Objective Deep carbonate reservoirs have an enormous potential for oil and gas exploration. However， due to their complex diagenesis， they are highly heterogeneous and dense. To clarify the modifying effect of hydro-thermal fluid activity on the carbonate reservoirs in a petroliferous basin， this study investigated Upper Carboniferous strata in the southwestern Tarim Basin. Methods The main study area includes some key well locations in the Bachu Uplift and Maigaiti Slope， and typical field outcrop profiles in the Kunlun piedmont thrust belt. Previous research on hydrothermal fluid activity has mainly focused on the northern and Tazhong region of the Tarim Basin， mostly concentrating on the Ordovician System. These studies have accumulated rich experience and obtained many results； however， generally little exploration has been carried out in the southwestern Tarim Basin. To strengthen the basic research， the method of combining geology and geochemistry was adopted in the study area： core observation， thin sections， cathodoluminescence， scanning electron microscopy， isotope data， rare earth element characteristics and previous information were used to identify the indicators of hydrothermal activity in the target formation， defining the alteration mode of carbonate reservoirs in the study area and establishing their logging responses to alteration by the heated fluid. Results A detailed classification of the petrology of the study area found that the presence of typical hydrothermal minerals （e.g.， fluorite， barite， and saddle-shaped dolomite） is an indicator of hydrothermal fluid activity. The geochemical responses of these carbonate rocks to modification by hydrothermal fluids includes high ⁸⁷Sr/⁸⁶Sr values， very low δ¹⁸O， light rare earth element enrichment， loss of heavy rare earth elements， and positive Eu anomalies. Hydrothermal fluids often contain many chemically active substances and release a large amount of heat energy in their interaction with rock and produce physical and chemical reactions with the rock. In particular， such reactions promote strong dissolution of carbonate rocks. Conclusions It has been demonstrated that hydrothermal fluids have both positive and negative effects on the alteration of carbonate rock reservoirs. In the constructive role， the high temperature and rapid flow rate of hydrothermal fluids have strong chemical dissolution and mechanical erosive effects on the rock， expanding migration channels， increasing reservoir porosity， improving pore structure， and generally enhancing reservoir physical properties. Most of these occur at the earliest stage of hydrothermal activity and in the proximity of fault zones. They are identified in the logging response by high acoustic time difference， neutron porosity， low natural gamma and low resistivity values. The dissolution pores and fractures are developed over a large zone， and most are not filled. Conversely， a destructive effect occurs at lower temperature and pressure of the hydrothermal fluid， and is recognized by hydrothermal mineral infill in pores and fractures. As the fluidity decreases， the material carried by the hydrothermal fluid is constantly precipitated， forming new mineral combinations filling pre-existing pores and fractures， which reduces reservoir porosity and damages pore structure. This type of alteration mostly occurs in the late stage of hydrothermal activity far from the fault zone. It is evident in logging response by high resistivity and low natural gamma and acoustic time difference， and low neutron porosity； the pores and fissures are mostly isolated and extensively filled. Overall， however， the target strata were mainly affected by constructive hydrothermal dissolution and its positive impact on reservoir development.

Objective In geological logs of shale oil cores from the Chang 7 oil member of the Yanchang Formation in the Longdong region， Ordos Basin， for a long time the resolution of single layer thickness of each rock type has been basically 10 cm， resulting in a large number of rock-type combinations being described as a single rock type. Exploring a new method for the quantitative study of shale oil rock-type combinations and reservoir capacity benefits the efficient exploration and development of shale oil in the Chang 7 oil member. Methods In this study， the shale oil rock types in the Chang 7 oil member were re-identified by high-resolution core observation （single layer thickness resolution 1-5 cm） together with stereo microscope and thin-section identification of 405 samples and analysis of physical property data， then the rock-type combinations and reservoir capacity of Chang 7 oil member were explored quantitatively. Results There are 11 main rock types in the shale oil of Chang 7 oil member of the Yanchang Formation in the Longdong region of the Ordos Basin. Firstly， four combinations of rock-type form （unitype， stratified type， interstratified type and interstratified type） and 65 rock-type combinations were quantitatively identified for the first time. Secondly， a new method is proposed for calculating reservoir capacity on the basis of quantitative evaluation of the reservoir capacity of each of the 11 rock types， combined with the thickness percentage of each rock type， for 65 rock-type combinations. Conclusions This study demonstrates that， to guide the efficient exploration and development of the shale oil in the Chang 7 oil member， the traditional single rock-type study for shale oil should be modified to encompass the study of rock-type combinations. However， this research for the Chang 7 oil member is at the exploratory stage； further improvement will be achieved by examining the effect of combining these findings with a large amount of shale oil exploration and development data.

