Abstract: With the decreasing of adjacent well design spacing of cluster wells and infill wells,only using adjacent well distance scanning calculations and traditional separation factors to monitor the adjacent well distances of cluster wells cannot meet the demand of practical project.Wellbore trajectory error analysis and adjacent well distance scanning are combined,and the relative positions between reference point error ellipsoids and comparison point error ellipsoids are considered in the calculation of oriented separation factors.The oriented separation factors are more accurate than traditional separation factors to describe the probability of hole intersection,and the oriented separation factors can provide a more scientific basis for adjacent well anti-collision.So the oriented separation factors can better meet the demand of practical project.The difference between oriented separation factor and traditional separation factor was introduced,and the oriented separation factors of normal-plane distance scanning,the nearest distance scanning and horizontal distance scanning were obtained with the method of space analytic geometry.The oriented separation factors of the nearest distance scanning are generally used to be the basis of adjacent well anti-collision.Finally,a calculation example was given,and the result indicated that the traditional separation factors was smaller than the oriented separation factors in cluster wells which were mainly constituted by directional wells and extended reach wells,and the oriented separation factors had important field application value in the design and drilling process of cluster wells and infill wells.