工作液密度降低对水泥环界面胶结的影响

固井后工作液密度的降低会造成水泥环与套管和地层脱离胶结，从而形成微环隙，导致水泥环的层间封隔失效。根据厚壁圆筒理论，建立了更符合水泥环受力状况的套管-水泥环-地层力学模型，给出了工作液密度降低对水泥环与套管及地层间所受到的应力位移计算式。模拟计算结果表明，在相同井深处，工作液密度降低值越大，水泥环受到的应力值越大，界面处越容易产生微环隙。对于相同密度降低值，水泥环受到的应力值和产生微环隙的可能性随井深的减小而减小。结合模拟计算值和试验，测试不同水泥浆体系的水泥石与模拟套管的胶结强度值，选择和设计不同的水泥浆体系或降低合理的工作液密度值以防止微环隙产生的新途径。

Effect of density reduction of operating fluid in casing on interface cementation of cement sheath

The density reduction of operating fluid after well cementing may cause many problems such as disturbing the relation between cement sheath and formation, developing micro-annulus, disabling interlayer isolation of cement sheaths. The thick-walled cylinder theory was used to establish a casing-cement-formation mechanical model favorable for bearer features of cement sheaths. The formulas for describing displacement and stress of cement sheath were obtained when the density of operating fluid reduced during work after well cementing. Analog calculation showed that at the same well depth, the more value of density reduction would result in the bigger value of stress cement sheath. When the value of density reduction was same, the smaller well depth would result in the smaller value of stress cement sheath. By combining results of analog calculation and cementing strength between cement and simulated casing, a new technical means was proposed to prevent micro-annulus fractures. Selecting and designing different slurry system and reducing the value of fluid density can prevent the interface cementation from generating micro-annulus.