EOS Modeling and Experimental Observations of Three-Hydrocarbon-Phase Equilibria

Abstract

An equation-of-state (EOS) fluid characterization has been developed to model three-hydrocarbon-phase equilibria. The fluid characterization was developed as part of the enriched-gas EOR research program for the Kuparuk hydrocarbon miscible flood on the North Slope of Alaska. Laboratory experiments with the Kuparuk fluid system have quantitatively identified the third hydrocarbon phase as a second equilibrium liquid, high in asphaltene content and 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 of the third phase and the oil's pentane-insoluble fraction. The characterization uses a total of 16 components, with the heaviest two representing the pentane-soluble and pentane-insoluble portions of the C36+ fraction. The properties of these heavy pseudocomponents control the development and behavior of the heavy phase. The EOS fluid characterization was used to study three-phase, enriched-gas-drive displacement mechanisms. For the Kuparuk fluids, a condensing/vaporizing displacement mechanism is predicted in a three-phase environment Reservoir-condition micromodel displacements were conducted to observe the phase behavior and displacement mechanisms during Kuparuk enriched-gas displacements. Micromodel observations are consistent with a near-miscible condensing/vaporizing mechanism and qualitatively agree with EOS predictions. Introduction A hydrocarbon miscible flood is being conducted in the Kuparuk River Field on 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 Sands of the Kuparuk River formation, a stratified and highly faulted sandstone reservoir. The enriched gas injected at the project is a blend of lean produced gas with scrubber and low-temperature separator liquids (enriching fluids)produced onsite. Project design calls for the injection of a 30% hydrocarbon pore-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 the reservoir. 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 weight percent of the C7+ fraction. An extensive laboratory program was undertaken to provide phase behavior data for designing and operating the EOR project. The laboratory program identified a third hydrocarbon phase when miscible injectant was mixed with reservoir oil. The three-phase equilibria observed with the Kuparuk oils and enriched gases differ from those reported in the literature for other enriched gas/crude oil mixtures and CO2/hydrocarbon mixtures. In the systems reported in the literature, three phases exist in a relatively narrow temperature-pressure composition window and consist of a liquid, a vapor, and a second liquid lighter than the first and rich in components comprising the injectant. In some systems, asphaltenic flocculation and deposition may also occur.

Performance evaluation and optimization of the Kuparuk hydrocarbon miscible water-alternating-gas flood

“…have been conducted. The 2Z-04 oil has a low asphaltene content, while the 1E-08 oil, whose composition is reported by Godbole et al, (1992) has one of the richer asphaltene contents in the field. The slimtube results indicated that the two oils have essentially the same minimum miscibility enrichment (MME) level (see Fig.…”

“…The EOS developed by Godbole et al (1992) predicts the formation of a second, more viscous, liquid hydrocarbon phase. The three hydrocarbon phases exist over a relatively large portion of the phase envelope.…”

“…Initially the EOS used in the simulation studies, reported in this paper, was a 12-component adaptation of the 16-component Godbole et al (1992) formulation. When this EOS was used in finely gridded models, it occasionally predicted the formation of a second liquid phase.…”

Thermodynamic modelling of asphaltene precipitation and related phenomena

“…Of particular interest from a modelling perspective is the nature of the instability responsible for the precipitation of asphaltene-rich phases for which both solid-liquid [48,49] and liquid-liquid [50] immiscibilities have been suggested, which has given rise to some disagreement in the approach to model these systems.…”

Estimating Onset of Precipitation of Dissolved Asphaltene in the Solution of Solvent + Precipitant Using Artificial Neural Network Technique

“…Scatchard-Hildebrand [7], Flory-Huggins [7,36], and Scott-Magat [37] polymer solution theories) to model phase behavior of asphaltenecontaining fluids [1,2,5,7,8,14,[20][21][22][23]. In addition to these models, there are also other models, which are based on cubic equations of state [17,24]. New thermodynamic models have recently been developed, which can take into account the micellar / aggregation natures of asphaltenes [5,13,16,[26][27][28][29][30][31].…”