Search Results (110)

Lithofacies, as an integrated representation of key reservoir attributes including mineral composition and organic matter enrichment, provides crucial geological and engineering guidance for identifying “dual sweet spots” and designing fracturing strategies in deep shale gas reservoirs. However, reliable lithofacies characterization remains particularly challenging owing to significant reservoir heterogeneity, scarce core data, and imbalanced facies distribution. Conventional manual log interpretation tends to be cost prohibitive and inaccurate, while existing intelligent algorithms suffer from inadequate robustness and suboptimal efficiency, failing to meet demands for both precision and practicality in such complex reservoirs. To address these limitations, this study developed a super-integrated lithofacies identification model termed SRLCL, leveraging well-logging data and lithofacies classifications. The proposed framework synergistically combines multiple modeling advantages while maintaining a balance between data characteristics and optimization effectiveness. Specifically, SRLCL incorporates three key components: Newton-Weighted Oversampling (NWO) to mitigate data scarcity and class imbalance, the Polar Light Optimizer (PLO) to accelerate convergence and enhance optimization performance, and a Stacking ensemble architecture that integrates five heterogeneous algorithms—Support Vector Machine (SVM), Random Forest (RF), Light Gradient Boosting Machine (LightGBM), Convolutional Neural Network (CNN), and Long Short-Term Memory (LSTM)—to overcome the representational limitations of single-model or homogeneous ensemble approaches. Experimental results indicated that the NWO-PLO-SRLCL model achieved an overall accuracy of 93% in lithofacies identification, exceeding conventional methods by more than 6% while demonstrating remarkable generalization capability and stability. Furthermore, production simulations of fractured horizontal wells based on the lithofacies-controlled geological model showed only a 6.18% deviation from actual cumulative gas production, underscoring how accurate lithofacies identification facilitates development strategy optimization and provides a reliable foundation for efficient deep shale gas development. Full article

Low-pressure N₂ adsorption experiments were conducted on 20 samples from the Doushantuo Formation in the Yichang area to quantitatively characterize their pore structures and fractal properties. The samples are mainly composed of quartz, dolomite, and clay minerals, with minor amounts of feldspar, calcite, and pyrite. The N₂ adsorption–desorption isotherms display typical type IV characteristics with a pronounced hysteresis loop, indicating that mesopores are dominant. The specific surface areas range from 3.78 to 11.49 m²/g, and the total pore volumes range from 0.0039 to 0.0169 mL/g, with mesopores contributing most of the total pore volume. Fractal analysis based on the FHH model reveals two distinct fractal dimensions (D_f): D_f1 = 2.5–2.9 for small pores and D_f2 = 2.0–2.3 for large pores. The fractal dimensions are negatively correlated with TOC, quartz, and carbonate contents but positively correlated with clay and pyrite contents. Higher organic matter content tends to produce relatively smooth organic pores, reducing pore heterogeneity, whereas higher clay content increases surface roughness and structural complexity. Overall, the heterogeneity of pore structures in the Doushantuo Formation shales is primarily controlled by mineral composition and organic matter content. These results provide new insights into the pore characteristics and storage potential of Ediacaran marine shales. Full article

Longmaxi shale is one of major and earliest shale gas formations in China, which hosts significant reserves and produces substantial amounts of natural gas. A thorough understanding of how mineral composition and geomechanical properties govern fracture initiation and propagation in the Longmaxi shale is therefore essential in designing hydraulic fracturing operations. In this study, nine core samples from different layers of the Longmaxi shale in Well A at Sichuan Basin were collected and a series of experiments were conducted, including X-ray diffraction, triaxial and uniaxial compression tests, brittleness index assessment, scanning electron microscopy, and nuclear magnetic resonance. Results reveal that samples from layers S6–S9 are rich in clay minerals, whereas layers S1–S5 are dominated by siliceous minerals. From the top to the bottom of the reservoir, a noticeable increase presents in total organic carbon (TOC), porosity, natural gas content, and silica mineral proportion. Young’s modulus shows a positive correlation with silicon mineral content but a negative correlation with clay content. Under high-stress conditions, shale with low quartz content tends to exhibit ductility, which inhibits fracture propagation. Quantitative models were established to predict brittleness and interpret the mechanical behavior of marine shale reservoirs. Full article

