酸性油气田油套管选材设计

Design and Material Selection for Casing and Tubing Used in Sour Oil and Gas Field

在酸性环境下,屈服失效准则已不适用,环境断裂是主要的失效模式.因此,有针对性地改变油套管的设计和选材,将能够减少或防止油套管失效事故的发生.在满足屈服准则设计的基础上,对T95抗硫套管和C110准抗硫套管进行断裂力学设计,根据NACE D法试验计算出材料的临界应力强度因子K_(ISSC),利用失效评估图(FAD)求出在不同条件下的T95和C110抗内压断裂强度.计算结果表明C110的抗内压断裂强度都要低于T95,对己下入C110套管的井,防止后期作业诱发裂纹至关重要.因此,酸性油气田油套管设计在满足屈服设计准则时,也要满足断裂力学设计准则,这一新的断裂力学设计方法为酸性油气田油套管设计和选材提供了重要参考价值.

In sour environments,yield failure criterion is no longer applicable and environmental fracture is the main failure mode for tubing and casing.Therefore,a reasonable design and material selection for the casing and tubing are of significance for reducing or preventing premature failures of them.On the base of satisfying the yield criterion,a fracture mechanics re-design of casings of the conventional sulfur resistant steel T95 and quasi-sulfur resistant steel C110 were performed.According to the environmental fracture toughness of material KISSC calculated by NACE D method,the ductile rupture strength by interior pressure is predicted by Failure Assessment Diagram（FAD） under various conditions.Numerical and experimental comparisons show that ductile rupture stength by interior pressure for steel C110 is less than for steel T95, and thereby it is very important for the existent wells with C110 casing to prevent the taking place of cracks during the later stage operation.In conclusion,the design for casing and tubing used in sour oil and gas fields should meet not only the yield design criterion,but also the fracture mechanics criteria.The new design method presented in this paper provides an important reference for the design and material selection for casing and tubing used in sour environment.