大涝坝气田油管腐蚀原因分析及治理对策

Tubing Corrosion Analysis and Control Measures in Dalaoba Gas Field

大涝坝凝析气田油管在生产中多次出现腐蚀穿孔而报废,严重影响了该气田的安全生产。为找出该气田油管腐蚀失效的原因及其影响腐蚀的因素,有针对性地防治油管腐蚀,首先分析了该气田油管的腐蚀规律及油管腐蚀形貌特征,结合该气田生产介质和运行工况,进行了P110、13Cr和HP13Cr等3种材质油管的模拟腐蚀试验,分析了温度、CO2分压、Cl-质量浓度、流速等因素对油管腐蚀的影响程度。结果表明:对腐蚀程度影响最显著的是温度,流速和CO2分压次之,Cl-质量浓度较弱;油管腐蚀最严重的井段(600～2 500m)是在温度90℃、CO2分压0.19～0.37MPa条件下,CO2腐蚀、流体冲刷腐蚀和缝隙腐蚀共同作用下造成的。同时分析了丝扣类型和环空保护液对油管腐蚀的影响,认为偏梯型扣的FOX螺纹油管较梯形扣EUE螺纹油管抗腐蚀性强,CT/TPK-2型环空保护液能有效防止油管外壁发生腐蚀。提出采用"封隔器+环空保护液+13CrFOX螺纹油管+P110EUE螺纹油管"的完井方式防治油管腐蚀,腐蚀最严重的600～2 500m井段选用13CrFOX螺纹油管。

Tubing corrosion failures have happened several times in Dalaoba Condensate Gas Field and are a serious production issue.In order to understand the reasons of corrosion failure and factors affecting corrosion,and to prevent further corrosion,the corrosion characteristics were analyzed.Combined with field production media and operating condition,corrosion tests were conducted using three different tubing materials,P110,13Cr and HP13Cr.The effect of temperature,CO2 partial pressure,chloride mass concentration and flow rate were investigated.The results showed that the most important factor is temperature,followed by flow rate,CO2 partial pressure,and chloride mass concentration.The most serious corrosion happened in tubing from 600 m to 2 500 m at 90 ℃,CO2 partial pressure of 0.19~0.37 MPa.Tubing corrosion were caused by CO2 corrosion,erosion-corrosion and crevice corrosion of fluid.In addition,the effect of thread type and annular solution to the corrosion were studied.It turned out that the FOX trapezoidal buckle had better corrosion resistance than EUE tubing threaded,and CT/TPK-2 solution can effectively prevent corrosion.The combination of packer,13Cr and P110 EUE thread tubing is recommended for corrosion prevention and 13Cr tubing is recommended for the most severe corrosion well section between 600 m and 25 00 m.