ABSTRACT The Upper Triassic black shales in the Sichuan Basin are formed in three stages and are predominantly situated at the forefront of the Longmenshan (LMS) thrust belt. These formations are a result of three rapid subsidence events in the foredeep and the development of an underfilled foreland basin, triggered by three intense thrust nappe movements of the LMS orogenic wedge during the Late Triassic. The lateral migration of black shales in the LMS foreland basin, from the northeast to the southwest, suggests that thrust nappe movements of the LMS orogenic wedge predominantly occurred in the northeastern region during the early Late Triassic and gradually shifted toward the southwestern region in the later Late Triassic. The ongoing convergence between the North China Craton and the Yangtze Block at this time likely influenced this migration process.

印支期泸州-开江古隆起位于四川盆地东部，由于其顶部广泛发育的岩溶不整合面是四川盆地重要的油气储集层而受到广泛关注，但是关于该古隆起的形成时间及成因机制长期存在很大分歧，既影响了对印支期上扬子地区构造演化的认识，也不利于四川盆地油气勘探工作.基于地震、钻井和野外露头资料，详细分析泸州-开江古隆起顶部不整合面，结合区域构造事件、全球海平面变化等资料，利用前陆盆地系统演化模型对泸州-开江古隆起的演化过程及动力机制进行系统分析.认为泸州-开江古隆起的形成及发展期在晚三叠世卡尼期-诺利期，消亡于瑞替期，该古隆起是晚三叠世龙门山前陆盆地系统的一个组成单元——前缘隆起，其演化过程主要受控于晚三叠世龙门山造山楔的构造负载和前陆盆地沉积物的沉积负载.晚三叠世，在华北板块和羌塘地体共同向扬子陆块西缘汇聚的构造背景下，扬子陆块西缘发生NW-SE向地壳缩短，导致龙门山造山楔向扬子克拉通的逆冲推覆作用，控制了泸州-开江古隆起的形成与演化.

Shale gas is one of the hot spots of energy development. Due to the strong heterogeneity and low physical properties of shale gas reservoirs, and the complex influencing factors of pore development, it is necessary to conduct a comprehensive analysis of the control factors of high-quality reservoirs. The sedimentary characteristics, mineral composition, pore structure and controlling factors of high quality reservoir development are studied on the basis of thin section, scanning electron microscopy (SEM) and QEMSCAN analysis, X-ray diffraction (XRD), total organic carbon (TOC), Nano-CT scanning and Low-pressure N2 adsorption (N2GA) analysis on shale samples from the Longmaxi Formation in South Sichuan Basin. The results show the following: (1) According to lithology, sedimentary structure, organic carbon content and mineral composition, six sedimentary microfacies can be divided. (2) Organic matter pores are developed in organic-rich siliceous shale and organic-rich silty shale at the bottom of the first member of the Longmaxi formation, with average porosity of more than 5% and permeability of more than 2 × 10−3 μm2, which is conducive to the formation of high-quality shale gas reservoirs. (3) The contents of siliceous and TOC are positively correlated with porosity and specific surface area, while the contents of carbonate and clay minerals are negatively correlated with reservoir quality. (4) In the first member of the Longmaxi formation, the sedimentary water depth becomes shallower from bottom to top, and the sedimentary environment changes from a reduction to an oxidation environment. The contents of siliceous and organic matter decrease, while the contents of clay minerals and carbonate minerals show the opposite trend. The difference in sedimentary microfacies affects the distribution of mineral and organic matter and controls the heterogeneity of the shale reservoir.

基于沧东凹陷地震剖面和新生代残留盆地结构的详细分析,利用平衡剖面技术,结合沉积体系演变特征,系统研究了沧东凹陷的原型盆地构造演化过程.结果表明沧东凹陷新生代经历了坳陷期(孔三段-孔一下亚段沉积期)、断陷期(孔一上亚段-东营组沉积期)和坳陷期(馆陶组-平原组沉积期)3 个演化阶段.在断陷期,盆地演化主要受沧东和徐西两条边界断层的控制,盆地伸展作用具有逐渐减弱的特点,并且边界断层伸展作用具有自北西向南东迁移的特点.沧东凹陷新生代的构造演化受控于岩石圈上部简单剪切伸展和岩石圈下部纯剪切伸展的共同作用.

