Quantitative analysis on collision risk of vertical hole section of infill horizontal well in cluster well pattern in Yanchang Oilfield

To develop low-permeability and low-abundance oil reservoirs economically and efficiently in Yanchang Oilfield, infill horizontal wells are arranged at the old well sites.Thus, the vertical hole sections in the cluster pattern are dense, so the collision risk is rigorous.To evaluate the collision risk of vertical hole sections accurately, the horizontal displacement deviation of vertical hole sections in horizontal wells in Yanchang Oilfield was analyzed based on actual drilling data.Then, the collision risk of vertical hole sections in infill wells was quantified by means of mathematical statistics.It is indicated that the horizontal displacement deviation of actual trajectory of vertical hole section in the same hole depth is in accordance with the normal distribution.And with the deepening of the hole, its mean and variance increase gradually, the shape of normal distribution becomes flatter and flatter, and the hole location become moreand more uncertain.This method was applied in horizontal well Xing 4003 Ping 34.It is shown that quantitative analysis on the collision risk of vertical hole section based on probability statistics and confidence calculation can discriminate the collision risk of vertical hole section more accurately, and provides the new reference for the trajectory design of vertical hole section of infill horizontal well in cluster pattern.