空心微珠低密度水泥环完整性试验研究

为了提高空心微珠低密度水泥环的长期封固能力，开展了循环载荷及高内压工况作用下的水泥环完整性试验研究。利用三轴岩石力学测试系统，采用轴向循环加卸载的方法，分析了循环加卸载过程中水泥石的损伤形变规律；在试验基础上，结合厚壁圆筒理论，分析了高内压工况下水泥环的封固完整性。试验结果表明:循环加卸载与高内压工况均能使空心微珠低密度水泥环丧失力学封固完整性。为此，优选了可分散性纤维FK对空心微珠低密度水泥浆进行增韧改性，改性后的水泥浆性能良好，可满足固井施工要求；增韧水泥石的抗拉强度、协调形变能力和承压能力均有所提高，弹性模量下降。研究结果表明，可分散性纤维FK增韧效果较好，为进一步提高低密度水泥环完整性提供了理论依据和优化手段。 

Experimental Study on the Integrity of Low-Density Cement Sheath with Hollow Microsphere

In order to improve the long-term sealing capacity of low-density cement sheath with hollow microsphere,the experimental studies for cement sheath integrity under the working conditions of cyclic loading and high internal pressures have been conducted,and analyzed the damages and deformation law of set cement by using the method of cyclic axial loading and unloading in tri-axial rock mechanics system. On the basis of experiment,the isolating integrity of cement sheath under high internal pressure was evaluated by thick-wall cylinder theory. Experimental results showed that both cyclic loading and high internal pressures could lead to the losses in isolating integrity of low-density cement sheath with hollow microsphere. Therefore,the dispersible fiber FK was optimized to enhance the toughness of the low-density cement sheath with hollow microsphere. The modified cementing slurry has good performances,which can meet the requirements of cementing operation. The tensile strength,coordinated deformation capacity and loading capacity of the modified set cement were all improved,while the elasticity modulus was reduced. The results indicated that dispersible fiber FK had a good effect on toughness increment,which may provide the theoretical basis and optimization method to enhance the integrity of the low-density cement sheath.