Objective In this study， the effect of seasonal lake level changes on the sedimentary characteristics， growth process， and sedimentary architecture of the finger bar in shallow delta fronts is clarified. Methods Based on the modern mud and sand and hydrological data of finger bar in the Ganjiang Delta， sedimentary numerical simulation software Delft3D， which is commonly used in China and elsewhere， is used to conduct numerical simulation of the sedimentation of the finger bar under seasonal lake level changes and constant lake level conditions， comparing the differences in sedimentary architectures. Results The study shows that under seasonal lake level changes， the finger bar exhibit the following sedimentary architecture and growth evolution characteristics： （1） There are few finger bar， small curvature （average ~1.42）， long length （average ~9.2 km）， thick in the middle， and thin at the edge， with a thickness difference of 15.4 m. There is no evident confluence between the finger bar， presenting a plane combination style dominated by bird-foot shape. （2） The finger bar develop deep distributary channels， the natural levees are wide and thick， and the thickness of the single-stage accretionary body in the mouth bar is large. （3） The finger bar exhibit stable growth. During lake level drop， the finger bar undergo progradation， the distributary channels are mainly eroded-extended， and mouth bar deposits are formed at the front edge of the distributary channels. The distributary channels are also affected by the mouth bars and undergo diversion and breach， forming multiple terminal distributary channels， and the natural levees are almost undeveloped； during lake level rise， the finger bar undergo retrogradation， the erosion of the distributary channels is weak， the distributary channels are abandoned and optimized， and the natural levees on both sides of the distributary channels accumulate and continue to thicken. For constant lake level， the finger bar show the following sedimentary architecture and growth evolution characteristics： （1） There are many finger bar， with large curvature （average ~1.53）， short length （average ~7.2 km）， large overall thickness （maximum and minimum thickness differ by only 4.8 m）， and no evident topographic difference； multiple finger bar are constantly bifurcated and merged locally， forming a complex the finger bar network， and the plane combination style of the finger bar is mainly interlaced. （2） Deep distributary channels are developed in the finger bar， the single-stage accretion body of the estuary bar is thick， but the most important difference is that there is no natural levee deposition. （3） The growth process of the finger bar is relatively simple， with multiple the finger bar growing simultaneously， intertwining with each other， and finally forming an interlaced plane combination style. Conclusions Therefore， seasonal lake level change is an important formation condition for the finger bar at the front of shallow deltas， promoting the development of natural levees， improving the stability of distributary channels and the finger bar， and playing an important role in controlling the sedimentary architecture and growth process of the finger bar.

Objective The reservoirs in the bottom conglomerate of the Qingshuihe Formation in the Gaoquan structural zone of the Sikeshu Sag， southern Junggar Basin， are strongly heterogeneous. The objective was to clarify the development and distribution of high-quality reservoirs in the study area. Methods The sedimentary and reservoir characteristics of the Qingshuihe Formation were examined by facies analysis in cores， well logs and seismic records， and a model of the sedimentary evolution was established based on paleogeomorphological data. The influence of microgeomorphology on the distribution of high-quality reservoirs is clarified. Results Three slope breaks developed in the Gaoquan structural zone， each striking northwest-southeast and comprising groove and platform paleogeomorphological units. A regressive fan delta was formed on the slope breaks during lake transgression， each of which formed conglomerate reservoirs 10-15 m thick. Groove and platform areas controlled the mud content of the reservoirs. Brown conglomerate with high mud content readily developed in the groove areas. Gray or gray-green conglomerate with low mud content developed in the platform areas， forming high-quality reservoirs. Conclusions Groove/platform units at slope breaks controlled the formation and distribution of high-quality reservoirs in the Qingshuihe Formation. The most favorable reservoirs in the study area are in the platform units at each slope break.