The uplift mechanism of the Cenozoic Longmenshan has two endmember modes: upper crustal shortening and lower crustal flow. The two modes will cause different tectonic deformation responses in the Sichuan basin and form different basinmountain systems. In order to determine the tectonic deformation characteristics of the basin-mountain system in the southern Longmenshan and the frontal area and its dynamic indicative significance, seven sandstone samples from Well Ledi 1 in the southern Longmenshan frontal area were analyzed by low-temperature thermochronology（AFT and AHe） to constrain the exhumation characteristics of the front area. The results show that the shallow strata in the frontal area of the southern Longmenshan have experienced a rapid exhumation stage（～500 to 700 m/Ma） of ～10 to 11 Ma since the Miocene（～21 Ma）.This rapid exhumation stage is synchronized with the rapid exhumation time revealed by the predecessors in the southern Longmenshan. Combined with regional geological data, it is believed that the thrust and nappe from the southern Longmenshan to the southeast at ～10 to 11 Ma, caused the tectonic stress to be transferred to the basin through the multi-layered detachment layers in the southwestern Sichuan basin, resulting in large-scale tectonic deformation and rapid exhumation in the front area. This knowledge indicates the uplift mechanism of the southern Longmenshan is the upper crustal shortening model.

There exist divergent views about the Indosinian tectonic nature of basin and the evolution of basin-range pattern in the southwest margin of the Yangtze block. Detrital zircon U-Pb dating and detrital provenance analysis of sandstone samples from the Upper Triassic-Lower Jurassic of Xiangyun Section in the western Chuxiong basin were carried out. The results show that the detrital sources of the Upper Triassic Yunnanyi Formation and Luojiadashan Formation are mainly from the Middle-Lower Triassic and Permian in the Upper Yangtze region. The detrital sources of the Upper Triassic Baitutian Formation and the Lower Jurassic Fengjiahe Formation are mainly from the Songpan-Ganzi terrane and Kangdian ancient land. Combined with the sedimentary environment evolution and regional geological setting, it is considered that the orogeny is relatively weak during the earlier Late Triassic, and Chuxiong basin is an underfilled basin, whose clastic source supply is insufficient. From the later Late Triassic to Early Jurassic, the tectonic evolution of Chuxiong basin was controlled by the thrust nappe of Ailaoshan orogenic belt,but the sedimentary filling process of Chuxiong basin was mainly controlled by the rapid rise of Songpan-Ganzi orogenic belt.

Low-resistance shale reservoirs have prospected in many high-mature shale gas plays with distinct yields. It is worth investigating the reasons for the difference in the production of low-resistance shale. And this needs to start from the genetic mechanism of shale low resistance. The genesis of shale low resistance is currently considered to be closely related to high-mature organic matter, which is the most important storage space for shale gas. Therefore, it is necessary to study the relationship among organic matter properties, pore structure of shale reservoir space, and shale resistivity. Herein, the typical low-resistivity shale in southern China was examined using X-ray photoelectron spectroscopy, gas adsorption, high-pressure mercury intrusion porosimetry. The results show that compared with conventional resistivity shale, low resistivity shale has smaller pore volume and specific surface area and higher organic matter graphitization degree. The high degree of graphitization significantly reduces the rock resistivity. In addition, graphitization changes the mechanical properties of organic matter. Under the action of compaction and tectonic movement, the macropores decrease sharply, the mesopores increase first and then decrease, and the micropores change little with the degree of graphitization. The change in the size and shape of the organic pores results in the collapse of the organic pores and the contact of the pore walls, which further increases the migration path of the electronic currency on the conductive organic matter and makes the rock resistivity lower. When the degree of graphitization exceeds 15%, poor pore development leads to lower resistivity, and due to poor reservoir space, such shales are extremely risky for exploration.

