Study on Quantitative Assessment of CO 2 Leakage Risk Along the Wellbore Under the Geological Storage of the Salt Water Layer

In the process of CO 2 geological storage in the salt water layer, CO 2 leakage along the wellbore will seriously affect the effective storage of CO 2 in the target geological area. To solve this problem, based on the investigation of a large number of failure cases of CO 2 storage along the wellbore and failure cases of gas storage wells in the injection stage of the wellbore, the influencing factors of CO 2 leakage risk along the wellbore were investigated in detail. Based on the analytic hierarchy process (AHP) and extension theory, 17 basic evaluation indexes were selected from 6 perspectives to establish the evaluation index system of CO 2 leakage risk along the wellbore. The established evaluation system was used to evaluate the leakage risk of a CO 2 storage well in the X gas field of BZ Block. The results showed that the influencing factors of tubing had the smallest weight, followed by cement sheath, and the influencing factors of casing–cement sheath interface and cement sheath–formation interface had the largest weight, accounting for 23.73% and 34.32%, respectively. The CO 2 storage well leakage risk evaluation grade was Ι, with minimal leakage risk. The CO 2 storage effect was excellent. The evaluation system comprehensively considers the tubing string, cement sheath, and micro-annulus interface, which can provide a scientific basis for the risk assessment of CO 2 leakage along the wellbore under the CO 2 geological storage of the salt water layer.