Helium, vital for advanced technologies, is generated in the crust via uranium (U) and thorium (Th) decay. The crystalline basement is a proven source of helium. In contrast, the role of sedimentary rocks, while often considered significant, has lacked definitive proof. This study provides the isotopic evidence to deconvolve these two crustal sources and verify the significant role of sediment. Our analysis of the Dongsheng Gas Field, Ordos Basin, China, reveals that air-derived noble gases reflect open-system water-gas equilibration, a process occurring within the reservoir. Whereas crust-derived noble gases likely pre-aggregated and migrated together with hydrocarbons, thereby preserving a clear signature of their original sources. Within this preserved signature, a depletion of Ne-21* (where * denotes a crustal origin) is observed. This depletion produces an unusual negative correlation between Ne-21*/Ar-36 and Ar-40*/Ar-36, in contrast to the expected positive trend. This pattern is interpreted as the mixing of a fluid from coal-bearing strata (Ar-40*/Ar-36 = 130 +/- 10) with a Ne-21*-depleted fluid from the basement (Ar-40*/Ar-36 = 2250 +/- 150). Modeling suggests that only similar to 0.26 % of basement-generated Ne-21* is retained. We propose a helium accumulation model in which initial preservation was inefficient owing to the absence of a seal, whereas the main accumulation was driven by hydrocarbon charging, which acted as a carrier fluid stripping helium from coal-bearing strata. These results demonstrate that U- and Th-rich sedimentary rocks can serve as a potential helium source in natural gas, which refines exploration strategies for helium in cratonic basins.

Understanding diagenetic processes plays a crucial role in evaluating the quality of tight reservoirs. In this study, we aimed to examine diagenetic facies and thereby assess reservoir quality by conducting an integrated analysis of porosity, petrology, permeability, mineralogy, mercury injection, and stable isotopic data in core samples from the Permian Shan 2 and He 1 members (Shan 2-He 1 Mbr) in China's Ordos Basin. Early compaction and precipitation of diagenetic minerals have significantly reduced primary pore space in these members, although certain sandstones have retained anomalously high porosity. These high-porosity reservoirs have been shaped by many factors, with dissolution identified as the predominant mechanism. Detailed petrographic observations and assessments of the primary minerals, the minerals' genesis, and associated diagenetic processes revealed seven distinct diagenetic facies differentiated by their sand-grain populations, types of cementation, clay matrix contents, and volcanic tuffaceous sediment (VTS). The main interstitial fillings consist of VTS, clay minerals, quartz overgrowths, and calcite (ferrocalcite). Clasts and VTS-dissolved sandstone have mainly formed Class I reservoirs with highly unstable grains and good secondary pores resulting from the dissolution of the grains and VTS. VTS tight sandstone, siliceous cementation tight sandstone, illite-siliceous cementation tight sandstone, and calcite cementation tight sandstone have formed Class II reservoirs with high rates of interstitial filling and cementation. Sandstone tightly cemented by illite has poor reservoir properties and has mainly formed Class III reservoirs. This classification underscores the critical importance of understanding diagenesis, diagenetic facies, and especially the diagenetic features of VTS for accurately assessing reservoir quality. A comprehensive understanding of these factors may facilitate more effective hydrocarbon exploration and exploitation in this area. (c) 2025 Sichuan Petroleum Administration. 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/).

