Determination of Dogleg Severity and Side Force for Stuck Pipe Prevention.

Abstract

A drill pipe is said to get stuck if it cannot be pulled out of the hole without damaging it and exceeding the maximum allowable hook load. Stuck pipe results from various causes such as excessive dogleg severity (DLS) and side force (SF). Dogleg severity refers to the measure of change of inclination and or direction of the borehole expressed in degrees per 30 meters of course length. When the DLS increases the wellbore becomes tight and may create keyseats which result into high side forces on the drill string during tripping operation. The stuck pipe incidence interferes with drilling schedule and results in non-productive time (NPT) and added drilling and rig cost. The main objective of the present work was to create a Matrix Laboratory (MATLAB) data agent that was used to calculate and give report whenever allowable limit of DLS and side force is exceeded. This was necessary for minimization of the possibility of stuck pipe incidence during tripping operation. The objective was met by selecting mathematical models from literatures based on their accuracy and usability. The models were incorporated with the real time drilling data (RTDD) and survey data using the data agent generated to perform computations of DLS and side force. The outputs were then validated using the base case data given. It was generally observed that the data agent generated performed well and from the computations it was seen that the highest value of DLS by the model was 7. 7 ⁰/ 30 m seen from 34/10-C-47 wellbore at around 3556 mMD. This value deviated for more than 156 % from the recommended and allowable value of DLS. The maximum value of computed side force was 1.3 ton observed at 3788 mMD of the 34/10-C-47 wellbore. This force was seen to increase by 30% of the recommended and acceptable value. The present work was very significant because it produced data agent using MATLAB that was used to compute DLS and side force, this agent was also used to locate the areas in the well with acceptable and non-acceptable DLS and side force. However, the model selected for calculation of side force was not realistically validated due to lack of effective and efficient side force base case data. The main recommendation on the work was to make an improvement of the model used to compute DLS by considering the effect of survey interval between two points. This can be done by including a specific scale factor for taking into account such an effect