Optimization of fluorinated wettability modifiers for gas/condensate carbonate reservoirs

Significant reduction in well productivity of gas/condensate reservoirs occurs because of reduced gas mobility caused by the presence of condensate/water liquid phases around the wellbore. There are certain fluorinated wettability modifiers that are capable of delivering a good level of oil and water repellency to the rock surface, making it intermediate gas-wet and alleviating such liquid blockages. The main objective of this experimental work has been to evaluate the performance of such chemicals for wettability alteration of carbonate rocks, which have received much less attention in comparison with sandstone rocks. Screening tests, including contact-angle measurements, unsteady-state-flow tests, and compatibility tests with brine, were performed by use of mainly anionic and nonionic fluorosurfactants. Results demonstrated that on positively charged carbonate surfaces, the anionic chemicals were sufficiently effective to repel the liquid phase, whereas the nonionic chemicals showed an excellent stability in brine media. A new approach of combining anionic and nonionic chemical agents was proposed to benefit from these two positive features of an integrated chemical solution. A number of low- And high-permeability carbonate-core samples were successfully treated by use of chemicals selected through screening tests. Optimization of the solution composition and its filtration before injecting it into the core proved very effective in reducing/eliminating the risk of possible permeability damage because of deposition of large chemical aggregates on the rock surface. The chemical solution optimized in this study can be considered as a potential wettability modifier for mitigating the negative impact of condensate/water banking in gas/condensate carbonate reservoirs.