渤中凹陷古近系沙河街组相对高孔渗储层成因分析——以QHD35-2-1井为例

A genetic analysis of the reservoir with relatively higher porosity and permeability in Paleogene Shahejie Formation,Bozhong sag:a case of wellQHD 35-2-1

渤中凹陷古近系沙河街组砂岩具有粒度细(粉砂)、成岩演化程度高、埋藏深(大于3 000m)、物性差的特征,是否发育相对高孔渗储层是制约该地区深层油气勘探的关键问题。根据渤中凹陷QHD35-2-1井的测井、取心及测试资料,研究了深层砂岩的成岩机制和高孔渗储层的成因,结果表明:渤中凹陷深层古近系沙河街组砂岩处于中成岩期—晚成岩期,砂岩粒度细,咸水低温钙质沉淀胶结,这些因素对深部储层孔渗的发育与保存不利;高温及高异常压力的存在,使得粉砂岩储层中矿物成分大量溶蚀,形成了受异常压力保护的原生粒间孔隙,以及长石、碳酸盐岩胶结物与岩屑等溶蚀形成的次生孔隙,从而构成了深埋条件下的相对高孔渗储层。

In Bozhong sag,Bohai bay basin,the sandstone in Paleogene Shahejie Formation is characterized by fine grain size（silts）,higher diagenesis,deep burial（3 000 m） and poor petrophysical properties,and the development of reservoirs with relatively higher porosity and permeability is a key problem to restrict oil and gas exploration in the deep play.The deep sandstone diagenesis and the origin of reservoirs with relatively higher porosity and permeability are studied,according to the logging,core and testing data from well QHD35-2-1,and the results have indicated that several factors are detrimental to development and preservation of porosity and permeability in the deep Shahejie Formation sandstone,including its middle to late diagenesis stages,fine grain size and cementation of calcareous precipitation in saline water and low temperature.The existence of high temperature and abnormally high pressure,however,had resulted in dissolution of much mineral compositions,preservation of some primary intergranular pores protected by the abnormally high pressure and formation of secondary pores due to dissolution of feldspar,carbonate cement and lithic,therefore forming a reservoir zone with relatively higher porosity and permeability under deep burial.