Abstract

The 8 TH reservoir is a "supermature" field which has been in production for more than 65 years. It was waterflooded for more than 50 years resulting in a current water cut of 96 %. The field contains medium viscous oil (in-situ viscosity 19 cP) and hence was considered for polymer injection despite the high water cut which was suggested by some authors to be challenging for polymer injection.

An inverted five spot unconfined polymer injection pilot was performed to reduce the subsurface uncertainties, determine if polymer flooding could lead to incremental oil in "supermature" fields, improve the operating and monitoring capabilities and improve the economic model for full-field implementation.

The results of the pilot show that an increase in 5- 10 % of the recovery factor can be achieved in the pilot area. The reasons for incremental oil production by polymer injection in this "supermature" field are acceleration along high permeable flow paths but more importantly substantial flow diversion in this heterogeneous reservoir. In the pilot area, the highest oil production since 1978 was achieved.

The main uncertainties related to surface handling of the polymer solution prior to injection, injectivity and incremental oil recovery could be reduced by monitoring of various parameters. In particular tracers and molecular weight distribution of polymers were measured to improve the understanding of the polymer solution effects on reservoir performance.

In addition, numerical simulations concerning injectivity and reservoir performance were performed to further improve the understanding of the processes and be able to optimize the operations. The simulations included polymer solution injection induced fractures as well as geological, reservoir fluid/relative permeability and polymer solution property uncertainties and allowed forecasting under uncertainty.

The cost structure of the polymer pilot was used to evaluate full-field economics taking learning curves, upscaling and costs optimisations into account.

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