The Effect of Low-salinity Water on Wettability and Oil Recovery by Core Flooding Test: A Case Study in the Shadegan Oil Field

In most carbonate reservoirs, the amount of oil recycled depends on the spontaneous uptake of brine in the matrix and oil extraction in that matrix towards the cracks. The injection of modified water makes this process possible by changing the wettability of the matrix block towards more water-wet. The rate of wettability change is one of the factors that makes the injection of low-salt water economically. Therefore, this study aims to identify the effect of ion type on the rate of wettability change to modify the composition of the water used for flooding into the reservoir so that the maximum use of this process is to increase oil production from the reservoir. The effect of sodium, magnesium, calcium and sulfate ions on oil recovery from carbonate reservoirs was investigated by a dynamic contact angle test. The results show that increasing the concentration of surfactants such as magnesium, calcium, and sulfate could rise (1) the wettability towards water-wet and (2) the rate of wettability change. In contrast, neutral ions, such as sodium ions, were resulted in a rate reduction in which surface ions change to wettability. Elimination of sodium ions would result in approximately the same amount of change in wettability but in a lesser time from 24 to 2 hrs. The results of the secondary injection showed that although the presence of sodium did not have a significant negative effect on oil recovery, the removal of sodium ions significantly could be improved the sweep efficiency of oil. In modified water, the sodium ion from +0.1 mol to +0.001 magnesium sulfate solution was eliminated. Instead, +0.1 mol sodium sulfate was added to enhance the breakthrough time from 0.31 to 0.43 seconds for injected pore volume. So, the second enhcanced recovery was increased in compare to first EOR.