工程科学与技术2025，Vol.57Issue(5)：66-78,13.DOI:10.12454/j.jsuese.202301059
热流固耦合作用下干热岩地热井套管‒水泥环胶结面应力场分析
Stress Field Analysis of Casing‒Cement Sheath Interface in Dry Hot Rock Geothermal Well Based on Thermal‒Hydraulic‒Mechanical Coupling
摘要
Abstract
Objective The development and utilization of dry hot rock resources help China achieve its dual carbon goals.The reliability of the wellbore sys-tem is crucial for the development of dry hot rock resources.However,the casing cement sheath bonding surface in wellbore system components is a relatively weak structure,and when the wellbore is subjected to thermal‒hydraulic‒mechanical(THM)coupling,the casing-cement sheath in-terface(CCSI)is prone to breakage,reducing the reliability of the wellbore system.This study aims to understand the fracture mechanism of the casing cement sheath bonding surface. Methods The research method of this study was theoretical research and numerical calculation.Using the superposition principle,the boundary conditions of the model were decomposed into axisymmetric and non-axisymmetric boundary conditions.The model under non-axisymmetric boundary conditions obtained displacement and stress field expressions through the elastic thick-wall theory.Under axisymmetric boundary con-ditions,the model considered the coupling effect of the temperature field,mechanical field,and fluid flow field,and the expressions of each field were functions of position and time.Using the Laplace transform and inverse transform,the solution of the model was obtained.The inverse La-place transform employed the Stehfest algorithm,and MATLAB software was used for numerical analysis. Results and Discussions The undetermined coefficients of all fields were time functions.Except for λE1=0,the temperature field coefficients of casing,CCSI,cement sheath,and formation all changed logarithmically with time.The coefficients λC1,λC2,and λD2 increased with time,whereas the coefficients λD1 and λE2 decreased with time.The coefficients of the mechanical field and fluid flow field of casing,CCSI,cement sheath,and formation followed a logarithmic change law,except for λC3 and λD3,which followed a linear change law.λF1,λF2,λD3,λD4,λD5,λD6,λE3,λE4,λE5,and λE6 increased with time.The coefficients λC3,λC4,λC5,and λC6 decreased with time.Published temperature curves were selected to verify the temperature field of the THM coupling model in this study.The results were found to be consistent by comparing the temperature curves at three moments.Published radial stress and radial displacement curves were also selected to verify the mechanical field of the THM coupling model,and the results were similarly consistent.Therefore,the establishment and solution process of the combinatorial THM coupling model proposed in this study was accurate.Based on the engineering background of a dry hot rock well in the Chabcha area,Gonghe Basin,Qinghai Province,the temperature curve and radial stress curve of all surfaces in the wellbore system over time were studied.Due to the thin thickness of CCSI,the transformation law of the bonding surface between the casing and CCSI was essentially the same as that of the bonding surface between CCSI and the cement sheath.The temperature at CCSI decreased to the temperature of the casing inner wall in 2.3 days;however,the cement-formation inter-face reached the temperature of the casing inner wall in 6.9 days.The radial stress at CCSI decreases briefly at first and then increases,with the mini-mum value of 6.31 MPa occurring at 0.2 days.The curve exhibits an exponential change,while the radial stress curve of the cement sheath-formation interface shows a linear change.The curve of radial stress versus radius shows that the radial stress increases rapidly in the casing,and the growth rate slows after reaching CCSI.The radial stress at CCSI is larger,while the failure strength of CCSI is relatively low,making CCSI more prone to failure than other locations.Further analysis was conducted on the influence of CCSI THM coupling parameters on the radial stress at the bonding surface between casing and CCSI.The radial stress decreased initially and then increased with the increase of the ratio of elastic modulus be-tween CCSI and cement sheath.When the ratio was 0.33 and 1.67,the radial stress was maximum,and when the ratio was 1.11,the radial stress was minimum.Changes in CCSI Poisson's ratio had little influence on radial stress during the initial period;however,after approximately 4.6 days,the influence became greater.With an increase in Poisson's ratio,the radial stress of CCSI first decreased and then increased.When the Poisson's ratio was 0.30,the radial stress was minimum,and when the Poisson's ratio was 0.34,the radial stress was maximum.With the increase in porosity,the growth rate of radial stress gradually increased.When the porosity was in the range of 0.1～0.3,the growth rate of radial stress was small,while for porosity greater than 0.4,the growth rate of radial stress was large.With the increase in the T‒O coefficient,the radial stress first decreased and then increased.When the T‒O coefficient was 1.0,the radial stress was minimum,and when the T‒O coefficient was 2.0,the radial stress was maximum.After a certain period,the growth rate of the radial stress remained unchanged.The radial stress increased with the increase in temperature differ-ence.The greater the temperature difference,the greater the growth rate of radial stress.When the temperature difference exceeded 200℃,the growth rate of radial stress was significantly higher than when the temperature difference was below 200℃.The maximum tensile stress criterion was chosen for tension,and the M‒C criterion was selected for compression to assess CCSI damage. Conclusions When the elastic modulus,Poisson's ratio,and T‒O coefficient of CCSI are similar to the corresponding properties of the cement sheath,they are more effective in reducing the radial stress at the interface between the casing and CCSI and in protecting the integrity of the casing-interface-cement-formation system.Lower formation temperatures and lower interface porosity have the same effect in reducing CCSI damage.This study holds great significance for ensuring the integrity of wellbore protection in dry hot rock geothermal wells.关键词
干热岩地热井/热流固耦合/套管‒水泥环胶结面/应力场/理论解Key words
dry hot rock geothermal wells/thermal‒hydraulic‒mechanical coupling/casing-cement sheath interface/stress field/analytical solution分类
能源科技引用本文复制引用
赵新波,秦翊玮,吕健,梁凯,何晓红,赵世军,张立松..热流固耦合作用下干热岩地热井套管‒水泥环胶结面应力场分析[J].工程科学与技术,2025,57(5):66-78,13.基金项目
国家自然科学青年基金项目(52104004 （）
12302264) （）
