Three marine shale formations of the Middle-Upper Permian—the Gufeng Formation (P₂g), the 3^rd member of the Wujiaping Formation (P₃w₃) and the 1^st member of the Dalong Formation (P₃d₁), are well developed in the northeastern Sichuan Basin, representing promising new targets for enhancing shale gas reserves and production. Based on extensive core testing data, this study analyzes their geochemical characteristics, reservoir features and proposes corresponding development strategies to provide theoretical support for shale gas exploration in China. The key findings are as follows: (1) All three shale formations exhibit high organic matter abundance, with average total organic carbon (TOC) contents of 9.82% (P₂g), 6.60% (P₃w₃) and 6.01%(P₃d₁), respectively. The organic matter is classified as type II₁, and the maturity(R_o) exceeds 2.0%, indicating significant hydrocarbon generation potential. The Gufeng Formation is dominated by siliceous shale and calcareous shale facies, whereas P₃w₃ and P₃d₁ primarily consist of siliceous shale and mixed shale facies. The brittleness index of all three formations exceeds 70%. Organic pores are the dominant pore type, with mesopores serving as the primary pore category. (2) The P₃w₃ exhibits well-developed laminated fractures, highest pore connectivity index (average value of 5.17), high porosity and high gas content; the P₂g has moderate pore connectivity index (average value of 2.57), high porosity and gas content; the P₃d₁ shows poor laminated fracture development, the lowest pore connectivity index(average value of 1.69), the lowest porosity value and relatively high gas content.(3) Compared to the Longmaxi Formation in southern Sichuan Basin, these three shale formations are characterized by high TOC content, high brittleness index, high gas content, thin thickness and deep burial depth. Targeted development technologies are thus required. Favorable areas for shale gas enrichment of these three formations are primarily distributed in the southeastern segment of the Kaijiang-Liangping Trough and the Chengkou-Fengjie-Lichuan-Shizhu area of the Chengkou- E'xi Trough.

Taking the middle and upper sections of the Pinghu Formation on the Pinghu slope in Xihu Sag as an example, by synthesizing the research achievements of coastal sedimentary systems at home and abroad, this study innovatively integrates paleogeomorphology, sedimentary characteristics of tidal flat areas, and coastal sedimentary models to explore their impacts on tidal dynamics and sedimentary system distribution, providing key basis for subsequent large-scale lithologic trap oil and gas exploration and development. Comprehensive application of drilling and logging data, seismic data, and sedimentary process numerical simulation techniques is conducted to simulate the spatio-temporal evolution of the sedimentary system. Through qualitative description and quantitative measurement, the distributions of unique sedimentary units such as tidal channels, tidal gullies, tidal sand ridges, and tidal sand sheets are clarified, the controlling effects of coastal topography and sea-level changes on tidal sedimentary sand bodies are revealed, and three sedimentary models, namely barrier coast, barrier-free underwater low-relief coast, and barrier-free gentle slope coast, are constructed to improve the theoretical framework of coastal sedimentary systems. Further comparative analysis between numerical simulation and actual data shows that barrier coast sand bodies are sheet-like distributed during low sea-level periods, while underwater low-relief coast sand bodies are ribbon-like distributed during high sea-level periods. For the first time, large-scale tidal sand ridges in barrier and underwater low-relief sedimentary environments and restricted tidal channel sand bodies are identified as key targets for oil and gas exploration.

