工程科学与技术2025，Vol.57Issue(5)：91-100,10.DOI:10.12454/j.jsuese.202400110
CO2注入引起的流固耦合作用对井筒损伤研究
Study on Wellbore Damage Caused by CO2 Injection‒Induced Hydromechanical Coupling
摘要
Abstract
Objective Wellbores can be damaged due to multiphysical coupling during geological CO2 storage in deep saline aquifers,which compromises wellbore integrity and creates potential leakage pathways for CO2.This study proposes a fully coupled hydromechanical model to simulate the two-phase flow of brine and CO2 near the wellbore and to investigate the mechanical responses of the reservoir rock and cement sheath. Methods The wellbore structure in the model consisted of casing,a cement sheath,and the surrounding reservoir rock.The reservoir was consid-ered a saturated,homogeneous,isotropic elastic medium,with deformation characterized as small,linear elastic deformation.Pore pressure diffu-sion was governed by the Biot storage model,while the two-phase flow for brine and CO2 was described by Darcy's law and the Brooks‒Corey model.Since pore pressure increase led to wellbore damage during CO2 injection,the indirect variation in reservoir porosity and permeability was also considered,showing a correlation with changes in average effective stress.The mechanical response and pore pressure variation were fully coupled,and the Coulomb failure criterion was utilized to evaluate the damage risk of both the reservoir rock and the cement sheath.It was found that damage to the cement sheath depended on its inherent properties,the surrounding stress state,and changes in pore pressure.Therefore,the ef-fects of initial porosity,permeability,and elastic modulus of the reservoir rock,as well as the stress ratio and injection rate,on CO2 migration and damage to the wellbore and reservoir rock were analyzed.The initial porosity and permeability of the reservoir rock were described using the Weibull distribution. Results and Discussions The influence of various factors on CO2 migration and damage to the wellbore and reservoir rock was examined.Analy-ses of the benchmark model showed that CO2 saturation and average pressure distributions were closely related,with the highest pore pressure oc-curring near the injection well.Pore pressure changed significantly from 0.5 to 4.0 days,with maximum average pressure changes initially reach-ing 5 MPa and increasing up to 15 MPa as the pore pressure diffused.This increase reflected the influence of boundary conditions on the migra-tion of CO2.Heterogeneity in reservoir porosity and permeability significantly affected distributions of both pore pressure and CO2.Initial CO2 saturation exhibited a distinctly nonuniform pattern.As CO2 migrated,its distribution became more uniform but still depended on variations in po-rosity and permeability.Previous field simulations indicated that reservoir heterogeneity and the presence of fractures can significantly alter CO2 migration patterns.For the wellbore model,despite boundary constraints limiting further pressure diffusion,heterogeneity impacted CO2 migra-tion and pore pressure distribution,influencing potential damage to the wellbore and surrounding areas.It was found that the injection rate,reser-voir porosity,and permeability controlled CO2 migration,with the stress ratio and elastic modulus being largely negligible,as indicated by analyz-ing CO2 saturation and pore pressure at 4 days.In cases of low porosity and permeability,a higher injection pressure was required,resulting in greater CO2 saturation and extended migration distances,though excessive pressure posed a risk of fracturing.Since CO2 migration was linked to pore pressure diffusion,pressure-induced damage was mainly influenced by injection rate and changes in reservoir characteristics.Damage to the reservoir rock was attributed to increased porosity and permeability resulting from CO2 injection,as well as mechanical damage at the cement sheath interface.Analysis showed that porosity changes induced by effective stress variation ranged between 0 and 0.001.Permeability changes reached up to 0.03 mD and were even higher locally,with local increments reaching up to 0.06 mD.The Coulomb failure criterion indicated vary-ing degrees of damage under different conditions.Scenarios such as low injection rate and high permeability delayed damage onset beyond 1 day,while low permeability or high injection rates accelerated damage,potentially fracturing the rocks.Damage initially appeared as point damage,potentially evolving into surface damage with continuous injection,occurring at the reservoir-cement sheath interface.The integrity of the cement sheath depended on its properties,the surrounding stress conditions,and variations in pore pressure.For high CO2 injection volumes,increasing the reservoir's porosity and permeability reduced pressure buildup.Visual analysis revealed damage at the interface between the cement sheath and the casing.Nonuniform changes in the Coulomb failure criterion at these interfaces,influenced by heterogeneity in reservoir rock properties,can result in radial cracks within the cement sheath. Conclusions This study employs a two-phase hydromechanical coupling model to assess the impact of multiple factors on wellbore and surround-ing rock damage caused by CO2 injection.The findings indicate that CO2 migration is aligned with pore pressure diffusion,resulting in both com-pression and expansion of internal pores.Although reservoir heterogeneity influences CO2 migration,the injection rate and initial permeability play a more critical role in determining CO2 flow and pore pressure distribution.Damage typically occurs at the reservoir-cement sheath interface and the cement-casing interface.Reducing injection rates and increasing reservoir permeability can help mitigate damage to reservoir rocks and the cement sheath.The elastic modulus and stress ratio have limited influence on damage.As the damage evolves from point to surface,enhanc-ing permeability in low-permeability reservoirs is recommended to sustain high CO2 injection rates and reduce the risk of cement sheath failure.关键词
流固耦合/两相渗流/井筒损伤/CO2注入/水泥环失效/非均质性Key words
hydromechanical coupling/two-phase flow/wellbore damage/CO2 injection/cement sheath failure/heterogeneity分类
能源科技引用本文复制引用
张瑶,李霞颖,李琦,马纪元,钟屹岩,陈博文..CO2注入引起的流固耦合作用对井筒损伤研究[J].工程科学与技术,2025,57(5):91-100,10.基金项目
NSFC区域联合基金项目(U23A20671) （U23A20671）
湖北省自然科学基金创新群体项目(2021CFA030) （2021CFA030）
岩土力学与工程国家重点实验室开放基金项目(SKLGME023018) （SKLGME023018）
