Research and Application of Anti-corrosion Technology in Downhole Oil and Gas Fields

Acidic gas reservoirs contain both H2S and CO2 simultaneously underground, and most of them are water-bearing gas reservoirs. The underground corrosive environment is harsh, and long-term safe production faces challenges. Therefore, this paper analyzes in detail the anti-corrosion principles and adaptability of three methods: material anti-corrosion, chemical agent anti-corrosion, and coating/plating anti-corrosion. Taking the application of downhole anti-corrosion technology in XX block as an example, it expounds the anti-corrosion principles, application situations and effects of three anti-corrosion processes: “High sulfur-resistant carbon steel tubing and corrosion inhibitor”, tungsten alloy plating tubing and nickel-based alloy tubing. The on-site implementation difficulty and cost of different anti-corrosion processes were compared, and the anti-corrosion processes that ensure the safe production throughout the life cycle of gas wells were comprehensively obtained. The conclusion is that: The anti-corrosion process of “high sulfur-resistant carbon steel tubing and corrosion inhibitor” can effectively prevent corrosion of the tubing above the injection valve, but cannot prevent corrosion of the tubing below the injection valve. It is only applicable to the wellbore environment where the water-gas ratio is less than 2.5 cubic meters per 10,000 cubic meters and the gas production is less than 200,000 cubic meters per day, and is affected by multiple factors such as the injection equipment, the injection timing, and the performance of, the corrosion inhibitor. The anti-corrosion method of nickel-based alloy materials is simple and it is the optimal anti-corrosion scheme for sulfur-containing gas Wells, but the cost is high. The anti-corrosion effect of tungsten alloy coated oil pipes is comparable to that of nickel-based alloy oil pipes, and compared with nickel-based alloys, the cost is reduced by about 70%, which is conducive to the benefit development of gas fields. However, the long-term adaptability needs to be determined based on the results of downhole corrosion detection at present.