Study On The Heat And Mass Transfer Physics Between Wellbore And Formation During The Cyclic Superheated Steam Stimulation Process

Cyclic steam stimulation(CSS)is an effective method for heavy oil development.Traditional single-tube injection of saturated steam is restricted by low oil displacement efficiency(ODE)and steam channeling.In order to increase the ODE of heat carrier,multi-component thermal fluid(MCTF)and superheated steam(SHS)are adopted to improve the hydrothermal cracking efficiency and reservoir permeability;on the other hand,concentric dual-tube well(CDTW)is used to inject SHS at the heel and toe points of horizontal wellbore.This paper takes the CDTW with SHS injection as the research object,and carries out following research works.Firstly,the heating effect by frictional work is characterized.The energy conservation equation is re-derived.By coupling with the SHS model,the flow model in ground pipelines and vertical wellbores are established.By coupling with the air heat-conduction model,transient heat conduction model,and turbulence heat transfer model,a comprehensive wellbore/formation coupled model is established.By adopting the equation of actual state of mixed gas,the model can be extended to simulate the MCTF flow.In addition,the two-phase flow model is also used.The model was used to successfully explain the physical mechanism of a small decrease in SHS temperature in the wellbore under high-speed SHS injection condition.Secondly: considering the effect of heat transfer inside wellbore on the distributions of SHS temperature and the phase change point,the Joule-Thomson effect,and the difference of flow direction of SHS in long tube and annuli,a SHS flow model with heel/toe points injection is established.Based on this,taking the uniform SHS injection as the research object,considering the difference in the flow direction of SHS in the long tube and annuli,energy conservation equations are established respectively.Combined with the mass conservation equation in annuli on both sides of the packer considering the variable mass flow characteristics,a uniform SHS injection model is established.On this basis,by coupling with reservoir SHS soak model and transient heat conduction model,the horizontal wellbore/reservoir coupled model is established.The model is used to reveal the physical mechanism of non-uniform SHS absorption,and an optimization method for SHS injection parameters is proposed.Thirsly,Considering the SHS flow characteristics in full-length wellbore and the influence mechanism of the SHS phase change,a model for full-length wellbore is established.Then,the oil layer is divided into SHS zone,saturated steam zone,hot water zone and cold zone.Considering the decreasing temperature in the SHS zone,the concept of "leading-edge temperature" is proposed.By assuming that the temperature of the SHS zone is linearly decreasing,a reservoir energy conservation equation is established,and the analytical solution of the radius of the SHS zone is derived by using the Laplace transform.Using this model can effectively improve the historical fitting accuracy.Based on this,sensitivity analysis is conducted.Finally,a numerical mode is used to study the dynamic characteristics of the reservoir during SHS injection.Lastly,By carrying out physical simulation experiments of heavy oil rheological properties at different temperatures and shear rates,and of heavy oil non-Newtonian fluid seepage characteristics at different temperature and permeability combinations,the non-Newtonian flow characteristics of heavy oil samples are analyzed.Based on this,it is proposed that the hot water zone can be subdivided into two parts,the non-Newtonian fluid zone and the Newtonian fluid zone,and the production prediction model for cyclic SHS stimulation is established.This model is used to reveal the production dynamics of cyclic SHS stimulation under different production regimes.Finally,a numerical model is used to study the dynamic changes of the oil layer during SHS flooding.