Genesis of reservoir heterogeneity and its impacts on petroleum exploitation in beach-bar sandstone reservoirs: A case study from the Bohai Bay Basin, China

Abstract

Reservoir characteristics of beach-bar sandstone reservoirs in the 2nd member of the Shahejie Formation in Banqiao Sag are studied by means of well logging interpretation, thin section observation and physical property analysis. Further, the influence of deposition, diagenesis and internal architecture interface on reservoir quality are quantitatively analyzed. On this basis, the geneses of reservoir heterogeneity of beach-bar sandstone reservoirs are summarized. The following results are obtained. (1) Primary pores, secondary pores and micro-fractures are the main types of reservoir space in the study area, and the primary intergranular pore is the main pore type; the microscopic heterogeneity of reservoirs is strong, and the physical properties of beach-bar reservoirs in different regions vary widely. (2) Tectonic-deposition, diagenesis and reservoir internal architecture work in unison to cause the heterogeneity of beach-bar reservoir quality in the 2nd member of the Shahejie Formation in Banqiao Sag; the locations and scales of beach-bar sand bodies are obviously different in different fault blocks in the study area, determining the macroscopic distribution of beach-bar reservoirs; differential diagenesis intensifies the degree of reservoir heterogeneity; the fine-grained argillaceous deposits between different architecture units of beach-bar reservoirs are critical to the quality of reservoirs. (3) The differential distribution of beach-bar reservoir quality parameters in the study area affects the spatial heterogeneity of reservoirs, which not only controls the original oil/gas distribution, but also has a significant influence on the effect of waterflooding and leads to the local enrichment of remaining oil.