Design and Evaluation of Perforation Performance Using Dynamic Under Balance – North Sea Case Histories

Abstract

Abstract Dynamic under balance (DUB) pressure is being used by operators to improve completion efficiency and minimize formation damage. An understanding of the pressures generated when perforating allows the prediction of the level of pressure differential required to overcome the surge pressure generated, leaving a clean connection between the wellbore and the reservoir. Results reported by different operators indicate success with the DUB technique; certain criteria have been developed for the determination of the optimum conditions for its use. From the published information, type of reservoir fluid, interval length and formation mechanical properties are some of the main considerations for a successful design and implementation of the technique. Talisman Energy UK has used DUB for perforating several wells in the North Sea. A detailed job design process was implemented starting with the need to characterize the level of formation damage that existed in the wells. Three (3) main damaging mechanisms were quantified; damage resulting from fluid and solids invasion into the reservoir matrix, mechanical damage generated during drilling operations and actual damage caused during the perforation process. Perforation programs were developed and executed based on a clear understanding of the rock mechanical response to the DUB generated by the gun and taking into consideration perforating debris and fluid inflow required to clean the tunnels. The results from this work indicate that current design criterion for the selection of the optimum DUB pressure is limited and it is not clear about the physics and hydrodynamics of the clean up process.