Wellbore Implosion: Case Study of Perforation Enhancement

Abstract

Good perforating practices are equally important for water injectors as for producers to achieve effective and efficient reservoir pressure support, which, in turn, results in better field productivity. An aspect of good perforating practice is to achieve clean perforations so that the injection skin is minimized. Dirty perforations, whether due to perforation debris or crushed zones around the perforation tunnel can affect a well's injectivity. This problem is further compounded when well injection starts as particles in injection water quickly accumulate at the perforations, causing rapid injectivity drop. Therefore, clean perforations are important to deliver good well injectivity. This is a case study of a wellbore implosion technique on perforations of injector wells in a field in Oman. Compared to perforating in a high-pressure reservoir, achieving clean perforations in a lowpressure reservoir is more difficult as perforating has less potential to breakdown the crushed zone and to purge the crushed material together with the debris from the perforation tunnels. This problem may be overcome by the wellbore implosion technique, using a dynamic underbalance system.Various perforating systems were tried for injector wells in this field. Reactive liner shaped charge, propellant system, and post-perforating dynamic underbalance techniques were used in the same well. A dynamic underbalance gun that creates wellbore implosion was designed, and recorded pressure gauge data were matched to the simulated data. Reservoir properties of each well from the logs and from the well injectivities after applying the above-mentioned perforating systems were compared. As the principle in this case study is perforation cleanup, it is also relevant to producers. It is also relevant to other wells whether on land or offshore, both producers and injectors of any pressure regime that could be suffering from poor cleanup of perforations.