Risk assessment of corroded casing based on analytic hierarchy process and fuzzy comprehensive evaluation

Casing corrosion during CO2 injection or storage results in significant economic loss and increased production risks. Therefore, in this paper, a corroded casing risk assessment model based on analytic hierarchy process and fuzzy comprehensive evaluation is established to identify potential risks in time. First, the corrosion rate and residual strength characteristics are analyzed through corrosion tests and numerical simulations, respectively, to determine the risk factors that may lead to an accident. Then, an index system for corroded casing risk evaluation is established based on six important factors: temperature, CO2 partial pressure, flow velocity, corrosion radius, corrosion depth and wellhead pressure. Subsequently, the index weights are calculated via the analytic hierarchy process. Finally, the risk level of corroded casing is obtained via the fuzzy comprehensive evaluation. The corroded casing risk assessment model has been verified by a case well, which shows that the model is valuable and feasible. It provides an effective decision-making method for the risk evaluation of corroded casing in CO2 injection well, which is conductive to improve the wellbore operation efficiency.