The Medicine Hat Glauconitic C Pool is located partially inside the city limits of Medicine Hat, Alberta, Canada. This 15-18° API oil pool is under waterflood. Reservoir management strategies in the pool are limited by the reservoir quality, wellbore architecture and business environment. Surface land access due to the expanding Medicine Hat city limits and pre-existing wellbore orientations have constrained the waterflood pattern and infill drilling options. Current estimates indicate 21% of the oil in place will be recovered at the end of the waterflood.
The polymer flood pilot was started in 2012 with a goal to achieve 6% incremental recovery with a one year initial response time. The pilot's designed injection rate was 6,300 bbl/d (1000 m3/d) in 5 injectors, each representing different reservoir conditions and injection patterns. Following injection, pre-existing water channels and high permeability streaks resulted in rapid polymer breakthrough in as little as 48 hours in some cases.
To increase the efficiency of the polymer flood and reduce cycling polymerized water, a new approach to reservoir management had to be considered:
Each of the 5 patterns inside the pilot was monitored and managed individually, with a fit-for-purpose strategy in mind.
Although 1 year to response was estimated, after four months, oil rates and oil cuts increased unexpectedly. However, after reaching peak production, the expected steep decline was observed.
New reservoir management strategies were implemented in order to slow the decline and attempt to increase the incremental recovery from 6% to 10%: attempts to block water channels in the injectors, producer shut-ins and frequent injection target changes proved beneficial.
The polymer pilot has exceeded expectations to date.
This case study provides an outline of the changes that were made and the results that have been observed.