Objective In the middle and late stages of oil and gas field development， studying sand architecture is the key to accessing residual oil and enhancing recovery. Precise interpretation of similar outcrops provides a comparable prototype model for predicting underground reservoir architecture. Methods The shallow-water delta profiles of the Yan’an Formation in the Kaokaowusugou and Gulf Mining Industry in the Ordos Basin were the research objects. UAV oblique photography was used to obtain images of massive outcrops from which 3D digital outcrop models were established. Detailed interpretation of digital outcrop architecture was then carried out by combined field observation and indoor analysis. Results Developmental characteristics and evolutionary models of shallow-water delta front architecture during a time of rising lake levels were defined. When the lake level is low， mainly trunk-type distributary channels are developed， measuring 23.30-48.40 m wide × 0.89-1.81 m thick， with an average width-to-thickness ratio of 26.74. The sandbody superposition patterns are mainly overlay type. As the lake level rises， fork-type distributary channels， mouth bars， sand sheets and subaqueous distributary bays gradually develop. The width of the mouth bar is 53.90 m， thickness is 2.21 m， width-to-thickness ratio is 24.39， and the sandbody superposition patterns is mainly lateral splicing type. When the lake level is higher， mainly terminal-type distributary channels， mouth bars and sheet sand architectural units are developed. Terminal-type underwater distributary channels， which are isolated in muddy deposits， have widths ranging from 4.70 to 25.30 m， thickness from 0.40 to 1.03 m， and the width-to-thickness ratio from 11.75 to 24.56. Conclusions When the source supply of material is relatively stable， an increase in lake level enlarges the accommodation space. The architectural units evolve from trunk-type to terminal-type distributary channels， depositing mouth bars and sand sheets. The size of the sandbody decreases， but its width-to-thickness ratio increases. Overall， the ratio between sandstone and stratum thickness decreases， spatial connectivity decreases， and reservoir heterogeneity is enhanced.

Objective The architecture of marine sandy beach-bar reservoirs is complex， and dominant seepage channels and barriers are developed. The current lack of architecture models for underground reservoirs means that there are few effective guidelines for the recovery of residual oil. Methods A system is proposed for recognizing the architecture patterns of marine sandy beach-bar reservoirs from outcrops in the Hudson Donghe sandstone， obtained through the use of satellite photographs and numerical simulations. Results The depositional architecture of individual sand bars within composite beach-bars is affected by many factors （e.g.， shoreline shape， coastal slope， wave direction and height）. Multiple types of sandbar may be formed （e.g.， conical bar， crescent-moon-shaped bar， positive linear bar， nonlinear inclined bar and sandy beach bar）. Based on the identification of boundaries between individual sandbars， and guided by the architecture mode， 13 sandbars of different sizes were identified in the C1 layer in the study area， comprising five crescent-moon-shaped bars， seven forward linear bars and one oblique bar. Differences in scale are evident between different sandbar types： the length of crescent-moon-shaped bars is about 1.5-3.0 km； the length of oblique bars is about 4.5-5.0 km； and the length of positive linear bars is more than 6 km. The sandbars exhibit either progradational or retrogradational stacking patterns； bars in the C1 layer exhibit progradational lateral separation and progradational lateral stacking patterns. The migration rate of the coastline has affected the stacking relationship between the sandbars. Numerical simulations and outcrop observations indicate differences in the developmental patterns of the internal accretion bodies， including top accretion， top- and side accretion， and different interval types. Three internal interlayer patterns were identified in the C1 layer： a two-stage “top- and side-accretion” feature in the No. 16 sandbar， and “side accretion” in the No. 19 sandbar. The slopes of the top and side accretion interlayers range from about 1°-3° to 3°-7°. The layers between No. 14 and 15 sandbars are arranged in an “interval” pattern. Conclusions The fine characterization of the internal architecture of marine sandy beach-bar reservoirs described in this study can effectively guide the recovery of remaining oil.

