鄂尔多斯盆地塔巴庙地区奥陶系风化壳岩溶相特征

CHARACTERS OF KARST FACIES OF THE ORDOVICIAN WEATHERED CRUST OF TABAMIAO AREA IN ORDOS BASIN

鄂尔多斯盆地北部东段塔巴庙地区奥陶系风化壳岩溶作用过甚 ,破坏了地层的连续性及储集性能 ,是导致该区风化壳气藏勘探效果不佳的主要原因之一。根据研究区内钻井岩心及电测资料 ,可从风化壳中鉴别出 6种岩溶相。壳面堆积相为混杂堆积角砾岩 ,分布有限 ,物性很差 ,不可能成为储层或气层 ;洞顶相为镶嵌角砾或微 -粉晶云岩 ,溶蚀缝洞发育 ,是优良的储层或气层 ;洞底相为暗色灰岩 ,局部发育溶蚀缝洞 ,是潜在的储层或气层 ;隔层相为微 -粉晶云岩 ,亦为裂缝 -孔隙性储层或气层 ;坍塌相角砾云岩 ,成分单一 ,物性多变 ,也是一种潜在的储层或气层 ;洞穴充填相主要是泥质角砾岩 ,甚至出现泥岩 ,物性很差 。

The karstification in the study area is so strong that the strata continuity and reservoir characteristics have been disrupted. This is one of the most important factors that limit the achievements of gas exploration in the Ordovician weathered crust of the Tabamiao region in Ordos Bas. Cores and log data from thirteen wells in the study area show that six karst facies can be identified in the weathered crust. The six facies have different petrologic characteristics that would make different contributions to the formation of gas reservoirs in the weathered crust. The surface accumulation facies mingled with limestone and dolomite breccias is characterized by the limited distribution and poor reservoir characteristics. It is, therefore, unable to be a gas reservoir. The cave roof facies that consists of mosaic dolomite and /or dolomicrite breccias with well developed karst fissures and caves is an excellent gas reservoir. The cave floor facies composed of dark limestone is a potential gas reservoir for its locally developed karst fissures and caves. The cave story facies that consists of dolomicrite is a karst fissure pore type gas reservoir. The slump dolomite breccia characterized by unitary lithology can also be a potential gas reservoir. The cave filling facies composed mainly of argillaceous breccia or mudstone has very poor reservoir quality, it is unable to be a gas reservoir, but may be an additional gas source.