Coexistence mechanism of multi-types of reservoir pressure in the Malang depression of the Santanghu basin, China

This paper focuses on the distribution and coexistence mechanism of the various pressure systems in the Malang depression of the Santanghu basin, northeast of the Xinjiang Uyghur Autonomous Region, China. According to the classification standard of formation pressure, The calculated pressure coefficient showed that the Xishanyao Formation (J2x) is underpressured, the reservoirs of the Lucaogou Formation (P1l) are both normally and overpressured, and the Upper Pennsylvanian (C2) presents the coexistence of a normally pressured system and an underpressured system. The permeability of the Xishanyao Formation (J2x) improve from the southwest to the northeast of the basin, resulting in a relatively easy fluid supply to the reservoirs, and the pressure coefficient increases gradually. Tectonic uplift had a significant influence on the decrease in the reservoir pressure. However, a difference in source-reservoir assemblages caused a difference in fluid recharge and original pressure in reservoirs during hydrocarbon accumulation. The difference in reservoir connectivity causes a difference in the fluid supply during later tectonic movement, finally leading to the formation of different pressure systems. Thus, the basic mechanism for the coexistence mechanism of the various pressure regimes in this area is the disequilibrium of the fluid supply under the restriction of oil accumulation conditions.