Characteristics of Jurassic mudstone overpressure and its control on oil and gas accumulation in Turpan Depression

The reservoirs discovered in the Turpan Depression are mainly distributed in the Middle Jurassic, some distributed in the Upper Jurassic, Cretaceous, and Tertiary. The characteristics of the mudstone overpressure are studied to reveal the relationship between reservoir distribution and mudstone overpressure. There are several overpressure mudstone cap-rocks in the depression, of which the most steady and the best one is in the Middle Jurassic Qiketai Formation. The distribution of reservoirs in the Jurassic and the sequences above is dominantly controlled by mudstone overpressure. In the regions without mudstone overpressure, reservoirs are often destroyed because of frequent fault activities. Reservoirs have different dependence on the overpressure mudstone sealing. Overpressure mudstone seals oil reservoirs indirectly, although it seals gas reservoirs and gas-cap reservoirs directly. Without rock salt or gypsum in the multicycle basins in West China, mudstone overpressure plays an important role in hydrocarbon accumulation and reservoir preservation.