Cleanup of Filter Cake Formed by Drilling and Completion Fluids: Removal of Internal and External Filter Cake Formed on Rock Formations During Well Production

The flow initiation pressure (FIP) is used as an estimate of the differential pressure (between the reservoir and the well) required to initiate production of oil or gas. The standard practice to measure FIP uses a constant flowback rate. This method is shown to be inadequate to measure the FIP. An improved flowback method, which uses a series of constant differential pressures, is used instead to measure the FIP. This method closely represents the constant drawdown between the reservoir and the wellbore. In addition the permeability during flowback is measured at increasing differential pressures. Two types of drilling fluids (sized calcium carbonate and bentonite) are used for the filtration experiments on porous media ranging in permeability from 4 to 1500 md. Both single-phase and two-phase experiments are conducted in lab- simulated open-hole and perforated completions. Small values are found for the FIP in all the experiments (considerably smaller than those measured using the constant flowback method). A Bingham fluid in a network of pores is used to model the cleanup of the internal filter cake during flowback.