Thousands of well perforation jobs are executed successfully around the world each month; however, certain perforation jobs require special design considerations to minimize the risk of equipment damage due to perforating gunshock loads, such as bent tubing and unset packers. Perforating gunshock loads generate pressure waves in the completion fluid and stress waves in structural components. The magnitude, duration, and timing of these waves depend on job parameters that can be adjusted by the design engineer, such as type, length, and loading of guns, number of shock absorbers, distance from sump packer to bottom of guns, and distance from completion packer to top of guns. The sensitivity of peak loads and gunstring movement to key design parameters can be evaluated with a software tool specifically developed to predict well-perforation induced transient fluid-pressure waves and the ensuing structural loads. All relevant aspects of well perforating events are modeled, including gun carrier filling after firing, wellbore pressure waves and associated fluid movement, wellbore pressurization and depressurization by reservoir pressure, and the dynamics of all relevant gunstring components, including shock absorbers, tubing, and guns.
Existing fast-gauge pressure data from a large number of perforation jobs were used in previous jobs to verify that predictions made by using software simulation are sufficiently accurate, both in magnitude and time; thus, the transient pressure loading on well components is sufficiently accurate to predict the structural dynamics response and the associated gunstring loads. In this paper, we present case studies that show how key elements used for gunshock mitigation are simulated, and the sensitivity of peak loads and deformation to gunstring elements, such as shock absorbers, gun types and loading, tubing size and weight, and packer placement.
With this software, we evaluate the dependence or sensitivity of peak loads and gunstring movement to key design parameters, and when necessary, design changes are made to reduce potentially unsafe load conditions. The design verification and optimization methodology described in this paper reduces significantly the risk of nonproductive time and fishing 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 to date in the Gulf of Mexico.