Evaluation of Formation Damage/Completion Impairment Following Dynamic Filter-Cake Deposition on Unconsolidated Sand

Abstract

Abstract Evaluation of formation and completion (gravel pack and screen only) flow capacity damage in unconsolidated formation material has proven difficult in the laboratory because typical core flood equipment does not adequately confine the formation material to allow drilling and cleanup fluids to be circulated at representative shear rates and pressures over the formation face. A testing protocol and equipment have been developed which allows dynamic flow and fluid loss across unconsolidated formation material at shear rates, temperatures, differential pressures, and times representative of mud circulation rates in the wellbore. The dynamically prepared filtercakes grow to an equilibrium thickness depending on the shear rate, differential pressure, and temperature and are more representative in composition and mass to wellbore filtercakes so that their damage to formation, gravel packs and / or screens can be better evaluated. The effectiveness of cleanup systems can also be determined by circulating the fluids across the mud filtercakes at typical shear rates, differential pressures and temperatures before allowing static soak conditions. At the end of the test, the screen and formation material or screen, gravel pack and formation material are stressed together simulating a wellbore collapse. The permeability of the formation plus gravel pack and screen or formation and screen only are then measured and compared to the initial values to determine flow capacity impairment. Introduction Openhole completions in poorly consolidated formations require that the drill-in fluid, the sand control system and the cleanup system for removal of the drill-in fluid filtercake all perform together in order to provide acceptable solids control and production rates. Laboratory evaluation techniques for drilling fluid filtercake damage to the flow capacity have generally involved the generation of filtercakes on consolidated formation material or cores in a static fluid loss condition. The fluid loss into the formation and the properties of the filtercake have such a direct bearing on the results of any laboratory test which attempts to evaluate cleanup systems and flow capacity damage. It is important to create the filtercake in a manner which closely resembles the wellbore conditions. This is especially true when optimizing systems for use in completions in soft sands which will have gravel packs or screen only completions. The remaining filtercake in a wellbore can have a severe impact on the flow capacity of a sand control screen or gravel pack and screen.1,2,3 The present work discusses a method for creating dynamically deposited filtercakes on unconsolidated formation material and determining the flow capacity damage to the sand control method and formation resulting from the filtercakes.