As an essential unconventional oil and gas resource, shale oil is of great significance to energy replacement and socio-economic development. Total organic carbon (TOC) and pyrolyzed hydrocarbon (S1), as key parameters for hydrocarbon reservoir evaluation, are important guides for practical exploration. Usually, the high precision determination of TOC and S1 requires sample collection and laboratory analysis, but is often compromised due to the cost and the limitation of coring continuity. With the advent of the digital age, increasingly intelligent methods are being employed in this field, such as Δlog R, support vector regression (SVR), and backpropagation neural network (BPNN). However, Δlog R has low performance, SVR does wrong in feature extraction, and BPNN is prone to local optimum. The coefficients of determination (R2) for TOC prediction using the three methods registered values of 0.25, 0.69, and 0.74. In contrast, the R2 values for S1 prediction were 0.23, 0.54, and 0.58. Thus, a low-cost, intelligent, and high-precision method to predict TOC and S1 is needed. This paper proposes a new model for predicting TOC and S1 in shale reservoirs based on an improved Deep learning network model (Encoder-ECA) based on the Transformer. With nearly 3 000 rock samples selected from the Jurassic Da’anzhai Member of the Sichuan Basin, China, and sedimentary facies variations in the study area, our results show that the Encoder-ECA model achieves an R2 of 0.86 for TOC content prediction and an R2 of 0.82 for S1 content prediction. In addition, the Encoder-ECA model was successfully applied to the recently implemented exploratory well evaluations in the study area, and the prediction results were used to optimize the sweet spot section, with a combined daily production of 22.4 mcf of oil and 33 600 mcf of gas. Simultaneously, data from different basins will be utilized to validate the applicability range of the model. This research demonstrates the great potential of deep learning technology in unconventional resource evaluation. It confirms the application of the Encoder-ECA model in the exploration practice of lacustrine facies shale oil and gas.

The lacustrine shale of the Jurassic Lianggaoshan Formation in the Sichuan Basin is a key shale oil exploration target. Reconstructing redox conditions of depositional processes is essential for understanding the distribution of organic-rich shale intervals. Geochemical and redox-sensitive elemental thresholds are effective indicators, however, due to different geological settings, commonly used proxies and previously established thresholds are difficult to apply to the Lianggaoshan shale. To identify suitable redox proxies for the Lianggaoshan shale, this study investigated and evaluated these commonly used indicators, including redox-sensitive element enrichment factor, bi-metal ratio, C-S-Fe-P system, etc. To accurately characterize the redox conditions of the study area, this study relied on the co-variation theory of above proxies within the redox framework according to three key redox thresholds (T1, T2, T3), quantitatively re-evaluated and calibrated their thresholds separately. The results indicate that the fixed thresholds among widely used proxies are not fully applicable to the studied succession. Reassessment of Corg/P and bi-metal ratios based on co-variation theory suggests that the Corg/P ratio is the most useful for redox analysis to the studied succession, while V/(V + Ni), (Cu + Mo)/Zn, Ni/Co, and V/Cr are not fully applicable, and the Fe/Al ratio is completely inapplicable. Among trace element enrichment factors, CuEF, VEF, and NiEF also have good effects on the recovery of redox conditions. It is essential to calibrate the thresholds of proxies that have provided useful results based on the proxy covariation theory prior to their application. By selecting the most effective proxies, the redox thresholds of elemental indicators can be accurately quantified and calibrated based on the “simple” or “compound” covariation patterns. A comparison of the recalibrated thresholds shows that T2 and T3 are similar, whereas T1 and T2 differ significantly. Based on the threshold range established from the Corg/P ratio, this study reveals that the Lianggaoshan Formation shale was predominantly deposited under persistent euxinic conditions, which were occasionally interrupted by oxic conditions induced by seasonal events. Our study provides a method and process for threshold value correction of lacustrine shale in other basins.

