Segment selection effect on directional well trajectory fitting accuracy and accurate measurement method

The current method of well survey calculation is assuming the segment is a specific curve, however, the actual well trajectory is unknown. Therefore, error exists between calculated and actual well trajectory. In order to analyze the relationship between the accuracy of trajectory fitting and segment selection，according to field data, radius of curvature method is used to match the two kinds of trajectory caused by segment selection. Fitting results show that there are errors between the fitting trajectories because of the different choice of the segment length and location. This paper makes a qualitative analysis of the causes of errors. The results show that the reason is the frequent conversion of drilling methods. Accordingly, four methods which can effectively decrease the errors of the well survey calculation are presented, and the feasibility of each method is discussed in order to acquire the exact position of wellbore trajectory by accurate measurement and calculation. The method has guiding significance to achieve perfect target of the directional well and the anti-collision of the cluster well.