Research on Corrosion Resistance of Cement Sheath Interface in Sour Gas Wells

Downhole anticorrosion in sour gas wells is one of the technical problems in the petroleum engineering field, and the research on the corrosion of the cement sheath, which is the “first barrier of the wellbore”, is highly valued. Aiming at the problems existing in the current research on the corrosion of the underground cement sheath, a test method for interfacial corrosion is proposed, and experimental analysis methods such as X-ray diffraction and scanning electron microscopy are used to explore the corrosion mechanism of cement sheath in cementing of sulfur-containing gas wells in Sichuan and Chongqing. The results show that the corrosion depth of cement stone is proportional to the partial pressure of hydrogen sulfide and the corrosion time, the compressive strength value of cement stone after corrosion is inversely proportional to the hydrogen sulfide partial pressure value and the corrosion time. Due to the gradual enrichment, accumulation and migration of products after the cement stone is corroded by acid gas, the cement stone forms a relatively stable dense layer or corrosion transition zone, the porosity and permeability of cement stone after corrosion increased with corrosion time, showing the characteristics of first increase and then decrease and finally make it more difficult for the corrosive medium to enter the interior of the cement stone. It is an important method to maintain the long-term sealing and chemical integrity of the mud sheath in sour gas wells that making the cement sheath form a relatively stable corrosion transition zone as soon as possible, or reducing the corrosion rate of the cement sheath, while maintaining a certain corrosion depth.