Search Results (881)

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

The Upryamoye ore field is located in the Chukotka metallogenic belt in Northeast Russia. The orebodies are hosted within Late Jurassic–Early Cretaceous greenschist-facies metamorphosed rocks and structurally controlled by NW-trending fold-and-thrust dislocations. Based on geological exploration, petrographic, mineralogical, and geochronological studies, new data on the geological structure and composition of gold–quartz mineralization of the Upryamoye ore field are presented. Optical and scanning microscopy were used to study the lithological features of the host rocks and determine the ore textures and the morphology and internal structure of native gold, auriferous pyrite, and arsenopyrite. Qualitative and quantitative characterization of the ore minerals was carried out using SEM-EDS and EPMA. To determine the age of the gold mineralization, Re-Os dating of arsenopyrite and U-Th/He dating of pyrite were performed. The results show that the orebodies comprise carbonate–quartz and sulphide–carbonate–quartz saddle reef veins in both the fold hinge and limbs, as well as mineralized shatter zones and mylonite zones that trace thrust faults. The main ore minerals are arsenopyrite and pyrite, associated with minor amounts of galena, sphalerite, chalcopyrite, tetrahedrite, and bournonite. Native gold is distributed extremely unevenly, forming thin and finely dispersed inclusions in pyrite and arsenopyrite. U-Th/He isotopic analyses of auriferous pyrites suggest that gold mineralization in the Upryamoye ore field occurred at 123 ± 4 Ma. The data obtained by Re–Os dating of auriferous arsenopyrite are inconsistent with direct geological observations but indicate that Os in the arsenopyrite was derived from the crustal source. According to a number of characteristic features of mineralization, the Upryamoye ore field is attributed to a metamorphic genetic type of orogenic low-sulphide gold–quartz deposits. The ore-forming process was long and multi-stage, occurring during the final collisional phase and the beginning of the extensional phase of the Chukotka orogen. Full article

Judging from the current global exploration trend, ultra-deep layers have become the main battlefield for energy exploration. China has made great progress in the ultra-deep field in recent decades, with the Tarim Basin and Sichuan Basin as the focus of exploration. The Sichuan Basin is a large superimposed gas-bearing basin that has experienced multiple tectonic movements and has developed multiple sets of reservoir–caprock combinations vertically. Notably, the multi-stage platform margin belt-type reservoirs of the Sinian–Lower Paleozoic exhibit inherited and superimposed development. Source rocks from the Qiongzhusi, Doushantuo, and Maidiping formations are located in close proximity to reservoirs, creating a complex hydrocarbon supply system, resulting in vertical and lateral migration paths. The structural faults connect the source and reservoir, and the source–reservoir–caprock combination is complete, with huge exploration potential. At the same time, the ultra-deep carbonate rock structure in the basin is weakly deformed, the ancient closures are well preserved, and the ancient oil reservoirs are cracked into gas reservoirs in situ, with little loss, which is conducive to the large-scale accumulation of natural gas. Since the Nvji well produced 18,500 cubic meters of gas per day in 1979, the study of ultra-deep layers in the Sichuan Basin has begun. Subsequently, further achievements have been made in the Guanji, Jiulongshan, Longgang, Shuangyushi, Wutan and Penglai gas fields. Since 2000, two trillion cubic meters of exploration areas have been discovered, with huge exploration potential, which is an important area for increasing production by trillion cubic meters in the future. Faced with the ultra-deep high-temperature and high-pressure geological environment and the complex geological conditions formed by multi-stage superimposed tectonic movements, how do we understand the special geological environment of ultra-deep layers? What geological processes have the generation, migration and enrichment of ultra-deep hydrocarbons experienced? What are the laws of distribution of ultra-deep oil and gas reservoirs? Based on the major achievements and important discoveries made in ultra-deep oil and gas exploration in recent years, this paper discusses the formation and enrichment status of ultra-deep oil and gas reservoirs in the Sichuan Basin from the perspective of basin structure, source rocks, reservoirs, caprocks, closures and preservation conditions, and provides support for the optimization of favorable exploration areas in the future. Full article

