The carbonate ramp deposits from the Ordovician Penglaiba Formation in the Tarim Basin, Xinjiang: sedimentary characteristics and their implications for petroleum exploration

The dolostones widely developed in the Ordovician Penglaiba Formation are selected as one of the major targets for petroleum exploration in the Tarim Basin, Xinjiang. The distribution of the reservoir rocks is obviously controlled by the sedimentary facies. According to the seismic interpretation, outcrop and borehole data, the dolostones in the Penglaiba Formation are interpreted as the carbonate ramp deposits. The sedimentary model is manifested in the slightly rimmed-restricted platform model. Judged from the seismic-stratigraphic analysis and the variations of stratigraphic thickness, development of the oolitic shoals, and lithologic characteristics, the Penglaiba Formation is speculated to settle down in the ramp sedimentary environment composed of the inner ramp, middle ramp and outer ramp facies. The middle ramp and outer ramp facies are believed to be favourable for the development of the oolitic shoals. The widespread middle ramp high-energy carbonate shoals in the areas of northern Tazhong uplift, Shunnan-Gucheng zone and southern Tabei uplift are delineated as the favourable areas for petroleum exploration in the dolostone reservoirs in the Penglaiba Formation. The new information presented in this study may serve as a useful reference to the future petroleum exporation in the Penglaiba Formation in the Tarim Basin.