A combined experimental and theoretical investigation on application of wettability modifiers in gas-condensate reservoirs

Well productivity of gas-condensate reservoirs can be severely impaired by condensate/water blockage around the wellbore. Improving resident phase mobility by altering the rock wettability to intermediate gas-wet has been proposed as an efficient and long-term remedial solution to this issue.
Evaluating the performance of such a costly chemical treatment process for real field applications through experimental and theoretical investigations is crucial, something which has been addressed here. In this work different groups of chemicals were used to alter wettability of various carbonate rock surfaces. The impact of a number of important parameters on the reservoir performance was also studied in our numerical simulation exercise.
The main findings of performed experiments are: a) anionic and to lesser extent non-ionic fluorochemicals are effective wettability modifiers for carbonate minerals, b) by increasing the chemical concentration typically oil-repellency increases and water-repellency either does not change or decreases, c) permeability damage due to excess chemical deposited on mineral surfaces becomes more sever in low permeability rocks. Using alcohols instead of water-based solvent and/or filtration of chemical large aggregates can to some extent reduce the undesired rock permeability impairment and d) temperature has a significant albeit non-monotonic effect on the interaction between chemical and the rock surface, especially at its elevated limits.
Numerical simulation results demonstrated that alcohol (compared to water)-based chemical solutions have better performance, especially at higher volumes of the injected chemical and in tighter rocks due to the reduced adverse effect of solution back-flow. The improvement factor of relative permeability and durability of chemical treatment showed significant impact on increasing the benefits of such a process. On the other hand, reduction of the rock permeability due to excessive chemical deposition had considerable adverse effect on the treatment performance, especially when a water-based solvent was used.
These results provide valuable practical guidelines on design and application of such treatment solutions for field trials.