Mechanism And Experimental Studies Of Electrical Heating And CO₂ Assisted Steam Assisted Gravity Drainage（SAGD） In Developing Extra-heavy Oil Reservoirs

Steam assisted gravity drainage（SAGD）technology is an effective technology for developing extra-heavy oil reservoirs.However,significant amounts of heat loss and injected steam limts the application of SAGD.This work reveals the solution,aiming at extra-heavy oil reservoir with interlayer,the production mechanism and development method of electrical heating+CO₂assisted SAGD are investigated by combining physical simulation and numerical simulation.First,aiming at the interlayer between wells,several kinds of physical experiments were carried out to explore the mechanism of interlayer cracks under the high temperature.Studies show that the difference in thermal conductivity and thermal expansion characteristics of minerals,the difference in thermal expansion of mineral components,and the mineralization of quartz and clay minerals are the main causes of cracks in the interlayer at high temperatures.Second,aiming at electrical heating-assisted SAGD preheating,a three-dimensional physical simulation experiment was designed,and the temperature rise characteristics between wells was studied;Water is the best injection fluid for the wellbore by conducting wellbore fluid priority experiments.The mechanism of electrical heating assisted SAGD preheating was analyzed further through numerical simulation.Electric heating can evenly preheat SAGD injection-production wells in heavy oil reservoirs with interlayers,with better viscosity reduction effect and lower cost.Third,the physical properties of PVT,such as oil density,oil viscosity,and dissolved gas-oil ratio of extra-heavy oil samples were measured through laboratory experiments under the different temperature and pressure conditions mixed with CO₂.On this basis,one-dimensional sand pack displacement experiments were designed to determine the oil displacement efficiency of CO₂.Finally,the production characteristics and production mechanism of electrical heating+CO₂assisted SAGD in Xinjiang Fengcheng oilfield was studied through physical experiments and numerical simulation.The characteristics of steam chamber in production process were analyzed,The development effects of four different development methods of SAGD were compared,and the electric heating-CO₂ assisted SAGD program had the best production effect.The research in this paper can serve as a reference for the effective development of extra-heavy oil reservoirs.