A new PVT simulation method for hydrocarbon-containing inclusions and its application to reconstructing paleo-pressure of gas reservoirs

PVT numerical simulation of fluid inclusions was an important method to reconstruct the paleo-pressure of hydrocarbon accumulations; however, in high-maturity gas reservoirs, gas-liquid petroleum inclusions were very rare, so the traditional PVT simulation methods could not be applied. It was urgent to develop a new method. Hydrocarbon-containing inclusions were widely distributed in gas reservoirs. They could dissolve a little gaseous hydrocarbon and their trapping temperatures were close to homogenization temperatures. Using PVTsim software and combining with some parameters such as vapor/liquid ratio and homogenization temperature of hydrocarbon-containing inclusions, a new PVT simulation method was proposed to get the trapping pressure of inclusions, which was then applied to reconstruct the paleo-pressure of the Yuanba gas reservoir in the northeastern Sichuan Basin. The Xujiahe reservoir developed weak overpressure at about 160 Ma, and the pressure coefficient reached 1.11. Then the paleo-pressure increased rapidly until 148 Ma at which time the pressure coefficient reached 1.86. At about 100 Ma, the paleo-pressure reached its peak, but the pressure coefficient decreased to 1.60 because the formation burial depth was the deepest. The comprehensive analyses of hydrocarbon generation, paleo-pressure evolution and reservoir-cap combination indicated that the overpressure transferred from source rock to reservoir through the process of hydrocarbon generation and accumulation was an important mechanism for the development of overpressure in the Xujiahe reservoir.