高温酸性气藏油层套管选材探析——以四川盆地元坝气田为例

四川盆地川东北地区元坝气田钻井完钻井深度都大于7 000 m，其主力二叠系上统气藏高温且含H₂S和CO₂，气井的油层套管选材困难。通过Corrosion Analyzer软件模拟，初步明确了该气藏的腐蚀规律，即温度小于60 ℃条件下主要以电化学腐蚀为主，大于110 ℃表现为电化学腐蚀与点蚀共同作用；井筒pH值较低，从井底到井口模拟的pH值均小于3；在井筒压力范围内，压力的变化对电化学腐蚀的影响不大。通过对国内外相似气藏的油层套管选用情况，以及110SS和镍基合金套管腐蚀室内实验结果的分析，结合行业标准对酸性介质气藏油层套管材质选择的有关规定和气藏实际情况，推荐了适合该气藏的油层套管材质：油层套管尽量选用低钢级材质，封隔器预计座封井段及以下选用高镍基合金材质，并必须保证封隔器预座封井段的固井质量。

Material selection of the production casing in high-temperature sour gas reservoirs in the Changxing Formation,Yuanba Gas Field,northeastern Sichuan Basin

The total depth of those drilled and completed wells in the Yuangba Gas Field, northeastern Sichuan Basin, is more than 7000 m; the upper Permian Changxing pay zones are under high temperature and contain a certain content of H₂S and CO₂. This leads to a great difficulty in material selection of tubular goods for production casing in those gas wells. Through the simulation software of Corrosion Analyzer, the corrosion law is preliminarily clarified for the above mentioned gas reservoirs. When the formation temperature is below 60 ℃, the downhole environment will be threatened mostly by electrochemical corrosion; when above 110 ℃, both electrochemical and pitting corrosion will co act on the downhole environment. In the simulation, the pH values are all less than 3 from bottomhole to wellhead. Within the range of downhole pressure, the pressure change has little impact on the electrochemical corrosion. In addition, case histories in other similar gas reservoirs at home and abroad are summed up, indoor corrosion test results are analyzed of 110SS and Ni based alloy casings, and according to the industrial criteria, the related regulations are also discussed for the tubular goods selection of production casing especially for sour gas reservoirs. On this basis, the tubular goods material for the production casing is recommended herein in this paper for gas reservoirs in this study area: the low grade steel material should be adopted as much as possible for production casings; high Ni based alloy material should be chosen for the predicted packer sealed well section as well as the part below it, which will guarantee the cementing quality at the said well sections. This recommendation for material selection in this field has been proven to be helpful by successful field practices.