玛东地区下乌尔禾组储集层成岩作用与成岩相

Diagenesis and Diagenetic Facies of the Reservoir in the Lower Wuerhe Formation of Eastern Mahu Sag

基于大量岩心、岩石薄片、铸体薄片、扫描电镜及X射线衍射等资料分析认为,玛东地区中二叠统下乌尔禾组储集层的成岩作用有压实作用、胶结作用、溶蚀作用等,其中压实作用和胶结作用使该区储集层物性变差,而溶蚀作用,尤其是长石和浊沸石的溶蚀,使储集层物性得到改善。综合分析成岩作用类型和演化序列,认为研究区下乌尔禾组储集层的成岩演化主体处于中成岩阶段A期,部分埋藏较深的储集岩处于中成岩阶段B期或晚成岩阶段A期。根据成岩作用、胶结物含量及孔隙类型,将下乌尔禾组储集层划分为贫泥中粗砂—细砾岩弱压实成岩相、少量方沸石—浊沸石胶结中粗砂—砾岩溶蚀成岩相、含泥砂砾岩钙质胶结成岩相、方沸石—浊沸石胶结砂砾岩弱溶蚀成岩相、白云质砂砾岩硅质—钠长石胶结成岩相和富泥砂砾岩片沸石胶结成岩相。其中最有利的成岩相是贫泥中粗砂—细砾岩弱压实成岩相,其次是少量方沸石—浊沸石胶结中粗砂—砾岩溶蚀成岩相,而富泥砂砾岩片沸石胶结成岩相物性最差,是最为不利的成岩相。

Based on the analysis of core, rock thin section, cast thin section, SEM and X-ray diffraction data, it is considered that the dia-genesis of the lower Wuerhe formation of Middle Permian in the eastern Mahu sag includes compaction, cementation and dissolution,among which compaction and cementation resulted in poorer petrophysical properties, and the dissolution, especially the dissolution of feld-spar and laumontite allowed the improvement of the reservoir physical properties. The comprehensive analysis of type and evolution of thediagenesis shows that the diagenetic evolution of the lower Wuerhe formation is mainly at the Stage A of middle diagenesis period in thestudy area, partial reservoirs with relatively large burial depth are at Stage B of middle diagenesis period or at Stage A of late diagenesis pe-riod. According to diagenesis, cement content and pore type, the lower Wuerhe formation is classified into 6 diagenetic facies such as weak-compaction diagenetic facies of mud-poor medium-coarse sandstone—fine conglomerate, dissolution diagenetic facies of analcite—laumon-tite-cemented medium to coarse sandstone—conglomerate, calcite-cemented diagenetic facies of shaly sandy conglomerate, weak-dissolu-tion diagenetic facies of analcite—laumontite cemented sandy conglomerate, silicon—albite cemented diagenetic facies of dolomitic sandyconglomerate and heulandite-cemented diagenetic facies of mud-rich sandy conglomerate, among which the weak-compaction diagenetic fa-cies of mud-poor medium-coarse sandstone—fine conglomerate is the most favorable, dissolution diagenetic facies of analcite—laumontite-cemented medium to coarse sandstone—conglomerate is secondly favorable and the poorest facies is heulandite-cemented diagenetic faciesof mud-rich sandy conglomerate.