四川盆地南部中-上寒武统储层成岩作用

四川盆地南部中—上寒武统(洗象池群)储层为一套碳酸盐岩局限台地沉积,其岩性为粗粉晶—细晶白云岩、砾屑白云岩、砂屑白云岩、鲕粒白云岩等。成岩作用主要有压实作用、胶结作用、白云石化作用、岩溶作用、破裂作用等,白云石化作用和岩溶作用是形成优质储层的关键。白云石化的机理为混合水白云石化。岩溶作用具有多期性,包括沉积期岩溶、风化期岩溶、埋藏期古岩溶和褶皱期古岩溶等,以风化期岩溶为主。压实作用和胶结作用破坏了大量的原生孔隙和次生孔隙。压实作用主要发生在浅埋藏期,它与埋藏期胶结一同作用使孔隙度由原来的15%左右骤降至2%～3%左右。随着后来的岩溶作用和破裂作用等,部分储层的孔隙度又扩大到4%～5%左右,以晶间孔和晶间溶孔为主要储集空间类型。

Diagenesis of Middle and Upper Cambrian Reservoirs in Southern Part of Sichuan Basin

It is demonstrated that the Middle and Upper Cambrian reservoirs in southern part of Sichuan Basin are sediments in a restricted carbonate platform,which are mainly composed of silty-fine dolostone,dolorudite,dolorenite,oolitic dolostone,and so on.Diagenensis mainly include compaction,cementation,dolomitization,dissolution and fracturing.Dolomitization and karstification are the keys of forming excellent reservoirs.The dolostone that oc-curred in bank environment in this area is originated from mixed dolomitization.Karstification that took place during several phases includes depositional,emerged,buried and folded karst,in which the emergence karst is the main karstification.Compaction and cementation destroyed a majority of primary and secondary pores,which resulted in decreasing porosity to 2%～3% from about 15%.Consequential karstification and fracturing brought on increasing porosity to 4%-5% in parts of the reservoirs and intracrystalline pores and intracrystalline solution pores are common.