海相细粒沉积层理类型及其油气勘探开发意义

海相细粒沉积层理是恢复沉积环境的重要标志，更是影响着细粒沉积岩的储层品质及可压裂性。细粒物质通过生物作用、生物化学作用和机械分化作用形成之后，以单颗粒、絮凝颗粒、泥岩内碎屑、岩屑、有机—矿物集合体（“海洋雪”）及浮游动物粪球粒等形式，通过风力、低密度流、重力及底流等搬运至海洋，最终以垂直沉降和/或侧向加积的方式沉降下来。细粒物质可形成2种纹层（泥纹层和粉砂纹层）、2种纹层组（泥纹层组和粉砂纹层组）和2种层（递变层和均质层），并构成5大类层理（块状层理、递变层理、韵律层理和年纹层、水平层理和交错层理）。黑色海相细粒岩泥纹层和粉砂纹层由于物质组成、孔隙类型及结构、面孔率、孔径分布、微裂缝类型及密度等差异，从而造成不同层理类型细粒岩储层品质差异。同时，不同层理细粒岩由于纹层发育程度、单纹层厚度、泥纹层和粉砂纹层比例、连续性、形态和几何关系等差异，从而造成其岩石力学性质及裂缝扩展规律差异。

Main Bedding Types of Marine Fine-Grained Sediments and their Significance for Oil and Gas Exploration and Development

Bedding type of black marine fine-grained sediments is an important indicator for reconstructing the paleosedimentary environment,since it affects the quality and fracturability of shale in oil and gas reservoirs.After finegrained materials are formed by biogenic,chemical or biochemical debris genesis,they are carried into the ocean in the form of single particles,flocs,muddy intraclasts,lithics,organo-mineralic aggregates,and fecal pellets by wind,low-density flow,gravity,and bottom currents.The fine-grained sediment is deposited via suspension settling and/or advective sediment transport processes close to the sediment-water interface.After the fine-grained materials settle,two types of laminae(clayey and silty),two types of laminaset(clayey and silty)and two types of bedding(graded and homogeneous beds)develop,forming five major bedding types(massive,graded,rhythmic and varve,horizontal,and cross-bedding).Of these,the massive bedding may be divided into bioturbation-formed type and homogeneous type.In addition,horizontal bedding occurs in four types:graded(claystone),siltstone-bearing,graded(siltstone to claystone),and interlaminated siltstone and claystone.In black marine fine-grained sediments,the clayey and silty laminae differ in material composition,pore type and pore structure,plane porosity,pore size distribution and microfracture type and density,resulting in different shale reservoir quality.In addition,bedding types vary in geomechanical properties and crack-propagation behavior due to the different development of the stratum(thickness,thickness difference,continuity,morphology and geometric relationship).