The Kuqa Depression, a prolific hydrocarbon province in China's Tarim Basin, hosts a dual-sourcepetroleum system with Jurassic coal-bearing and Triassic lacustrine strata. However, the origins and accumulation mechanisms of hydrocarbons in the Dibei Structural Belt remain contentious, particularlyregarding contributions from Jurassic (J(2)kz, J1y) versus Triassic (T(3)h, T(2-3)k) source rocks, compoundedby ambiguities in biomarker interpretations and uncalibrated thermal models. Advanced geochemicalfingerprinting - including sterane distributions, gammacerane indices (GI; ratio of gammacerane to C30hopane), and delta & sup1;& sup3;C isotopes - was integrated with calibrated burial-thermal modeling and structural analysis,which allowed us to clarify source contributions, hydrocarbon charging history, and structural controlson accumulation. Geochemical results demonstrated that Yangxia Formation (Paleogene; a major regionalseal and secondary reservoir unit within the Kuqa Depression) oils exhibit "inverted-L" sterane patterns(C27 < C29) and delta & sup1;& sup3;C values of -26 parts per thousand to -23 parts per thousand, confirming derivation from Jurassic coal measures. Incontrast, Ahe Formation (Jurassic; a major regional sandstone reservoir unit within the Kuqa Depression)hydrocarbons displayed "V-shaped" sterane ratios (C27 > C29), delta & sup1;& sup3;C values of -32 parts per thousand to -30 parts per thousand, and elevatedGI (0.21-0.32), indicative of Triassic lacustrine sources. Notably, the identification of Triassic-sourcedhydrocarbons in deep Ahe reservoirs challenged previous Jurassic-centric models, resolving ambiguitiesthrough multiproxy integration. Burial-thermal modeling, constrained by fluid inclusion homogenizationtemperatures (80 degrees C-160 degrees C), revealed three charging phases: phase I (19-16 Ma, Jidike Fm.), phase II (16-12 Ma, Kangcun Fm.), and phase III (5-1 Ma, Kuqa Fm.), with phase III Himalayan tectonics criticallyreshaping paleo-accumulations into an inverted "gas-below-oil" stratification (phase reversal due to tectonicreorganization). Structural analysis revealed (1) two boundary-fault anticlinal traps (defined by opposednorth- and south-dipping thrust faults) with vertical gas migration in Ahe sandstones and (2) fault-sealed tightgas accumulations controlled by reservoir quality. These findings highlighted the dominant contribution ofTriassic sources to deep gas reservoirs in Dibei and underscored the importance of multiphase tectonicevolution and source-reservoir coupling. This study provided a predictive framework for hydrocarbonexploration in fold-and-thrust belts, advocating prioritized assessment of fault connectivity and Triassicsaline lacustrine source deposits.

Taking the Middle-Upper Cambrian Xixiangchi Group in the central-southern Sichuan Basin as an example,this study investigates the sedimentary characteristics and evolutionary history of tempestites using field outcrop,core,thin-section and logging data,and elucidates the patterns and processes by which storms have reworked grain shoal reservoirs in carbonate platforms,thereby identifying the zones with favorable reservoirs.The results indicate that:(1)The Xixiangchi Group develops massive storm deposits,with five intervals occurred in a complete storm sedimentary sequence;Xixiangchi Group exhibits six typical storm depositional sequences,with storm-related grain shoals developed in settings such as mixed tidal flats,intra-platform depressions,and margins of the intra-platform depressions.(2)During the deposition of the Xixiangchi Group,storm activities were mainly in the southeastern,central and southwestern parts of the Sichuan Basin.Overall,storm action showed an initial increase followed by a decrease.(3)The impact of storms on the reworking of grain shoal reservoirs varies across different facies zones.The intra-platform depression margins,influenced by storm centers,experienced strong reworking,leading to the vertical stacking of storm-related grain shoals and normal grain shoals,which expands the scale of the shoal complex.Furthermore,storms enhance the penecontemporaneous dissolution,favoring the development of large-scale high-quality reservoirs.The intra-platform depressions and mixed tidal flats,controlled by the storm centers,were weakly modified,possibly inducing scattered storm-related grain shoals under low-energy conditions.The degree of karst modification is generally low,and local conditions are favorable for reservoir development.(4)The Dazu-Hechuan-Guang'an area,strongly reworked by storm activities,exhibits a large scale of storm-related grain shoals with good physical properties,providing favorable conditions for the development of contiguous,high-quality grain shoal reservoirs,so it can be regarded as a key target for subsequent exploration of the Xixiangchi Group.

