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.
W-field is a small satellite field that started seeing some means of pressure depletion. Field development study recommended waterflood as the most effective option to arrest the reservoir pressure decline and enhance the oil production and recovery. The size and the satellite location of the field could not economically justify a conventional water flood project. A "DumpFlood" concept was implemented where a single well is used as a source of water supply and inject domain. The well was perforated in the deeper water reservoir Z and on the injection target reservoir H. The well was completed by an advanced ESP that was designed to produce and inject in the same wellbore across the two set of perforations. Surveillance program was put in place and implemented focusing on reservoir pressure monitoring in the surrounding wells, production metering and periodical surface flow of the dump flood to assess its productivity and injectivity. Downhole gauges were installed in the dumpflood well across the two units to monitor the reservoir pressure behaviour and the calibration of the injection rate. The concept proved its success, an injection water rate of around 1200bpd was achieved in the target zone. Pressure response and some segneficant oil gain in the range of 40% was noticed in the w-feild. The concept is now under review for further implementations in the same field and the design is ongoing to apply the concept in other two fields in the area. The dumpflood concept allowed an economical waterflood project to be applied in Z fields with the expectation of significant oil recovery to be achieved.
X-field located in the west Central Oman is in a mature stage of development from the Permian Gharif formation reservoirs. These stacked reservoirs have been historically produced commingled since 1984 with natural depletion until 1998. Since then the field is under water flood. Produced water is mainly re-injected and gas is used for gas lift and the rest is liquefied and exported.
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