松辽盆地北部深层气井CO_2腐蚀预测方法

PREDICTION OF CO_2 CORROSION IN DEEP GAS WELLS,NORTHERN SONGLIAO BASIN

松辽盆地北部深层气井井深、温度高、压力高。天然气中含有CO2,地层水矿化度高,井液中含有一定量的Cl-,井下管柱腐蚀为CO2和水引起的电化学腐蚀。随着温度的升高,腐蚀速率先增大后减小,80℃时腐蚀速率达到最大值;降低溶液pH值、增加溶液中的Cl-浓度、提高CO2分压以及介质的流速,均加剧了油管腐蚀;通过灰色关联量化计算影响CO2腐蚀因素关联度,温度、CO2分压、Cl-浓度、pH值和流速是影响CO2腐蚀的主要因素;根据DWM腐蚀预测模型的函数关系,利用现场腐蚀监测和实验数据计算相应的系数,建立了适合松辽盆地北部深层气井的CO2腐蚀速率预测模型。

As the HT/HP deep wells in northern Songliao Basin, they have CO2 in natural gas, high salinity of formation water and chloride ions in well fluid. The downhole string corrosion belongs to an electrochemistry corrosion caused by CO2 and water. The corrosion rate increases and then slows down with a temperature increase, and reaches the maximum point at 80℃. The oil tubing will be corroded rapidly when the pH value is reduced, the Cl-concentration, CO2 partial pressure and media flow velocity are increased. Using gray correlation method to quantify and calculate the correlative degree of all the factors which affect CO2 corrosion, we found that temperature, CO2 partial pressure, Cl-concentration, pH value and flow velocity are main factors. According to the functional relation of DWM corrosion predictive model, and the relative coefficient calculated from the in-situ monitoring and experimental data, another predictive model of CO2 corrosion rate, has been established and is very suit for the deep gas wells in northern Songliao Basin.