The Jurassic sedimentary rocks in the Sichuan Basin are a natural archive for resolving the controversy about the Early and Middle Jurassic tectonic evolution of the Qinling Orogenic Belt (QOB) after the closure of the Paleo-Tethys Ocean. This study focuses on the Nuoshuihe and Guanghuicun sections in the northeastern margin of the Sichuan Basin, providing new data on sandstone petrography, heavy minerals, and detrital zircon geochronology. The evolution of drainage pathways in the Early to Middle Jurassic is quantitatively reconstructed using the DZmix program and both new and published detrital zircon geochronology data. The sediments of the Lower Jurassic Ziliujing Formation, corresponding to the post-orogenic extension stage revealed by published igneous rocks, were mainly derived from the Yangtze Craton (YZC; average 98 %), sediment supply to the Middle Jurassic Lianggaoshan Formation transitioned gradually from the northern margin of the YZC (average 72.6 %) in the Lower Member to the QOB (average 84.2 %) in the Middle and Upper members. The percentage derived from the YZC increased again in the Shaximiao Formation (75 %). Previous sedimentological studies in the Sichuan Basin show that the lacustrine depocenter of the various members migrated from southeast to northwest, together with the deformation time of strike-slip shear zones in the QOB published by mylonitic rocks Ar-40/Ar-39 data (similar to 178-143 Ma), all suggesting the short-time intracontinental orogenic uplift of the QOB during the deposition of Lianggaoshan Formation after post-collision extension. Based on these findings, we can infer that the long-range effects of the Paleo-Pacific Plate subduction along the East Asia or/and asynchronous closure of the Paleo-Tethys Ocean, could be potential mechanisms driving block rotation and intracontinental orogenic adjustments in the Middle Jurassic, rather than continuous collisional orogeny since Middle Triassic.

Accurate fluid characterization is critical for reservoir development planning and typically relies on pressure-volume-temperature (PVT) experiments. However, in structurally complex reservoirs, fluid classification based solely on laboratory measurements can lead to misinterpretations. In the Gongshanmiao block of the Sichuan Basin, initial PVT analysis suggested that the reservoir was a condensate gas system. Subsequent field development revealed inconsistencies with this interpretation, including abnormal gas–oil ratios and atypical pressure build-up behavior that deviated from expected condensate gas reservoir performance. To resolve this discrepancy, this study proposes a diagnostic framework that integrates geoscience and engineering data, including fluid sampling, 3D structural modeling, production performance analysis, pressure build-up testing, and hydraulic fracturing data. The integrated analysis revised the initial PVT-based interpretation, and the results indicated that the reservoir is more accurately characterized as a saturated oil system with an overlying gas cap, rather than a condensate gas reservoir. Furthermore, the integrated interpretation clarifies the structural trapping mechanism and delineates the spatial extent of the gas cap. Overall, the proposed approach provides an integrated geoscience-engineering workflow for fluid reclassification in structurally complex reservoirs, which reconciles laboratory fluid analysis with field production behavior, offering a systematic framework for fluid interpretation in similar geological settings.

In order to understand the tectonic control on shale oil migration and accumulation, samples of the Daanzhai Member of the Lower Jurassic Ziliujing Formation from the well core in a tectonically stable area and upright anticline outcrop were selected for total organic carbon (TOC) content analysis, rock pyrolysis, fluorescence scanning, and scanning electron microscopy. The results show the following: (1) In the tectonically stable area, the TOC of shale oil reservoirs is positively correlated with S1, and a high OSI interval usually occurs in high-TOC shales. The oil content of the limestone lamina decreases with an increasing distance from black shale. The vertical migration of shale oil into or across the lamina is not obvious and is mainly micro-scale. (2) The migration pathway includes a lamina interface, shell–clay interface, calcite cleavage, feldspar or calcite dissolution pores, and quartz or kaolinite intergranular pores. Large-scale shale oil migration time occurs at the peak of oil generation. (3) In the area of strong tectonic deformation, the formation of fractures in limestone further promotes the migration of oil from shale into the lamina. (4) The re-migration of shale oil during the uplift and deformation period involves three processes: upward migration in a clay matrix, then entry and migration along the limestone–shale interface from the lateral pinch-out points of the lamina, migration into the lamina joints, and then short diffusion into the limestone. (5) The migration of shale oil in the Daanzhai shale was controlled by the history of hydrocarbon generation and tectonic deformation and occurred in several stages.

