40
The Chemistry and Technology of Petroleum
In order to classify petroleum, heavy oil, and bitumen, the use of a single parameter such as viscosity is not enough. Other properties such as API gravity, elemental analysis, composition, and the
properties of the fluid in the reservoir as well as the method of recovery need to be acknowledged.
The United States Congress (US Congress, 1976) has defined tar sands as
The several rock types that contain an extremely viscous hydrocarbon which is not recoverable in its
natural state by conventional oil well production methods including currently used enhanced recovery
techniques.
By inference, conventional petroleum and heavy oil are recoverable by well production methods
(i.e., primary and secondary recovery methods) (Chapter 6) and by currently used enhanced recovery techniques (EOR methods) (Speight, 2009). It might also be added that the deposits in which
bitumen is found require prior fracturing techniques to overcome the low permeability and allow
the passage of fluids.
2.2.11 Pour PoInt
Tar sand bitumen is a naturally occurring material that is immobile in the deposit and cannot
be recovered by the application of enhanced oil recovery technologies, including steam-based
technologies. On the other hand, heavy oil is mobile in the reservoir and can be recovered by the
application of enhanced oil recovery technologies, including steam-based technologies.
Since the most significant property of tar sand bitumen is its immobility under the conditions of
temperatures and pressure in the deposit, the interrelated properties of API gravity (ASTM D287)
and viscosity (ASTM D445) may present an indication of the mobility of oil or immobility of
bitumen, but in reality these properties only offer subjective descriptions of the oil in the reservoir.
The most pertinent and objective representation of this oil or bitumen mobility is the pour point
(ASTM D97).
By definition, the pour point is the lowest temperature at which oil will move, pour, or flow
when it is chilled without disturbance under definite conditions (ASTM D97). In fact, the pour
point of an oil when used in conjunction with the reservoir temperature gives a better indication of
the condition of the oil in the reservoir than the viscosity. Thus, the pour point and reservoir temperature present a more accurate assessment of the condition of the oil in the reservoir, being an
indicator of the mobility of the oil in the reservoir. Indeed, when used in conjunction with reservoir
temperature, the pour point gives an indication of the liquidity of the heavy oil or bitumen and,
therefore, the ability of the heavy oil or bitumen to flow under reservoir conditions. In summary,
the pour point is an important consideration because, for efficient production, additional energy
must be supplied to the reservoir by a thermal process to increase the reservoir temperature beyond
the pour point.
For example, Athabasca bitumen with a pour point in the range 50°C–100°C (122°F–212°F)
and a deposit temperature of 4°C–10°C (39°F–50°F) is a solid or near solid in the deposit and will
exhibit little or no mobility under deposit conditions. Pour points of 35°C–60°C (95°F–140°F) have
884
934
966
1000
1,000
10,000
Conventional
crude oil
100,000
1,000,000
Heavy
crude oil
Tar sand
bitumen
100
10
Viscosity, mPa, cP
Density, kg/m
3
35
20
15
10
Gravity, °API
FIGURE 2.3 Classification of petroleum, heavy oil, and bitumen by API gravity and viscosity.
The Chemistry and Technology of Petroleum
In order to classify petroleum, heavy oil, and bitumen, the use of a single parameter such as viscosity is not enough. Other properties such as API gravity, elemental analysis, composition, and the
properties of the fluid in the reservoir as well as the method of recovery need to be acknowledged.
The United States Congress (US Congress, 1976) has defined tar sands as
The several rock types that contain an extremely viscous hydrocarbon which is not recoverable in its
natural state by conventional oil well production methods including currently used enhanced recovery
techniques.
By inference, conventional petroleum and heavy oil are recoverable by well production methods
(i.e., primary and secondary recovery methods) (Chapter 6) and by currently used enhanced recovery techniques (EOR methods) (Speight, 2009). It might also be added that the deposits in which
bitumen is found require prior fracturing techniques to overcome the low permeability and allow
the passage of fluids.
2.2.11 Pour PoInt
Tar sand bitumen is a naturally occurring material that is immobile in the deposit and cannot
be recovered by the application of enhanced oil recovery technologies, including steam-based
technologies. On the other hand, heavy oil is mobile in the reservoir and can be recovered by the
application of enhanced oil recovery technologies, including steam-based technologies.
Since the most significant property of tar sand bitumen is its immobility under the conditions of
temperatures and pressure in the deposit, the interrelated properties of API gravity (ASTM D287)
and viscosity (ASTM D445) may present an indication of the mobility of oil or immobility of
bitumen, but in reality these properties only offer subjective descriptions of the oil in the reservoir.
The most pertinent and objective representation of this oil or bitumen mobility is the pour point
(ASTM D97).
By definition, the pour point is the lowest temperature at which oil will move, pour, or flow
when it is chilled without disturbance under definite conditions (ASTM D97). In fact, the pour
point of an oil when used in conjunction with the reservoir temperature gives a better indication of
the condition of the oil in the reservoir than the viscosity. Thus, the pour point and reservoir temperature present a more accurate assessment of the condition of the oil in the reservoir, being an
indicator of the mobility of the oil in the reservoir. Indeed, when used in conjunction with reservoir
temperature, the pour point gives an indication of the liquidity of the heavy oil or bitumen and,
therefore, the ability of the heavy oil or bitumen to flow under reservoir conditions. In summary,
the pour point is an important consideration because, for efficient production, additional energy
must be supplied to the reservoir by a thermal process to increase the reservoir temperature beyond
the pour point.
For example, Athabasca bitumen with a pour point in the range 50°C–100°C (122°F–212°F)
and a deposit temperature of 4°C–10°C (39°F–50°F) is a solid or near solid in the deposit and will
exhibit little or no mobility under deposit conditions. Pour points of 35°C–60°C (95°F–140°F) have
884
934
966
1000
1,000
10,000
Conventional
crude oil
100,000
1,000,000
Heavy
crude oil
Tar sand
bitumen
100
10
Viscosity, mPa, cP
Density, kg/m
3
35
20
15
10
Gravity, °API
FIGURE 2.3 Classification of petroleum, heavy oil, and bitumen by API gravity and viscosity.