AN IMPROVED LABORATORY METHOD TO ESTIMATE FLOW INITIATION PRESSURES AND RETURN PERMEABILITIES DURING FLOWBACK

The flow initiation pressure (FIP) is used as an estimate of the differential pressure required between the reservoir and the well to initiate production. The standard method to measure FIP uses a constant flowback rate. However this method is incorrect and results in much higher estimates for FIP. An improved flowback method that closely represents a constant drawdown in the field is applied, to measure the FIP. In addition the permeability during flowback is measured at these increasing steps of differential pressures, resulting in a spectrum of return permeabilities as a function of drawdown. Two types of drilling fluids (sized calcium carbonate and bentonite) are used 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 to measure the FIP and the return permeability spectra. Small values for FIP are found in all the experiments (considerably smaller than presented in the literature with the constant flowback rate method). The small values of FIP suggest that the pressure gradients are sufficient in the field to initiate production especially if the well are vertical but may not initiate production in horizontal wells or if the over‑balance was very high during drilling (>500 psi). The FIP and the return permeability are controlled by the cleanup of the internal filter cake. A Bingham fluid in a network of pores is used to model the cleanup of the internal filter cake. The model as well as the experiments indicates that very large pressure gradients are required to cleanup the entire internal filter cake. However, a pressure gradient of 10 psi / inch during production is needed to keep skin factor < 1 for open‑hole completed wells drilled with an over‑balance of ~ 100 psi.