The Altyn Tagh Fault plays a critical role in understanding the tectonic evolution of the northern margin of the Tibetan Plateau. However, considerable debate persists regarding its activity and deformation history. This study investigates volcanic rocks from the Beidayao-Jianquanzi-Hanxia-Hongliuxia area in the eastern segment of the fault. By employing zircon U-Pb dating, whole-rock geochemistry, and Sr-Nd isotope analysis, we aim to elucidate their petrogenesis and tectonic setting, thereby providing new insights into the crustal evolution of the eastern Altyn Tagh Fault. Zircon U-Pb dating of the Hongliuxia rhyolite yields a weighted mean ²⁰⁶Pb/²³⁸U age of 106.6 ± 0.6 Ma, indicating an Early Cretaceous eruption. Geochemically, the western part of the study area (Beidayao and Jianquanzi) is dominated by basalts that exhibit significant enrichment in large ion lithophile elements and light rare earth elements, together with high Nb concentrations (>20 ppm), as well as high Nb/La (0.64–1.12) and Nb/U (29.8–35.42) ratios, consistent with the characteristics of high-Nb basalt. In contrast, the eastern area (Hanxia and Hongliuxia) is characterized by andesitic rocks that display typical continental arc affinities, marked by enrichment in Th, U, and Pb and depletion in Nb, Ta, and Ti. Isotopically, the basalts show initial ⁸⁷Sr/⁸⁶Sr ratios of 0.706–0.707 and ε_Nd (t) values ranging from −3.2 to 0.8, whereas the andesites possess more radiogenic Sr isotopic compositions, with (⁸⁷Sr/⁸⁶Sr)_i ratios of 0.710–0.717, and more negative ε_Nd (t) values from −11.4 to −1.5, suggesting derivation from an enriched mantle source. Integrating geochemical data with regional geological records, we propose that the eastern part of the Altyn Fault experienced a significant intracontinental extensional setting during the Early Cretaceous, where asthenospheric mantle upwelling played a key role in the generation of the volcanic rocks. This study provides key petrological and geochemical constraints on Early Cretaceous deformation and activity along the Altyn Tagh Fault, and also offers a valuable reference for understanding the evolution of similar fault systems. Full article

Assessing and forecasting hydrocarbon resource potential (HRP) is of great significance. However, due to the complexity and uncertainty of geological conditions during hydrocarbon accumulation, it is challenging to accurately establish HRP models. This study employs machine learning methods to construct a HRP assessment model. First, nine primary controlling factors were selected from the five key conditions for HRP: source rock, reservoir, trap, migration, and accumulation. Subsequently, three prediction models were developed based on the backpropagation (BP) neural network, BP-Bagging algorithm, and BP-AdaBoost algorithm, with hydrocarbon resources abundance as the output metric. These models were applied to the Dongpu Depression in the Bohai Bay Basin for performance evaluation and optimization. Finally, this study examined the importance of various variables in predicting HRP and analyzed model uncertainty. The results indicate that the BP-AdaBoost model outperforms the others. On the test dataset, the BP-AdaBoost model achieved an R² value of 0.77, compared to 0.73 for the BP-Bagging model and only 0.64 for the standard BP model. Variable importance analysis revealed that trap area, sandstone thickness, sedimentary facies type, and distance to faults significantly contribute to HRP. Furthermore, model accuracy is influenced by multiple factors, including the selection and quantification of geological parameters, dataset size and distribution characteristics, and the choice of machine learning algorithm models. In summary, machine learning provides a reliable method for assessing HRP, offering new insights for identifying high-quality exploration blocks and optimizing development strategies. Full article

Metabasic rocks (eclogites and amphibolites) from four Betic ophiolite outcrops (Lugros, Almirez, Cóbdar, and Algarrobo), comprising Ol-Px gabbros, dolerites, and MORB-affinity basalts, were studied. U-Pb SHRIMP zircon dating yielded Early to Middle Jurassic ages (187–174 Ma). At Cóbdar and Algarrobo, several magmatic levels were identified (187 ± 1.7 to 174 ± 1.8 Ma, and 184 ± 1.8 to 180 ± 1.6 Ma, respectively). In Lugros, two gabbros were dated to 187 ± 2.5 and 184 ± 1.4 Ma, while a dolerite dyke intruding serpentinites in Almirez gave 184 ± 1.6 Ma. Algarrobo xenocrystic zircons, predominantly Precambrian, resemble those from the MAR (13° N–15° N) in age and chemistry, suggesting a similar tectonic setting. δ¹⁸O values (4.2–6.2‰) of Betic ophiolite zircons (gabbros, basalts, dolerites) match those of MAR and SWIR samples, reflecting also oceanic alteration. Some zircons preserve δ¹⁸O variations linked to Jurassic (~150 Ma) oceanic metamorphism and later orogenic overprints. REE patterns show depletions in HREE and Y, with localized enrichments in LREE and Hf, which are more marked in metamorphically recrystallized zones. Xenocrystic zircons may derive from Precambrian protoliths assimilated during Jurassic magma ascent near transform faults. This integrated geochronological and geochemical evidence provides the key constraints for a revised geodynamic framework, confirming the existence of a Betic Jurassic ocean basin, which is a crucial precursor to the Alpine orogenic events that shaped the region. Full article

