Predicting Pressure Behavior and Dynamic Shock Loads on Completion Hardware During Perforating
Authors: Canal Antonio Carlos , Miletto Priscilla , Schoener-Scott Martin F. , Medeiros Jovineto , Barlow Darren 
Published: July 2010

The first oil-well casing-perforating job was performed in 1932 by the Lane-Wells Company. who pioneered the bullet-gun perforating technique. With the steadily increasing demand for oil and gas over the last decades, operators have been forced to explore deeper, hotter reservoirs to find the most prolific reservoirs. These deep, high-pressure opportunities have required constant changes to equipment and services to increase their technical capabilities so that they can perform effectively in the more critical environments to which they are subjected. These environments include the ever-increasing high-pressure and high-temperature reservoirs into which exploration has been venturing. Perforating has been continuing to require higher-shot densities, propellants, and larger perforating guns to meet these new challenges.

A major problem with these environmental increases, however, has concerned the difficulty to predict dynamic wellbore behaviors that would cause tubulars to collapse and bend and packers to unset as perforating guns were detonated. Research to understand pressure behavior during the perforation event in addition to the solid loading that is imparted to the tubulars, packers, and other completion hardware in the perforating bottomhole assembly was needed, if the industry was to go forward with a high level of confidence that wells could be completed safely and cost effectively.

This paper discusses a shock-wave modeling computer-software program that evaluates the mechanical risk factors of well components to ensure that the health, safety, environment, and service-quality needs of a design are covered and that the proposed equipment configurations will maintain mechanical integrity. A time-marching, finite-differences technique is applied as the numerical method for both fluids and solids. The software is installed on a personal computer, and typically, executes the models in several minutes to several hours, depending on job-design complexity.

The physics-based model has been validated with special high-speed recorders that sense pressure, temperature and acceleration at a sampling frequency of 115,000 samples per second.

Data from two oil and gas wells offshore Brazil will be used to demonstrate the success of the operating configurations generated from use of this program.

Introduction

It is a fact that perforating-gun detonation creates dynamic loading on tubulars, packers, casing and other completion equipment, and the importance of having the capability to predict dynamic wellbore behaviors through modeling continues to increase in importance (Garcia et al., 2009) (Weaver et al, 2009). Relying on old " rules of thumb?? or using standard mechanical configurations with shock absorbers to cover all perforating cases can lead to catastrophic results. A major service and engineering company has developed a software program that accurately simulates the dynamic and loading forces created during perforating. This tool provides the capability to plan and design the well completion accordingly. The software modeling service determines the dynamic pressure behavior during the perforation event in addition to the solid loading that is imparted to the tubulars, packers, and other completion hardware in the bottomhole assembly (BHA).

The physics-based numerical model accounts for fluid dynamics and dynamic failure of solids by accounting for pressures on the surface, drag, internal stress waves and reflections, and gravity.

The time-marching finite difference technique is applied as the numerical method for both fluids and solids, and basically, simulates downhole performance of proposed string configurations in the particular environment to which it will be subjected. The software is compiled on a personal computer, and typically, executes in periods of several minutes to several hours, depending on the complexity of the job design. The numerical solution accounts for failure modes such as: