Summary
Analytical models of gasflooding are important for enhanced-oil-recovery
(EOR) screening, for interpretation of laboratory data, and for streamline
modeling. Introduction of two Lagrangian coordinates linked with one of the
components and with the overall two-phase flux results in splitting the
compositional model into an auxiliary system and an independent scalar
equation. The number of equations in the auxiliary system is less by one if
compared with the compositional model, making analytical modeling possible for
more practical cases. The auxiliary system contains only thermodynamic
functions and is independent of transport properties. Therefore, phase
transitions and minimum miscibility pressure for gas injection are also
independent of transport properties. The new splitting method is applicable for
both self-similar solutions of continuous gas injection and nonself-similar
solvent-slug problems. Analytical solution for four-component oil displacement
by a nitrogen-based solvent was obtained using the splitting technique. The
compositional two-phase model contains an elliptic region if and only if an
elliptic region is also present in the auxiliary system. Calculations for
several four-component mixtures exhibit existence of an elliptic region in
compositional modeling.
Introduction
Miscible displacement is characterized by the injection of fluids that mix
totally or partially with reservoir fluid (Lake 1989; Latil 1980). Basically,
there are three main distinct miscible-hydrocarbon-solvent
processes--miscible-slug injection, enriched-gas injection, and high-pressure
lean-gas injection (van Poolen 1980). The miscible-slug process consists of the
injection of a slug of liquid hydrocarbon driven by a chase fluid, which may be
natural gas or even water. The enriched-gas process is essentially the
injection of a slug of enriched natural gas displaced by lean gas or water. In
the third process, lean gas is injected at high pressure to achieve retrograde
evaporation of oil and the formation of a miscible phase between gas and oil
phases flowing in the reservoir. The most important technical problem of
miscible-hydrocarbon injection, besides its cost, is related to the high
mobility ratio of solvent to crude oil. As oil price increased, carbon dioxide
became a natural substitute for hydrocarbons in miscible flooding processes. It
is also suitable for continuous injection during production lifetime, depending
on the thermodynamic behavior of its mixture with reservoir fluid. Recently,
more attention has been given to the injection of inert gas, such as nitrogen
(N2) or flue gas, with promising results.
© 2009. Society of Petroleum Engineers
View full textPDF
(
689 KB
)
History
- Original manuscript received:
9 July 2007
- Meeting paper published:
15 April 2007
- Revised manuscript received:
28 February 2008
- Manuscript approved:
29 February 2008
- Published online:
16 March 2009
- Version of record:
1 March 2009
View Cart