Research on the distribution and development of black shales in the Lianggaoshan Formation has been deficient,which has hindered exploration for lacustrine shale oil in the Sichuan Basin.Our study characterized the well logging data,core samples,outcrops,and geochemistry of black shales in the Lianggaoshan Formation in the Sichuan Basin.Our analysis focused on the lake basin evolution and the migration characteristics,paleoenvironmental features,formation mechanisms,and developmental model of the black shales.The results indicated that black shales in the Lianggaoshan Formation exhibited significant lateral migration,with an overall thickening trend from east to west.Within the 1st Member of the formation,black shale occurred as a single thick layer in the eastern region that gradually thinned toward the central region.Multiple sets of shale developed within the 2nd and 3rd members,and these had lower thicknesses than the 1 st Member and migrated toward central Sichuan.Paleoproductivity and terrigenous input were the main factors controlling the deposition of black shales.A semi-humid climate influenced the deposition of black shales,bringing abundant freshwater,terrigenous debris,and nutrients into the basin.Decomposition of organic matter consumed oxygen in sediment and bottom water,causing localized oxygen deficiency in the strata.

The Middle Jurassic Lianggaoshan and Shaximiao Formations are the primary crude oil reservoirs in the central Sichuan Basin, offering significant resource potential. However, studies on reservoir characterization across different lithologies remain limited. This study focuses on fluvial–deltaic sandstones, siltstones, and lacustrine shales, analyzing pore types, structures, pore size distribution, and connectivity using various methods, including X-ray diffraction (XRD), thin-section analysis, scanning electron microscopy (SEM), high-pressure mercury injection, low-temperature nitrogen adsorption, and nuclear magnetic resonance (NMR) spectroscopy. The results show that sandstones exhibit the largest pore space, followed by siltstones, while shales have the smallest pore space. These reservoirs are relatively tight, with poor connectivity and high heterogeneity. Sandstone reservoirs, with their high quartz content, represent high-quality reservoirs because of their relatively good connectivity. Therefore, areas with well-developed natural fractures in sandstone are considered high-quality targets. For nanoscale reservoirs in siltstone and shale, horizontal fracturing is essential to improve reservoir properties, provided that source–reservoir matching is adequate. This study offers a detailed reservoir characterization across different lithologies, providing new insights for the optimization of favorable crude oil zones in the central Sichuan Basin.

Recent tests at wells such as Longxing 1, Ping’an 1, and Puluye 1 have yielded high-yield industrial oil and gas flows, confirming the promising exploration and development potential of the Jurassic shale oil in the Sichuan Basin. However, the insufficient integration of geology and engineering has led to a lack of unified understanding of geological and engineering “sweet spots,” resulting in a relatively low level of exploration and development of Jurassic shale oil. Based on the concept of geological and engineering integration, a comprehensive geological evaluation approach has been constructed, with geological comprehensive research as the foundation, satisfying engineering requirements and achieving effective development as the goal, and engineering geological mechanics as the theoretical bridge. Taking Well G119H in the central Sichuan region as an example, an integrated geological and engineering evaluation was conducted, achieving a significant breakthrough of 20 tons of daily oil production and 6000 cubic meters of daily gas production in the Liang-2 section of Well G119H. This demonstrates that the integrated geological and engineering technology is an important technical strategy and theoretical system for the exploration and development of shale oil.

To further guide the exploration and development of shale oil in the Da'anzhai Member of the Jurassic Ziliujing Formation in the Sichuan Basin, it is urgent to clarify the favorable lithofacies of shale oil. In this study, core observation, thin section authentication, high pressure mercury injection, NMR, rock pyrolysis analysis and other experiments were used to analyze the reservoir space types, pore structure characteristics and oil-bearing properties of different lithofacies of shale series in the Da'anzhai Member. The results show that mainly six types of lithofacies are developed in the Da'anzhai Member: massive (argillaceous) shell limestone, layered argillaceous shell limestone, layered shell shale, laminar shell-bearing shale, massive shell-bearing clay shale and foliated siltstone-bearing clay shale. The physical properties of shale in the Da'anzhai Member are much better than those of shell limestone, and with the increase of calcareous content, the pore size of the shale gradually increases, but the total pore volume and total connected volume gradually decrease. The average free oil value ( S1) of the shale series in the Da'anzhai Member is 1.31 mg/g, with moderate oil-bearing property. The S1 values of the foliated siltstone-bearing clay shale and the laminar shell-bearing shale are relatively higher, which are 2.37 mg/g and 1.82 mg/g, respectively. In summary, it is believed that the foliated siltstone-bearing clay shale and the laminar shell-bearing shale have good reservoir properties and high oil-bearing properties. The lithofacies combination of the two can be a key exploration target for shale oil in the Da'anzhai Member.

