New advances in the study of Ordovician sedimentary reservoirs in Lunnan, Tarim basin

Abstract：Recently major advances have been made in the study of Ordovician sedimentary reservoirs in Lunnan, Tarim Basin. Three weathering crust reservoir systems of two phases have been found: one Hercynian reservoir system occurs at the top of the Ordovician and two Caledonian systems in the interior of the Ordovician. The Ordovician reef bank-facies reservoir in Lungudong is determined to be a weathering crust karst fissure-cave one, and a reef bank-facies reservoir is found in the Sangtamu Formation. In the early deposition of the Sangtamu Formation, a reef-forming environment occurred, with small organic reefs developed locally. The previous division of Ordovician sedimentary facies is revised, and the location of the Ordovician carbonate platform margin is shifted eastward for 30 km. The thermal subsidence mechanism is proposed for the interpretation of the formation of the weathering crust reservoir inside the Ordovician. It is thought that there existed a thermal uplift and subsidence movement in the Tarim basin during the early Late Ordovician, which resulted in nonuniform uplift of the Lunnan area and erosion and exposure of the Lianglitag Formation, thus forming the weathering crust karst reservoir system in the area and revealing good petroleum prospects in the Lunnan area.