超深井油页岩地层水泥环材料参数优选及井筒完整性评价

Optimization of Cement Sheath Material Parameters and Wellbore Integrity Evaluation for Oil Shale Formation in Ultra-Deep Wells

摘要: 针对超深井油页岩地层高地应力与高内压工况下水泥环韧性评价不足、材料参数优选缺乏依据的问题，基于ABAQUS建立水泥环数值模型，采用混凝土损伤塑性本构描述水泥环非线性力学行为，系统研究弹性模量5~30 GPa、泊松比0.16~0.28范围内6组参数组合下的应力分布与环向应力–应变全曲线，以峰值应力、韧性指数、残余强度及软化行为为指标优选材料参数。研究结果表明，低弹性模量与高泊松比的协同作用可显著改善水泥环力学韧性，A2组(弹性模量5 Gpa，泊松比0.26)综合性能最优，韧性指数最高，达3.58 MJ/m³，较A3组(弹性模量15 Gpa，泊松比0.16)提高27.4%，且软化段平缓。与A3组相比，A2组水泥环内壁环向应力的周向波动明显减小，危险点应力集中得到有效缓解。优选参数与现有弹韧性水泥浆配方可实现范围一致，具备工程转化可行性。建议超深井油页岩地层固井水泥环采用低弹性模量、高泊松比的韧性材料参数，以降低高地应力与高内压作用下的内壁应力集中，延缓裂纹的萌生和扩展，从而保障水泥环的长期密封完整性。

Abstract: To address the insufficient toughness evaluation of cement sheath and the lack of basis for material parameter optimization under high in-situ stress and high internal pressure in ultra-deep oil shale formations, a numerical model of the cement sheath was established based on ABAQUS. The concrete damaged plasticity (CDP) constitutive model was adopted to describe the nonlinear mechanical behavior of the cement sheath. Six parameter combinations with elastic moduli ranging from 5 to 30 GPa and Poisson’s ratios ranging from 0.16 to 0.28 were systematically studied, focusing on stress distribution and hoop stress-strain full curves. Material parameters were optimized using peak stress, toughness index, residual strength, and softening behavior as evaluation indicators. The results show that the synergistic effect of low elastic modulus and high Poisson’s ratio can significantly improve the mechanical toughness of the cement sheath. Group A2 (elastic modulus of 5 GPa and Poisson’s ratio of 0.26) exhibits the best comprehensive performance, with the highest toughness index reaching 3.58 MJ/m³, which is 27.4% higher than that of Group A3 (elastic modulus of 15 GPa and Poisson’s ratio of 0.16), and a gentle softening stage. Compared with the conventional Group A3, the circumferential fluctuation of hoop stress on the inner wall is reduced, and the stress concentration at the critical point is effectively alleviated. The optimized parameters are consistent with the achievable range of existing elastic-tough cement slurry formulations, demonstrating engineering conversion feasibility. It is recommended that the cement sheath in ultra-deep oil shale formations adopt tough material parameters with low elastic modulus and high Poisson’s ratio, which can reduce stress concentration on the inner wall and delay crack initiation and propagation under high in-situ stress and high internal pressure, thereby ensuring the long-term sealing integrity of the cement sheath.