How to Choose the Suitable Steel of Wellhead, Wellbore, and Downhole Tools for Acid Gas Reinjection Flooding

The material selection of injection gas wells in acid gas flooding is the bottleneck of the successful implementation of the technical scheme. Through standard and literature research, the materials of the wellhead, wellbore, and packer for reinjection well in acid gas flooding are preliminarily established, and then the suitable materials are further screened by using the weight-loss and surface characterization method. Finally, a new type of packer is designed to optimize the wellbore material. The results show that 35CrMo (CR = 0.0589 mm/y) steel is used for wellhead materials, 625 alloy steel is selected as the sealing surface, and 625 or 825 alloys (with CR ≤ 0.0055 mm/y) steel is used for wellhead sealing material. The main material of the packer is 718 Alloy (with CR ≤ 0.0021 mm/y). The cost of T95 steel within 20 years (1263 ten thousand yuan) of service is much smaller than that of G3 alloy (1771 ten thousand yuan), but after 30 years of service, its cost is close to that of G3 alloy. A kind of downhole packer for acid gas reinjection is designed. Among them, G3 alloy steel tubing is used between the packer and the relief valve, T95 steel tubing is selected above the packer and below the safety valve, and the packer is set in the G3 steel tubing. The serious pitting corrosion of T95 steel in the liquid phase environment is due to the uneven deposition of FeS and FeCO3 on the steel surface.