通过岩心观察及野外露头考察,结合地震、测井及各类测试分析成果,对四川盆地东部地区中-下侏罗统沉积体系进行研究,探讨川东地区侏罗系沉积体系对烃源岩及储集层发育的影响和控制.川东地区中-下侏罗统主要发育一套湖泊-三角洲-河流相沉积体系,形成了一套巨厚的陆源碎屑岩与湖相碳酸盐岩沉积建造.中-下侏罗统发育一个相对完整的湖侵-湖退旋回,其中:自流井组东岳庙段、马鞍山段及大安寨段以广泛发育的湖泊相沉积为特征;自流井组珍珠冲段及凉高山组湖泊-三角洲均较为发育;沙溪庙组开始发育广泛的河流相沉积.早-中侏罗世川东地区为四川盆地东部的汇水区,同时受周缘多个物源和水系控制,受南-北向构造挤压影响,珍珠冲段-沙溪庙组沉积时期湖盆中心逐渐向北迁移.烃源岩主要发育在东岳庙段、马鞍山段、大安寨段及凉高山组下段等较高湖平面时期,致密砂岩气、陆相页岩油和页岩气均具有较大的勘探潜力,多物源交汇的稳定湖盆区是优质烃源岩的主要发育区和有利的勘探区域.

Thick sequences of terrestrial multicolored mudstones of the Middle Jurassic Shaximiao Formation in the Sichuan Basin, Southwest China, effectively recorded paleoclimate and paleoenvironment changes. The paleoenvironment of the Shaximiao Formation is reconstructed by using detailed sedimentological and elemental geochemical analysis of the multicolored mudstones. The provenance, paleoclimate, paleosalinity, and paleoredox conditions are distinguished by using the discriminant indicators of CIA, C-value, Sr/Cu, Rb/Sr, Th/U, V/Cr, and V/(V + Ni). The results show that all samples derive primarily from felsic igneous rocks and intermediate rocks rather than recycled sediments. The mudstone sequences were deposited under semiarid and semihumid regions with paleoclimate evolved to drier and cooler conditions from lower to upper Shaximiao Formation. Such a paleoclimate coincided with the records of several basins in the lower paleolatitudes of the Northern Hemisphere and were possibly affected by the Middle Jurassic global geological events such as wildfire, paleogeographic reorganizations, and seaway dynamics change. The paleowater body belongs to a typical terrestrial freshwater environment, although the paleosalinity increased significantly during arid periods. The multicolored mudstones were deposited in oxidation and weak-oxidation to weak-anoxic conditions. We also propose a detailed conceptual paleoenvironment model for Shaximiao Formation, with a large perennial lake surrounded by limited alluvial plain during a period of high lake level and small ephemeral lakes scattering extensive alluvial plain during a phase of low lake level.