The tight gas resource potential of the Lower Jurassic Ahe Formation in Dibei area of the eastern Kuqa Depression is enormous, making it a promising region for increasing oil and gas reserves and production. For a long time, the coupling relationship between sweet spot model and oil and gas enrichment of tight sandstone reservoir in Ahe Formation is unclear, which restricts the efficient exploration and development of tight oil and gas reservoirs.Based on microscopic reservoir characterization, geological modeling, fault-fracture characterization and reservoir analysis, this paper investigates the sweet spot characteristics and hydrocarbon enrichment patterns of tight sandstone reservoirs in the Ahe Formation, and evaluates their resource potential. The study reveals that the Ahe Formation reservoirs exhibit an alternating distribution of tight layers and low-porosity/high-permeability zones laterally. Reservoir properties are significantly enhanced by fault-fracture modification, developing sweet spot areas at four hierarchical scales. The fracture-pore systems controlled by class I-II faults extend east-west direction, characterized by large scale and favorable porosity-permeability properties. The fracture-pore systems controlled by class Ⅲ-Ⅳ faults/fractures are small in scale and pinch out within tight sandstones. The first hydrocarbon charging event in the Ahe Formation reservoirs occurred between 18 and 12 Ma, with porosity ranging from 15% to 18% during this phase. The primary charging fluid was crude oil, which accumulated in structural highs to form conventional oil reservoirs. However, these reservoirs were subsequently severely disrupted, leading to complete dissipation of the accumulated hydrocarbons. The second hydrocarbon charging phase commenced since 5 Ma, during which the reservoir underwent rapid densification, with porosity reduced to 6%-8%. Natural gas efficiently migrated along faults and fractures, accumulating preferentially within sweet spot zones of the reservoir. Class Ⅲ and Ⅳ faults/fractures zones establish effective connectivity between sandstone units within the Ahe Formation, forming optimal configurations with adjacent tight reservoirs and overlying mudstones. These structural features constitute critical controls on both trap effectiveness and hydrocarbon accumulation. The favorable area for oil and gas enrichment in tight sandstone of the Ahe Formation can reach 106 km², mainly concentrated in the central and southern platform areas of the Dibei Slope. The lithological trap resources of natural gas are 1 699 × 10⁸ m³ and petroleum are 778 × 10⁴ t.

This study addresses the core issues of unclear sequence architecture and sedimentary evolution patterns of the bioclastic limestone member of the Carboniferous Bachu Formation in eastern Tazhong area, Tarim Basin. Based on a wealth of data, including core, thin section, logging, and geochemical data, we conduct an in-depth analysis of the petrological characteristics of the bioclastic limestone member, construct the sequence stratigraphic framework for this member, and explore its control on sedimentation and reservoir formation. The research findings demonstrate that: (1) The bioclastic limestone member in the eastern Tazhong area represents a mixed siliciclastic-carbonate sedimentation within a marine-terrestrial transitional setting, mainly composed of micritic to peloidal limestone/dolomite, calcarenite/doloarenite to calcirudite/doloyunrudite, mixed rocks, and transitional lithologies, with a relatively high content of terrigenous clastics. The distribution of lithologies exhibits distinct vertical segmentation and lateral zonation patterns. (2) Based on variations in lithology and sedimentary facies, the bioclastic limestone member, along with the underlying Donghe sandstone member, the lower mudstone member, and the overlying middle mudstone member, forms a complete three-order sequence. The bioclastic limestone member itself represents a complete transgressive-regressive sequence, with the middle submember recording the relatively deepest marine flooding conditions during deposition. (3) The eustatic cycles exert a decisive influence on the evolution of sedimentary microfacies and diagenetic processes. The lower and upper submembers, deposited in shallow waters, are dominated by supratidal dolomicrite (dolomudstone) facies within evaporitic tidal flats. During relative sea-level rise in the middle submember, high-energy grain shoal complexes developed within intertidal settings, where superimposed high-frequency exposure events drove meteoric dissolution and penecontemporaneous dolomitization, thereby generating high-quality reservoirs with superior storage capacity. These dolomitized grain shoal and dolomicrite flats with pinprick vugs together constitute the most favorable reservoir facies of the bioclastic limestone member in the eastern Tazhong area, Tarim Basin, and represent the primary targets for future exploration and development.

