陇东地区煤层气井油管柱腐蚀机理研究

煤层气井油管柱腐蚀导致的管柱穿孔和频繁卡泵是制约陇东地区煤层气资源开发的关键因素，确定煤层气井油管腐蚀形貌特征与产物成分，查明其腐蚀机制对于气井管材选型、防护措施改进意义重大。利用扫描电镜（SEM）及二次电子图像（SE）、背散射图像（BSE）对油管柱腐蚀产物膜形貌进行微观表征，采用能谱分析（EDS）标定腐蚀产物元素类型及含量，并通过X射线衍射分析了腐蚀产物的矿相，在此基础上提出本区煤层气井油管腐蚀机理及防护措施：本区煤层气井N80油管钢在高矿化度Cl^-、HCO₃^-地层水环境发生强烈CO₂腐蚀作用，形成多层结构腐蚀产物（FeCO₃）膜，由于腐蚀产物膜与金属基体结合强度低，在井筒流动介质冲刷下易发生剥离，且腐蚀产物膜疏松多孔致密性差，Cl^-易穿过产物膜接触金属基体，形成自催化腐蚀电偶，加速局部阳极溶解，生成大量点蚀坑，加剧了腐蚀穿孔伤害程度。选择含3% Cr油管材、加缓蚀剂（原油）与射孔完井是实现本区煤层气井油管柱整体腐蚀防护的可行措施。

Corrosion Mechanisms of Tubing String of Coalbed Methane Wells in Eastern Gansu

The perforation of the oil tubing string caused by the corrosion and the frequent stuck pumps in coalbed methane(CBM)wells are the key factors restricting the development of CBM resources in eastern Gansu.This paper,by using scanning electron microscopy(SEM)and secondary electron image(SE),back scattering(BSE)to characterize the microstructure of corrosion scale and the energy spectrum analysis(EDS)calibration element types and contents of corrosion products,and through X-ray diffraction analysis of component of products,the corrosion mechanisms and protection measures of tubing string of CBM wells were proposed:CO2 corrosion occurs to N80 steel of CBM Wells in this area in high salinity formation water,Cl^?,HCO3^?,forming a multilayer structure corrosion scale(FeCO3).Due to the low bonding strength between the corrosion scale and metal matrix in the wellbore flow,medium scour easily occurs under the stripping,and corrosion scale is porous density,Cl^?contacts the metal matrix to form autocatalytic galvanic corrosion,accelerate the localized anodic dissolution,and to generate a large number of spot corrosion pit,exacerbating the corrosion perforation damage.The selection of 3%Cr oil tubing,corrosion inhibitor(crude oil)and perforation completion is a feasible measure to realize the integral corrosion protection of tubing String of CBM wells in this area.