鄂尔多斯盆地中南部三叠系延长组8油层组成岩作用及其对储层物性的控制

Diagenesis and controls on the physical properties of the Triassic Chang-8 oil reservoirs in the south-central part of the Ordos Basin

关键词:  鄂尔多斯盆地  三叠系  延长组  8油层组  成岩作用  储层物性

Key words:  Ordos Basin  Triassic  Yanchang Formation  Chang-8 oil reservoirs  diagenesis  physical property of reservoirs

摘要:

鄂尔多斯盆地中南部延长组8油层组主要成岩作用包括压实作用、石英次生加大、自生绿泥石膜生长、次生高岭石化、连晶方解石交代、长石溶蚀。根据铸体薄片,碳氧同位素分析,确定了各种主要成岩产物的空间分布和成因,分析了成岩产物分布与现今总面孔率的关系,从而确定8油层组的物性主要受石英次生加大、连晶方解石、长石溶孔、剩余原生孔隙分布的控制。石英次生加大和连晶方解石发育的地方,储层物性差;具自生绿泥石膜的剩余原生孔隙和长石溶孔发育的地方,储层物性好。

Abstract:

The diagenesis of the Triassic Chang-8 oil reservoirs in the south-central part of the Ordos Basin includes compression, secondary overgrowth of quartz, secondary kaolinization of mica and matrix, overgrowth of authigenic chlorite membrane on the walls of primary pore spaces, replacement of intergranular matter and grain rims by intergrown calcite, nonselective dissolution of intergranular matter and grain rims and filling of asphalt into the secondary solution openings, and dissolution of feldspar. The present paper deals with the spatial distribution and origin of diagenetic products, and the relationship between the distribution of diagenetic products and existing total planar porosities on the basis of cast thin sections and carbon and oxygen isotopic data.The physical properties of the Triassic Chang-8 oil reservoirs are mainly controlled by secondary overgrowth of quartz, intergrown calcite replacement, feldspar solution openings, and distribution of residual primary porosities with authigenic chlorite membrane. The physical properties are generally poor in the areas where secondary overgrowth of quartz and intergrown calcite are developed. On the contrary, the physical properties are relatively good in the areas where the residual primary porosities with authigenic chlorite membrane and feldspar solution openings are developed.