The eastern Sichuan Basin in China holds vast potential for oil and gas exploration in the Lower-Middle Jurassic strata. However, the geological characteristics and hydrocarbon accumulation patterns of this region remain largely unclear. During the deposition period of the Lower-Middle Jurassic strata, the eastern Sichuan is characterized by the formation of multiple sets of source, reservoir, and caprock assemblages through depositing lake-delta-fluvial deposits, which have great exploration potential. The Jurassic source rocks in eastern Sichuan are mainly developed in the Dongyuemiao Member, Da’anzhai Member, and Liangshan Formation. These source rocks have a total organic carbon (TOC) content greater than 1 and a varying range of organic matter maturity, with a Ro value of 0.8–2.0. The kerogen in these source rocks is primarily type II, with a smaller proportion being type III. A range of reservoir rocks can be found in the Jurassic strata of eastern Sichuan, with sandstone reservoirs being predominantly found in the Liangshan Formation, Shaximiao Formation, and Zhenzhuchong Member. Shale reservoirs are mostly present in the Dongyuemiao, Da’anzhai, Liangshan, and Maanshan Members, and there is a limited distribution of limestone reservoirs in the Da’anzhai Member and Dongyuemiao Formation. The arrangement of source rocks and reservoir rocks in eastern Sichuan has led to the formation of three types of reservoir-forming combinations, including lower generation and upper storage, self-generation and self-storage, and composite. Sandstone reservoirs are typically of lower generation and upper storage, shale reservoirs are primarily of self-generation and self-storage, and limestone reservoirs are mostly composite. The exploration of Jurassic oil and gas in eastern Sichuan should prioritize “layer and area selections.” The Da’anzhai, Dongyuemiao, and Liangshan shale reservoirs should be the primary exploration targets, with the semi-deep lake deposits in the syncline area being the most favorable. The degree of fracture development in the exploration area also has a significant impact on the shale oil and gas content. The Liangshan Formation and Shaximiao Formation sandstone reservoirs can serve as secondary exploration targets, with anticline areas that have better sealing conditions being more favorable. Limestone reservoirs have limited distribution, and exploration areas with high and steep fractures are relatively more advantageous.

The Lower Jurassic Da’anzhai Member in the Sichuan Basin is one of the important distribution series of strata of shale oil and gas （tight oil and gas）,but its drilling and test results are worse,so it is in urgent need to research the geological characteristics of favorable intervals and select the favorable exploration areas.Based on field outcrop,core,logging,and geophysical data,this paper studies the geological characteristic of the Da’anzhai Member shale oil and gas,analyzes the control factors of shale oil and gas enrichment,and selects the favorable exploration areas.And the following research results are obtained.First,the Da’anzhai Member is a set of mixed strata of shell limestone and black shale.The shale mineral is mainly composed of clay,followed by quartz and calcite,with a small amount of feldspar and pyrite,and the content of brittle minerals is medium.Second,the pore type is mainly inorganic pore,with a small number of organic pores,and multi-scale fractures such as shell edge fracture and joint fracture are developed.The physical properties decrease with the increase of shell content.Third,the abundance of organic matter in shale is moderate to good with average TOC of 1.34%.The organic matter is mainly of mixed type with a small amount of sapropel type and humic type.R o averages 1.11%,the degree of thermal evolution is low in the south and high in the north,and it is overall in the stage of maturity to high maturity.The oil content is moderate with chloroform asphalt"A"content averaging 0.26%.Fourth,the average S 1 value of pyrolysis free hydrocarbons is 1.27 mg/g,and the average OSI is 84.35mg/g.The lower limit of hydrocarbon source for shale oil and gas enrichment is TOC＞1.5% and R o ＞0.9%.The hydrocarbon expulsion efficiency is lower vertically,and the sections with higher oil content index （OSI＞100 mg/g） are mainly distributed in the middle of thick shale.Fifth,the movable oil saturation is generally less than 20%.Due to the influence of texture fractures and shale bedding fractures,the oil mobility in the samples of limestone interbedded with shale and shale with interbedded limestone is better than that in limestone and shale.In conclusion,the Da’anzhai Member shale has great potential in shale oil and gas exploration and development,high hydrocarbon generation quality,multi-scale fractures,and high formation pressure are the key factors for the enrichment and high production of shale oil and gas in the basin,and the favorable exploration areas are mainly distributed in the Santai-Yilong and Nanchong areas of central Sichuan Basin.