In recent years,the Ordos Basin has undergone a reevaluation,transitioning from a perception of a single block to a focus on understanding the influence of multiple stages and fault systems on hydrocarbon accumulation.This study utilizes the latest 3D seismic and drilling data alongside a theoretical model of strike-slip fault to analyze fault geometry and kinematics in the Xunyi-Yijun area of the basin's southern region.The mechanisms of fault formation are predicted and the related impacts on the formation and accumulation of deep carbonate rocks are also discussed.The results indicate the presence of three fault systems in the Xunyi-Yijun area,with decoupling between deep and shallow layers.The Lower Paleozoic strike-slip faults exhibit distinct characteristics,including high vertical structure,dip swing,and a"flower-shaped"structure in the section.The faults display"compression shear in the northwest,tension shear in the center,and segmental deformation on trunk fractures"on their planes.Moreover,the Lower Paleozoic strike-slip faults experienced two stages of tectonic activities with greater intensity observed from the Late Ordovician to the Silurian,marking the primary period of fault development.The activity intensity during the Middle to Late Permian was relatively weaker,with faults exhibiting inherited strike-slip charac-teristics.These faults formed two groups,one with a NE strike and the other with a NW strike.Additionally,during the second stage of the Caledonian period,ocean subduction and closure lead to stress being transferred to the basin interior.It is believed that the NE and NW strike basement weak zones existed in the southern Ordos Basin.As a result,the Lower Paleozoic strike-slip fault system likely formed due to the activation of oblique compression.This fault system has the potential to enhance the physical properties of deep carbonate reservoirs and create high-quality karst or tectonic fracture reservoirs in the Xunyi-Yijun area.Moreover,The formation of the"upper source and lower reservoir-lateral source and lateral reservoir"combination along the strike-slip fault belt is an area of interest for deep oil and gas exploration in the Xunyi-Yijun region.

The Permian Shan 2 and He 1 members (Shan 2-He 1 Mbr) are the main tight gas-producing intervals in the Ordos Basin. This reservoir mainly comprises low-permeability and ultra-low-permeability fluvial–deltaic sandstones. However, the formation of tight sandstone reservoirs, particularly those associated with volcanic tuffaceous sediment, remains poorly understood. Therefore, in this study, we aimed to identify the most favourable mechanism for reservoir formation using petrological, mineralogical, scanning electron microscopy with energy dispersive spectroscopy, X-ray diffraction, and porosity and permeability analyses to investigate the characteristics and porosity changes of the Shan 2-He 1 Mbr. The reservoir consists predominantly of lithic and lithic quartz sandstones, with an average porosity of 6.07% and average permeability of 0.434 mD. Depositional processes were crucial in controlling reservoir formation. Different sedimentary microfacies exhibited varying physical properties, of which coarse-grained braided bars and channel fill that formed in high-energy environments exhibited superior petrophysical properties. Rapid early compaction was the main cause of reservoir densification. Additionally, illite cement, secondary quartz grain enlargement, and late-stage carbonate cement negatively affected the reservoir quality. Secondary pores formed through the dissolution of terrigenous clasts, volcanic tuffaceous sediment (VTS), and carbonate cement. Diagenetic processes introduced heterogeneity and modified the reservoir, resulting in an effective reservoir space that comprises dissolution and intercrystalline pores, with limited primary pores. The reservoir physical properties were influenced by the sedimentary facies, siliceous mineral content, diagenetic processes, and the presence of VTS. Therefore, a comprehensive understanding of these factors is vital for identifying favourable reservoir formation conditions in the Shan 2-He 1 Mbr.