Multiple sets of the carbonate-evaporite paragenesis systems developed in the Cambrian Longwangmiao, Gaotai, and Xixiangchi formations in the Sichuan Basin, rich in hydrocarbon resources. However, the lack of understanding of their development characteristics and sedimentary evolution hampers hydrocarbon exploration. Based on the comprehensive database of core, thin section, logging, seismic data, and high-resolution lithofacies paleogeographic mapping, the types of lithofacies association, sedimentary facies, and model, and hydrocarbon potential were discussed. The carbonate-evaporite paragenesis system shows six types of lithofacies association: gypsum dolomitic flat-grain shoal; dolomitic-argillaceous lagoon-grain shoal; gypsum lagoon-grain shoal; calcareous-dolomitic(argillaceous-dolomitic) lagoon-evaporation lagoon; argillaceous dolomitic flat-gypsum dolomitic flat; and gypsum lagoon-salt lagoon. The Cambrian in the Sichuan Basin is characterized by tidal flat, lagoon, carbonate platform, and evaporite platform combination sedimentary system, indicative of a depositional paleogeographic pattern of one depression within two uplifts. The Longwangmiao Formation is carbonate ramp sedimentary model, with well-developed medium-scale gypsum lagoons and grain shoals. The Gaotai Formation shows two well-developed large gypsum-salt lagoons in the eastern and southern Sichuan regions. Small-scale grain shoals are distributed at the edge of the lagoon, and large-scale high-energy grain shoals are distributed at the platform margin. Grain dolostone shows rich intergranular dissolved pores or vugs. The high-quality hydrocarbon source rocks of the Qiongzhusi Formation superimpose caprocks of thick evaporite of the Gaotai Formation and mixed rock of lower member of the Xixiangchi Formation. This indicates that the sub-salt of the Longwangmiao and Canglangpu Formation, post-salt of the Xixiangchi Formation, and inter-salt of the Gaotai Formation yield great potential for hydrocarbon accumulation. This study provides new insights and methods for the hydrocarbon exploration of the carbonate-evaporite paragenesis system in Sichuan Basin.

Since transmission losses, internal multiples, and mode conversions are not considered, conventional inversion methods based on the Zoeppritz equations and related approximations have limited capability in high-resolution inversion of thin interbeds. Reflectivity methods, which account for these wave propagation effects, are more suitable for inverting thin interbeds; however, most related studies approximate thin interbeds as several isotropic thin beds, which are inadequate for complex thin interbeds containing thin vertical transverse isotropy (VTI) beds. In this study, thin VTI beds with the characteristics of short-term cycles are regarded as the fundamental compositional units of thin interbeds. We propose a joint PP- and PS-wave amplitude variation with angle inversion method for thin interbeds containing thin VTI beds. The method uses second-order approximations to the Kennett equations for thin interbeds containing thin VTI beds as the forward operator. The inversion objective function is established using the Levenberg–Marquardt algorithm, incorporating sparse constraints to improve the stability and resolution of the five-parameter inversion. Inversion results from model tests and field data demonstrate that the proposed method more accurately extracts elastic parameters and anisotropic information from thin interbeds compared to conventional methods based on the exact Zoeppritz equations, effectively improving inversion accuracy and offering a technical advancement for fine prestack inversion of complex thinly interbedded reservoirs.

Based on microscopic observations, total organic carbon (TOC) content measurements, and major, trace, and rare earth element analyses of core samples from the Cambrian Qiongzhusi Formation shale at different structural positions within the Deyang–Anyue rift trough of Sichuan Basin, this study employs a combined geochemical and random forest algorithm to qualitatively and quantitatively identify the controlling factors of organic matter enrichment in black shales, and to elucidate the patterns of organic matter enrichment under the influence of tectono-sedimentary differentiation within the rift trough. The results are obtained in four aspects. First, the Qiongzhusi shales were deposited under a warm and humid climate with intense chemical weathering. From the extra-trough to the intra-trough settings, paleoproductivity and sedimentary environmental restriction gradually increased, whereas terrigenous detrital input and redox potential progressively decreased. Moreover, hydrothermal activity intensity diminished from the trough margin toward the extra-trough and intra-trough areas. Second, vertically, layers 1 and 3, which remained under persistently high productivity and reducing conditions, exhibit high organic matter enrichment; layer 5 shows relatively high enrichment due to the high level of organism abundance period; layer 7, characterized by limited marine transgression, exhibits the lowest enrichment, attributed to reduced productivity, weakened reducing conditions, and enhanced activities of terrigenous detritus and hydrothermal inputs. Third, the random forest model demonstrates a satisfactory performance in fitting the organic matter enrichment in black shales, revealing that it is primarily governed by paleoproductivity, secondarily by redox conditions, and to a lesser extent influenced by terrigenous detrital input and hydrothermal activity. Fourth, for organic-rich shale gas exploration, vertically, layers 1, 3, and 5 all show great exploration potential; laterally, priority should be given to the central intra-trough area north of the central zone of the rift trough. These findings contribute to a better understanding of the organic matter enrichment mechanisms in the Qiongzhusi Formation shales of the Sichuan Basin, and provide a geological theoretical basis for shale gas exploration and source rock evaluation.

