Extreme Overbalance Perforation
Extreme Overbalance Perforation is a method of perforating a well by applying a very high pressure surge to the formation. Pressure surges are designed to overcome fracture initiation pressure and break down each perforation tunnel with a very short fractures. Extreme Overbalance Perforation approach has been found to be a more effective technique than overbalance or underbalance perforations for water injection wells.
Once the perforation guns are at depth, the string is filled with small amount of liquid (brine, acid, solvent or frac fluid) at top of the gun. Rest of the string is filled with compressed gas (Nitrogen) before initiating the perforation sequence. On detonation, liquid is driven into the perforation at very high rate due to rapid expansion of gas and initiates fractures to extend effective wellbore radius.