Seismic identification and reservoir prediction of reef flat of Upper Ordovician in northern and southern slopes of Katake Uplift, middle Tarim Basin

When the Lianglitage Formation of the Upper Ordovician deposited, the Katake Uplift in the Tarim Basin was a large-scale isolated platform of carbonate rocks. According to seismic geology as well as drilling and logging data, the seismic and sedimentary facies of the southern and northern slopes were classified as shelf-basin, marginal slope, platform margin, and open platform depositional systems. In the platform margin, the subfacies of reef, bioclastic bank and reef depression were identified. The reef-bank complex was featured by a stacked "tower" structure vertically, and retrograding-aggradational migration horizontally, showing that sea level changes controlled the phased growth of reef flats. Using pattern, palaeogeomorphology and attribute recognition methods, the distribution range of reef-bank complex was further delineated. Prediction results showed that the platform slope edge mainly developed bioclast, calcarenite beach and oolitic beach facies in the west of the northern slope, and the high and steep slope developed reef on the central platform margin; while on the southern slope, platform margin reefs and shoals developed in the northwestern Ka2 block and the southern Ka1 block, showing favorable conditions for the formation of beads-like reef-type oil and gas reservoirs.