179
Recovery of Heavy Oil and Tar Sand Bitumen
product of cracking and pyrolysis, which is deposited on the rock matrix. The amount of fuel burned
is an important parameter because it determines how much air must be injected to burn a certain
volume of reservoir.
Chemical reactions are of two main categories: (1) oxidation, which occurs in the presence of
oxygen, and (2) pyrolysis, which occurs at elevated temperatures.
In general, at low temperature, oxygen combines with the oil to form oxidized hydrocarbons such
as peroxides, alcohols, or ketones. This generally increases the oil viscosity but could increase oil
reactivity at higher temperature. When oxygen contacts the oil at higher temperature, combustion
occurs resulting in production of water and carbon oxides.
Of all the reactions that can occur during in situ combustion, only low-temperature oxidation can
increase the viscosity of the oil. If the fire flood is conducted properly, low-temperature oxidations
are minimized because most of the oxygen injected is consumed at the burning front.
Distillation allows transport and production of the light fractions of the oil leaving behind the
higher-boiling or nonvolatile constituents. These higher-boiling constituents often contain the
majority of the undesirable compounds, which may contain sulfur or metals.
Forward in situ combustion by itself is already an effective in situ upgrading method with field
improvements in gravity reported to be as much as 6°API (Ramey et al., 1992).
Another possible in situ upgrading technique involves a combination of solvent injection and
combustion. Cyclic oil recovery has numerous advantages both technically and economically. It
can also be easily optimized in a given oil reservoir. Cyclic injection of solvents, either gas or
liquid, followed by in situ combustion of a small part of the reservoir to increase the temperature
near the well but also to clean the wellbore region of all the residues left by the solvents. Alternate
slugs of solvent and air would be injected and production would occur after each solvent slug injection and after each combustion period. The process could be repeated until an economic limit is
reached. One important fact to note is that both solvent injection and in situ combustion have been
proven to be effective in a variety of reservoirs; however, the combination of the two methods has
never been tried.
The most significant effect will be the precipitation and/or deposition of high molecular weight
constituents such as asphaltene constituents or wax constituents. The produced oil is expected to
be slightly upgraded by the solvent cycle. Unlike the classic well to well in situ combustion, we
would only try to improve near wellbore conditions by burning the solid residues left after the solvent cycle. The benefits of using combustion at this stage are expected to include (1) productivity
improvement through removal of the heavy ends left from the solvent cycle, (2) possible deactivation
of the clays near the wellbore due to the high temperature of the combustion, and (3) reduced viscosity of the oil due to temperature increase.
Forward in situ combustion by itself is already an effective in situ upgrading method with
improvements in API gravity by as much as 6°. Other work (Greaves and Xia, 2004, 2008; Greaves
et al., 2001, 2005) has followed up on this potential but direct application of these laboratory results
to the field is difficult, such technology deserves further research.
However, while in situ combustion is a relatively inexpensive process, it has major drawbacks.
The high temperatures in the presence of oxygen which are encountered when the process is
applied cause coke formation and the production of olefins and oxygenated compounds such as
phenols and ketones, which in turn cause major problems when the produced liquids are processed
in refinery units. Commonly, the processing of products from thermal cracking is restricted to
delayed or fluid coking because the hydrocarbon is degraded to a degree that precludes processing
by other methods.
One concept that relates to upgrading during in situ recovery utilizes a unique combination of operations to achieve hydrovisbreaking in formations in which heavy oil and commonly
encountered levels of formation permeability combine to limit fluid mobility (Graue, 2001). The
benefits of introduction of hydrogen during in situ retorting offer much promise. The possible
application of such methods for selective separation of the metal constituents is an obvious benefit.
Recovery of Heavy Oil and Tar Sand Bitumen
product of cracking and pyrolysis, which is deposited on the rock matrix. The amount of fuel burned
is an important parameter because it determines how much air must be injected to burn a certain
volume of reservoir.
Chemical reactions are of two main categories: (1) oxidation, which occurs in the presence of
oxygen, and (2) pyrolysis, which occurs at elevated temperatures.
In general, at low temperature, oxygen combines with the oil to form oxidized hydrocarbons such
as peroxides, alcohols, or ketones. This generally increases the oil viscosity but could increase oil
reactivity at higher temperature. When oxygen contacts the oil at higher temperature, combustion
occurs resulting in production of water and carbon oxides.
Of all the reactions that can occur during in situ combustion, only low-temperature oxidation can
increase the viscosity of the oil. If the fire flood is conducted properly, low-temperature oxidations
are minimized because most of the oxygen injected is consumed at the burning front.
Distillation allows transport and production of the light fractions of the oil leaving behind the
higher-boiling or nonvolatile constituents. These higher-boiling constituents often contain the
majority of the undesirable compounds, which may contain sulfur or metals.
Forward in situ combustion by itself is already an effective in situ upgrading method with field
improvements in gravity reported to be as much as 6°API (Ramey et al., 1992).
Another possible in situ upgrading technique involves a combination of solvent injection and
combustion. Cyclic oil recovery has numerous advantages both technically and economically. It
can also be easily optimized in a given oil reservoir. Cyclic injection of solvents, either gas or
liquid, followed by in situ combustion of a small part of the reservoir to increase the temperature
near the well but also to clean the wellbore region of all the residues left by the solvents. Alternate
slugs of solvent and air would be injected and production would occur after each solvent slug injection and after each combustion period. The process could be repeated until an economic limit is
reached. One important fact to note is that both solvent injection and in situ combustion have been
proven to be effective in a variety of reservoirs; however, the combination of the two methods has
never been tried.
The most significant effect will be the precipitation and/or deposition of high molecular weight
constituents such as asphaltene constituents or wax constituents. The produced oil is expected to
be slightly upgraded by the solvent cycle. Unlike the classic well to well in situ combustion, we
would only try to improve near wellbore conditions by burning the solid residues left after the solvent cycle. The benefits of using combustion at this stage are expected to include (1) productivity
improvement through removal of the heavy ends left from the solvent cycle, (2) possible deactivation
of the clays near the wellbore due to the high temperature of the combustion, and (3) reduced viscosity of the oil due to temperature increase.
Forward in situ combustion by itself is already an effective in situ upgrading method with
improvements in API gravity by as much as 6°. Other work (Greaves and Xia, 2004, 2008; Greaves
et al., 2001, 2005) has followed up on this potential but direct application of these laboratory results
to the field is difficult, such technology deserves further research.
However, while in situ combustion is a relatively inexpensive process, it has major drawbacks.
The high temperatures in the presence of oxygen which are encountered when the process is
applied cause coke formation and the production of olefins and oxygenated compounds such as
phenols and ketones, which in turn cause major problems when the produced liquids are processed
in refinery units. Commonly, the processing of products from thermal cracking is restricted to
delayed or fluid coking because the hydrocarbon is degraded to a degree that precludes processing
by other methods.
One concept that relates to upgrading during in situ recovery utilizes a unique combination of operations to achieve hydrovisbreaking in formations in which heavy oil and commonly
encountered levels of formation permeability combine to limit fluid mobility (Graue, 2001). The
benefits of introduction of hydrogen during in situ retorting offer much promise. The possible
application of such methods for selective separation of the metal constituents is an obvious benefit.