Water injection is applied as a well-established process in different reservoirs for pressure maintenance and oil recovery enhancement in the petroleum industry. Scale formation is a common challenging issue in the water injection process. In this paper, mixed salt scaling, especially that of the typical sulfate salts, is studied.
Scale formation is resulted from incompatible interactions between the injection and formation water. Precipitation of the unwanted solid materials on a surface is responsible for some problems as the formation damage, and short life of the completion equipment and surface facilities. In this experimental study, through static and dynamic tests, co-deposition of various salts during water injection is examined. Static tests are performed so as to obtain properties of the mixed salt precipitation. Further dynamic tests are conducted with different variables like the pressure, temperature, concentration, and the degree of salinity.
Several studies conclude that the success of the water injection process is mainly dependent on both fluid-rock and fluid-fluid interactions. They have also mentioned the coexistent precipitation of the salts in the water systems; nevertheless, the referred studies focus on the single salt than mixed salts due to the complexity of the process. Permeability reduction is affected by different parameters such as the mixing ratio of the injected water to the formation water, concentration, salinity, temperature, pressure, pH, and injection rate.
This research is carried out in realistic conditions so that the permeability reduction is precisely and appropriately measured by well-designed equipment. This study considers the mixed salt composition which could give a better insight into the permeability reduction than the former works, especially those which only investigated the single salt scaling. At last, a better understanding of the mechanism of inorganic scale deposition on the rock surface is provided.