Geochemistry of formation waters in the Shiwu depression of the Songliao basin, northeast China, shows a distinct variation in different pressured systems. The study area is composed of terrigeneous clastics in fluvial-lacustrine environments, which contain formation water with salinity ranging from less than 1000 to 12,000mg/l. Water composition varies with depth and hydrochemical regions. In the underpressured strata deposited during the rifting period, formation water is characterized by water type of CaCl2 with higher salinity. NaHCO3-dominanted water with lower salinity occurs in the normally pressured strata deposited during the post-rifting period. In the transition area between the normally pressured and underpressured zones, total dissolved solid (TDS) content ranges from 1000 to 7600mg/l and increases with depth. In this halite-free basin, brackish water may be attributed to the evaporation of formation water and water–rock interaction. In the deep buried underpressured water, a predominated diagenesis reaction resulting in Ca and Cl enrichment and reduction of Na may be related to albitization of plagioclase following the basinal fluid line (BFL). The results of this study indicate that salinity variation of formation water and diagenesis reaction is closely related to hydrochemical environments within different pressured systems.

Diapiric structures are well developed and occur in most of the central part of the Yinggehai Basin, on the western side of the South China margin. A strong thermal anomaly due to hot fluid flows occurs in the diapiric zone, as evidenced from vitrinite reflectance (Ro), clay mineral transfomation, mid fluid inclusion homogenization temperatures. This anomaly results from hydrothermal fluid flow along vertical faults from overpressured compartments into the overlying Late Miocene and Quaternary smld rich layers. The magnitude of thermal mlomaly is related not only to the distance to which the vertical fault is hydraulically open, but the permeability of rocks interconnected with the faults, intense heat transfer for convection of fluids occurs in the smld rich intervals adjacent to vertical faults. Abnormal orgmfic matter maturation, together with rapid transformation of clay minerals, which occurs at certain intervals within the present day normally pressured system mid normal conductive temperatures in a diapir, can be used to identify palaeo high pressure zones. Abnomal high temperatures measured from a drill stem test in a diapir can be inferred to be the results of recent expulsion of hydrothermal fluid flow. The results of this study suggest that thermal fluid expulsion along faults plays ml important role in the modification of thermal regimes, the enhancement of organic matter maturation, and rapid transformation of clay minerals, as well as the accmnulation of hydrocarbons in diapiric structures of the Yinggehai Basin, South China Sea.

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。

盆地流体动力学是综合利用地质、地球物理、地球化学手段和计算机模拟等技术, 通过对温度场、压力场和化学场等各种物理化学场的综合研究, 在流体输导网络的格架下,再现盆地内流体运动过程及其活动规律的多学科综合的研究领域。流体是控制盆地中物质演变和能量再分配的主导因素, 它对沉积盆地的油气生成、运移和成藏过程与成矿作用等都可起到重要的控制作用。因此受到国内外地学界高度重视。近十多年来, 盆地流体研究在盆地流体流动样式、流体输导网络、流体与岩石相互作用、流体示踪技术、流体模拟技术等方面取得了长足的进展。随着盆地流体领域的新理论和新技术的应用将会给资源勘查带来更大的发展。

流体动力系统是盆地流体分析中的核心问题。本文以莺歌海盆地和东营凹陷为例,分别探讨了泥2流体底辟型和盐底辟型盆地流体动力系统特征。研究表明,超压盆地内流体动力系统决定了不同成因流体流动的驱动机制和方向及流体域分布,进而控制油气运聚的全过程。