东营凹陷南坡低渗透储层孔隙结构及有效性分析

Pore structure and effectiveness of low-permeability reservoirs on the south slope of Dongying depression

为了明确胜利油田低渗透砂岩孔隙结构特征及有效储层需满足的条件,选取东营凹陷南斜坡沙河街组三段(E_(s3))低渗透砂岩为研究对象,在分孔隙结构类型的基础上,利用压汞、氮气吸附与AutoScan等资料研究了不同孔隙结构类型的特征及储层有效性,认为低渗透砂岩储层有效性受孔径分布及最小孔径下限的约束.研究结果表明:低渗透砂岩孔径介于100~10 000nm的大孔较发育,中孔表现为狭缝状的毛细孔,孔径主要集中在3~7nm,且平均孔径大,孔隙体积、比表面积较小;储层的有效性与孔隙分布的均匀性与集中程度关系密切,进而确定出Es3有效储层的大孔孔径下限约为160nm,且大于该孔径的孔隙占比为90%以上,对应的孔隙度与渗透率下限约为8.0%和0.10mD,这为今后低渗透砂岩储层流体识别及有效储量估算与开发提供参考.

To investigate the pore structure of low-permeability sandstone and the conditions to be met by effectiveness reservoirs,core samples from Es3 formation on south slope of Dongying sag were selected as research objects.Based on the types of pore structure,mercury intrusion experiment,nitrogen adsorption experiment and AutoScan analysis were conducted.The re-sults show that the effectiveness of low-permeability sandstone reservoir depends on the pore size distribution and minimum pore size lower limit.Macropores with size ranging from 100 to10 000 nm develop well in low permeability sandstone.Mesopores,appearing as slit capillary pores,have the most typical size ranging from 3 to 7 nm.Its average pore size is large,while the pore volume and specific surface area are small.The effectiveness of reservoirs is found to be closely related to the homogeneity and intensity of pores;consequently,the lower size limit of macropores in effective reservoirs of Es3 is determined as 160 nm,and more than 90% pores are larger.The correspondent lower limit for porosity and permeability are around 8.0% and0.10 mD.The findings would provide evidence for fluid identification,effective reserves estimation and development in low-permeability sandstone reservoirs.