Seismically active faults may control fluid flow while affecting regional geohazards. Here, we analyzed fluid migration processes along a large fault in a carbonate and evaporite sequence of the western Sichuan basin, adjacent to the Mw 7.9 Wenchuan earthquake. This study focuses on the architecture of the Pengxian fault (PXF), which is a dominant blind thrust at the frontal zone between the Sichuan basin and the Longmen Shan range. The PXF is ~55 km long with a damage zone thicker than 1 km, which apparently affected the regional migration of hydrocarbons. For the analysis, we used 3D seismic survey data, geochemical data, and core samples from a gas reservoir in the western Sichuan basin. The results indicate: (1) the PXF damage zone is separated into two vertical mechanical blocks by a ductile detachment zone of Triassic anhydrite; (2) bitumen occurrences and carbon isotope analyses indicate that gas and fluid migration across the anhydrite of this detachment zone occurred along the PXF damage zone; (3) the PXF damage zone served as a preferential conduit for subsurface fluid flow and acted as a fault valve in a seismic cycle. We anticipate that fluid communication along fault damage zones could lead to fault weakening and associated hazards in seismically active regions.

The dual role of late-stage carbonized kerogen as both a gas source and a seal is critical for assessing ultra-deep subsurface systems. This study investigates a Maidiping Formation kerogen (Ro-Bitumen approximate to 2.54%), a natural analogue for ultra-deep organic matter in Sichuan Basin, to constrain its structural characteristics and bifunctional behavior. Multiscale characterization reveals a nanoporous carbon framework composed of small fused aromatic domains (typically similar to 3 & times; 3 rings), poorly aligned stacking motifs, an expanded interlayer spacing, and dispersed heteroatoms. These empirical constraints guided the construction of a representative 3-D molecular model (C3066H1960N28O168S14) featuring short aliphatic chains, oxygen/nitrogen/sulfur functional groups, and microporous aromatic clusters. Reactive molecular dynamics simulations quantified the kerogen's dual functionality: the peak pyrolysis rate indicates a latestage methane potential of 25.94 mL/g (STP), while the model exhibits strong sealing capacity reflected in high methane adsorption (33.8 mg/g) and a very low self-diffusion coefficient (0.2243 & times; 10-7 cm2/s). These findings demonstrate that overmature kerogen acts as an active, bifunctional geomaterial, which provides anew molecular-level framework for assessing integrated source-seal systems in ultra-deep exploration. (c) 2026 China University of Geosciences (Beijing) and Peking University. Published by Elsevier B.V. on behalf of China University of Geosciences (Beijing). Thi s is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Fault damage zone permeability governs fluid migration, fault mechanics, and seismic rupture dynamics. Here, we investigate the permeability structure of the Triassic damaged stratigraphy beneath the frontal Longmen Shan fault system-a key structure within the Sichuan Basin-through direct analysis of deeply drilled core samples (similar to 6800 m depth) from the LS1 borehole. We integrated mineralogical analyses, permeability measurements under in situ stress conditions (5-125 MPa effective pressure) using the pore pressure oscillation (PPO) method with distilled water, and microstructural observations. X-ray diffraction (XRD) results reveal a pronounced mineralogical contrast between intact and damaged fault-zone samples. The intact anhydrite (Anh-01) is dominated by anhydrite (similar to 89 %) with minor dolomite (similar to 10 %), whereas the mixed dolostone-anhydrite cataclasites (Dol-Anh-01 and Dol-Anh-02) contain progressively higher dolomite (40-93 %) and illite (1-6 %), together with accessory quartz, feldspars, and trace gypsum. The co-occurrence of soluble feldspars and illite indicates fluid-mediated alteration and phyllosilicate network development during cataclastic deformation, consistent with fluid-rock interaction documented in active fault zones. Permeability decreases nonlinearly with increasing effective pressure: a sharp reduction at 5-25 MPa likely reflects fracture closure, followed by gradual compaction at 40-125 MPa. The damage lithology, rich in brittle dolomite-anhydrite fragments (>40 %), shows permeability of 10(-20)-10(-18) m(2), whereas the intact anhydrite exhibits lower values (10(-21)-10(-19) m(2)). Permeability anisotropy arises from (i) brittle block abundance, (ii) weak-phase alignment (e.g., clay films along microfractures), and (iii) mineralogically driven pore-network heterogeneity. We propose a dynamic permeability model in which seismic slip enhances fracture connectivity (permeability surge), followed by postseismic self-sealing through compaction and mineralization-a feedback mechanism modulating fluid overpressures and recurrence intervals. This study provides the first in situ constraints on the hydromechanical behavior of an evaporite-carbonate damaged stratigraphy at seismogenic depths in Longmen Shan range. The results challenge assumptions of static permeability in fault models and highlight the necessity of integrating lithological heterogeneity and transient hydraulic processes in seismic hazard assessments.

