Summary
This paper describes methods for the simulation of first-contact miscible
(FCM), multicontact miscible, and vaporizing gas drive, which include logic to
account for bypassed oil. Dispersion control is included for FCM cases.
First-contact miscibility may be simulated in fully compositional mode with
any number of components, N SUBSCRIPTc , or in two-pseudocomponent
equation-of-state (EOS) mode. Pseudoization is performed internally in the
model so that hydrocarbon-fluid density and viscosity, as functions of pressure
and composition, are the same as calculated in N SUBSCRIPTc -component mode.
Bypassed oil and dispersion control are based on an extension of Koval's (1963)
method. This procedure allows the user to adjust the fractional flow of oil
during upscaling or history matching to match fine-grid or historical results.
This feature can be used to simulate both water-alternating-gas (WAG) and
tertiary-recovery projects where solvent injection is preceded by a
water-injection period.
Example cases are included to illustrate the techniques presented in this
paper. Results are also given on the efficiencies of the algorithms.
Introduction
Simulation of miscible and vaporizing gas-drive processes in heterogeneous
reservoirs with a compositional model requires the proper treatment of bypassed
oil, "viscous fingering," and "channeling" that may occur on a
model-sublayer basis. Data from a sidetrack well near an injector in the
Prudhoe Bay miscible-gas project indicate that miscible-flood residual-oil
saturations, S SUBSCRIPTorm , in the field are on the order of 5% pore volume
in the well-swept zones and are higher in less-swept zones (McGuire et al.
1995, 2001, 2002). This residual, or "bypassed," oil saturation will be
vaporized in conventional compositional simulators with continued gas injection
even when S SUBSCRIPTorm is included in the water/hydrocarbon relative
permeability algorithm.
Methods for predicting the performance of unstable miscible displacement in
heterogeneous reservoirs have been presented previously by other authors (Koval
1963; Todd and Longstaff 1972; Thomas et al. 1991; Ballin et al. 2001). Koval
developed an analytical method analogous to the Buckley-Leverett theory for
calculating oil recovery as a function of both solvent-/oil-viscosity ratio
(i.e., fingering) and the local level of heterogeneity (i.e., channeling) in
porous media. Todd and Longstaff presented the development of a two-component
hydrocarbon numerical simulator for prediction of miscible-flood performance in
a modified black-oil simulator. They also described a three-component model,
which required inclusion of a fourth conservation equation in an existing
three-phase simulator. Thomas et al. presented channeling logic in a modified
black-oil model similar to that introduced by Koval to simulate the feasibility
of nitrogen injection in the fractured Ekofisk reservoir. Ballin et al.
describe a compositional upscaling method for the simulation of produced-gas
injection in the Cupiagua gas/condensate reservoir that modifies the velocities
of individual pseudocomponents.
This paper presents generalized methods for the simulation of FCM,
multicontact miscible, and vaporizing gas-drive processes. The techniques allow
bypassed oil to be calculated implicitly as a function of pressure and
composition during the simulation. Dispersion control for simulation of FCM
processes is based on an extension of Koval's method. A single parameter is
used to adjust the amount of dispersion during upscaling or history matching to
match fine-grid or historical results. This feature can be used to simulate
solvent-injection and WAG-injection processes and tertiary-recovery projects
where solvent is preceded by water injection. Example cases are presented that
illustrate both the bypassed-oil and dispersion-control techniques introduced
in the paper.
© 2007. Society of Petroleum Engineers
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History
- Original manuscript received:
22 June 2004
- Meeting paper published:
26 September 2004
- Revised manuscript received:
26 February 2007
- Manuscript approved:
17 May 2007
- Version of record:
20 October 2007
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