Knowing the productivity to expect from a well is highly dependent on how deep the perforation penetrates. Besides the quality and explosive load of the shaped charge, the type of rock and the stress it is subjected to help determine penetration depth.
Using the equipment capable of stresses and pore pressures at extremes found in deep, outer-shelf wells, a made-for-purpose perforation laboratory offers insights regarding perforation behavior. Care was taken in the tests to ensure the configuration used matched a typical downhole setup including the applied stress on the rock target. Using Sandia National Laboratories' CTH shock wave physics software, computer simulations were run to compare with the results to offer further insight.
The results from the tests did not necessarily follow trends from extrapolating data from similar tests conducted at lower pressures, historically using matching net stress as a substitute prior to obtaining higher pressure-capable equipment. It was observed that a large increase in pore pressure resulted in only a small decrease in perforation penetration. Formations with various rock properties behaved differently, and with the new higher capacity equipment the ability to quantify these differences was improved. Other attributes beside penetration were observed such as perforation tunnel geometry differences between the high and moderate unconfined compressive strength (UCS) rocks.
This paper discusses the effects on the magnitude of penetration and quality of perforation tunnel in both the high and moderate strength rocks, and possible implications on flow. Simulation runs were conducted on the effects to a perforation at elevated pressure and compared to the test results showing the value of conducting such simulations and insights gained.