Objective The Late Triassic was a crucial period for the Mesozoic Qiangtang Basin evolution. However， the previous research concentrating on the sedimentology of the Upper Triassic strata is rare in the Qiangtang Basin， making it not conducive for elaborately analyzing the characterization of Late Triassic sedimentary evolution and predicting the distribution of source and reservoir rocks. Methods Based on the measured section， we synthesized the thin section， grain size of detrital particle， and typical primary sedimentary structure to identify the sedimentary facies of the Jiapila Formation， Bolila Formation， and Bagong Formation in the Jiang’ai Darina section and then establish the Late Triassic sedimentary evolution model in the central Qiangtang Basin. In addition， the whole-rock and clay minerals， physical properties， and total organic carbon （TOC） contents of sandstone and mudstone samples were analyzed to evaluate the characteristics of source and reservoir rocks. Results （1） In the Jiang’ai Darina section， the sedimentary facies of the Upper Triassic strata have experienced the evolution of the fan-delta facies → barrier-free coastal facies → carbonate ramp facies → neritic shelf facies → delta facies upward， and ten subfacies and eight microfacies were identified. （2） The Upper Triassic strata in the study area constitute an upward deepening transgressive succession and then a shallower regressive succession. The transgressive succession is mainly composed of the Jiapila Formation and Bolila Formation， whereas the regressive succession is primarily composed of the Bagong Formation. （3） The sandstone samples from the Jiapila Formation and Bagong Formation are ultra-low porosity and permeability reservoirs with secondary pores primarily. The mudstone samples of the Bagong Formation from the Jiang’ai Darina section are poor source rocks and non-source rocks， whereas they improve to the north （Woruoshan section）. We inferred that the depression between Jiang’ai Darina and Woruoshan may develop well source rocks and have a good exploration prospect based on the latest tectono-lithofacies paleogeographic data， but confirmation is required. Conclusions These results would provide a valuable reference for the researches of Late Triassic sedimentary-tectonic evolution and oil and gas resource evaluation in Qiangtang Basin.

Objective The Carnian Pluvial Episode （CPE） was a critical climatic perturbation in the Late Triassic， marked by a pronounced transition to warmer and more humid conditions. These environmental changes sub-stantially facilitated the accumulation of fine-grained sediments and the enrichment of organic matter. This study aims to elucidate the sedimentary and geochemical responses of Chang 7 member of the Yanchang Formation in the Ordos Basin to the CPE， by examining thick successions of organic-rich black shales. Methods A multi-proxy analytical approach was employed using core samples from well ZK903. Biomarker compounds serve as the principal dataset， supported by analyses of organic carbon isotopes， trace element geochemistry， and clay mineral assemblages. These proxies were used to reconstruct the paleoclimatic conditions， redox environment， paleosalinity， and organic matter sources across Chang 7 member to Chang 8 member. On this basis， an organic matter enrichment model was developed to interpret the basin’s response to the CPE. Results In the Ordos Basin， the Chang 7₃ submember records a distinct lithological transition from sandstone to black shale， signaling intensified influence from the CPE and progressively increasing organic matter accumulation. Geochemical proxies， including Sr/Cu and Sr/Rb ratios， together with clay mineral data， indicate a climatic shift from arid-hot to warm-humid conditions. Redox-sensitive parameters such as V/Cr and U/Th， along with biomarker ratios （Pr/Ph and Ts/（Ts+Tm））， point to a significant reduction in bottom-water oxygen levels during this interval. Additionally， increased Sr/Ba ratios and a higher gammacerane index （GI） suggest elevated precipitation and lake-level rise， which led to enhanced water column stratification and diminished vertical mixing. These conditions promoted the development of a freshwater， anoxic environment conducive to the preservation of organic matter. Notably， elevated values of ∑C{}_{{\mathrm{21}}^{-}} /∑C{}_{{\mathrm{22}}^{+}} and C₂₇/C₂₉ （ααα）R ratios in the Chang 7₃ interval indicate a shift in the biotic community structure， with a dominance of lower aquatic organisms， particularly algae， as the primary contributors to the organic matter pool. Conclusions The CPE exerted a profound influence on the paleoclimate and depositional dynamics of the study area. Enhanced thermal and hydrological conditions， in conjunction with lake stratification， promoted the accumulation of fine-grained sediments and created favorable conditions for both primary productivity and the preservation of organic matter. These factors jointly facilitated the formation of organic-rich black shales （oil shales） in the Yanchang Formation， underscoring the role of global climatic events in shaping regional hydrocarbon potential.

Objective The geological conditions in the Junggar Basin hinterland are diverse， and the crude oil properties are complex. To address the issues of crude oil type classification and oil and gas source identification in this area， a study was conducted on the hydrogen isotopic characteristics of n-alkanes （δ²H_alk） in the mixed-source crude oils from the Junggar Basin hinterland. Methods Gas Chromatography-Mass Spectrometry （GC-MS）， Gas Chromatography-Isotope Ratio Mass Spectrometry （GC-IRMS） and Gas Chromatography-Thermal Conversion-Isotope Ratio Mass Spectrometry （GC-TC-IRMS） techniques were employed to analyze biomarker compounds and conduct hydrogen isotope analysis of n-alkane monomers in 33 crude oil samples from different strata. Results Three types of crude oil were identified in the Junggar Basin hinterland： Type I originated from the Jurassic coal-bearing source rocks （J₁b）， with the lightest hydrogen isotopic composition due to the significant input of terrestrial higher-plant organic matter； Type II mainly originated from the Permian Fengcheng Formation source rocks （P₁f）， with Type II_A derived from lacustrine sedimentary environments in transitional marine-terrestrial settings， featuring a low Ga/C₃₀H ratio and relatively heavy hydrogen isotopic composition， while Type II_B had a lighter hydrogen isotopic composition and a higher Ga/C₃₀H ratio； Type III crude oil mainly originated from the Permian Lower Wuerhe Formation source rocks （P₂w）， with a light hydrogen isotopic composition of n-alkanes. Conclusions The combination of hydrogen isotopic analysis of n-alkanes and biomarker compound analysis is able to precisely classify crude oil types and clarify their sources， which is highly significant for oil source tracking and crude oil classification throughout the Junggar Basin.

Objective Climate change caused by astronomical orbital parameters is closely related to biological turnover and sedimentary evolution of the ocean and lakes， which in turn affects the organic matter enrichment in the strata. The Late Paleozoic coal-bearing rock system in North China is dominated by coal， mudstone， siltstone， sandstone and tuff observed in a number of depositional cycles in the vertical direction. It is also an important system for current oil and gas exploration and development. The aim of this study is to systematically reveal the influence of the astronomical orbital cycle on organic matter enrichment in this coal-bearing system. Methods Natural gamma logging sequences were obtained for four wells （sampling distance 0.05 m） and continuous mineral elements for one well （sampling distance 1 m） in western North China. Astronomical cyclotron time series data and elemental geochemical analysis of typical samples were used to clarify the pattern of organic matter enrichment in stratigraphic cyclotrons at different scales. Results （1） Six 1.2 Myr ultra-long obliquity cycles and eighteen 405 kyr long eccentricity cycles are recognizable in the Carboniferous-Permian Benxi Formation， Taiyuan Formation and Shanxi Formation. （2） Using Mg/Ca， SiO₂/Al₂O₃， Fe/Mn and V/（V+Ni） ratios as paleoclimate and paleoredox proxies， six long-period variations and 18 medium-period variations were identified， all corresponding with ultra-long obliquities and long eccentricities. （3） Comparative analyses of paleoenvironmental restoration and organic carbon content during the depositional period of the Benxi Formation-Shanxi Formation show that paleoclimate evolution and organic matter enrichment are basically synchronized and controlled by the astronomical orbital cycle， and that during periods of increasing ultra-long obliquity or long eccentricity the climate is warm and humid and the reducing nature of bodies of water is enhanced， which promotes organic matter enrichment. Conclusions The above results reveal Carboniferous-Permian climate change in North China influenced by the astronomical orbital cycle and the development of a constrained organic matter-rich sedimentary system， and find that the paleoclimate change during the same period was obviously constrained by the long eccentricity. The findings can be used as a reference for the study of global climate evolution and organic matter enrichment mechanism in the Permian.