Experimental Investigation of the Influence of Perforating on Gravel-Pack Impairment

Abstract

Analysis of the performance of perforated, gravel-packed wells compared with openhole gravel-packed wells has indicated that the perforation could be responsible for the low productivity of internally gravel-packed wells. A series of laboratory experiments on weak rock (UCS = 1200 psi) was conducted to quantify this. Castlegate sandstone rock samples, 7 in. in diameter and 18 in. long, were perforated with shaped charges under downhole conditions. The perforations were gravel packed by circulating a gravel slurry past the tunnel entrance while applying a differential pressure. The preperforation, post-perforation and post-gravel-pack productivities of the core samples were monitored at different flow rates (5 to 20 b/d/perf). Sectional photographs of the core samples were taken at post-gravel-pack conditions for qualitative analysis. Performance evaluation of gravel-packed realistic perforations (debris and loose sand in the tunnel removed by drawdown-induced flow) versus ideal perforations (debris and loose sand removed by external means) showed the post-gravel-pack productivities of realistic perforations to be much lower than ideal perforations in oil-phase as well as water-phase experiments. Injection of fluid after gravel packing only temporarily unplugged the perforation tunnel. The study shows the importance of fines-and debris-free perforation tunnels in maintaining the productivities of gravel-packed completions.