Taking the Cambrian Xiaoerblak section in the Keping outcrop area as an example, this study aim to clarify the differences in the characteristics and distribution patterns of dolomite reservoirs of the Upper Cambrian Xiaqiulitage Formation in the western Tarim Basin. Based on a systematic analysis of rock thin section, carbon and oxygen isotope compositions, and U-Pb dating, the conclusions are drawn as follows:(1) The Xiaqiulitage Formation, with a total thickness of 350 m, is divided into six members, and is composed of grain dolomite, thrombolite dolomite, stromatolite dolomite, and laminated microbialite dolomite. Seven lithofacies association and two third-order sequences are identified in the Xiaqiulitage Formation, reflecting the overall transition of tidal flat subfacies to inner platform shoal subfacies from bottom to top. (2) The reservoir spaces are dominated by matrix dissolution pores, vugs (dissolution cavities), and intergranular fractures within breccias. The columnar stromatolitic dolomite and thrombolitic dolomite exhibit the best physical properties, followed by grain dolomite, with the overall characteristics of moderate-to-high porosity and moderate-to-low permeability. A comprehensive evaluation indicates that the reservoir properties are optimal in Member 1, Member 2, and Member 6, while Member 5 ranks slightly lower. (3) The dolomite was formed during the early diagenetic stage, and reservoir development is primarily controlled by the combined effects of sedimentary microfacies, unconformity surfaces, and high-frequency sequences. The reservoirs can be classified into two types: unconformity-karst dolomite reservoirs and inner mound-shoal dolomite reservoirs. This research provides critical support for evaluating favorable exploration zones in the Cambrian dolomite plays of the western Tabei area, and offers reliable evidence for hydrocarbon reservoir assessment, particularly in the Xiongying region.

With the continuous expansion of oil and gas exploration into ultra-deep and ancient strata in the three major marine cratonic basins, challenges such as unclear favorable exploration zones have emerged. Therefore it is imperative to deepen research on depositional models for critical geological periods. Based on the summary of the Neoproterozoic-Paleozoic tectonic-sedimentary differential evolution characteristics of the three major basins, this paper analyzes the controlling effects of tectonic differentiation on sedimentary evolution. It is pointed out that the three ancient marine cratonic basins exhibit a tectonic differentiation pattern of "rift-depression-uplift", driving carbonate platforms undergoing an evolutionary cycle of "isolated platform-ramp-rimmed platform", and the formation and evolution of rifts control the sedimentary differentiation of platforms and the similarity of the vertical sourced-reservoer-cap assemblages. Four new models of carbonate sedimentation were established: "multi-type platform margins" and "double shoals" ramp models, carbonate-gypsum/salt symbiotic system model, fault terrace platform margin model of Dengying Formation in Sichuan Basin, and continuously expanding platform margin sedimentary model of Cambrian in Tarim Basin. The "multi-type platform margins" and "double shoals" ramp model reveal that the continental margin and rift margin, depression margin, paleo-uplift of inner ramp and lagoon periphery are favorable mound-shoal development areas. The carbonate-gypsum/salt symbiotic system model reveals that the margin of the paleo-uplift during transgression period is a favorable shoal development area. The fault terrace platform margin sedimentary model indicates that multiple syndepositional fault systems control the formation of step-like platform margins of the 2nd member of Dengying Formation in Sichuan Basin, with thick mound-shoal complexes developed on high fault blocks. The continuous extension platform margin sedimentary model reveals that the Cambrian platform margin belt of Lunnan-Gucheng area in Tarim Basin has undergone the evolution of mud-rich ramp→low-angle progradational ramp/weakly rimmed platform→vertically aggrading platform→laterally prograding rimmed platform. The new understanding of carbonate sedimentary models confirms that the mound-shoal belts around the paleo-rift of the three ancient marine craton basins are still important areas for increasing oil and gas reserves and ensuring resource succession. In addition, new fields such as gravity flow deposits in slope facies and marlstones in evaporative lagoon facies are worthy of exploration. The establishment of the new models of carbonate sedimentation strongly supports the deployment of oil and gas exploration, and also provides a new direction and ideas for future exploration.

