四川盆地深层微生物碳酸盐岩储层特征及其油气勘探前景

摘要

微生物碳酸盐岩是油气勘探储层的新类型。四川盆地微生物碳酸盐岩储层主要发育在上震旦统灯影组和中三叠统雷口坡组。灯影组微生物碳酸盐岩储层主要发育在灯二段和灯四段。灯影组微生物碳酸盐岩遍布全盆，岩石结构具有全盆地相似性，灯二段以凝块石和葡萄石为主，灯四段以纹层石和叠层石为主。灯二段储集空间主要为喀斯特孔洞、葡萄-花边状孔洞、微生物体腔孔、微生物格架间孔和凝块间溶孔，灯四段则以窗格孔和喀斯特孔洞为主。灯影组微生物碳酸盐岩优质储层形成的主控因素是微生物席、白云石化和风化壳喀斯特作用。雷口坡组微生物碳酸盐岩主要分布在川西地区的雷四段，主要为叠层石和凝块石，储集空间主要为微生物窗格孔和格架孔。雷口坡组微生物碳酸盐岩优质储层形成的主控因素是微生物礁滩（微生物席）、白云石化和埋藏溶蚀作用。目前，在灯影组和雷四段微生物碳酸盐岩储层均已发现大型气田，并具有非常广阔的勘探前景。四川盆地西部中北段是深层－超深层海相领域油气勘探的最有利地区之一。%Microbial carbonates are a new type of hydrocarbon reservoir rocks.Microbial carbonates in the Sichuan Basin mainly distribute in the Upper Sinian Dengying Formation and the Middle Triassic Leikoupo Formation.The microbial carbonate reservoirs of the Dengying Formation mainly occur in the 2nd and 4th member of the formation (called simply Deng-2 and Deng-4 member)and they are of the same characteristics in the whole Sichuan Basin.The microbial carbonates of the Deng-2 are mainly thrombolite and prehnite,and those of the 4th member are mainly laminate and stromatolite. The main reservoir spaces of the Deng-2 are karst pores,botryoidalis pores,visceral pores of microorganism,pores in framework of microorganism,and thrombolite boundary dissolution pore, while those of the 4th member are mainly fenestrule and karst pores.It shows that the main depositional environments of the high-quality reservoirs of the Dengying Formation are tidal microbial flat controlled by microorganism in the shallow water,and the microbial structure is the main factor controlling the original difference of the microbial carbonate reservoir properties.Early Cambrian Mianyang-Changning intracratonic sag and Tongwan weathering crust karsts control the final distribution of the high-quality reservoir rocks.The research reveals that the main controlling factors of the high-quality microbial carbonate reservoir rocks in the Dengying Formation are microbial flat, dolomitization and weathering crust karstification.The microbial carbonates of the middle Triassic Leikoupo Formation mainly develops in the 4th member in the west Sichuan Basin,which is composed of stromatolite and thrombolite with fenestrule and visceral pores of microorganism as main reservoir spaces.Its main depositional environment is limited evaporation tide.Well developed microorganism leads to the formation of microbial reefs and beaches which determine the distribution of the high-quality reservoir rocks.The main controlling factors of the high-quality microbial carbonate reservoir rocks in the Leikoupo Formation are microbial reefs (beaches ), dolomitization and deep-bury karstification.Large-scale gas fields have been discovered in the microbial carbonates of both the Dengying Formation and the 4th member of the Leikoupo Formation in the Sichuan Basin.The middle-northern part of the west Sichuan Basin is one of the most favorable areas for exploring hydrocarbon in the deep and ultra-deep marine carbonates.