1 Oil and Gas Development Management Department, Sinopec Southwest Oil and Gas Company, Chengdu 610041, China; 2 Southwest Mudlogging Branch of Sinopec Matrix Corporation, Mianyang 621000, Sichuan, China; 3 Institute of Exploration and Development, Sinopec Southwest Oil and Gas Company, Chengdu 610041, China

During the development of reef?shoal reservoir of Upper Permian Changxing Formation in the Yuan?ba gas field, the variation of the depth of target layer caused by various factors and reservoir heterogeneity havebrought great difficulties to the accurate drilling of the target geological bodies in the horizontal wells. In order to successfully drilling into the high?quality reservoirs, the authors analyze the geological pattern of reef reservoir distribution according to the previous research results of biohermal reservoir distribution law, combined with the geological data from drilling, logging and geophysics, and then establish the horizontal well trajectory optimization and control technology through the combination of accurate prediction of reservoir depth, lithology identification, reser?voir evaluation, and formation water identification, etc. Furthermore, the horizontal well trajectories in various reservoirs with bottom water, multi reefs, thin interbeds and thicker reefs are established. This technology has been widely used in the development of Yuanba gas field. The reservoir drilling encounter rate of horizontal wells is 82?? 1%, which has achieved remarkable results in improving productivity, and the average open flow rate of the test well reaches 292 × 104 m3 / d. This technology maximizes the producing reserves and enables more penetration of high?quality reservoirs.