176
The Chemistry and Technology of Petroleum
the soaking drum effluent are mixed with recycle hydrogen and separated in the hot separator where
the gas is cooled, passed through a separator, and recycled to the heater and soaking drum effluent. The
liquids from the hot and cold separator are sent to the stabilizer section where purge gas and synthetic
crude are separated. The gas is used as fuel and the synthetic crude can now be transported or stored.
7.4.1.2 Solvent Processes
The main solvent process for quick and convenient surface upgrading using a solvent is dilution. By
this means, heavy oil can be diluted sufficiently so that the blend meets the specifications for shipping by pipeline or other means of transportation where specification must be met.
Dilution of heavy oil has been studied using various solvents, in terms of aromaticity, chemical nature, and viscosity (Speight, 2007, 2009; Motaghi et al., 2010). Dilution with low viscosity
hydrocarbons, such as light crude oil or naphtha, has shown that the viscosity reduction efficiency
is controlled by the sole viscosity of the diluent and not by its aromaticity. However, while blending
diluents of different chemical nature and polarity can enhance viscosity reduction there is always
the risk (especially with paraffin-based solvents) that separation of asphaltene constituents will
occur (Mitchell and Speight, 1973; Speight, 1979, 2007).
Solvent deasphalting processes allow removal of sulfur and nitrogen compounds as well as
metallic constituents by balancing yield with the desired feedstock properties (Ditman, 1973). In the
process, the feedstock is mixed with dilution solvent from the solvent accumulator and then cooled
to the desired temperature before entering the extraction tower. Because of its high viscosity, the
charge oil can neither be cooled easily to the required temperature nor will it mix readily with solvent in the extraction tower. By adding a relatively small portion of solvent upstream of the charge
cooler (insufficient to cause phase separation), the viscosity problem is avoided.
The choice of solvent is vital to the flexibility and performance of the unit. The solvent must be
suitable, not only for the extraction of the desired oil fraction, but also for control of the yield and/or
quality of the deasphalted oil at temperatures which are within the operating limits (Speight, 2007).
7.4.2 uPgrAdIng durIng In sItu reCovery
Finally, recent developments in upgrading of heavy oil (Ancheyta and Speight, 2007; Speight,
2007) indicate that the near future could see a reduction of the differential cost of upgrading heavy
oil as refineries evolve beyond this century (Speight, 2011). These processes are based on a better
understanding of asphaltene solubility effects at high temperatures, the incorporation of a catalyst
that is chemically precipitated internally during the upgrading, and the improvement of hydrogen
addition or carbon rejection.
In situ upgrading can reduce the viscosity of heavy oil by cracking long hydrocarbon chains and
can improve oil quality by reducing or removing asphaltene constituents and resin constituents.
Asphaltene constituents may contain iron, nickel, and vanadium, which are damaging to refineries.
Excess carbon, in the form of coke, may be left in the reservoir.
The upgraded oil flows more readily into the wellbore (increasing recovery factor), is easier to
lift to surface, and may eliminate the need for a diluent for pipeline transportation. Furthermore,
in situ upgrading might eliminate the need for surface upgrading facilities, thus reducing capital
investments. In a conventional thermal process (e.g., SAGD), the heavy oil is heated in situ, but it
may cool after being produced to surface. It then has to be reheated for upgrading. In situ upgrading
may be more energy efficient as well.
However, the increased mobilization of heavy oil in the reservoir by partial upgrading is not a
new idea and still has many hurdles to overcome before it can be considered close to commercial.
The product will be less viscous than the heavy oil in place but some property changes such as high
olefin content from cracking are not necessarily positive.
There are three main approaches for heating the reservoir: (1) steam distillation, (2) mild thermal
cracking—visbreaking, and (3) partial combustion.
The Chemistry and Technology of Petroleum
the soaking drum effluent are mixed with recycle hydrogen and separated in the hot separator where
the gas is cooled, passed through a separator, and recycled to the heater and soaking drum effluent. The
liquids from the hot and cold separator are sent to the stabilizer section where purge gas and synthetic
crude are separated. The gas is used as fuel and the synthetic crude can now be transported or stored.
7.4.1.2 Solvent Processes
The main solvent process for quick and convenient surface upgrading using a solvent is dilution. By
this means, heavy oil can be diluted sufficiently so that the blend meets the specifications for shipping by pipeline or other means of transportation where specification must be met.
Dilution of heavy oil has been studied using various solvents, in terms of aromaticity, chemical nature, and viscosity (Speight, 2007, 2009; Motaghi et al., 2010). Dilution with low viscosity
hydrocarbons, such as light crude oil or naphtha, has shown that the viscosity reduction efficiency
is controlled by the sole viscosity of the diluent and not by its aromaticity. However, while blending
diluents of different chemical nature and polarity can enhance viscosity reduction there is always
the risk (especially with paraffin-based solvents) that separation of asphaltene constituents will
occur (Mitchell and Speight, 1973; Speight, 1979, 2007).
Solvent deasphalting processes allow removal of sulfur and nitrogen compounds as well as
metallic constituents by balancing yield with the desired feedstock properties (Ditman, 1973). In the
process, the feedstock is mixed with dilution solvent from the solvent accumulator and then cooled
to the desired temperature before entering the extraction tower. Because of its high viscosity, the
charge oil can neither be cooled easily to the required temperature nor will it mix readily with solvent in the extraction tower. By adding a relatively small portion of solvent upstream of the charge
cooler (insufficient to cause phase separation), the viscosity problem is avoided.
The choice of solvent is vital to the flexibility and performance of the unit. The solvent must be
suitable, not only for the extraction of the desired oil fraction, but also for control of the yield and/or
quality of the deasphalted oil at temperatures which are within the operating limits (Speight, 2007).
7.4.2 uPgrAdIng durIng In sItu reCovery
Finally, recent developments in upgrading of heavy oil (Ancheyta and Speight, 2007; Speight,
2007) indicate that the near future could see a reduction of the differential cost of upgrading heavy
oil as refineries evolve beyond this century (Speight, 2011). These processes are based on a better
understanding of asphaltene solubility effects at high temperatures, the incorporation of a catalyst
that is chemically precipitated internally during the upgrading, and the improvement of hydrogen
addition or carbon rejection.
In situ upgrading can reduce the viscosity of heavy oil by cracking long hydrocarbon chains and
can improve oil quality by reducing or removing asphaltene constituents and resin constituents.
Asphaltene constituents may contain iron, nickel, and vanadium, which are damaging to refineries.
Excess carbon, in the form of coke, may be left in the reservoir.
The upgraded oil flows more readily into the wellbore (increasing recovery factor), is easier to
lift to surface, and may eliminate the need for a diluent for pipeline transportation. Furthermore,
in situ upgrading might eliminate the need for surface upgrading facilities, thus reducing capital
investments. In a conventional thermal process (e.g., SAGD), the heavy oil is heated in situ, but it
may cool after being produced to surface. It then has to be reheated for upgrading. In situ upgrading
may be more energy efficient as well.
However, the increased mobilization of heavy oil in the reservoir by partial upgrading is not a
new idea and still has many hurdles to overcome before it can be considered close to commercial.
The product will be less viscous than the heavy oil in place but some property changes such as high
olefin content from cracking are not necessarily positive.
There are three main approaches for heating the reservoir: (1) steam distillation, (2) mild thermal
cracking—visbreaking, and (3) partial combustion.