Experimental Investigation of Inorganic Scale Deposition during Smart Water Injection - A Formation Damage Point of View

Abstract

Smart water injection is determined as an effective EOR process to change the wettability and interfacial tension for better micro/macro sweep efficiencies. This water contains reactive ions such as〖 Mg〗^(2 ), 〖Ca〗^(2 ) and〖〖 SO〗_4〗^(2-) which can act as potential determining ions and change the surface charge of calcite rocks. One of the major concerns in the execution of an effective waterflood, especially in tight carbonate reservoirs, is the incompatibility between the formation brine and the injecting water. This research work aims to investigate the most important challenge of waterflooding process related to the possible formation damage because of inorganic scale deposition during experimental smart water injection. At the first stage, sea water as the basis for smart water were prepared to examine the impact of determining ion such as〖 Mg〗^(2 ), 〖Ca〗^(2 ), and 〖〖SO〗_4〗^(2-) and the salinity of the injected brine on total amount of 〖CaSO〗_4 precipitation. The tests were performed to find the effects of each ion at static and dynamic conditions. According to the obtained results, as the concentration of 〖〖SO〗_4〗^(2-) in the injecting water increases from 1⁄4 to 1 times of its concentration in ordinary sea water, the 〖CaSO〗_4 deposition increases smoothly, which was accelerated beyond that. Hence, as the increasing of the sulfate concentration improved the wettability alteration ability of the smart water, however calcium sulfate deposition was noticed which make permanent formation damage. Besides, the test results showed that 〖CaSO〗_4 deposition increases smoothly as the concentration of 〖Ca〗^(2 ) in the sea water increases. On the contrary, the presence of 〖 Mg〗^(2 ) ion in the sea water, increases the solubility of 〖CaSO〗_4 and subsequently, lower scale formation was noticed by increasing the concentration of magnesium. This study also showed that, there is an optimum salinity (5 times dilution in sea water salinity) in which the minimum amount of 〖CaSO〗_4 is deposited. The findings would enable us to optimize the ion contents of smart water for both, better oil sweep efficiency and lower risk of formation damage.