consistent with the K1jf biomarker characteristics in the west. Therefore, the Type A crude oil is likely generated from the K1jf source rock that accumulated in turbidite sand bodies of the K1jf and/or migrated to the K1sh reservoir through strike-slip faults. Type B crude oil is dominated by low gammacerane, moderate pristane/phytane, high C27 regular sterane and 1,2,5-trimethylnaphthalenes, which is in good agreement with the K1sh4 features. The basin simulation revealed that hydrocarbon generation of source rocks in the Jiufotang and Shahai formations was linked to a rapid subsidence of the basin, which was induced by intense extension with the NCC destruction during the Early Cretaceous. Subsequently, the rapid subduction of the Western Pacific plate during the earliest Late Cretaceous led to the development of extensive epigenetic fractures, enabling extensive hydrocarbon migration in the Fuxin Basin. This study sheds light on oil sources in sedimentary basins in an extensional setting and provides insights into the dynamic process of hydrocarbon generation and migration associated with NCC evolution. PubDate: 2023-11-08
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Abstract: Abstract Carbonate rocks are geologically complex due to the diagenetic processes they experience before and after lithification. Diagenetic processes alter their matrix and pore structure leading to the modification in their sonic velocities. Understanding the effect of these diagenetic features on the seismic velocities is crucial to have a reliable image of the subsurface. The dataset used in this study comprises well logs, and core data. Core data were analyzed using different methods (i.e., thin section analysis, X-ray diffraction (XRD) analysis, and scanning electron microscopy (SEM images)) to investigate the presence or absence of different diagenetic processes in each depth interval of the Sarvak formation. In order to minimize porosity effects on velocity variations, we divided all porosity data into five equal porosity classes and performed bar chart analysis in each class. The results indicated that bioturbation (through stiff pore creation and infilling with stiff minerals) and compaction (through pore space volume reduction) increase velocities, but dissolution increased velocities only for the low porosity samples (through moldic and vuggy pores creation) while reduced it in the high porosity samples (through the interconnection of the isolated pores). Furthermore, porosity enhancement (through increasing pore space volume), micritization (through porosity reduction inhibition during compaction), open fracture (through creation of soft pores and cracks), and neomorphism (through the creation of microporosity during compaction) reduce sonic velocities. PubDate: 2023-11-07
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Abstract: Abstract Hot dry rock (HDR) has great development potential because of its advantages of clean, environmental protection and renewable. The study of physical and mechanical properties of HDR is one of the important links in the process of geothermal energy development. Previous studies have mainly focused on the granite thermal reservoir but research on the sandstone thermal reservoir, especially the physical properties of sandstone after multiple thermal shocks, is scarce. Therefore, in this study, cyclic thermal shock experiments of sandstone at different temperatures are carried out, and the variation law of P-wave velocity of sandstone after heat treatment is revealed. It is found that the P-wave velocity of red sandstone decreases with the increase of temperature and cycle times, especially when the temperature is higher than 400 °C, the maximum change rate of wave velocity reaches 52.6%. It is particularly noteworthy that the P- wave velocity of sandstone increases abnormally at about 600 °C. And this article puts forward three hypotheses to explain the wave velocity anomaly. In addition, the nonlinear relationship model among P-wave velocity, temperature and number of cycles is established for the first time, and the correlation coefficient R2 is more than 0.9. This study serves as a reference for the development and utilization of the sandstone geothermal reservoir. PubDate: 2023-11-06
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Abstract: Abstract A non-uniform basement condition usually causes dump disasters. Two sets of base friction tests were carried out to discuss the deformation mechanism of the waste dump with partial-weak and total-hard basement. By the image speckle analysis and point-tracking technology, dump displacements and strains were obtained, and the deformation mechanism, stability, failure process of the waste dump were analysed. We could concluded that: (1) a waste dump with total-hard basement has higher stability than that with partial-weak basement. (2) The dump displacement exhibits a distribution of five flat regions that are connected by four steep increasing regions. (3) The dump deformation could be categorized into