异常压力环境下流体活动及其油气运移主通道分析

沉积盆地的油气生成、运移和成藏过程与盆地流体作用密切相关, 而异常压力环境下流体活动有其特殊性, 因而与之相关的油气运移和成藏也有其特殊性.对于异常压力体系(包括高压和低压)而言, 存在2类流体系统, 即半开放型和封闭型流体系统.前者由于封闭层的间歇开启导致流体幕式释放, 后者以封闭层内热对流作用为主.按照封闭层开启的成因机制可划分为3类, 即水力破裂或流体压裂型、断裂型、断-压双控型.封闭层的间歇开启构成异常压力环境下油气运移的主通道.这些流体活动和油气运移在海底以及盆地的浅层和深层显示不同地球物理特征, 如气苗、麻坑、气烟囱和流体底辟带等.同样, 还可以利用岩石中残留的一些标记或异常现象示踪盆地流体活动, 如流体包裹体、地层水化学、有机地球化学异常、成岩作用异常、流体场动态模拟等.这些特征和标志为流体和油气运移主通道的识别, 同时也为异常压力环境下油气勘探提供重要的依据. 

Fluid Flow and Hydrocarbon Migration Pathways in Abnormally Pressured Environments

Hydrocarbon generation, migration and accumulation are closely related to activity of the basin fluid. Fluid flow in abnormally pressured environments shows different hydrodynamic processes as a result of associated distinct models of hydrocarbon accumulation. Two kinds of fluid flow systems have been classified in abnormally pressured environments including overpressure and underpressure, i.e. semi-opened and closed systems. In the former, opening of seal beds result in episodic fluid expulsion; but in the latter, thermal convection is dominant in anomalous pressured system. The opening mechanisms of seal beds can be grouped into three kinds of patterns, hydrofracturing, faulting and combination action of both faulting and pressuring. Opening of seal beds constitutes main pathways of hydrocarbon from abnormally pressured system. These fluids flowing from deep overpressured strata to seafloor have been identified using different geophysical data, which are imaged as gas blow-out, pockmark, chimney, fluid diapir, and so on. Some resided remarks or anomalous phenomena recorded in depositional rocks can be used to identify the active processes of fluid, such as fluid inclusions, geochemical features of formation water, anomaly in organic matters and diagenetic processes. At the same time, quantitative modeling can be used to present the dynamic processes of fluid flow. These results can constrain the realm of main migration pathways of fluid flow and hydrocarbon, and provide the useful information for hydrocarbon exploration in abnormally pressured environments.