Shale reservoir has strong heterogeneity in mineral composition and oil content even at a short distance in the same interval. To better understand the accumulation mechanism of shale oil and hydrocarbon migration tendency in the interval, and explore the main influencing factors of distribution. This paper employed various methods, including thin‐section observation, TOC (total organic matter (OM)) analysis, rock pyrolysis, Soxhlet extraction, group component separation, and GC–MS (gas chromatography mass spectrometry) analysis of saturated hydrocarbons. The shale oil samples were collected from an exploratory well in the Songliao Basin, and the distribution and enrichment characteristics of shale oil interlayers were analysed. The results show that the first member of Qingshankou Formation (K 2 qn 1 ) could be divided into six small layers. From Q1 to Q6, the lithofacies could be divided into three types: high‐frequency laminar shale, massive shale, and bioclastic shale. The lacustrine matrix shale of K 2 qn 1 in Songliao Basin has medium TOC, and high oil contents, OM conversion rate. The TOC ranges from 1.5 to 4.2 wt%, S 1 varies between 1.4 and 4 mg/g, S 2 falls within the range of 4 to 10.6 mg/g, Tmax ranges from 351 to 497°C, and the OSI varies between 57 and 115.34 mg HC/g rock. The lower part of the K 2 qn 1 , Q1–Q4, characterized by high‐frequency laminar shale, contained residual shale oil, while the upper part of the K 2 qn 1 , Q5 and Q6, characterized by bioclastic shale and massive mudstone, and are dominated by in‐situ type shale oil. The crude oil in K 2 qn 1 is homologous, and primarily undergoes micro‐migration. The Q5–Q6 section has the highest light oil content, while other regions with notable light components are located in the middle of Q1, the upper sections of Q2, Q3, and Q4.Q1–Q4 are primarily composed of residual shale oil, whereas Q5–Q6 is primarily composed of in‐situ shale oil, and the primary micro‐migration direction of shale oil occurs laterally within Q1–Q4. The lateral migration of each section mainly occurs at the upper part of Q3 and Q4, the lower part of Q1 and Q2, the bottom of Q5, and the interface between Q6 and the second member of Qingshankou formation (K 2 qn 2 ). The block mudstone retains in‐situ shale oil, especially light hydrocarbons. Within the high‐frequency laminar shale, there is strong horizontal connectivity, and lateral hydrocarbon expulsion serves as the primary mechanism for micro‐migration in Q1–Q4. This paper can provide reference values for K 2 qn 1 Formation shale oil and the migration and differential reservoir formation of medium and high‐maturity matrix shale oil.

近年来峨眉山大火成岩省及其地幔柱成因研究取得了重要进展,但关于地幔柱在四川盆地的作用范围和二叠纪成盆动力学机制等方面存在认识分歧.基于大量文献调研并结合近期研究,采用深部地幔活动控制表层系统演变的研究思路,系统梳理峨眉山大火成岩省及其深部地质特征.地幔柱是诱发峨眉山玄武岩大规模喷发并形成大火成岩省的主导因素,但地幔柱仅对四川盆地部分地区具有直接影响,具体表现为地幔柱上涌引起地壳隆升并导致中二叠统茅口组顶部出现地层差异剥蚀和对盆地中南部二叠纪沉积的控制作用,而盆地中北部中晚二叠世—早三叠世拉张槽群和"凹凸相间"沉积-构造格局的形成则主要受控于南秦岭洋岩石圈板块的拉张.

It has not been clearly understood whether the hydrocarbon generated from the argillaceous sourcerocks of the Lower Cambrian Qiongzhusi Formation could upward pass through the regional cap rocks of the Lower-Middle Cambrian gypsum rocks and accumulate in the Middle-Upper Cambrian Xixiangchi Group reservoir, namely the cross-formational hydrocarbon accumulation, in the eastern Sichuan Basin. Therefore, the studies on the reservoir solid bitumen in the Xixiangchi Group and the sealing performance of the regional cap rocks of the Lower-Middle Cambrian gypsum rocks were carried out, and the cross-formational hydrocarbon accumulation of the Cambrian oil and gas and its significance for natural gas exploration were discussed. It was shown by synthetic studies that the reservoir solid bitumen in the Xixiangchi Group mainly originated from the argillaceous source rocks of the Lower Cambrian Qiongzhusi Formation. The sealing integrity of the regional cap rocks of the Lower-Middle Cambrian gypsum rocks was damaged to some extent by the reactivated basement faults and the large nascent faults in the Middle Permian to Middle Triassic though it had good sealing performance in geological times, which could provide convenient vertical pathways for the Cambrian cross-formational hydrocarbon accumulation in the eastern Sichuan Basin. Three evolutionary stages were built up about the Cambrian hydrocarbon migration and accumulation as follows. Stage 1 is the formation of the Cambrian pre-salt early paleo-reservoirs in the period ofthe Late Silurian to the Early Permian (S3-P1), stage 2 is the one of the Cambrian cross-formational hydrocarbon accumulation in the period of the Middle Permian to the Middle Triassic (P2-T2), and stage 3 is the formation of the Cambrian late paleo-gas reservoirs in the period of the Late Triassic to the Early Cretaceous (T3-K1). The cross-formational hydrocarbon accumulation is an important feature of hydrocarbon accumulation in multi-cycle superimposed basins, and the reactivated basement faults and the large nascent faults in the period of the MiddlePermian to the Middle Triassic are important clues to the Xixiangchi Group primary paleo-gas reservoirs. Identification and evaluation of the Xixiangchi Group primary paleo-gas reservoirs will be the key points and the main challenges to natural gas exploration in the study area.