The Upper Triassic Xujiahe Formation (T(3)x) represents a critical terrestrial source rock system in the Sichuan Basin, exhibiting pronounced vertical and lateral heterogeneity. Previous stratigraphic subdivisions relied primarily on lithological correlations rather than a systematic sequence stratigraphic framework. This approach has led to significant inconsistencies in source rock evaluation. Furthermore, recent discoveries of large gas fields, coupled with data from newly drilled wells, necessitate a comprehensive reassessment of this system. In this study, we re-evaluate the geochemical characteristics and spatial distribution of these source rocks within a newly established sequence stratigraphic framework. This assessment utilizes a robust dataset comprising total organic carbon (TOC) content, Rock-Eval pyrolysis, and vitrinite reflectance (Ro) measurements. The results indicate that the source rocks of the New Member 5 (T(3)x(5)) in the slope belt of Central Sichuan exhibit the highest hydrocarbon generative potential. These rocks are characterized by high organic abundance (with 40% of samples showing TOC >= 2.0 wt.%), are dominated by Type III and II2 kerogen (humic-sapropelic), and have reached the mature to high-maturity stage (Ro ranging from 1.0% to 1.7%). Notably, the cumulative thickness of these high-quality source rocks reaches 100 similar to 150 m. Specifically, the T(3)x(5) intervals in the Qiulin and Tianfu areas are identified as the most favorable hydrocarbon-generating centers. This reassessment under the new stratigraphic division provides a refined theoretical basis for future exploration targeting the Xujiahe Formation in the Sichuan Basin.

Significant exploration progress has been made in ultra-deep clastic rocks in the Kuqa Depression, Tarim Basin, over recent years. A new round of comprehensive geological research has formed four new understandings: (1) Establish structural model consisting of multi-detachment composite, multi-stage structural superposition and multi-layer deformation. Multi-stage structural traps are overlapped vertically, and a series of structural traps are discovered in underlying ultra-deep layers. (2) Five sets of high-quality large-scale source rocks of three types of organic phases are developed in the Triassic and Jurassic systems, and forming a good combination of source-reservoir-cap rocks in ultra-deep layers with three sets of large-scale regional reservoir and cap rocks. (3) The formation of large oil and gas fields is controlled by four factors which are source, reservoir, cap rocks and fault. Based on the spatial configuration relationship of these four factors, a new three-dimensional reservoir formation model for ultra-deep clastic rocks in the Kuqa Depression has been established. (4) The next key exploration fields for ultra-deep clastic rocks in the Kuqa Depression include conventional and unconventional oil and gas. The conventional oil and gas fields include the deep multi-layer oil-gas accumulation zone in Kelasu, tight sandstone gas of Jurassic Ahe Formation in the northern structural zone, multi-target layer lithological oil and gas reservoirs in Zhongqiu–Dina structural zone, lithologic-stratigraphic and buried hill composite reservoirs in south slope and other favorable areas. Unconventional oil and gas fields include deep coal rock gas of Jurassic Kezilenuer and Yangxia formations, Triassic Tariqike Formation and Middle-Lower Jurassic and Upper Triassic continental shale gas. The achievements have important reference significance for enriching the theory of ultra-deep clastic rock oil and gas exploration and guiding the future oil and gas exploration deployment.

