关键词: 微生物储层, 碳酸盐岩, 牛津阶, 上侏罗统, 阿姆河盆地

Abstract: The Upper Jurassic Oxfordian microbial limestone layer is the most important oil & gas exploration target layer in eastern Amu Darya Basin. Clarifying the characteristics and genesis of this microbial reservoir has important theoretical and practical significance for oil & gas exploration and development. Based on cores, thin sections, physical properties and geochemical analysis data of 36 wells, combined with logging and seismic data, the sedimentary microfacies characteristics, reservoir petrology and physical properties, reservoir space characteristics and reservoir types were studied, and the genesis of microbial limestone reservoir was discussed. The results show that the depositional environment of Karabek Sag-Sandy Klei uplift-Beishkent depression is undulating up gentle slope, and microfacies of microbial adhesion mound, reef, shoal, mound shoal or reef shoal are widely developed. Thrombolite is the best reservoir rocks with type Ⅱ. Pellets, sand, biological limestone, which are formed by microbial aggregation or bonded, is the secondly developed reservoir rocks with type Ⅲ. The depositional environment of Kisar piedmont front is bottom gentle slope, mainly developed microfacies containing microbial particles muddy limestone, and reservoir rocks are microbial granular micrite limestone and micritic limestone with type Ⅳ reservoir, which formed by tectonic movement and dissolution transformation. It is concluded that favorable microbial adhesion mounds, reefs, shoals have been in a shallow buried diagenetic environment with a long time, which is conducive to preservation of primary intragranular pores. It is an important foundation for the development and formation of Oxfordian microbial rock reservoirs in the study area. The faults and microcracks, formed in two stages of tectonic movement(Late Yanshan 119 Ma, Early Himalayan 61.31 Ma), are beneficial for the reservoir reformation of microbial mound, reefs, shoal microfacies. It is another important condition for the development and formation of microbial limestone reservoirs in the study area. Three types of fluid superimposed dissolution and reformation on the reservoir, including hydrocarbon rapidly invading and dissolution by organic acid, high temperature formation fluid and deep hydrothermal fluid, TSR reaction, are the key for the development and formation of microbial reservoirs in the study area.

Key words: microbial reservoir, carbonate, Oxfordian, Upper Jurassic, Amu Darya Basin