Page 24 - Fundamentals of Enhanced Oil and Gas Recovery

12 Amirhossein Mohammadi Alamooti and Farzan Karimi Malekabadi

bubble-point pressure, oil formation volume factor, crude oil viscosity, and surface
tension are the main crude oil properties.

1.9.8 Crude Oil-Specific Gravity
Crude oil-specific gravity is defined as the ratio of the oil density to the water density
at ambient pressure and temperature.
ρ
γ 5 o
o
ρ
w
One of the most practical parameters in the oil industry is API gravity. This
parameter, which is measured in the field and laboratory, is calculated as follows:
141:5
API 5 2 131:5
γ o

1.9.9 Solution Gas Ratio

The amount of standard cubic feet of gas dissolved in one stock tank barrel of oil at a
certain pressure and temperature is called solution gas ratio, R s . This parameter
depends on gas gravity, API gravity, temperature, and especially pressure. For certain
undersaturated oil reservoirs, by reducing the pressure, the solution gas ratio remains
constant. When the pressure drops below the saturation pressure, the gas solubility
decreases by pressure decline. Fig. 1.6 shows a typical curve for the solution gas ratio
as a function of pressure.

1.9.10 Bubble Point Pressure
Bubble point pressure is defined as the pressure at which the first gas bubble
appears in crude oil. In other words, above the bubble point pressure the crude oil is

Saturation pressure

R s

P

Figure 1.6 Solution gas oil ratio.