The deeply buried (>4500 m) Cambrian Xixiangchi Formation in the Sichuan Basin, southwestern China, hosts significant reserves of natural gas. A comprehensive analysis combining petrographic, paleo-thermometric, geochemical, and petrophysical materials of the dolostone from the Xixiangchi Formation was conducted to provide insight into deeply buried carbonate reservoirs and decipher the complex diagenetic history. Dolomite-mudstone, fine-crystalline dolostone, and fine-crystalline dolomite cement of the Xixiangchi Formation underwent sabkha and reflux dolomitization. Medium- to coarse-crystalline dolostone, dolo-grainstone, and medium- to coarse-crystalline dolomite cements were then formed by burial dolomitization. These dolomites display delta C-13 ratios and REE patterns comparable to seawater, with progressively depleted delta O-18 ratios at greater burial depths. Dolo-grainstone originating from the platform shoal facies exhibits higher primary porosities and well-developed inter-particle pores compared to dolo-mudstone and crystalline dolostone lithologies, which are typically associated with the low-energy tidal flat and/or restricted platform environments. The initial spatial heterogeneity of primary porosity was subsequently modified by meteoric alteration and repeated episodes of dolomitization, which contributed to the development of secondary porosity. These processes increased the resistivity to compaction, and open fractures increased reservoir permeability. During the deep burial regime, saddle dolomite and calcite cements were precipitated at high fluid temperatures (up to 220 degrees C). Thermochemical sulfate reduction is characterized by the occurrence of anhydrite, hydrocarbon, and high homogenization temperatures and significantly low delta C-13 ratios (av.=-23.7 parts per thousand) of calcite cements. Deep burial dissolution is significantly constrained by: corrosion of late diagenetic minerals, and the occurrence of bitumen in the center of pores. Mechanisms for the deep-burial dissolution include hydrothermal alteration and thermochemical sulfate reduction. This study indicates the complex diagenetic evolution of Cambrian Xixiangchi Formation, providing significant insights into global deep-burial carbonate reservoir potential.(c) 2025 The Authors. Published by Elsevier B.V. on behalf of China University of Petroleum (Beijing). This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4. 0/).

The high-frequency cycles seen in the carbonates of the Cambrian Xiann & uuml;dong Formation in the Sichuan Basin commonly exhibit a certain coupling relationship with the development of grain shoals; this influences the accuracy of reservoir predictions and the selection of favorable zones for hydrocarbon. MATLAB-based wavelet transform technology is employed to analyze the characteristics of the high-frequency sequences in the Xiann & uuml;dong Formation, establish a sequence stratigraphic framework, and clarify their vertical and horizontal relationships with the development of grain shoals. The results indicate that using the Dmey wavelet for continuous wavelet transform of gamma ray (GR) curves effectively reflects regional sedimentary cycles. In the Xiann & uuml;dong Formation, we identified two third-order sequences, five fourth-order sequences, and ten fifth-order sequences, all of which exhibit a strong correlation with the one-dimensional wavelet curves derived from wavelet transformations. In the sequence stratigraphic framework, early deposition of the Xiann & uuml;dong Formation briefly inherited transgressive processes from the Qiongzhusi Formation, and subsequently underwent a long and frequently fluctuating regressive phase. This study elucidates the development characteristics of grain shoals during marine regressions, and identifies lithology primarily as oolitic limestone, oolitic dolostone, doloarenite, silty oolitic limestone, and silty oolitic dolostone. Longitudinally, grain shoals are primarily distributed in the SQ12, SQ21, and SQ22 intervals, and are characterized by the interbedded development of thin and thick layers. They form predominantly during the regressive phase of fourth-order sequences. Planarly, they exhibit a belt-like distribution in the southwest-northeast direction. These findings provide novel insights for conducting high-frequency sequence stratigraphy studies utilizing logging data. They also possess practical implications for constructing high-precision sequence stratigraphic frameworks as well as for predicting the distribution of grain shoals within the study area. (c) 2025 Petroleum Exploration and Production Research Institute Corporation, SINOPEC. Publishing services by Elsevier B.V. on behalf of KeAi Communications Co. Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

After years of exploration and development in the Shunbei oil and gas field, Tarim Basin, a series of technologies for ultra-deep fault-controlled fractured-vuggy target prediction, evaluation, and well location design have been formed, applicable to the No.1 and No.5 fault zones. As exploration efforts shift from the main No.1 and No.5 fault zones to the northeastern and northwestern fault zones in the eastern and western regions, the underground geological conditions become more complex, and exploration costs rise significantly. Existing reservoir characterization, target selection, and well trajectory design technologies are inadequate for the precise delineation of ultra-deep fault-controlled fractured-vuggy systems and high-yield well trajectory optimization. Through comparative analysis of the internal structural characteristics and seismic response variations of different regions and different types of strike-slip fault zones, integrated with actual well seismic calibration statistics and forward modeling, this study established a robust seismic identification model for high-yield and stable production wells. This model, based on the "source-connected faults + bead-string + deep chaotic high-amplitude background", provided a systematic framework for reservoir prediction and target selection. The Q-compensation seismic data processing technology developed through research improved the imaging resolution of fault-controlled fractured-vuggy systems in low signal-to-noise ratio seismic data under desert environments. Based on this, a reservoir quantification sculpting and target spatial positioning technology, centered on "facies-constrained inversion, " was established, which improved the accuracy of fault-controlled reservoir description and the precision of target selection. In response to the complex geological conditions of the overlying strata and Ordovician target layers in the Shunbei area, as well as challenges such as loss, overflow, and wellbore collapse during drilling, a key integrated geological engineering technology process focused on drilling risk prediction was established. This process included methods for optimizing well trajectories, selecting well locations, predicting formation pressures before drilling, and predicting wellbore stability, which improved drilling safety and efficiency. Drilling results from Shunbei's No. 4 and No. 8 fault zones indicated that the target selection and design technology for fault-controlled reservoirs could accurately identify and predict ultra-deep heterogeneous fractured-vuggy body targets, guide and optimize drilling trajectory design, avoid and reduce engineering risks along the drilling path, and improve the drilling success rate and high-yield well construction rate for large-scale reservoirs.

