固井水泥射孔力学响应规律及损伤特征

Mechanical response and damage characteristics of cement during perforation

为解决射孔完井作业中固井水泥损伤问题,建立射孔弹侵彻井筒数值模型,基于LS-DYNA有限元软件,计算射孔段固井水泥的力学响应,分析固井水泥射孔力学响应特征;利用射孔弹侵彻实验,确定射孔后固井水泥的损伤特征,研究水泥抗压强度、抗拉强度、剪切模量对射孔过程中水泥等效应力峰值影响规律。结果表明:射孔弹起爆后形成的应力波初期振荡减小,随后逐渐趋于稳定。固井水泥应力峰值位置出现在水泥第一界面上孔道表面。在射孔过程中,孔道周围首先出现主裂纹,而后在孔道附近出现网状微裂纹。随水泥抗拉强度、抗压强度的增加,固井水泥等效应力峰值增加。随水泥剪切模量的增加,固井水泥等效应力峰值降低。为提高水泥抗冲击能力,建议选取高强度、低剪切模量固井水泥。

Focused on the problem of cement damage in perforation completion,a numerical model of wellbore penetrating by shaped charge is set up.The mechanical response of cement during perforation is calculated and the cement damage characteristics after perforation is analyzed based on LS-DYNA software;the damage characteristics of cement are determined by perforation experiment.The influence law of compressive strength,tensile strength and shear modulus of cement on effective stress peak of cement during perforation is studied.The results show that the stress wave formed by the detonation of shaped charge oscillates initially with a reducing tendency and then gradually stabilizes.The stress peak position of cement appears on the surface of perforation tunnel at the first cement interface.During the perforating process,the main crack first appears around the tunnel,and then the microcracks appear near the tunnel.The effective stress peak of cement increases with the increase of cement tensile strength and compressive strength,decreasesing with the increase of cement shear modulus.In order to improve the impacting resistance capacity of cement around the perforation tunnel,it is recommended to select cement with high strength and low shear modulus.