Search Results (290)

A combination of fault and fracture analyses, paleostress reconstructions from calcite twins, and U-Pb dating of syn-kinematic calcite mineralization provides new insights into the Cretaceous–Tertiary tectonic evolution of the Provence fold-and-thrust belt. This approach helped unravel 90 million years of polyphase deformation in this belt, which represents the eastward continuation of the northern Pyrenees. Focusing on three main targets along an NNE-SSW transect oriented roughly parallel to the regional Pyrenean shortening (the southernmost Nerthe range, the Bimont Lake area, and the northern Rians syncline), we date a wide range of scales and natures of deformation structures such as stylolites, veins, mesoscale faults, and major thrust fault zones. The reconstructed long-lasting tectonic history includes (1) the Durancian uplift and related NNE-SSW extension (~110 to 90 Ma); (2) the ~N-S Pyrenean compression related to the convergence then collision between Eurasia and Iberia and the Corsica–Sardinia block (~80 to 34 Ma); the Oligocene E-W to WNW-ESE extension related to the West European Cenozoic Rift System (ECRIS) and the Oligo–Miocene NW-SE to NNW-SSE extension related to the Liguro-Provençal Rifting (LPR); and a middle-late (?) N-S to NW-SE Alpine compression. We show that the Pyrenean shortening in Provence occurred during two main phases, 81–69 Ma and 59–34 Ma, coeval with the inversion of the pre-Pyrenean rift and the main Pyrenean collision, separated by a tectonic quiescence as described in the Pyrenees. Together with the published literature, our U-Pb ages also support the overall northward (forelandward) in sequence propagation of Pyrenean shortening across Provence. Our U-Pb results further allow us to refine the interpretation of local and regional fracture sets and reveal unsuspected polyphase development of fractures sharing a common strike. Beyond regional implications, our study shows that sampling structures of various natures and scales for U-Pb geochronology is probably the most efficient strategy to encompass the entire time interval of deformation in fold-and-thrust belts. Full article

This study investigates the hydraulic connection of surface karst features within the Northern segment of the Edwards Balcones Fault Zone Aquifer, using a combination of 2D and pseudo-3D Electrical Resistivity Tomography (ERT) at an outcrop near Salado, Texas. The study site features several surface fractures whose hydrological functions are not well understood. Nine ERT profiles and two pseudo-3D models were used to evaluate the connection between surface fractures and subsurface karst conduits. Karst features at the study site were physically evaluated using characteristics such as morphology, which resulted in the identification of three surface fractures (F1, F2, and F3). The ERT results showed several high-resistivity anomalies interpreted as a poorly fractured zone and low-resistivity water-filled conduits within the Edwards Formation. Furthermore, the result reveals that slow hydraulic connectivity exists in F1 and F2; however, F3 presents a low-resistivity zone that extends vertically into the subsurface, which suggests that F3 may serve as a potential recharge feature to the Edwards Aquifer. These findings are corroborated by a water percolation test, as water penetrated more at F3 compared to F1 and F2. This study showed that the combined application of 2D and pseudo-3D ERT can successfully delineate potential recharge pathways in an exposed karst system, thereby constituting a supportive approach providing critical insight into recharge and the vulnerability of karst aquifers to contamination. Full article

This study aims to explore the development characteristics and evolutionary patterns of strike–slip fault zones in carbonate rocks, through quantitative characterization of fault elements and their interrelationships. Taking three strike–slip fault zones in the Daniudi Block of the northeastern Ordos Basin, China, as examples, we analyzed the distribution of fault damage zone width and throw along the strike of the fault zones at equal intervals, based on data derived from 3D seismic interpretation. The relationship between damage zone width and throw was also explored. The results indicate the following: (1) The throw–distance curve of strike–slip fault zones exhibits bimodal or multimodal patterns. As the peak of the curve is located near the overlap zone of the fault, this signifies that the fault is in the independent stage, whereas a peak situated in the middle of a fault segment suggests that the strike–slip fault has achieved integrity through “hard linkage”. (2) The width of the fault damage zone is controlled by the scale of the fault zone and its associated structures. (3) A strong power–law relationship exists between the damage zone width and throw, with a more pronounced positive correlation observed in the Taigemiao Fault Zone. (4) The strike–slip fault zone is primarily composed of a “ternary” structure, including fault core, damage zone, and fracture zone, and has undergone three evolutionary stages. Analyzing the relationships among fault elements contributes to understanding the interaction and evolutionary history of subsurface strike–slip faults in the study area. Full article

