Solubility and Displacement Behavior of a Viscous Crude With CO2 and Hydrocarbon Gases
- R.A. DeRuiter (Arco Alaska Inc.) | L.J. Nash (ARCO Oil and Gas Co.) | M.S. Singletary (ARCO Oil and Gas Co.)
- Document ID
- Society of Petroleum Engineers
- SPE Reservoir Engineering
- Publication Date
- May 1994
- Document Type
- Journal Paper
- 101 - 106
- 1994. Society of Petroleum Engineers
- 1.8 Formation Damage, 5.4.1 Waterflooding, 5.4.10 Microbial Methods, 4.3.3 Aspaltenes, 4.6 Natural Gas, 5.2.1 Phase Behavior and PVT Measurements, 5.4.2 Gas Injection Methods, 5.5 Reservoir Simulation, 4.1.4 Gas Processing
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This study investigates the solubility and displacement behavior of aviscous crude oil with carbon dioxide and light hydrocarbon gases. The oil isfrom the West Sak formation, which predominantly overlies the Kupawk formationin the Kupamk River Unit. North Slope, Alaska. The West Sak formation hasvariable oil quality both vertically and laterally within the reservoir. Thereservoir temperature for this formation is low because of the extensivepermafrost zone in the region. Two oil samples with gravities of 14.0 and 18.5deg. API (0.9725 and 0.9433 g/cm ) are studied in this paper over a temperaturerange of 60 deg. to 75 deg. F (15 deg. to 24 deg. C) and pressures up to 2000psi (13.8 MPa).
The solubility behavior of West Sak gas/oil mixtures is investigated instatic PVT experiments. Methane and carbon dioxide solubilities. measured interms of K-values, are found to be functions of pressure and temperature butnot oil composition. Ethane solubility behavior shows liquid-liquid phaseequilibria with both bubble Point and dew point phenomena analogous tovapor-liquid behavior. Propane and point phenomena analogous to vapor-liquidbehavior. Propane and n-butane are found to be first-contact miscible with WestSak oil except at high solvent concentrations where the precipitation of asolid, asphaltenic phase occurs. Multi-contact experiments with a generic richgas/methane mixture and West Sak oil show extensive oil stripping into theupper solvent phase resulting in an increasingly viscous residual oil phaseafter several contacts.
The dynamic behavior of the West Sak gas/oil mixtures is investigated withslim tube displacements. Slim tube displacements with ethane show thatmiscibility is possible and occurs via a condensing-vaporizing mechanism. Slimtube displacements with a generic rich gas/lean gas mixture show first-contactmiscible, multi-contact miscible, and immiscible behavior with increased leangas dilution. Unusual behavior in several of the displacements is attributed tothree-phase equilibria.
The West Sak formation is located on the North Slope of Alaska andpredominantly overlies the Kuparuk formation in the Kupawk River predominantlyoverlies the Kuparuk formation in the Kupawk River Unit (1). A structure map ofthe reservoir is given in Figure 1 which shows the approximate location of theoil accumulation. Figure 2 shows a type log for the reservoir. Reservoir depthranges from 2000 to 4500 feet (610 to 1370 m); however, due to the proximity ofthe permafrost in the region, the reservoir temperature ranges from onlypermafrost in the region, the reservoir temperature ranges from only 50 deg. to10 deg. F (10 deg. to 38 deg. C) at these depths.
The West Sak reservoir covers an area of approximately 300 square miles (770km) and is estimated to contain 13 to 20 billion barrels (2.0 X 10 to 3.2 X 10m ) of oil in place. Oil gravity ranges from 12 to 22 deg. API (0.9860 to0.9218 g/cm ) and varies both vertically and laterally within the reservoir.The oil is considered to be saturated at reservoir conditions with methane asthe predominant solution gas component.
The West Sak reservoir is not currently under development. In 1983. awaterflood pilot was initiated to evaluate waterflood response and drillingtechnology necessary for field development. Although the pilot was considered atechnical success and improved the pilot was considered a technical success andimproved the understanding of the potential reservoir performance, theperformance indicated that the reservoir would be only marginally economic atcurrent oil price conditions. Consequently. considerable effort has been spentto develop alternative technologies to produce the West Sak reservoir,including immiscible or miscible gas injection. The abundance of a variety ofgas streams on the North Slope makes gas injection look very promising fordeveloping the West Sak reservoir.
In order to accurately assess the potential of any recovery method involvinggas injection for West Sak, it is essential to have a thorough understanding ofthe physical properties of West Sak oil as well as the phase behavior relatedto the injectant gas/oil system. In an immiscible gas process in a viscousreservoir, the dominant phase behavior mechanisms affecting reservoirperformance are viscosity reduction and oil phase swelling. In addition, oilstripping by the injection gas can lead to improved recovery. In order toquantify these benefits, experimental gas solubility measurements are required.In a miscible gas process, the minimum miscibility pressure (MMP) or theminimum miscibility enrichment (MME) are two important parameters affectingprocess performance. In order to quantify these parameters affecting processperformance. In order to quantify these parameters, slim tube displacements areusually performed. parameters, slim tube displacements are usually performed.In this study, static equilibrium experiments were performed to measure thesolubilities of methane, ethane, propane, n-butane, and carbon dioxide (CO ) inWest Sak oils. Physical properties, including gas-oil ratio (GOR), viscosity,density, volume, and composition, were measured for the live phases presentafter equilibration in singlecontact and multi-contact experiments.
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