变内压条件下膨胀水泥与地层机械性能的匹配

以膨胀水泥和地层作为研究对象,以维持井筒完整性为目的,利用弹性力学理论,借助有限元方法模拟分析了套管内压变化条件下膨胀水泥和地层机械性能对井筒完整性的影响,研究了两者机械性能的匹配关系。研究表明:膨胀水泥弹性模量越大,水泥环内最大米塞斯(Mises)应力越大;膨胀水泥泊松比越大,水泥环内最大Mises越小,水泥环内最大周向应力越小。地层弹性模量越大(地层越硬),水泥环内最大Mises应力越大,水泥环内最大周向应力越小;地层泊松比对水泥环内最大Mises应力和最大周向应力的影响较小。建议硬地层(弹性模量大)匹配弹性模量较小、泊松比较大的膨胀水泥,重点预防水泥环的挤压破坏;软地层且内压较小时匹配弹性模量较大、泊松比较大的膨胀水泥,重点预防水泥环的周向拉伸破坏。

Mechanical Property Matching Between Expansive Cement and Formation Under Internal Casing Pressure Change

Taking the expansive cement and formation as the study object, in order to keep well integrity, the effect of expansive cement property and formation property on the well integrity under internal casing pressure change was studied by elastic mechanics and finite element method. The matching relation between the expansive cement property and the formation property was revealed. The results show that, the larger the elastic modulus of the expansive cement, the higher the maximum Mises stress in cement sheath; the larger the Poisson's ratio of expansive cement, the lower the maximum Mises stress and the maximum circumferential stress in cement sheath; the larger the elastic modulus of formation (Hard formation), the higher the maximum Mises stress and the lower the maximum circumferential stress in cement sheath. The Poisson's ratio of formation has little effect on the maximum Mises stress and the maximum circumferential stress in cement sheath. The expansive cement with low elastic modulus and high Poisson's ratio is advised to be used in hard formation to prevent crushing failure of cement sheath. The expansive cement with high elastic modulus and high Poisson's ratio is advised to be used in soft formation to prevent the circumferential tensile failure of cement.