Shock-tube core experiments have provided an important finding, that is, the low frequency acoustic field generated by planar shock waves can induce pure Stoneley waves in a borehole, with their amplitude attenuations demonstrating a definite correlation with fracture width and permeability. Accordingly, a method was proposed to transmit low frequency planar shock waves in a borehole through axially polarized axial vibration, thereby continuously inducing pure Stoneley waves. Equations were also derived for calculating fracture width and permeability from Stoneley wave amplitude attenuation. Moreover, the permeability logging prototype was successfully developed, together with acquisition and processing software incorporating amplitude-attenuation extraction and permeability calculation. The operability, stability, and measurement performance of the logging tool were tested and verified in two standard wells, R91 in the Bohai Bay Basin and LS2 in the Tarim Basin. In the 10 000-meter-deep well SDTK1 in the Tarim Basin, matrix and fracture permeability curves of extra-deep Cambrian carbonate formations were obtained in a single downhole logging. The results were immediately calibrated with the data of quasi-in-situ nuclear magnetic resonance (NMR) permeability measurement on full-diameter drilling cores taken from the same interval of the well. The results show that the proposed method performs well in quantitative permeability evaluation of extra-deep carbonate reservoirs and provides a new technical approach for permeability logging evaluation in other types of reservoirs. This theoretical and technological breakthrough provides an innovative means for quantitative permeability evaluation in reservoir logging.

Intraplate small-displacement strike-slip faults cannot be accurately identified and quantitatively analyzed by conventional techniques. To clarify the tectonic characteristics and deformation process of intraplate small-displacement strike-slip faults, structural physical simulation experiments were designed based on the geological conditions of the study area. Taking the Fuman Oilfield in the northern Tarim Basin as an example, laser scanning was adopted to elaborately and quantitatively analyze the deformation features and differences of left-lateral strike-slip fault at each evolutionary stage. This study indicates that the deformation of the F_I17 fault zone in the Fuman Oilfield evolves in four stages: diffuse deformation, R-shear fracture, branched fault interconnection, and through-going principal displacement zone (PDZ) connection. During the evolution of the strike-slip fault zone, en echelon anticlines serve as a diagnostic marker for R-shear fracture, and their uplift amplitude represents a vital parameter to classify evolutionary stages. A “Net Deformation Magnitude” method is proposed, which can effectively remove post-tectonic stratigraphic deformations irrelevant to strike-slip-related folds and extract fold geometries and uplift amplitudes solely generated by strike-slip faulting. This method further enables quantitative characterization of along-strike heterogeneities in deformation intensity and connectivity of strike-slip fault zones, thereby realizing integrated seismic-geological interpretation. A case study of the Fuman Oilfield demonstrates that the F_I17 fault zone is currently in the branched fault interconnection stage, characterized by alternating through-going and disconnected segments along its strike. The findings establish a geological model for the refined interpretation of intraplate small-displacement strike-slip faults. Furthermore, the newly recognized fault-karst traps associated with R-shear fractures are expected to become promising new targets for hydrocarbon exploration.

Based on data including seismic interpretation, well logs and core slice, analyses were conducted on seismic reflection patterns, stages and distribution of faults, planar distribution of sedimentary facies, types of reservoir spaces, and genesis of reservoirs. This study identified the types of Ordovician carbonate platforms in the Manxi area of the Tarim Basin, analysed the controlling factors for high- quality reservoirs and hydrocarbon accumulation, established an accumulation model, and proposed potential exploration targets of oil and gas. The research indicates that the Ordovician in the Manxi area is characterized by a rimmed platform depositional system, where the platform-margin reef-shoal complexes cover an area of approximately 5 091 km². These complexes, superimposed with multi-stage karstification and reticulated fractures, form high-quality fracture-cavity reservoirs, which exhibit a north-south orientation, large-scale distribution, and excellent storage capacity. The Ordovician platform-margin reef-shoal zone is situated within the hydrocarbon-generation center comprising the source rocks in the Precambrian Yuman rift trough, the Yuertusi Formation, and the Cambrian to Ordovician platform-margin foreslope facies. Large-scale hydrocarbon-enriched zones are densely distributed in a north-south trend within the interval from the Ordovician Penglaiba Formation to the third member of the Yingshan Formation, while exhibiting a linear distribution pattern from the second member of the Yingshan Formation to the Yijianfang Formation. Guided by these insights, Well Qingyu 2 was drilled, and it achieved a high flow rate of 105.6×10⁴ m³/d gas from the second member of the Yingshan Formation during test, with a stable tubing pressure of 107 MPa. This records a significant exploration breakthrough in the Ordovician platform-margin zones in the Manxi area, and reveals a new domain for reserve growth. The research results provide valuable guidance for exploring ultra-deep carbonate reservoirs in the Tarim Basin.

