Page 145 - Fundamentals of Reservoir Engineering

MATERIAL BALANCE APPLIED TO OIL RESERVOIRS 84

free gas starts to accumulate. The primary recovery factor from such a reservoir is very
low and will seldom exceed 30% of the oil in place.

p i

R ( producing GOR )

p
b

pressure
R si decline

watercut (%)

time

Fig. 3.4 Schematic of the production history of a solution gas drive reservoir

Two ways of enhancing the primary recovery are illustrated in fig. 3.5. The first of these
methods, water injection, is usually aimed at maintaining the pressure above bubble
point, or above the pressure at which the gas saturation exceeds the critical value at
which the gas becomes mobile. The unfortunate consequences of starting to inject
water below bubble point pressure are illustrated in exercise 3.3.

compressor

gas injection

water treatment
plant oil

production sealing
well
fault

water
injection

OWC