Effect of Sodium Citrate and Calcium Ions on the Spontaneous Displacement of Heavy Oil from Quartz Surfaces

The dynamic displacement of heavy oil from solid surfaces by water plays a significant role in the oil recovery process. In this work, a bitumen-water-quartz system was applied to study the effect of sodium citrate and calcium ions on the dynamic displacement of bitumen from quartz surfaces. It was found that the addition of calcium ions slowed down the bitumen displacement rate and generated daughter droplets during the receding process. In contrast, the presence of sodium citrate not only accelerated the displacement of bitumen from quartz surfaces, but also led to a smaller contact angle at the end of the experiments. Moreover, calcium ions were chelated by the added sodium citrate, which counterbalanced the detrimental effect of calcium ions on the bitumen displacement. The reduced interfacial tension of bitumen-water interface and the increased negative charges on both bitumen and silica surfaces by sodium citrate were considered the reasons of the improved bitumen displacement process. To better understand the underlying physics, both the hydrodynamic model and molecular kinetic model were employed to analyze the dewetting dynamics of heavy oil from quartz surfaces under the effect of calcium ions and sodium citrate.