three phases: continuous deformation phase, crack-failure phase and final stability phase. In crack-failure phase, the deformation process of a total-hard basement waste dump presents a traction-crack-slide feature, but that of a partial-weak basement waste dump exhibits a subsidence-crack-rotation pattern. (4) In the deformation process, a total-hard basement waste dump is mainly affected by tensile stress, and its crack type is classified as tensile crack. While a partial-weak basement waste dump is subject to the coupling action of tensile and shear stress, and its crack type is shear crack. Both total-hard and partial-weak basement waste dumps show volume expansion. (5) With regard to the deformation control project of partial-weak basement waste dumps, strengthening the weak basement and increasing the anti-sliding force of the dump slope are recommended to reduce the vertical and horizontal deformation. These results have guiding significance for the deformation mechanism, stability evaluation and reinforcement measures of partial-weak basement waste dumps. PubDate: 2023-11-06
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Abstract: Abstract The assessment of Coal burst risk (CBR) is the premise of bump disaster prevention and control. It is the implementation criterion to guide various rock burst prevention and control measures. The existing static prediction and evaluation methods for CBR cannot be effectively combined with the results of underground dynamic monitoring. This study proposed a mining-induced seismicity information quantification method based on the fractal theory. Deep learning methods were used to construct a deep learning framework of coal burst risk (DLFR) based on the fractal dimension of microseismic information. Gray correlation analysis (GRA), information gain ratio (IGR), and Pearson correlation coefficient are used to screen and compare factors. Statistical evaluation indicators such as macro-F1, accuracy rate, and fitness curve were used to evaluate model performance. Taking the Gaojiapu coal mine as a case study, the performance of deep learning models such as BP Neural Network (BP), Support Vector Machine (SVM) and its optimized model based on particle swarm optimization (PSO) algorithm under this framework is discussed. The research results' reliability and validity are verified by comparing the predicted results with the actual results. The research results show that the prediction results of CBR in DLFR are consistent with the actual results, and the model is reliable and effective. The mining-induced seismicity quantification can solve the problem of insufficient training samples for the CBR. With this, different pressure relief measures can be formulated based on the results of the CBR predictions to achieve "graded" precise prevention and control. PubDate: 2023-11-06
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Abstract: Abstract The large-scale extraction of coal resources in the western mining areas of China has resulted in a significant loss of water resources, which is a challenge for coordinating resource extraction with ecological preservation in the mining areas. Although underground reservoir technology can effectively solve this problem, measuring the storage capacity of underground reservoirs through engineering experiments is costly and time-consuming. Currently, there is a lack of accurate, reliable, and low-cost theoretical calculation solutions, which greatly restricts the promotion and application of underground reservoir technology. The theoretical calculation methods for underground reservoir capacity were studied based on parameters from the Shendong mining area in China. A water storage structure model for coal mine underground water reservoirs was established, taking into account the settlement boundaries of the bedrock and loose layers in shallow coal seams, based on the key layer theory and the spatial structure model of the mining roof. The mathematical expression for the load on the coal-rock mass in the goaf was derived considering the rock breaking characteristics of the mining roof. The model determined the range of each water storage area, including the zone of loose body, zone of gradual load, and the compacted zone, based on the strength of the water storage capacity. The key parameters for calculating the water storage capacity were determined using a modified model for shallow thick loose layers and thin bedrock movement. Finally, a calculation method for the storage capacity was obtained. Based on the real data from the 22,615 working face of a mine in the Shendong mining area, the water storage capacity of the underground reservoir in the goaf was jointly calculated using FLAC3D, Surfer 12.0 and the proposed calculation method. The calculated water storage capacity was approximately 1.0191 million m3. Although this result was 2.20% smaller than the on-site water pumping experiment data, it still verifies the feasibility of the above calculation method for determining the water storage capacity of underground water reservoirs. PubDate: 2023-10-31
