Geothermal well construction typically consists of a slotted production liner to support the wellbore and provide a conduit for produced reservoir fluids. To maintain the integrity of the well, the production liner is designed with a dual barrier system - a seal assembly at the top of the liner and a cement sheath between the formation and the liner. The integrity of barrier elements can compromise due to the degradation caused by acidic gases such as H₂S and CO₂ that usually exist in geothermal reservoirs. In this paper, experimental and numerical studies were conducted to evaluate dual barrier system's performance and identify its failure modes at various downhole conditions.

In this study, an experimental setup was designed to replicate the production liner dual barrier system consisting of a cement sheath and elastomer O-rings. The hydraulic and mechanical integrity of the seal assembly and the cement sheath barriers were investigated by conducting pressure tests. EPDM elastomer and neat class H cement were used as the barrier materials. The performance of elastomer was investigated after aging in an autoclave at 1000 psi and 180°F under CO₂ exposure. The performance of the cement was evaluated at different wait on cement (WOC) intervals. Verified finite element models (FEM) were developed to simulate the response of barrier elements under different conditions.

Results indicated that exposure to CO₂ compromised the hydraulic integrity of the seal element. The structural integrity of the elastomer was also jeopardized after CO₂ aging, as evident by the blisters and cracks visually detected on elastomers’ surfaces. Verification by sealability test indicates that FEA modeling can be a reliable tool for estimating seal performance if elastomer material properties are known for the design conditions. Simulation results demonstrate that CO₂ exposure can reduce the sealability of EPDM elastomer (measured in terms of contact stress) by up to 37%.

For cement, the experimental results demonstrated insufficient interfacial bonding between cement and the inner pipe, as evidenced by the leak pathways observed during the hydraulic integrity tests. WOC time improves the hydraulic integrity of cement barrier element. Mechanical properties of cement cured at the elevated temperatures of up to 350°F were used in the FEA model to investigate the impact of temperature and wellbore pressure load on cement integrity. The results revealed that tensile hoop stress induced by the wellbore pressure loads is a likely failure mechanism that compromises the mechanical integrity of cement in geothermal wells. Results indicate that neat Class H cement may not serve as a reliable barrier in case of a defective seal assembly of a liner hanger. Overall, this paper identifies some of the barrier elements’ major limitations and provides recommendations for designing barriers and improving well integrity.

地热井建设通常由开缝的生产衬管组成，以支撑井眼并为生产的储层流体提供管道。为了保持井的完整性，生产衬管设计有双重屏障系统-衬管顶部的密封组件和地层与衬管之间的水泥护套。由于通常存在于地热储层中的酸性气体（例如H ₂ S和CO _2）引起的降解，屏障元件的完整性会受到损害。在本文中，进行了实验和数值研究，以评估双屏障系统的性能并确定其在各种井下条件下的失效模式。

在这项研究中，设计了一个实验装置来复制由水泥护套和弹性体O形圈组成的生产衬里双重阻隔系统。通过进行压力测试，研究了密封组件和水泥护套屏障的水力和机械完整性。EPDM弹性体和纯净的H类水泥用作阻隔材料。在高压釜中于1000 psi和180°F的暴露于CO _2的条件下老化后，研究了弹性体的性能。在不同的水泥等待时间（WOC）下评估水泥的性能。开发了经过验证的有限元模型（FEM），以模拟障碍物在不同条件下的响应。

结果表明暴露于CO ₂损害了密封元件的水力完整性。CO ₂老化后，弹性体的结构完整性也受到损害，这在弹性体表面上目测可见的水泡和裂纹是明显的。通过密封性测试的验证表明，如果在设计条件下已知弹性体材料特性，则FEA建模可以成为评估密封性能的可靠工具。模拟结果表明，暴露于CO ₂可以使EPDM弹性体的密封性（按接触应力衡量）最多降低37％。

对于水泥，实验结果表明水泥与内管之间的界面结合不充分，如在水力完整性测试期间观察到的泄漏路径所证明的那样。WOC时间改善了水泥阻隔元件的水力完整性。在FEA模型中使用了在高达350°F的高温下固化的水泥的机械​​性能，以研究温度和井眼压力负荷对水泥完整性的影响。结果表明，井筒压力载荷引起的张紧环应力是一种可能的破坏机制，损害了地热井中水泥的机械​​完整性。结果表明，如果衬管悬挂器的密封组件有缺陷，则纯净的H类水泥可能无法用作可靠的屏障。全面的，