川西中部地区高压“次生气藏”形成过程中的古压控制作用

川西中部地区上三叠统碎屑岩中既发育有原生气藏也伴生有丰富的“次生气藏”,并以“次生气藏”埋深浅、气质好、经济效益高而引起人们的广泛重视。异常高压是这类气藏的显著特点。重点讨论了以“次生气藏”为主的这一复合性非常规气藏的成藏模式及古压控制作用。侏罗系储层中天然气来源于下伏上三叠统须家河组上部源岩;地层中存在的断裂及纵向上延伸的裂缝发育带是天然气向上运移的通道,并控制着“次生气藏”的分布;上三叠统中的超高压是天然气向上运移的动力,在上覆侏罗系红层储集体中表现为差异聚集。异常高压可作为该区内寻找“次生气藏”的重要标志。

THE PALEO-PRESSURE CONTROL MECHANISM IN THE PROCESS OF FORMING HIGH PRESSURE SECONDARY POOLS IN THE CENTRAL PART OF WEST SICHUAN

In the central part of west Sichuan, the upper Triassic tight clastic strata is not only developed with many original pools, but also associated with secondary pools. Common attentions are given to the secondary pools for their shallow burial depth, good gas quality and better economics. Abnormal high pressure is a notable characteristics of these pools. This paper focuses on the pooling model and paleopressure control mechanism of the unconventional composite pools which are predominated by secondary pools. The natural gas in Jurassic reservoirs is sourced from the underlain upper Triassic source rock in the upper part of Xujiahe formation. The faults and vertical fissures in the strata are conduits for gas vertical migration, which are also controlling the distribution of secondary pools. The Triassic over-pressure is acting as driving force for vertical gas migration, resulting in differential accumulations in the top over-lying Jurassic red formation. The over-pressure can be used as an indication for looking for secondary pools in this region.