套管表面润湿性对固井界面胶结强度的影响

Effects of Casing Surface Wetting on Interfacial Bonding Strength of Cement

油基钻井液黏附使套管表面变为亲油性,影响固井界面（套管与水泥环）胶结强度。通过测定不同润湿性的套管与水泥环的胶结强度,探究了套管表面润湿性影响界面胶结强度的规律,结合原子力学显微镜分析了其影响机理;同时研究了表面活性剂类型、浓度及温度等因素对套管表面润湿性的影响。结果表明：随表面活性剂浓度的增加,套管表面亲水性增强,阴离子型表面活性剂LAS效果最好;通过表面活性剂的乳化增溶作用,套管表面黏附的大部分油膜被携带走,从而使亲水性套管表面裸露出来。胶结强度随套管表面亲水性的增大（水在其表面接触角的减小）而增大,在接触角62°数63°时出现突变;随LAS浓度的增大接触角呈降低趋势,当LAS浓度小于5 g/L时,接触角减小较快,当LAS浓度大于20 g/L后,接触角几乎不变,LAS加量应在20 g/L以内。此外,温度对LAS润湿反转能力有一定的促进作用。

Oil-based drilling fluid adhesion makes the casing surface change into lipophilic, which will influence bonding strength between casing and cement sheath. By measuring the bonding strength between casing with different wettability and cement sheath, the effect of the casing surface wettability on the interface bonding strength was explored, and the influence mechanism was analyzed using atomic force microscopy, in addition, effect of the surfactant type and concentration, temperature on the surface wettability of casing was probed. Results showed that with the increase of the surface concentration, the casing surface became more hydrophilic, and the effect of anionic surfactant LAS was the best. Through emulsification solubilization of surfactants, most of the oil adhered on the casing surface was carried away, so that the hydrophilic casing surface was exposed. The bonding strength increased with the increase of the hydrophilicity of the cashing （decrease of the surface contact angle）, and changed in mutation at contact angle of 62°-63°. The contact angle decreased with the increase of the LAS concentration, the contact angle decreased rapidly when the surfactant concentration was less than 5 g/L; the contact angle changed little when the surfactant concentration was more than 20 g/L, as a result, the LAS amount should be within 20 g/L. in addition, temperature had a promoting effect on the LAS reverse wetting ability.