柴北缘N1井储层的源控成岩演化与钙质夹层成因

Source-rock-derived diagenetic evolution and origin of calcareous interlayer in reservoirs of well N1 in the northern Qaidam Basin

以柴达木盆地北缘N1井为例,通过镜下观察和地化分析,探讨埋藏成岩阶段一类钙质夹层的形成过程。结果表明:N1井储层中的钙质夹层被两期烃源岩热降解成因方解石胶结(Ca1,Ca2),含少量沥青浸染高岭石;相邻高孔渗层溶蚀作用强烈,可见残余方解石、高岭石和两期沥青(Hy1,Hy2);钙质夹层非方解石直接沉淀而成,而是在烃源岩两期生排烃控制下储层成岩演化(高岭石—Hy1—Ca1—溶蚀、高岭石—Hy2—Ca2)的结果,即早期溶蚀成因Ca1型和晚期Ca2型钙质夹层的叠加。

Taking well N1 in the northern Qaidam Basin as an example,the formation of one type of calcareous interlayer in burial diagenetic stage was investigated using microscopic observation and geochemical analysis.The results show that the calcareous interlayers in the sandstone reservoir of well N1 are thermal degraded by the source rocks as calcite cementation(Ca1 and Ca2),which contain minor bitumen-stained kaolinite.The corrosion of adjacent porous interlayers is strong,and the residual calcite,kaolinite,as well as two episodes of bitumen(Hy1,Hy2)can be observed.The calcareous interlayers are not generated by direct precipitation of calcite,but it is a result of diagenetic evolution(Kaolinite-Hy1-Ca1-dissolution/kaolinite-Hy2-Ca2)which is controlled by two epiosodes of hydrocarbon generation and expulsion in source rocks.In other words,the calcareous interlayers in well N1 results from the superposition of early-stage dissolution-generated Ca1-type and late-stage Ca2-type calcareous interlayers.