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

Abstract

Summary 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 [unconfined compressive strength (UCS) = 1,200 psi] was conducted to quantify this. Castlegate sandstone rock samples, 7-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 pre-perforation, 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) vs. "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.