川西须家河组气藏气井CO_2腐蚀机理分析

CO_2 corrosion mechanism in gas wells of the Xujiahe gas reservoirs,western Sichuan Basin

川西须家河组气藏属于高温、高压、含CO2酸性气体的有水气藏,在气井开采过程中,发现部分气井管柱腐蚀严重,存在重大安全隐患,严重影响了气井正常生产,制约了川西上三叠统须家河组气藏的高效开发。为此,通过气井管柱腐蚀形貌特征与腐蚀产物组成分析,明确了川西须家河组气井腐蚀类型主要为CO2腐蚀。通过井口挂片试验、室内腐蚀模拟实验及腐蚀分析软件模拟实验,研究了气井的腐蚀机理,结合川西须家河组气井腐蚀环境,分析了腐蚀的主控因素,根据正交实验数据极差分析,找出了各腐蚀因素对气井腐蚀速率的影响(从大到小排序为气井压力、温度、pH值、水气比、CO2含量和流速),并提出了通过提高气井管柱自身抗腐蚀性能或阻碍腐蚀介质与气井管柱接触(如涂层、表面处理、加注缓蚀剂等方法)来保护井下油管的腐蚀预防措施。

Gas reservoirs in the Xujiahe Formation,western Sichuan Basin,are characterized by high temperature,high pressure,water bearing and a content of acid gases like CO2.During the process of gas production,serious corrosion occurs on the tubing strings of some gas wells there,posing a threat to normal production and thus restricting the highly efficient development of gas reservoirs in this district.In view of this,through an analysis of corrosion morphology features and corrosion product elements,the CO2 corrosion is regarded as the main corrosion type for the gas wells in the Xujiahe gas reservoirs.In addition,the corrosion mechanism is analyzed based on a number of experiments including corrosion coupons at wellhead and laboratory corrosion simulation by the aid of corrosion analysis software.In combination with the actual corrosion environment of gas wells in the Xujiahe Formation,the main influencing factors of corrosion are deeply investigated.According to the data from orthogonal experiment treated with range analysis,the effects of all corrosion factors on the corrosion rate of tubing strings are found in the descending order of the corrosion degree as follows: gas well pressure,temperature,pH value,water/gas ratio,CO2 content,and flow rate.Finally,for the protection of downhole tubing strings,corrosion prevention and control measures are put forward from two aspects: the corrosion resistance of those tubing strings can be significantly improved;coating,surface pretreatment,and corrosion inhibitors can be adopted to protect the downhole tubing and strings from CO2 corrosion.This will provide foundation accordingly for the corrosion prevention and control in fields.