The Changning area, located in the south of the Sichuan Basin, has obtained commercial shale gas from the Silurian Longmaxi Formation, which is characterized by rich organic matter, large hydrocarbon generation, and high gas content. A series of studies have been carried out on the shale of the Wufeng Longmaxi Formation in the Changning area, including mineral petrological characteristics, shale reservoir characteristics, and accumulation characteristics. Although there are studies on the gas-bearing characteristics of the Wufeng Formation-Longmaxi Formation shale in the Changning area, the research is not systematic. In this work, based on isothermal adsorption experiments, field desorption experiments, and well log interpretation, the gas-bearing characteristics of the Longmaxi Formation shale in the Changning area were studied in detail. The results showed that the average of saturated-adsorbed methane gas volume of the Longmaxi Formation is 1 m3/t, which demonstrated that the Longmaxi shale reservoirs had strong adsorption capacity. The total gas content of section Long11-1, Long11-2, Long11-3, and Long11-4 is greater than 2 m3/t, which were the prolific shale gas layers. The Long12 sub-member has the lowest total gas content, ranging from 0.34 m3/t to 3.84 m3/t, with an average of 1.59 m3/t. The free gas content of the Longmaxi Formation in the Changning area was slightly smaller than the adsorbed gas content and it shows increasing trend from the bottom to top, while the adsorbed gas content shows an opposite trend. With the top of Long11-3 as the circumscription, the adsorbed gas accounts for the main part of shale gas in the lower part and the free gas shale in the upper part.

天然裂缝是页岩储层中重要的储集空间和渗流通道,控制页岩气的富集和保存条件.利用地表露头、岩心、EMI成像测井、薄片和扫描电镜资料,在研究四川盆地长宁地区五峰组—龙马溪组页岩储层天然裂缝发育特征和主控因素的基础上,分析了不同成因类型天然裂缝对页岩含气性的影响.研究区宏观裂缝以构造裂缝和成岩裂缝为主,微裂缝主要为构造微裂缝和粒间缝.构造裂缝的优势方位为北西—南东向、北北东—南南西向、北东东—南西西向和东西向,以中高角度裂缝为主.构造裂缝的发育程度受构造、脆性和岩石力学层厚度3个主要因素控制.与断层距离越近,页岩构造裂缝越发育;褶皱核部的构造裂缝比翼部更发育;页岩脆性矿物质量分数越高,构造裂缝越发育;岩石力学层厚度越小,层内张裂缝的发育程度越高.不同成因类型的天然裂缝对页岩气含气性影响不同,穿层剪切裂缝影响页岩气的保存条件,层内张裂缝和页理缝有利于页岩气的富集,因而需要分类型进行页岩储层天然裂缝的评价和预测.

China’s most successful horizon for shale-gas exploration and development is the Upper Ordovician Wufeng Formation through the Lower Silurian Longmaxi Formation in its Upper Yangtze Region. In this study, the Wufeng–Longmaxi Formation black shales in the Upper Yangtze Region are analysed to determine their microstructural characteristics, total organic carbon (TOC) content, and well log characteristics and to identify information on the parameters of Earth’s orbit from its gamma-ray (GR) data series. Then, paleoenvironmental modes are established over a long time scale. On this basis, the Earth’s orbital control on organic matter enrichment in the black shales is examined. The black shales of the Wufeng Formation and the lower Longmaxi Formation are rich in biogenic siliceous fossils and framboidal pyrite. Their TOC content, GR value, and uranium (U) content increase gradually from the bottom of the Wufeng Formation to the Guanyinqiao Member at its top, peak at the Guanyinqiao Member, and then decrease gradually up to the Longmaxi Formation. Approximately six and seven long eccentricity cycles can be identified from the GR curves of the Wufeng Formation and the lower Longmaxi Formation, respectively. During the long eccentricity minima, corresponding to Earth’s cold period, the black shales have a relatively high level of enrichment of organic matter. This study can provide an important reference for investigating the mechanism by which Earth’s orbits control the climate and sedimentary environment, as well as the mechanism of organic matter enrichment.