Numerous studies have investigated the provenance of the Upper Triassic Xujiahe Formation, but there are still controversies concerning the provenance of this formation in the northern part of the Sichuan Basin. This research combines sandstone grain point-counting, heavy mineral assemblage analysis, and electron microprobe measurements of heavy mineral compositions to examine the provenance of the Xujiahe Formation in the Guangyuan, Wangcang, Nanjiang, and Tuhuang sections located in the northern part of the Sichuan Basin. The results show that the sandstone composition, unstable heavy mineral type and garnet composition are similar for samples from Guangyuan, Wangcang, Nanjiang sections, characterized by abundance of garnet and chromian spinel. Garnet types are predominantly almandine and pyrope, which are mainly derived from amphibolite-to granulite-facies metasedimentary rocks. In contrast, samples from the Tuhuang section are characterized by lack of chromian spinel and existence of pyroxene, with garnet of almandine type and derivation from intermediate-acidic magmatic rocks, and with pyroxene of augite and diopside types and derivation from alkaline-subalkaline volcanic arc basalt magma or subalkaline oceanic floor basalt magma. Comprehensive analysis shows that the provenance of the Guangyuan, Wangcang, and Nanjiang sections includes Triassic turbidites from the Songpan-Ganzi Fold Belt and west Qinling Orogen and Paleozoic strata in the Longmenshan thrust belt. The Tuhuang section, by contrast, receive sediment from the North China Block and Qinling Orogen. These findings, in combination with previous provenance and sedimentary studies, support the existence of two distinct source to sink systems in the northern part of the Sichuan Basin during the Late Triassic. The provenance study of the Xujiahe Formation also demonstrates the limitation of the detrital zircon U-Pb method and underscores the importance of the combination of multiple provenance analysis methods for the effective discrimination of complex source to sink systems. (c) 2025 Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences AND Research Institute of Petroleum Exploration and Development, PetroChina. Publishing services by Elsevier B.V. on behalf of KEAI Communications Co. Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

[Background]The Ordos Basin enjoys abundant natural gas resources,which generally bear helium,making this basin hold great helium resource potential.In this case,detailed exploration is essential for the future transition from natural gas-helium joint exploration to special helium exploration in the basin.[Objective and Method]To systematic-ally investigate the distribution and potential of helium resources in the Ordos Basin,natural gas samples were taken from different areas of the basin for analysis and tests.To examine the primary factors controlling helium accumulation and enrichment,this study conducted a systematic analysis of the basement,sedimentary rock layers,fault systems,and tectonic evolutionary process of the basin.[Results and conclusions]Two helium enrichment patterns are identified in the basin and can be further subdivided into three types.Specifically,two helium enrichment patterns are determined ac-cording to their carrier types:alkane and geothermal water as carriers.The alkane-carried gas can be further subdivided into two types based on the distance between gas reservoirs and the basement.The first type is represented by the Dong-sheng gas field,characterized by the direct contact between gas reservoirs and the basement(vertical distance:less than 50 m)and an average helium volume fraction of 0.118％.The second type is exemplified by the Qingyang gas field,characterized by the near-distance contact between gas reservoirs and the basement(vertical distance:less than 1 500 m)and an average helium volume fraction of 0.105％.The geothermal water-carried gas refers to helium-rich water-soluble gas migrating via deep-seated faults.Such gas is represented by the Weihe graben,characterized by vertical distances of 1 500-5 000 m from water-soluble gas above geothermal water to the basement and an average helium volume fraction of 2.5％.By analyzing the geological characteristics and helium enrichment factors of helium-rich areas,this study de-termined the primary factors controlling helium enrichment.Specifically,ancient U-and Th-rich granites in the shal-lowly buried basement are identified as important helium source rocks while also providing a material basis for helium enrichment.The deep-seated faults play a key role in connecting helium to shallow reservoirs.For instance,the basal strike-slip fault zone within the Qinyang gas field produces controlling effects on the Qingyang and Zhengning gas fields,also serving as a play fairway for helium enrichment.In the Qingyang gas field,areas with large-scale faults in the gas layers of the Taiyuan Formation exhibit high helium volume fractions(average:0.105％).The formation of large-scale helium is inseparable from natural gas and water,with helium always emerging as an associated product.There-fore,effective reservoir-cap rock assemblages favor helium enrichment.Based on research on the magnetic anomalies and the distribution characteristics of deep-seated faults in the Ordos Basin,this study identified two optimal helium en-richment areas:shallow-buried areas of basal granites and areas with deep-seated faults.In combination with the current reservoir-cap rock configurations of gas fields,it determined nine play fairways with a total area of 40 000 km2 in the basin:the Hetao Basin,the Yimeng paleocontinent,the northern Tianhuan sag,the Dingbian fault zone,the Zhidan-Jiaxi-an fault zone with a strong magnetic field,the Zij inshan volcanic rock invasion zone,the Qingyang paleo-uplift,the Yichuan-Huanglong fault zone,and the Weihe graben.