Based on the latest high-precision gravity, magnetic and three-dimensional seismic exploration data in the western margin of the Ordos Basin, the fine analysis of Paleozoic tectonic system and the re-understanding of hydrocarbon accumulation conditions are carried out. The research shows that, by redefining the classification of faults, four types of structural styles are identified, including back thrust belt, hanging wall syncline, footwall in-situ rock mass uplift belt, and strike-slip-thrust imbricate belt. According to the characteristics of source-reservoir configuration, five hydrocarbon accumulation models are established, including the Hengshanbao structural trap gas reservoir group in the northern zone, the tight gas accumulation in the intra-source syncline in the hanging wall and concealed uplift structure controlled accumulation in the footwallof of the thrust belt in the central zone, the low-mature shale self-generation and self-storage in the southern zone, and the grain beach + dual-source hydrocarbon supply in the platform margin. Combined with the analysis of exploration results, five favorable exploration areas are delineated: the Hengshanbao complex structural area in the northern zone, covering 410 km², which belongs to the realistic and efficient exploration target area; the concealed uplift belt in the central zone, covering 1 800 km², which is the first breakthrough in the 8^th member of Lower Shihezi Formation; the Carboniferous Yanghugou Formation in the central zone, which has been revealed with the potential for coal-rock gas and tight sandstone gas accumulation within the source; the marine shale oil in the Middle Ordovician Wulalike Formation in the southern zone, covering 275 km², with Well YT3 achieving an industrial breakthrough; and the western platform margin of the Ordovician strata, covering about 5 300 km². These findings have guiding significance for further breakthrough, expansion, and reserves addition in subsequent oil and gas exploration activities in the western margin of the basin.

The hydrocarbon accumulation patterns of ultra-deep, marine shale in the northeastern Sichuan Basin remain unclear. Taking the Permian Dalong Formation in Well Tiebei 1 L-HF in the Puguang area, northeastern Sichuan Basin, as an example, this study integrated petro-mineralogical, geochemical, and micro-scale characterization techniques to systematically reveal the enrichment mechanisms of primary organic matter and the reservoir-forming conditions of shale and establish the hydrocarbon micro-migration and accumulation model. The main findings are obtained in three aspects. First, three core lithofacies, i.e. siliceous, calcareous and mixed shales, are identified vertically in the Dalong Formation. Siliceous shale, dominated by sapropelinite, possesses the optimal primary hydrocarbon-generating potential. Mixed shale exhibits the TOC (average 9.31%) exceeding that of the siliceous shale (average 6.85%), indicating that the current organic matter distribution is controlled by late-stage hydrocarbon redistribution rather than solely by primary deposition. Second, a multi-scale cross-lithofacies composite pore-fracture system is identified. Siliceous shale provides basic storage space of hydrocarbon and horizontal transport; calcareous shale contains fractures in calcite veins, which act as migration “transfer stations” of hydrocarbon; and mixed shale develops tectonic tensile fractures and dissolution pores. Together, these elements support fluid conduction in ultra-deep settings. Third, the micro-migration mechanism of “in-source enrichment and lithofacies-controlled migration” is confirmed for ultra-deep shale hydrocarbons. Within an overpressure compartment, driven by hydrocarbon generation-induced overpressure, hydrocarbons undergo stepwise micro-migration along the siliceous shale (source) → calcareous shale (conduit) → mixed shale (sink) path, inducing short-distance fractionation and redistribution of components.

