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Recovery of Heavy Oil and Tar Sand Bitumen
number distribution to the original heavy oil. The bottom layer has the lowest solvent concentration
and the highest concentration of heavy components.
The heavy oil in the bottom layer after its dissolved solvent is flashed off has much higher viscosity than the original heavy oil. These experimental results indicate that in a solvent-based heavy
oil recovery process, the solvent–heavy oil mixture in the top and middle layers can be recovered
because of its lower viscosity, whereas the heavy oil in the bottom layer may be left behind in the
heavy oil reservoir because of its higher viscosity. In this way, the produced heavy oil is in situ
upgraded during the solvent-based heavy oil recovery process.
The application of low-boiling hydrocarbon solvents has received significant recent interest.
These light hydrocarbons have a natural tendency to separate asphaltene constituents and offers
promise of some in situ upgrading. However, there has been little work done to determine reservoir
damage or deposit damage caused by asphaltene separation and, in addition, the site specificity of
each reservoir and each deposit needs to be considered before any company charges ahead into a
Light Brigade at Balaclava situation.
An extension of solvent recovery is the combined use of solvents and thermal stimulation to
achieve some degree of in situ upgrading. The potential move to less severe primary upgrading will
place more emphasis on conversion at the secondary stage as well as heteroatom removal.
7.4.2.5 Microbial Enhanced Oil Recovery
Another mechanism for in situ upgrading is bioconversion or bacterial upgrading. The process
depends on microbes that can convert the bitumen to lower viscosity oil or methane. These microbes
may be naturally occurring or injected into the reservoir. As additional nutrients are normally
required for this process to take place at reasonable rates, these must be injected. However, since
microbial recovery methods are relatively slow processes, there is likelihood (unfortunately) that
such a process would be applied solely as a final clean-up process.
7.4.3 ePIlogue
There is (or will be) an obvious future need for partial upgrading during or immediately after recovery. On the other hand, hydrogen addition must be used during upgrading in order to stabilize the
upgraded heavy oil, which could mean that the cost of partial upgrading is not much reduced as
compared to full upgrading. Therefore, the only choice currently is no upgrading or full upgrading.
Other goals could be to achieve breakthrough in upgrading technologies such as nonthermal coking
methods that would use far less energy or such as gasification at 800°C (1470°F) which is far less
than current commercial temperatures. The technology where changes do occur involves combustion of the oil in situ. The concept of any combustion technology requires that the oil be partially
combusted and that thermal decomposition occur to other parts of the oil. This is sufficient to cause
irreversible chemical and physical changes to the oil to the extent that the product is markedly different to the oil in place. Recognition of this phenomenon is essential before combustion technologies are applied to oil recovery.
Although this improvement in properties may not appear to be too drastic, nevertheless, it usually is sufficient to have major advantages for refinery operators. Any incremental increase in the
units of hydrogen/carbon ratio can save amounts of costly hydrogen during upgrading. The same
principles are also operative for reductions in the nitrogen, sulfur, and oxygen contents. This latter
occurrence also improves catalyst life and activity as well as reduces the metals content.
In short, in situ recovery processes (although less efficient in terms of bitumen recovery relative
to mining operations) may have the added benefit of leaving some of the more obnoxious constituents (from the processing objective) in the ground. Processes that offer the potential for partial
upgrading during recovery are varied but usually follow a surface process. Not that this be construed as an easy task, there are many disadvantages that arise from attempting in situ upgrading.
Recovery of Heavy Oil and Tar Sand Bitumen
number distribution to the original heavy oil. The bottom layer has the lowest solvent concentration
and the highest concentration of heavy components.
The heavy oil in the bottom layer after its dissolved solvent is flashed off has much higher viscosity than the original heavy oil. These experimental results indicate that in a solvent-based heavy
oil recovery process, the solvent–heavy oil mixture in the top and middle layers can be recovered
because of its lower viscosity, whereas the heavy oil in the bottom layer may be left behind in the
heavy oil reservoir because of its higher viscosity. In this way, the produced heavy oil is in situ
upgraded during the solvent-based heavy oil recovery process.
The application of low-boiling hydrocarbon solvents has received significant recent interest.
These light hydrocarbons have a natural tendency to separate asphaltene constituents and offers
promise of some in situ upgrading. However, there has been little work done to determine reservoir
damage or deposit damage caused by asphaltene separation and, in addition, the site specificity of
each reservoir and each deposit needs to be considered before any company charges ahead into a
Light Brigade at Balaclava situation.
An extension of solvent recovery is the combined use of solvents and thermal stimulation to
achieve some degree of in situ upgrading. The potential move to less severe primary upgrading will
place more emphasis on conversion at the secondary stage as well as heteroatom removal.
7.4.2.5 Microbial Enhanced Oil Recovery
Another mechanism for in situ upgrading is bioconversion or bacterial upgrading. The process
depends on microbes that can convert the bitumen to lower viscosity oil or methane. These microbes
may be naturally occurring or injected into the reservoir. As additional nutrients are normally
required for this process to take place at reasonable rates, these must be injected. However, since
microbial recovery methods are relatively slow processes, there is likelihood (unfortunately) that
such a process would be applied solely as a final clean-up process.
7.4.3 ePIlogue
There is (or will be) an obvious future need for partial upgrading during or immediately after recovery. On the other hand, hydrogen addition must be used during upgrading in order to stabilize the
upgraded heavy oil, which could mean that the cost of partial upgrading is not much reduced as
compared to full upgrading. Therefore, the only choice currently is no upgrading or full upgrading.
Other goals could be to achieve breakthrough in upgrading technologies such as nonthermal coking
methods that would use far less energy or such as gasification at 800°C (1470°F) which is far less
than current commercial temperatures. The technology where changes do occur involves combustion of the oil in situ. The concept of any combustion technology requires that the oil be partially
combusted and that thermal decomposition occur to other parts of the oil. This is sufficient to cause
irreversible chemical and physical changes to the oil to the extent that the product is markedly different to the oil in place. Recognition of this phenomenon is essential before combustion technologies are applied to oil recovery.
Although this improvement in properties may not appear to be too drastic, nevertheless, it usually is sufficient to have major advantages for refinery operators. Any incremental increase in the
units of hydrogen/carbon ratio can save amounts of costly hydrogen during upgrading. The same
principles are also operative for reductions in the nitrogen, sulfur, and oxygen contents. This latter
occurrence also improves catalyst life and activity as well as reduces the metals content.
In short, in situ recovery processes (although less efficient in terms of bitumen recovery relative
to mining operations) may have the added benefit of leaving some of the more obnoxious constituents (from the processing objective) in the ground. Processes that offer the potential for partial
upgrading during recovery are varied but usually follow a surface process. Not that this be construed as an easy task, there are many disadvantages that arise from attempting in situ upgrading.