Huhehu Sag is a sag with high exploration degree in Hailar Basin. With large sedimentary thickness, complete stratigraphic development and excellent oil generation conditions, it is the main oil- and gas-producing sag in Hailar Basin. The primary source rocks are the Nantun Formation, with the Tongbomiao and Damoguaihe Formations as secondary sources. Hydrocarbon accumulation periods in the sag were comprehensively analyzed using methodologies including source rock hydrocarbon generation-expulsion history, authigenic illite dating of reservoirs, and fluid inclusion homogenization temperature analysis. Results reveal two major accumulation stages: Stage 1 (125–90 Ma), corresponding to the depositional period of the Yimin Formation, represented the peak paleo-geothermal regime and the primary hydrocarbon accumulation phase. Intensive hydrocarbon generation and expulsion, coupled with robust migration dynamics, facilitated large-scale oil and gas pooling. Stage 2(65 Ma-now), from the deposition of Qingyuangang Formation to the present, uplift and denudation reduce the burial depth of source rocks, the hydrocarbon generation intensity is weakened. This phase involved secondary adjustments of pre-existing reservoirs and continued charging of newly generated hydrocarbons. The Huhehu Sag is a typical half-graben structure. Fault-block and fault-lithologic reservoirs dominate, distributed zonally along gentle and steep slopes. Lithologic reservoirs primarily occur near or within the central hydrocarbon-generating sub-sags. The most favorable hydrocarbon accumulation zones are located in the sub-sag centers and adjacent areas with high-quality reservoirs. Full article

The Manicouagan impact structure in northeastern Canada is one of the largest, well-documented impact sites among Phanerozoic structures. Once considered a candidate for the cause of end-Triassic extinctions, radioisotopic dating of impact melt rock has established the age of the impact as middle to late Norian. In contrast to the clearly defined association between the Chicxulub structure and the K-Pg boundary, however, the sedimentary record of the Manicouagan impact is unusually sparse, with verified ejecta deposits currently limited to a single deep-marine occurrence (Japan) and one well-documented deposit in a continental (fluvial) setting (England). Sedimentary layers at the top of a widespread seismically deformed zone in a continental sequence in the Upper Triassic (Norian) Blomidon Formation, Fundy Basin, contain sparse, potentially impact-derived grains (shocked quartz and spherulitic grains) that are interpreted as impact ejecta that were reworked within a playa-lacustrine environment. The presence of these ejecta suggests that the seismic deformation resulted indirectly from the Manicouagan impact via reactivation of a nearby fault system. Paleomagnetic correlation of the ejecta-bearing strata in the Blomidon Formation to the Newark astrochronostratigraphic polarity time scale suggests a temporal discrepancy in the correlation of the Newark time scale to the magnetostratigraphic record of the Upper Triassic. This hypothesis is supported by recent correlations of the geomagnetic polarity time scale to the Newark time scale. Full article

This study investigates geothermal waters in the Xinjiang region through hydrogeochemical methods, including cluster analysis, ionic ratios, and isotopic analysis. Cluster analysis categorized the geothermal water samples into three distinct groups (G1, G2, and G3). The predominant hydrochemical facies are SO₄-HCO₃-Na, SO₄-Cl-Na, and Cl-Na types, whose formation is controlled by multiple factors. Evidence from molar ratios of major ions suggests that geothermal waters in Group G1 are predominantly governed by water–rock interactions, whereas Groups G2 and G3 are mainly influenced by evaporative concentration. Hydrogen and oxygen isotopic signatures confirm that meteoric water serves as the primary recharge source for these geothermal waters. The spatial correlation between regional tectonic features and most geothermal discharge points demonstrates a consistent relationship between geothermal water occurrence and structural distribution in Xinjiang. Additionally, a conceptual circulation model is proposed wherein meteoric water undergoes deep circulation following local recharge, ascends along fault zones under tectonic pressure, and mixes with shallow groundwater. This research primarily elucidates the hydrogeochemical characteristics and recharge mechanisms of geothermal resources in Xinjiang, thereby providing a scientific basis for their future development and utilization. Full article

Ensuring the stability of surrounding rock in underground excavations is a critical prerequisite for safe mining operations. This study examines the mechanisms of wedge failure formation and determines the performance of a combined support system (rock bolts + shotcrete) through probabilistic analysis. Field investigations in the Zhylandy ore field (Kazakhstan) included fracture mapping, rock mass quality assessment (RQD), fracture frequency (FF), and in situ stress measurements, which confirmed a thrust-faulting regime. Numerical modeling with Dips ver.8 and UnWedge ver.6 software (Rocscience) identified critical excavation orientations of 120° and 141° associated with maximum-volume wedge formation, as well as a “safe orientation window” of 70° ± 10°. The probabilistic analysis showed that rock bolts alone yield a factor of safety (FS) < 1.2, whereas the combined support system increases FS to 2.4–3.5, significantly reducing the likelihood of wedge failures. An adaptive framework integrating numerical modeling with intelligent monitoring (“monitor → update model → adjust support”) is proposed, allowing real-time adjustment of support parameters and optimization of material consumption. The practical significance of this work lies in providing design-ready recommendations for support selection and excavation orientation, contributing to accident prevention and sustainable mining operations. 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

