Abstract: Since the shale gas development area at the edge of the Sichuan Basin is subject to superimposed transformation of multi-stage tectonics and tectonic complexity, it results in large changes in formation velocity, makes difficult to accurately build a velocity model with poor well-seismic matching, and affects the drilling catching rate of horizontal wells. To this end, we combined conventional 3D seismic well calibration, established a standard formation, analyzed the anisotropy of the formation, clarified the longitudinal and transverse variation characteristics of the formation velocity, corrected the burial depth coefficient and the occurrence, and took the longitudinal velocity and transverse velocity superposition calculation to establish the velocity field;dynamically update the velocity field by applying the formation information of the wells to ensure the accuracy of the drill-following models,improving the accuracy of seismic prediction target depth and the judgement of the occurrence variation pattern. In the practical application of this method, the error between target prediction and actual drilling is reduced to 7.7 m, which is much higher than the seismic resolution, which proves the rationality and adaptability of this technical method, and can be widely used in geosteering of horizontal wells.

Key words: shale gas, steering while drilling, 3D seismic, target prediction, dynamic velocity