Origin of Overpressure and its Effect on Hydrocarbon Enrichment in the Hinterland of Junggar Basin, NW China

Abstract

Overpressure is widely developed in deep petroliferous strata in the hinterland of the Junggar Basin. However, a comprehensive understanding of its origin and effect on hydrocarbon distribution and enrichment remains lacking. In this study, we employ five empirical methods and comprehensive geological analysis to identify the origin of overpressure, and uncover the effect of overpressure on hydrocarbon enrichment. The results indicate that disequilibrium compaction is not a significant factor in overpressure generation. Instead, hydrocarbon generation, pressure transfer and diagenesis are the primary causes. The empirical methods support this conclusion. There is a positive correlation between overpressure intensity and source rock thickness and maturity. Notably, widespread cross-formational migration of hydrocarbon bearing fluid occurred, with sandstone overpressure exceeding that of adjacent shale in non-source strata. Furthermore, there is a distinct transformation from smectite to illite near the top of overpressure. Hydrocarbon generation pressurization and pressure transfer significantly effect hydrocarbon enrichment. The overpressure caused by hydrocarbon generation drives hydrocarbon migration and accumulation, establishing an optimal energy configuration between reservoir and cap rock. Faults play a crucial role in hydrocarbon vertical migration and pressure relief. The overpressure in reservoirs can reduce the porosity and permeability thresholds and enhance the charging capacity of oil and gas.