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Abstract: Abstract Micro-seismic (MS) technique can be used to appreciate rock failure process and severity of damage by quantifying micro-earthquakes in terms of time, location, grade, and energy release. Based on 3D laser detection and high-precision micro-seismic monitoring, this study analyzes the MS activity, stress and displacement evolution linked with the instability/failure property of hidden goaf incorporating several blasting disturbances in an open pit mine. MS monitoring outcomes reveal two arch fracture zones in the goaf roof, and MS occasions are mostly intense at rock-intersecting interface of north–south goafs. Evolution of apparent stress, apparent volume, and displacement reveals that the goaf is currently in a stable state. The current investigation offers a novel field method and view of inspecting the stability of goaf subjected to blasting disturbance in mines. PubDate: 2023-10-30
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Abstract: Abstract Effect of temperature on physico-mechanical properties is an important research topic for engineering applications such as underground coal gasification, exploitation of deep oil and gas resources, extraction of geothermal energy and burial of nuclear waste. This paper aims to investigate the variation of physico-mechanical and drilling properties of sandstones from the Zonguldak Hardcoal Basin at different temperatures (from room temperature to 600 °C). The results show that with the increase in the temperature of the sandstone, the geomechanical parameters and leeb hardness properties decrease, while the drilling rate index and porosity properties increase. Especially, the geomechanical properties of sandstone decrease sharply above 500 °C as the critical temperature of the rock. The average geomechanical properties (uniaxial compressive strength, tensile strength and Young modulus) and Leeb hardness values decreased by %35.3, 30.0, 50.3 and 14 respectively when the sandtone samples heated the 600 °C. On the other hand, the drilling rate index increased by 24.14% and the porosity increased by 470 times compared to its initial value at room temperature. Based on the findings of the present study, statistical analysis (correlation analysis) were revealed between rock physico-mechanical and drilling properties of sandstone and temperature. In the light of this fact, obtained results show that is of great importance to study the changes in the physico-mechanical and drillability properties of the rock after the heating process. PubDate: 2023-10-27
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Abstract: Abstract Estimating in-situ stress in shale oil reservoirs is critical for predicting hydraulic fracture height. However, the varied longitudinal lithology and transverse isotropy challenge the regional evaluation of ground stress. A new method based on the Kaiser effect method and the Sn Model was proposed to evaluate regional ground stress from point to point. Kaiser tests obtained the regional tectonic stress coefficients. Combined with the dynamic and static transformation of elastic parameters, the Sn ground stress calculation model suitable for the Northern Shaanxi Area was constructed. According to the calculation results of ground stress in the Chang 7 section of 600 wells in this region, the plane distribution maps of maximum horizontal ground stress (SH) and the difference between SH and Minimum horizontal stress (Sh) were drawn. It was found that the SH in this area was between 20 and 60 MPa, and the So was between 2.6 and 8.8 MPa. Compared with the 3D finite element method simulation results, the forward modeling results coincided well with the inversion results in this research. The causes of the plane distribution of ground stress in the Chang 7 section were explained by regional tectonic stress and paleo topography. It was found that the movement of plate and shell and deposition were critical factors of regional ground stress distribution. The research results provide a reference for further integration of geologic and engineering in evaluating shale oil reservoirs. PubDate: 2023-10-24
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Abstract: Abstract In order to solve the problems of low ROP and short service life of the bit drilling in deep and hard formation, a new technology of hobbing-cone hybrid PDC bit which has combined the advantages of conventional PDC bit and the hobbing-cone is proposed in this paper. The bit is developed and applied on basis of the structure design and the contrast experiment between the hobbing-cone bit and the conventional roller-cone hybrid PDC bit. The indoor drilling experiments show that the hobbing-cone hybrid PDC bit can form groove-shaped crushing pits in the bottom-hole. The teeth on the roller have high circumferential coverage on bottom-hole rock and an obvious pre-fracture effect on the rock. The experiment result shows that ROP of the hobbing-cone hybrid PDC bit is 20–30% lower in soft rock but 15–20% higher in hard rock, indicating that the bit is more suitable for hard rock drilling. Moreover, in the field application, average ROP of the hobbing-cone hybrid PDC bit is 126.1% higher and the footage is 89.6% longer than the comparisons, while wear status of the bit after drilling is quite good. Field application results show that the hobbing-cone hybrid PDC bit has good drilling effect in directional and hard formations, which can be well adapted to the drilling of applied wells (blocks) and directional sections with good steering performance, making it an optimization to improve the working performance in complex and hard-to-drill formations. PubDate: 2023-10-21
