油套管特殊螺纹接头密封性试验评价方法探析

Discussion on Evaluation Methods for Sealing Test of Tubing and Casing Premium Connection

对储气库注采井等高压气井油管柱泄漏数据统计分析发现,现场特殊螺纹接头泄漏的比例远大于实验室。通过了API RP 5C5—2017 CAL IV实验室内系统评价和下井前气密封试验的油管特殊螺纹接头,在井下服役一段时间后仍然发生泄漏。为此,对内外螺纹上扣啮合后存在的间隙进行简化,建立有限元数值模拟模型,分析了充满螺纹脂的螺纹接头的密封压力;基于气体状态方程,分析了泄漏气体冲破螺纹脂密封压力逸出接箍的时间。分析结果表明,依据API RP 5C5—2017标准推荐做法,内外螺纹均涂抹螺纹脂上扣,即使试验过程中特殊螺纹接头金属密封发生泄漏,泄漏的气体也可能因被封闭在接箍内的孔隙中而无法被检测到,从而导致错误的评价结果。

Statistical analysis of leakage data from high-pressure gas wells such as injection and production wells in gas storage facilities revealed that the proportion of leakage from premium connections on site was much higher than that in the laboratory.The premium connections of tubing and casing that passed the test evaluation according to API RP 5C5—2017 CAL IV and the gas seal test before running still experienced leakage after serving for a period of time.This article simplifies the gap between the pin and box after make-up,establishes a finite element simulation model,and analyzes the sealing pressure of thread filled with compound.Based on the gas state equation,the time for the leaked gas to break through the pressure of the compound seal and escape from the coupling was analyzed.The analysis results indicate that when both pin and box threads are coated with the compound for make-up according to the recommended practice of API RP 5C5—2017,the leaked gas may be trapped in the pores inside the coupling and cannot be detected even if the metal seal of the premium connection leaks during the test,which leads to incorrect evaluation results.