针对四川盆地凉高山组层序地层格架的建立及有利区优选复杂多变的难题,利用四川盆地凉高山组测井及地震等资料,识别不同尺度的标志层,建立标志层的测井-地震识别标准,利用区域格架线搭建层序地层格架,通过井震结合分析,厘清全盆地凉高山组岩性、相带变化关系,并结合有利相带分布及"源储"配置关系,优选有利勘探区.研究表明:以水进界面作为标志层,搭建层序地层格架,能够快速确定烃源岩与储层发育层位、厚度及分布范围;优选凉高山组凉一3亚段为有利烃源岩发育层位,凉二1亚段为有利储层发育层位;凉一3亚段烃源岩发育区,即盆地东北部及边缘龙岗-梁平一带页岩厚度较大,最厚处可达60-80 m,是下一步勘探的有利目标区.研究成果丰富了四川盆地凉高山组层序地层、沉积演化及勘探区优选等相关勘探研究工作,也为同类油藏的勘探开发提供了理论依据.

This paper discusses the sedimentary environment and source supply in the sedimentary area and their coupling relationship through a detailed description of the deposits from the Ziliujing Formation to Shaximiao Formation of the Lower–Middle Jurassic on the Tieshan section in the Dazhou City, northeastern Sichuan Province, through sedimentary characterization, determination of the paleocurrent direction, analysis of heavy minerals, and detrital zircon U–Pb dating. The results show that the Zhenzhuchong Member is sufficiently supplied with detrital sediments and is dominantly composed of fluvial-delta deposits. The Dongyuemiao Member—the first member of the Lianggaoshan Formation—is dominated by lacustrine deposits, with the detrital supply increased initially in the early Lianggaoshan. The second member of the Lianggaoshan Formation suggests a significant increase in detrital supply, with shrunken lake basin and changed paleocurrent direction. The Shaximiao Formation reveals a complete disappearance of the lake basin in the northern Sichuan Basin. The comprehensive analysis on source supply indicates that the change in source property is apparently coupled with the change in the sedimentary environment, both controlled by orogenesis around the basin. It is inferred from the zircon age distribution that the changes in the sedimentary environment and source supply during the late Ziliujing period and the middle and late Lianggaoshan period resulted from the uplifting of the Micangshan Mountain, Dabashan Mountain, and Qinling Mountain, respectively.

Based on the data of outcrops, seismic sections, thin sections, heavy mineral assemblages and detrital zircon U-Pb dating, the sedimentary characteristics, lake level fluctuation and provenance characteristics of the Middle Jurassic Lianggaoshan Formation (J2l) in eastern Sichuan Basin, SW China, were investigated to reveal the control of tectonic movements of the surrounding orogenic belts on the sedimentary systems. The J2l mainly developed a delta—lake sedimentary system, which contained a complete third-order sequence that was subdivided into four lake level up-down cycles (fourth-order sequence). The lake basins of cycles I and II were mainly distributed in eastern Sichuan Basin, while the lake basins of cycles III and IV migrated to central Sichuan Basin, resulting in the significant difference in sedimentary characteristics between the north and the south of eastern Sichuan Basin. The provenance analysis shows that there were three types of provenances for J2l. Specifically, the parent rocks of Type I were mainly acidic igneous rocks and from the proximal northern margin of the Yangtze Plate; the parent rocks of Type II were intermediate-acid igneous rocks and metamorphic rocks and from the central parts of the southern and northern Qinling orogenic belts; the parent rocks of Type III were mainly metamorphic rocks followed by intermediate—acid igneous rocks, and from the North Daba Mountain area. It is recognized from the changes of sedimentary system and provenance characteristics that the sedimentary evolution of J2l in eastern Sichuan Basin was controlled by the tectonic compression of the Qinling orogenic belt. In the early stage, the lake basin was restricted to the east of the study area, and Type I provenance was dominant. With the intensifying north-south compression of the Qinling orogenic belt, the lake basin expanded rapidly and migrated northward, and the supply of Type II provenance increased. In the middle and late stages, the uplift of the North Daba Mountain led to the lake basin migration and the gradual increase in the supply of Type III provenance.

