川西地区须家河组异常压力演化与天然气成藏模式

川西地区须家河组发育异常高的流体压力, 组内构成了互层式的生、储、盖组合, 探讨异常高压背景下的天然气运移成藏特点及其规律具有重要意义.根据大量实测压力数据, 得出了川西地区异常压力在纵向和平面上的分布规律.以现今实测压力、压实研究和包裹体测试获得的古压力为约束条件, 应用所建立的异常压力数学模型恢复异常压力的演化历史. 研究发现, 地层压力的纵向分布可概括为南部地区的“两段式”和北部地区的“三段式”, 北部的超压幅度最大, 平面上超压中心位于梓潼凹陷.早侏罗世—古近纪须家河组内发育沉积型超压, 新近纪—现今则新增构造型超压.以流体压力的分布及其演化为主线, 结合其他主要成藏要素, 建立了3种典型的天然气成藏模式. 

Evolution of Abnormal Pressure and Model of Gas Accumulation in Xujiahe Formation, Western Sichuan Basin

It is of importance to research characteristics and its nature of gas migration and accumulation within abnormal high pressure. Overpressures are observed in Xujiahe Formation, western Sichuan basin, in which a complete assemble of source, reservoir and caprock in interbedded pattern includes. Distribution of overpressure is plotted in vertical and in plane based on a number of data of measured pressure in sandstone reservoir. The evolution history of abnormal pressure is restored mainly by means of the numerical model on abnormal pressure, which are restrained by present measured pressures and ancient pressures calculated from compaction and fluid inclusion in sandstones. Vertical pattern of formation pressure includes a type of "two segments "in southern part and a type of "three segments" in northern part, and amplitude of overpressure in the latter is higher than in the former. The zone of strong overpressure is located in the Zitong sag. Overpressure increase in Xujiahe Fm from Early Jurassic to Paleocene is due to depositional factor, and comes from the effects of tectonic movement since Neocene. Three kinds of models of gas accumulation typically are put forward taking account of distribution and evolution of fluid pressure as well as other major elements of accumulation.