低渗透砂岩微孔特征与孔隙结构类型的关系——以东营凹陷南斜坡沙四段为例

摘要

The low permeability sandstone reservoir has become an important exploration target,but the variety of micro-pore structure makes the logging response characteristics difficult to reflect reservoir features clearly.The data of mercury injection,nuclear magnetic resonance (NMR),physical properties,thin sections and CT were used to analyze the pore structure of low permeability beach bar sandstone of the fourth member of Shahejie Formation (Es4)in southern slope of Dongying Sag.The pore structure were divided into three types and five subtypes:type Ⅰ (Ⅰ1 and Ⅰ2),type Ⅱ (Ⅱ1 and Ⅱ 2) and type Ⅲ.The pore structure type is controlled by mineral content,grain size and diagenesis.The volume and features of micropores (pore throat radius less than 0.024 8 μtm) are important factors that cause the differences of pore structure types.The relationships among micropore volume,mineral content,grain size and electric properties were analyzed.It is found that mineral content and grain size affect micropore volume and features.In addition,the micropore volume is closely related to the electric properties.Logging curves are sensitive to the change of micropore volume,so it is helpful for dividing pore structure type in wellbore and identifying effective reservoirs.%低渗透砂岩已成为油气增储上产的重要勘探开发目标,但孔隙结构类型多样、微孔发育使得测井响应特征难以明显反映储层及其有效性.利用压汞、核磁共振、物性、薄片及CT等资料分析东营凹陷南斜坡沙四段(Es4)低渗透滩坝砂岩孔隙结构,并将其划分为三大类五小类,即:Ⅰ类(Ⅰ1和Ⅰ2)、Ⅱ类(Ⅱ1和Ⅱ2)和Ⅲ类.孔隙结构类型受控于矿物、粒径及成岩作用等的综合影响,微孔(孔喉半径＜ 0.024 8 μrn)含量及其特征是造成孔隙结构类型差异的重要因素.在此基础上,分析矿物含量、粒径、电性与微孔含量的关系,发现矿物、粒径影响微孔含量及特征,且微孔含量与电性特征关系密切.利用测井曲线对低渗透砂岩微孔含量变化的敏感性,有助于在井筒剖面进行孔隙结构类型划分及识别有效储层.