Microfacies Characteristics and Sedimentary Environment of Ordovician Carbonate Rocks from Gucheng Region in Eastern Tarim Basin

The eastern Tarim Basin is a new field of petroleum exploration because the Ordovician carbonate reservoir hosts abundant oil and gas resources. However, researches on depositional microfacies and evolution are inadequate with a low exploration degree. Using the microfacies analysis method and making full use of core, logging, well logging, seismic and rock slice, the microfacies, sedimentary characteristics and distribution of Middle-Early Ordovician carbonate rocks in Gucheng region, eastern Tarim Basin have been analyzed. The results have shown that 8 microfacies are recognized in these carbonate rocks, and the spatial distribution pattern of carbonate microfacies are established with different microfacies associations. Combining with macro geological background, the Middle-Early Ordovician Formation in Gucheng region can be divided into limited platform, open platform, platform margin, and carbonate ramp. And then, the evolution of Early-Middle Ordovician sedimentary environment has been discussed, it's believed that the transgressive platform margin shoals formed favorable reservoir facies belts for Ordovician carbonate rocks, because the sea is relatively shallow and gradually deepened.