Total has been operating oil and gas production from a series of heterogeneous reservoirs offshore Abu Dhabi since 1974. One of the main oil producing reservoirs of Jurassic age has been the subject of a number of EOR studies at lab and field scale to achieve a higher ultimate recovery factor. In 1991, TABK initiated its first gas injection EOR Pilot with full-field expansion in 1997. In 2014 a successful Chemical EOR Pilot was carried out that showed a significant drop in residual oil saturation around the target well. As all the pumping equipment was available for the Chemical EOR project a window of opportunity opened up at short notice to perform a second EOR test on other wells. The literature has recently highlighted successful applications of a relatively cheap commercially available enzyme in mature oil wells around the world with no environmental impact. This would be the first Enzyme EOR application in the Middle Eastern carbonates and, if successful, could provide a logistically simple, cheap method for enhancing oil recovery and assist Abu Dhabi to achieve its objective of 70% recovery factors. Although there had been no time to evaluate the product in Total’s labs it was decided to go ahead with the test anyway in the spirit of supporting ADNOC’s initiative to accelerate the application of emerging technologies. This paper discusses the design, reservoir monitoring and lessons learnt from a "Huff-n- Puff" application of Enzyme EOR. In terms of operations, the campaign was completed successfully; it demonstrated that the application poses no risk of flow assurance or to the environment and has provided invaluable experience of incorporating an EOR Pilot in day-to-day operations. In terms of EOR effect, an increase in oil rate is observed in only one well with no significant decrease in the water cut; in addition, the increase could be equally explained by well stimulation and/or better well stability (less slugging).
Total has been operating oil and gas production from a series of heterogeneous reservoirs offshore Abu Dhabi since 1974. Today's world class recovery factor is due to early application of new technologies such as ESPs, gas lift, multi-lateral wells, field-wide tracer and state-of-the art reservoir monitoring and well management. But the main contributor to this high recovery factor is the application of EOR through Immiscible Tertiary Gas Injection since as early as 1991 in 2 of the main reservoirs, it resulted in a recovery factor of over 50% in one of the main reservoir; a top class achievement for a carbonate reservoir and it is still contributing to more than 15% of today's field production. After 17 years of production, the water cut reached almost 90% in one of the main reservoir. It was imperative to improve oil mobility and recovery in the reservoir to guarantee long term production. Of the various EOR methods considered, injection of natural gas was found to be the most technically and commercially viable. Several laboratory experiments and simulation studies have been performed to confirm the benefit of gas injection. Then, 2 successful pilots in 1991 and 1993 resulted in the decision to develop the technique on a full field configuration. The Tertiary Gas Injection has been developed on the 2 main reservoirs of the field. These 2 reservoirs have comparable OOIP but very different properties and configuration. One reservoir is 160m thick with good vertical communication and has pressure support by an active bottom aquifer. The second reservoir has 14 thin layers; each layer is 3 to 20m thick and is separated from each other by anhydrite layers with no aquifer support. This paper will describe the practical experience of immiscible Tertiary gas injection, present the results after 24 years of injection and analyze the possible reasons for differences in performance between the wells and reservoirs. In addition, it will describe how today's strong reservoir management, integrating surface constraints, helps to optimize the production leading to a constant level of production over the past 4 years; which, for a mature oil field that normally declines at 10–15% per year, represents a great achievement.
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