Experimental research on the influence of heterogeneous distribution of oil and water on calcite cementation from external sources during multiple oil emplacements in clastic reservoirs

Abstract

The influence of oil emplacement on calcite cementation from external sources is a topic of significant concern that is surrounded by controversy. Microscopic heterogeneity of oil-water distribution is probably the crux of the controversy. However, the influence of the heterogeneous distribution of oil and water on calcite cementation has not been directly observed and demonstrated. In this study, visual physical simulation experiments of multistage oil emplacement and calcite precipitation were conducted in glass micromodels. The processes of multistage oil emplacement and calcite precipitation occurred alternately. Characteristics of heterogeneous distribution of oil and water and the calcite precipitation processes were clearly observed and recorded in real-time under a microscope during the experiments. Three important factors, including heterogeneous distribution of the sizes of pore-throat spaces, the previously charged oil, and the presence of precipitated oil-wet calcites, jointly control the heterogeneous distribution of oil and water in the pore-throat spaces. With the supply of materials from external sources, relatively rapid material advection resulted in abundant calcites precipitation in the interconnected pore-throat spaces completely filled with water. With the gradual increase in the proportion of oil to water in pores and throats, a gradual decrease occurred in the diffusion rate and relatively low-content calcites precipitated in water-bearing position in pores and water films. Calcites scarcely precipitated in the pores completely filled with oil. Experimental results are of significance for the processes of carbonate precipitation after oil emplacement in clastic reservoirs. The reservoirs with high paleo-oil saturation after first-stage oil emplacement are conducive to formation of high-quality reservoirs.