Natural gases from deep to ultra-deep Ediacaran–Cambrian carbonate reservoirs in the Sichuan Basin exhibit complex geochemical signatures, including widespread isotope reversals, inconsistent with conventional single-source maturation models. These features reflect the combined effects of multi-source mixing and intense post-emplacement thermal alteration. Integrated geochemical data and quantitative modeling constrained by thermal simulation experiments indicate that the gases are multi-source mixtures in which external oil-cracking gas provides the dominant charge (typically 40–60%), with additional contributions from in situ source rock-derived thermogenic gas. In the most thermally mature reservoirs, extreme isotopic signatures result from intense fluid-mediated alteration, characterized by near-complete ethane cracking (δ13C2 of up to –23.6‰) and hydrogen isotope rollover (δ2H-CH4< –155‰) caused by methane-water interaction. Quantitative modeling results further show that diffusive loss, while significant for the gas volume, played a subordinate role in the isotope fractionation. In this study, we established a multi-stage genetic model for these gases, in which an initial mixing event was subsequently overprinted by intense, in situ geochemical reactions.

Liquid hydrocarbons (LHCs) derived from humic organic matter (HOM) exhibit high potential for late-stage gas generation through recombination reactions. The biomarker composition and isotopic geochemical signatures of these LHCs can provide insights into the origin, maturity, and depositional environment of organic matter. Semi-open system thermal simulation experiments were performed on typical low-maturity humic source rocks from the Ordos Basin. The resulting LHCs were quantitatively characterized, followed by separation into compound-grouped fractions and subsequent analysis by GC–MS and stable carbon and hydrogen isotopic measurements. Based on the yield characteristics of LHCs, the applicability of biomarker parameters in HOM is systematically assessed, and the carbon and hydrogen isotopic fractionation mechanisms of alkanes are explored. The results demonstrate that: (1) LHCs are generated throughout the entire pyrolysis process of HOM, with the C15+ resins and asphaltenes fraction accounting for a relatively high proportion. The n-alkanes in HOM are dominated by short- to medium-chain homologues. Within the maturity range covered by pyrolysis experiments, the δ13C values of compound-grouped fractions are heavier than −27‰; those of n-alkanes are heavier than −29‰, and the corresponding δD values are lighter than −140‰, (2) the distribution of n-alkanes, relative content composition of steranes, and carbon isotopic compositions of polar fractions collectively indicate that the organic matter was predominantly derived from terrestrial C3 plants. Isoprenoid alkane ratios and the gammacerane index suggest that the source rock was deposited in a dysoxic freshwater environment, and terpane parameters exhibit a favorable correlation with thermal maturity across the oil-generation window, and (3) the kinetic isotope effect (KIE), along with cracking of polar compounds and C15+ aromatic hydrocarbons, causes the average δ13C values of n-alkanes to initially increase and subsequently decrease. Throughout thermal maturation, aromatic moieties and unsaturated cross-linked structures in HOM undergo hydrogen isotopic exchange with D-depleted formation water. Cracking via active free-radical reactions further amplifies this isotopic exchange, yielding n-alkanes with lighter average δD values. The distinct linear distribution patterns between δ13C and δD values of n-alkanes can be utilized to discriminate mixed-source oils and provide preliminary maturity assessment. This study enhances the understanding of the geochemical characteristics of LHCs derived from HOM and provides a scientific basis for the evaluation of hydrocarbon generation potential, gas-source correlation, and maturity in humic source rocks.

