| The steam stimulation and oil recovery method can reduce the viscosity of heavy oil,which is conducive to improving the recovery rate of heavy oil,but this method needs to inject high-temperature steam into the well,so that the casing and cement ring are subjected to greater thermal stress,the casing may yield,and the integrity of the cement ring and the cementation interface between it will also indirectly lead to the failure of the casing.At present,many Thermal Recovery Wells in heavy oil fields have suffered damage such as casing necking,rupture and fault,and the number of casing damage wells increases successively with steam stimulation rounds,which seriously affects the exploitation of heavy oil.Therefore,in order to realize the safe and efficient mining of thermal wells,multiple rounds of research on the mechanical properties of thermal wells casing and cement ring were carried out.Based on this,the research in this paper mainly includes the following:(1)The mechanical test of high and low temperature thermal circulation casing and cement stone was carried out,and the mechanical properties of TP110 H casing and cement stone under the condition of 50～350°C temperature change temperature were studied for up to 16 rounds,and the results showed that the elastic modulus of TP110 H casing decreased rapidly at high temperature,and when the high temperature and thermal cycle rounds increased,the yield strength and tensile strength were significantly reduced,and the elongation and section shrinkage rate after breaking increased.As the creep rate of TP110 H casing increases with the increase of thermal cycle rounds,the creep behavior is more obvious at higher stress levels.When the thermal cycle cycle of cement stone is lower,the tensile and compressive strength increases with the increase of thermal cycle rounds,and the thermal cycle is increased,the strength of cement stone decreases,the thermal cycle has little effect on the elastic modulus of cement stone,and the performance of conventional density cement stone is generally better than that of low-density cement slurry.(2)The steam stimulation and oil production methods and working conditions are systematically introduced,the heat transfer process of thermal wells is studied based on the theory of heat transfer,the temperature field expression of the "casing-cement ringformation" combination is derived,and the stress and displacement expressions of casing,cement ring and formation under internal and external pressure and thermal load are derived based on the thick-walled cylinder theory and the basic theory of thermoelasticity,which provides a theoretical basis for the research of this paper.(3)The thermal coupling analysis of Thermal Recovery Well casing and cement ring was carried out by ABAQUS software,and four situations of conventional straight well section,coupling joint,inclined section and side drilling branch point in the upper part of the packer were analyzed,and the casing and cement ring were in the range of elastic deformation,and the main reason for the sealing failure of the wellbore in the upper well section of the packer was that the cementation interface of "casing-cement ring" was damaged,and the cementation strength of the interface should be improved as much as possible.(4)The influence of steam injection pressure,ground stress,cement elastic modulus and prestress on the cumulative strain of casing in the lower part of the packer was analyzed,and the safety of casing was evaluated by using a strain-based design method,and appropriately increasing the steam injection pressure was conducive to prolonging the service life of casing,under the condition of uneven ground stress,the casing stress rose sharply,which seriously affected the service life of casing,and the use of low elastic modulus cement when cementing could improve the cumulative strain of casing,and the cumulative strain could be effectively reduced by applying pull-up prestress.Increase the number of casing steam stimulation and mining rounds. |
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