Page 37 - Fundamentals of Enhanced Oil and Gas Recovery

An Introduction to Enhanced Oil Recovery 25

the fluid will try to move through the fracture because fractures usually have high
permeability and can transfer hydrocarbons quickly. Many oil-producing regions
have a permeability that varies in two directions (i.e., vertical and horizontal) and
reduces vertical and areal sweep efficiencies. Areas and layers with low or high per-
meability create a transverse continuity in all or part of the reservoir. Where such
layering exists in permeability, water will flow faster through the permeable layers.
3. Arrangement of injection and production wells
The shape of the flow in the reservoir (depending on the arrangement of the
injection and production wells) will have an impact on areal sweep efficiency, so
that the higher the level of contact between the displacing and displaced fluids is,
the greater the sweep efficiency will be. Therefore it can be said that when a com-
plete contact surface appears between two fluids, a linear displacement will follow,
and sweep efficiency can become 100%.
4. Reservoir rock matrix
The rock has been used with respect to its chemical composition, and its
water-wettability or oil-wettability has a decisive role here. Consequently, the bet-
ter the reservoir material is, the easier it will be for the fluid to flow through it. In
contrast, the weak quality of the reservoir rock will stop the flow of fluid in the
reservoir. In the case of rocks such as inderite and limestone, hydrocarbon cannot
flow in there at all [1].

1.14.3 Volumetric Displacement Efficiency and Material Balance
The volumetric (sweeping) displacement often uses the principles of material bal-
ance to calculate the rate of efficiency. For example, the displacement process in
which the percentage of initial oil saturation is reduced to the percentage of residual
oil saturation occurs in its contact point with the displaced fluid. If this process is
assumed to be piston-like, the displaced oil can be expressed using the following
formula:

S o1 S o2
N P 5 V P 2 V P E V
B o1 B o2
where N P refers to displaced oil, S o1 represents the percentage of oil saturation at
the beginning of the displacement process, S o2 denotes the percentage of oil satura-
tion remaining at the end of the process in the area where the oil is in contact with
the fluid, B o1 signifies the volumetric coefficient of oil formation at the beginning
of the displacement process, B o2 points to volumetric coefficient of oil at the end of
displacement, and V P is the volume of the pore space of the reservoir. In the above
equation, the division of the two sides of the equation into the amount of OIP at
the beginning of the process (N 1 ) expresses the amount of fractional recovery,