柴达木盆地北缘侏罗系砂岩孔隙发育特征

柴达木盆地北缘侏罗系砂岩岩性以中-粗砂岩为主,次为含砾粗砂岩和中细砂岩,胶结物含量低,储集空间以原生孔隙为主,次生溶孔为辅,孔隙度与今埋深不具相关性.由于胶结作用和溶蚀作用较弱,不足以引起压实减孔量的差异,因此成岩压实作用就成为孔隙演化和保存的主要控制因素.侏罗系砂岩今埋藏深度下压实减孔量达20%～2%,不同地区成岩压实减孔量随今埋藏深度的变化率近于一致,但相同深度下的成岩压实减孔量却不尽相同,这主要与构造演化史密切相关,尤其与砂岩在埋藏过程中所经历的最大古埋藏和后期剥蚀量有着内在联系.目前砂岩孔隙度的大小代表的是65～12Ma期间砂岩达到最大埋深时的孔隙度,因此古埋深越大,孔隙度越小.

CHARACTERISTICS OF POROSITY DEVELOPMENT OF JURASSIO SAND-STONE IN THE NORTHMARGIN OF QAIDAM BASIN

The Jurassic sandstone in the north margin of Qaidam Basin consists of medium coarse size sandstone,conglomerate sandstone and fine sand with low content of cement.The reservoir spaces of the sandstone are mainly primary porosity with a small part of secondary porosity.Diagenetic compaction was the controlling factor of porosity evolution and preservation.The porosity reduction of the Jurassic sandstone caused by compaction at present burial depth is 20%～32%,and it is related to tectonic evolution history,especially to the maximal paleo burial depth and the maximun of post denudation.The present porosity formed during 65～12 Ma when the sandstone was in the maximun buried depth.So it is considered that the deeper of the sandstone buried,the smaller the porosity would be.