Aromatic hydrocarbons (AHc), as major constituents of coal and petroleum systems, are widely used as geochemical proxies for depositional environment, organic matter source, and thermal maturity. In this study, semi-open pyrolysis experiments were conducted on low-maturity humic organic matter (HOM) from the Ordos Basin. After fractionation of the liquid products, the aromatic fractions of retained oil (ReO) and expelled oil (ExO) were analyzed by gas chromatography–mass spectrometry (GC–MS), and 145 aromatic compounds from 16 homologous series were identified. Naphthalene, phenanthrene, dibenzothiophene (DBT), and pyrene series were selected to evaluate maturity parameters and to examine molecular processes relevant to late-stage gas generation. The results indicate that: (1) these aromatic series generally exhibit a unimodal abundance pattern during HOM maturation, with an initial increase followed by a decline, and the phenanthrene series remains dominant; (2) alkyl aromatic parameters can record thermal maturity within a defined window (Meas-Ro approximately 0.85–1.42%), among which alkyl phenanthrene parameters show the highest sensitivity, consistent with observations from sapropelic organic matter (SOM) and coal; and (3) the aromatic-rich framework of HOM favors the formation of thermally stable pyrobitumen and may provide methyl-derived methane during late-stage gas generation. At Meas-Ro values above 1.42%, the abundances of naphthalene and phenanthrene decrease markedly, suggesting consumption during high-maturity transformation, although the contributions of non-hydrocarbons and asphaltenes require further investigation. This study supports the application of aromatic maturity parameters in humic-derived liquid hydrocarbons and provides new constraints on late-stage gas generation from HOM. The findings provide a geochemical basis for evaluating the gas-generation potential of coal-bearing source rocks and may contribute to the exploration of deep and ultra-deep coal-derived gas accumulations.

Carbonate source rocks with low total organic carbon (CSRLTOC) are widely distributed in global petroleum systems, yet their hydrocarbon generation potential, expulsion efficiency, and contribution to large-scale accumulations remain controversial, particularly in tectonically active basins. This study focuses on the Middle Triassic Leikoupo Formation (T(2)l) in the Western Sichuan Depression, northwestern Sichuan Basin, to constrain gas origins and accumulation mechanisms through integrated geochemical and geological analyses, with particular emphasis on distinguishing between gas generated in situ from CSRLTOC and gas derived from deeper Paleozoic sources through fault-assisted migration. The results indicate that T(2)l natural gas is derived primarily from CSRLTOC, characterized by extremely high dryness and isotopic signatures reflecting advanced thermal maturity. Quantitative two-endmember mixing models show that contributions from secondary oil-cracking gas are limited (mostly < 20%), consistent with the widespread absence of solid bitumen and oil-phase inclusions, suggesting no large-scale paleo-oil accumulations formed or subsequently cracked. The thermal and burial history reveals strong temporal coupling between the peak gas generation of the CSRLTOC and Late Yanshanian trap development, while Himalayan tectonic compression activated fracture systems that enhanced expulsion efficiency. Collectively, the Leikoupo Formation gas reservoirs in the Western Sichuan Depression formed under a source-reservoir integrated accumulation model characterized by late-stage tectonic activation and proximal accumulation, providing new insights for hydrocarbon exploration in structurally active CSRLTOC basins.

The oxygen isotope composition (δ18O) of Phanerozoic seawater has been widely investigated, but the δ18O values of Precambrian seawater remain poorly constrained, with ongoing debate over whether they were substantially lower than those of Phanerozoic seawater. To address this question, we analyzed the clumped isotopes of limestones from the North China Craton to reconstruct Mesoproterozoic seawater temperature and δ18O values. Our results indicate that the Mesoproterozoic seawater had a temperature of 26.9° ± 0.4°C and a δ18O value of -6.3 ± 0.2 per mil (relative to standard mean ocean water). This δ18O estimate aligns with previous inferences from geochemical modeling, marine iron oxides, and oxygen isotope ensembles, supporting the hypothesis that Mesoproterozoic seawater was isotopically lighter than its Phanerozoic counterpart. These findings provide insights into the Earth's paleoclimate and the evolution of seawater composition during the Mesoproterozoic era.

