S135钻杆和Cr13阀片在柴油机尾气环境中腐蚀行为比较研究

Comparative study on corrosion between drill stem S135 and valve plate Cr13 in diesel tail gas drilling environment

柴油机尾气欠平衡钻井技术具有保护油气层和提高钻速等优点,但柴油机尾气成分复杂,可引起井下钻杆的严重腐蚀和地面压缩机阀片的失效。模拟柴油机尾气环境腐蚀试验表明:相同条件下,Cr13平均腐蚀速率远低于S135,试片在动态液相中的平均腐蚀速率远大于动态气相。在温度为100℃,总压为12 MPa,反应时间120 h和流速2 m/s时,2种钢材的腐蚀速率达到最大。Cr13钢表面的腐蚀产物膜成膜颗粒细小均匀,而S135钢表面的腐蚀产物膜成膜颗粒粗大不均匀,因而S135钢腐蚀速率远大于Cr13。S135钢液相腐蚀产物空隙率大、致密性差、疏松多孔,不能完整地覆盖试样表面,对基体不能产生保护作用,而S135钢气相腐蚀产物膜均匀覆盖整个表面,起到了对腐蚀介质的阻隔作用,发生的是典型的均匀腐蚀,因而腐蚀速率相对较低。柴油机尾气环境可引起井下钻杆的严重腐蚀,该技术不适合于产水气井和高压气井,通过合理的预防措施可减缓阀片失效。

The underbalanced drilling technology on diesel tail gas has the advantages of protecting oil and gas reservoirs and improving the rate of penetration. However, it may result in the severe corrosion of down hole drilling stems and the failure of compressor valve plates on the ground, clue to the complicated composition of the diesel tail gas. The simulating test of the corrosion in the diesel tail gas drilling environment shows that under the same conditions the average corrosion rate of Cr13 is far behind the S135. On average, the corrosion rate of Cr13 in dynamic liquid phase greatly exceeds that in dynamic gas phase. The corrosion rates of the two kinds of steel reach the highest when the temperature is 100 ℃, the total pressure is 10MPa, the response time is 120 h, and the fluid velocity is two meters per second （m/s）. Particles of corrosion product films on the surface of Cr13 steel are fine and uniform, while those of S135 stell are coarse and uneven. So the corrosion rate of S135 is much higher than that of Cr13. The corrosion products of S135 steel in liquid phase feature in large porosity, poor compactness, and great looseness, so they can efficiently cover the surface of samples and to protect the base. However, the corrosion products of S135 stell in gas phase can uniformly cover the surface of samples, and can effectively obstruct corrosion media. Typical uniform corrosion occurs. Subsequently, the corrosion rate of S135 steel in gas phase is in relatively lower. Diesel tail gas may lead to severe corrosion of drill stems, so the technology is not suitable for water -production gas wells and high pressure gas wells. Valve plates failure can be alleviated by taking rational preventing measures.