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Abstract: Abstract Coalbed methane production failures through hydraulic fracturing in the Linxing gas field in China have encountered significant setbacks, hindering efforts to enhance the recovery of deep CBM reserves in the region. To address this challenge, we investigate the potential of directional wells with multiple hydraulic slots as a stimulation technology for deep coalbed methane extraction. This study presents two numerical models to evaluate the effectiveness of this technology. The first model is a continuum damage numerical model based on the Material Point Method, which simulates large deformations and complex contact behaviors induced by hydraulic slotting in the deep coal seam. The second model is a wellbore-pore coupling model to simulate the gas extraction process. We verified both numerical models against theoretical and experimental results. We conducted a case study in the Linxing gas field using these models. The investigation assessed stress relief, gas desorption, and permeability enhancement around a large deformed hydraulic slot, as well as the gas extraction performance of a directional well with multiple slots. The results indicate that (1) The Linxing gas recovery failure may be attributed to unsuccessful hydraulic fracturing based on the history matching analysis of field production; (2) Hydraulic slotting causes gradual compaction of the slot until full closure, and results in a rapid stress drop exceeding 7 MPa in the elliptical zone surrounding the slot, which is the large plastic damage zone; (3) The enhanced permeability in plastic zone exceeds ten times the natural coal permeability, leading to total gas desorption of 556 m3 from elastic and plastic zones; (4) Performance optimization can be achieved through reducing slot length and increasing slot width when using directional well with multiple slots. In summary, this research demonstrates the efficiency of directional wells with multiple slots in enhancing gas recovery from deep coal seams. PubDate: 2023-10-18
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Abstract: Abstract Recent laboratory and field studies suggest that temporal variations in injection patterns (e.g., cyclic injection) might trigger less seismicity than constant monotonic injection. This study presents results from uniaxial compressive experiments performed on Red Felser sandstone samples providing new information on the effect of stress pattern and rate on seismicity evolution. Red Felser sandstone samples were subjected to three stress patterns: cyclic recursive, cyclic progressive (CP), and monotonic stress. Three different stress rates (displacement controlled) were also applied: low, medium, and high rates of 10−4 mm/s, 5 × 10−4 mm/s, and 5 × 10−3 mm/s, respectively. Acoustic emission (AE) waveforms were recorded throughout the experiments using 11 AE transducers placed around the sample. Microseismicity analysis shows that (i) Cyclic stress patterns and especially cyclic progressive ones are characterized by a high number of AE events and lower maximum AE amplitude, (ii) among the three different stress patterns, the largest b-value (slope of the log frequency-magnitude distribution) resulted from the cyclic progressive (CP) stress pattern, (iii) by reducing the stress rate, the maximum AE energy and final mechanical strength both decrease significantly. In addition, stress rate remarkably affects the detailed AE signature of the events classified by the distribution of events in the average frequency (AF)—rise angle (RA) space. High stress rates increase the number of events with low AF and high RA signatures. Considering all elements of the AE analysis, it can be concluded that applying cyclic stress patterns in combination with low-stress rates may potentially lead to a more favourable induced seismicity effect in subsurface-related injection operations. PubDate: 2023-10-17
