Effects of Brine on Crude Oil Viscosity at Different Temperature and Brine Composition - Heavy Oil/Water Interaction

For decades, it has been observed that temperature has a significant impact on viscosity reduction, mainly, in heavy and extra-heavy oils where increasing the temperature will improve the flow of oil through the reservoir. Austad and his group have reported that three main ions (SO₄²⁻, Mg²⁺, Ca²⁺) are potential determining ions for improving oil recovery in carbonate rocks. Both of them must act together. Their studies focused on studying light oils. At the same time, they pointed out the importance of injected fluid/crude oil/rock interactions.

Water injection is the most widely used oil recovery technique which has been extensively applied globally in both light and heavy oil reservoirs for decades. Historically, the composition of injection water is dictated by the source of water available for injection. However, recent investigations have shown that the composition of the flood water can have a significant impact on oil recovery achived by water flood. Both total salinity and individual ions content of water have been shown to affect the performance of water flood. It has also been observed that interactions between water and crude oil may affect the oil viscosity. Most of the available research results are on light oil systems but the impact of water composition and its interactions with heavy oil have not been investigated.

In this paper, we have experimentally investigated the interactions between brine and heavy oil. The focus of the study was largely on the impact of brine on heavy crude oil viscosity. Four different heavy oil samples were selected from a group of reservoirs and tested in this study. Experiments were conducted using different types of water at different temperatures. Synthetic seawater, formation water, normal brine and distilled water were used as selected brines. The heavy oils were brought in contact with selected brines such that each sample (system) consisted of 80/20 (brine/heavy oil) volume percent. The viscosity and water contact of the each oil was measured before and after the oil had been in contact with brine.

The results of this paper indicate the crude oil viscosity may be altered due to contact with brine. The composition of brine as well as crude oil affect whether the oil viscosity increases, decreases or remains unchanged. The results are important for water injection and handling both on the surface and also in the reservoir.