Carbonate platforms provide important sedimentary archives for paleoceanography and recording paleoenvironments. The aim of this study was to decipher the control of platform evolution and its constraint on the chemostratigraphic correlation in the Lower Cambrian at the eastern part of the Yangtze Platform. With the petrological observation, XRD, as well as C and O isotope analysis, two third-order sequences (SQ1 and SQ2) and six fourthorder sequences (PSQ1, PSQ2, PSQ3, PSQ4, PSQ5, and PSQ6) were recognized in the Longwangmiao Formation. Thirteen lithofacies (Lf-1–Lf-13) and three facies associations (shoreface, upper offshore, and lower offshore) were identified across the proximal to distal range of the platform. The correlation between logged outcrop sections suggested that the carbonate platform evolved from a homoclinal ramp in PSQ1 to a more distally deepened geometry in PSQ2, with this evolution driven by synsedimentary fault activity. From PSQ2 to PSQ3, the geometry evolved from a ramp to a rimmed platform associated with depleted d13C values and an increasing Chemical Index of Alteration (CIA) index. Such a transition of platform geometry may be attributed to the enhanced rate of carbonate production due to intense weathering and nutrient input. The final evolution of the Eastern Yangtze Platform (PSQ4) seemed to have been driven by falling relative sea levels and resulted in the formation of a flat-topped morphology, associated with subaerial exposure and depleted in d13C (LNE2). The two final sequences recognized in outcrops, PSQ5 and PSQ6, were only recognized in the distal reaches of the deposit and were interpreted to be “missed beats” in the sense that the sea level did not transgress the platform top. This study suggests the importance of carbonate production driven by chemical weathering on the control of platform geometry and sequence stratigraphy..

Oxygen isotope (delta 18O) of paleolake water is a key indicator for reconstructing the formation temperature and diagenetic history of lacustrine carbonate minerals. In this study, we use clumped isotopes (Delta 47) of lacustrine shell limestones to determine the surface erosion thickness and delta 18O of Early Jurassic lake water in the northern Sichuan Basin. We analyzed nine shell limestone and seventeen shale samples from the Early Jurassic Da'anzhai Member (J1z4) in the Yuanba area. Whether the shell's shapes are well or partially preserved, the J1z4 shell limestones in the Yuanba area show no significant recrystallization and dull cathodoluminescence. These characteristics suggest that the shell limestones did not undergo significant diagenetic alteration during late burial. The Delta 47 values of the J1z4 shell limestones range from 0.448 f 0.005%o to 0.463 f 0.006%o, yielding clumped isotope temperature (T Delta 47) of 64.4 f 0.8 to 69.7 f 1.4 degrees C, which is significantly higher than the Early Jurassic paleotemperature. It suggests that the Delta 47 of shell limestones was altered by solid-state reordering, meaning the T Delta 47 does not reflect the initial formation temperatures. By integrating organic matter's maturation model (Easy% Ro) of coexisting shales with Delta 47 solid-state reordering model of calcite, we constrained the maximum burial temperature (-170 degrees C) and the initial formation temperature (-28 degrees C) of these shell limestones. Based on reported paleotemperature gradient, we estimated that the surface erosion thickness was about 1500 m. Furthermore, using the determined initial formation temperatures and conventional oxygen isotope thermometer, we determined that the delta 18O values of the Early Jurassic lake water in the Sichuan Basin, which ranged from -10.8%o to -8.0%o (SMOW). The reconstructed paleotemperature and delta 18O of lake water suggest that the Early Jurassic in the Sichuan Basin was warm and humid, which was favorable for the deposition of organic-rich lacustrine shale. The methods developed in this study, which employ Delta 47 of shell limestones to reconstruct the maximum burial temperature and paleolake environmental conditions, demonstrate broad applicability to the Sichuan Basin and similar lacustrine basins. (c) 2025 The Authors. Publishing services by Elsevier B.V. on behalf of KeAi Communications Co. Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Paleokarst is a major contributory factor for natural gas reservoir development of the Middle Permian Maokou Formation in Sichuan Basin, South China. To promote the reliability of the paleokarst geomorphology estimations, which are fundamental for the prediction of paleokarst reservoir distribution, a process combining sequence stratigraphic correlation, paleokarst genesis analysis, paleogeographic reconstruction and sequence stratigraphic thickness variation studies is implemented. Three 3rd-order sequences (named TR1–TR3) are defined in the Maokou Formation based on the literature and the carbonate δ13C chemostratigraphy, according to which 147 boreholes and outcrops are correlated via lithology, well log and seismic data. The results of sequence stratigraphic correlation reveal that thickness variations of TR3 stratigraphy are complicated and heterogenous, including three areas of abnormally thinned strata: southern Sichuan Basin, northern Sichuan Basin and Chengdu region. However, along with the paleokarst and paleogeographic studies, only the stratigraphic thinning of southern Sichuan Basin is related to subaerial exposure and karstification, whereas that of northern Sichuan Basin and Chengdu region are due to sedimentary differentiation. Consequently, the paleokarst geomorphology of Maokou Formation is estimated from stratigraphic thickness combined with sedimentary factors. The paleohigh located at the Luzhou region in southern Sichuan Basin, where the TR3 stratigraphy is absent. Around the peleohigh, most of the basin acted as karst slope and karst basin with gentle gradients. Meanwhile, the northern part of basin shows little evidence of paleokarst inside the Maokou Formation, appearing to be continuous sedimentary platform. The paleogeomorphology pattern is consistent with the discovered distribution of Maokou paleokarst reservoir and can be utilized in play evaluation.

