Completion of cased and cemented wells by shaped-chargeperforation results in damage to the formation, which cansignificantly reduce well productivity. Typically,underbalanced conditions are imposed during perforation in aneffort to remove damaged rock and shaped-charge debris fromthe perforation tunnel. Immediately after the shaped-charge jetpenetrates the formation, there is a transient surge of fluidfrom the formation through the perforation and into the wellbore. Experimental evidence suggests that it is this transientpressure surge that leads to the removal of damaged rock andcharge debris leaving an open perforation tunnel.We have developed a two-stage computational model tosimulate the perforation process and subsequent pressure surgeand debris removal. The first stage of the model couples ahydrocode with a model of stress-induced permeabilityevolution to calculate damage to the formation and theresulting permeability field. The second stage simulates thenon-Darcy, transient fluid flow from the formation andremoves damaged rock and charge debris from the perforationtunnel. We compare the model to a series of API RP19Bsection 4 flow tests and explore the influence of fluid viscosityand rock strength on the final perforation geometryand permeability.
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