Assessing Casing Integrity in Existing Wells for Reuse in Geologic Sequestration

Abstract In the evaluation of depleted oil and gas fields for suitability as CO2 sequestration reservoirs, existing wells can be considered as a repurposed project injection or monitoring wells. First, the wells in consideration must demonstrate mechanical integrity consistent with regulatory requirements. Second, existing casing must be proven to be capable of withstanding all loads that could be applied to the well throughout the life of the injection project. A rigorous workflow was proposed for comprehensive assessment of casing integrity which includes analyzing and characterizing anomalous features in the casing, quantifying the impact of the defects to the well material strength, and modeling the expected casing design loads for the well considering the strength degradation caused by the defects. Analysis of both internal and external casing defects is used to determine the percentage of remaining body wall (RBW) throughout the well. If the RBW is suitable to withstand the design loads based on API calculations, the well is suitable for re-use. However, if the API calculations indicated the RBW is not sufficient to meet the working stress design (WSD) design factors and if dimensions of the defects are quantified, the well defects can be analyzed using a different method before the well is ruled out for repurposing. This more nuanced approach may prove the strength of the material is greater than initial evaluation and therefore suitable for re-use. The result is that existing assets can be more easily repurposed in appropriate CO2 geologic sequestration applications, reducing the overall impact to project cost, emissions, and surface disturbance. The use of high-resolution defect mapping and comparison of general corrosion width across the circumference allows the use of advanced methods to determine if the Kuriyama method for collapse strength is an alternative to API calculations that conservatively assume the maximum defect depth is applied uniformly across the casing circumference.