Effects of Potassium Ion on Low Salinity Waterflooding in Sandstone Formation
F. Srisuriyachai, S. Meekangwal, C. Charoentanaworakun and Y. Vathanapanich
Event name: IOR 2017 - 19th European Symposium on Improved Oil Recovery
Session: Poster Introductions 1
Publication date: 24 April 2017
Info: Extended abstract, PDF ( 2Mb )
Price: € 20
Multi-Component Ion Exchange (MIE) is a mechanism that has been proven to take place during low salinity waterflooding. In sandstone surface, oil containing organic acid may be attached onto rock surface through an aid of divalent ion binding. Substitution of monovalent ion onto the linking divalent ion site results in liberation of oil. Minimum quantity of divalent ion such as Calcium ion and Magnesium ion together with presence of monovalent ion in injected brine would be therefore favorable conditions for the MIE mechanism. In this study, spontaneous imbibition test is performed to observe ability in replacement of monovalent ion by excluding effect from injection rate. Formation brine is prepared to have total salinity of 100,000 ppm, using an average ion proportion from sandstone oilfields around the globe. Effects of Potassium ion which is much smaller in quantity in brine and seawater compared to Sodium ion, is investigated. From the experiment, Potassium Chloride solution at 35,000 ppm can imbibe into rock sample with total increment of water saturation of 0.42, whereas Sodium Chloride solution at the same salinity can only increase water saturation of about 0.27. Potassium ion is usually accompanied by 1-4 molecules of water, whereas Sodium ion is surrounded by 5-11 molecules. This causes hydrated Potassium to be smaller in size and more active in replacing divalent ion compared to hydrated Sodium. Lowering concentration of Potassium Chloride to 5,000 ppm shows an adverse effect on imbibition ability. As number of active monovalent ion is reduced, replacement of divalent ion occurs slowly. As a result, only 0.24 of water saturation is increased from initial water saturation. Comparing to seawater at the same total salinity which contains Potassium ion only 369 ppm, seawater imbibes at higher degree compared to solely Potassium Chloride which is about 0.47 of water saturation. This can be explained that, adequate total salinity could favor Potassium ion to approach the surface. Moreover, presence of Calcium ion would help induce liberation of oil through formation of Calcium Carboxylate complex. Last, seawater without Potassium ion is prepared to confirm effect of Potassium ion and it is observed that 0.40 of water saturation is increased during the test. In summary, Potassium ion is more potential in replacing divalent ion compared to Sodium ion. A presence of only small quantity of Potassium ion is adequate for spontaneous imbibition as this can be offset by presence of other potential ions.