Characteristics and Origin of Conglomerate Diagenetic Traps in the Junggar Basin

Abstract

Summary Oil-gas reservoirs in sandy conglomerate diagenetic traps, developed in the fan delta of the Triassic Baikouquan Formation, Mahu sag, Junggar Basin, are different from lithologic reservoirs controlled by sedimentary facies. In this study, mineralogical and petrological data are employed to evaluate formation. The results indicate that reservoirs developed in the sandy conglomerate of distributary channels in the fan delta front, with the boundary controlled by reservoir quality. Differences in reservoir quality were controlled by differential diagenesis generated from detrital feldspar concentrations, paleogeotemperature environment, and formation fluids in the sandy conglomerate. Reservoir qualities of the Baikouquan Formation were improved during deep burial due to the formation of secondary pores from feldspar dissolution. Feldspar dissolution mainly depends on feldspar concentrations, acid formation water, and paleo-temperatures. When all three conditions are not satisfied the reservoir quality cannot be effectively improved and instead becomes a diagenetic dense layer that acts as a barrier to oil and gas. Therefore, they are diagenetic traps. This is a newly identified type of trap, and this study enriches the understanding of oil and gas accumulation in complex superimposed basins.