This study examines the influence of tectonically induced mineralogical and microfabric changes on the strength of different rocks within the Hanzel Fault Damage Zone (FDZ) in the Tethyan Himalayas, Pakistan. Integrating field observations, petrographic analysis, and laboratory experiments (uniaxial compressive strength (UCS), Brazilian tensile strength (BTS), ultrasonic pulse-wave velocity (UPV), and porosity), this study systematically characterizes the spatial variations in intact rock strength across horizontal distance from the fault core to the outer limit of the FDZ. Seven rock units—granites (biotite granite, leucogranite schist, granodiorite schist, and diorite) and amphibolites (foliated amphibolite, amphibolite, and plagioclase amphibolite)—were sampled at varying distances (−500 to +4035 m) from the fault core. Results reveal that proximity to the fault core correlates with significant strength reductions (40%–70%): granitic rocks exhibit lower UCS (41–59 MPa) and BTS (4.8–6.7 MPa) compared to distal amphibolites and diorites UCS (75–107 MPa) and BTS (10–13.67 MPa). Petrographic analysis identifies key factors that reduce strength, including high mica content (up to 33%), pervasive micro-fracturing, S-C fabrics, and mineral alteration. These features increase porosity (up to 1.21%) and reduce UPV (2867–3315 m/s) in fault-proximal rocks. Moderate inverse relationships (R² = 0.68–0.72) between mica percentage and UCS/UPV confirm phyllosilicates as primary strength controls. The spatial variation in rock strength is attributed to ductile–brittle deformation processes, with foliated or schistose textures increasing in proximity to the fault core. This study demonstrates that tectonic processes significantly influence the mineralogy and microfabric within FDZs, leading to variations in rock strength with direct implications for stability in tectonically active regions. Full article

The Nezamabad Fault System (NFS) in the Fars area of the Zagros Fold–Thrust Belt represents a persistent, basement-rooted transverse shear zone that fundamentally controls the regional hydrocarbon system. This study integrates seismicity distribution, isopach analysis, and tectono-stratigraphic modeling from the Triassic to the Cenozoic to unravel how recurrent basement reactivation governs trap evolution. Isopach maps reveal a pronounced southwest-thickening asymmetry, with Triassic successions exceeding 1400 m, indicating long-term differential subsidence during four key phases: (1) Triassic syn-rift salt accumulation (Dashtak Formation) forming the primary detachment; (2) Jurassic–Early Cretaceous passive subsidence promoting source rock deposition; (3) Mid-Cretaceous transpression enhancing reservoir dolomitization; and (4) Late Cretaceous–Cenozoic inversion generating hybrid traps. Seismicity analysis of over 240 events confirms the 256-km-long NFS is a crustal-scale structure, with most foci at 10–33 km depth and others extending to 150 km, implying lithospheric stress transfer. This deep-crustal activity has periodically reorganized stress, enhanced fracture permeability, and rejuvenated traps through seismic pumping and cross-scale mechanical coupling. The results demonstrate that hydrocarbons in the Fars area are not a passive outcome of folding but a dynamic expression of lithospheric coupling. The findings establish a predictive framework for identifying analogous basement-influenced petroleum systems in other foreland fold–thrust belts worldwide. Full article

The Ordovician No. 6 fault zone reservoir in the Shunbei Oilfield exhibits ultra-deep-burial, high-pressure, and high-temperature conditions. Its pronounced tectonic control and significant heterogeneity render traditional in situ stress prediction methods—based on linear elasticity and anisotropy assumptions—inadequate for accurately characterizing the evolution and uncertainty of carbonate reservoir stiffness. Therefore, quantitatively predicting the development patterns and distribution characteristics of the Shunbei No. 6 structural fault zone is crucial for the exploration and development of Ordovician carbonate reservoirs in the Shunbei region. This study integrates wave impedance inversion with high-confining-pressure PFC particle flow biaxial test results to establish a constitutive calibration system consistent with seismic and experimental data. It introduces a nonlinear weakening function incorporating higher-order derivative constraints to fuse structural fracture and effective stress weakening effects, enabling dynamic correction of elastic parameters. This approach establishes a novel in situ stress prediction model. Simulation results indicate a predicted range for maximum horizontal principal stress between 201 and 261 MPa, with minimum horizontal principal stress ranging from 124 to 173 MPa. Predicted stress values for three key wells exhibit measurement errors within 6.92% compared to actual logging data, displaying a zoned spatial distribution consistent with regional tectonic stress evolution patterns. Simultaneously, sensitivity analysis reveals that the Young’s modulus fitting accuracy improved from 0.89 to 0.95, with a 43% reduction in mean square error, with the proportion of outliers reduced to below 1%. This significantly enhances response continuity and numerical stability in high-gradient disturbance zones and stiffness drop regions. The new model explicitly incorporates the nonlinear coupling between fracture geometry and pore pressure disturbance into the parameter field, eliminating systematic bias along fracture zones. Higher-order derivative constraints suppress numerical oscillations in high-gradient areas, stabilizing variance and preventing anomaly propagation. Residual distributions exhibit enhanced symmetry and reduced spatial autocorrelation, effectively suppressing numerical oscillations and divergence in complex fracture zones while significantly improving stress prediction accuracy for the study area. Overall, this research provides novel methodologies for predicting in situ stresses in ultra-deep carbonate reservoirs, offering engineering guidance and parameterization references for scheme deployment in complex fractured karst systems. Full article

