川东地区中二叠统茅口组一段储层特征与形成模式

Reservoir characteristics and development model of the Middle Permian Mao-1 Member in eastern Sichuan Basin

川东地区中二叠统茅口组一段(茅一段)非常规泥质灰岩储层近期取得重大勘探发现。基于野外露头剖面及钻井岩心观察,通过薄片鉴定、物性分析、X射线衍射、氮气吸附、氩离子抛光扫描电镜、总有机碳含量(TOC)测定、CT扫描以及测井分析等手段,对茅一段泥质灰岩储层及其主控因素进行研究。结果表明,川东地区茅一段主要发育泥晶灰岩、泥晶生屑灰岩、生屑泥晶灰岩和(含)泥质生屑泥晶灰岩等4种岩石类型以及粒缘孔(缝)、有机质孔、溶孔(缝)、裂缝、滑石收缩孔(缝)等5类储集空间。其中,泥晶灰岩和泥晶生屑灰岩孔隙度低,有机质含量低,储集性能差;生屑泥晶灰岩和(含)泥质生屑泥晶灰岩孔隙度高,有机质含量高,储集性能好。茅一段储层受岩相、有机质丰度和成岩作用的综合控制,生屑泥晶灰岩微相和(含)泥质生屑泥晶灰岩微相中的原始孔隙发育好且富含粘土矿物;粘土矿物转化形成的粘土微孔和有机质孔为茅一段主要的储集空间;白云石化作用和溶蚀作用为茅一段提供了部分储集空间。基于此,提出茅一段优质储层发育模式:沉积期,由于原始组构差异,生屑泥晶灰岩和(含)泥质生屑泥晶灰岩中的原始孔隙发育;中-深埋藏期,海泡石发生成岩转化,形成粘土微孔和有机质孔,同时释放富镁成岩流体,发生白云石化;深埋藏期,酸性流体进一步改造储层,使生屑泥晶灰岩和(含)泥质生屑灰岩储层发育为优质储层。

Significant exploration discoveries have recently been made in unconventional argillaceous limestone of the first member of the Middle Permian Maokou Formation(Mao-1 Member)in the eastern Sichuan Basin.An integration of field outcrop and core observation,thin section identification,petrophysical analysis,X-ray diffraction,nitrogen adsorption,Ar-ion field emission scanning electron microscopy(FE-SEM),TOC measurement and CT scanning,as well as well logging data interpretation,is applied to the study of reservoir characteristics and controlling factors of the Mao-1 Member argillaceous limestone.It is shown that micrite,micritic bioclastic limestone,bioclastic micritic limestone and argillaceous bioclalstic micritic limestone dominate the Mao-1 Member with intergranular pores(fractures),organic pores,dissolved pores(fractures),fractures and talc shrinkage pores(fractures)well developed as reservoir spaces.The micrite and micritic bioclastic limestone,among others,are low in porosity and organic matter content,and with poor storage capacity.While bioclastic micritic limestone and argillaceous bioclastic micritic limestone,are high in porosity and organic matter content,and of good reservoir capacity.The Mao-1 Member reservoirs in the eastern Sichuan Basin are under the joint control of sedimentary lithofacies,organic matter abundance and diagenetic process.The bioclastic micritic limestone and argillaceous bioclastic micritic limestone microfacies are the most favorable reservoirs rich in pores and clay minerals.The clay micropores and organic pores generated from clay mineral transformation function as the main storage space in the Mao-1 Member;besides,the pores related to dissolution and dolomitization contribute another part of the reservoir space.Finally,the reservoir development model of the Mao-1 Member in the eastern Sichuan Basin is established.During the sedimentary period,due to the differences in original fabric,the bioclastic micritic limestone and argillaceous bioclastic micritic limestone have original pores well developed;during the medium to deep burial phase,sepiolite underwent diagenetic transformation,forming a large number of clay micropores and organic pores,meanwhile releasing Mg2+-enriched diagenetic fluid and resulting in dolomitization;and during the deep burial period,under the modification of acid fluid,high-quality reservoirs formed in bioclastic micritic limestone and argillaceous bioclastic micritic limestone formations.