In recent years, natural gas exploration breakthrough has been made in the Ordovician Majiagou Formation of Ordos Basin, but the formation and evolution of natural gas have not been thoroughly studied. Taking Daniudi gas field as an example, the typical characteristics of oil-cracked gas in Majiagou Formation are determined through the identification of bitumen in the core and thin section, the occurrence of hydrocarbon inclusions and Raman spectroscopy testing, and the analysis of geochemical data of natural gas. The formation conditions of oil-cracked gas are comprehensively analyzed, and the formation and evolution process of oil-cracked gas in Majiagou Formation are analyzed through the simulation of burial history and thermal history. The results show that: (1) Bitumen filling with diverse occurrences is found in the fractured porous reservoir of Majiagou Formation, and it is a dry bitumen with high degree of thermal evolution. Three phase hydrocarbon inclusions of oil, gas and bitumen are captured in calcite veins of Majiagou Formation, which confirms the existence of oil cracking gas process. (2) Based on the crossplot of geochemical index such as ln(C₁/C₂) and ln(C₂/C₃) of natural gas, it shows that the internal natural gas of Majiagou Formation is mainly oil-cracked gas. (3) During the deposition period of 3^rd member of Majiagou Formation, Daniudi and its surrounding areas were situated at the margin of a saline depression, where thick source rocks of argillaceous dolomite and dolomitic mudstone developed with interbedded evaporates, creating favorable conditions for thermochemical sulfate reduction (TSR). (4) In the Early Jurassic, source rocks produced a large amount of oil. Under the effect of the relatively high paleotemperature in the Early Cretaceous, high-temperature oil cracking occurred, and TSR reaction occurred with significantly increased H₂S content in the natural gas of O₁m₅⁵-O₁m₅⁶ of Majiagou Formation in Daniudi gas field. (5) In Daniudi and surrounding areas, the source rocks of Majiagou Formation became mature earlier in the south and later in the north, and natural gas mainly migrated and accumulated from south to north along the strike-slip faults. This study has certain significance for the internal gas exploration of Majiagou Formation in Ordos Basin.

The Maokou Formation of Middle Permian has huge resource potential and is an important target for natural gas exploration in Sichuan Basin. In recent years, significant exploration breakthroughs have been made in the dolomite of the 2^nd member of Maokou Formation in central Sichuan Basin, and the gas production of several wells has exceeded one million cubic meters, which reveals the huge exploration prospect in this field. However, the genesis of dolomite is still unclear, which restricts the prediction of dolomite distribution. Focusing on the core exploration wells in Hechuan area, a detailed description of the petrological characteristics based on core and thin sections is carried out, and representative samples of dolomite and limestone are selected for carbon oxygen isotope, strontium isotope, rare earth element, and U-Pb dating analysis. Taking into account the geological background, it was clarified that: (1) Dolomite is mainly developed in the middle-upper part of the 2^nd member of Maokou Formation, with a thickness of 1-25 m, and its original rock is grainy limestone. (2) The dolomitization fluid is mainly seawater, and dolomitization occurred in the quasi-contemporaneous period-early burial period. (3) The shoal developed in a relatively paleogeomorphologic high part of the 2^nd member of Maokou Formation was susceptible to syngenetic karstification, and a large fracture-cavern system developed in the phreatic zone. Fracture-cavern system were filled with bioclastic particles, marl and Mg²⁺ rich seawater, and dolomitization occurred during the shallow burial process. Based on the new research results of dolomite genesis, it is clear that the paleogeomorphologic high part is the favorable area of dolomite of the 2^nd member of Maokou Formation, which provides a basis for the prediction of dolomite reservoir distribution in the study area and effectively guides the exploration deployment.