This work addresses the challenge of fluid identification in complex low-porosity buried-hill reservoirs in the Bohai Sea by developing a fluid identification method based on the coupled responses of energy spectra and time spectra. First, a regularized spectral decomposition algorithm is employed to analyze pulsed neutron gamma-ray spectra and obtain the carbon-to-oxygen (C/O) yield ratio, enhancing the capability of quantitatively characterizing differences in oil and water signal responses under low-porosity conditions. Second, an oil-water identification method is established by integrating energy-spectrum and time-spectrum parameters, improving the accuracy of oil-water discrimination in complex lithological environments. Finally, a gas layer identification parameter is introduced to distinguish gas-bearing zones and fluid-bearing zones, which is then combined with the oil and water identification results to form a three-phase fluid identification workflow. Field applications in drilled wells penetrating granite gneiss buried hills and carbonate buried-hill reservoirs in the Bohai Sea demonstrate that the proposed method significantly enhances the response contrast between oil and water under low-porosity conditions, substantially reduces the uncertainty of single-parameter interpretation, and enables accurate discrimination among oil, gas, and water. The method provides an effective solution for fluid identification in complex low-porosity buried-hill reservoirs in the Bohai Sea.

Based on data from cores, well logs, seismic profiles, and carbon isotopic compositions, this study constrains the chronostratigraphic framework using carbon isotopic excursion events and applies cyclostratigraphic methods to establish a high-resolution isochronous stratigraphic framework for the Permian Longtan Formation-Triassic Feixianguan Formation in the Sichuan Basin. Through single-well sedimentary evolution analysis and well-seismic integration, the sedimentary characteristics and the patterns and petroleum geologic significance of carbonate platform evolution during the deposition of the Longtan Formation-Feixianguan Formation are systematically revealed. The results show that the Longtan Formation-Feixianguan Formation exhibits 19 to 22 long eccentricity cycles across the entire basin. The difference in cycle counts is attributed to the significant local absence of the top part of the Permian Changxing Formation. Sedimentation rates gradually increase from the southwest to the northeast of the basin. The sedimentary system is overall controlled by a “high productivity, high supply” background, and jointly influenced by sea-level changes and terrigenous input. The Changxing Formation shows progradational ramp characteristics locally, while the Longtan Formation- Feixianguan Formation presents a carbonate ramp sedimentary model. The “tectonics-climate-astronomy” multi-level synergistic driving mechanism governed carbonate platform development, the regional tectonic setting established the macro-paleogeographic framework and accommodation space configuration for carbonate platform development, while the rhythmic sedimentary infilling and the production intensity of carbonate factories were significantly modulated by paleoclimate and astronomical orbital signals. The three factors exhibited stage-wise synergistic evolution in time and space, collectively driving the formation, development, and demise of carbonate platforms. This study provides a new sedimentary model and basis for an in-depth understanding of sedimentary characteristics and carbonate platform evolution patterns during the Permian-Triassic transition in the Sichuan Basin.

Reservoirs of the 4^th Member of the Sinian Dengying Formation (Deng-4 Member) around the Deyang-Anyue intraplatform rift in the Sichuan Basin are highly heterogeneous, alongside with unclear genesis and distribution of high-quality reservoirs. This study investigates the reservoirs of the Deng-4 Member in the Ningqiang area in the northern segment of eastern side of the rift, compares them with those in the Penglai area in the central segment and the central Sichuan paleouplift in the southern segment, and analyzes the differential development mechanisms of reservoirs on the eastern side of the rift. First, the Deng-4 reservoirs are facies-controlled, with stromatolite, framestone, and thrombolite dolomites serving as the main carriers of reservoir hosts. The preservation of pores was mainly controlled by early dolomitization, acid generation from microbial organic matter, a burial history characterized by prolonged shallow burial followed by late-stage accelerated deep burial, and early hydrocarbon charging. Second, the reservoirs show a differential pattern of development. The rimmed platform-margin reservoirs in the southern and northern segments of the rift have better development than the extensional fault-step platform-margin reservoirs in the central segment of the rift. The mode of prolonged shallow burial followed by late-stage accelerated deep burial in the northern segment is more conducive to the preservation of pores compared to the mode of continuous and uniform burial in the central and southern segment. Third, during the deposition of the lower-upper Deng-4 Member, the platform-margin microbial mound-shoal complex prograded from east to west perpendicularly to the platform-margin belt, and migrated from south to north parallelly to the platform-margin belt. The lower Deng-4 reservoirs are mainly distributed in the central and southern segments, the middle Deng-4 reservoirs in the central segment, and the upper Deng-4 reservoirs in Langzhong-Wangcang area of the northern segment and Penglai area of the central segment. These insights reveal that the Langzhong-Wangcang area in the northern segment of the rift, the central Sichuan paleouplift in the southern segment and the Penglai area in the central segment, has great potential of reservoir development in the Deng-4 Member.