In the field of tunnel engineering, it is often difficult to avoid crossing active faults. During an earthquake, tunnels across faults are highly vulnerable to damage. Therefore, conducting research on their mechanical responses and failure mechanisms is of great significance. This paper takes Xianglushan Tunnel as a research example and uses finite element software to carry out numerical simulation of the tunnel under the action of the left-lateral normal fault activity. Moreover, the effectiveness of this model is verified using the actual measurement data of the damaged tunnels during the Kumamoto earthquake. By comparing the damage conditions and stress states of the tunnel under the action of left-lateral normal faults and strike-slip faults, and conducting a systematic and refined study on relevant fault parameters, the following research results are obtained: First, compared with oblique-slip faults, strike-slip faults cause more severe damage to the tunnel; second, tunnel damage is mainly concentrated in the area where the fault slip surface is located; third, an increase in fault displacement can significantly exacerbate structural damage and is the main factor leading to tunnel failure; fourth, the dip angle of the fault affects the stress distribution of the tunnel. As the dip angle increases, the damaged area gradually shrinks; fifth, the change in the width of the fault fracture zone will alter the failure mode of the tunnel. Reasonably choosing to cross a wider fault can reduce the structural damage. This research provides theoretical support and practical reference for the seismic design of tunnels across faults. Full article

Determining the timing of hidden faults that terminate beneath the subsurface remains a significant challenge. For this contribution, seismic fault interpretation, fracture diagenesis analysis, and U-Pb dating of fracture cements are integrated to constrain the activity of hidden thrust faults in the southeastern Sichuan Basin. The results show that the EW- and NW-trending hidden thrust faults developed in the Permian, while the NE-trending faults have inherited later fault activity till the Cenozoic. The hidden thrust fault propagates upward from the top of the Upper Permian to the Lower Triassic strata. Fault inversion within the Permian is firstly identified by the thickness variation between the two fault walls. Core-based fracture diagenesis analysis indicates that multiple fractures and associated dissolution porosity developed within the tight matrix reservoir. In situ U-Pb dating of fracture cements yields ages of 247.4 ± 2 Ma and 234.8 ± 9.1 Ma, indicating that the hidden fault activity predates the Early Triassic. The absence of strata, evidence of structural uplift, and fault inversion collectively suggest that the first faulting in the eastern Sichuan Basin occurred at the end of the Middle Permian. The findings highlight that fracture–cave reservoir along the hidden thrust fault zone has been controlled by the coupling of the fracturing and karstification at the end of the Middle Permian, and is the key target for high gas production. Full article

The carbonate reservoir of the NT oilfield in the Precaspian Basin is a fracture-pore type with an extremely complex fracture network, comprising both high-angle structural fractures and abundant low-angle bedding-parallel fractures. Both fracture types significantly impact waterflood development, making effective prediction and characterization of the complex fracture network crucial for optimizing waterflooding and development plans. Using core, imaging logging, conventional logging, seismic, and production performance data, we predicted the distribution of high-angle structural and low-angle bedding-parallel fractures. A discrete fracture network (DFN) was constructed by grouping fractures based on strike and dip angles, and the influences of fractures with different dip angles on the initial production of individual wells and production decline rates were analyzed. Results show that high-angle fracture distribution is effectively predicted by combining imaging logging data with seismic volumes processed via ant-tracking technology, while low-angle fractures are well predicted using conventional logging, imaging logging, and seismic data processed by dip deviation. High-angle fractures are predominantly developed near and parallel to faults; low-angle fractures are mainly distributed in fold limbs. Fractures were grouped into northeast, southeast, southwest, northwest high-angle fractures, and low-angle fractures. Fracture modeling indicates a reservoir fracture porosity of 0~0.27% and permeability of 10~100 mD. With increasing fracture density, single-well initial productivity and production decline rates are higher in high-angle fracture zones than in low-angle fracture zones. Low-angle fractures contribute to ~56.45% of high-angle fractures’ production and affect production decline at ~82.5% of high-angle fractures’ level. This method is significant for predicting and modeling complex fracture networks in other reservoirs. Full article

