Principal controlling factors of the formation of the Ordovician buried hill gas accumulations and regional gas prospect evaluationn in the Bachu Rise, Tarim basin

Abstract：The Ordovician buried hills in the Bachu rise, Tarim basin, has good gas prospecs. The Hetianhe gas field and well Shan 1 gas accumulation were discovered in this area. The area has good hydrocarbon source rocks, a well-matched association of reservoir and cap rocks and a very large trap so；it is an advantageous area for petroleum exploration. According to an integrated study of the characteristics of the Hetianhe gas field and well Shan 1 gas accumulation, the authors suggest that the formation of gas accumulations was principally controlled by hydrocarbon source rocks, faults, unconformity and karstification. So long as the four controlling factors can match well, large gas accumulations can be formed. Based on this study, combined with exploration practice in carbonate gas accumulations both at home and abroad, the distribution characteristics of carbonate gas accumulations are summarized as follows: they are distributed along paleo-uplifts, along faults, along unconformities and near hydrocarbon source rocks. According to the principal controlling factors and distributing characteristics of buried hill gas accumulations, in the study area the zone south and west of the pinch-out line of the Silurian and Ordovician, the line of wells Shan 1 and Macan 1 and the Selibuya fault zone should be chosen as the chief exploration targets. In addition, a systematic study should be carried out on the Kalashayi fault zone where karst is well developed.