在川中地区大安寨段烃源岩抽提物中检测出丰富的重排藿烷系列、重排补身烷系列、重排甾烷系列及C26+长链三环萜烷系列的分子标志物组合.结合烃源岩的有机质来源、沉积环境、热演化程度特征,探讨上述甾烷、萜烷分布特征指示的地质地球化学意义.结果表明:重排类化合物与C26+长链三环萜烷系列存在着某些相同的富集途径,重排藿烷系列富集途径多于重排补身烷系列、重排甾烷系列及C26+长链三环萜烷系列;特殊的甾烷、萜烷分布特征指示,烃源岩中有机质以湖泊内源(藻类和细菌等)为主,形成于范围局限的弱还原环境,高丰度的重排化合物指示,有机质热演化处于成熟阶段.此外,特殊的甾烷、萜烷分布特征还可能指示了特定的酸性粘土矿物、钙质沉积催化和形成环境中发育的特殊生物族群.综上,研究结果对分子标志物异常组合的地球化学应用具有重要的示范意义.

为精细评价陆相页岩储层特征,有效指导页岩油勘探开发,以四川盆地中部侏罗系自流井组大安寨段页岩层系为例,综合应用岩心精描、薄片鉴定、扫描电镜观察、核磁共振、氮气吸附和测井解释等定性和定量的分析方法,对页岩层系岩相和储层微观特征进行研究.提出了页岩层系岩相划分方案,认为大安寨段页岩层系具有以裂缝和溶蚀宏孔为主的微米级储集空间和纳米级孔、缝构成的双重介质,明确了纹层状含介壳页岩及薄层状介壳灰质页岩/泥质介壳灰岩为有利储集岩类,岩相类型和成岩作用是造成储集性能差异的主要因素,富有机质页岩与介壳灰质夹层形成源储一体的有利配置.研究结果表明:大安寨段页岩层系主要包括纹层状长英质页岩、纹层状含介壳页岩、层状—块状黏土质粉砂岩、薄层状介壳灰质页岩、薄层状泥质介壳灰岩和块状介壳灰岩6种岩相类型;块状介壳灰岩孔隙度平均为1.01％,其他(含介壳)页岩孔隙度平均为1.12％～4.85％,页岩层系储集空间以纳米级孔隙为主,形态以狭缝状为主,孔径主要分布为10～5×103 nm,介孔和宏孔发育.大安寨段湖相页岩层系含油气性较好,有机质发育的纹层状或薄层状(含介壳)页岩受有机酸溶蚀增孔的作用,形成大量次生孔隙,从而形成了源储一体的富有机质页岩与介壳灰质夹层有利配置,夹层中(微)裂缝和溶蚀宏孔为游离烃提供主要的储集空间,页岩基质内广泛发育的纳米孔,孔径小、连通性较差,两者形成的微纳米级孔-缝双重介质,使大安寨段油气稳产成为可能,对于四川盆地的陆相页岩油气勘探开发具有重要的意义.

The Lower Jurassic Lianggaoshan Formation in Sichuan Basin is a deltaic-lacustrine deposit, with the sub-center of deposition in eastern basin. The research on shallow exploration was not valued in the past due to the high-steep structures developed in the eastern basin. In this study, the Jurassic Lianggaoshan Formation was analyzed in terms of petrological and organic geochemical characteristics, reservoir properties, hydrocarbon-bearing potential, and preservation conditions by using the methods of field outcrops,cores, thin sections, scanning electron microscopy, X-ray diffraction, and nitrogen adsorption, indicating a great exploration potential of shale oil and gas in this high-steep structural zone. Results show that the shale in Lianggaoshan Formation is 34 m thick on average,dominated by Type II kerogen with minor Type III, with an average TOC of 1.4%, Ro of 1.0%–1.4%, and average porosity of 3.49%,showing good geological conditions. The Lianggaoshan Formation is the mixed deposits of siltstone, fine sandstone and organic-rich shale, with two types of high-quality reservoirs（sandstone and shale） developed. The source-reservoir assemblage is favorable for hydrocarbon enrichment. The shale exhibits an average content of brittle minerals of 61.3%, small horizontal stress difference, and formation pressure in the syncline area greater than 1.0, which are conducive to reservoir stimulation and hydrocarbon accumulation. The areas, 5 km away from the fault zone and deeper than 1 000 m of burial depth, have good preservation conditions and great exploration potential. Favorable exploration zones such as Kaijiang, Fuling and Zhongxian were identified.