While marine dolomites formed under near surface conditions have been considered to be potentially reliable archives of past oceanic conditions, this interpretation comes with significant challenges because diagenetic alteration frequently produces diverse fabrics with large geochemical variability. It has been suggested that the Ediacaran dolomites in South China (Hamajing Member, Dengying Formation) recorded the oceanic conditions present at the time they formed, yet these dolomites are composed of five different fabrics (stromatolitic, micritic, oolitic, saddle dolomites and fibrous–radial dolomite cements) and show large variations in multiple geochemical isotope proxies (carbon, oxygen, clumped, magnesium and the sulphur of carbonate‐associated sulphate). This study establishes a paragenetic sequence for these dolomites by combining the clumped and the oxygen isotopic compositions, thereby assessing whether they are geochemically representative of the original seawater. Using this diagenetic framework, the micritic and stromatolitic dolomites show a closed‐system behaviour (low water–rock ratios; <0.3) and are largely resistant to the hydrothermal alteration during late diagenesis. In contrast, the ooid and cement fabrics have been affected by the hydrothermal fluid precipitating saddle dolomite in the open‐system condition with the high stimulated water–rock ratios (>1). Furthermore, in a closed‐system environment, the elevated δ 24 Mg and δ 34 S values in the stromatolitic dolomite reflect the isotopic Rayleigh fractionation that enriches the 26 Mg and 34 S through rock‐buffered recrystallization, coupled with microbial sulphate reduction. These results demonstrate that the complex signals in early marine dolomite should be carefully evaluated when used as a palaeoproxy.