为查明陆相页岩烃源特征及生油气潜力,采用有机碳含量(TOC)、镜质体反射率(Ro)、有机岩石学、干酪根碳同位素及族组分碳同位素测定等多种测试方法,开展川东北不同地区自流井组页岩有机地球化学特征及对比研究,明确主要地化参数特征及差异,并重点探讨有机质类型的研究对页岩油气勘探的意义.研究结果表明:自流井组东岳庙段与大安寨段页岩w(TOC)主要介于 0.5％～2.0％,平均值>1.2％,有机显微组分以镜质体、丝质体为主,其次为固体沥青及微粒体,Ⅱ1、Ⅱ2及Ⅲ型有机质均有发育,以Ⅱ2 型为主,有机质处于成熟-高成熟阶段,具备较好的页岩油气勘探潜力;川东涪陵地区东岳庙段东一亚段页岩有机质类型纵向上频繁变化,向上东二亚段—东三亚段页岩干酪根碳同位素存在倒转变轻现象,推测与运移烃混入有关,并提出页岩层段纵向上有机质类型变化的精细确定,有助于判识不同层段生烃能力与有机质孔发育程度的差异.

Unconventional lacustrine shale formations are characterized by strong heterogeneity and intensive lithological variations in the vertical direction. Nevertheless, most studies focused merely on the organic-rich intervals due to the successful exploration and development of marine shale gas resources. This study systematically analyzed the overall pore system of the Triassic Chang 7 lacustrine shale formation in the Ordos Basin, China, using geochemical, petrological, mineralogical and petrophysical methods. In addition, the statistical analysis method of spearman rank correlation was employed for the intensive data analysis. The results showed that rock components and diagenetic processes have significantly different effects on the development of multi-lithologic pore systems in lacustrine shale formations. Organic-rich laminated shale (ORLS) and argillaceous siltstone (AS) show a bimodal, while the medium organic matter massive shale (MOMMS), fine sandstone A (FSA), and coarse sandstone B (CSB) exhibit unimodal pore size distribution. Organic matter negatively affects the pore volume and positively influences the pore throat, while clay minerals generally play a negative role except for ORLS. Quartz is conducive to the pore development of the reservoir except that it blocks some pore space in ORLS. Meanwhile, feldspar boosts the pore volume of all reservoirs and inhibits the pore throat of ORLS and MOMMS. Calcite and dolomite have negative effects on the entire pore system. Pyrite and siderite could facilitate pore throat preservation but inhibit pore space development. The diagenetic analysis shows that thermal maturation of organic matter and mineral dissolution play important roles in promoting pore development, while cementation and mechanical compaction have counteracting effects. The assemblage of ORLS and CSB acts as the most favorable reservoirs for lacustrine shale oil exploration under ideal conditions. The pore size distribution of the lacustrine shale oil reservoir with random multi-lithologies shows that macropores and mesopores are the main reservoir space. This study contributes to a better understanding of sweet spot prediction in the notoriously complicated lacustrine shale formation.

