Comparison of shaped-charge perforating induced formation damage to gas- and liquid-saturated sandstone samples

Abstract

This paper presents the results of two perforation tests performed to investigate porosity and permeability damage in the crushed zone due to shaped-charge perforating in gas-saturated and liquid-saturated Berea sandstones. Perforation experiments were conducted using conventional 6-g HMX explosive charges on 10-cm (4-in.)-diameter Berea sandstone cores saturated with either low viscosity silicone oil or nitrogen gas. During perforating, 6.9 MPa (1000-psi) effective stress and 5.2 MPa (750 psi) underbalance conditions were applied. Perforation flow tests before and after perforating were performed according to API-RP43 procedures. Permeability around the perforation tunnel was mapped using a viscous fluid injection method. Porosity was mapped by employing X-ray CT (computerized tomography) scanning and image quantification. Computation of permeability and porosity, as well as analysis of the images, show that, for the specific charge and test conditions used, the type of fluid saturating the rock results in significantly different perforation geometries and damage under the same operating conditions. In the gas-saturated core, a zone of compacted rock about 6 mm thick and with 6–8% less porosity than the average rock surrounded the perforation tunnel. Near the entrance hole, the compaction was more severe when compared to other locations along the tunnel. The liquid-saturated core had a clean tunnel with a larger diameter and deeper penetration than the gas-saturated core. The liquid-saturated rock had no compacted zone. Permeability damage extended approximately 1.5 cm from the center of the perforation in the liquid-saturated core. The particle size distribution data in the crushed zone, for both cases, show that there was grain fragmentation in the rock. However, it was more severe in the gas-saturated core.