西昌盆地五峰组—龙马溪组页岩气保存条件研究

Preservation condition for shale gas of Wufeng-Longmaxi Formations in Xichang Basin

保存条件是影响页岩气富集高产的关键因素。本文综合利用地质、钻井等资料,分析了西昌盆地五峰组-龙马溪组的顶底板条件、构造特征、地层压力特征和气体组分,从宏观和微观两个方面对影响页岩气保存的主要指标进行了研究,在此基础上开展了西昌盆地保存条件综合评价。结果表明:盆地各凹陷主要由走滑-冲断带相隔,凹陷内地层缓倾,构造样式表现为宽缓-开阔褶皱,由于受到盆缘断裂冲断作用的影响,盆缘褶皱常表现为紧闭-闭合褶皱,地层近于直立,局部发生倒转;西昌盆地内部构造缩短量较少,缩短率均<20%,指示整个盆地内部构造变形强度较弱;盆地南部布拖区域,龙马溪组页岩可形成典型压力封存箱式地质结构,箱内与箱外存在一定压力系数差,箱内地层压力稳定,保存条件好;综合多期构造作用下的断裂和裂缝发育状况、隆升剥蚀、构造变形条件等因素,在西昌盆地东缘优选出昭觉和布拖两个页岩气有利区。

In this paper,based on data of drilling wells and geological survey,the main factors affecting the preservation of shale gas such as the lithological conditions of roof and floor rocks,strucure conditions,pressure conditions,and gas components of the Wufeng-Longmaxi Formations in Xichang Basin are detailedly studied from both macro and micro aspects.The results show that the depressions in Xichang Basin are separated by strike-slip belts or thrust belts.Strata within depressions are gently dipping,usually developing broad,slow and open folds.Due to activities of thrust faults in basin margins,folds usually appear as tight folds and strata are often nearly upright or even overturned in basin margins.Within Xichang Basin,tectonic deformation is weak.Shale rocks of Longmaxi Formation in Butuo,which is located in the southern Xichang Basin,have formed the typical pressure sealing box-type geological structure which is propitious to shale gas.Based on an overall consideration of structural deformation conditions of fault,fracture,uplifting and the erosion of Xichang Basin,it is suggested that Zhaojue and Butuo are two favorable areas for shale gas in the eastern edge of Xichang Basin.