External filter cakes are used to minimize fluid loss and solids invasion to a formation from drilling and completion fluids. Subsequently, the cake must be removed to increase the flow area and minimize skins, especially for openhole and gravel-packed completions in horizontal and deviated wells. Experimental data is presented to show that the pressure required to initiate flow into the wellbore after building up a filter cake is affected by rock perme- ability: mud properties, such as particle size and cake yield strength: flowback velocity: and overbalance pressure. Mudcake liftoff tests, mud particle size, and rock pore-throat size distribution measurements were performed to understand the factors that contribute to cake removal. The mechanisms that con- trol filter-cake removal are discussed.
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