Search Results (3,160)

This study investigates the heterogeneity of pore structures in lacustrine shale gas reservoirs, with a specific focus on shales from the Lower Cretaceous Shahezi Formation in the Lishu Fault Sag of the Songliao Basin. By integrating multi-scale characterization techniques—including high-pressure mercury intrusion, N₂/CO₂ adsorption, and nuclear magnetic resonance (NMR)—we examined the pore networks across five identified lithofacies: organic-rich clayey shale, organic-rich mixed shale, organic-rich siliceous shale, organic clayey shale, and organic mixed shale. The results indicate that mesopores (2–50 nm) constitute the dominant fraction of pore volume (31.7%–56.6%), followed by micropores (<2 nm) and macropores (>10 μm). Notable lithofacies-dependent variations were observed: organic-rich clayey shale exhibits abundant organic pores, clay interlayer pores, and intragranular dissolution pores with favorable connectivity; organic-rich siliceous shale is mainly dominated by inorganic pores with limited organic porosity; mixed shales are characterized by clay mineral contraction fractures and intergranular pores. The key controlling factors are mineral composition and organic matter abundance: clay content shows a positive correlation with pore volume and surface area in organic-rich clayey shale, but a negative correlation in organic mixed shale. Brittle minerals (quartz and feldspar) generally reduce porosity through compaction. Total organic carbon (TOC) displays a weak positive correlation with mesopore volume, while thermal maturity (Ro = 1.2%–1.73%) exerts influences that vary by lithofacies. In contrast to marine shales—which are dominated by high-maturity (Ro > 2.0%) organic pores and quartz-supported frameworks—terrestrial shales primarily rely on inorganic pores derived from clay minerals (e.g., illite). This study clarifies the relationships among lithofacies, pore structure, and controlling factors, thereby providing a basis for evaluating the gas potential of terrestrial shales. Full article

The ambiguous evolution of the depositional system in the Pinghu Formation of Block K, Xihu Depression, East China Sea Basin, has long constrained the accuracy of reservoir prediction in this area. Based on petrological analysis, sedimentary system identification, and depositional model reconstruction, this study systematically elucidates the sedimentary evolution of the Pinghu Formation in Block K. The results indicate that the Pinghu Formation exhibits diverse lithologies and multiple types of grain-size distribution, reflecting complex hydrodynamic conditions. The early stage was dominated by tidal processes with fluvial influence, transitioning to fluvial dominance in the late stage. The depositional system evolved through a complete sequence: the early stage (E2pSQ1) was characterized by a tide-dominated delta, the middle stage (E2pSQ2) by fluvial-tidal interaction, and the late stage (E2pSQ3) by an overwhelmingly fluvial-dominated system. This evolution was controlled by the combined effects of a persistently increasing sediment supply and episodic relative sea-level fall, with the transition mechanism primarily governed by tectonic-eustatic coupling. In the lowstand systems tract of the middle-upper section, a “high-supply, high-progradation” fluvial-dominated delta developed in the Kongbei fault-step zone, whereas a “low-supply, low-progradation” minor fluvial system formed in the Kongnan fault-step zone. Here, tidal reworking was weak, and tidal flats developed only locally. In contrast, the highstand systems tract in the middle-lower section was dominated by a tide-dominated delta in the Kongnan fault-step zone, while the Kongbei fault-step zone remained a “low-supply, low-progradation” minor fluvial system. The established depositional models provide a geological basis for reservoir prediction and hydrocarbon exploration in the Pinghu Formation of Block K. Full article

In the extraction of shale gas and oil, the vibration characteristics of the drill string significantly influence wellbore quality, potentially leading to wellbore instability, excessive tool wear, and diminished drilling efficiency. This study tackles the challenges associated with drill string vibrations by developing an integrated technical framework of multi-field coupled dynamic modeling, Sobol-based key parameter identification, and NSGA-II-driven multi-objective structural optimization, and proposes a synergistic vibration suppression strategy combining structural parameter adjustment and hydraulic damper configuration based on multibody dynamics and finite element analysis. Initially, a dynamic model that accounts for the coupling between the wellbore and the drill string is developed to scrutinize the impact of various vibration modes on wellbore quality. Subsequently, detrimental vibrations are mitigated through the optimization of structural parameters, including but not limited to stiffness distribution and the strategic placement of vibration absorbers. Finally, the efficacy of the optimized design is substantiated through numerical simulations and field experiments. The results demonstrate that the optimized drill string achieves a simulation average reduction of 30% in lateral vibration amplitude across the rotational speed range of 60–120 RPM and a simulation average improvement of 25% in the attenuation of axial vibration energy. These enhancements notably bolster drilling stability and elevate wellbore quality. This research furnishes both theoretical and technical underpinnings for the efficient development of shale gas and oil resources. Full article

