Experimental investigation of surge flow velocity and volume needed to obtain perforation cleanup

Underbalanced perforating has been practiced for a number of years to minimize formation damage in and around the perforation tunnel. High transient flow rates are thought to sweep crushed rock and charge debris into the wellbore, leaving a clean tunnel. With sufficient underbalance, formation damage surrounding the tunnel is also reduced. In practice, the minimum underbalance and the volume of surge flow required per perforation become part of the completion design. Recent theoretical studies predict that most of this cleanup process occurs early in the transient flow process, suggesting that large transient flow volumes may not be needed. Using a modified standard test procedure from the American Petroleum Institute, transient flow rates into perforations in Berea Sandstone have been measured, varying underbalances and surge flow volume. Flow rate, instantaneous core flow efficiency (CFE) and local flow velocity are reported as a function of time, starting ∼ 0.5 s after firing. sults indicate that (1) where sufficiently high underbalance is used, CFE reaches its maximum value within the first 1–3 s. Subsequent transient flow and quasi-static flow do not further increase flow performance. (2) Tests with large and small surge flow volumes behave similarly. This observation is consistent with early cleanup. (3) At lower underbalance, CFE was reduced as expected. However, the ultimate value was still obtained within the first second of transient flow. The remainder of the surge flow did little to improve performance.