This study addresses the challenge of low working gas ratios in China’s underground gas storage (UGS) facilities by optimizing geomechanical evaluations to enable safe pressure increases and capacity expansion. Through mini-fracturing tests conducted at the Liaohe Gas Storage Group, a cross-validated analytical framework was established, integrating the square-root-of-time, Geomechanical (G) function, and flow-back pressure–volume methods. This framework enables precise determination of the dynamic maximum safe pressure, effectively balancing storage efficiency against the risks of fracture and fault activation. The results indicate that the minimum horizontal stress is 37% higher in the caprock than in the reservoir, confirming the integrity of the natural stress barrier. A mere 0.39% discrepancy in interpretation results validates the consistency of the methodology. The derived three-dimensional (D) in situ stress model reveals that the upper sandstone section exhibits 15–20% higher horizontal stress than deeper intervals, acting as a secondary barrier against fracture propagation. Theoretically, we propose a ‘stress differential gradient sealing’ mechanism to explain the buffering effects observed in the sandstone–mudstone transition zone. Practically, we developed a standardized testing protocol for complex geological conditions, which achieved a 15% increase in the maximum safe operating pressure at the Liaohe facility. This study provides critical insights for optimizing gas storage operations. Full article

The aim of this work was to investigate the evolution of the mechanical integrity of the selected offshore oil reservoir during its life cycle. The geomechanical stability of the reservoir formation, including the caprock and base rock, was investigated from the exploitation phase through waterflooding production to the final phase of enhanced oil recovery (EOR) with CO₂ injection. In this study, non-isothermal flow simulations were performed during the process of cold water and CO₂ injection into the oil reservoir as part of the secondary EOR method. The analysis of in situ stress was performed to improve quality of the geomechanical model. The continuous changes in elastic and thermal properties were taken into account. The stress–strain tensor was calculated to efficiently describe and analyze the geomechanical phenomena occurring in the reservoir as well as in the caprock and base rock. The integrity of the reservoir formation was then analyzed in detail with regard to potential reactivation or failure associated with plastic deformation. The consideration of poroelastic and thermoelastic effects made it possible to verify the development method of the selected oil reservoir with regard to water and CO₂ injection. The numerical method that was applied to describe the evolution of an offshore oil reservoir in the context of evaluating the geomechanical state has demonstrated its usefulness and effectiveness. Thermally induced stresses have been found to play a dominant role over poroelastic stresses in securing the geomechanical stability of the reservoir and the caprock during oil recovery enhanced by water and CO₂ injection. It was found that the injection of cold water or CO₂ in a supercritical state mostly affected horizontal stress components, and the change in vertical stress was negligible. The transition from the initial strike-slip regime to the normal faulting due to formation cooling was closely related to the observed failure zones in hybrid and tensile modes. It has been estimated that changes in the geomechanical state of the oil reservoir can increase the formation permeability by sixteen times (fracture reactivation) to as much as thirty-five times (tensile failure). Despite these events, the integrity of the overburden was maintained in the simulations, demonstrating the safety of enhanced oil recovery with CO₂ injection (EOR-CO₂) in the selected offshore oil reservoir. Full article