To understand the characteristics of variation in porosity and permeability, the physical properties of the shale reservoir under different stress conditions play an important role in guiding shale gas production. With the shale of the Wufeng-Longmaxi Formation in the south of the Sichuan Basin as the research object, stress-dependent porosity and permeability test, high-pressure mercury injection, and scanning electron microscope test were performed in this study to thoroughly analyze the variation in physical properties of different shale lithofacies with effective stress. Besides, the stress sensitivity of different lithofacies reservoirs was evaluated by using parameters such as pore compressibility coefficient (PCC) and porosity sensitivity exponent (PSE), while the optimized support vector machine (SVM) algorithm was adopted to predict the coefficient of reservoir porosity sensitivity. According to the research results, the porosity and permeability of shale reservoirs decline as a negative exponential function. When the effective stress falls below 15 MPa, the damage rate of permeability/porosity increases rapidly with the rise of effective stress. By contrast, the permeability curvature of the shale reservoirs plunges with the rise of effective stress. It was discovered that a higher siliceous content results in a higher permeability curvature of shale, indicating the greater stress sensitivity of the reservoir. The ratio of matrix porosity to microfracture porosity determines the PSE, which is relatively low, and low aspect ratio pores contribute to high porosity compressibility and stress sensitivity. Young's modulus shows a negative correlation with pore compressibility and a positive correlation with Poisson's ratio. High clay minerals have a large number of low aspect ratio pores and a low elastic modulus, which leads to both high PCC and low PSE. Based on the principal component analysis, a multiclassification SVM model was established to predict the PSE, revealing that the accuracy of the sigmoid, radial basis function (RBF), and linear kernel function is consistently above 70%. According to error analysis, the accuracy can exceed 80% with the RBF kernel function and appropriate penalty factor. The research results serve to advance the research on the parameters related to overburden pressure, porosity, and permeability. Moreover, the optimized SVM algorithm is applied to make a classification prediction, which provides a reference for shale reservoir exploration and development both in theory and practice.

川南地区龙马溪组深层页岩展现了极大的勘探潜力,但目前对此类储层的孔隙连通性发育特征仍然缺乏详细深入的认识.文中选取泸州和长宁西地区6 口深层井龙马溪组的6块样品为研究对象,用扫描电镜直接观察样品孔隙形态,运用低温气体吸附和高压压汞等实验手段研究孔隙结构特征,采用去离子水/正癸烷自吸斜率评估亲水/亲油孔隙网络的连通性特征.基于实验结果,讨论了页岩优势矿物组成、镜质组反射率R.、总有机碳质量分数TOC和孔隙结构参数对孔隙连通性的影响.有机质孔、有机质-黏土矿物复合孔、有机质-黄铁矿复合孔为连通性较好的孔隙类型,粒间孔及溶蚀孔的连通性相对较差;亲油孔隙网络较亲水孔隙网络更为发育,也更有利于页岩气的运聚;高含量的石英、适量的黏土矿物、适宜的热演化程度、高TOC以及高孔隙体积易于形成优势连通通道,进而提高储层孔隙连通性.整体上,泸州地区储层孔隙连通性要优于长宁西地区.

上扬子地区上奥陶统五峰组—下志留统龙马溪组是中国页岩气勘探开发最成功的层位.开展该套地层黑色页岩高频层序划分,有助于理解有机碳在页岩中的分布特征.以上扬子地区N211井的五峰组—龙马溪组黑色页岩为研究对象,分析了自然伽马(GR)与总有机碳含量(TOC)特征,基于旋回地层学理论划分了黑色页岩高频层序.结果表明:上扬子地区五峰组和龙马溪组下部黑色页岩GR值与TOC值整体上由五峰组底部到五峰组顶部的观音桥段逐渐变大,观音桥段出现极大值,再由观音桥段向龙马溪组逐渐变小.利用GR频谱分析及其滤波曲线,在五峰组和龙马溪组下部分别识别出约6个和7个长偏心率周期,据此,将五峰组和龙马溪组下部划分为12个完整的四级层序和1个不完整的四级层序.该研究可为黑色页岩高频层序划分提供典型案例,并为上扬子地区五峰组—龙马溪组页岩气甜点段预测提供参考,即:在五峰组—龙马溪组页岩高频层序结构中,层序边界附近的黑色页岩有机质富集程度相对较高.

