Page 32 - Fundamentals of Enhanced Oil and Gas Recovery

20 Amirhossein Mohammadi Alamooti and Farzan Karimi Malekabadi

other hand, most gas injection processes are applicable in light oil reservoirs.
Temperature is a restriction for chemical injection processes, making the design of a
stable chemical injectant difficult.

1.12 VISCOUS, CAPILLARY, AND GRAVITY FORCES

The success of any EOR method depends on microscopic displacement effi-
ciency to extract oil from pores in porous media. All of the EOR processes are conju-
gated with slug injection through the porous media. Capillary and viscous forces in
reservoirs influence the efficiency of displacement of the injected slug. In other words,
these forces with gravity forces determine distribution of all phases in the reservoir
and also cause trapping or mobilization of phases in a multiphase system.
Understanding and studying these forces in reservoirs is significantly necessary in the
design of any EOR process.
Differential pressures across the porous media reflect opposing or driving forces to
displace fluids. Wherever two immiscible fluids coexist in a pore or tube, a curved
surface is formed between the fluids. The pressure at the interface of two phases is not
the same, and a differential pressure is created, which is called capillary pressure.
Typically, the not-wet phase pressure more than the wetting phase pressure determines
the curvature of the interface. The capillary pressure can work as a resisting force or
driving force in different conditions. These forces come from the interfacial tension,
contact angle of the fluids, and radius of the pore. Many equations are suggested to
describe this force. The Young Laplace equation is one of the most famous
equations.
2γcosθ
P c 5
r p
where
γ is the interfacial tension
r is the pore radius
θ is the contact angle of two phases
Viscous forces in reservoirs are the result of fluid flow through porous media.
These forces can be shown by differential pressure parameters in Darcy’s equation for
porous media. If the porous media is considered as a bundle of tubes, the concept of
viscous force can be formulated as follows:
μLv
DP 5
r 2