THE DIFFERENT SEDIMENTARY ENVIRONMENT EVOLUTION OF UPPER ORDOVICIAN CARBONATE IN THE TARIM BASIN, NW CHINA

The Upper Ordovician Lianglitag Formation carbonate, Tarim Basin, is an important oil and gas reservoirs. This paper take Tahe Oilfield and Tazhong Oilfield as the key areas, comparative study the differences in depositional environment and its impact on the development of carbonate original-penecontemporaneous reservoir space during the period of Lianglitag Formation. Study showed that: Tahe Oilfield and Tazhong Oilfield belonged to two different platforms at Lianglitag Formation. Lianglitag Formation carbonate in Tahe area was gentle slope to weak rimmed platform with low growth rates, water energy was weak; while Lianglitag Formation carbonate in Tazhong area was strong rimmed platform with fast build up, high-energy reef developed. Because of deeper water, high-energy facies few developed, and with strong marine cementation, the primary pores little seen in Tahe area overall. While Tazhong No.1 belt region near shallow water area, the reef and beech at platform margin were prone to suffer exposure, more primary porosity can be retained in Tazhong area with weak cementation. Compared with Tahe, Lianglitag Formation carbonate in Tazhong took the advantage of original sedimentary environment, high-energy reef and beech constituted a very good material basis for forming high-quality reservoir at later.