ICE 2022

Summary

Overpressure is widely developed in petroliferous basins, which is closely related to the generation, migration, accumulation and preservation of hydrocarbon. The Junggar Basin is rich in oil and gas resources. The overpressure could be found generally in the oil and gas bearing strata of Jurassic in the Hinterland of the Junggar Basin. Four empirical methods including logging curves combination method, Bowers method, velocity-density crossplotting method, porosity comparison method were applied to identify the origin of overpressure and a comprehensive analysis based on geological conditions of different genetic mechanism was carried out. Then, fluid inclusion microthermometric, PVTx and basin modeling techniques were applied to study the overpressure evolution process of Jurassic strata. The results of empirical methods and comprehensive geological analysis are consistent. The overpressure intensity in the source rocks is closely related to the maturity and hydrocarbon generation intensity of the source rocks and the origin of overpressure is hydrocarbon generation. Overpressure in non-source rock strata are mainly caused by pressure transfer. The pressurization process of Jurassic reservoirs is consistent with the reservoirs forming time. There are three different overpressure evolution models: (1) Pressurization-decompression model: Hydrocarbon was supplied by Permian source rocks and hydrocarbon accumulation caused pressurization(145~77Ma). Then, tectonic adjustment and continuous pressure relief occurred in the reservoirs(77Ma~present). (2) Pressurization-decompression- Pressurization model: Hydrocarbon was supplied by Permian source rocks, and the first stage of hydrocarbon accumulation caused pressurization(135~80Ma). Then, small tectonic uplift and pressure relief occurred in the reservoirs(80~40Ma). After that, Jurassic source rocks generated and discharged hydrocarbon and the second stage of hydrocarbon accumulation caused pressurization in the reservoirs(40Ma~present). (3) Pressurization-strong Pressurization model: Hydrocarbon was supplied by Permian and Jurassic source rocks successively and there is no tectonic uplift and obvious pressure relief in the reservoirs. The pressurization caused by the second stage of hydrocarbon accumulation(135~80Ma) is significantly stronger than that caused by the first stage(35Ma~present). In this study, a series of mature methods were established to study the origins and evolution of overpressure in basins.