塔里木盆地志留系碎屑岩孔隙成因类型定量分析——以顺9井柯坪塔格组为例

碎屑岩储层孔隙主要成因类型鉴别,影响到进一步勘探时对储层预测方向的判断。塔里木盆地志留系储层大多为原生-次生复合孔和微孔,仅仅根据铸体薄片观察统计往往难以正确鉴别其主要孔隙成因类型。以顺9井志留系储层为例,在铸体薄片观察统计的基础上,根据相似岩性在相似埋藏条件下,原生孔隙受压实衰减程度相近,其残余原生孔含量相近的原理,综合分析埋深相近层段储层岩石学特征和实测孔隙度,定量化分析该储层段不同成因类型孔隙的含量。统计表明,顺9井志留系储层中原生残余粒间孔含量小于4.6%(实测孔隙度3.2%~14.6%);现今发育的中-低孔储层,主要是叠加了次生溶蚀孔形成的,孔隙度相对较高的储层以次生孔为主。该定量化分析方法可正确判别储层孔隙类型。

Quantitative analysis of pore genetic types in the Silurian clastic rocks in the Tarim Basin: A case study of the Kepingtage Formation in well Shun9

The identification of pore genetic types in clastic reservoirs affects reservoir prediction. The Silurian reservoirs in the Tarim Basin mainly include primary-secondary composite pores and micro-pores. It is difficult to identify their genetic types by conventional cast thin section observation. A case study was made in the Silurian reservoirs in well Shun9 based on cast thin section observations. Primary pores decrease to a similar extent under compression in formations of similar lithologies buried to similar conditions, resulting in similar residual primary pore contents. We studied the lithologic features and measured porosity of formations with similar burial depths, and quantitatively determined the contents of pores of different genetic types. Primary residual intergranular pores account for less than 4.6% (measured porosity 3.2%-14.6%) in the Silurian reservoirs in well Shun9. Present reservoirs with medium and low porosities were formed due to secondary dissolution, and the reservoirs with high porosities were mainly composed of secondary pores. The quantitative analysis is helpful for the identification of pore genetic types.