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Deep Alex井是位于墨西哥湾的一口气井,其井底温度370?(188℃),压力16800lb/in2(116MPa)。井底气中含H2S和CO2,其中H2S最大分压为0·25lb/in2(1·7kPa),CO2分压即井底压力为672lb/in2(463kPa)。此井完井所用材料为22Cr双相不锈钢(UNS S31803),此钢经冷拔至最低屈服强度125klb/in2(862MPa)。该井的生产环境是在室内建立的22Cr双相不锈钢的使用环境极限范围之内。油管的使用及其本身的性能都执行NACE MR0175标准。此井的环空完井液是11·0ppg的CaCl2溶液,其中包含除氧剂及高温无机缓蚀剂;完井时的添加剂含量没有规定。1999年末,Deep Alex井产气一个月之后,生产油管即出现断裂,导致关井。此故障及其后续的井控操作都没有造成人员受伤和环境污染。故障分析和随后的实验室试验证明,此次故障原因是环境导致的22Cr双相不锈钢开裂,22Cr钢开裂是由于环空CaCl2完井液中的NaSCN缓蚀剂分解产生的H2S引起的。
Deep Well is a gas well located in the Gulf of Mexico with a bottom hole temperature of 370 ° C (188 ° C) and a pressure of 16800 lb / in2 (116 MPa). The bottom gas contains H2S and CO2, of which the maximum partial pressure of H2S is 0.25lb / in2 (1.7kPa), and the partial pressure of CO2 is 672lb / in2 (463kPa). The well completion material was 22Cr duplex stainless steel (UNS S31803), which was cold drawn to a minimum yield strength of 125 klb / in2 (862 MPa). The well’s production environment is within the limits of the environment in which the 22Cr duplex stainless steel is built indoors. The use of tubing and its own performance are implemented NACE MR0175 standard. The well completion fluid is a 11.0 ppg CaCl2 solution containing an oxygen scavenger and a high temperature inorganic corrosion inhibitor; the additive content is not specified at completion. In late 1999, a month after the production of the Deep Alex Well, production tubing fractured, shutting down the well. This fault and its subsequent well control operations caused no injuries and environmental pollution. Fault analysis and subsequent laboratory tests show that the cause of the fault is environmental cracking of 22Cr duplex stainless steel and cracking of 22Cr steel is caused by the decomposition of H2S caused by NaSCN corrosion inhibitor in the annulus CaCl2 completion fluid.