The cratonic strike-slip fault zone is an important hydrocarbon accumulation zone in the ultra-deep carbonate rock field of Tarim Basin. At present, the natural energy of the oil reservoirs in the strike-slip fault zone is insufficient, and the decline rate of the oil reserves is fast. It is urgent to deepen the understanding of the geological characteristics of such oil reservoirs, explore new development methods, and investigate countermeasures for enhancing recovery rate. Based on the detailed study of the 12th and 17th fault zones in Fuman Oilfield through comprehensive analysis of outcrops, drilling, seismic surveys, core thin sections, production dynamics, well tests and other data, the types of reservoir space, internal structural characteristics and hydrocarbon accumulation features of the fractured breccia reservoirs are precisely characterized. Appropriate countermeasures for enhancing recovery rate are proposed. The research results indicate: (1) The fractured breccia reservoirs belong to vertical plate-shaped oil reservoirs. The reservoirs develop in the fault core and fracture zone, their reservoir space types are breccia interstitial pores, cavities and structural fractures formed by cataclasis. (2) The ultra-deep fractured breccia reservoirs are initially deposited as tight lithofacies, with very low pre-existing formation porosity and permeability, preserving a low amount of original formation water. There was no significant dissolution of atmospheric water in the later stage, which led to the fractured reservoir bodies having the characteristics of high oil column (up to one thousand meters) and being water-free or having little water content. (3) In terms of geological understanding, detailed description of reservoirs and development methods, three aspects of understanding transformation have been formed: from fault-controlled karst reservoir to fractured breccia reservoir, from description of fault-karst oil reservoir to the internal structure description of fractured breccia oil reservoir, from water injection development to gas injection development.

For the Carboniferous Huanglong Formation, an important natural gas production layer in Sichuan Basin, in low-relief structural zone on the west side of Huayingshan Fault, there are still problems of unclear accumulation conditions and undetermined favorable exploration zones due to low exploration degree. Based on exploration wells, 2D and 3D seismic data, a new round of evaluation is conducted on the distribution of strata, lithofacies paleogeography, and natural gas accumulation conditions of Huanglong Formation on the west side of Huayingshan Fault. The results show that: (1) The residual strata of Huanglong Formation with thickness mainly between 10-40 m are widely distributed (about 13 100 km²), and about 4 000 km² according to the new seismic interpretation is added in the northern Sichuan Basin. (2) The intertidal shoal dolomites are widely developed (about 8 200 km²), mainly in the Huanglong Member 2, followed by the Huanglong Member 3. The newly discovered Pingchang-Bazhong shoal belt covers an area of about 2 000 km². The thickness of dolomite reservoir of the shoal facies in HuangLong Member 2 is mainly 2-20 m. The reservoir has good physical properties, with an average porosity of 3.90%. (3) The source rocks of Wufeng Formation-Longmaxi Formation in the northern Sichuan Basin are widely developed covering an area of about 25 000 km², and the total thickness is 50-150 m in which the high-quality is 10-60 m. The source rocks of Wufeng Formation-Longmaxi Formation and the reservoirs of Huanglong Formation form favorable reservoir combination of lower generation and upper storage. (4) Controlled by the paleo-uplift slope zone, strata denudation zone, and large fault zone, the Huanglong Formation has developed two large trap groups, i.e., Pingchang-Bazhong, and Guang'an-Quxian, with diverse trap types dominated by lithological-stratigraphic traps and good preservation conditions. Four favorable exploration areas are predicted, indicating a promising prospect for natural gas exploration.

Diagenesis of reservoirs affects pore development, distribution and reservoir quality. Relevant studies on the Middle Triassic Leikoupo Formation in central Western Sichuan Basin are still blank. In order to reveal the diagenetic evolution characteristics of dolomite reservoirs in the study area and their influence on reservoir quality, and to provide a theoretical basis for the exploration of carbonate oil and gas, the study on the dolomite diagenesis of Leikou Formation in western Sichuan Basin is systematically analyzed on the basis of data analysis such as core and thin section observations, dolomite order degree analysis, fluid inclusions and carbon-oxygen stable isotope tests. The results show that: (1) The Leikoupo Formation in central Western Sichuan mainly develops two different types of dolomite: micritic dolomite and micritic algal clast dolomite. The low degree of ordering and low formation temperature of the dolomite crystals indicate that they were formed by penecontemporaneous dolomitization. The reservoir spaces mainly consist of dissolved pores developed along algal frameworks, intergranular pores, and tectonic breccia interstices. (2) The dolomite in the study area has mainly undergone diagenetic processes such as fracturing, dolomitization, dedolomitization, dissolution, micritization, cementation, and surface-induced demineralization. Among them, structural fracture and dissolution play an improving role in the physical properties of the reservoir. Deep dissolution is the fundamental factor for the development of deep secondary pores. (3) The correlation between the development characteristics of dissolution pores and structural breccia and structural fractures is confirmed: acidic fluids were injected along the fracture space into the remaining pore development areas such as sandy shoal and the framework of the algal layer to form secondary dissolution pores in the late Indosinian stage. Vertical fissures and late structural breccia were formed in the early stage of the Himalayan Movement, and late dissolution and calcite vein filling occurred. Horizontal fractures formed in the late Himalayan period, further improving the physical properties of the reservoir. The research has for the first time clarified the diagenetic sequence and pore evolution model of the dolomite reservoir of the Leikoupo Formation in central Western Sichuan Basin, and proposes a three-stage reservoir control mechanism of "structural fracture-fluid dissolution-fracture modification", providing new geological basis for the exploration of the Leikoupo Formation.

