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Phase diagrams are graphical representations of the liquid, vapor, and solid phases that co-exist at various ranges of temperature and pressure within a reservoir. Ternary phase diagrams represent the phase behavior of mixtures containing three components in a triangular diagram. Phase behavior of mixtures containing three components is represented conveniently on a triangular diagram such as those shown inFigure 1. Such diagrams are based on the property of equilateral triangles that the sum of the perpendicular distances from any point to each side of the diagram is a constant equal to the length of any of the sides. Several other useful properties of triangular diagrams are a consequence of this fact.
- Information Technology > Knowledge Management (0.41)
- Information Technology > Communications > Collaboration (0.41)
Phase diagrams are graphical representations of the liquid, vapor, and solid phases that co-exist at various ranges of temperature and pressure within a reservoir. Quaternary phase diagrams represent the phase behavior of mixtures containing four components in a pyramid-shaped diagram (a tetrahedron). Phase diagrams for systems with four components can be represented conveniently on a tetrahedral diagram like that shown inFigure 1a, which shows a quaternary phase diagram calculated with the Peng-Robinson[1] equation of state for mixtures of methane (C1), C3, C6, and hexadecane (C16) at 200 F and 2,000 psia. These phase diagrams have a property similar to that of ternary diagrams: the sum of the lengths of perpendicular lines drawn from a composition point in the interior of the diagram to the four faces of the diagram is a constant length. Hence, the fractions of four components can be represented by an extension ofEq.
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Phase diagrams are graphical representations of the liquid, vapor, and solid phases that co-exist at various ranges of temperature and pressure within a reservoir. Binary phase diagrams describe the co-existence of two phases at a range of pressures for a given temperature. Figure 1 is a pressure-composition (p-x-y) phase diagram that shows typical vapor/liquid phase behavior for a binary system at a fixed temperature below the critical temperature of both components. At pressures below the vapor pressure of Component 2,pv2, any mixture of the two components forms a single vapor phase. For instance, at pressurepb, two phases will occur if the mole fraction of Component 1 lies betweenxB and xE.
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- Information Technology > Knowledge Management (0.41)
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Abstract Black-oil fluid properties are determined by lab measurements or can be calculated through flash calculations of the reservoir fluid. Allowing for a variable bubble-point pressure in black- or volatile-oil models requires a table of fluid properties be extended above the original bubble-point. Reservoir simulation accuracy, however, may be affected by discontinuities in the input data and poor predictions of extrapolated fluid properties. Common practice is to add surface gas to the original oil in the lab and increase the pressure to reach a new bubble-point. Another approach is to use linear extrapolation of oil and gas K-values with pressure on a log-log plot, where K-values are equal to 1.0 at a pseudo-critical or convergence pressure. The latter approach results in discontinuities in the phase behavior. We calculate continuous black-oil fluid properties above the original bubble-point by adding a fraction of the equilibrium gas at one bubble-point pressure to achieve a larger bubble-point pressure. This procedure continues until a critical point is reached at the top of the pseudocomponent pressure-composition diagram. Unlike other methods commonly used or recently proposed, the approach provides a smooth and continuous pressure-composition curve to the critical point. The model further allows for reinjection of produced gas, methane, or CO2 to increase oil recovery for both volatile and black oils. We show how to tune the models to the MMP by matching the appropriate critical point pressure. Further, the approach allows the use of black-oil or volatile-oil properties for tight rocks where capillary pressure alters the saturation pressures by decreasing the bubble-point pressure or increasing the dew-point pressure. Bubble-point pressure in the new model is a function of both capillary pressure (effective pore radius) and gas content. The phase behavior is also described on ternary diagrams for up to four components (water, oil, gas, and CO2 or CH4) and three phases (aqueous, oleic, gaseous) to allow for miscible and immiscible injection (or soaking) of various gases. The new phase behavior could be easily incorporated in a compositionally-extended black- or volatile-oil simulator. The approach could also be extended to model gas condensate reservoirs with or without gas injection and capillary pressure.
- North America > United States > North Dakota > Sanish Field > Bakken Shale Formation (0.99)
- North America > United States > Montana > Williston Basin > Elm Coulee Field > Bakken Shale Formation > Middle Bakken Shale Formation (0.99)
- North America > United States > South Dakota > Williston Basin > Bakken Shale Formation (0.98)
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Before undertaking any type of compositional numerical simulation of a miscible flood, it is crucial to identify the phase behavior occurring in the reservoir. Phase diagrams are a typical method for representing phase behavior. Ternary diagrams and pseudoternary diagrams have been used for decades to visualize conceptually the phase behavior of injection-fluid/crude-oil systems. This is done by representing multicomponent fluids or mixtures by three pseudocomponents and then plotting fluid compositions in the interior of an equilateral triangle with apexes that represent 100% of each pseudocomponent and where the side opposite an apex represents 0% of that pseudocomponent. For example, the low-molecular-weight fraction might include methane and nitrogen and perhaps CO2 if CO2 is the primary injection solvent.
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