Page 312 - Standard Handbook Petroleum Natural Gas Engineering VOLUME2

Fluid Movement in Waterflooded Reservoirs 279

E, = volume of hydrocarbons (oil or gas) displaced from individual pores
or small groups of pores divided by the volume of hydrocarbons
in the same pores just prior to displacement
E, = pattern sweep efficiency (developed from areal efficiency by proper
weighting for variations in net pay thickness, porosity, and hydro-
carbon saturation): hydrocarbon pore space enclosed behind the
injected-fluid front divided by total hydrocarbon pore space of the
reservoir or project
E, = hydrocarbon pore space invaded (affected, contacted) by the injec-
tion fluid or heat-front divided by the hydrocarbon pore space
enclosed in all layers behind the injected fluid

Displacement Sweep Efficiency (ED)
Factors affecting the displacement efficiency for any oil recovery process are
pore. geometry, wettability (water-wet, oil-wet, or intermediate), distribution of
fluids in the reservoir, and the history of how the saturation occurred. Results
are displayed in the relative permeability curves (Figure 5-153) from which the
flowing water saturation (or conversely the oil saturation) can be obtained at
any total fluid saturation. As shown in Figure 5-157, displacement efficiencies
decrease as oil viscosities increase [139].
Volumetric Sweep Efficiency (E,)

Whereas displacement efficiency considers a linear displacement in a unit
segment (group of pores) of the reservoir, macroscopic or volumetric sweep takes

"20 30 40 10 60 70 80 IO 20 30 40 50 60 10
WATER SATURATION.% PORE VOL. WATER SATURATION.% PORE VOL.
Figure 5-157. Effect of oil viscosity on fractional flow of water 1331.