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The cracking and stability of liquid oil is of critical importance in the exploration of deep petroleum accumulations. Numerous studies have been conducted on oils to investigate the cracking process. However, limited research has been directed to the cracking of oil with different maturities. Here, gold tube pyrolysis experiments were conducted on lower maturity normal oil (LMO) and higher maturity condensates (HMC) samples to investigate the compositions of pyrolysis products and to estimate the stability of oil during continuous deep burial. The results indicated that oil cracking can be generally divided into two stages, namely light oil generation stage and gas generation, with a maturity boundary approximately EasyRo ∼1.5%. Most of oil cracking gas was generated at EasyRo ∼ 2.4 %, with maximum mass yield of C1-5 is 553.8 mg/g and 609.4 mg/g for LMO and HMC, respectively. The difference in gas yields between HMC and LMO indicates the higher gas potential during the cracking of light oil components. An obvious increase in the C19/C23 tricyclic parameters was observed with enhanced thermal maturity, which indicates the interpretation of tricyclic parameters of high mature oils should be made with caution. Although high maturity also influenced the ratios of gammacerane/αβ C30 hopane (G/H) and 4-methylsteranes/C29 steranes (4MSI), the altered corresponding values still fall within the suggested discriminating zones for the Dongying and Shahejie Formation source rocks. Thus, the G/H and 4MSI parameters can be utilized to characterize the high mature oil with Ro <1.3% in the Bohai Bay Basin (BBB) or other basins. The calculated activation energy of C1-5 generation for LMO displays a more discrete and lower distribution compared to the HMC, which may indicate relatively lower stability heavy hydrocarbons in LMO. Based on previous studies of petroleum charge, the kinetics of C1-5 generation of LMO were extrapolated to geological conditions, yielding a maximum depth of 5750 m for the occurrence of liquid oil in the BBB. This study underscores the high thermal stability of light oil fractions, which indicates that deep high mature oils may represent the preservation of directly charged light oil or the transformation by in-reservoir cracking of normal oil associated with continuous burial.

Microfractures can connect isolated pores within shale, significantly increasing the shale’s storage capacity and permeability, and benefiting shale gas exploitation. Therefore, the quantitative characteristics of microfractures are important parameters for shale reservoir evaluation. In this paper, taking the Jurassic Da’anzhai Member (J1z4) lacustrine shale in the Yuanba area of the northern Sichuan Basin as an example, we propose a method for comprehensive and quantitative characterization of shale microfractures that combines rock thin section (RTS) and scanning electron microscopy (SEM) observations. The different magnifications of RTSs and SEM images lead to the identification and characterization of microfractures of different scales using these two methods. RTSs are mainly used to characterize microfractures with widths larger than 10 μm, while SEM is mainly used to characterize microfractures with widths smaller than 10 μm. These techniques can be combined to comprehensively and quantitatively characterize microfractures of different scales in shale. The microfracture characterization results show that the average total porosity of the J1z4 shale is 4.46%, and the average microfracture surface porosity is 1.20% in the Yuanba area. The calculated average percentage of microfracture porosity to total porosity is 21.09%, indicating that the J1z4 shale reservoir space is dominated by pores and has the conditions for stable shale gas production and potential for shale gas exploration. However, the percentage of microfracture porosity to total porosity of shale near faults and fold zones approaches or exceeds 50%, which may lead to the loss of shale gas. The new method proposed in this study is also useful for quantitative characterization of shale microfractures in the Sichuan Basin and other basins.

Pore structure is an important parameter for the gas-bearing evaluation of lacustrine shale. However, the characteristics and influencing factors of pore structure and the shale reservoir capacity remain unclear due to the heterogeneity and complexity of shale reservoirs. This study focused on Da'anzhai shale to research the pore structure characteristics using a combination of field emission scanning electron microscopy, low pressure gas adsorption, and mercury intrusion porosimetry. The effects of different matrix components on multi-scale pore structure and the reservoir capacity are discussed. The results show that the total organic carbon (TOC) and vitrinite reflectance (Ro) are 0.7%–1.68% (average of 0.98%) and 1.42%, respectively. The organic macerals are vitrinite, inertinite, and solid bitumen, with the vitrinite predominating. The main minerals are clay minerals, quartz, and calcite. Matrix pores, including mineral-associated pores and organic matter pores, and microfractures jointly constitute the pore system of the Da'anzhai shale. Clay-mineral pores dominate, followed by organic matter pores. Pore sizes mainly range from 0.3 nm to 20 nm, reaching up to 10μm. Mesopore volumes are dominant, followed by micropores and macropores. The pore specific surface areas are 12.76–21.24 m2/g (average of 17.43 m2/g), of which micropores and mesopores account for 48.7% and 51.3%, respectively. TOC, organic macerals, and clay minerals are the controlling factors of the pore structure. In contrast, the impacts of Ro and the framework mineral content on shale pore structure are relatively weak. Da'anzhai shale has sufficient pore volume and specific surface area but the shale is dominated by clay mineral-associated large-size pores and microfractures with few organic micropores, resulting in limited adsorption capacity for the shale. A greater understanding of the pore formation mechanism of shale reservoirs is obtained through this study, which is of great significance for gas-bearing evaluations.

