Re-Development of a Forty-Year-Old Brown Field in South of Oman Producing from Five Different Stacked Reservoirs, Resulting in 50% Oil Gain by Doubling Water Injection

Abstract This paper showcases the impact of doubling water injection rate from 25k bbl/day to 50k bbl/day in a forty-year-old brown field which lead to 50% oil gain. This was achieved by executing activities to redevelop the five stacked reservoirs in this brown field for better reservoir management. The main activities in the field focused on: (1) de-commingling the water flooded reservoirs from the depletion reservoirs, (2) improving the vertical conformance of the waterflood units via dedicated injection through re-completing the injectors to tubing and casing injectors, Long & Short strings, (3) infill drilling to complete the patterns from 5-spot to 9-spot patterns to improve waterflood sweep, and (4) execute WRM optimization activities to increase injectivity in the water flooded reservoirs. One of the main challenges in wells commingling production form different units is that individual unit's contribution is not well understood, particularly when the reservoirs have different rock and fluid properties and under different drive mechanisms. Furthermore, there is not much control on each unit production/injection contribution when they are commingled. Therefore, a re-development plan calls for de-commingling production/injection and further infill drill wells to have better understanding and control on the individual unit performance. This approach improved the conformance of the five reservoir units, hence injection and production. Despite the challenges related to urban planning, surface capacity and the ongoing drilling activities, the executed activities resulted in a step change in managing the five different reservoirs, 50% oil production gain, 100% increase in injection as well as new production data from dedicated individual units for the first time from this old brown field. In summary, improving reservoir management through de-commingling waterflooded reservoirs as well as further infill drilling and change in water injectors completions resulted in a step change in the ability to inject water and hence production growth. The new development has opened further opportunities to continue developing reservoir units that used to be commingled resulting in reserves additions up to 10% of total field reserves. Furthermore, new approach is followed to produce the extremely high viscos oil of a reservoir by commingling, at surface, with nearby producers to ensure produced water pushes the extremely high viscos oil from the wellhead to the station.