Terrestrial shale strata generally has frequent and strong heterogeneity characteristics, thus affecting shale gas enrichment and target selection. In this study, samples from the Da’anzhai Member of Well A in Yuanba area have performed a series of experiments including total organic carbon ( TOC ) content measurement, rock pyrolysis, organic petrology, vitrinite reflectance ( R o ), whole-rock mineral composition, thin section analysis, focused ion beam scanning electron microscope, high-pressure Hg injection, nitrogen (N 2 ) adsorption, and methane (CH 4 ) isothermal adsorption. The results show that: (1) Da'anzhai (J 1 da) Member is a set of mixed sediments with various lithology, which consists of black shale and well-developed siltstone and carbonate rocks interlayers. The second section of the Da'anzhai Member (J 1 da 2 ) has relatively greater organic matter abundance (1.24% TOC ), better organic matter type dominated by type III and II, as well as higher maturity (1.67% R o ), which is the most favorable section of J 1 da. (2) J 1 da 2 shale strata can be divided into three shale lithofacies types, two interlayer lithofacies types, and three macro-lithofacies assemblage types. Among them, mudstone–limestone lithofacies assemblage (type AB-I) has preferable hydrocarbon generation conditions, better reservoir properties, and more developed shell limestone interlayers with better fracturing performance, is thought the most favorable interval. (3) The optimal interval and horizontal target of J 1 da 2 are further selected based on the source–reservoir coupling relationship, corresponding to the depth is 3909–3914 m, which imply the optimal horizontal target window for Well A. This study has application values not only for the identification of “sweet intervals” and well location deployment of J 1 da but also supports the later systematic studies of shale gas accumulation mechanism and enrichment regularity in Yuanba area.

为查明川北地区大安寨段页岩油气烃源、储集特征及富集有利层段,以岩芯观察描述为基础,以岩石学与矿物学、有机地球化学及页岩储层表征等理论方法与技术为指导,开展了大安寨段二亚段纵向上4个小层岩相、烃源、储集特征的精细表征与差异性对比研究,优选出了页岩油气富集有利层段,并提出勘探研究建议.研究结果表明:大安寨段二亚段富含(泥质)介壳灰岩、(泥质纹层状)粉细砂岩2种夹层,低—中碳黏土质页岩、中碳纹层—薄层状介壳页岩、低碳(纹层状)粉砂质页岩、低碳粉砂质介壳灰质页岩4种页岩岩相;②小层以中碳黏土质页岩、中碳纹层状介壳页岩为主,夹层相对少,页岩连续性较好;而④小层以中碳纹层状介壳页岩夹介壳灰岩为主,不同尺度介壳灰岩夹层多.页岩有机显微组分整体以镜质组为主,②、④小层固体沥青较发育,自下而上有机质类型发生6次变化,依次为Ⅲ—Ⅱ2—Ⅲ—Ⅱ2—Ⅱ1—Ⅱ2;②小层与④小层生油气能力相对较好,④小层略好于②小层.页岩储集物性明显好于夹层,②小层和④小层页岩生烃能力相对好,有机质孔较发育,含气量相对高,页岩烃源—储集—含(油)气性匹配关系相对好,评价认为大安寨段二亚段上部④小层纹层状介壳页岩段为最佳页岩油气富集层段,其次为下部②小层黏土质页岩层段.基于研究区大安寨段二亚段沉积非均质性强、含油气性好的层段时空分布不稳定的特点,建议重视砂、泥、灰混积差异,加强以小层为单元的岩相(组合)时空分布规律研究;重视保存条件与含气性差异,加强常规—非常规一体油气勘探选区、选层研究.

Breakthroughs of oil and gas exploration have recently been achieved via several wells in marl reservoirs of the first member of the middle Permian Maokou Formation in the southeastern Sichuan Basin. As a new type of unconventional gas reservoir, a lot of attention was attracted. In order to understand lithological characte-ristics and pore characteristics of marl reservoirs, lithological, pore types and pore structure characterization, works were carried out based on field and core samples. Results show that: (1) The TOC content of the marl reservoirs, which is mainly in outer gently sloping facies, is 0.76%-1.1%, with an increasing trend from northwest to southeast, similar to porosity changes. (2) Reservoir spaces of the marls mainly include organic pores, inorganic pores and microfractures. The organic pores can be classified into independent organic pores, organic pores with talc and intergranular organic pores of pyrite. The inorganic pores can be classified into intergranular pores, intercrystalline pores, and crystal dissolved pores. The microfractures can be classified into talc fractures, grain boundary fractures, and stress fractures. Organic pores are not dominant in the marl reservoirs, while microfractures are the most important reservoir space. (3) Combined characterization of cryogenic nitrogen adsorption, cryogenic CO2 adsorption, high-pressure Hg injection experiments and CT scan show that pores of the marls are mainly ink-bottle shaped with narrow neck and wide body. Micropores, mesopores and macropores are developed, with pore diameters of about 0.4-100 nm. The marls have obvious lithologic heterogeneity and poor connectivity. Fractures have an important influence on the connected pores. The marl in the first member of the Maokou Formation is a new type of unconventional reservoir, which has complex mineral composition and special pore characteristics. Targeted acid fracturing technology should be strengthen to promote the exploration and production of the marl reservoir.

页岩气勘探开发实践证实,页岩气地层压力参数对于评价页岩含气性和产能具有重要的判识意义.为了研究四川盆地渝东彭水地区常压页岩气的形成与演化,利用流体包裹体显微测温和激光拉曼光谱技术、盆地模拟和甲烷体系状态方程等恢复了该区PY1井上奥陶统五峰组—下志留统龙马溪组页岩燕山—喜马拉雅期构造抬升中的压力演化和含气量演化过程,深化了对常压页岩气形成与演化过程的认识.研究结果表明:①PY1井五峰组—龙马溪组页岩脉体甲烷包裹体捕获古温压结合页岩埋藏史—热演化史重建揭示构造抬升至距今约124 Ma,页岩层压力介于74.1～88.5 MPa,对应压力系数为1.36～1.63,页岩处于中等超压状态;②构造抬升至距今约100 Ma,页岩层压力介于38.6～49.5 MPa,对应压力系数为0.93～1.18,页岩处于常压状态;③页岩构造抬升过程中的压力演化可划分为3个阶段,第一阶段(距今145～100 Ma)、第二阶段(距今100～20 Ma)、第三阶段(距今20～0 Ma),页岩层压力和压力系数的下降主要受控于快速抬升导致页岩层温度降低和页岩气散失;④构造抬升过程中PY1井五峰组—龙马溪组页岩气散失量约为最大埋深阶段总含气量的35.3％.结论认为:①页岩压力和含气量演化研究可为进一步探讨常压页岩气保存条件提供重要信息;②燕山运动Ⅱ幕的差异改造可能是川东南超压和常压页岩气差异富集的关键控制因素.

评价优选陆相页岩油气富集有利层段、确定水平井最佳穿行靶窗是制约陆相页岩油气勘探开发的瓶颈.为此,以四川盆地东部复兴地区侏罗系自流井组东岳庙段页岩为研究对象,在岩心观察描述的基础上,采用岩石薄片、有机岩石学、干酪根碳同位素、氩离子抛光—扫描电镜及孔隙度测试等多种实验方法,以小层为单元开展了岩相、烃源及储集特征精细表征,探索性建立了陆相页岩油气有利层段评价方法.研究结果表明:①东岳庙段富有机质页岩主要发育在东一亚段,页岩黏土矿物含量高,富含毫米级—厘米级介壳纹层及薄层,以中碳—高碳黏土质页岩、中碳介壳纹层状黏土质页岩为主;②东一亚段页岩有机质类型纵向上发生了4次频繁变化,自下而上依次为腐殖型—偏腐殖混合型—偏腐泥混合型—偏腐殖混合型,不同层段生烃能力存在差异;③东一亚段上部第3小层、第4小层固体沥青较发育,有机质类型好,生烃能力强,有机质孔较发育,页岩油气有效储集能力好;④以总有机碳含量与孔隙度分析为基础,将有机岩石学与氩离子抛光—扫描电镜相结合,基于纵向微观源(有机显微组分)—储(有机质孔)匹配关系定性评价有利层段,结合有机质类型提出原始氢指数比评价参数,建立陆相页岩源—储耦合系数计算公式及评价标准,可实现陆相页岩油气有利层段定量评价.结论认为,建立的陆相页岩油气富集层段定性—定量评价方法,可满足陆相页岩油气钻井过程中水平井穿行层段优选的生产需求.

