Among various Enhanced Oil Recovery (EOR) processes and techniques, Malaysia's matured offshore oilfield which is currently under water injection for pressure maintenance appears to be amenable to water alternating gas (WAG) implementation. EOR screening studies show that WAG EOR application is ranked high among other EOR techniques and stands better chance of success techno-economically.

This paper addresses the immiscible water alternating gas (IWAG) core flooding experiments which were conducted to further investigate and to validate the efficiency of IWAG as a viable EOR technique in one of the highly-faulted, multi-stack reservoirs offshore Malaysia. The IWAG coreflooding experiments were performed on field core composites using current field production gas which has more than 60 % mole CO2. The composite core samples were initially saturated with live oil and irreducible formation water and then flooded with formation water to residual oil saturation at reservoir conditions. Following waterflooding, a number of WAG cycle slugs were injected. The displacements were conducted at pressures well below the estimated minimum miscibility pressure during these experiments.

The coreflood experimental results show that the IWAG injection has a potential to recover up to 7.0 % additional oil recovery over waterflooding. Injection fluids are sea water and CO2 rich produced hydrocarbon gas. Furthermore, almost 2.0 % of this incremental oil recovery can be attributed mostly to the hysteresis effects from IWAG process. In conclusion, the results of this laboratory IWAG project has provided the pertinent data required for constructing a reservoir simulation prediction model under IWAG process. Instead of the conventional drainage-imbibition curves input, WAGHYSTER parameters established from IWAG coreflood matching has been used for IWAG prediction evaluation and optimization scenarios for full-field scale implementation. Despite the limited available laboratory data which was based on certain rock properties, the history-matched numerical IWAG coreflood model and the established parameters such as Land's parameter, secondary drainage reduction factor and residual oil modification fraction forms the basis of input to further evaluate the sensitivity of these parameters on IWAG full-field implementation.

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