Managing Accelerated Water Breakthrough in High Permeability Contrast Waterflood Reservoirs, and Achieving Production Conformance Through Injection Redistribution Strategy
Authors: Nalasavagan Kausalyah , Abdul Rahman Harun bin , Azman Mohd Fairuz bin , Bakar Rizal bin 
Published: October 2022

Waterflooding for pressure maintenance often seems straightforward with key objective being voidage replacement as demonstrated through material balance. Even though pressure maintenance can be achieved, it may not directly translate into higher production if efficient sweep is not attained, and oil has been bypassed. This paper demonstrates a real case study at Field S on how swift and integrated mitigation plan successfully addressed the production impairment during the initial water injection period.

Field S started injection through newly drilled peripheral water injectors to fill up the voidage created by earlier production volumes hence tempered the pressure decline. Reservoir response was observed from downhole pressure gauges as early as after the first few days of injection in several producers. The first water breakthrough was then identified few months after at the most up-dip wells and resulted in producers died off. At the expense of voidage replacement ratio (VRR) performance, intermittent flow strategy was deployed as temporary measure, to revive and keep the producers flowing, while flow diverter chemicals have been under evaluation to serve as a more sustainable solution.

Impacted producers were determined to have good connectivity with the injectors as shown by streamline analysis, diagnostic plot, salinity measurement and log correlation. This is easily validated with pressure response recorded via PDG (pressure downhole gauge) throughout injection period. It was observed that high permeability contrast ratio presence across multiple sand lobes at the affected producers with the highest permeability was recorded up to Darcy range. While such contrast was absent at injectors, this specific sand lobe still effectively provides the preferential flow path between injectors to producers and lead to channeling effect.

Managing drawdown through choke optimization was ineffective as the short distance between injectors and producers allows rapid water charging through the high permeability streak. However, shutting-in injection temporarily managed to slow down water production almost promptly. Subsequently, intermittent injection strategy implementation enabled certain amount of solution gas being liberated to provide in-situ gas lift effect inside the tubing for continuous production.

The producers were successfully put back on production within weeks with close monitoring and surveillance. Next step, flow diverter chemical will be injected to partially block the channeling path, hence maximizing the well potential and oil recovery.

Production upset caused by early water breakthrough is a common issue in waterflood reservoir. However, by understanding the root cause, supported by prudent surveillance practices and operation flexibility, the production downtime can be minimized as showcased in this paper. Besides, geological and petrophysical input are pivotal in understanding reservoir or well performance issues.