Guest Editorial: The Difference Between CO2 EOR and CCS Injection Well Metallurgy

Abstract

_ The recent surge in development of CO2 carbon capture and storage (CCS) projects has brought focus on the requirements for corrosion resistance in the injection wells as required by US Environmental Protection Agency (EPA) permitting. In some cases, the long successful history of various metallurgies in enhanced oil recovery (EOR) wells has been cited as sufficient to allow the same completions for CCS injection wells. The lack of actual data on the long-term performance of these alloys in EOR wells in combination with the more stringent requirements for Class VI wells suggests otherwise. Introduction The recent significant influx of large amounts of government incentives for a variety of green initiatives including CCS and CCUS has created a rush to drill and complete CO2 injection wells. However, the necessary corrosion data to make informed choices for corrosion resistance in these wells is minimal at best. Some oil and gas professionals have argued that there is no difference between the more than 40 years of petroleum experience with CO2 EOR and planned CCS wells. This comparison is not a valid one and can be risky considering the need for very long-term containment of CO2 required by regulators. This article presents a comparison between CO2 EOR and CCS for injection well metallurgy and explains why this comparison is invalid. Background and Comparisons There is a 50-year successful history of CO2 EOR in petroleum production that has led to a consensus, largely without merit, that corrosion of injection-well equipment is manageable and does not result in long-term degradation of certain components such as casing. The reason there is little or no merit to applying this experience to CO2 CCS wells is the lack of data specific to the long-term corrosion resistance of casing that remains in the EOR wells. Rather, the industry generally simply plugs these wells with cement, and in the majority of cases without examining the casing before abandoning. Furthermore, industry rarely returns to inspect them after years of abandonment. In a few instances, logging and retrieval of cement cores and casing have been performed and analyzed. For example, analysis of cement and casing from the SACROC field that had been exposed to CO2 for over 30 years showed corrosion along the casing-cement interface (Carey et al. 2007). Laumb et al. (2016) reported substantial casing corrosion for a CO2 EOR well in the Weyburn field based on a series of logs over several years. Koplos et al. (2007) provided survey data from numerous CO2 EOR wells and found that 11.1% of the wells failed mechanical integrity tests and concluded that injection-well mechanical integrity is a concern for CO2 injection and storage due to the corrosivity of CO2 on downhole materials.