富有机质页岩中烃类动态运移对页岩气富集成藏的制约——以四川盆地龙马溪组为例

摘要

A shale gas reservoir is typically a continuous hydrocarbon reservoir, and its formation and enrichment cannot be separated from the shale.The generation,migration and accumulation of natural gas are the key factors for the effective accumulation of shale gas in shale. The Longmaxi shale in Sichuan Basin has excellent geochemical parameters and reservoir characteristics as indicated by organic geochemical analysis,X?ray diffraction and scanning electron microscopy and on drilling and outcrop data.We studied the tectonic evolution of well PY1 in Sichuan Basin and the thermal evolution history of organic matter in the Longmaxi shale. Compared to the Barnett shale,the Long?maxi shale was buried deeper,and was preserved in an open state due to tectonic activity,which was unfavorable for free gas accumulation. Kerogen in the Longmaxi shale belongs to types I and II. The early formed hydrocarbons discharged out of the shale in the form of oil,and only the late formed,overmature gas and secondary gas(from oil cracking)remained in the shale system,restricting the effective accumulation of shale gas to some extent.%页岩气作为一种典型的连续性油气藏,其形成和富集均发生在页岩中,因此页岩中天然气的形成、运移、聚集等过程是页岩气有效富集成藏的关键.以钻井及露头剖面为基础,采用有机地球化学分析、X射线衍射、扫描电镜等实验手段相结合,发现四川盆地龙马溪组页岩具有优异的地球化学参数和储层微观特征.以PY1井埋藏史为例,结合盆地区域构造演化史及龙马溪组页岩中有机质热演化史特征,通过与Barnett页岩对比发现,四川盆地龙马溪组页岩埋深相对较深,且后期构造运动导致其保存条件处于一个相对"开放"的状态,不利于页岩中游离气的赋存;同时龙马溪组页岩干酪根类型以Ⅰ或Ⅱ型干酪根为主,页岩在前期热演化过程中形成的烃类主要以石油的形式大范围排出页岩,仅晚期形成的过成熟气和滞留的油裂解气未脱离页岩系统,这在一定程度上制约了页岩气的有效富集成藏.