Reduction of Perforating Gunshock Loads

摘要

Thousands of well perforation jobs are executed successfully around the world each month; however, certainperforation jobs require special design considerations to minimize the risk of equipment damage due to perforating gunshockloads, such as bent tubing and unset packers. Perforating gunshock loads generate pressure waves in the completion fluid andstress waves in structural components. The magnitude, duration, and timing of these waves depend on job parameters that canbe adjusted by the design engineer, such as type, length, and loading of guns, number of shock absorbers, distance from sumppacker to bottom of guns, and distance from completion packer to top of guns. The sensitivity of peak loads and gunstringmovement to key design parameters can be evaluated with a software tool specifically developed to predict well-perforationinduced transient fluid-pressure waves and the ensuing structural loads. All relevant aspects of well perforating events aremodeled, including gun carrier filling after firing, wellbore pressure waves and associated fluid movement, wellborepressurization and depressurization by reservoir pressure, and the dynamics of all relevant gunstring components, includingshock absorbers, tubing, and guns. Existing fast-gauge pressure data from a large number of perforation jobs were used in previous jobs to verify thatpredictions made by using software simulation are sufficiently accurate, both in magnitude and time; thus, the transientpressure loading on well components is sufficiently accurate to predict the structural dynamics response and the associatedgunstring loads. In this paper, we present case studies that show how key elements used for gunshock mitigation aresimulated, and the sensitivity of peak loads and deformation to gunstring elements, such as shock absorbers, gun types andloading, tubing size and weight, and packer placement. With this software, we evaluate the dependence or sensitivity of peak loads and gunstring movement to key designparameters, and when necessary, design changes are made to reduce potentially unsafe load conditions. The designverification and optimization methodology described in this paper reduces significantly the risk of nonproductive time andfishing operations. Key technologies described in this paper enabled the successful execution of many deepwater high-pressure (HP) perforation jobs, including Petrobras’ Cascade and Chinook, the largest deepwater HP perforation jobs done todate in the Gulf of Mexico.