鄂尔多斯盆地东部奥陶系马家沟组五段5亚段微生物碳酸盐岩发育特征及储集意义

基于钻井岩心、铸体薄片和扫描电镜等资料，研究了鄂尔多斯盆地东部马家沟组五段5亚段底部微生物碳酸盐岩的发育、分布规律及储层特征，取得了以下几点认识：①微生物碳酸盐岩的发育时期具有明显的特殊性，膏盐岩—碳酸盐岩的岩性转换期是微生物碳酸盐岩的主要发育期；②微生物碳酸盐岩的岩石类型具有明显的地域性，明显受古地貌和海水盐度控制，自东向西，由潮间带向潮下带海水盐度逐渐降低，微生物岩的岩石类型由叠层石向凝块石转变；③微生物碳酸盐岩储层的孔隙类型具有明显的专属性，凝块石白云岩以发育晶间孔为主，叠层石白云岩以发育窗格孔为主；④凝块石白云岩受回流-渗透白云石化作用控制，呈环带状分布于中央古隆起东侧，叠层石白云岩与微生物诱导白云石化作用有关，呈层状连续分布于鄂尔多斯盆地东部米脂—神木地区。研究认为，微生物碳酸盐岩具备一定的储集性，可成为马家沟组碳酸盐岩、膏盐岩共生体系天然气勘探的重要目的层系。

Development characteristics and significance of microbial carbonate reservoirs in the fifth submember of Member 5 of Ordovician Majiagou Formation in the eastern Ordos Basin

Based on the data of drilling cores, casting thin sections, and scanning electron microscopy (SEM), this paper studies the development, distribution and characteristics of microbial carbonate reservoirs at the bottom of the fifth submember of Member 5 of Majiagou Formation in the eastern Ordos Basin, and gets the following understandings. (1) The development period of microbial carbonate rocks shows obviously special characteristics. The lithological transition period from gypsum rock to carbonate rock is the main development period of microbial carbonate rocks. (2) The rock types of microbial carbonate rocks have significantly regional characteristics and are obviously controlled by ancient landforms and seawater salinity. From east to west, the seawater salinity gradually decreases from the intertidal zone to the subtidal zone, and the rock types of microbolite change from stromatolite to clotted limestone. (3) The pore types of microbial carbonate reservoirs have obvious specificity. The thrombolite dolomite and the stromatolite dolomite are mainly characterized by the development of intercrystalline pores and algae framework pores, respectively. (4) Thrombolite dolomite is controlled by reflux-seepage dolomitization, and it is distributed in a ring-like shape on the east side of the central palaeohigh. The development of stromatolite dolomite with a lamellar structure is related to microbial-induced dolomitization, and it is continuously distributed in the Mizhi-Shenmu area of the eastern Ordos Basin. The research suggests that the microbial carbonate rocks have a certain degree of reservoir quality and can become an important target series of strata for gas exploration in the coexisting system of carbonate rock and gypsum rock in Majiagou Formation.