Evaluation of casing corrosion in different well sections and application of anti-corrosion schemes for shale gas wells in the southern Sichuan basin

The frequent occurrence of wellbore corrosion in shale gas development blocks within the southern Sichuan basin has led not only to the failure of well integrity but also severely restricted the safe and efficient development of shale gas resources. To address the challenge of well integrity failure caused by corrosion in shale gas wells, indoor experiments were conducted. These experiments were based on the typical service conditions of shale gas wells in two major blocks, C and L, located in the southern Sichuan basin. The aim was to evaluate the corrosion status of the entire well casing and analyze the underlying corrosion mechanisms. On this basis, a comparison was made including the corrosion resistance performance and the 20-year service feasibility of various anti-corrosion technologies. Based on the results, a casing anti-corrosion scheme was selected and subsequently applied in two field wells.Research has shown that the upper and middle sections of the casing predominantly experience CO 2 and microbial synergistic corrosion, while the lower section is mainly subject to CO 2 corrosion. As the temperature increases, the synergistic effect of CO 2 and microorganisms on corrosion diminishes. This results in more severe localized corrosion in the upper section of the casing compare to the middle section. When the temperature reaches the service condition typical for the lower section of the casing, CO 2 corrosion accelerates, leading to both localized and uniform corrosion falling within the extremely severe corrosion range. The uniform corrosion resistance of the antibacterial casing deteriorates with increasing temperature, although their resistance to localized corrosion remains good. Chemical anti-corrosion methods can significantly reduce the uniform and localized corrosion of the upper and middle sections of the casing, but high attention should be paid to the adaptability of the chemical under high temperatures. For a 20-year service life, two anti-corrosion schemes suitable for different shale gas blocks have been proposed. The research results can provide technical support for anti-corrosion to ensure the integrity of shale gas wells in the southern Sichuan basin.