Only next to thermal processes used to produce heavy oil, gas injection is the second most common enhanced oil recovery process. To increase the extent of effects of the gas on the heavy and semi-heavy oils in the reservoir by gas injection, the gas is generally injected intermittently with water. This mode of injection is called Water-Alternating- Gas (WAG) method. In recent years, there has been an increasing interest in WAG process both miscible and immiscible.

In this paper, an experimental study of immiscible Heated WAG (Heated Water-Alternating-Heated Gas) injection into a sand pack is presented for the first time. This new method is a combination of WAG and thermal process and can be used to produce heavy and semi-heavy oils from hydrocarbon reservoirs. Oil recovery efficiency resulting from Heated WAG injection was significant in comparison with unheated WAG injection. The original reservoir fluid was dead oil, and core flooding experiments were performed on it using carbon dioxide as the injection gas. In this experimental study, the sand pack was initially saturated with dead oil and irreducible formation water. A number of WAG and Heated WAG cycles with low and constant rate and, below the minimum miscibility pressure for this system were injected into sand pack alternatively.

Results of laboratory tests showed that oil recovery efficiency resulting from the immiscible Heated WAG injection is about 15% more than that of unheated WAG injection. These results also indicate that using heated water and heated CO2 instead of unheated water and CO2 can lead to interfacial tension reduction, oil swelling and viscosity reduction. Therefore, immiscible heated WAG injection can be used as an effective and feasible enhanced oil recovery method in heavy and semi-heavy oil reservoirs with significant improved results.

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