Pore structure and multifractal characteristics are two critical indicators for evaluating the heterogeneity of tight sandstone reservoirs. An integrated analysis comprising physical property tests, X-ray diffraction, casting thin sections, scanning electron microscopy, high-pressure mercury intrusion (HPMI), and constant-rate mercury intrusion (CRMI) is conducted on five samples from the Jurassic Sangonghe Formation in the northern Turpan-Hami Basin to investigate the full-scale pore size distribution (FPSD) and its multifractal characteristics. The results indicate that the pores in tight sandstone are mainly residual intergranular pores, dissolution pores, intercrystalline pores, and microfractures. The FPSD exhibits a bimodal or trimodal pattern, with dominant pore sizes ranging from 0.00516 μm to 1.15 $\mathsf{\mu }\mathrm{m}$. Two key multifractal parameters, the multifractal dimension range ($D_{min}-D_{max}$) and the relative dispersion ($R_d$), were utilized to effectively characterize pore structure heterogeneity and asymmetry. Higher $D_{min}-D_{max}$ values correspond to stronger heterogeneity, whereas lower $R_d$ values indicate a dominance of nanoscale pores. Furthermore, $D_{min}-D_{max}$ and $R_d$ exhibit negative correlations with permeability and clay mineral content, and positive correlations with feldspar content. This study demonstrates the utility of FPSD in characterizing pore structure and highlights the applicability of multifractal theory in assessing the heterogeneity of tight sandstone reservoirs. Full article

Bodanella lauterborni W.M. Zimmermann and Heribaudiella fluviatilis (Areschoug) Svedelius are members of brown algae (Phaeophyceae) that exclusively inhabit freshwater habitats. Heribaudiella fluviatilis is the most frequently reported freshwater brown alga, widely distributed in the Northern Hemisphere. In contrast, B. lauterborni, one of the rarest algae globally, has been reported in only four glacial Alpine lakes and has not been observed in nature for nearly 50 years. Since 2019, the species has been considered locally extinct at its type locality, and its presence in the other three lakes is also questionable. Here, we report the occurrence of B. lauterborni in three springs on the Vlasina Plateau (Southeast Serbia), being the first finding of the species in Southeast Europe and the fifth discovery globally in environmental conditions not previously described for the species. We also provide detailed data on the morphology, ecology, and biogeography of B. lauterborni and H. fluviatilis. Additionally, we report the non-obligate association Hildenbrandio rivularis-Heribaudielletum fluviatilis discovered in two rivers. Our findings significantly expand the known ecological and geographical range of phaeophytes, highlighting Southeast Europe as a refugium for freshwater Phaeophyceae biodiversity. Full article

The jacket platform has been widely used in offshore oil and gas development during the past several decades and faces the problem of decommissioning now due to approaching the design life. During the decommissioning process of a jacket platform, cutting the pile chords is one of the most important steps for removing the jacket. In the process of cutting, the freedom of the bottom of the jacket increases, decreasing its stability and potentially causing structure damage or failure. In this paper, the influence of the cutting sequences (cross-circulation cutting and clockwise-circulation cutting), offshore environmental conditions, and the overall weight of the jacket on the mechanical responses of the jacket platform during the cutting operation was investigated by using the commercial finite element package, SACS. The numerical results show that (1) during the circular cutting process, there is a negative correlation between the unit check (UC) values of the diagonal leg chords: the UC value of the leg chord at diagonal positions decreases by approximately 10%, and the final round of cutting is critical because the jacket platform has a high risk of failure with the UC value being likely to exceed 1.0; (2) the UC value of the piles downstream is 0.2 or much larger than that of the piles upstream, which controls the stability of the jacket during the cutting process; (3) the UC value at the skirt pile of the jacket roughly increases linearly with the weight of the jacket. Full article

As a core area for soil and water conservation on the Loess Plateau and a national primary shale oil production zone, Qingyang City faces an increasingly acute contradiction between its inherently fragile ecological base and energy development activities. From the dual perspectives of ecological regulating services and production-supporting services, this study selected six key ecosystem services—habitat quality (HQ), soil retention (SR), carbon storage (CS), water yield (WY), food supply (FS), and grassland forage supply (GS)—to comprehensively assess their spatiotemporal evolution, trade-off/synergy relationships, and driving mechanisms from 2000 to 2020. The results indicate: (1) Significant changes occurred in the total amounts and spatial patterns of all ecosystem services during 2000–2020. HQ showed a fluctuating upward trend, while SR, FS, and GS increased overall; by contrast, CS and WY generally declined. (2) Ecosystem services exhibited a differentiated pattern characterized by “intra-category synergy and inter-category trade-off.” Regulating and supporting services were generally dominated by synergistic relationships, although clear differences remained among specific service pairs; provisioning services generally showed trade-offs with regulating services, among which the trade-offs between FS–HQ and between FS–GS were the most pronounced, whereas FS–CS showed a certain degree of synergy. (3) Driving force analysis revealed a continuous decline in the influence of natural factors and a sharp intensification of human activity factors. Groundwater level and land-use intensity became core drivers of pattern shifts, with their explanatory power increasing significantly. The study reveals that ecosystem services in Qingyang have rapidly transitioned from being dominated by natural hydrothermal conditions to being profoundly reshaped by energy development activities, exposing the region to the ecological risk of a “resource curse.” These findings provide a scientific basis and management insights for achieving coordinated development between resource exploitation and ecological conservation in ecologically fragile areas of the Loess Plateau. Full article

