高温高压下G3镍基合金油管酸化腐蚀的力学性能

低渗透"三高"(高温、高压、高酸气含量)油气田开发过程中,普遍都会实施一体化管柱酸化增产作业,但其中一些油气井在酸化、生产过程中频繁出现管柱失效的问题。为了探究相关管材在酸液环境中的腐蚀行为和力学性能下降的原因,采用高温高压循环流动测试仪并辅以金相显微镜、SEM、EDS及力学性能测试技术,采用高温高压釜失重实验、力学性能测试对现场常用的P110管材、G3镍基合金管材进行了腐蚀评价及拉伸力学性能实验,评价其在生产及不同注酸工况下的腐蚀状况、腐蚀行为以及力学性能的变化规律。研究结果表明:①在生产和酸化工况下,镍基合金钢的腐蚀速率远小于碳钢;②随着注酸强度的增加,镍基合金钢和碳钢腐蚀速率增大,并且均大于NACE RP0775-2005标准规定的0.076 mm/a;③随着注酸强度的增加,镍基合金钢表面点蚀坑增多,腐蚀产物膜变厚,并且在10%、20%浓度酸液中的试样表面出现了腐蚀产物膜剥落的现象;④酸化后碳钢及镍基合金钢的力学性能降低,降低程度随酸液浓度、酸化时间的增加而趋于显著,并且镍基合金钢降低程度比碳钢更明显。结论认为:①酸化施工应采用酸化管柱和生产管柱分开的方式进行酸化作业,也可采用合理控制酸化时间的方式进行防护;②开采过程中推荐使用镍基合金油管材料。

Mechanical performance of acid corrosion of G3 nickel-base alloy tubings athigh temperature and pressure

In the development of low-permeability oil and gas fields with high temperature, high pressure (HTHP), and high acid gas content, the general approach is acid stimulation through an integrated pipe string. In some oil and gas wells, frequent pipe string failures occur during acidification and production. For the purpose of analyzing the corrosion behavior of tubulars in acid environments and the causes of mechanical performance degradation, HTHP circular flow testers were used together with metallurgical microscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and mechanical performance testing technologies; weight loss experiments and mechanical performance tests were carried out in HTHP kettles for corrosion evaluations and tensile mechanical performance testing on commonly-used P110 tubulars and G3 nickel-base alloy tubulars to evaluate the corrosion degree, corrosion behavior, and mechanical performance change rules of these tubulars during oil and gas production and under different acid conditions. The study results are as follows. (1) During oil and gas production and under different acid conditions, the corrosion rate of nickel-base alloy is much lower than that of carbon steel. (2) With the increase of acid density, the corrosion rates of both nickel-base alloy and carbon steel increase and are greater than 0.076 mm/a which is specified in the NACE Standard RP0775-2005. (3) With the increase of acid density, the number of corrosion pits increases and the corrosion product film becomes thicker on the surface of the nickel-base alloy; and the corrosion product film falls off from the surface of alloy samples in 10% and 20% acids. (4) The mechanical performance of the acidized carbon steel and nickel-base alloy degrades, which becomes more significant as the acid concentration and acid treatment time increase. The degradation of the nickel-base alloy is more significant than that of the carbon steel. The following conclusions are made. (1) Acid treatment should be conducted by separate acidizing string and production string, or the acid time should be properly controlled to avoid pipe string corrosion. (2) Nickel-base alloy tubulars are recommended for exploitation.