Research On Rheological Properties And Flow Characteristics Of Foamy Oil

Some of the heavy oil reservoirs in Canada and Venezuela show anomalous behavior under solution gas drive. When the reservoir pressure is below than bubblepoint pressure, the producing gas-oil ratio does not increase rapidly, and the pressure drop rate is slow. The term “foamy oil” originated from observations of stable foams in samples collected at the wellhead from many wells that produce under solution gas drive. In foamy oil, gas is highly dispersed in the oil in the form of small gas bubbles. However, the rheological properties and flow characteristics of foamy oil are very complicated, and many influencing factors are involved. Therefore, it is nessary to investigate to the rheological properties and flow characteristics of foamy oil by laboratory tests and numerical simulations.In this paper, an experimental device for testing the rheological properties of foamy oil was developed with the experimental system for testing the rheological properties of conventional crude oil firstly. This experimental device can achieve measurements on the rheological properties of foamy oil under different experimental conditions. Then, the flow characteristics of solution gas drive at different stages were studied by means of micromodel tests and sandpack flood experiments. To investigate the difference of foamy oil flow characteristics under high and low temperatures, the development features of solution gas drive under temperatures were studied by physical simulation. The microscopic displacement mechanisms and displacement efficiency of different recovery methods for heavy oil after solution gas drive were investigated by micromodel tests and sandpack flood experiments.The study results indicate that the foamy oil viscosity has linear relationship with the foam quality. The viscosity of foamy oil decreases with the increasing of shearing rate showing shear-thinning characteristic. The relation of foamy oil flow behaviour index and foam quality was established. The foamy oil flow behaviour index decreases with the increasing of foam quality. During the solution gas drive, gas was developed from the dispersed phase to the continuous phase gradually forming foamy oil flow. Foamy oil can increase the elastic energy, which can maintain the reservoir pressure, increase the production pressure drop and improve the performance of solution gas drive. The sandpack test results show that foamy oil can improve the performance of solution gas drive. Increasing temperature has both positive and negative effects on enhancing oil recovery. On one hand, the oil viscosity is lower with higher temperature, which can reduce the flow resistance during the solution gas drive. On the other hand, the foamy oil system is not stable with higher temperature, which does not provide positive contribution to improve oil recovery. The highest recovery of solution gas drive was obtained at 100 oC. During the subsequent water flooding after solution gas drive, oil with the dispersed gas bubbles was driven by the injected water, thereby forming water displacing foamy oil flow state. Because of the adverse mobility ratio caused by gas bubbles dispersed in the oil. The surfactant solution can penetrate into the heavy oil and the subsequent formation of gas bubbles and oil droplets in surfactant solution can reduce the mobility of water phase, thereby resulting in improved sweep efficiency.