一种石油专用管超弹性应变密封新技术

A new super-elastic strain sealing technology for OCTG

为了解决高温高压天然气井管柱泄漏问题,国内油气田使用了多种特殊螺纹油套管,但井筒密封性仍然无法得到保障。现行的接头密封面接触压应力设计法不能有效堵塞密封结构的泄漏通道,亟待研究发展石油专用管密封设计方法和密封技术。为此,在密封面压应力设计基础上,提出增加弹性应变设计,并实验验证技术有效性。研究结果表明:①采用弹性材料实现弹性应变密封设计,通过材料的应力应变循环试验,优选出弹性应变达到6%的超弹性合金Ti-Ni-X;②设计的多种密封结构使密封面产生足够大弹性应变,以堵塞接头在工厂制造或井下服役期间形成的泄漏通道;③研发出一种密封环超弹性应变密封套管,样品成功通过了上卸扣试验和API RP 5C5 CAL IV级B系列密封试验,最大试验载荷达到了95%管体应力包罗线,最大试验温度达到180℃。结论认为,超弹性应变密封新技术可作为新一代石油专用管及井口管件密封的技术储备,该技术有望提高气井管柱和井口管件的密封性。

Domestic oil and gas fields adopt various special thread tubings and casings to solve the problems of string leakage in high-temperature and high-pressure natural gas wells, but wellbore sealing cannot be guaranteed yet. The current contact compressive stress design method of connection sealing surface can not effectively block the leakage channels of sealing structures, so it is in an urgent need to research and develop a sealing design method and sealing technology for oil country tubular goods(OCTG). In this paper, an elastic strain design is proposed on the basis of the compressive stress design of sealing surface. In addition, the technical validity is verified experimentally. And the following research results are obtained. First, the elastic strain sealing design is realized by using elastic materials, and super-elastic alloy Ti-Ni-X with elastic strain of 6% is selected through a stress and strain cycle test. Second, several sealing structures are designed, which can generate enough elastic strain on the sealing surface, so as to plug the leakage channels of connections which are formed during factory manufacturing or underground service of connections. Third, a kind of sealing ring super-elastic strain sealing casing is developed, whose specimen successfully passes the make and break test and the B series sealing test of API RP 5C5CALIV class. The maximum test load reaches 95% of the casing stress envelope, and the maximum test temperature is high up to 180 ℃.In conclusion, as a new generation of technological reserve of OCTG and wellhead fittings sealing, this new super-elastic strain sealing technology is expected to improve the sealing capacity of strings and wellhead fittings of gas wells.