断-压双控流体流动与油气幕式快速成藏

通过对超压的成藏物质效应和能量效应分析,系统论述了超压盆地油气幕式快速成藏机理。超压对有机质热演化的抑制作用使深部源岩和时代较老的源岩与较年青的源岩(准)同时保持在有利的生排烃阶段,而超压伴生的流体排放延迟使深部超压源岩在不同温度、成熟度条件下生成的烃类在晚期集中排放,两者的共同作用增加了有效源岩的层位和体积,进而增大了晚期源岩的累积排烃速率,为油气晚期快速成藏提供了重要的物质基础。超压可以引起未变形地层的水力破裂和超压流体的初次排放;超压流体的二次排放受超压和断裂特征的共同控制,即断压双控流体流动。超压的成藏物质效应和能量效应决定了新构造运动(或晚期构造运动)控制下的油气快速成藏:①油气成藏由多幕次流体充注完成,每一幕次包括稳态汇聚期和瞬态充注期;②油气成藏速率异常高,大型油气田可在0.1Ma内形成;③构造活动在油气成藏过程中具有建设性作用,晚期构造(或新构造)控制油气分布。

Overpressure-fault controlled fluid flow and episodic hydrocarbon accumulation

The development of overpressure in sedimentary basin has the important material and energy effects on oil and gas accumulation. Overpressure retardation of organic matter maturation can keep the deeply buried source rocks and the relatively old source rocks in the favorite hydrocarbon-generation and hydrocarbon-expulsion stage simultaneously with the young source rocks. The resultant delay in fluid release would lead to the centralized expulsion of hydrocarbon generated at different temperature and maturity, which increased the interval and volume of effective source rocks and further increased the accumulative hydrocarbon-expulsion rates. Such a process is favorable for late-stage rapid accumulation of hydrocarbon. Overpressure can cause natural hydraulic fracturing of strata, which is an important way for the primary expulsion of overpressure fluid flow. The secondary expulsion of overpressure fluid was controlled by overpressure development and the nature of faults. This kind of fluid flow may be called as overpressure-fault controlled fluid flow. The combination of the material and energy effects of overpressure determined the rapid hydrocarbon accumulation controlled by neotectonic movement or late-stage tectonic activities. The hydrocarbon accumulation was accomplished by episodic fluid injections. Each episode included steady converging and transient injection periods. The episodic accumulation rate was very high, and the large oil-gas fields could be formed within 0.1 million years. The tectonic activities had the constructive role for hydrocarbon accumulation. The neotectonic movement or late-stage tectonics controlled hydrocarbon distribution.