高含硫油气井套管安全系数的合理取值

Fitness-for-Service of safety factor for sour service casing

随着高含硫油气田的开发,油套管的工作环境也趋于恶劣和复杂。在酸性条件下,油套管的屈服失效准则已不适用,环境断裂是主要的失效模式,即使满足按屈服准则设计的安全系数,仍不能保证结构的安全。提出了以环境断裂力学评价为基础的油套管适用性评价方法——以环境断裂临界应力百分比为基础进行管柱强度安全系数的设计。本评价方法的标准是:在工作条件下,只要油井管环境断裂临界应力不小于所要求的油井管屈服强度相应的百分比,油井管就能安全运行。环境断裂临界应力的试验评价方法通常采用NACE方法A即NACE标准恒载荷拉伸试验方法,对该方法及相关的数据处理作了介绍。同时结合本评价方法,对国外有关的环境断裂临界应力的相关标准进行了研究。

With the exploitation of high sulfur gas fields, the working environment of tubing and casing gets worse and more complicated. Under sour environment, the yield failure criterion of casing is no longer applicable, Environmental cracking （EC） is the main failure mode. Even if the safety factor meets the yield criterion, safety of the structure cannot still be ensured. Therefore, the tubing and casing＇s Fitness-for-Service assessment method, which is based on mechanical evaluation of environmental cracking, is proposed in this paper. This method is design safety factor of string strength on the basis of threshold stress percentage of environmental cracking. The criterion of this evaluation method is： in working condition, if the threshold stress of environmental cracking of tubing and casing is no less than the percentage corresponding to the required yield strength of tubing and casing, tubing and casing would run safely. Test evaluation method of threshold stress of environmental cracking usually adopts NACE method A, refers to the NACE Standard Tensile Test. This test and its relevant data handling are introduced in this paper. At the same time, the foreign relevant criteria on threshold stress of environmental cracking are studied with this assessment method.