Characteristics and origin of dolomite reservoirs in Lower Ordovician Yingshan Formation, northern slope of Tazhong uplift, Tarim Basin

At present, the rich oil-and-gas resources discovered in the Ordovician Yingshan Formation in the northern slope of the Tazhong uplift of the Tarim Basin mainly exist in limestone karst fracture-cave reservoirs which are controlled by the unconformities on the top of the Yingshan Formation. With the deepening of exploration, dolomite reservoirs in the Yingshan Formation have been found in some new exploratory wells, and the reservoir spaces mainly include intercrystal pores, solution pores and vugs. Dolomite reservoirs have good physical properties and are thick locally; however, their horizontal comparisons are poor. According to core, slice observation, cathodoluminescence, REE and isotopic analyses, the favorable dolomite reservoirs in the Yingshan Formation had experienced buried dolomitization and strong dissolution, and was influenced by hot fluid in the late stage. Distributed widely and controlled by underground fluid activities, the dolomite reservoirs are the key types and targets for explorations in carbonate reservoirs in the Yingshan Formation in the northern slope of the Tazhong uplift of the Tarim Basin.