Reduction of Perforating Gunshock Loads

Abstract

Summary 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, such as bent tubing and unset packers, from perforating gunshock loads. Perforating guns 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 gun-string 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 gun-string 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 gun-string 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 gun-string 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 gun-string movement on/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 significantly reduces 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 performed to date in the Gulf of Mexico.

Study of Downhole Shock Loads for Ultra-Deep Well Perforation and Optimization Measures

“…It shows that the best shock absorption effect can be achieved by optimizing the installation positions of shock absorbers, which is the middle of the perforated string connecting the packer and perforating gun. In order to meet the needs of the practical application, the formula for reducing the peak pressure on the packer can be fitted with condensing different installation positions and different number of shock absorbers, as shown in Equation 17: (17) where ∆P 1 , ∆P 2 , ∆P 3 are the reduction values of perforating peak pressure on the packer with one, two, three shock absorbers, respectively. The red dashed line represents the peak pressure (133.79 MPa) on the packer without the installation of shock absorbers.…”

“…From the above analysis, combining Equation (17) with Equation (20), the pressure difference between the upper and lower end of the packer can be calculated by Equation 21:…”

“…The influencing factors of perforating shock loads in ultra-deep wells were studied by Chen et al, it was found that the axial force of perforated string was affected by factors such as "pocket" length, well fluid density, string length, perforation depth, well depth and perforating gun loading strategy [16]. Baumann et al comprehensively summarized all influencing factors of perforation design, including the length of perforated interval, types, and sizes of perforated string, shaped charges, cable, and conveyance, rathole length, installation position of the packer, type and number of shock absorbers, wellbore and formation pressure with fluid properties [17]. The numerical simulation of the perforating process with a single perforation bullet was carried out by Teng, and the effects of shock loads on the perforated string were explored by static analysis [18].…”

Numerical Investigation of Downhole Perforation Pressure for a Deepwater Well

“…It is important to account for the reservoir condition since it can act as an absorber or reflector (based on porosity, permeability, etc.) of shock waves that eventually affects the propagation and strength of shock waves within the wellbore [24,25]. Therefore, these theoretical empirical formulas can only be used as a preliminary reference for qualitative analysis of downhole perforation pressure.…”