A chemical Enhanced Oil Recovery process by means of polymerflooding has been implemented successfully in a large sandstone field in the south of Oman since 2010. To date, very good response was observed from the polymer flood due to improved sweep efficiency. A common measure of success for such a chemical EOR process is the incremental oil Recovery Factor over the existing mature waterflood.

One of the challenges in this EOR project is the estimation of the incremental oil reserves attributed to polymer flooding. The difficulty is due to the lack of analogue fields where polymer flooding is implemented. Furthermore, polymer flooding has been implemented over a mature waterflood making it difficult to allocate the remaining oil reserves.

This paper is presenting the oil reserves estimation methodology for the chemical EOR project. The definitions for estimation, classification and reporting of petroleum resources are based on the society of Petroleum Engineers (SPE) Petroleum Resources Management System (SPE-PRMS). This methodology is based on calculation of patterns STOIIP and range of recovery factors extrapolated from different sources (simulations, pilots, corefloods, analytical analysis). Furthermore, the oil reserves estimation was supported by full field 3D dynamic models where the initial period of polymerflood has been used for calibration. It was concluded that the polymerflood can give incremental recovery factor of about 10% on top of the waterflood recovery.

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