The developmental characteristics and formational stages of natural fractures are of great significance for shale oil and gas accumulation in complex structural areas. We determined the developmental characteristics and formational stages of fractures in the Wufeng - Longmaxi Formation in the Sangzhi Block, Hunan Province, China based on outcrops, cores, optical microscopy, cathodoluminescence, scanning electron microscopy, energy spectrum analysis, fluid inclusion homogenization temperature, micro laser Raman spectrum analysis, and acoustic emission analysis. Furthermore, we deduced the possible fracture formational depth, filling time, and stress magnitude of structural fractures in rocks, and established the development model of structural fractures of time series. The results show that the Wufeng - Longmaxi Formation fractures can be divided into tensile fractures, compression-torsion fractures, and strike-slip fractures in terms of the combination characteristics of fracture plane and the roughness of fracture plane. The fractures mainly occurred in the late Yanshanian - Himalayanian period after the violent uplift. In the process of burial-hydrocarbon generation, it experienced at least six stages of repeated process of splitting, healing, re-splitting, which reflected the periodic release of local stress caused by the continuous westward push of Xuefeng uplift. The microcracks of different periods have obvious differences in orthogonal polarization and cathodoluminescence reflection characteristics. The cathodoluminescence spectrum ranges from orange red to bright yellow, and some even do not glow, which is a comprehensive performance of mineral filling composition, crystal size, crystallization degree and alteration degree. The gas generated in the early stage are easy to enter the early opened fractures. With the continuous opening and healing, the shale gas has a continuous dynamic process of enrichment, dispersion, re-enrichment, and re-dispersion, which affects the distribution and preservation of shale gas.

利用有机岩石学、干酪根碳同位素、X?射线衍射、场发射扫描电镜等实验测试资料,阐述了川东南—黔西北地区上二叠统龙潭组海陆过渡相页岩烃源岩品质、储层发育及含气性特征,并探讨了孔隙类型和含气性的主控因素.研究表明,川东南—黔西北地区龙潭组泥页岩总有机质丰度高(TOC值平均为3.50％)、热演化程度高(RO值平均为2.23％),有机显微组分以镜质体为主,惰质体次之,以Ⅲ型干酪根为主,是一套优质气源岩.页岩储层具有较好的物性(孔隙度平均为5.56％),孔隙类型以黏土矿物孔为主,其中伊/蒙混层间微孔隙较发育,主要为介孔—微孔,有机质孔基本不发育.泥页岩吸附气含量和总含气量变化较大.有机显微组分是控制龙潭组高成熟富有机质页岩有机孔隙发育的首要因素,有机质丰度是控制页岩吸附能力和含气性的重要因素.

The Lower Jurassic shale in the northeastern Sichuan Basin is one of the main research intervals of continental shale gas. The shale pore structure is an important indicator for evaluating the reservoir capacities of shale reservoirs. We concentrate on the pore structure to indicate reservoir capacity using several testing methods, for example, N 2 adsorption-high-pressure mercury pore size combined experiments, X-ray diffraction (XRD) experiments, and the total organic carbon ( TOC ) method. The results show that the clay mineral content of the continental shale is high. The pore type is mainly a mineral matrix pore, followed by an organic matter pore, and the microcracks are locally developed; the distribution interval of the main pore size is mesoporous, between 10 and 50 nm; the pore volumes and specific surface areas of the continental shale reservoirs are negatively correlated or unrelated to the TOC , mainly due to the failure of pore development in the organic vitrinite and fusinite and the occupation of pore volume and adsorption sites by the soluble organic matter. The larger pores are mainly formed by clay minerals; the reservoir capacities of the continental shale reservoirs were evaluated using a two-factor evaluation method of the pore volume and specific surface area. It was found that the continental shale mainly comprises free reservoirs and has a storage gas capability level of II–IV. The research results elucidate the pore structure characteristics and reservoir capacities of the continental shale reservoirs in the northeastern Sichuan Basin, having important theoretical and guiding significance for the gas-bearing evaluation and dessert target optimization of the continental shale in the study area.

