Characteristics Of The Lower Middle Ordovician Carbonate Reservoirs In The Shunnan Area Of ??the Tarim Basin

Aiming at solving the shortage, this paper deals with the geological characteristics of the Lower-Middle Ordovician in the ShunNan area of Tarim Basin. This paper describes the features and analyses the main controlling factors of the Lower-Middle Ordovician carbonate reservoir in the ShunNan area by consulting documents, analyzing relevant well samples, using geophysical methods such as well logging, seismic, combining with resevoir geology, sedimentary petrology, lithofacies paleogeographic and other disciplines based on oil and gas reservoir geology throry.The complex of Lower-Middle Ordovician reservoirs in Shunnan area contains grainstone, packstone, bicoclast limestone, mudstone, fine crystalline dolomite with subhedral shape, dolo-limetsone and silicified limestone. There are four major reservoir types incluing fracture-pore type, fracture-vug type, fracture type, and dissolution vuggs/cave type, with dissolution vuggs, intraparticle pore, intreparticle pore, moldic pore, and fracture.According to the sedimentary facies study, it suggests the carbonate platform developed during Lower-Middle Ordovician. Dolostone and limestone interbedding distributed in Yinshan formation, which indicated several transgression and regression in small scale happened in early Ordovician time basinal transgression. During Middle Ordovician time, the research area depositional facies is open marine carbonate platform, developed several sets of carbonate sand shoal and lagoon/tidal flate cycles, which are widely distributed in Yijianfan formation.There are some identification signs associated with syngenetic meteoric dissolution, which present the exposure of carbonate sand shoal in relative sea level decrease related to the third order sequence and high-frequency sequence. After that, the carbonate porosity increased with the help of meteoric water dissolution, which became reservoir major pore space during diagenesis.Multiple stages of tectonic movement are examined in research area, and some has positive impact on carbonate reservoir development. The NE, NEE strike-slip fault formed in middle Caledonian to Hercynian connecting the silica rich fluid from deep part and carbonate rocks, producing an open water-rock interaction system which increase the dissolution area and enhance the dissolution strength to optimize the reservoir. Therefore, both fracture system and deep hydrothermal fluids play significant roles in carbonate reservoir development.