Abnormal overpressure distribution and natural gas accumulation in foreland basins, Western China

Abnormal overpressure occurs in the forelandbasins of Kuqa, South Junggar and West Sichuan in China.The pressure coefficients are high. Overpressure exists inwide areas and various strata. The layers of overpressurehave a very close relationship with lithology, and the area ofoverpressure is controlled by the piedmont depression. Themechanisms of overpressure formation in the Kuqa andSouth Junggar Depression include disequilibrium compac-tion and tectonic compression; the importance of these twofactors varies in different basins and in different stages of thesame basin. Different models of gas accumulation are estab-lished to explain the relationship between overpressure dis-tribution and gas pool formation, and the influence of over-pressure on the gas pools. These models include: (i) theviolent tectonic movement leads to the pool formation inoverpressure belt (Kela-2 gas field in Kuqa); (ii) the pres-sure releases at shallow part and the gas pool forms in latetime (Hutubi gas field in southern Junggar Basin); (iii)through the pressure transfer the gas migrates and accumu-lates (Xinchang gas field in Western Sichuan Basin).