A fast computational model for wellbore pressure transients while perforating with dynamic underbalance

Abstract

Perforations provide the critical production link between the reservoir and a cased well completion. Though perforating with shaped-charge jet penetrators is common practice today, they can leave behind tunnel debris and formation damage layers surrounding the perforations that significantly reduce well productivity. Perforating with a dynamic pressure underbalance has become a standard technique to provide better cleanup of debris and damage layers by enhancing the surge flow through tunnels (i.e., perforation cleanup). However, effective use of dynamic underbalance in practical perforating job design requires an understanding of three critical and interdependent processes: First, the generation of the underbalanced pressure transient, and how it depends on job design parameters such as wellbore geometry, gun configuration, and reservoir data; Second, how the magnitude and timing of the pressure underbalance drives the surge flow through perforation tunnels; Finally, the cleanup process itself, and how it depends on the generated surge flow. Though the latter two processes have received much attention from researchers over the past few decades, the design and optimization of the pressure underbalance itself has not. In this paper, a fast computational model for the generation of a dynamic underbalance is presented. The model is based on dominant physics. The effectiveness of this model is demonstrated by comparing results with pressure gage data obtained during API-RP 19B Section IV testing.