Ion-engineered waterflooding in carbonate reservoir and its consequences on formation damage & flow assurance

Ion-engineered or smart waterflooding is a recent buzzword among the EOR technologies due to the promising laboratory results and a few positive pilot results reported from different parts of the world. In most cases multivalent anions (SO4 2-, PO4 3- etc.) are mixed with injected sea water in increased proportion to suitably alter rock wettability and improve recovery. It is well known that when negatively charged Sulfate comes in contact with positively charged ions such as; Calcium, Barium, Strontium or Iron ions (generally present in high concentration in the formation water), they form hard scale mass, leading to reservoir damage and well flow obstruction. Though ionengineered water flooding is an attractive proposition in view of its environment friendly and low cost approaches, its long term impact on reservoir damage and productivity impairment, due to incompatibility scaling has not been addressed so far.;In this study incompatibility issues that may arise due to the injection of the suggested smart or engineered water are studied extensively, using scale prediction software ScaleChem and also experimentally through "Dynamic Differential Scaling Loop" to investigate scaling potential of various smart water compositions that have been found to enhance oil recovery. In addition, a correlation was drawn which helped in optimizing the concentration of scale forming ions, and the additional recovery may be useful for pilot implementation. Lastly investigation is made to find suitable scale inhibitor/s which can be co-injected to avoid scaling tendencies of the water mixture and their consequences on oil recovery efficiency.;From an extensive study, it has been found that after the introduction of scale inhibitor Polyphosphate-M into high sulfate injection water no scale precipitation was detected within 5 hours with a concentration of 100 ppm Polyphosphate-M and 4 times extra sulfate ions in Abu Dhabi sea water. In addition, contact angle measurements, interfacial tension and Zeta-potential showed the positive effect or neutrality of Polyphosphate-M on wettability alteration, as well as other surface properties which are indicative of improved oil recovery. This is supported by Amottt drainage test.