Despite the increase of hydrocarbons exploitation from green fields in the last decades, the majority of the global production is still sustained by brown fields contribution. Rejuvenation of mature assets, as the one described in this work, plays a crucial role in current low oil price scenario, improving production with limited investments and risks.

Object of this work is an offshore oil field in the UK area in production since 1996. The field is developed by means of water injection for pressure maintenance and gas injection for disposal, with current water-cut higher than 90% and gas-breakthrough in wells close to the disposal area. After the acquisition of the operatorship in 2014, an asset rejuvenation project started, involving an integrated analysis of the field, based on the review of all available static and dynamic data. Combination of basic reservoir engineering tools and advanced modeling simulators was the key element of the performed analysis. This paper shows how an integrated workflow, combining skills from different professional families, allowed to find low cost opportunities with short time-to-market.

Production data analysis highlighted low efficiency of current water injection: majority of the injected volume is produced without displacing additional oil. Moreover, the new reservoir compositional model showed presence of by-passed oil in the crestal part of the field not displaced due to gravitational segregation effect.

Thanks to the better understanding of the field characteristics and fluids movement, different actions were planned in order to maximize oil recovery. In particular, a screening of possible IOR/EOR techniques showed immiscible WAG as the most promising one to recover un-swept attic oil. Several sensitivities were performed on water and gas injection rates, cycles duration and gas composition, in order to properly evaluate and maximize the expected additional recovery. Based on modeling results, two currently shut-in injectors were selected for a WAG pilot phase. The feasibility study highlighted that only minor plant changes were required, due to the availability of both water and gas injection facilities. This aspect drove the project economics into favorable evaluation. Moreover, moving gas injection from disposal to WAG mitigates well production problems in the disposing area, turning gas injection from an issue to opportunity extending field life.

This paper gives a detailed description of the rejuvenation project ongoing on an UK field which main outcome is the start-up of a WAG project. Advanced workflow, combining streamlines and conventional simulators, was used for waterflooding assessment and optimization. This integrated project was carried out with short time to market and minimal expenditure, showing how EOR processes can be an opportunity for field rejuvenation even in a low oil price environment.

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