Corrosion Behavior and Mitigation Strategy for “Three-Highs” Gas Wells: A Case Study of Marine Carbonate Reservoirs in Sichuan-Chongqing, China

The Lower Permian M Formation marine carbonate gas reservoir in Block X of the Sichuan Chongqing exploration area has extreme working conditions with moderate H2S content (0.57–0.97%), moderate CO2 content (2.59–5.59%), and high formation pressure (70–80 MPa). Gas wells face challenges such as multi medium synergistic corrosion, large productivity differences, and limited economic viability. This article addresses the above issues for the first time by analyzing the dual corrosion mechanism, selecting corrosion-resistant pipes (nickel-based alloys/nickel–tungsten alloy coatings), evaluating the adaptability of corrosion inhibitor processes, and real-time monitoring and warning of corrosion risks. A collaborative anti-corrosion technology system of “mechanism material process monitoring” is constructed, and the first successful field implementation was carried out in this block. The experiment shows that the uniform corrosion rate of nickel–tungsten alloy coating under extreme working conditions (122 °C/85 MPa) is only 0.004 mm/a, which is more economical than traditional nickel-based alloys (cost reduction of 69%); CT2 series corrosion inhibitors can selectively inhibit the corrosion rate of gas wells with different water contents (efficiency > 82%). The combination of electromagnetic flaw detection and multi arm wellbore logging technology has achieved dynamic monitoring of downhole pipe corrosion. This system has been successfully applied in seven gas wells in Block X, achieving controllable corrosion risks, cost reduction and efficiency improvement, and providing a replicable technical paradigm for the safe and economic development of marine high-sulfur gas reservoirs.