高温油气引发套管附加载荷预防模型

在高温油气井生产过程中，由高温引起的套管附加载荷对套管的安全系数要求较高，其中套管密闭环空中流体受热膨胀，对套管环空两侧表面会施加一个热膨胀压力。这种由于井筒周围温度升高而产生的热膨胀应力可达到套管的抗内压或抗外挤强度极限。因此，在高温油气井中必须采取有效的措施来预防这种附加载荷，而这方面研究在国内还比较少。为此，采用向套管环空中注入可压缩流体来降低环空压力，根据体积相容性原理，建立套管密闭环空热膨胀预防模型，并依据所建模型分析给定工况下热膨胀应力变化。研究结果表明：在密闭套管环空中注入一定量的可压缩液体，可有效地预防热膨胀应力。据此可提前采取措施来预防环空流体热膨胀所引起的套管损坏，从而保障高温油气井中的套管安全。

A MODEL FOR PREVENTION OF CASING ADDITIONAL LOAD FROM HIGH TEMPERATURE OIL AND GAS

During the production of high temperature oil or gas wells, there are usually strict specifications on the casing safety factor due to the additional load from the high temperature. Fluid expansion in the sealed casing annulus exerts on the annulus surface a pressure which can exceed the limits of internal and external pressure strength. So, it is important to take effective methods to prevent such additional load. One of the methods is to inject compressible fluid into the annulus. Based on volume compatibility principle, a prevention model can be built to analyze stress variation in the sealed casing annulus during thermal expansion under certain working conditions. Study results showed since the injection of certain amount of compressible fluid into the annulus can effectively help defend the stress caused by thermal expansion, measures can be taken to avoid casing damage thus to ensure safe production of high temperature wells.