Microbial carbonate reservoirs are the main petroleum exploration targets in the upper submember of the fourth member of the Middle Triassic Leikoupo Formation in the western Sichuan Basin. To improve understanding of the distribution and reservoir characteristics of microbial carbonates, detailed facies descriptions and reservoir characterizations were performed under the framework of cyclostratigraphy. Ten facies can be identified and grouped into four facies associations in two transgressive-regressive cycles, within an epeiric marine carbonate platform in the western Sichuan Basin. In Cycle 1, Emei taphrogeny caused the formation of the Longmenshan subaqueous paleo-uplift, which formed a relatively restricted tidal flat environment and developed large-scale microbialites on its eastern side. In the central area, wavy to domal stromatolitic dolowackestone (F3) and thrombolitic dolomudstone (F4) are developed in the intertidal and subtidal of the central area with steep substrate gradients and restricted seawater circulation. Laminated microbial dolowackestone (F2) is mainly developed in the intertidal of the southern area with low substrate gradients and restricted seawater circulation. Intraclast dolograinstone (F6) are widely developed in the subtidal shoals of the northern area, which is frequently disturbed by tides and waves with better seawater circulation. In Cycle 2, increasing relative sea level weakened the barrier of Longmenshan subaqueous uplifts to waves, the restricted subtidal environment developed the intraclast dolograinstone (F6) and intraclast packstone-grainstone (F7), occupying the platform with better seawater circulation and higher energy. The framework or inter-clot pores of F2, F3 and F4, interparticle pores of F6, and vugs resulting from syn-depositional dissolution are the dominant pore types. High-quality reservoirs are mainly distributed in the regressive microbialites (F2–F4) of Cycle 1 in the central area and intraclast dolograinstone (F6) of Cycle 1 and Cycle 2 in the northern area. The porosity of microbialites and intraclast dolograinstone reservoirs mainly ranges from 2.26% to 10.00%, with a mean value of 4.96%. The permeability mainly ranges from 0.01mD to 13.98mD, with a mean value of 4.63mD. This study proposed a depositional framework of microbialites and evaluated its control on reservoir quality, which is of great significance for the further study of microbial carbonate reservoirs.

渤海湾盆地烃源岩有机质类型以Ⅰ-Ⅱ型为主,是典型的富油裂陷湖盆.以渤海海域(渤海湾盆地海域部分)渤中地区为例,从天然气来源与成因判识剖析油型盆地干酪根的生气特征以及深层天然气勘探前景.结果表明,对于相同热演化程度的干酪根而言,其热解气的量与烃源岩的氢指数呈正相关关系,而且大部分干酪根热解气在Ro=1.5％之前已经生成.生气强度表明,即使对于热演化程度相对偏低的富油盆地,以干酪根热解为主的天然气生气量仍满足大中型气田形成的物质基础.高生产率主导的倾油型母质具有相对重的沉积有机碳同位素组成,因此乙烷碳同位素较重的天然气不一定是来源于偏腐殖型或者煤系烃源岩,也可能来自较高成熟度的倾油型母质.以R.=1.5％为界,早期生成原油深埋裂解整体可分为两个阶段:第一阶段原油裂解轻质化,该阶段油裂解生成的天然气量相对少,第二个阶段轻质油大量裂解生成天然气,表明生油高峰期(浅层)充注的原油在深埋过程具有较高的热稳定性,深层仍可能富集规模轻质油或凝析油气.