Although the composition of hearth gas in a blast furnace is still composed of CO, H₂, and N₂, after injecting shale gas, which replaces some pulverized coal, the proportion of CO, H₂, and N₂ in the hearth gas will change with the introduction of H₂. Further, the reduction process of vanadium-titanium magnetite sinter (VTMS) will be significantly impacted. Hence, the energy–mass balance and replacement ratio model was used to calculate the composition of hearth gas under different injection conditions using production data from a VTM blast furnace in the Panxi area of China. In order to investigate how shale gas injection affects the reduction process, the weight loss rates of VTMS under various reduction atmospheres were obtained through a series of thermogravimetric experiments. Additionally, X-ray diffraction (XRD) analysis was performed on select reduced samples to determine the alterations in sinter phases before and after the reaction. The impact of shale gas injection on the reduction process of VTMS was analyzed by phase transformation and kinetic analysis. The results of the research show that the reduction process of VTMS is improved with the increase in shale gas injection. Using the ln-ln analytical method, the linear relationship between ln(−ln(1 − α)) and lnt under different cases was found. The reaction mechanism of VTMS under shale gas injection circumstances is characterized by random nucleation, which is subsequently followed by growth. The integration formula associated with its dynamic function is G(α) = [−ln(1 − α)]^3/4. Full article

With the increasing global demand for energy, the development of unconventional resources has become a focal point of research. Among these, shale gas has drawn considerable attention due to its abundant reserves. However, its low permeability and complex fracture networks present substantial challenges. This study investigates the composite fracturing technology combining supercritical CO₂ and slickwater for shale gas extraction, elucidating the mechanisms by which it influences shale fracture roughness and conductivity through an integrated approach of theory, experiments, and numerical modeling. Experimental results demonstrate that the surface roughness of shale fractures increases markedly after supercritical CO₂–slickwater treatment. Moreover, the dynamic evolution of permeability and porosity is governed by roughness strain, adsorption expansion, and corrosion compression strain. Based on fluid–solid coupling theory, a mathematical model was developed and validated via numerical simulations. Sensitivity analysis reveals that fracture density and permeability have a pronounced impact on shale gas field productivity, whereas fracture dip angle exerts a comparatively minor effect. The findings provide a theoretical basis for optimizing composite fracturing technology, thereby enhancing shale gas extraction efficiency and promoting effective resource utilization. Full article

Shale gas pressure post-production accompanies the entire production process. The depth of the tubing is crucial for the entire life cycle of production, especially influencing the production dynamics in the middle and later stages of downward-inclined Wells. The full dynamic multiphase flow simulation method is adopted, combined with wellbore structure, fluid composition (gas), gas layer temperature and pressure gradient, production dynamic data, etc., to establish the wellbore structure model of the gas well, simulate the production dynamics under different formation pressures and tubing depths, and determine a reasonable tubing depth. Considering the material balance of the constant-volume gas reservoir and the critical formation pressure of the gas well’s self-injection, the cumulative gas production of the gas well at different tubing depths was analyzed. Taking 11210-1-well as an example, it was believed that when the tubing depth reached 4000 m, the self-injection production time could be extended by 206 days, and the cumulative gas production increased by 5.1 × 10⁶ m³, compared with the tubing depth of 2983 m. The gas production is increased by approximately 12.2 × 10⁶ cubic meters when the tubing depth is 2000 m. The research conclusion can provide theoretical guidance for the optimization of tubing depth during the drainage and production process of shale gas downward-inclined horizontal Wells. Full article

Permeability of fissured sorbing rocks, such as coal and shale, controls gas transport and is relevant to a variety of scientific problems and industrial processes. Multiple gas transport and rock deformation mechanisms affect permeability evolution, including gas rarefaction effects, gas-sorption-induced anisotropic matrix–fracture interaction, and anisotropic deformation induced by effective stress variation. In this paper, a generic anisotropic permeability model is proposed to address the impacts of the above mechanisms and effects. Specifically, the influence of matrix–fracture interactions on permeability evolution is depicted through the nonuniform matrix swelling caused by the gas diffusion process from fracture walls into the matrix. The following characteristics are also incorporated in this model: (1) anisotropic mechanical and swelling properties, (2) arbitrary box-shaped matrix blocks due to the anisotropic rock structure, (3) adsorbability variation of different matrix blocks because of complex rock compositions, (4) adsorption hysteresis, and (5) dynamic tortuosity. The directional permeability models are derived based on the anisotropic poroelasticity theory and anisotropic swelling equations considering adsorption hysteresis. We use a gas-invaded-volume ratio to describe the nonuniform swelling of matrix blocks. Additionally, swelling of blocks with different adsorption and mechanical properties are characterized by a volume-weighted function. Finally, the anisotropic tortuosity is defined as a power law function of effective porosity. The model is verified against experimental data. Results show that four-stage permeability evolution with time can be observed. Permeability evolution in different directions follows its own ways and depends on anisotropic swelling, mechanical properties, and structures, even when the boundary conditions are identical. Adsorption hysteresis controls the local shrinkage region. Tortuosity variation significantly affects permeability but has the smallest influence on the local swelling region. The existence of multiple matrix types complicates the permeability evolution behavior. Full article

