Laboratory Studies for Light-Oil Air Injection Projects: Potential Application in Handil Field
- Cedric Clara (Total Exploration Production) | Marc Durandeau (Total Exploration Production) | Gerard Quenault (Total Exploration Production) | Tuyet-Hang Nguyen (Centre National de la Recherche Scientifique)
- Document ID
- Society of Petroleum Engineers
- SPE Reservoir Evaluation & Engineering
- Publication Date
- June 2000
- Document Type
- Journal Paper
- 239 - 248
- 2000. Society of Petroleum Engineers
- 5.3.4 Reduction of Residual Oil Saturation, 5.2.1 Phase Behavior and PVT Measurements, 4.1.5 Processing Equipment, 5.4.2 Gas Injection Methods, 4.1.2 Separation and Treating, 5.7.2 Recovery Factors, 2.4.3 Sand/Solids Control, 5.4 Enhanced Recovery, 4.3.4 Scale, 5.5.2 Core Analysis, 5.8.7 Carbonate Reservoir, 5.4.7 Chemical Flooding Methods (e.g., Polymer, Solvent, Nitrogen, Immiscible CO2, Surfactant, Vapex), 1.6.9 Coring, Fishing
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Air injection into light-oil reservoirs is now a proven field technique.Because of the unlimited availability and the nil access cost of the injectant,the application potential of this improved recovery process is promising whenassociated with the lack of available hydrocarbon gas sources for injection.One of the keys of a successful air injection project is the evaluation of theprocess by carrying out representative laboratory studies. Therefore, anoriginal laboratory strategy was proposed to assess the recovery potential byair injection into light-oil reservoirs, and to help the determination and thequantification of optimal operating conditions.
In this paper, the air injection technique applied to light-oil reservoirsis explained. Then, the laboratory strategy proposed for the evaluation of anair injection project is described, and the experimental objectives, devices,and procedures are explained. In order to provide reliable experimental data,high-pressure and high-temperature experiments (up to 40 MPa and 500°C) areperformed with consolidated reservoir cores and reservoir oils, atrepresentative conditions of the air injection process in light-oilreservoirs.
Finally, a laboratory evaluation regarding a potential application for anair injection pilot in the Handil field (Mahakam delta, Indonesia) is presentedand discussed.
Air Injection Process into Light-Oil Reservoirs.
When air is injected into a reservoir, the oxygen contained in the airreacts with the hydrocarbons by various oxidation reactions. Heat is evolvedfrom these reactions. High initial reservoir temperatures promote larger heatproduction. Two study cases must then be differentiated in the light-oilreservoir.
1. When the thermal losses through the rock are limited compared with theheat generated by the reactions, the temperature in the reservoir increases. Inthis case, complete oxidation reactions providing carbon-oxide gases can beself-ignited in the reservoir. As reported in recent studies, 1 theoxygen is then consumed in a confined zone called an oxidation (or combustion)front. The size of this zone depends on the air injection rate, thecharacteristics of the oil, and the formation. In light-oil reservoirs, typicaloxidation front temperatures of 200 to 400°C (about 400 to 800°F) can bereached. The produced combustion gases consist of CO 2 and CO withCO/CO2˜0.15, depending on the temperatures reached and the oilcharacteristics.
2. When the thermal losses through the rock are high, or when the heatrelease is not high enough to increase the temperature significantly (in thecase of high-water saturations or low-oil saturations), the oxidation reactionsoccur at a temperature close to the initial reservoir temperature. In thiscase, oxidation reactions can be partial with a lower carbon-oxide generationthan in the previous case. The oxygen consumption occurs then through a largerreservoir zone, the size of which depends upon the oilreactivity.2
Several field experiences**3,4 have shown that high levels ofCO2 may be produced. This would suggest that spontaneous ignition,with generation of a high-temperature front and the production of associatedcarbon-oxide gases, is most likely occurring in light-oil reservoirs. Thegeneration of a high-temperature oxidation zone (200 to 400°C) is preferablebecause of a higher oxygen uptake potential, a more efficient carbon-oxidegeneration, and the creation of an oil bank downstream of the thermal front.Both of the latter factors contribute to the improvement of the recovery. Inboth cases, the important point to assess is oxygen consumption to preventoxygen arrival at the producers. This is one of the main objectives of airinjection experiments.
Reservoir Zones to be Distinguished.
When a high-temperature thermal front is ignited, four main zones can bedistinguished in the reservoir (Fig. 1):
The zone swept by the combustion front, where the residual oil saturation islow and the temperature higher than the initial reservoir temperature.
The oxidation front where oxygen is consumed. The temperature can reach400°C Part of the original oil is burnt (about 5 to 10% OOIP) and CO2 and COare produced. The gas formed by the remaining nitrogen from the air and thecombustion gases is called "flue gas" (typically, 85% of N2 13% of CO2 and 2%of CO) and sweeps the reservoir downstream.
A short zone downstream of the combustion front where thermal effectsparticipate in the formation of an oil bank. This oil bank is partiallydisplaced by the flue gas and by hot water or a steam front according to thereservoir conditions.
A wide zone downstream of the combustion front where no thermal effectsoccur. This zone, which contains original oil, is not affected by the thermaleffects and is swept by the flue gas.
When the oxidation reactions occur at low temperature (close to thereservoir temperature), three main zones can be distinguished:
A zone around the injector which is swept by the injected air. In this area,residual oil saturation is low. The oil is partially oxidized but can no longerconsume oxygen.
A large oxidation zone where oxygen is consumed by the residual oil leftafter flue gas sweeping. The oxygen concentration in the gas phaseprogressively decreases from 21 to 0%.
A wide zone downstream of the oxidation zone, swept by the flue gas atreservoir temperature, as in the previous case (high-temperature front).However, in this case, less carbon oxides have been generated by oxidationreactions and the flue gas is mainly composed of nitrogen.
In practice, both cases can co-exist in a given reservoir, according to thelocal reservoir properties.
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