东营凹陷地层流体特征与油气成藏

Formation fluid characteristics and hydrocarbon accumulation in the Dongying Sag,Shengli Oilfield

根据地层水地球化学特征及分布特点,建立东营凹陷古近系沙河街组地层水主要成因类型划分标准,明确了有效烃源岩层排出的沉积-埋藏水与油气运移宏观规律的一致性和其对油气运移的辅助指示作用。综合地层水分布及压力场特征将古近系流体划分为3个流体系统:常压开放流体系统、超压封闭流体系统和过渡带流体系统,分析了不同流体系统内成藏流体特征、成藏动力和流动方式的差异。根据向储集层充注的含烃流体特征和圈闭泄水方式,划分出3种典型含烃流体富集模式。超压封闭流体系统内油富集以高含油饱和度流体充注排挤地层水富集模式为主,容易形成连续型油藏,成藏流体含油饱和度、含烃流体充注压力、圈闭的泄流条件等影响油气的富集程度;常压开放流体系统中的油藏多为低饱和度流体充注-水溢出模式和低饱和度流体充注-水渗出富集模式,充注的含烃流体数量、含烃流体的含油饱和度、圈闭幅度和盖层封油能力等影响油富集程度。

Based on the analysis of geochemical characteristics and distribution of different formation waters, a new origin identification standard was established for the formation water in the Paleogene Shahejie Formation in the Dongying Sag. The migration paths of the connate water expelled from source rocks are similar to those of the hydrocarbons coming from the same rocks, so the geochemical characteristics of the connate water coming from the source rocks can be used as auxiliary indexes to study hydrocarbon migration. Considering fluid pressure and formation water distribution, the Paleogene fluids are divided into three fluid systems： normal-pressure open fluid system, high-pressure closed fluid system, and transition fluid system. The differences in hydrocarbon-bearing fluid characteristics, hydrocarbon migration dynamic, hydrocarbon-bearing fluid flow type between these fluid systems were studied. According to characteristics of the hydrocarbon-bearing fluid charging into traps, and formation water drainage pattern, three typical oil accumulation models were classified. In the high-pressure closed fluid system, the main oil accumulation mode is high oil saturation fluid entering traps and displacing formation water, and ＂continuous＂ reservoirs are prone to form, and fluid oil saturation, fluid charging pressure and fluid seeping conditions affect reservoirs＇ oil accumulation extent. In the normal-pressure open fluid system, the main oil accumulation modes include low oil saturation fluids enter a trap while formation water is overflowing out of the trap, and low oil saturation fluids enter a trap while formation water is seeping out of the trap. The amount of hydrocarbon-bearing fluid, fluid oil saturation, trap height, and caprock sealing ability affect reservoir＇s oil accumulation extent.