Understanding the effects of salinity on bitumen-calcite interactions

Abstract

Recovery of heavy oil from carbonate oil ores is always a challenge by water-flooding process which is highly dependent on the water chemistry. Herein, experimental tests (by atomic force microscopy (AFM), quartz crystal microbalance with dissipation (QCM-D)) and molecular dynamic (MD) simulation have been conducted to understand the exact role of salinity (cations and anions) in influencing the bitumen-CaCO3 interactions. It is found that the addition of K+ and Ca2+ cations (up to 10 mM) into the solution would decrease the repulsive force strength (range from 20 nm to less than 5 nm), and even converts the repulsion force into adhesion force. However, the SO42− anions are observed to be able to strengthen the bitumen-CaCO3 repulsion force. This is different from that for processing quartz oil sands. In QCM-D measurement, additional ions inhibit the bitumen-calcite adsorption behavior but the effect is influenced by the ionic types and strength. Based on the zeta potential measurement and MD simulation, it is found that the Ca2+ cations are more preferred to adsorb on both the CaCO3 surface and bitumen. The adsorbed Ca2+ cations perform as ion bridges linking the oil and CaCO3 surface. Therefore, the accumulation of Ca2+ cations in the solution will deteriorate the oil recovery from carbonate oil reservoirs. However, SO42− anions are more inclined to only adsorb on the CaCO3 surface and prevent the adsorption between bitumen and calcite surface. Therefore, rejecting Ca2+ or increasing SO42− in the low salt water would be helpful for the EOR of carbonate oil reservoirs