Application of Enzyme EOR in a Mature UAE Offshore Carbonate Oil Field

Abstract

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).

Potentials of Enzyme Enhanced Oil Recovery: A Review

“…On the contrary, wettability alteration from weakly oil-wet/neutral-wet to more water-wet condition was hypothesised as one of the possible factors that militated against positive effect of enzyme EOR applications in three of the four wells in carbonate reservoir studied by Jabbar et al [27]. They however did not carry out any wettability investigations on the reservoir used in their study.…”

“…This further showed the capacity of enzymes to withstand high salinity and their efficiency in such salinity medium. Also in the enzyme EOR study carried out by Jabbar et al [27] on four carbonate wells with salinity range of 222,000 -247,300 ppm, they observed no difference in the behavior of the wells before and after it applications, which suggest its stability in that reservoir system.…”

“…Most studies that reported on enzymes EOR however did not investigate their solubility. For instance, in the enzyme EOR study carried out by Jabbar et al [27], they observed hard scale in the tubing used for enzyme slug injection, of which they did not know the source. This suggests the possibility of enzyme interactions with the tubing material and/or the transporting medium but since no prior test on the enzyme's behaviour in the brine was carried out, it was difficult to conclude on the source of the observed scale.…”

“…For example, Udoh and Vinogradov [26] investigated the aqueous behaviour of an enzyme in brines of different pH based on their composition and they observed stable behaviour of enzyme in all brines. Jabbar et al [27] also monitored the pH of the system during their enzyme EOR applications in four carbonate reservoir wells and they observed slight reduction in pH of two wells (wells 1 and 2), while no pH change was observed with the other two wells (wells 3 and 4). Furthermore, Udoh and Vinogradov [5] also monitored the pH of all the effluents from their carbonate core flooding and they observed distinct pH trend at low temperature.…”

“…The first application of enzyme EOR in carbonate reservoir was reported by Jabbar et al [27]. This field application was carried out on one of the carbonate reservoirs in the Middle Eastern without any prior laboratory test on rock and fluid compatibility of the process.…”