Due to the highly complex geological environment of the Tibetan Plateau, landslides occur frequently, and signs of ancient landslide reactivation are widespread, posing significant threats to major infrastructure and local communities. Taking the Lumei landslide in Cuomei County as a case study, detailed field investigations were conducted, and Sentinel-1A SAR data (84 scenes from January 2017 to December 2023) were collected to characterize surface deformation. Both PS-InSAR and SBAS-InSAR methods were applied for long-term time-series monitoring, and the results of the two techniques were comparatively analyzed. Furthermore, the influencing factors of landslide deformation were explored on the basis of analyzing the deformation characteristics. The findings reveal that the surface deformation rate exhibits significant spatial heterogeneity, with deformation values decreasing progressively outward from the central region. The surface deformation rates obtained from PS-InSAR and SBAS-InSAR range from −36.55 to −21.81 mm/yr and from −30 to −10 mm/yr, respectively. Both methods indicate a general subsidence trend along the line-of-sight (LOS) direction and show strong spatial consistency and high correlation. By combining the high-precision point results obtained from PS-InSAR and the spatially continuous surface results derived from SBAS-InSAR, the fine spatial deformation characteristics of the Lumei landslide are revealed. The research results can provide an important reference for landslide monitoring, disaster prevention and mitigation in this region. Full article

We report the discovery of a new palaeoscolecid worm specimen from the Bainiuchang area, southeastern Yunnan, China. The specimen exhibits a cylindrical body with annulations, each bearing two rows of Hadimopanella-type sclerites, along with plates, platelets, microplates, and implanted plates. These features are compatible with the diagnosis of the genus Wronascolex, and the specimen is tentatively assigned to Wronascolex sp. However, given the limited number and preservation of the available specimens, which preclude a detailed demonstration of the scleritome morphology for comparison with other palaeoscolecid worms, this assignment should be treated as tentative. This specimen may be the first record of a soft-bodied fossil from the Miaolingian Series (Wuliuan Stage) strata of southeastern Yunnan. Its taphonomic features—preservation as carbonaceous compressions accompanied by iron-rich films—are broadly consistent with Burgess Shale-type (BST) preservation. Whole-rock geochemical analysis of samples from the fossil-bearing interval yielded redox proxy values suggestive of suboxic to weakly reducing depositional conditions, broadly comparable to those reported from some BST deposits, such as the Mackenzie Mountains locality of Canada. However, these geochemical results are preliminary and based on a limited number of samples. Taken together, these observations suggest the possibility that the Bainiuchang area may host a BST Lagerstätte. Should this be confirmed, such a deposit would postdate the Chengjiang and Guanshan biotas (Cambrian Series 2, eastern Yunnan) and predate the Fulu biota, which is the only confirmed BST Lagerstätte in southeastern Yunnan to date. Furthermore, this discovery extends the known paleogeographic range of the genus Wronascolex southward to the southwestern margin of the South China Block. It also represents, to our knowledge, the first reported occurrence of soft-bodied fossil preservation in the Wuliuan Stage of Yunnan Province. Full article

Shale gas exploration in the Shixi block, Guizhou, faces significant challenges due to complex geological structures and normal pressure. To reduce exploration risk, we propose an integrated “Four-in-One” evaluation workflow that combines geological sweet spots, engineering feasibility, preservation conditions, and paleogeomorphology. The workflow features a ‘cap-constraint’ velocity model to reduce structural uncertainty and a tiered multi-scale discontinuity detection strategy for low-SNR seismic data. Application of this workflow in the Shixi block delineated two Class I favorable zones (42.61 km²) with estimated resources of 8.33 billion cubic meters. Drilling results from 56 horizontal wells validate the accuracy of our prediction model, confirming that preservation condition is the primary controlling factor for gas accumulation in this normally pressured setting. This study provides a practical reference for shale gas assessment in structurally complex, normally pressured regions. Full article

