Research On Heat Transfer And Viscosity Reduction Mechanism Of CO₂ Assisted Steam Stimulation

The recovery difficulty of super heavy oil reservoir is higher than ordinary heavy oil because of its high viscosity and bad fluidity. CO2 Assisted Steam Stimulation exploiting super heavy oil is a new oil production technology which has extensive application prospect. In this thesis, the numerical calculation model of temperature field when the injection of liquid CO2 was established. It can be used to calculate the temperature of well bore, casing and formation. Calculation procedure was compiled and a field example was simulated. The results show that the temperature rise of fluid CO2 is little because of insulation measures like insulated tubing and N2 in casing annular and the temperature of CO2 arriving bottom hole has larger difference as different injection rate. The mathematical model of formation temperature field was established based on flow and heat transfer theory in porous media. The influence of CO2 injection was analyzed in different rate by using reservoir simulation software. And it can be referred to design the injection scheme. With the help of PVT devices in high temperature and pressure, experiment research of CO2 solubility in dehydrated crude oil and watered oil was conducted. And the volume factors correlating to each solubility were calculated. The results show that the solubility of CO2 in Zheng 411 super heavy oil decreases with the ascension of temperature and increasing with the ascension of pressure; the volume factor of super heavy oil increases with the ascension of CO2 dissolved quantity; in same temperature and pressure condition, the solubility of CO2 in watered oil is less than the one in dehydrated crude oil. Using viscosity measurement device of oil-gas-water mixture in high temperature and pressure, experiment research of viscosity-temperature character was conducted for super heavy oil and the oil dissolved CO2. The viscosity of ultra heavy oil dissolving CO2 was measured in different gas/oil ratio and water content. The influence of CO2 dissolving in ultra heavy oil on the viscosity and volume factor was analyzed. The results show that the viscosity of dehydrated ultra heavy oil and the hydrated ultra heavy oil has exponential relation to temperature; CO2 has obvious effect on the degradation of viscosity, and degradation ratio increase with the increasing of gas-oil ratio; pressure influence little on the viscosity of gas-oil mixture. Interfacial tension between CO2 and super heavy oil was measured using interfacial tensiometer. The results show that CO2 can reduce oil-gas interfacial tension; the interfacial tension between CO2 and oil decreases with the increasing of pressure.