Based on core observations, thin section identification, well logging and seismic data of the Permian strata in the western Sichuan Basin, this study systematically discusses the constraints of Middle and Late Permian two-phase volcanism on paleotectonic evolution and sedimentary filling. It further reveals a long-neglected Chengdu-Santai volcanic paleo-uplift developed continuously in the study area and clarifies its controlling effects of formation and evolution on sedimentary reservoirs. The results indicate that two suites of volcanic rocks are developed in the Permian strata of western Sichuan Basin. The lower volcanic rocks of the Middle Permian Maokou Formation are predominantly composed of basalt and volcanic breccia, whereas the upper volcanic rocks of the Upper Permian Longtan Formation are mainly basalt and volcaniclastic rocks, recording two episodic volcanic eruption events that occurred in the middle depositional stage of the Maokou Formation and the early depositional stage of the Longtan Formation. Paleogeomorphological reconstruction shows that the volcanism during the middle Maokou depositional stage initially formed the embryonic paleo-uplift on the western Sichuan carbonate platform. Continuous vertical stacking and lateral expansion of volcanic materials during the early Longtan depositional stage finally shaped a sub-elliptical paleo-uplift plunging northeastward. This paleo-uplift extends approximately 200 km northeastward along its major axis, with a minor axis ranging from 70 km to 110 km in the east-west direction. The uplift high is located in the Well area YS1-YT1, with a maximum relative relief of 300 m. Affected by late tectonic activities and persistent sedimentary filling and leveling, the paleo-uplift completely disappeared during the deposition of the third member of the Feixianguan Formation. Formed by the synergistic effect of the clockwise northward rotation and drift of the South China Plate and mantle plume hotspot activity during the Permian, this paleo-uplift dominated the paleogeographic pattern of the central and western Sichuan Basin during its development. Specifically, tidal flat-barrier shoal sedimentary systems developed around the volcanic highland during the middle to late Maokou depositional stage, and high-energy facies belts were widely distributed around the volcanic paleo-uplift during the Changxing depositional stage. This study confirms that the volcanic paleo-uplift and its peripheral zones are favorable hydrocarbon exploration areas for the Maokou and Changxing formations, providing a new perspective for Permian oil and gas exploration in the Sichuan Basin.

Based on microscopic observations, total organic carbon (TOC) content measurements, and major, trace, and rare earth element analyses of core samples from the Cambrian Qiongzhusi Formation shale at different structural positions within the Deyang-Anyue rift trough of Sichuan Basin, this study employs a combined geochemical and random forest algorithm to qualitatively and quantitatively identify the controlling factors of organic matter enrichment in black shales, and to elucidate the patterns of organic matter enrichment under the influence of tectono-sedimentary differentiation within the rift trough. The results are obtained in four aspects. First, the Qiongzhusi shales were deposited under a warm and humid climate with intense chemical weathering. From the extra-trough to the intra-trough settings, paleoproductivity and sedimentary environmental restriction gradually increased, whereas terrigenous detrital input and redox potential progressively decreased. Moreover, hydrothermal activity intensity diminished from the trough margin toward the extra-trough and intra-trough areas. Second, vertically, layers 1 and 3, which remained under persistently high productivity and reducing conditions, exhibit high organic matter enrichment; layer 5 shows relatively high enrichment due to the high level of organism abundance period; layer 7, characterized by limited marine transgression, exhibits the lowest enrichment, attributed to reduced productivity, weakened reducing conditions, and enhanced activities of terrigenous detritus and hydrothermal inputs. Third, the random forest model demonstrates a satisfactory performance in fitting the organic matter enrichment in black shales, revealing that it is primarily governed by paleoproductivity, secondarily by redox conditions, and to a lesser extent influenced by terrigenous detrital input and hydrothermal activity. Fourth, for organic-rich shale gas exploration, vertically, layers 1 and 3 hold greater exploration potential than layer 5; laterally, priority should be given to the central intra-trough area north of the central zone of the rift trough. These findings contribute to a better understanding of the organic matter enrichment mechanisms in the Qiongzhusi Formation shales of the Sichuan Basin, and provide a geological theoretical basis for shale gas exploration and source rock evaluation.

