含烃盐水包裹体PVT模拟新方法及其在气藏古压力恢复中的应用

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

流体包裹体PVT数值模拟法是恢复地层古压力的重要手段,但在高成熟天然气藏储层中,因缺乏气液两相石油包裹体,传统的PVT模拟方法无法应用,探索新方法刻不容缓。含烃盐水包裹体在天然气藏储层中普遍存在,具有能溶解微量轻烃、并且捕获温度与均一温度非常接近的特性。利用PVTsim数值模拟软件,结合包裹体气液比、均一温度等参数,提出了一种新的含烃盐水包裹体PVT模拟方法,并应用于恢复川东北元坝气藏的古压力。实验结果显示:元坝地区须家河组储层在160 Ma左右时发育弱超压,压力系数达到1.11;随后古压力迅速增大,至148 Ma左右时,压力系数达到1.86;在100 Ma时,古压力达到最大,但地层埋深也最大,压力系数有所降低,达到1.60。基于须家河组烃源岩生烃演化、储层古压力演化以及生储盖组合特征综合分析表明,烃源岩生烃产生的大量超压流体充注储层,引起的压力传递是储层发育超压的重要原因。

PVT numerical simulation of fluid inclusions was an important method to reconstruct the paleopressure 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 to1.60 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.