The Impact of CO2 Injection for EOR its Breakthrough on Corrosion and Integrity of New and Existing Facilities

摘要

Carbon Dioxide (CO2) Injections for Enhanced Oil Recovery (EOR) is used to increase the amount of crude oil that can be extracted from reservoirs. The CO2 injected becomes miscible with the reservoir oil. The resulting miscible fluid has the favorable properties of lower viscosity, enhanced mobility and lower interfacial tension as compared to an oil reservoir without CO2. However, the produced oil through this EOR contains greater amounts of CO2 and with the re-injection of produced CO2 this breakthrough will increase over time. This paper is based on Abu Dhabi Company for Onshore Petroleum Operations' (ADCO) experience with regards to CO2 EOR studies on asset integrity, material selection and corrosion mitigation. It serves as a guide to the main factors effecting CO2 corrosion, an assessment on what to look for in major equipment and the recommended material of construction and corrosion mitigation / control methods. Dry CO2 is not corrosive, however when dissolved in an aqueous phase it will produce carbonic acid (H2CO3) which starts the corrosion process. Under ideal conditions Iron Carbonate (FeCO3) scales will form which act as a protective layer preventing further corrosion. As the CO2 increases this will increase the corrosion rate as no protective scale will be present. Factors effecting CO2 corrosion and the FeCO3 protective scale are discussed; Water Wetting, Partial Pressure, Temperature, pH, Flow Regime & Velocity and Effect of H2S. In addition, a corrosion assessment highlighting areas of importance, material selection and mitigation methods is made on new and existing facilities; CO2 Injection Systems, Downhole Equipment, New Oil Producers and Existing Facilities. Lack of free water will prevent any CO2 corrosion from occurring. This is especially important in the injection systems for transporting CO2 as, in the absence of free water, Carbon Steel can be used. Based on ADCO's experience, downhole completion material of non-sour CO2 injector wells should be Super 13 Chromium and for Oil Producers Carbon Steel with Corrosion Inhibition with Nickel Alloy for the tubing section under the packer. For Oil Producers, this is subject to a case by case study. The use of Corrosion Resistant Alloys (CRA) or going with Carbon Steel with Corrosion Inhibition is the main dilemma. This is dependent on the dominating form of corrosion, formation of protective scales and the ability to maintain a stringent corrosion mitigation and monitoring regime. Finally, for existing equipment, evaluation of the current condition of the equipment is important. This will guide the mitigations required. Some prevention methods include corrosion inhibition, neutralizing acidity of service and material upgrade to CRA. Type of method used should be based on company preference and life cycle cost analysis. This paper serves as a guide to ADCO's experience for knowledge sharing and further development of ideas and innovations.