TIGHT OIL SECONDARY MIGRATION MECHANISM AND ACCUMULATION CONTROLLING FACTORS: A CASE STUDY OF JURASSIC IN SICHUAN BASIN

Currently, studies of tight oil enrichment mainly focus on determining the static geological features and controlling factors. Though these studies can help evaluating tight oil sweet spots, the research of dynamic migration mechanism of tight oil can raise the accuracy of tight oil sweet spots prediction.

In this study, tight oil of Jurassic in Sichuan Basin was taken as an example, and the migration pathway, force and seepage process were analyzed in respect of secondary migration of tight oil, and based on dynamic research, the controlling factors of tight oil enrichment was evaluated to predict the sweet spots. Migration physical analog experiment, cast and fluorescent thin sections, FESEM and ESEM were utilized in the research. According to the research, tight oil migrated under the huge migration driving force with low speed non-darcy percolation in low efficient migration path. The migration underwent three percolation phases, including stagnation, nonlinearity, and quasi-linear. The migration patterns of tight oil in study area are characterized by migrating through both of the pores and fractures, causing both of them oil-bearing in micro-scale, and regional short distance migration in macro-scale. Due to such a migration mechanisms, profitable source rock controls the distribution of tight oil play, and most of the tight oil favorable areas locate within the boundary of 40×10⁴t/km² of hydrocarbon generating intensity in study area. High permeability and porosity of reservoir sweet spots support the formation of tight oil sweet spots, while fracture is closely related to the high capacity wells.