基于高压压汞-恒速压汞的低渗砂岩储层孔隙结构评价

Evaluation of pore structure in low permeability sandstone reservoir based on high pressure-constant velocity mercury injection

利用岩心、岩石薄片、分析化验、高压压汞、恒速压汞、相渗实验等资料,对高北斜坡中深层低渗砂岩的孔隙结构进行了研究与评价。结果表明:高北斜坡中深层储层岩石主要为长石岩屑砂岩、岩屑长石砂岩,储层发育原生残余粒间孔、次生粒间溶孔、次生粒内溶孔和微裂隙等4种孔隙类型,为低孔特低渗、中孔低渗储层;考虑到恒速压汞实验在表征微小孔隙上的缺陷,提出了高压压汞-恒速压汞实验联合评价微观孔喉结构的方法,全尺度表征低渗储层孔隙结构;建立了高压压汞-恒速压汞联合评价孔喉半径频率分布叠合图,以0.12,50.00μm孔隙半径为界限,将全孔喉半径尺度划分为高压压汞、高压压汞-恒速压汞联合和恒速压汞等3个表征区;明确了低渗储层喉道的大小决定连通孔隙的多少,渗流能力主要受喉道控制,喉道越大,渗透能力越强,驱油效率越高。文中研究成果可为低渗砂岩储层的孔隙结构评价及油气勘探提供借鉴。

The pore structure of middle-deep low permeability sandstone reservoir in Gaobei slope is evaluated by use of core data,thin section,analysis test,high pressure mercury injection,constant velocity mercury injection and phase permeability experiment.The results show that the rock types of the middle-deep reservoirs in Gaobei slope are mainly feldspar lithic sandstone and lithic feldspar sandstone,and there are four types of pores,including primary residual intergranular pores,secondary intergranular dissolved pores,secondary intergranular dissolved pores and micro-fractures.The reservoir is of low porosity,ultra-low permeability and middle porosity and low permeability.Considering the disadvantage of constant-velocity mercury injection for characterizing micro-pores,the method of high pressure-constant velocity mercury injection experiment is put forward to combinedly evaluate micro-pore throat structure,and characterize pore structure of low permeability reservoir in full scale.The superimposed map of the pore throat radius frequency distribution for the combined evaluation of high pressure mercury injection and constant velocity mercury injection was established.The pore throat radius is divided into three areas by taking 0.12μm and 50.00μm pore radius as the boundary,i.e.,high pressure mercury injection,high pressure-constant pressure mercury injection and constant pressure mercury injection.It is clear that the size of throat in low permeability reservoir determines the number of connected pores,and the seepage capacity is mainly controlled by throat.The larger the throat,the stronger the permeability and the higher the oil displacement efficiency.These knowledges can be used for reference in evaluation of pore structure and oil and gas exploration of low permeability sandstone reservoir.