EOS Modeling and Experimental Observations of Three-Hydrocarbon-Phase Equilibria
- S.P. Godbole (ARCO E and P Technology) | K.J. Thele (ARCO E and P Technology) | E.W. Reinbold (Arco Alaska Inc.)
- Document ID
- Society of Petroleum Engineers
- SPE Reservoir Engineering
- Publication Date
- May 1995
- Document Type
- Journal Paper
- 101 - 108
- 1995. Society of Petroleum Engineers
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- 413 since 2007
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An equation-of-state (EOS) fluid characterization has been developed tomodel three-hydrocarbon-phase equilibria. The fluid characterization wasdeveloped as part of the enriched-gas EOR research program for the Kuparukhydrocarbon miscible flood on the North Slope of Alaska. Laboratory experimentswith the Kuparuk fluid system have quantitatively identified the thirdhydrocarbon phase as a second equilibrium liquid, high in asphaltene contentand heavier than the original oil.
A three-phase EOS fluid characterization was developed to match both two-and three-phase experimental data using a modified Peng-Robinson EOS.Experimental observations identified a relationship between the development ofthe third phase and the oil's pentane-insoluble fraction. The characterizationuses a total of 16 components, with the heaviest two representing thepentane-soluble and pentane-insoluble portions of the C36+ fraction. Theproperties of these heavy pseudocomponents control the development and behaviorof the heavy phase.
The EOS fluid characterization was used to study three-phase,enriched-gas-drive displacement mechanisms. For the Kuparuk fluids, acondensing/vaporizing displacement mechanism is predicted in a three-phaseenvironment
Reservoir-condition micromodel displacements were conducted to observe thephase behavior and displacement mechanisms during Kuparuk enriched-gasdisplacements. Micromodel observations are consistent with a near-misciblecondensing/vaporizing mechanism and qualitatively agree with EOSpredictions.
A hydrocarbon miscible flood is being conducted in the Kuparuk River Fieldon the North Slope of Alaska. The EOR project covers an area of 5120 acres(2070 ha) at Drill Sites 1Y and 2Z. The flood is conducted in the A and C Sandsof the Kuparuk River formation, a stratified and highly faulted sandstonereservoir. The enriched gas injected at the project is a blend of lean producedgas with scrubber and low-temperature separator liquids (enriching fluids)produced onsite. Project design calls for the injection of a 30% hydrocarbonpore-volume slug of enriched gas injected alternately with water at a 1:1volume ratio for mobility control.
Fluid properties at Kuparuk vary somewhat across the areal extent of thereservoir. Oil gravities range from 18 to 25 degrees API (0.90 to 0.95 g/cm3)and asphaltene content (measured as pentane insolubles) from 3 to 17 weightpercent of the C7+ fraction.
An extensive laboratory program was undertaken to provide phase behaviordata for designing and operating the EOR project. The laboratory programidentified a third hydrocarbon phase when miscible injectant was mixed withreservoir oil.
The three-phase equilibria observed with the Kuparuk oils and enriched gasesdiffer from those reported in the literature for other enriched gas/crude oilmixtures and CO2/hydrocarbon mixtures. In the systems reported in theliterature, three phases exist in a relatively narrowtemperature-pressurecomposition window and consist of a liquid, a vapor, and asecond liquid lighter than the first and rich in components comprising theinjectant. In some systems, asphaltenic flocculation and deposition may alsooccur.
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