W ith focus on the sedimentary，geoˉchem istry，reservoir，and gas potential，a prelim inary study is perˉformed on the form ing conditions and characteristics of the shale gas in the Lower Silurian Longmaxi Formation and the Lower Cambrian Qiongzhu Formation in the Upper Yangtze region by using outcrop，drilling，and core data.The results indicate that an Early Paleozoic shallowˉdeep water shelf sedimentary environment controlled the development and distribution of the organicˉrich black shale in the formations.The black shale is the thickest in the depocenter on the deep water shelf.TheirTOC values are generally high.Horizontally，the distribution of organic rich black shale（TOC>2%）is in accordance with that of the shelf.In contrast，vertically，theymainly occur in the m iddleˉlower and bottom parts of the formations and have a continuous thickness of30-50m and a TOC value over4%.Being sim ilar to the gasˉbearing shale in America，the black shale is rich in brittlem ineˉrals，but unitary in clay m ineral type，and contains no smectite.The matrix contains wellˉdeveloped pores and m icroˉfissures，occurring in threadlike，netted and honeycomb shapes.The measured porosity of core samples ranges from2%to16%，indicatingmoderate poroperm characteristics.Active gas shows occur during drilling in the black shale.Gas content of core samples is above the industrial development threshold.Isothermal adsorption simulation of the samples also shows a high methane adsorption capacity.The overall gas potential is sim ilar to

从露头、钻井、岩心等资料出发，以沉积、地球化学、储层及含气性等为重点，对上扬子区下寒武统筇竹组和下志留统龙马溪组页岩气形成的地质条件与特征进行了初步探索，指出上扬子区早古生代的浅海-深水陆棚沉积环境控制了筇竹组、龙马溪组富有机质黑色页岩的发育与分布，深水陆棚沉积中心黑色页岩厚度最大;黑色页岩有机碳含量（TOC）普遍较高，平面上富有机碳黑色页岩（TOC>2%）与深水陆棚相分布一致，纵向上富有机碳黑色页岩集中发育在各组的中下部-底部，连续厚度约30～50m，有机碳含量在4%以上;黑色页岩脆性矿物丰富、含量大，粘土矿物单一、无蒙脱石，与美国产气页岩相似;基质孔隙、微裂缝发育，成丝状、网状及蜂窝状分布，岩心实测孔隙度为2%～16%，具有较好的孔、渗能力;黑色页岩钻井气显示活跃，岩心含气量在最低工业开发含气门限之上，等温吸附模拟甲烷吸附能力强，综合含气性特征与北美产气页岩类似。总体认为，中国上扬子区下古生界筇竹寺组、龙马溪组具有优越的页岩气形成地质条件，是较现实的页岩气勘探开发领域。

The Sichuan basin is an oil-bearing and gas-rich basin with extensive development of the Lower Silurian Longmaxi Formation shale in southwestern China. The gas shows in the shale were identified in exploration wells mainly located between southeastern Sichuan basin and western Hubei-eastern Chongqing. The thickness of the Silurian Longmaxi Formation shale ranges from 65 to 516m. The base of the Longmaxi Formation shale is graptolite-rich transgressive black shale. Its thickness increases eastward in the study area, similarly as the sand content in the formation, with the latter also increasing stratigraphically upward. The Longmaxi Formation is comprised by eight lithofacies, including laminated and nonlaminated mudstone/shale, dolomitic siltstone, laminated lime mudstone/shale, argillaceous siltstone, laminated and nonlaminated silty mudstone/shale, fine grained silty sandstone, calcareous concretions and nonlaminated shale enriched organic matter. Longmaxi Formation contains 0.2% to 6.7% of organic carbon (TOC). The organic matter is overmature, with Ro 2.4%~3.6% and dominated by type II-kerogen. Quartz silt, which is the second important component of the shale gas reservoir quality, occurs as laminae and/or disseminated and varies from 2%~93% in the shale. The size of quartz silt ranges from 0.03 to 0.05mm, with terrigenous origin. Porosity measured on core samples of the shale from the Longmaxi Formation in exploratory wells ranges from 0.58% to 0.67%. The microporosity observed in the thin sections of the shale is about 2%, and dominated by the intercrystal and intragranular pores, with the pore size ranging from 100nm to 50μm. The formation mechanism of the shale reservoirs includes favorable mineral composition, diagenesis and thermal cracking of organic component.There are some differences between Longmaxi Formation shale and Barnett shale in USA. The former is burial deeper, higher degree of thermal evolution, lower gas content, denser, more quartz of terrigenous origin. The prevailing low content of organic matter and highly variable quartz content in the Longmaxi Formation shale suggests there are only marginal conditions for exploration of shale gas resource. However, the high variability in both the content of TOC and quartz in the shale indicates that locally, particularly in the southeastern part of the basin, favorable conditions for shale gas may have developed. More detailed paleogeographic, burial history, gas content and quartz origin studies are needed to better access shale-gas potential of the Silurian Longmaxi Formation shale.