This study presents an integrated geophysical and hydrogeological characterization of fault systems in the sandstone-hosted uranium deposit within the K₁b² Ore Horizon of the Bayin Gobi Basin. Employing 3D seismic exploration with 64-fold coverage and advanced attribute analysis techniques (including coherence volumes, ant-tracking algorithms, and LOW_FRQ spectral attenuation), the research identified 18 normal faults with vertical displacements up to 21 m, demonstrating a predominant NE-oriented structural pattern consistent with regional tectonic features. The fracture network analysis reveals anisotropic permeability distributions (31.6:1–41.4:1 ratios) with microfracture densities reaching 3.2 fractures/km² in the central and northwestern sectors, significantly influencing lixiviant flow paths as validated by tracer tests showing 22° NE flow deviations. Hydrogeological assessments indicate that fault zones such as F11 exhibit 3.1 times higher transmissivity (5.3 m²/d) compared to non-fault areas, directly impacting in situ leaching (ISL) efficiency through preferential fluid pathways. The study establishes a technical framework for fracture system monitoring and hydraulic performance evaluation, addressing critical challenges in ISL operations, including undetected fault extensions that caused lixiviant leakage incidents in field cases. These findings provide essential geological foundations for optimizing well placement and leaching zone design in structurally complex sandstone-hosted uranium deposits. The methodology combines seismic attribute analysis with hydrogeological validation, demonstrating how fault systems control fluid flow dynamics in ISL operations. The results highlight the importance of integrated geophysical approaches for accurate structural characterization and operational risk mitigation in uranium mining. Full article

This study focuses on tunnel construction in fault fracture zones and systematically investigates the energy evolution and damage catastrophe mechanisms of surrounding rock during excavation, based on energy conservation principles and cusp catastrophe theory. A tunnel instability prediction and support optimization framework integrating energy damage evolution and intelligent optimization algorithms was developed. Field tests, rock mechanics experiments, and Discrete Fracture Network (DFN) numerical simulations reveal the intrinsic relationships among energy input, dissipation, damage accumulation, and instability under complex geological conditions. Particle Swarm Optimization–Back Propagation (PSO-BP) is applied to optimize tunnel support parameters. Model performance is evaluated using the Mean Absolute Error (MAE), Mean Squared Error (MSE), Mean Absolute Percentage Error (MAPE), and R-squared (R²). The results show that upon reaching structural mutation zones, the system damage variable (ds), displacement, and dissipated energy increase abruptly, indicating critical instability. Numerical simulation and catastrophe feature analysis demonstrate that energy-related damage accumulation is effectively suppressed, the system damage variable decreases significantly, and crown stability is greatly enhanced. These findings provide a theoretical basis and practical reference for optimizing tunnel support design and controlling instability risks in complex geological settings. Full article

This study investigates slope stability in an open-pit mining area by integrating engineering geological surveys, field investigations, and laboratory rock mechanics tests. A coordinated multimethod analysis was carried out using finite element-based numerical simulations from both two-dimensional and three-dimensional perspectives. The integrated approach revealed deformation patterns across the slopes and established a multiscale analytical framework. The results indicate that the slope failure modes primarily include circular and compound types, with existing step slopes showing a potential risk of wedge failure. While the designed slope meets safety requirements under three working conditions overall, the strongly weathered layer in profile XL3 requires a slope angle reduction from 38° to 37° to comply with standards. Three-dimensional simulations identify the main deformations in the middle-lower sections of the western area and zones B and C, with faults located at the core of the deformation zone. Rainfall and blasting vibrations significantly increase surface tensile stress, accelerating deformation. Although wedges in profiles XL1 and XL4 remain generally stable, coupled blasting–rainfall effects may still induce potential collapse in fractured areas, necessitating preventive measures such as concrete support and bolt support, along with real-time monitoring to dynamically optimize reinforcement strategies for precise risk control. Full article

Exploration of coalbed methane (CBM) has long been plagued by critical technical challenges, including a low signal-to-noise (S/N) ratio in seismic data, difficulty identifying thin coal seams, and inadequate accuracy in interpreting complex structures. This study presents an innovative methodological framework that integrates artificial intelligence (AI) with advanced seismic processing and interpretation techniques. Its effectiveness is verified through a case study in the North Bowen Basin, Australia. A multi-scale seismic data enhancement approach combining dynamic balancing and blue filtering significantly improved data quality, increasing the S/N ratio by 53%. Using deep learning-driven, multi-attribute fusion analysis, we achieved a prediction error of less than ±1 m for the thickness of thin coal seams (4–7 m thick). Integrating 3D coherence and ant-tracking techniques improved the accuracy of fault identification, increasing the fault recognition rate by 30% and reducing the spatial localization error to below 3%. Additionally, a finely tuned, spatially variable velocity model limited the depth conversion error to 0.5%. Validation using horizontal well trajectories revealed that the rate of reservoir encounters exceeded 95%, with initial gas production in the predicted sweet spots zone being 25–30% higher than with traditional methods. Notably, this study established a quantitative model linking structural curvature to fracture intensity, providing a robust scientific basis for accurately predicting CBM sweet spots. Full article