Page 340 - Intelligent Digital Oil And Gas Fields

284 Intelligent Digital Oil and Gas Fields

recovery reserves extraction by altering reservoir wettability, oil displace-
ment mechanism, and residual oil saturation. However, chemical processes
have had technical and economic challenges to widespread utilization. By
implementing automation (DOF) principles, chemical EOR should gain
efficacy as described in this section. By definition, the alkaline is a base
(i.e., soap) that easily dissolves in water, and the solution base has a pH
greater than 7.0. In the oil industry, the alkaline solution has been used
to reduce the interfacial tension (IFT) of the remaining oil in situ, altering
the original rock wettability and generating a reduction in the residual oil
saturation (S orw ) after the primary water injection. Polymers are a large chain
of molecules (synthetic or natural) that if injected with the water injection
process can increase both the viscosity and the density of the water. The
polymers are used to reduce the water mobility (ρ w /μ w ) in the formation
and therefore generate a uniform sweep efficiency displacing oil. Surfactants
(also called micelle) are organic compounds that reduce the IFT between
different fluids (oil-water); surfactants are used as emulsions or foam agents
to absorb the oil phase and generate miscible displacement (one fluid)
between oil and water. These three types of chemical injection can also
be mixed, designated as ASP (alkaline, surfactant, and polymers injection).
The sequence of injection, slug size, total volume, chemical concentration,
brine concentration, and injection rate depend on reservoir property distri-
butions across the field.
The chemical injection strongly depends on dominant forces governing
the reservoir; these are viscous, gravity, and capillary forces. The reduction
of interfacial forces and residual oil saturation can be explained using the cap-
illary number expression.

Q w μ
N c ¼ w (7.8)
A σ cosθ

where μ is the displacing fluid, Q w is the displacing Darcy flow rate, θ is the
contact angle between oil and water, and σ is the IFT between the displacing
fluid and the displaced fluid (oil).
In the situation where gravity has a significant component between
forces, the potential gradient between the displacing and displaced fluids
generates gravitational forces dominated by the density differences
(oil-water) but countered by capillary effect; the bond number or buoyancy
factor can be expressed as.