To address the shortage of characterization scale of field outcrops, we used the characteristics of unmanned aerial vehicle(UAV) oblique photography with a wide field of view and a high degree of quantification for image acquisition, data processing, and geological interpretation of the outcrops of the Shaximiao Formation in the Sichuan Basin. We established a 3D digital outcrop model(DOM), which combines the advantages of visualization and digitization the 3D DOM to interpret the characteristics of typical channel sand bodies. Within the study area, we have identified three types of channel deposition: composite channel deposition, crevasse channel deposition, and abandoned channel deposition. Among these, the composite channel deposition was mainly sandstone, the bottom contains conglomerate, with large cross-bedding, and the maximum thickness of the single sand body was 1.96 m. The crevasse channel deposition was mainly fine sandstone and siltstone, with massive bedding and small cross-bedding, and the maximum thickness of the single sand body was 0.64 m. The abandoned channel deposition dominated by mudstone with thin sandstone, the sandstone was mainly lenticular in section, and the maximum thickness of the single sand body was 0.28 m. We identified the depositional model of the studied region, which is dominated by braided river deposition, based on the growth size and correspondence of the sand bodies. The research provides a comparative foundation for the detailed characterisation of the underground reservoir sands found in the Jurassic Shaximiao Formation in the Sichuan Basin. It also serves as a reference for the effective study of UAV oblique photography technology in the field.

The Jurassic tight sandstone oil and gas exploration and development in the eastern Yangxia Sag is a new field. To elucidate the origin, accumulation process and potential of tight oil and gas, the authors have conducted comprehensive analyses employing methodologies encompassing source rocks, oil geochemistry, and fluid inclusions. The results show that the abundance of organic matter of Jurassic source rocks is high, and the type of organic matter is of Ⅱ-Ⅲ and in mature evolution stage. The main source rocks of oil and gas are Huangshanjie Formation and Jurassic coal-bearing source rocks. Ahe Formation developed two stages of hydrocarbon charging, and the period is later than the reservoir densification time. Yangxia Formation oil charged before the reservoir densified, and the late gas charged after the reservoir densified. Hydrocarbon generation intensity of Jurassic source rocks has reached the basic conditions for the formation of tight gas reservoirs. Controlled by the difference of source rocks distribution and accumulation process, tight sandstone oil and gas accumulation conditions are better in the depression direction than in the southeast margin area. This study is of practical importance for expanding the exploration field and selecting favorable areas in the eastern Yangxia sag.