The Xujiahe Formation (FM) is a significant source rock layer in the Sichuan Basin. In recent years, a growing number of scholars believe that the shale gas potential of the Xujiahe Formation is equally substantial, with the first member of the formation being the richest resource. The deposition of Member (Mbr) 1 of Xujiahe FM represents the first and most extensive transgression event within the entire Xujiahe Formation. This study investigates the sedimentary environment and organic matter (OM) enrichment mechanisms of the dark mud shales in the Mbr1 of Xujiahe FM on the southeastern margin of the Sichuan Basin, utilizing methods such as elemental geochemistry and organic geochemistry analyses. The results indicate that these dark mud shales possess a relatively high OM abundance, averaging 2.20% and reaching a maximum of 6.22%. The OM is primarily Type II₂ to Type III. Furthermore, the paleoclimate during the Mbr1 period in the study area was warm and humid with lush aquatic vegetation. Intense weathering and ample precipitation transported large amounts of nutrients into the lacustrine/marine basin, promoting the growth and reproduction of algae and terrestrial plants. Correlation analysis between the Total Organic Carbon (TOC) content and various geochemical proxies in the Mbr1 mud shales suggests that OM enrichment in the study area was primarily controlled by the climate and sedimentation rate; substantial OM accumulation occurred only with abundant terrigenous OM input and a relatively high sedimentation rate. Redox conditions, primarily productivity, and terrigenous detrital input acted as secondary factors, collectively modulating OM enrichment. Event-driven transgressions also played an important role in creating conditions favorable for OM preservation. Synthesizing the influence of these multiple factors on OM enrichment, this study proposes two distinct composite models for OM enrichment, dominated by climate and sedimentation rate. Full article

The laminae of lacustrine shale in China have been systematically identified and characterized by a combination of core/slice observations, mineral compositions, geochemical analysis, pore structure characterization, and oil-bearing evaluation. The shale of the Chang 7 Member, Yanchang Formation, Ordos Basin was examined as an example in the study. Four types of laminae are developed in the Chang 7 Member, including felsic laminae (FQL), clay laminae (CLL), organic matter laminae (OML), and tuff laminae (TUL). The shale reservoirs exhibit significant heterogeneity. Of these, FQL and TUL have superior reservoir characteristics. The pore diameter of TUL is primarily composed of micrometer-sized secondary pores that are generated during the diagenesis process, while mesopore and macropore development are dominant in FQL. The main source laminae in the Chang 7 Member of the Ordos Basin are the OML and CLL, while the main reservoir laminae are the FQL and TUL. Some of the hydrocarbons produced by hydrocarbon generation are stored in the pore space inside the laminae, while the majority migrate to the inorganic pores of the adjacent FQL and TUL. It confirms that OML and CLL afford abundant shale oil, the combination of organic pores and inorganic pores in FQL and TUL serve as reservoir space, and the “clay generation-siliceous reservoir” shale oil enrichment model is established in the Chang 7 Member of Ordos Basin. Full article

