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 8th 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.
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.
The localized thermal anomalies caused by exothermic pyrite oxidation and their 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% of its 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 the mud weight to 1.6 g/cmc 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 the challenges of uncertain interwell injection-production relationships, high monitoring costs, and limited production data that constrain reliable interwell-connectivity evaluation 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, connected units are identified. The proposed framework was applied to 37 wells in the Y fault zone of Field 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 connected 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.
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. The present TOC of mixed shale (average 9.31%) exceeds 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 hydrocarbon. 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.
