During geologic CO₂ storage, integrity of injection wells is of utmost importance. Tensile radial stresses at casing-cement and cement-rock interfaces caused by relatively cold CO₂ flowing down the tubing may induce debonding and create microannuli. Microannuli represent potential leakage paths. Thermal stresses can be reduced by using softer cement (“flexible cement”). Numerical simulations show that benefits of soft cement are more pronounced in relatively hard (stiff) rocks. In a very soft rock, there might be as good as no effect of lowered cement stiffness on thermal stresses, while tensile strength of such cement might be severely reduced. Thus, to fully benefit from soft (flexible) cement in CO₂-injection wells, such cement should be set against sufficiently stiff rock. Effect of rock stiffness on tensile radial stress build-up during cooling is stronger than that of cement stiffness. As a result, the benefits of carefully adjusting the cement stiffness might be offset by natural variation in the rock properties. Soft cement also reduces the stress build-up in the cement sheath caused by far-field in-situ stress variation during injection. The mechanism here is the arching effect in the near-well area: the rock effectively shields the cement sheath from in-situ stress changes. In order to fully exploit benefits of soft cement here, the rock again must be sufficiently stiff.

在地质CO ₂储存期间，注入井的完整性至关重要。顺着管道向下流动的相对较冷的CO ₂在套管-水泥和水泥-岩石界面处产生的径向拉伸应力可能会导致脱胶并产生微环。微量环表示潜在的泄漏路径。可以通过使用较软的水泥（“柔性水泥”）来降低热应力。数值模拟表明，在相对坚硬（坚硬）的岩石中，软水泥的好处更为明显。在非常软的岩石中，降低水泥刚度对热应力的影响可能没有效果，而这种水泥的拉伸强度可能会严重降低。因此，要充分受益于CO _2中的软（柔性）水泥-注入井，此类水泥应放置在足够坚硬的岩石上。冷却过程中，岩石刚度对径向张应力的影响要比水泥刚度强。结果，仔细调整水泥刚度的好处可能会被岩石性质的自然变化所抵消。软质水泥还可以减少由于注入过程中远场原位应力变化而在水泥护套中形成的应力。此处的机理是在近井区域的拱形效应：岩石有效地屏蔽了水泥护套免受现场应力变化的影响。为了充分利用软水泥的优势，岩石必须再次足够坚硬。