为研究深层页岩有机质石墨化特征及其对储层孔隙的控制作用,选择川南不同地区的深层龙马溪组页岩样品,首先,开展有机质分离、激光拉曼以及X射线光电子能谱实验,确定深层龙马溪组页岩的拉曼等效成熟度及有机质石墨化程度;其次,分别开展页岩及其对应有机质的二氧化碳吸附及氮气吸附实验,表征储层特征;最后,对比有机质石墨化对于储层孔隙的影响.研究结果表明:长宁西深层页岩拉曼等效成熟度均高于3.6％,石墨化程度均达到20％以上,而泸州地区深层页岩拉曼成熟度均低于3.2％,石墨化程度均低于13％,长宁西深层页岩拉曼等效成熟度及石墨化程度均比泸州深层页岩的高;不同深层样品间石墨化程度与成熟度存在良好的正相关关系;在深层页岩中,有机质为深层页岩提供了超过70％的孔体积和超过50％的比表面积.随着石墨化程度增高,有机质塑性增强,孔隙壁面复杂程度降低,孔体积和比表面积均降低,孔体积在孔径为2～30 nm的中孔段和大于50 nm的宏孔段降低更加明显,比表面积的降低则主要体现在孔径小于3 nm的孔隙中.

川南长宁地区经历多期构造演化过程，页岩裂缝内部发育大量流体包裹体，利用流体包裹体进行气藏古温压恢复可为不同构造单元页岩气藏压力演化、保存条件研究提供重要依据。本文通过显微岩相学观察、流体包裹体测温、激光拉曼光谱分析、盆地数值模拟等方法，研究长宁地区双龙—罗场及天宫堂构造单元地质流体活动及古压力演化。研究结果表明：川南长宁地区脉体富含大量的气-液两相包裹体和气相包裹体以及少量沥青包裹体；不同构造单元流体充注期次存在差异，双龙—罗场向斜为2期流体充注，天宫堂背斜发生3期充注；长宁地区成藏过程划分为低压缓慢抬升、高压快速埋藏、高压缓慢调整、超压持续深埋和晚期抬升改造5个阶段；晚期抬升改造的强烈程度直接关系着页岩气能否形成气藏；双龙—罗场向斜超压原因是液态烃裂解生气造成超压，后期改造过程中超压未被完全破坏。天宫堂地区在抬升过程中受到NW和NE向叠加的挤压应力，形成NE向通天断裂，超压条件被破坏。

吸附气是页岩气的重要赋存形式和组成部分.为了明确四川盆地长宁地区五峰组—龙马溪组一段页岩在埋藏过程中吸附气含量的演化规律,利用页岩等温吸附实验、钻井现场解吸和测井综合解释资料,建立了页岩吸附气含量与地层温度、地层压力、页岩TOC等主要影响参数的多元回归数学公式,结合典型评价井(N201井)的埋藏史、热史,对不同地质时期页岩吸附气含量进行定量计算.计算结果表明:自侏罗纪有机质开始大量生气以来,页岩吸附气含量随着埋藏深度的增加逐渐升高,到白垩纪末期吸附气含量达到4.42 m3/t;古近纪以来,随着上覆地层被大幅度剥蚀,页岩吸附气含量逐渐降低至现今的1.67 m3/t.

基于地表露头、钻井资料,对四川盆地上三叠统黑色泥页岩的时空分布特征进行了详细的分析.在此基础上,对黑色泥页岩所记录的前陆盆地系统演化过程进行了研究.四川盆地上三叠统黑色泥页岩主要发育在龙门山冲断带的前缘地区,反映了晚三叠世龙门山造山楔的强烈逆冲推覆控制前陆盆地的沉积充填过程.晚三叠世,龙门山造山楔经历了三次较为强烈的造山作用,导致前渊地区快速沉降,形成欠补偿前陆盆地,为须一段、须三段和须五段三套黑色泥页岩的沉积提供了有利条件.四川盆地上三叠统须一段、须三段和须五段黑色泥页岩依次向南东迁移,表明晚三叠世龙门山造山楔具有显著地向南东推覆的特征.

