Page 76 - Introduction to Petroleum Engineering

60 PROPERTIES OF RESERVOIR FLUIDS
Oil viscosity increases because of compression of the oil above BP pressure.
Oil viscosity μ at pressure p above BP pressure p can be estimated using
o b
−
µ = µ + δµ ( pp b ) (3.24)
ob
o
o
p
where μ is live oil viscosity at BP pressure and δ μ is the change in oil viscosity
p o
ob
above BP pressure due to increasing pressure. The value of δ μ for the oil viscosity
p o
shown in Figure 3.6 is approximately 8 × 10 cp/psi for pressures greater than BP
−5
pressure. The value of the slope δ μ is positive since oil viscosity increases as
p o
pressure increases for pressures greater than BP pressure.
3.6 WATER PROPERTIES
The presence of water in geologic formations means that the properties of water must
be considered. Water properties are discussed in this section.
Formation Volume Factor. The effects of pressure and temperature on the
volume of water very nearly cancel, so the FVF of water is approximately 1.0 RB/
STB for most reservoirs.
Viscosity. The viscosity of water depends on pressure, temperature, and compo-
sition. At reservoir conditions, water will contain dissolved solids (mostly salts) as
well as some dissolved hydrocarbon gases and small amounts (<1000 ppm) of other
hydrocarbons. The effects of temperature and composition on water viscosity at
14.7 psi (1 atm) of pressure are shown in Figure 3.7. Viscosity of pure water is near
1 cp at room temperature, but it is much less at typical reservoir temperatures.

1.40
0 wt% salts
1.20 10 wt% salts
20 wt% salts
Viscosity at 1 atm (cp) 0.80
1.00

0.60

0.40
0.20

0.00
50 100 150 200 250 300 350 400 450
Temperature (°F)
FIGURE 3.7 Effect of temperature and dissolved salts on viscosity of water at 14.7 psi (1 atm).