蜀南自贡地区茅口组岩溶储层成因及地震预测方法

Genesis and seismic prediction of Maokou karst reservoirs in Zigong,southern Sichuan

近年来,四川盆地下二叠统茅口组大量非构造圈闭钻井获得高产,证实了岩溶储层是茅口组岩性气藏的一个重要控制因素。但岩溶储层的成因及地震响应特征尚不明确,不同地区的岩溶储层预测方法不尽相同。通过对蜀南自贡地区茅口组构造特征、地层特征和岩溶储层地震响应特征研究,得出以下5方面认识:①台内滩相是岩溶储层发育的物质基础,自贡地区茅口组台内滩相主要在茅三段和茅二b段发育;②东吴运动差异抬升是研究区岩溶储层的主控因素;③断层形成于茅口组沉积之后,茅口组顶部岩溶储层受后期局部持续风化控制,茅口组内部岩溶储层受后期断层改造控制;④距茅口组顶距离不同,岩溶储层地震响应特征不同,茅三段表层型岩溶储层物性与茅口组顶部波峰振幅呈负相关,茅二b段内幕型岩溶储层物性则与茅口组内部波峰振幅呈正相关;⑤表层型岩溶储层在平面上不依赖断层且具有一定规模。

Despite many wells with high yields from non-structural traps in the Lower Permian Maokou Formation,the Sichuan Basin,which demonstrates that karst reservoirs are an important type in Maokou lithologic gas reservoirs,the genesis and seismic responses of karst reservoirs are uncertain;thus,it is difficult to assess various seismic techniques used in different areas.Based on the study of structural and stratigraphic features and seismic response of karst reservoirs in the Maokou Formation,Zigong area,southern Sichuan,following conclusions are reached.Intra-platform beaches,which mainly turn up in Mao3 and Mao2b,are the material basis of karst reservoirs.Differential uplift caused by the Dongwu movement is the major control on karst reservoirs in the area of interest.Faults occurred after the deposition of the Maokou Formation;karst reservoirs at Maokou top were dominated by later sustained weathering locally,and those inside the Maokou Formation were reworked by later fault activities.Seismic responses of karst reservoirs vary with the distance to Maokou top;there is a negative correlation between epikarst reservoir properties in Mao3 and peak amplitude at Maokou top,and there is a positive correlation between internal karst reservoir properties in Mao2b and interior peak amplitude in the Maokou Formation.The occurrence of epikarst reservoirs of scale is not dependent on faults.