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Abstract: Abstract Cut blasting, in which new surfaces and relief space for subsequent blasting are created, is one of the most critical steps in the establishment of large-diameter long-hole (LDL) stopes. To reduce the damage to the chamber roof caused by stemming recoil and improve the rock breaking effect, 15 groups of small-scale model tests with minimum burdens of 3, 4, 5, 6, and 7 cm and stemming lengths of 0, 2, 4, 5, 6, and 7 cm were designed to optimize the matching relationship between the stemming length and minimum burden. First, through the model tests, values were obtained for ten evaluation indexes related to the total mass of fragments, crate size, fragment size, fragmentation energy consumption, and stemming recoil area. Then, the normal cloud combination weighting method was used to combine six subjective and objective weighting methods, and combined weights were obtained. Finally, the test schemes were optimized according to the Euclidean distance and similarity. The test results showed that the best blasting scheme involves a burden of 5 cm and a stemming length of 5 cm, followed by that involving a burden of 4 cm and a stemming length of 4 cm, and the optimal stemming length is approximately equal to the minimum burden. A field test of LDL stope cut blasting was conducted, with a stemming length of 2.2 m and a minimum burden of 2.2 m in the boreholes. The highly satisfactory field blasting effect indicates that the stemming length and minimum burden are reasonable. PubDate: 2023-10-16
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Abstract: Abstract The integration of multiscale datasets, including seismic, well-logs and stratigraphy, is providing a precise picture about reservoir evaluation and spatial distribution. This study focuses on the seismic interpretation and sequence stratigraphic analysis of the Bahariya Formation in the South Umbaraka oilfields (Selkit, Khepri, and Sethos), located in the Western Desert of Egypt. Seismic interpretations reveal various structural closures, including anticlinal domes and faulted anticlines in different fields. The study area is divided into northern and southern blocks separated by a major fault, and structural cross sections provide valuable information on reservoir zones regarding lateral extension, thickness variation, and fault distribution. The Bahariya Formation is subdivided into two depositional sequences: Lower Bahariya sequence (BAH.SQ-1) and Upper Bahariya sequence (BAH.SQ-2) with distinct wireline-log characteristics, seismic reflections, and lithofacies variations. BAH.SQ-1 comprises mixed siliciclastic-dominated units with some carbonate units, while BAH.SQ-2 consists of mixed siliciclastic and carbonate units. Multiple sequence boundaries, depositional surfaces, and systems tracts are identified within BAH.SQ-1 and BAH.SQ-2, indicating changes in sedimentary environments and sea-level fluctuations. The petrophysical evaluation reveals promising reservoir zones in both the Lower and Upper Bahariya sequences. However, the Lower Bahariya sequence exhibits superior reservoir characteristics in terms of net-pay thickness, shale volume, effective porosity, and water saturation. Particularly, the sandstone-dominated LST-1 within the Lower Bahariya Formation is identified as a favorable reservoir zone. Conversely, the Upper Bahariya Formation has limited reservoir potential. This study underscores the significance of sequence stratigraphy and reservoir architecture, emphasizing the role of faulting, folding, and depositional environments in the distribution and quality of reservoir zones. The findings contribute valuable insights into the structural and stratigraphic characteristics of the Bahariya Formation, enhancing understanding of hydrocarbon plays and reservoir distribution in the studied area. PubDate: 2023-10-16
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Abstract: Abstract A significant deposition of black shales occurred during the Mesoproterozoic Oxygenation Event (MOE). In order to investigate the hydrocarbon generation potential and organic matter enrichment mechanism of these shale deposits, we studied the Xiamaling Formation shale in the North China region as a representative sample of the Mesoproterozoic shale. The research involved organic petrology, organic geochemistry, mineralogy, and elemental geochemistry. The following observations were made: (1) The depositional environment of the Xiamaling Formation shale can be categorized as either oxic or anoxic, with the former having shallow depositional waters and high deposition rates, while the latter has deeper depositional waters and slower deposition rates. (2) Anoxic shales exhibited significantly better hydrocarbon generation potential compared to shales deposited in oxic environments, although the latter still demonstrated high hydrocarbon generation potential. (3) Shales deposited in anoxic environments displayed higher paleoproductivity compared to those deposited in oxic environments. The high deposition rate in oxic environments slowed the decomposition and mineralization of organic matter, leading to the formation of high-quality shales. In contrast, the strong paleoproductivity, along with favorable preservation conditions, accounted for the high hydrocarbon potential of anoxic shales. PubDate: 2023-10-16
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