Page 84 - Principles of Applied Reservoir Simulation 2E

Part I: Reservoir Engineering Primer 69

8.2 Enhanced Oil Recovery

Improved recovery technology includes traditional secondary recovery
processes such as waterflooding and immiscible gas injection, as well as
enhanced oil recovery (EOR) processes. EOR processes are usually classified
as one of the following processes: chemical, miscible, thermal, and microbial.
A brief description of each of these processes is presented here. The literature
on EOR processes is extensive. For more detailed discussions of EOR processes,
including screening criteria and analyses of displacement mechanisms, see such
references as Taber and Martin [1983], Lake [1989], Martin [1992], Taber, et
al. [1996], and Green and Willhite [1998].

Chemical
Chemical flooding methods include polymer flooding, micellar-polymer
or surfactant-polymer flooding, and alkaline or caustic flooding. Polymer
flooding is designed to improve the mobility ratio and fluid flow patterns of a
displacement process by increasing the viscosity of injected water containing
polymer, Micellar-polymer flooding uses a detergent-like solution to lower
residual oil saturation to waterflooding. The polymer slug injected after the
micellar slug is designed to improve displacement efficiency. Alkaline flooding
uses alkaline chemicals that can react with certain types of in situ crude. The
resulting chemical product is miscible with the oil and can reduce residual oil
saturation to waterflooding.

Miscible
Miscible flooding methods include carbon dioxide injection, natural gas
injection, and nitrogen injection. Miscible gas injection must be performed at
a high enough pressure to ensure miscibility between the injected gas and in situ
oil. Miscibility is achieved when interfacial tension (IFT) between the aqueous
and oleic phases is significantly reduced. The desired IFT reduction is typically
from around 1 dyne/cm to 0.001 dyne/cm or less. Any reduction in IFT can
improve displacement efficiency, and a near miscible process can yield much
of the incremental oil that might be obtained from a miscible process. If reservoir