柴油机尾气负压钻井中的腐蚀行为研究

柴油机尾气负压钻井属气基欠平衡钻井，具有保护油气层和提高钻井速度等优点，但柴油机尾气成分复杂对石油管材可产生不同程度的腐蚀。为此，模拟柴油机尾气环境，考察温度、压力和流速对S135钢的动态液相、动态气相平均腐蚀速率及局部腐蚀速率的影响，并对腐蚀产物形貌和成分进行了分析。结果表明，相同条件下动态液相中的平均腐蚀速率和局部腐蚀速率远大于动态气相；随温度升高，腐蚀速率先增大然后降低；随压力或流速的增大，腐蚀速率升高。柴油机尾气环境可引起井下石油管材的严重腐蚀，该技术不适合于产水气井和高压气井。

STUDY ON CORROSION BEHAVIORS OF DIESEL ENGINE TAIL GAS DRILLING

Diesel engine tail gas drilling is a kind of gas-based underbalanced drilling, with advantages of protecting oil/gas reservoirs and improving ROP. However, due to complex composition, the diesel tail gas will give rise to severe corrosion to oil country tubular goods. Investigations were made as per the effects of temperature and flow rate on the average corrosion rates and local corrosion rates of dynamic liquid and gas phases towards S135 steel, under the simulated corrosive diesel engine tail gas environment. Analysis was made on the appearing status and compositions of the corroded objects. The results show that, under the same conditions, the average and local corrosion rates of dynamic liquid phase exceed that of dynamic gas phase. The corrosion rate will increase first and then decrease when temperature is increased, and increase with pressure and flow velocity. Since the diesel engine tail gas can result in severe corrosion to downhole oil tubulars, underbalanced drilling with diesel tail gas is unsuitable for water-producing gas wells and high pressure gas wells.