源-储一体是页岩储层有别于常规储层的特性,陆相富有机质页岩层系具有页岩与夹层频繁互层、夹层类型多、有机质类型多样、储层非均质性更强的特点.为查明陆相页岩源-储关系及成因,以四川盆地自流井组页岩为例,采用岩石薄片鉴定、氩离子抛光-扫描电镜鉴定、有机碳含量测定及氦气孔隙度测试等多种实验技术手段,宏观上分析源(TOC)、储(孔隙度)参数的相关性,微观上分析无机矿物、有机质、无机矿物孔及有机质孔(缝)之间的相互作用、相互影响.识别出了3种宏观源-储耦合类型:源-储较高相关型、源-储中等相关型、源-储弱相关型,提出有机质相关孔隙的发育程度决定了源对储贡献的大小,是源与储耦合关系的核心.将宏观-微观相结合,建立了不同岩相组合控制下的陆相页岩源-储耦合发育模式,提出源-储耦合关系的差异对页岩油气的富集程度具有重要控制作用,纯页岩型、页岩夹薄层介壳灰岩型岩相组合的源(TOC较高,有机质类型好)、储(有机质孔相对较多)发育条件好,源与储相关性相对较高,是陆相页岩油气富集最有利的岩相组合类型.

陆相页岩层系岩性复杂、非均质性强,制约了储层甜点优选和探井部署.为查明四川盆地侏罗系页岩层系不同岩相类型的储集特征和含气能力,以元坝地区Y2井自流井组大安寨段为例,采用有机碳含量测定、全岩X射线衍射、岩石薄片鉴定、聚焦离子束扫描电镜、高压压汞—氮气吸附联合测定以及物性分析等手段,划分了大安寨段二亚段(后文简称大二亚段)页岩及夹层的岩相类型,并针对不同岩相类型开展储集物性、孔隙结构、含气性及可压性研究,在此基础上评选了优势岩相和岩相组合.结果表明,Y2井大二亚段页岩层系可划分为3大类6亚类页岩岩相,2大类6小类夹层岩相以及3种宏观岩相组合.页岩孔隙类型以粘土矿物层间孔、方解石溶蚀孔等无机孔为主,为页岩气的赋存提供了储集空间.计算页岩总含气量为2.59～4.38 m3/t,游离气平均占比67％,具有较好的勘探潜力,但优势岩相的脆性矿物含量仅为50％,可压性较差.综合评价认为,AB-Ⅰ型岩相组合中页岩页理和纹理发育,生烃条件好,含气量和游离气比例较高,存在可压性较好的夹层,是元坝地区Y2井大二亚段最有利的勘探储层类型.

为了分析含气陆相页岩中石英矿物的成因、分布及其影响因素,以四川盆地自流井组含气页岩层段为主要研究对象,利用X射线衍射分析、普通薄片、扫描电镜、阴极发光、电子探针及元素地球化学分析测试手段,识别出陆源石英和成岩过程中形成的石英.陆源石英在阴极光下表现为棕色光,粒径较大.成岩过程中形成的石英在阴极发光下不发光,晶形较好,粒径较小.根据成岩作用的不同,将成岩过程中形成的石英细分为黏土矿物转化过程中形成的石英和硅质交代介壳边缘形成的石英.分析不同成因的石英分布特征发现,东岳庙段内石英矿物主要为陆源输入和黏土转化成因;马鞍山段内的石英主要为陆源石英;大安寨段内的石英则为硅质交代自生和陆源输入成因.在此基础上,总结了陆相页岩中不同成因石英的影响因素,包括沉积环境和地层压力.在沉积环境方面,随陆源物质输入的增加,陆源石英增加.同时,适合的湖水盐度,有利于介壳生物的生存,为硅质交代介壳形成石英提供物质基础.此外,地层的异常高压会抑制黏土转化,减少硅质析出,阻碍自生石英的沉淀.