Based on the geological characteristics and development practices of low-permeability oil and gas resources in China, this study extends the conventional understanding that such reservoirs are typically tight and highly heterogeneous and proposes the theory of relative homogeneity in low-permeability reservoirs. As to this theory, its concept is systematically articulated, its connotation is clarified, and its mathematical model is constructed. Based on the successful development practices of low- and ultra-low-permeability reservoirs in the Ordos Basin, and incorporating pore-throat structure, sand body scale, seepage mechanisms, waterflooding displacement patterns, water-cut rise rate, natural decline rate, and recovery factor, the practice standards for the theory of relative homogeneity are established. Subsequently, the identification criteria for the theory of relative homogeneity are comprehensively elaborated from multiple dimensions, ranging from microscopic to macroscopic scales, from reservoirs to fluids, and from sedimentary geology to reservoir development engineering. Practical applications in development pilot areas have demonstrated that the complementarity and synergistic development of the “relative homogeneity” and “heterogeneity” concepts have effectively driven the optimization of development schemes, including drilling, fracturing, and injection-production, providing reliable theoretical support for the development of low-permeability reservoirs.

Based on the geological characteristics of the JD reservoir-based underground gas storage (UGS) facility, two-dimensional visual plate physical models representing vertical and areal heterogeneity were constructed. UGS operation was experimentally simulated under two injection-production schemes. An experimental-scale compositional reservoir model was also developed to characterize the spatial sweep patterns under different heterogeneity configurations and injection-production modes. The results show that the vertically heterogeneous model generally achieves higher oil displacement efficiency than the areally heterogeneous model. The relative sweep efficiencies of the two models depend on the injection-production scheme. Their difference is small after a single depressurization cycle, whereas the vertically heterogeneous model exhibits higher sweep efficiency after repeated depressurization cycles. Compared with a single cycle, repeated depressurization cycles increase the injection-production pressure difference and intensify cyclic flow perturbations. These effects weaken the persistent dominance of preferential flow pathways on injection-production process, promote fluid mobilization in medium- and low-permeability zones, and markedly improve sweep efficiency during UGS operation. Given vertical heterogeneity, increasing heterogeneity intensifies gravity differentiation and interlayer channeling, suppresses the sweep into low-permeability zones, and reduces sweep efficiency. Given areal heterogeneity, by contrast, increasing heterogeneity enhances the flow conductivity of high-permeability zones and improves displacement effectiveness within the swept areas, thereby increasing the overall sweep efficiency. Accordingly, stratified injection-production combined with graded pressure drawdown is recommended for vertically heterogeneous reservoirs to suppress channeling through high-permeability zones and improve the utilization of low-permeability zones. For areally heterogeneous reservoirs, optimized well placement and zonal injection-production should be combined with multistage depressurization cycles to improve storage-capacity utilization efficiency and operational stability.

