多管柱热应力模型预测采气井口装置的抬升

井口装置抬升现象常见于稠油热采井、注采井,生产气井却十分罕见。由于高产气井在生产过程中井口温度高,大温差使得井口附近自由段套管产生热应力变化,进而导致井口装置抬升,破坏气井完整性、损坏地面流程,引发灾难性的后果。为此,分析了因大温差导致套管热应变而引起井口装置抬升的机理,建立了气井井口装置抬升的多管柱热应力模型,并对井口装置的抬升高度进行了实例计算,其预测结果与实际监测结果十分接近,预测结果可靠。研究认为:随着气井产量的增加,井口温度逐渐升高,井口装置抬升高度将不断升高;而表层套管自由段长度对井口装置的抬升高度最为敏感,多层套管固井质量差时对井口装置抬升高度影响较大。最后指出了气井井口装置抬升带来的安全风险,并提出大产量气井应以保证固井质量、合理配产以及加强气井环空压力监测等3项技术措施来预防、监测采气井口装置抬升。

Uplift prediction of gas-producing wellhead equipments of gas production wells by use of a multi-string thermal stress model

Wellhead equipment uplift is very common in heavy oil thermal recovery wells and injection-production wells, but rare in gas production wells. Wellhead temperature of a high-yield gas well became much higher in production, and great temperature difference resulted in the changes in casing thermal stress at the free sections around the wellhead, further leading to wellhead equipment uplift, damage to gas well integrity and surface facilities, and even catastrophic consequences. In this connection, an analysis was conducted to find out the mechanism of wellhead equipment uplift that was caused by casing thermal stress change due to a great temperature difference. by use of a multi-string thermal stress model was established for the wellhead equipment uplift of a gas well. Moreover, the uplifted height of wellhead equipment was calculated according to examples. The prediction results were reliable and very close to actual monitoring results. Research findings showed that with the increase in gas well production, wellhead temperature gradually increased and wellhead equipment uplifted height continually went up, but the length of the free section of surface casing was highly sensitive to the uplifted height of wellhead equipment and exerted a great impact on the uplifted height in case of poor multilayer casing cementing. Finally we pointed out the safety risks resulted from the wellhead equipment uplift of a gas well, and recommended three technical measures of guaranteeing cementing quality, rationally allocating production amount, and enhancing the monitoring over the annular pressure of a gas well to prevent and monitor the wellhead equipment uplift.