Mitigating the Impact of CO2 Breakthrough within EOR Projects on the Surface Facilities Integrity
Authors: AlSuwaidi Mohamed Humaid , AlBreiki Najat Ahmed 
Published: November 2016

Carbon Dioxide (CO2) injections have the dual benefit of enhancing ultimate oil recovery and reducing the carbon footprint. Because of the economic and environmental benefits, Abu Dhabi Company for Onshore Petroleum Operations Ltd. (ADCO) is considering CO2 injection in its fields as an Enhanced Oil Recovery (EOR) mechanism. To get a firsthand assessment of the CO2 injection behavior, several pilots are planned and some are already in progress. This paper covers the main findings of Asab CO2-EOR Pilot Project; lessons learnt from previously implemented EOR project and challenges faced during the conceptual stage of this project.

To ensure smooth and uninterrupted flow of ADCO's oil production, it was imperative for the Technical Center – Engineering to be conscious about the surface facilities integrity, because the surface facilities as well as transfer lines and flow lines after CO2 injection would undergo material degradations due to corrosion with the existence of CO2 in different behaviors; whereas the long term integrity of the material components is critical to the injection pilot period of time.

Since the acceptance of CO2 injection as a safe and reliable EOR mechanism, it shall prove that the surface facilities were assessed from various aspects, which may be highlighting development of integrity issues before they become acute; therefore, different information were reviewed, including production profiles and the condition of existing facilities, hazards and risk indentification, materials of construction, corrosion related data, production and composition scenarios expected after CO2 breakthrough.

The main outcome of the risk management review and as part of mitigation, the CO2 shall be transported in a dense phase with a certain H2S concentration to reduce the risk of the corrosion rates on the transport pipeline. As well as, several recovery methods were proposed to reduce the CO2 impact on the downstream surface facilities to ensure their intigrity. Corrosion risk assessment considered as the backbone of this study as it provides the ammunition to enable appropriate selection of inspection, monitoring and mitigation strategies, implementation and analysis.

External corrosion specialist was consulted to undergo a study, which emphasized on evaluating the impact of Asab CO2 injection pilots project on existing and new facilities. The study aimed on predicting corrosion rates for carbon steel under different scenarios, which was used as an input for Technical Center – Engineering to decide whether carbon steel with inhibition or corrosion resistant alloys (CRA) would be more adequate from a techno-economical point of view.

During the performance of the work, the external specialist used the latest version of Multicorp (v. 5.2.105) as basis for predicting corrosion rates in CO2/H2S containing environments. It has been drawn from the study conducted that low concentrations of H2S decreased significantly CO2 corrosion rates under otherwise similar conditions, due the formation of semi-protective sulfide films. There is some degree of uncertainty on the corrosion rates predicted for Asab conditions because of high variability of the H2S concentration that can be expected after the CO2 breakthrough and its impact on corrosion.

The ways of mitigating CO2 corrosion constraints menace with the current technology of low costs material. Henceforth, it was noticed that the principles of corrosion must be understood to effectively select the suitable material and to design, fabricate, and use metal structures for the optimum economic life of surface facilities along with safety and the integrity of ADCO operations.