An Improved Understanding of Performance of Wettability Alteration for Condensate Banking Removal Under Steady-State Flow Conditions
Authors: Fahimpour J. , Jamiolahmady M. 
Published: November 2015

The impaired productivity of gas-condensate wells due to condensate banking is believed to improve, on a relatively permanent basis, if the wettability of the wellbore region is altered towards intermediate gas-wet conditions using oil-repellent chemical agents. The low interfacial tension (IFT) and high velocity conditions existing near the wellbore, complicates the flow mechanisms in gas-condensate systems, in comparison to that in conventional systems. This work presents an experimental investigation on the application of wettability modifiers under complex flow conditions at high capillary number and inertial effects, dominating the gas-condensate well performance.

In most available experimental studies, evaluating the performance of wettability alteration, unsteady-state flow tests with conventional fluids have been performed. In few cases the pseudo-steady state techniques using condensing fluids have been employed albeit working at high-IFT values above 4 mN/m. However, the exclusive flow features of condensing systems can only be properly captured if steady-state core experiments, at low-IFT limits below 3 mN/m, are conducted. This paper, for the first time, presents the results of series of unique steady-state relative permeability measurements performed on a carbonate core sample before and after the chemical treatment using an anionic wettability modifier agent. A binary gas-condensate mixture of C1-nC10 was employed to measure the relative permeabilities at several IFTs, varying from 0.77 to 10.8 mN/m, and velocities, varying from 20 to 636 m/d, under different gas-condensate fractional flow ratios.

The results of the conducted unsteady-state displacement tests of C1 by C10, showed a significant reduction in the measured pressure drops across the core, confirming an acceptable degree of wettability alteration. Moreover, the level of flow performance improvement was the same at both high- and low-IFT limits. This contradicted the results of contact angle and steady-state tests performed using the same gas-condensate fluids. That is, the results of these measurements demonstrated that the improvement in steady-state relative permeability due to wettability alteration gradually diminishes with decreasing IFT. For instance, the relative permeability improvement factor of about 3-4 was observed at high IFT of 10.8 mN/m. This number was reduced to 1.1 when IFT of the system was decreased to 0.77 mN/m. This trend was in line with that observed during the contact angle measurements. Moreover, the post-treatment velocity-dependent relative permeabilities, measured at low-IFT conditions, showed a more pronounced effect of improvement in relative permeability due to the positive effect of capillary number (coupling).

Results from this work highlight that if conventional experimental approaches are employed, the productivity of the chemically stimulated wells can be noticeably overestimated, especially at lower IFTs. The new findings presented in this paper provide valuable insights into practical application of wettability alteration technique for removal of condensate banking.