Study On The Mechanisms Of Thermal Ternary Combination Huff-puff In Ultra-heavy Oil Reservoir

Ultra-heavy oil of which viscosity is more than 5×104mPa·s in reservoir has a poor mobility or even is unmovable. The conventional huff-puff method has many problems: higher water-cut escalating rate and decline rate, lower final oil recovery. So a new technology was suggested which was called thermal ternary combination huff-puff to exploit the ultra-heavy oil. This new technology was defined as that some oil-soluble viscosity reducers and CO2 were injected with steam to decrease the viscosity of crude oil and to enhance producing energy with the purpose of improving the effects of cyclic steam injection.Through the laboratory PVT test on ultra-heavy oil–CO2 mixed system and long core test using different displacing mediums (steam, steam+CO2, steam+CO2+ oil-soluble viscosity reducers), and based on the analysis of the mechanisms and the effects of displacement, it is concluded that injecting viscosity reducers and CO2 with steam can decrease viscosity of extra-heavy oil, produce elastic energy, so as to enhance the efficiency of oil displacement.According to the results of physical model experiment, a numerical model was built, on the basis of optimization of conventional steam stimulation parameters in the ultra-heavy oil reservoir, injection-production parameters were contrasted and optimized, then optimal case was obtained. The result showed that thermal ternary combination huff-puff improved 2.37% recovery comparing to conventional steam stimulation.The study indicated ternary combination huff-puff can improve the effect of conventional steam stimulation on ultra-heavy oil comparatively, it opened up a new way for the development of China's ultra-heavy oil reservoir.