Study On Heat Transfer And Flow Law Of Boiler Flue Gas Assisted High Temperature Steam Heavy Oil Thermal Recovery

With the natural depletion of heavy oil and multiple rounds of throughput development,most oil fields have entered the middle and late stages of decreasing production.The simple steam injection technology has problems such as large energy loss along the wellbore and rapid decline of formation energy.Boiler flue gas assisted high-temperature steam thermal recovery technology has become one of the promising technologies in heavy oil extraction as it not only reduces steam heat loss and improves thermal sweep efficiency,but also helps to reduce carbon dioxide emissions.The heat loss during the flow and heat transfer of the fluid in the wellbore and reservoir directly affects the exploitation effect of heavy oil.The research on the physical properties and the flow and heat transfer patterns of mixed fluids of flue gas and steam can provide theoretical guidance and technical support for the application of this technology in the efficient thermal recovery of heavy oil.From the physical properties of boiler flue gas and saturated steam,a calculation model for the thermal properties of the mixture of boiler flue gas and high-temperature steam was established.The variation law of specific volume,enthalpy,viscosity and thermal conductivity under high temperature and pressure are analyzed systematically,and compared with the thermal properties of water vapor before and after the addition of boiler flue gas.The results show that the specific heat capacity and enthalpy of the gas mixture will decrease,indicating that the function of adding flue gas is not to increase the heat of the gas mixture,but to use of the heat insulation and thermal expansion of the flue gas.Based on the model of heat transfer and gas-liquid two-phase flow in a vertical wellbore,the actual state equation of the gas mixture and the transient thermal conductivity function of reservoir formation temperature were introduced.The composition of heat transfer resistance in the wellbore was calculated and the values of each resistance were compared,and the variation of heat loss and fluid parameters of the boiler flue gas and high temperature steam mixture in the wellbore with the depth of the wellbore were obtained.Secondly,the Fluent software was used to model boiler flue gas and water vapor condensation heat transfer in the wellbore.The Mixture method and the Lee phase transition model were used to simulate the condensation heat transfer process of mixed fluids in the vertical wellbore under the condition of variable wall temperature.The influence of different injection ratios of flue gas on the condensation heat transfer coefficient of water vapor was investigated.The results show that the heat transfer coefficient is 28.91%lower than that of pure steam when the proportion of flue gas is10%.Finally,the study was conducted to optimise the design of boiler flue gas assisted high temperature steam injection parameters,and the sensitivity analysis of the wellhead injection parameters was carried out to investigate the influence of each factor on wellbore pressure and steam dryness.With the objective of improving the efficiency of the oilfield thermal recovery process,the four main factors of flue gas flow rate,steam flow rate,inlet pressure and steam dryness for wellhead injection were optimised using an orthogonal design optimisation method,and the optimum combination of parameters was determined to be steam dryness 0.8,steam flow rate 8 t/h,flue gas flow rate 600 Nm~3/h and wellhead pressure 15 MPa.Combined with the geological parameters of the YQ west test block and the optimized injection parameters,the reservoir application simulation is carried out to obtain the sweep situation of the heavy oil field with different wellbore pressures and steam dryness.