Page 19 - Fundamentals of Enhanced Oil and Gas Recovery

An Introduction to Enhanced Oil Recovery 7

P c

Threshold
pressure

S wi
S w
Figure 1.3 Capillary pressure curve for imbibition process.

Commonly, reservoirs contain two or three fluids. Consequently, this concept is
modified to an improved saturation-based function, “effective permeability.”
Effective permeability is the potential of a porous medium to be saturated with
other fluids. Also relative permeability is defined as the ratio of effective perme-
ability to absolute permeability. Relative permeability shows the ability of a system
for flowing fluid in the presence of other fluids. The range of this dimensionless
parameter is between 0 and 1. The value and curvature of the relative permeability
definitely depends on wettability of the rock. Maximum water relative permeability
for a strongly water-wet system will not exceed more than 0.2. Also the cross
point of oil and water relative permeability curves occurs in water saturation more
than 0.5. Another important parameter influencing relative permeability is satura-
tion history. Relative permeability functions are strongly sensitive to hysteresis
effect. In other words, like capillary pressure function, relative permeability is dif-
ferent for both drainage and imbibition processes.

1.9 RESERVOIR FLUID PROPERTIES

Hydrocarbons accumulated in reservoirs treating multiphase consist of complex
mixtures. The range of pressure and temperature varies largely in the petroleum
industry. The differences in mixture composition, pressure, and temperature lead to
the formation of different reservoir types. To predict phase behavior, different
experiments are carried out on reservoir fluids. Consequently, for modeling these
experiments and fluid phase behavior many equations of states are developed. Deep
cognition of phase behavior of reservoir hydrocarbon is vital during the first
production period and consequently in enhanced production design.