To address the problem of high-precision microstructure identification in the deep No. 8 coal seam of Carboniferous Benxi Formation in the Ordos Basin, “elemental fingerprints” of the deep coal seam and its roof and floor strata were constructed, and measurement points along the horizontal well were mapped to their corresponding reference positions in the vertical profile of the pilot well, thereby enabling the identification of microstructural features along the horizontal section of deep coalbed methane horizontal wells. First, based on elemental logging data and constrained by the lithological framework, candidate elements were determined for distinguishing the coal seam from its roof and floor strata and for identifying different coal lithotypes. Then, the candidate elements were screened using the coefficient of variation to obtain the characteristic elements for microstructure identification. The concentrations of the characteristic elements were adjusted using Z-score normalization, and the combination of characteristic-element concentrations at the same measurement point was expressed as a vector, termed an “elemental fingerprint”. Subsequently, the elemental fingerprints of the pilot well were matched with those of the horizontal section to determine the vertical-profile positions and distributional variations of the horizontal section. Finally, horizontal-well drilling information was integrated to determine the locations and types of microstructures developed along the horizontal section, thereby guiding adjustments to the drilling direction of the bit. Field drilling and hydraulic- fracturing practices demonstrate that the elemental fingerprint-based microstructure identification method can accurately identify microstructural features (e.g. small-scale folds, superimposed faults, and tectonically disturbed zones) along the horizontal section, and provide technical support for the optimized design of drilling and hydraulic fracturing in deep coalbed methane horizontal wells.

To address the challenges of uncertain interwell injection-production relationships, high monitoring costs, and limited dynamic reservoir data restricting the interwell connectivity during the early development of fractured-vuggy carbonate reservoirs, an interwell connectivity evaluation framework integrating transient disturbance propagation with steady-state production similarity is developed. Under this framework, changes in operating conditions, including well opening, well shut-in, and choke adjustment, are identified as disturbance events. An impulse response function (IRF) is used to characterize transient propagation, while an adaptive multi-feature penalized dynamic time warping (AMP-DTW) method is employed to quantify steady-state production similarity. Coupling with information-theoretic weighting and Leiden clustering, connectivity units are identified. The proposed framework was applied to 37 wells in the Y fault zone of Oilfield A. The results indicate that a total of 379 valid disturbance events are identified, and the self-identification accuracy of the proposed AMP-DTW method reaches 91.6%. The weights assigned to transient disturbance information and steady-state similarity information are 0.584 and 0.416, respectively, indicating that transient responses contribute more to interwell connectivity identification under the current development conditions. The study area is divided into six major connectivity units and five isolated wells, and the resulting partitioning is broadly consistent with the geological segmentation of the fault zone. The proposed framework provides a practical basis for evaluating interwell connectivity in fault-controlled fractured-vuggy reservoirs where systematic injection-production data and direct monitoring measurements are limited.

Effective propping of multi-stage fractures is challenging in shale oil and gas reservoirs stimulated by full-domain propped fracturing. This paper discusses the three-dimensional multi-level fracture propping technique, a component of the full-domain propped fracturing technology. The mechanism of proppant transport within multi-level fractures is thoroughly analyzed, and the control strategies for three-dimensional multi-level fracture propping and proper implementation paths are elaborated. Due to retardation by narrow fracture walls and severe fracturing fluid leakoff, proppant exhibits poor transport capacity and high settling velocity within shale fractures, resulting in limited longitudinal and lateral placement coverage. Additionally, proppant struggles to divert into branch fractures at fracture junctions, which ultimately reduces the effective propped volume of multi-level fractures. Adjusting pumping rate, fracturing fluid viscosity and proppant particle size can modify the intra-fracture proppant placement pattern to a certain extent, yet such measures show limited performance in improving far-fracture placement. To achieve three-dimensional multi-level fracture propping in shale, two targeted technologies are proposed. One is high-efficiency proppant placement in main fractures based on structure-driven proppant transport, which adopts proppant-fiber clusters as fundamental transport units instead of pure proppant grains to alter particle settling and packing behaviors, thereby greatly expanding the propped volume of main fractures. The other is graded propping by optimizing transport unit dimensions and improving particle entry capacity to mitigate insufficient propping in branch fractures. The full-domain propped fracturing technology has been fully or partially applied in pilot and comparative tests at nearly 300 wells in 11 oil and gas fields within China, with satisfactory results obtained. This technology is expected to be widely deployed for developing various unconventional oil and gas reservoirs in the future.

