Underbalance perforation flow experiments were performed on reservoir and outcrop sandstones to investigate the perforation damaged zone. Cores from several different formations were perforated under reservoir conditions. After perforating, the cores were examined using CAT scans (Computer Aided tomography), thin sections and mercury porosimetry. In conjunction with these measurements, permeabilities in the damaged zone were measured using a mini-permeameter and radial flow permeameter or were estimated from pore size distribution.
The density and porosity of the damaged zone (at least for saturated rocks) is essentially the same as that in the undamaged rock. The damaged zone is not compacted, contrary to suggestions made in earlier work. However, the creation of this zone involves the destruction of large pores. The volume lost from these pores is replaced by microfractures created when rock grains are fractured by penetration of the shaped charge jet. This reduction in the average pore size causes a reduction in the permeability within the damaged zone. Although direct measurement of this permeability was made difficult by naturally occurring permeability variations, unambiguous measurements were obtained.
Based on this work an understanding of the factors which control the permeability in the perforation damaged zone is advanced.