Effect of Low Salinity on the Oil Desorption Efficiency from Calcite and Silica Surfaces

Low-salinity water flooding has been suggested to improve oil recovery in sandstone reservoirs. However, application in carbonate reservoirs is still controversial. In this work, a quartz crystal microbalance (QCM) was used to investigate the impact of the chemical composition of crude oils and crystal surfaces on the adsorption/desorption efficiency of oil components upon exposure to various salinity solutions to reveal the potential of enhancing oil recovery from carbonate reservoirs. The surface charge of carbonate rock is characterized by ζ potential measurements. For QCM-D measurements, Norwegian and North Sea crude oils with various acid numbers were used, while calcite and silica crystals were used to mimic carbonate and sandstone reservoirs. The results reveal that the amount of adsorption is correlated to the concentration of polar organic components present in the oil and the type of surface mineral. Subsequent desorption showed that low amounts of desorption are reported upon exposure to seawater for both surfaces examined, while 2 and 10 times diluted seawater achieved the highest desorption efficiency. These observations are supported by ζ potential measurements for carbonate rock and previous electrokinetic studies for silica surfaces. Generally, increasing the content of negative polar components in crude oil leads to a reduced desorption from the calcite surface compared to the silica surface. Low-salinity water flooding seems not to be an optimal technique to improve oil recovery from carbonate reservoirs with high acidity and heavy crude oil.