To explore the geological characteristics and exploration potential of the Carboniferous Benxi Formation coal rock gas in the Ordos Basin, this paper presents a systematic research on the coal rock distribution, coal rock reservoirs, coal rock quality, and coal rock gas features, resources and enrichment. Coal rock gas is a high-quality resource distinct from coalbed methane, and it has unique features in terms of burial depth, gas source, reservoir, gas content, and carbon isotopic composition. The Benxi Formation coal rocks cover an area of 16×104 km², with thicknesses ranging from 2 m to 25 m, primarily consisting of bright and semi-bright coals with primitive structures and low volatile and ash contents, indicating a good coal quality. The medium-to-high rank coal rocks have the total organic carbon (TOC) content ranging from 33.49% to 86.11%, averaging 75.16%. They have a high degree of thermal evolution (Ro of 1.2%–2.8%), and a high gas-generating capacity. They also have high stable carbon isotopic values (δ13C1 of –37.6‰ to –16‰; δ13C2 of –21.7‰ to –14.3‰). Deep coal rocks develop matrix pores such as gas bubble pores, organic pores, and inorganic mineral pores, which, together with cleats and fractures, form good reservoir spaces. The coal rock reservoirs exhibit the porosity of 0.54%–10.67% (averaging 5.42%) and the permeability of (0.001–14.600)×10−3 μm2 (averaging 2.32×10−3 μm2). Vertically, there are five types of coal rock gas accumulation and dissipation combinations, among which the coal rock-mudstone gas accumulation combination and the coal rock-limestone gas accumulation combination are the most important, with good sealing conditions and high peak values of total hydrocarbon in gas logging. A model of coal rock gas accumulation has been constructed, which includes widespread distribution of medium-to-high rank coal rocks continually generating gas, matrix pores and cleats/fractures in coal rocks acting as large-scale reservoir spaces, tight cap rocks providing sealing, source-reservoir integration, and five types of efficient enrichment patterns (lateral pinchout complex, lenses, low-amplitude structures, nose-like structures, and lithologically self-sealing). According to the geological characteristics of coal rock gas, the Benxi Formation is divided into 8 plays, and the estimated coal rock gas resources with a buried depth of more than 2 000 m are more than 12.33×1012 m3. The above understandings guide the deployment of risk exploration. Two wells drilled accordingly obtained an industrial gas flow, driving the further deployment of exploratory and appraisal wells. Substantial breakthroughs have been achieved, with the possible reserves over a trillion cubic meters and the proved reserves over a hundred billion cubic meters, which is of great significance for the reserves increase and efficient development of natural gas in China.

Based on the research progress of the geological theory of coal-formed gas, the contributions of coal-formed gas to the natural gas reserves and production in China and to the development of natural gas in major gas-producing basins are analyzed, and the key favorable exploration zones for coal-formed gas in China are comprehensively evaluated. The following results are obtained. First, coal measures are good gas source rocks, and hydrocarbon generation from coal measure was dominated by gas, followed by oil. Second, a natural gas genetic identification index system based on stable isotopes, light hydrocarbon components, and biomarkers is established. Third, the quantitative and semi-quantitative factors controlling the formation of large gas fields, represented by the indicator of gas generation intensity greater than 20×108 m3/km2, are identified to guide the discovery of large gas fields in China. Fourth, coal-formed gas is the major contributor to the current natural gas reserves and production of China, both accounting for over 55%. The high proportion of coal-formed gas has enabled the Tarim, Sichuan and Ordos basins to be the major gas production areas in China. Fifth, coal rock gas is an important field for future exploration of coal-formed gas, and key zones include the Carboniferous Benxi Formation (Fm) in the Wushenqi-Mizhi area of the Ordos Basin, the Permian Longtan Fm in central-southern Sichuan Basin, the Jurassic Xishanyao Fm in the southern margin and Luliang uplift of the Junggar Basin. Sixth, tight gas is the main area for increasing reserves and production, and the favorable exploration zones include the Carboniferous–Permian in southern Ordos Basin and the Bohai Bay Basin, and the Triassic Xujiahe Fm in the transition zone between central and western Sichuan Basin. Seventh, the Jurassic in the southern margin of the Junggar Basin is a key favorable exploration zone for subsequent investigation of conventional coal-formed gas. These insights have valuable theoretical and practical significance for further developing and improving the theory of coal-formed gas, and guiding the exploration of coal-formed gas fields in China.

The Cambrian pre-salt dolomite sequence in the Tarim Basin is a target zone of great strategic significance for hydrocarbon exploration in the basin. Using the results of the interpretation of 3D seismic data from Lunnan and 2D seismic data covering the whole basin, and based on a synthesis of outcrop data, drilling data, well logs, core data, and thin-section data, and the findings from previous studies, this paper studies the characteristics of the facies of the Middle–Lower Cambrian in the platform area in the Tarim Basin, the formation and evolution of platform margins, and the sedimentary characteristics, lithofacies, and paleogeographic characteristics of the Middle–Lower Cambrian series. Based on the types of lithofacies and the seismic facies analysis, the sedimentary facies of the Middle–Lower Cambrian strata can be classified into the five types. From bottom to top, the Middle–Lower Cambrian have experienced several development stages, including the deposition of continental shelf sediments of the Yuertusi Formation, gently sloping non-rimmed platform margin sediments of the Xiaoerbulake Formation, weakly rimmed platform margin sediments of the Wusongger and Shayilike formations, and strongly rimmed platform margin sediments of the Awatage Formation. In each stage, the platform margin shifted further east relative to its location in the previous stage. Based on these results and previous studies, the lithofacies and paleogeography maps of the Middle–Lower Cambrian in the Tarim Basin are modified, and the implications for hydrocarbon exploration in this area are discussed.