四川盆地是中国西南部重要的含油气盆地,在东部和南部地区下志留统龙马溪组页岩广泛发育。在川东南、鄂西渝东地区的勘探井中志留系具有良好的气显示。研究区龙马溪组厚65~516m,底部为一套海侵沉积的富含笔石的黑色页岩,龙马溪组向上和向东砂质和钙质含量增加,演变为浅水陆棚沉积。龙马溪组主要由层状-非层状泥/页岩、白云质粉砂岩、层状钙质泥/页岩、泥质粉砂岩、层状-非层状粉砂质泥/页岩、粉-细粒砂岩、钙质结核、富含有机质非层状页岩8种岩相组成。总有机碳含量(TOC)为0.2%~6.7%。有机质以II型干酪根为主,Ro为2.4%~3.6%。页岩中石英矿物含量在2%~93%,主要呈纹层状或分散状分布,主要为陆源碎屑外源成因。龙马溪组页岩岩心孔隙度为0.58%~0.67%,渗透率为0.01×10 -3 μm 2 ~0.93×10 -3 μm 2 。扫描电镜下龙马溪组页岩微孔隙度为2%左右,主要包括晶间孔和粒内孔,孔隙直径为100nm~50μm。页岩储层的形成机理主要为有利矿物组合、成岩作用和有机质热裂解作用。龙马溪组与美国Barnett页岩具有一定差异,主要表现在龙马溪组页岩埋藏较深、热演化程度较高、含气量较低、储层较致密、以陆源成因石英为主。对于评价下志留统龙马溪组页岩气勘探前景而言,今后须重点加强针对龙马溪组底部黑色硅质岩系石英成因、成熟度、埋藏史、含气量等方面的研究,以及进行详细的古地貌和古环境恢复。

The Paleozoic shales in South China are of high maturity and in the shale formations there are multiple types of pores and fissures, particularly welldeveloped micro and nanoscale pores. A correct understanding of pore features is the basis of the study of shale gas storage, interaction between reservoir properties and fluids, adsorption, permeability, porosity and gas migration. Observation and physical test were integrated to study the pore features of marine shales in South China. The observation methods include visual inspection, optical microscope, SEM, NMR spectroscopy, and smallangle Xray scattering. They were used to describe the geometry, connectivity and fillings of pores, to count the dominant azimuth and density of pores, and to take photographs. All these data were used to determine the genetic types of shales. The physical tests include the Helium porosity test, mercury injection, low temperature liquid nitrogen adsorption, low temperature CO 2 adsorption, etc. They were used to measure pore volume, size and distribution of pore diameter, pore structure, and specific surface area. All these data were used to evaluate the gasbearing capacity of shales. The following conclusions are drawn. The nanopores in the shale formations are dominated by intrakerogen, intergranular, intercrystalline and dissolution nanopores. Their pore throats are sheetlike or curved leaflike and pore diameters are in the range of 10~1000 nm. The nanopores (pore diameter: 30~100 nm) are the main part of connected reservoir space of tight reservoirs. Shale reservoir space can be classified into 5 types according to pore diameters, namely fissures （pore diameter:＞10000 nm）, macropores （pore diameter: 1000~10000 nm）, mesopores （pore diameter: 100~1000 nm）, transient pores （pore diameter: 10~100 nm）, and micropores （pore diameter:＜10 nm）.

我国南方古生界页岩成熟度高，页岩储层孔隙、裂隙类型多样，微米—纳米级孔隙发育。正确认识页岩孔隙特征是研究上述地区页岩气赋存状态，储层性质与流体间相互作用，页岩吸附性、渗透性、孔隙性和气体运移等的基础。为此，采用观察描述和物理测试两类方法对南方海相页岩孔隙特征进行了研究：前者通过手标本、光学显微镜、扫描电镜、核磁共振光谱学法、小角度X射线散射法等手段直观描述页岩孔隙的几何形态、连通性和充填情况，统计孔隙优势方向和密度，拍摄照片等，以确定页岩成因类型；后者通过He孔隙率测定、压汞实验、低温液氮吸附、低温CO 2 吸附等方法定量测试页岩孔容、孔径大小及其分布、孔隙结构、比表面积等，以评价页岩含气性。结果表明：该区古生界页岩储层中纳米级孔隙以干酪根纳米孔、颗粒间纳米孔、矿物晶间纳米孔、溶蚀纳米孔为主，喉道呈席状、弯曲片状，孔隙直径介于10～1 000 nm，主体范围为30～100 nm，纳米级孔隙是致密储层连通性储集空间的主体；按孔径大小，将页岩储集空间分为5种类型：裂隙（孔径大于10 000 nm）、大孔（孔径介于1 000～10 000 nm）、中孔（孔径介于100～1 000 nm）、过渡孔（孔径介于10～100 nm）、微孔（孔径小于10 nm）。