Shale oil and gas reservoirs are characterized by low porosity and low permeability. The development of ultra-long horizontal wells can significantly increase reservoir contact area and enhance single-well production. Shale formations exhibit distinct bedding structures, high formation pressure, high rock hardness, and strong anisotropy. These characteristics result in poor drillability, slow drilling rates, and high costs when drilling horizontally, severely restricting efficient development. Therefore, accurately predicting the drillability of shale gas wells has become a major challenge. Currently, most scholars rely on a single parameter to predict drillability, which overlooks the coupled effects of multiple factors and reduces prediction accuracy. To address this issue, this study employs drillability experiments, mineral composition analysis, positional analysis, and acoustic transit-time tests to evaluate the effects of mineral composition, acoustic transit time, bottom-hole confining pressure, and formation drilling angle on the drillability of horizontal well reservoirs, innovatively integrating multiple parameters to construct a nonlinear model and introducing three intelligent optimization algorithms (PSO, AOA-GA, and EBPSO) for the first time to improve prediction accuracy, thus breaking through the limitations of traditional single-parameter prediction. Based on these findings, a nonlinear regression prediction model integrating multiple parameters is developed and validated using field data. To further enhance prediction accuracy, the model is optimized using three intelligent optimization algorithms: PSO, AOA-GA, and EBPSO. The results indicate that the EBPSO algorithm performs the best, followed by AOA-GA, while the PSO algorithm shows the lowest performance. Furthermore, the model is applied to predict the drillability of Well D4, and the results exhibit a high degree of agreement with actual measurements, confirming the model’s effectiveness. The findings support optimization of drilling parameters and bit selection in shale oil and gas reservoirs, thereby improving drilling efficiency and mechanical penetration rates. Full article

Shale gas wastewater from hydraulic fracturing poses significant environmental risks due to its high salinity and complex inorganic composition. This study investigates the behavior of major and trace inorganic constituents across a full-scale treatment train in the Sichuan Basin, China. Despite multi-stage processes including equalization, flocculation, flotation, biological reactors, membrane filtration, and clarification, key inorganic species such as Cl, Na, Br, Sr, Li, and B remained largely persistent in the final effluent with values of 13,760, 8811, 70, 95.9, 26.6, and 60.2 mg/L, respectively. Geochemical tracers including Br/Cl (average: 0.0022 mM/mM), Na/Br (average: 125 mg/mg), and Sr/Ca (average: 0.15 mM/mM) ratios, combined with halide endmember mixing models, revealed that salinity primarily originated from highly evaporated formation brines, with limited evidence for halite dissolution or external contamination. Elevated Sr (average: 89.3 mg/L) and Ca (average: 274 mg/L) levels relative to Mg (average: 32 mg/L) suggest significant water–rock interaction. Environmental risk assessments showed that concentrations of several elements in treated effluent greatly exceeded national and international discharge or reuse standards. These findings underscore the limitations of conventional treatment technologies and highlight the urgent need for advanced processes and regulatory frameworks that address the unique challenges of high-TDS (total dissolved solids) unconventional wastewater. Full article

The current plunger gas lift production process still relies on the traditional ‘one-to-one’ control configuration, where one controller manages a single gas well. This approach does not fulfil platform requirements for centralized, efficient, and unified coordination and management of multiple wells. To increase production, improve efficiency, and mitigate safety risks, this article offers an intelligent optimization method for a collaborative plunger gas lift in multi-objective, multi-well platforms. The method integrates mechanistic modeling and data-driven approaches to develop a collaborative model for multiple wells on the platform, accounting for inter-well pressure interference and pipeline backpressure. A particle swarm optimization algorithm is implemented to solve the model, with a composite fitness function balancing maximum daily gas production and minimum production fluctuations. A case study on the XXX Platform shows that the method enhances total gas production, reduces production fluctuations, and lowers system backpressure compared to the current operating schedule. Implemented via a localized edge computing architecture, it supports real-time scheduling, providing technical references for shale gas development. Full article

Marine–continental transitional shale is a promising unconventional gas reservoir, playing an increasingly important role in China’s energy portfolio. However, compared to marine shale, research on marine–continental transitional shale’s fractal characteristics of pore structure and complete pore size distribution remains limited. In this work, high-pressure mercury intrusion, N₂ adsorption, and CO₂ adsorption techniques, combined with fractal geometry modeling, were employed to characterize the pore structure of the Shanxi Formation marine–continental transitional shale. The shale exhibits generally high TOC content and abundant clay minerals, indicating strong hydrocarbon-generation potential. The pore size distribution is multi-modal: micropores and mesopores dominate, contributing the majority of the specific surface area and pore volume, whereas macropores display a single-peak distribution. Fractal analysis reveals that micropores have high fractal dimensions and structural regularity, mesopores exhibit dual-fractal characteristics, and macropores show large variations in fractal dimension. Characteristics of pore structure is primarily controlled by TOC content and mineral composition. These findings provide a quantitative basis for evaluating shale reservoir quality, understanding gas storage mechanisms, and optimizing strategies for sustainable of oil and gas development in marine–continental transitional shales. Full article