Cambrian subsalt dolomite is an important strategic area for natural gas exploration in the Tarim Basin. The gypsum-salt rocks, argillaceous mudstone and argillaceous dolomite strata developed in large areas of the Middle Cambrian can be used as good caprocks. The sealing ability and favorable area distribution of the Middle Cambrian caprock in the Tarim Basin are studied through the lithofacies paleogeography and microscopic evaluation of the Middle Cambrian strata in this paper. Based on the 2D seismic interpretation covering the entire basin, combined with data from drilling, outcrops, well logging, core samples and thin sections, the sedimentary characteristics and lithofacies paleogeography of the Middle Cambrian were studied and then the thickness of the Middle Cambrian gypsum-salt rocks, gypsiferous mudstone and gypsiferous dolomite was analyzed in the Tarim Basin. Studies suggest that the Middle Cambrian is primarily characterized by the development of restricted-platform facies. In the Awati Depression, the northern part of the Tazhong Uplift, the southern part of the Manxi Low Uplift, and the central and northern parts of the Bachu Uplift, the thickness of the gypsum-salt rock strata is relatively large. Moreover, centered on the northern part of the Bachu Uplift, the thickness of the gypsum-salt rocks decreases irregularly towards the periphery, forming a circumferential distribution. To investigate the sealing ability of caprocks, 64 core samples from four wells were examined under a microscope, and physical parameters as well as breakthrough-pressure tests were conducted. By establishing correlations between various parameters, the sealing ability of different rock types in the Cambrian formation within the study area was quantitatively assessed. The research suggests that gypsum-salt rocks exhibit superior sealing ability compared to gypsiferous mudstone and gypsiferous dolomite, but factors such as faults and geological conditions of gypsum can influence the sealing performance of caprocks. According to both micro- and macro-scale evaluations of the Cambrian strata in the study area, along with constraints imposed by actual drilling exploration results, a comprehensive evaluation method for assessing caprock sealing ability has been established. The results suggest that the Awat Depression, the western and southern parts of the Manxi Low Uplift, the northern and western parts of the Tazhong Uplift, and the central part of the Tabei Uplift are favorable areas for the development of caprocks.

The purpose of this study is to address the challenges and limitations related to vibroseis in ultra-deep exploration in the desert region of Tarim Basin. The research analyzes the root causes of abnormal noise in vibroseis surface wave in desert areas and assesses the influence of near-surface factors on the quality of seismic data through forward modeling. In terms of data acquisition, the implementation of nonlinear sweeping signals is employed to improve the energy of low frequency signals. The implementation of a multi-level and multi-domain noise suppression technique effectively enhances the role of the near offset signal in seismic processing for migration. This approach has been successfully applied to the Shunbei Oil Field, resulting in a notable enhancement of the vibroseis' ability to characterize ultra-deep fault-controlled fracture-cavity reservoirs in desert regions. As a result, it highlights the potential of vibroseis as a viable alternative to explosive sources.

Based on the methodology for petroleum systems and through the anatomy and geochemical study of typical helium-rich gas fields, the geological conditions, genesis mechanisms, and accumulation patterns of helium resources in natural gas are investigated. Helium differs greatly from other natural gas resources in generation, migration, and accumulation. Helium is generated due to the slow alpha decay of basement U/Th-rich elements or released from the deep crust and mantle, and then migrates along the composite transport system to natural gas reservoirs, where it accumulates with a suitable carrier gas. Helium migration and transport are controlled by the transport system consisting of lithospheric faults, basement faults, sedimentary layer faults, and effective transport layers. Based on the analysis of the helium-gas-water phase equilibrium in underground fluids and the phase-potential coupling, three occurrence states, i.e. water-soluble phase, gas-soluble phase and free phase, in the process of helium migration and accumulation, and three migration modes of helium, i.e. mass flow, seepage, and diffusion, are proposed. The formation and enrichment of helium-rich gas reservoirs are controlled by three major factors, i.e. high-quality helium source, high-efficiency transport and suitable carrier, and conform to three accumulation mechanisms, i.e. exsolution and convergence, buoyancy-driven, and differential pressure displacement. The helium-rich gas reservoirs discovered follow the distribution rule and accumulation pattern of “near helium source, adjacent to fault, low potential area, and high position”. To explore and evaluate helium-rich areas, it is necessary to conduct concurrent/parallel exploration of natural gas. The comprehensive evaluation and selection of profitable helium-rich areas with the characteristics of “source-trap connected, low fluid potential and high position, and proper natural gas volume matched with helium’s” should focus on the coupling and matching of the helium “source, migration, and accumulation elements” with the natural gas “source, reservoir and caprock conditions”, and favorable carrier gas trap areas in local low fluid potential and high positions.