研究四川盆地长宁地区龙马溪组第一段下亚段-五峰组主力产气层的有机质演化历史.在15口钻井岩心薄片的沥青反射率测定和地层厚度趋势法估算喜马拉雅期的地层剥蚀厚度基础上,应用盆地模拟软件对20口完钻评价井和24口人工虚拟井的埋藏史和有机质的热演化史进行模拟计算,结果显示:(1)页岩的沥青反射率在2.15％～4.57％,平均等效镜质体反射率为2.41％;(2)页岩有机质在中二叠世-早三叠世达到生油高峰,中三叠世-早白垩世处于大量生气期;(3)古近纪以来,受喜马拉雅构造抬升与地层剥蚀作用影响,地层温度大幅度降低,页岩有机质生烃作用趋于停止.长宁地区龙马溪组第一段下亚段-五峰组页岩生气高峰较早,保存条件对页岩气富集具有重要影响.

The highly complex geology of the Sichuan Shale gas play, especially in relation to natural fracture systems at different scales, affects the hydraulic completion efficiency and performance. Ant-tracking-based workflows and borehole image data are regularly used to optimize completion campaigns, but bridge-plug-stuck and screen-out risks are still high. The lack of sufficient understanding and accurate identification of the natural fracture systems are the major challenges to address these engineering risks. Surface microseismic monitoring campaigns were conducted over several wells of the Changning field, Sichuan Basin, China. The surface receivers were placed in a radial pattern to record microseismicity generated by hydraulic fracturing. The failure mechanism of all mapped microseismic events (i.e., strike, dip, rake, etc.) was extracted using a moment tensor inversion (MTI) method. Improved understanding of the natural fracture systems and their influence during the hydraulic fracturing process has been achieved by integrating the regional geological data, pumping data and MTI results. Several hydraulic fracturing cases that stimulated near natural fracture systems were investigated. The microseismic monitoring results show that (i) most of the hydraulically induced fractures located in the vicinity of the natural facture or fault did not propagate along the regional maximum stress direction, (ii) the bridge plug got stuck and (iii) screen-out happened frequently in these areas. Moment tensor inversion reveals that (i) the dominant failure mechanism of the natural fractures different from hydraulically induced fractures, (ii) more than one group of natural fractures develop along different directions. Real-time adjustments of the pumping schedule and bridge-plug settings were conducted to reduce engineering risks based on the improved understanding of natural fractures, which proved effective. The innovation of using surface microseismic monitoring results to improve understanding of natural fractures and reduce the engineering risks in real time represents a key step forward to mitigate natural fracture influence and improve the effectiveness of stimulation.

Pore evolution in organic-rich shale is widely reported to be related to thermodynamic reactions, but its connection with tectonic deformation is overlooked. A systematic comparative analysis was conducted in the Changning area to detect the tectonic deformation of organic-rich shale. The study encompassed mineralogical composition, petrography, and porosity, along with the state of tectonic stress and pore pressure in the Wufeng-Longmaxi shale of a basement-involved fold-thrust belt located in the southern Sichuan Basin. The content of both total organic carbon (TOC) and clay mineral was correlated with bulk porosity, indicating the relevance and impact of both organic and inorganic pores on bulk porosity. However, samples with a constant TOC or clay mineral content exhibited lower bulk porosity in wells located on the forelimb than in wells located on the crest and backlimb of the overthrust anticline. The variably elongated and slot-like morphology as well as the crude alignment of organic pores in samples from wells on the anticline forelimb suggest that the organic pores collapse under tectonic deformation. This observation was different from that of the spherical morphology of organic pores in samples from wells on the backlimb of an overthrust anticline. The ratio of horizontal stress to vertical stress (S-hmin/S-v or S-Hmax/S-v), simulated from well logs, was negatively correlated with the median bulk porosity in the Wufeng-Longmaxi shale within various cores. This suggests that a larger strain, under higher horizontal compression stress, decreased the bulk porosity in the shale of the forelimb areas, despite the content of the mechanically weak component (e.g., TOC or clay minerals) being similar in both. Additionally, the Wufeng-Longmaxi shale generally exhibited a higher pore pressure, but lower bulk porosity, in wells on the forelimb relative to the backlimb, which indicates that the collapsed pore system has, to some extent, inhibited the relief of maturation-induced overpressure during exhumation.