Underbalance perforation is one of the best practices to insure less damage to the perforation tunnels. Many papers described the effect of the underbalance perforation either static or dynamic on the cleanup of the perforation tunnel based on the King et al correlation presented in (1986). A complete understanding of the effect of both magnitude and duration of the underbalance during the perforation will help petroleum engineers to design a perforation job and achieve the maximum benefit of the perforation in connecting the well bore to the reservoir. A new approach to control not only the amount of the underbalance, but also the duration of this underbalance, has been applied in one of North Kuwait sandstone reservoirs. The results showed the duration of the underbalance during perforation has a significant effect on clean up the perforation tunnel.
Reduction and elimination of the perforating damage (perforating skin) ensures increased well productivity. Previously, the basic technique to clean perforation tunnels in order to decrease perforating damage was static underbalance. The static underbalance has been upgraded to dynamic using a down-hole production valve. The down-hole pressure data was collected by a fast reading down hole pressure sensor with 120,000 reading per second, capable of responding and recording virtual instantaneous pressure changes in the wellbore. A combination between dynamic and static underbalance has been configured to maximize the near well bore clean up around the perforation tunnel. A compressed gas, a packer setting depth and surface release valve were configured to control the duration of the static underbalance.
The results show a 50% improvement in well productivity compared with the other wells completed in the same layers. The technique provided optimum volume and duration of the underbalance for all layers with up to 500 psi difference in reservoir pressures. Since this technique was being used for the first time in this reservoir, several perforating simulations were run and evaluated to select the optimum scenario for this well. A deep perforation charge has been loaded in the optimum gun size to maximize the amount of the dynamic underbalance.
This paper will present the new technique of underbalance to give a clean perforation tunnel and evaluation of the impact compared to the conventional perforation techniques through pressure data and well modeling.