Reservoir diagenesis and fluid-rock interaction simulation of the Sulige gas field in the Ordos basin

Abstract：Based on a comparison in petrological features, diagenesis and reservoir characteristics between gas and non-gas reservoirs, the difference in their diagenetic facies is analyzed. Gas reservoirs are mainly developed in solution pore diagenetic facies of coarse-grained lithic quartzose sandstone and mud-bearing coarse lithic quartzose sandstone, whereas non-gas reservoirs mainly occur in compact diagenetic facies of mud-bearing medium-fine lithic quartzose sandstone and residual intergranular pore diagenetic facies of mud-bearing medium-coarse lithic quartzose sandstone. The mechanism of secondary pore formation was studied through fluid-rock interaction physical and mathematic modeling. The results show the following mechanism: during stage A of the middle diagenetic evolution phase, substantial organic acid was expulsed from source rocks and dissolved more soluble components such as tuff and feldspar in reservoirs of the Sulige gas field, thus forming secondary pores. The medium- and coarse-grained sediments and fine-grained sediments experienced different diagenetic evolution paths because of different energy intensities of their water bodies and their diagenesis. Medium- and coarse-grained sediments are easy to form gas reservoirs because their secondary pores are well developed, there are certain residual primary pores and the total porosity is high. However, fine sediments are not easy to form gas reservoirs because all their primary pores disappear, secondary pores are scarce and the total porosity is very low.