An Improved Laboratory Method to Estimate Flow Initiation Pressures and Near Wellbore Return Permeabilities

Abstract

The flow initiation pressure (FIP) is defined as the drawdown required to initiate flow when the well is put on production. The standard laboratory method used to measure FIP uses a constant flowback rate. However, as shown in this paper, this method results in a large overestimation of the FIP. Instead an improved flowback method that uses a series of constant differential pressures is shown to more accurately measure the FIP. This improved method closely mimics a constant drawdown applied in the production well. In addition, the method measures the return permeability during flowback as a function of the differential pressure (drawdown).Two types of drilling fluids (sized calcium carbonate and bentonite) are used on sandstones and carbonates with a wide range of permeability from 4 to 1500 md. Both single-phase (only brine) and two-phase (brine and oil) 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 and measured with a constant flowback rate). The small values of FIP suggest that the pressure gradients in the field should be sufficient to initiate production in most wells.It is shown that both the FIP and the return permeability are controlled by the internal filter cake and are not related to the removal of the external cake. However the mechanical properties of the external cake (which are related to the properties of the internal cake) can be used to estimate the FIP. The experiments suggest that for the drilling fluids used in this study a pressure drawdown of 120 psi/ft during production is needed to ensure a skin factor that is less than 1 in open-hole completions.