四川盆地元坝地区须家河组须三段储层古压力演化及主控因素

Paleo-pressure evolution of reservoir and its main controlling factors in the Third Member of Xujiahe Formation in Yuanba area, Sichuan Basin

关键词:  四川盆地  须家河组  超压  古压力演化

Key words:  Sichuan Basin  Xujiahe Formation  overpressure  paleo-pressure evolution

摘要:

针对四川盆地元坝地区上三叠统须家河组须三段致密砂岩储层,通过流体包裹体岩相学观察及包裹体均一温度、气液比、组分等参数的准确获取,采用PVTx法恢复包裹体古压力,并以包裹体古压力和现今压力为约束,采用盆地模拟法对储层古压力演化史进行模拟,分析古压力演化的主控因素。结果表明:须三段储层现今地层压力系数一般为1.05~1.93,最大可达2.27,属于常压—强超压范畴;储层古压力演化总体经历了“增加(J₁—J₃中期)、降低(J₃晚期)、再增加(K₁)、再降低(K₂—现今)”等4个阶段,其中晚侏罗世中期和早白垩世末期的剩余压力达到最大,平面上关键充注期的剩余压力表现出由北西向南东方向降低的趋势;烃源岩生烃、构造活动、源储配置及储层致密化是研究区储层压力演化的主控因素,其中生烃增压最为重要,其次为构造挤压增压,源夹储型的配置关系和储层致密化有利于储层超压的保存,而构造抬升剥蚀及断裂则控制了储层超压的释放。

Abstract:

Taking the tight sandstone reservoirs of the Third Member of the Upper Triassic Xujiahe Formation in Yuanba area of Sichuan Basin as an example, the paleo-pressure of the fluid inclusions was simulated with the PVTx technique by considering petrographic characteristics and obtaining parameters such as the homogenization temperature, vapor-liquid ratio and composition of the fluid inclusions. With the paleo-pressure of fluid inclusions and the present pressure as constraints, the paleo-pressure evolution history of the reservoir was simulated using a basin simulation method, and also the main controlling factors were investigated. The results show that the present formation pressure coefficient of the formation mainly ranges from 1.05 to 1.93, with the maximum of 2.27, which falls into the range between normal pressure and strong overpressure. The paleo-pressure evolution of the reservoir mainly experienced four stages, including increasing (from J₁ to middle of J₃), decreasing (late of J₃), increasing again (K₁), decreasing again (form K₂ to present). The residual pressures in the stages of Late Jurassic and Early Cretaceous are the maximum, which show a downward trend from northwest to southeast on the plane. Our analysis shows that hydrocarbon generation of source rocks, tectonic activity, the combination relationship between source rocks and reservoirs and reservoir densification are the main controlling factors for the reservoir pressure evolution. Particularly, hydrocarbon generation and tectonic compression are the first and second most important for the pressurization, respectively. The combination relationship between source rocks and reservoirs and reservoir densification are conducive to the preservation of reservoir overpressure, while the structural uplift, erosion and formation fracture control the overpressure release.