The recent exploration discoveries in Luzhou area indicate that the reef-shoal body of the Silurian Shiniulan Formation has certain potential for reservoir formation. A systematic study based on drilling, outcrop, and 3D seismic data is conducted to explore the development characteristics and exploration significance of the reef-shoal body of Shiniulan Formation. The results indicate that: (1) Reef/bioclastic limestone mainly develops at the top of the first member of Shiniulan Formation, with a thickness ranging from 6 to 40 meters, characterized by moderate-strong amplitude and medium-high frequency seismic reflection character. (2) Affected by the ancient uplift in central Sichuan, the first member of the Shiniulan Formation is developed at mixed tidal flats and intra-platform depressions, forming contiguous tidal edge reefs and shoals on the high terrain of the mixed tidal flats. At some high belts of the intra-platform depressions, intra-platform reefs/bioclastic shoals are developed. (3) The reservoir formation model of Shiniulan Formation is characterized by "near-source hydrocarbon generation, fault-mediated migration, lower-generation and upper-reservoir storage, and composite accumulation". The high-quality hydrocarbon source rocks of the Longmaxi Formation, the reef-shoal reservoir of the first member of Shiniulan Formation, the mudstone of the second member of Shiniulan Formation and the overlying strata form a good source rock-reservoir-caprock combination. The complex network fault system provides conditions for oil and gas migration, and the oil and gas filling period matches the trap formation period (P-K), laying the foundation for large-scale oil and gas accumulation. The Shiniulan Formation reef-shoal body is an important oil and gas exploration field worthy of attention.

The interaction between deep-water gravity flow and bottom flow is a currently hot topic in deep-water sedimentary research in the world. This study focuses on the Upper Eocene of the Rovuma Basin in East Africa, utilizing a comprehensive approach integrating drilling and 3D seismic data to investigate this geological topic. The sedimentary architectural elements and evolution characteristics under a high-frequency sequence stratigraphic framework is studied to reconstruct the depositional and evolutionary patterns of the submarine fan under the interaction of gravity and bottom currents in the Upper Eocene. The results show that: (1) The Upper Eocene submarine fan in the study area develops three types of sedimentary architectural elements: deep-water channels, overbanks and lobes. The channels can be further divided into two types: confined deep-water channels and semi-confined unidirectionally migrating channels. (2) The Upper Eocene third-order sequence can be divided into three fourth-order sequences: Ps1, Ps2 and Ps3. Among them, the Ps1 sequence develops a confined deep-water channel-lobe complex, the Ps2 sequence develops a semi-confined unidirectionally migrating channel-lobe complex, and the Ps3 sequence develops a lobe complex. The evolution of these sequences represents a cyclic evolution process within the third-order sequence under the background of continuous rise in sea level, changes in seafloor landform filling, attenuation of gravity flow energy, and relative enhancement of bottom currents.(3) Bottom currents could strip fine-grained materials in gravity flows accumulate on the northern side (downstream side of the bottom current) of the deepwater depositional system, forming asymmetric overbank/drift deposits with positive topography. This, thereby, restricts channels and lobes to southward erosion and deposition, resulting in the Eocene deepwater depositional system and depositional architectural elements that exhibit a unidirectional migration and stacking pattern on the upcurrent side. It is inferred that bottom currents may enhance the reservoir quality of gravity flow deposits.