Assessing seismic vulnerability and prioritizing railway tunnels for seismic rehabilitation are critical components of railway infrastructure management, especially in seismically active regions. This study focuses on a railway network in Northwest Iran, consisting of 103 old masonry rock tunnels. The vulnerability of these tunnels is evaluated under 12 active faults as seismic sources. Fragility curves derived from the HAZUS methodology estimate the probability of various damage states under seismic intensities, including peak ground acceleration (PGA) and peak ground displacement (PGD). The expected values of the damage states are computed as the damage index (DI) to measure the severity of damage. A normalized prioritization index (NPI) is proposed, considering seismic vulnerability and life cycle damages in tunnel prioritizing. Finally, a detailed prioritization is provided in four classes. The results indicate that 10% of the tunnels are classified as priority, 33% as second priority, 40% as third priority, and 17% as fourth priority. This prioritization is necessary when there are budget limitations and it is not possible to retrofit all tunnels simultaneously. The main contribution of this study is the development of an integrated, data-driven framework for prioritizing the seismic rehabilitation of aging masonry railway tunnels, combining fragility-based vulnerability assessment with life-cycle damage considerations in a high-risk and data-limited region. The framework outlined in this study enables decision-making organizations to efficiently prioritize the tunnels based on vulnerability, which helps to increase seismic resilience. Full article

Background: Despite the identification of various environmental factors that increase the risk of multiple sclerosis (MS), the effects of many factors on the etiology of MS remain to be elucidated. In this study, we aimed to investigate the effects of radon, a factor previously studied in relation to various other neurodegenerative diseases, on the epidemiology of MS. Methods: A door-to-door field study was conducted in residential areas with relatively high and low radon gas concentrations to determine the prevalence of MS. The study area comprises the Bolvadin and İhsaniye regions, which have different geological characteristics, such as seismic activity, active faults, and distributions of volcanic rocks. CR-39 detectors, with an accepted limit of 300 Bq/m³, were utilized to measure radon gas concentrations. During the screening field, the patients diagnosed with multiple sclerosis were confirmed with their hospital records. Mc Donald’s revised diagnostic criteria were used for multiple sclerosis diagnosis. Results: The regions were grouped into higher radon areas and lower radon areas. The İhsaniye city center, Kayıhan, Kemerkaya, Döğer, and Bolvadin city center were classified as higher radon regions, whereas Dişli, Yaylabağı, Gazlıgöl, and Özburun were identified as lower radon regions. A total of 40,841 individuals were surveyed in the field. The crude MS prevalence was 41.8/100,000 in settlements with high radon gas concentrations and 20.5/100,000 in settlements with low radon gas concentrations. Conclusions: In this study, we revealed that the prevalence of MS was greater in settlements with high radon gas concentrations than in settlements with low radon gas concentrations. These results demonstrated that radon gas is an important environmental risk factor in the etiopathogenesis of MS. Full article

The fracture evolution of brittle rock under 3D stress states remains poorly understood, particularly the role of deviatoric stress symmetry as characterized by the Lode angle (θ_σ). To address this knowledge gap, we systematically investigated sandstone using a true triaxial loading apparatus under a constant mean stress (100 MPa) while varying θ_σ from −30° to +30°, integrated with real-time acoustic emission (AE) monitoring and post-failure X-ray computed tomography. Our results demonstrate a critical linear reduction in peak strength with increasing θ_σ. This strength reduction is accompanied by a corresponding transition in failure mechanism, from a progressive mode dominated by dilation to an abrupt mode characterized by shear localization. Innovatively, we introduce a novel AE-based parameter (C), derived from the coupled evolution of AE energy and hit rates, which quantifies fracturing intensity in real-time without pre-defined lithological and monitoring scale. Furthermore, digital reconstruction reveals that consistent X-shaped polymodal fault networks are governed by sequential tensile–shear interactions. This key mechanistic insight prompts us to propose a new “deflected shear–tensile hybrid kinked fracture” classification, which more accurately captures the topological complexity of fractures under 3D stresses than conventional monomodal schemes. This study provides fundamental insights into 3D rock fracture mechanics and practical tools for enhancing safety and efficiency in deep geo-engineering. Full article