盐穴储气库氮气阻溶造腔过程中的管材腐蚀

受制氮工艺影响，在氮气阻溶过程中，注入的氮气中含有一定量的氧气，导致井下及井口金属材质出现腐蚀，影响后期储气库的安全平稳运行。通过室内高温高压腐蚀失重试验，并结合扫描电镜(SEM)和X射线衍射(XRD)等表面分析技术，分别测试了氮气阻溶造腔工况下氮气浓度、井下温度和井下压力对N80套管在高矿化度盐水环境中的气液两相腐蚀速率，量化了不同因素对管柱腐蚀的影响程度。实验结果表明:现场工况条件下，氮气浓度从80%增加到99.99%，液相腐蚀速率由1.362 9 mm/a降为0.041 9 mm/a，气相腐蚀速率由0.0176 mm/a变为无腐蚀状态；温度从10 ℃增加到40 ℃，液相腐蚀速率由0.341 4 mm/a升高到0.482 9 mm/a，气相腐蚀速率由0.0051 mm/a升高到0.0089 mm/a；压力从10 MPa升高至14 MPa，液相腐蚀速率由0.544 2 mm/a升高到0.605 9 mm/a，气相腐蚀速率由0.006 6 mm/a升高到0.008 9 mm/a。根据上述实验结果，在氮气阻溶造腔实际工况下，当氮气浓度高于95%时，N80造腔管柱气液两相腐蚀速率可满足3~5年的造腔需求，认为95%氮气浓度作为阻溶剂的使用纯度下限，可为氮气阻溶造腔现场操作及制氮方式选择提供依据。

Pipe corrosion in the cavity building process of nitrogen dissolution inhibitor used in salt-cavern gas storage

Due to the influence of nitrogen preparing process, there is a certain amount of oxygen in the injected nitrogen in the process of nitrogen dissolution inhibitor, which results in the corrosion of downhole and wellhead metal materials, so as to impact the safe and smooth operation of underground gas storage (UGS) in the late stage. The gas-liquid two-phase corrosion rates of N80 casing in the environment of high-salinity brine caused by nitrogen concentration, downhole temperature and downhole pressure under the working condition of the nitrogen dissolution inhibitor were determined by means of indoors high-temperature, high-pressure corrosion weight loss experiment, combined with surface analysis technologies, e.g. scanning electron microscope (SEM) and X-ray diffraction (XRD). What’s more, the influence degree of different factors on string corrosion was quantified. It is experimentally indicated that under the field working condition, the liquid corrosion rate is decreased from 1.362 9 mm/a to 0.041 9 mm/a and the gas corrosion rate is decreased from 0.017 6 mm/a to 0 when the nitrogen concentration is increased from from 80 % to 99.99 %. When the temperature is increased from 10 ℃ to 40 ℃, the liquid corrosion rate is increased from 0.341 4 mm/a to 0.482 9 mm/a and the gas corrosion rate is increased from 0.005 1 mm/a to 0.008 9 mm/a. When the pressure is increased from 10 MPa to 14 MPa, the liquid corrosion rate is increased from 0.544 2 mm/a to 0.605 9 mm/a and the gas corrosion rate is increased from 0.006 6 mm/a to 0.008 9 mm/a. These experimental results show that under the actual working condition of nitrogen dissolution inhibitor, the gas-liquid two-phase corrosion rates of N80 solution mining string can satisfy the requirements of 3-5 years’ solution mining when the nitrogen concentration is higher than 95%. It is concluded that the nitrogen concentration of 95 % is the lower limit of nitrogen blanket, which can provide the basis for the field operation of nitrogen dissolution inhibitor and the selection of nitrogen preparing methods.