PERFORMANCE OF FLUOROCHEMICALS ON WETTABILITY ALTERATION OF CARBONATE ROCKS TO ALLEVIATE CONDENSATE/WATER BANKING

摘要

Accumulation of condensate and water around gas-condensate wells,which is attributed to strong liquid wetting characteristics of reservoir rocks,can significantly reduce the well productivity.Altering rock wettability around the wellbore to intermediate gaswetting using appropriate chemical solutions has been proposed as a remedial work to alleviate the condensate/water blockages on a permanent basis. There are a number of experimental studies reported on the impact of such chemical treatment processes for sandstone rocks.However,there are limited studies for carbonate rocks,which have different minerals on the rock surface.In this work,the performance of two anionic and nonionic fluorochemicals on positively charged carbonate substrates were investigated.The impact of chemical concentration,water and alcohol-based carrier solvents at low and high temperatures ranging from 65°C to 190°C and brine were investigated by measuring the pre- and post-treatment contact angles.The performance of chemicals were then evaluated further by conducting a series of spontaneous imbibition and unsteady-state displacement tests on treated carbonate core samples at 130°C by chemical solutions with optimized concentration.In displacement tests,impact of the chemical delivery method,rate and volume of injected chemical and chemical concentration were also studied. The results of contact angle measurements highlighted the relative effectiveness of both anionic and nonionic fluorinated chemicals in altering the substrates wettability when delivered by a water-based solvent.A precipitated layer of anionic chemical was observed on the rock surface when the treatment temperature increased to 160°C and above.Using various alcohol-based solvents reduced the performance of both chemicals to some extent.Unlike the nonionic chemical,the anionic surfactant became unstable in solutions contaminated with brine. The optimized method of continuous injection of anionic chemical solution through the core resulted in a significant increase in oil mobility by a factor of 1.7.The results of conducted spontaneous imbibition tests were also in close agreement with those of the unsteady state displacement experiments.The nonionic chemical,on the other hand,was ineffective to alter the rock wettability as some level of plugging was observed at the core inlet face. These findings highlight the importance of various parameters affecting the wettability alteration process and the special care,which should be taken in design and implementation of such costly operations for field applications.