Considering that pressure wave wireless communication technology for water injection wells is limited in transmission success rate and efficiency, this study leverages the propagation characteristics of flow-rate disturbances throughout the entire pressurized pipeline flow system. The transmission characteristics of flow waves within water injection pipelines were revealed through numerical analysis and experiments. Based on these characteristics, corresponding signal generation devices, high-precision flowmeters, and a hybrid signal encoding system for flow wave communication were developed. This led to the successful creation of a surface flow wave communication terminal and a downhole water distributor. Depending on field conditions, a signal transmission strategy adapted to the characteristics of flow waves was formulated. Integrated with surface 4G mobile communication technology, a bidirectional wireless communication system from the surface terminal to the downhole water distributor was constructed. Ultimately, a complete set of efficient, low-cost downhole wireless communication technology based on flow wave control and a corresponding flow wave-controlled layered water injection technology were formed. These technologies have been tested and applied in 17 wells in the Jilin Oilfield, verifying their technical feasibility, accuracy, and reliability, but also successfully addressing long-standing technical challenges such as precise flow rate measurement for multiple downhole zones and simultaneous multi-layer measurement and regulation. This study provides a low-cost solution for the digital transformation of layered water injection development.

To address the computational challenges of 3D non-planar fracture propagation near the wellbore during hydraulic fracturing, a hybrid numerical model based on the Displacement Discontinuity/Fictitious Stress Method (DDM/FSM) and Finite Volume/Finite Element Method (FVM/FEM) was developed, incorporating a dynamic mesh tracking technique for the fracture front. This 3D non-planar model, constrained by wellbore boundary conditions, was validated for accuracy and reliability, and subsequently used to analyze fracture morphology under stress shadow effects and its key controlling factors. The results indicate that fracture propagation is jointly governed by far-field stress and wellbore-fracture induced stress. Specifically, wellbore-induced stress dominates initiation and reorientation of fractures within three times the wellbore radius, while far-field stress dictates the propagation direction beyond this range. Furthermore, initial fracture dip and fracture number significantly influence morphology: a larger angle between the fracture and the minimum principal stress increases the reorientation distance, whereas a higher number of initial fractures intensify differential propagation and localized reorientation behavior.

The localized thermal anomalies caused by exothermic pyrite oxidation and its geomechanical implications in the Pliocene Cisubuh Formation of the onshore North West Java Basin are investigated in this study. X-ray diffraction analysis, thermodynamic modeling, multistage triaxial tests, and swelling tests are conducted, and a coupled thermo-chemo-poroelastic geomechanical model is developed to evaluate wellbore stability under elevated temperature conditions. Thermodynamic modeling indicates that the heat released by pyrite oxidation is sufficient to explain the observed thermal anomalies in the Cisubuh Formation under ideal conditions. Field data further show temperature anomalies of 20-30 °C above the regional normal temperature in pyrite-rich intervals, supporting pyrite oxidation as the dominant diagenetic heat source. Laboratory triaxial and swelling tests under elevated temperature conditions reveal significant variations in chemical sensitivity within the Cisubuh shale, show that shales lose up to 15.25% cohesion and 13.09% internal friction coefficient after 5 d of fluid exposure. Model validation using data from Well X in the Subang Field demonstrates that abnormally high temperatures elevate the risk of wellbore instability, increasing mud weight to 1.6 g/cm³ prevents delayed collapse and maintains wellbore stability, while enabling drilling completion 3 d ahead of schedule, corresponding to an estimated operational saving of approximately USD 1.2 million.

To address two main challenges, i.e. insufficient proppant support in hydraulic fractures and limited oil mobilization from the matrix, in tight oil reservoirs, this study proposes a concept of “fracturing fluid-rock matrix synergistic modification” to formulate a modified slickwater system based on nano-droplets. This nano-modified slickwater system was investigated for its synergistic modification mechanisms through experimental techniques including rheological measurements, visualized proppant transport tests, three-phase interfacial atomic force microscopy measurements, wettability characterization, and core flooding experiments. The results indicate that the nano-modified slickwater system exhibits a low viscosity and high elasticity under high shear rates, which facilitates friction reduction and fracture propagation, and reflects a sharp increase of viscosity while maintaining the high elasticity through restoring the microscopic association structure under low shear rates, which enhances proppant transport by fracturing fluid in distal and branched fractures. This system releases nano-droplets after fluid breaking, which are then transported to deep matrix pores, altering the matrix wettability and improving the imbibition-driven oil displacement. It is concluded that the nano-modified slickwater system formulated following the concept of "fracturing fluid-rock matrix synergistic modification" is adaptive to working conditions, and it can simultaneously expand the volume of conductive fracture-network and enhance matrix productivity, enabling fracturing fluids to “enter, migrate, and modify” tight reservoir matrix economically and effectively. The proposed system offers a reliable technical foundation for efficient development of tight oil reservoirs.

