Diagenetic heterogeneity, pore throats characteristic and their effects on reservoir quality of the Upper Triassic tight sandstones of Yanchang Formation in Ordos Basin, China

Depending on the pore-throat size distributions from MICP analysis, three sandstone types with their own specific pore-throat characteristics were identified. Type Ⅰ sandstones generally contain a certain amount of mesopores (including a few macropores) and pore spaces are dominant intergranular pores, intragranular pores and even oversized pores. These sandstones generally correspond to Type A, B, C2 and D sandstones and thus represent good-quality reservoir. Type Ⅱ sandstones usually contain dominant transitional pores (77% in average) and their pore systems mianly consist of clay intercrystal microporosity and a few isolated intergranular or intragranular pores. Type Ⅲ sandstones are representative by relatively abundant micropores (17.7% in average) and pore spaces are dominant clay intercrystal microporosity. Type Ⅱ and Type Ⅲ pore structures generally correspond to Type C1 and E and thus represent poor-quality reservoir. This study gives insights into the link between different diagenetic features, pore structures and their impact on reservoir quality and this will be helpful for reservoir prediction.