The presence of source rock with a high concentration of kerogen is not a sufficient condition for petroleum formation, as maturation requires specific thermodynamic conditions. In this study, the artificial maturation of organic matter was investigated through hydrothermal treatment simulating the vaporization–condensation zones associated with in situ combustion and steam-assisted recovery processes. The experiments were conducted under an inert nitrogen atmosphere at 250–350 °C to reproduce oxygen-depleted thermal environments where hydrothermal reactions dominate. The results demonstrate that the bitumoid yield increases with temperature, reaching a maximum of 4.44 wt.% at 300 °C, followed by a decline at 350 °C due to secondary cracking. At the same time, gas generation increases significantly, with a more than five-fold rise in total gas yield between 250 and 350 °C. In parallel, the H/C atomic ratio of kerogen decreases from 1.17 in the initial sample to 0.52 at 350 °C, indicating progressive aromatization and advanced catagenetic transformation. These changes are accompanied by the conversion of high-molecular-weight kerogen into resins, asphaltenes, and subsequently lighter hydrocarbons. The study provides experimental evidence for the effectiveness of hydrothermal processes in inducing kerogen transformation under inert conditions, offering insights into the mechanisms governing artificial maturation in unconventional reservoirs. Full article

In order to reduce the environmental pollution caused by waste white mud from the papermaking process, this paper proposes a new method of preparing lightweight concrete using waste white mud and shale ceramsite, aiming to provide a new approach for the recycling of papermaking waste. The main objective of this study is to investigate the feasibility of utilizing paper-making white clay as a cement replacement in lightweight concrete and to systematically evaluate the influence of key parameters, such as white clay content, on its fundamental mechanical properties. Based on lightweight ceramsite concrete, paper-making white clay was used to replace cement in preparing white clay lightweight concrete. Through orthogonal tests, mix proportion design and optimization were carried out, and the effects of factors like water–binder ratio and white clay content on the compressive strength, splitting tensile strength, and early-age cracking resistance of the concrete were studied. The results show that with the increase in white clay content, the cube compressive strength of concrete first increases and then decreases. When the white clay content is 5%, the splitting tensile strength of the concrete is the highest at all ages, and when the white clay content is 15%, the internal structural compactness of the concrete is optimal. Full article

Highly deviated wells commonly exhibit large errors in horizon calibration because the logging path follows an inclined borehole trajectory, whereas post-stack seismic processing effectively treats wave propagation as vertical. This mismatch has received limited attention. Here, we performed horizon calibration and velocity-model building for highly deviated wells drilled in the Mahu Sag, Junggar Basin, and obtained three key findings. First, the assumed vertical travel path in post-stack data is the primary cause of the initial mis-tie for highly deviated wells. Second, calibration in the deviated interval requires a strategy distinct from that of vertical wells and may involve substantial stretching or squeezing of the original logs to achieve a consistent time-depth relationship. Third, the map-view projection of a highly deviated well is essentially linear; relative to vertical wells, it provides denser in situ velocity constraints and, with pseudo-well control, supplies 2D velocity information along the well-trajectory plane, thereby improving velocity-field modeling. Validation against drilling data showed that this workflow improved well ties and refined the velocity model, providing practical guidance for geological well planning and reducing drilling risk. Full article

The Jimusar shale reservoir exhibits extremely low permeability, classified as an ultra-low porosity and ultra-low permeability formation. Crude oil mobility is poor, and the reservoir demonstrates significant heterogeneity. Conventional horizontal well fracturing development fails to meet requirements, facing issues such as pronounced energy depletion in the formation, unclear oil–water distribution, and changes in formation stress direction. Based on the reservoir properties of the Jimusar shale oil reservoir, this paper establishes a fracture propagation model for horizontal wellbore hydraulic fracturing and a reservoir numerical model. It simulates the evolution of pressure fields, stress fields, and seepage fields at different time points during the fracturing and production phases of horizontal wells. Results indicate the following: (1) When fracturing fluid is injected into the formation, oil saturation around fractures rapidly decreases. During the initial production phase, oil saturation around fractures increases due to the recovery of some fracturing fluid and the sorption effect between fracturing fluid and crude oil. (2) Formation pressure around horizontal wells significantly increases upon fracturing fluid injection. The dual effects of fracture opening and fluid injection cause stress to rise near fractures. During production, both formation pressure and stress decrease near the wellbore, with greater pressure reduction in the near-wellbore zone than in the far-wellbore zone. However, formation stress decreases less near the wellbore due to stress concentration effects from fracture opening, resulting in a smaller reduction than in the far-wellbore zone. (3) The formation surrounding the fracture undergoes dual influences from fracture opening and fracturing fluid injection, causing deflection in the direction of near-wellbore stress. During the initial production phase, the impact of stress deflection gradually diminishes with ongoing production. However, after prolonged production, the deflection of formation stress intensifies. The conclusion states that this understanding clarifies the multi-field evolution patterns in fracturing production for horizontal well clusters, providing theoretical guidance for subsequent shale development processes. Full article