Experimental evaluation of the potential impacts of polymer breakthrough on topside operations at Yariguí-Cantagallo field conditions

Abstract

After a successful polymer injection pilot, Ecopetrol plans to deploy at full-field scale this enhanced oil recovery (EOR) technology on the Yariguí-Cantagallo field. Although a significant increase oil production is expected, the impact of the residual polymer on the produced water cycle should not be neglected. Indeed, after the polymer breakthrough, a significant part of the EOR chemical will be present in the produced fluids, and this may negatively impact the water/oil separation and the water treatment processes. An early review of this scenario provides an accurate vision of potential issues and, above all, enables to anticipate handling difficulties with produced fluids, and identifying mitigation strategies.

This paper proposes a specific and comprehensive experimental methodology to assess production risks using laboratory equipment designed to mimic the current separation processes of the Yariguí-Cantagallo field, which were as representative as possible. The objective is to highlight the impact of the residual polymer first on water/oil separation processes with bottle tests, electrostatic dehydration tests, and polymer fouling evaluation on heat exchangers and, second, on water treatment using long-term gravity separation tests, Jar test, flotation column, and walnut shell filtration unit. The assessment considered different scenarios in terms of polymer concentration, water-cut, water composition and initial oil content in the produced water. The compatibility between the polymer and some oilfield chemicals, such as demulsifiers and water clarifiers, was also investigated. The efficiency of these physical and chemical treatments was evaluated by monitoring the separation kinetics as well as by evaluating the quality of the phases with measures of water-in-oil content, oil-in-water content, or water turbidity.

For this case study and at laboratory scale, the polymer does not seem to stabilize tight emulsions, rather observing an improvement in water/oil separation kinetics. However, the quality of the separated water is strongly degraded with a higher oil content and some incompatibilities with current demulsifiers which reduce their efficiency have been observed. The risk of polymer precipitation or fouling on heat surface is very low under the experimental conditions tested. The performance of the different water treatment stages is slightly affected in the presence of polymer, even if the water quality remains good.

The operational risk assessment conclusions and pending recommendations draw the map of conditions where the residual polymer seems to cause problems or not. This anticipated experimental approach can provide clues and solutions to better manage the impact of the residual polymer in back produced fluids. Adjusting process parameters on existing surface facilities and working on chemical treatment optimization should ensure to produce oil, and release produced water on specifications. This challenge will be one of the keys for technical success and for upholding the expected economic performance of this EOR project.