Prediction and Reduction of Perforating Gunshock Loads

Most wells and particularly high-pressure wells are susceptible to gunshock damage when they are perforated with inappropriate gun systems and/or under suboptimal conditions. This paper presents a simulation methodology to predict gunshock loads for tubing-conveyed and wireline-conveyed perforating jobs. When planning perforating jobs in high-pressure wells, engineers strive to minimize the risk of equipment damage due to gunshock loads. The methodology described here helps engineers to identify perforating jobs with significant risk of gunshock related damaged, such as bent tubing and unset or otherwise damaged packers. When predicted gunshock loads are larger than the admissible loads, changes to the perforating equipment or job execution parameters are sought to reduce gunshock loads. This methodology enables completion engineers to evaluate the sensitivity of gunshock loads to changes in gun type, charge type, shot density and distribution, tubing size and length, number of shock absorbers, rathole length, and placement/setting of packers, among others. Fast gauge pressure data from perforating jobs shows that when model specifications are representative of the actual perforating jobs, the predicted wellbore pressure transients are accurate both in magnitude and time. Peak sustained pressure amplitudes at the gauges are on average within 10% of simulated values. With the methodology presented in this paper, engineers can evaluate perforating job designs in a short time, and they can optimize perforating jobs by reducing gunshock loads and equipment costs. The ability to predict and reduce gunshock loads and its associated damage is very important because of the high cost associated with most wells, particularly high-pressure wells. With the software presented in this paper engineers can optimize well perforating designs by minimizing the risk of gunshock related damage and the associated rig time losses.