基于API圆螺纹的气密封螺纹开发及评价

如果能在相对成本最低的API圆螺纹的基础上开发出一种低成本气密封螺纹替代目前的特殊螺纹接头,将带来巨大的经济效益。为此,按API Spec 5B标准,基于圆螺纹设计并加工了一种气密封螺纹结构,接箍中间增加了弹性密封圈,依靠弹性密封圈与套管螺纹的过盈配合实现密封。采用MSC.Marc/Mentat有限元分析软件对其进行了极限承载能力评价,然后按照ISO 13679标准对?73.02×5.51 mm J55钢级气密封螺纹实物进行了ISO 13679 B系试验、C系试验及弯曲条件下气体内压加拉伸试验。结果表明:(1)该气密封螺纹结构气密封性能良好,封堵管端最终内压循环与热循环试验的结果符合ISO 13679标准的要求;(2)该气密封螺纹结构抗内压强度、抗拉伸强度和抗外压挤毁强度均大幅高于GB/T 20657标准的要求。结论认为,该气密封螺纹结构可以在鄂尔多斯盆地低压气井开发中使用,具有大幅度节约套管成本的潜力,也可供新型气密封螺纹结构的设计借鉴。

Development of gas-tight threads based on API round threads and its evaluation

Great economic benefit will be made if a kind of low-cost gas-tight thread can be developed on the basis of API round thread with a relatively lowest cost to replace the existing premium thread. In this paper, a kind of gas-tight threads was designed and manufacturedbased on the round threads according to the API Spec 5B standard. An elastic sealing ring was added in the middle of the collar, and gas tightness was realized by virtue of the interference matching between the elastic sealing ring and the casing thread. Then, its ultimate bearing capacity was analyzed by using the finite element analysis software MSC.Marc/Mentat. Finally, ISO 13679 B series and C series tests, and tension tests under internal gas pressure in the bending setting were carried out on Ø73.02 × 5.51 mm J55 gas-tight threads accordingto the ISO 13679 standard. It is shown that the gas sealing performance of this gas-tight thread is good, and the results of ultimate internal pressure cycling and the thermal cycling test on sealing pipe ends meet the requirements of ISO 13679. Besides, its internal pressurestrength, tensile strength and collapse strength are much higher than those required by GB/T 20657 standard. It is concluded that this type of gas-tight threads can be used in the development of low-pressure gas wells in the Ordos Basin. It has the potential to cut down the casing cost greatly and it can be used as the reference for the design of new gas-tight threads.