The Silurian marine shale in the Sichuan Basin is currently the main reservoir for shale gas reserves and production in China. This study investigates the reservoir evolution of the Silurian marine shale based on fractal dimension, quantifying the complexity and heterogeneity of the shale’s pore structure. Physical simulation experiments were conducted on field-collected shale samples, revealing the evolution of total organic carbon, mineral composition, porosity, and micro-fractures. The fractal dimension of shale pore was characterized using the Frenkel–Halsey–Hill and capillary bundle models. The relationships among shale components, porosity, and fractal dimensions were investigated through a correlation analysis and a principal component analysis. A comprehensive evolution model for porosity and micro-fractures was established. The evolution of mineral composition indicates a gradual increase in quartz content, accompanied by a decline in clay, feldspar, and carbonate minerals. The thermal evolution of organic matter is characterized by the formation of organic pores and shrinkage fractures on the surface of kerogen. Retained hydrocarbons undergo cracking in the late stages of thermal evolution, resulting in the formation of numerous nanometer-scale organic pores. The evolution of inorganic minerals is represented by compaction, dissolution, and the transformation of clay minerals. Throughout the simulation, porosity evolution exhibited distinct stages of rapid decline, notable increase, and relative stabilization. Both pore volume and specific surface area exhibit a trend of decreasing initially and then increasing during thermal evolution. However, pore volume slowly decreases after reaching its peak in the late overmature stage. Fractal dimensions derived from the Frenkel–Halsey–Hill model indicate that the surface roughness of pores (D1) in organic-rich shale is generally lower than the complexity of their internal structures (D2) across different maturity levels. Additionally, the average fractal dimension calculated based on the capillary bundle model is higher, suggesting that larger pores exhibit more complex structures. The correlation matrix indicates a co-evolution relationship between shale components and pore structure. Principal component analysis results show a close relationship between the porosity of inorganic pores, microfractures, and fractal dimension D2. The porosity of organic pores, the pore volume and specific surface area of the main pore size are closely related to fractal dimension D1. D1 serves as an indicator of pore development extent and characterizes the changes in components that are “consumed” or “generated” during the evolution process. Based on mineral composition, fractal dimensions, and pore structure evolution, a comprehensive model describing the evolution of pores and fractal dimensions in organic-rich shale was established. Full article

In the global energy sector, water-bearing reservoir-typed gas storage accounts for about 30% of underground gas storage (UGS) reservoirs and is vital for natural gas storage, balancing gas consumption, and ensuring energy supply stability. However, when constructing the UGS in the M gas reservoir, selecting suitable areas poses a challenge due to the complicated gas–water distribution in the multi-layered water-bearing gas reservoir with a long production history. To address this issue and enhance energy storage efficiency, this study presents an integrated geomechanical-hydraulic assessment framework for choosing optimal UGS construction horizons in multi-layered water-bearing gas reservoirs. The horizons and sub-layers of the gas reservoir have been quantitatively assessed to filter out the favorable areas, considering both aspects of geological characteristics and production dynamics. Geologically, caprock-sealing capacity was assessed via rock properties, Shale Gouge Ratio (SGR), and transect breakthrough pressure. Dynamically, water invasion characteristics and the water–gas distribution pattern were analyzed. Based on both geological and dynamic assessment results, the favorable layers for UGS construction were selected. Then, a compositional numerical model was established to digitally simulate and validate the feasibility of constructing and operating the M UGS in the target layers. The results indicated the following: (1) The selected area has an SGR greater than 50%, and the caprock has a continuous lateral distribution with a thickness range from 53 to 78 m and a permeability of less than 0.05 mD. Within the operational pressure ranging from 8 MPa to 12.8 MPa, the mechanical properties of the caprock shale had no obvious changes after 1000 fatigue cycles, which demonstrated the good sealing capacity of the caprock. (2) The main water-producing formations were identified, and the sub-layers with inactive edge water and low levels of water intrusion were selected. After the comprehensive analysis, the I-2 and I-6 sub-layer in the M 8 block and M 14 block were selected as the target layers. The numerical simulation results indicated an effective working gas volume of 263 million cubic meters, demonstrating the significant potential of these layers for UGS construction and their positive impact on energy storage capacity and supply stability. Full article