Taking the Fengshun hydrothermal geothermal field in the Cathaysian orogenic system as an example, this study incorporates orogenic belt background elements into geothermal system and geothermal prediction research, and establishes a genetic model for the Fengshun geothermal field. The results show that the Fengshun area is characterized by well-developed Yanshanian granites with high radiogenic heat production rates, which serve as an effective heat source for the geothermal field. The area receives abundant rainfall, and the well-developed surface runoff, together with a topographic relief of nearly 1 km, provides ample water recharge. A system of steeply dipping conjugate shear faults forms the pathways for the long-distance migration of geothermal fluids. Mesozoic fractured granite bodies along the fault zones and Jurassic clastic rocks constitute the main geothermal reservoirs, whereas Triassic-Jurassic mudstones, shales, tuffs, and Quaternary clay layers act as effective regional caprocks. These features collectively create favorable conditions for a hydrothermal geothermal system in terms of heat source, water supply, reservoir, conduits and caprock. Along the Fenshui fault toward the southeast direction, surface runoff and groundwater flow occur simultaneously, creating favorable conditions for groundwater recharge, long-distance water circulation, and sustained heating of the groundwater. Downstream, the Lianhuashan fault zone and the continuously distributed granite bodies jointly form an effective barrier to groundwater flow, and the combination of the water-bearing reservoir and the obstructing structures constitutes a “ponding structure”. Deep-seated granites generating heat, deep groundwater undergoing long-distance circulation, shear faults conducting both water and heat, fractures and sand bodies providing storage space, fine-grained sedimentary caprocks offering thermal insulation, and lateral confinement by faults and granite bodies—all these elements together constitute the Fengshun hydrothermal geothermal enrichment model. The well-matched combination of heat source and water supply, fault conduits and water circulation, and reservoir and structural barrier is the key factor enabling the Fengshun geothermal field to be exploited continuously at stable temperature and high flow rate. This model explains the genetic mechanism of medium-high temperature geothermal anomalies in an orogenic setting and offers a reference for predicting and exploring geothermal resources in similar geological settings.

To understand the occurrence and migration mechanisms of helium in coal-measure gas, this study investigated anthracite from No. 3 coal seam of Lower Permian Shanxi Formation in the Jincheng mining area of the southern Qinshui Basin, China, through experiment analysis and molecular simulation. Firstly, low-temperature CO₂ and N₂ adsorption experiments were performed to characterize the multi-scale pore structure of anthracite, and accordingly, a 1-10 nm slit pore model of anthracite was constructed. Using grand canonical Monte Carlo, molecular dynamics and non-equilibrium molecular dynamics simulation methods, the effects of pore size, temperature, pressure, pore water, and associated gases (CO₂, CH₄, N₂, H₂) on helium adsorption, diffusion, and pressure-driven flow were systematically examined. The results show that helium exhibits weak enrichment near wall in nano-scale slit pores and coexistence of free gas in the pore center. Its interaction with coal wall is significantly weaker than those of CO₂, CH₄ and N₂, and is relatively close to that of H₂. Pore size, temperature and pressure all affect helium diffusion and flow behaviors. Smaller pores reduce helium diffusion coefficient and increase its viscosity, whereas larger pores facilitate helium migration. Pore water weakens continuous gas-phase pathways through film formation, permeation and interfacial friction, causing a sudden drop in helium diffusion coefficient at high water content stage. Strong adsorption of associated gases (CH₄ and CO₂) will further suppress helium diffusion, while H₂ as a lightweight carrier can enhance the diffusion ability of helium and H₂ itself to a certain extent. The research results provide theoretical references for understanding the microscopic migration and occurrence characteristics of helium in coal-measure gas.