Abstract:

The effect of downhole variable temperatures on the interfacial bonding strength is commonly encountered in well cementing. With the aid of a self-made interfacial bonding strength test device, the present experiment investigated the bonding strength of casing-cement and cement-formation interfaces in an isolation system composed of three types of cement slurry and five cores with different lithology at constant temperatures or alternately changed temperatures. The results showed that during the curing period of cement slurry, the effect of temperatures from ambience to 75℃on the bonding strength of the casing-cement interface was negligible, after concretion, the interfacial bonding strength decreased significantly with the variation of temperatures, and the reduction extent increased with the increase of the temperature difference or the number of temperature variations. The less the elastic modulus of set cement, the smaller the reduction extent of the bonding strength of the casing-cement interface with temperature variations. However, the decrease of the bonding strength of the cement-formation interface depended upon thermal expansion and mechanical properties of set cement. The more similar the property between set cement and cores, the smaller the reduction extent of the bonding strength of the cement-formation interface.

Key words: cementing, cement slurry, downhole temperature, isolation system, interfacial bonding strength, experiment

摘要：

针对复杂多变的井下温度影响固井界面胶结强度的问题，利用自主研制的界面胶结强度测试仪，在恒温或交替变温的条件下，对3类水泥浆体系和5种不同岩性岩心所形成的封固系统进行了第一与第二界面胶结强度的实验研究。结果表明，水泥浆凝固过程中，一界面胶结强度在室温到75℃范围内基本不受温度变化的影响；水泥浆凝固后，温度变化会使界面胶结强度显著降低，且降低幅度随温差和温度变化次数的增大而增大；水泥石弹性模量越小，一界面胶结强度随温度变化的降低幅度就越小；二界面胶结强度随温度变化的降低程度取决于水泥石的热膨胀和机械性能，与岩心性能越相近，胶结强度降低幅度越小。

关键词: 固井, 水泥浆, 井下温度, 封固系统, 界面胶结强度, 实验