180
The Chemistry and Technology of Petroleum
For example, partial oxidation in the presence of steam may produce hydrogen for immediate
pickup, and result in integrated recovery and significant upgrading.
The THAI process could well have a wider range of application than SAGD, but in any case, a
detailed knowledge of the reservoir is essential (Speight, 2013). SAGD generally works best in relatively thick (150 ft) homogeneous pay zones. It is possible that the THAI process will be effective
down to approximately 600 ft thick, as is common in many Saskatchewan heavy oil pools (Greaves
and Xia, 2004).
The THAI process potentially allows the inclusion of a catalytic upgrading stage since it provides favorable operating temperatures at the production well as the combustion zone is anchored
to the horizontal well (Greaves et al., 2001; Xia et al., 2002). The cracking reactions happening in
the mobile oil zone creates precursor conditions for the CAPRI process. The reactants are usually
water (steam) and combustion gases, which pass through the mobile oil zone and in contact with
the catalyst layer around the horizontal production well. The catalyst reacts with partially upgraded
THAI oil and further upgrades it.
Thus, adding a catalyst (such as iron) to a thermal process may enhance in situ upgrading, even at
the lower temperatures for steam injection (Jiang et al., 2005). Laboratory experiments combining
in situ combustion with a catalyst in a horizontal producing well produced significantly upgraded
oil. Thermal cracking occurred in the combustion zone, and additional upgrading was achieved by
catalytic cracking in the production well (Xia et al., 2002). The downhole catalytic upgrading produced light oil, characterized by a low viscosity, that was readily converted into gasoline and diesel
fractions, with a higher conversion on an FCC basis than that obtained with normal virgin bitumen
vacuum gas oil (Greaves and Xia, 2004; Greaves et al., 2005).
Thus, one form of in situ heavy oil upgrading involves the injection of a catalyst; hence the
CAPRI process involves the addition of gravel-packed catalyst, as used in a conventional refinery, between the tubing and the horizontal wellbore. Test results have shown the technique to add
6–8 API points on top of the THAI in situ upgrades.
7.4.2.4 Solvent Deasphalting
The application of light hydrocarbon solvents to reduce or eliminate natural gas for steam generation has received significant recent interest. These lower-boiling hydrocarbons also have a natural
tendency to cause asphaltene constituents to separate (Mitchell and Speight, 1973; Speight, 2009)
thereby offering promise of some in situ upgrading.
An alternate to catalytic upgrading is in situ deasphalting. Here, a solvent such as propane is
injected to drop out some of the asphaltene constituents and lower the viscosity of the heavy oil.
This could be a stand-alone process or an additional benefit to a solvent based recovery process such
as VAPEX.
During a solvent-based heavy oil recovery process, such as vapor extraction (VAPEX), a condensable solvent is injected into a heavy oil reservoir. Solvent dissolution into heavy oil and possible
asphaltene precipitation drastically reduce its viscosity so that the diluted heavy oil can flow toward
a production well. In the past, several physical modeling studies have shown that the produced
heavy oil has much less amount of heavy components than the original heavy oil. This phenomenon
is often referred to as in situ upgrading.
Typically, after a solvent is made in contact with heavy oil at a relatively high pressure for a sufficiently long time, the solvent–heavy oil system at equilibrium state can be roughly divided into
three different layers. The top layer is a solvent-enriched liquid phase, the middle layer comprises
heavy oil with the dissolved solvent, and the bottom layer mainly consists of heavy components.
The solvent–heavy oil mixtures in these three layers show rather different chemical and physical
properties, such as solvent concentration, carbon number distribution, and viscosity. The top layer
has the highest concentrations of solvent and light components and the lowest viscosity of heavy oil
even after its dissolved solvent is flashed off. The heavy oil in the middle layer has similar carbon
The Chemistry and Technology of Petroleum
For example, partial oxidation in the presence of steam may produce hydrogen for immediate
pickup, and result in integrated recovery and significant upgrading.
The THAI process could well have a wider range of application than SAGD, but in any case, a
detailed knowledge of the reservoir is essential (Speight, 2013). SAGD generally works best in relatively thick (150 ft) homogeneous pay zones. It is possible that the THAI process will be effective
down to approximately 600 ft thick, as is common in many Saskatchewan heavy oil pools (Greaves
and Xia, 2004).
The THAI process potentially allows the inclusion of a catalytic upgrading stage since it provides favorable operating temperatures at the production well as the combustion zone is anchored
to the horizontal well (Greaves et al., 2001; Xia et al., 2002). The cracking reactions happening in
the mobile oil zone creates precursor conditions for the CAPRI process. The reactants are usually
water (steam) and combustion gases, which pass through the mobile oil zone and in contact with
the catalyst layer around the horizontal production well. The catalyst reacts with partially upgraded
THAI oil and further upgrades it.
Thus, adding a catalyst (such as iron) to a thermal process may enhance in situ upgrading, even at
the lower temperatures for steam injection (Jiang et al., 2005). Laboratory experiments combining
in situ combustion with a catalyst in a horizontal producing well produced significantly upgraded
oil. Thermal cracking occurred in the combustion zone, and additional upgrading was achieved by
catalytic cracking in the production well (Xia et al., 2002). The downhole catalytic upgrading produced light oil, characterized by a low viscosity, that was readily converted into gasoline and diesel
fractions, with a higher conversion on an FCC basis than that obtained with normal virgin bitumen
vacuum gas oil (Greaves and Xia, 2004; Greaves et al., 2005).
Thus, one form of in situ heavy oil upgrading involves the injection of a catalyst; hence the
CAPRI process involves the addition of gravel-packed catalyst, as used in a conventional refinery, between the tubing and the horizontal wellbore. Test results have shown the technique to add
6–8 API points on top of the THAI in situ upgrades.
7.4.2.4 Solvent Deasphalting
The application of light hydrocarbon solvents to reduce or eliminate natural gas for steam generation has received significant recent interest. These lower-boiling hydrocarbons also have a natural
tendency to cause asphaltene constituents to separate (Mitchell and Speight, 1973; Speight, 2009)
thereby offering promise of some in situ upgrading.
An alternate to catalytic upgrading is in situ deasphalting. Here, a solvent such as propane is
injected to drop out some of the asphaltene constituents and lower the viscosity of the heavy oil.
This could be a stand-alone process or an additional benefit to a solvent based recovery process such
as VAPEX.
During a solvent-based heavy oil recovery process, such as vapor extraction (VAPEX), a condensable solvent is injected into a heavy oil reservoir. Solvent dissolution into heavy oil and possible
asphaltene precipitation drastically reduce its viscosity so that the diluted heavy oil can flow toward
a production well. In the past, several physical modeling studies have shown that the produced
heavy oil has much less amount of heavy components than the original heavy oil. This phenomenon
is often referred to as in situ upgrading.
Typically, after a solvent is made in contact with heavy oil at a relatively high pressure for a sufficiently long time, the solvent–heavy oil system at equilibrium state can be roughly divided into
three different layers. The top layer is a solvent-enriched liquid phase, the middle layer comprises
heavy oil with the dissolved solvent, and the bottom layer mainly consists of heavy components.
The solvent–heavy oil mixtures in these three layers show rather different chemical and physical
properties, such as solvent concentration, carbon number distribution, and viscosity. The top layer
has the highest concentrations of solvent and light components and the lowest viscosity of heavy oil
even after its dissolved solvent is flashed off. The heavy oil in the middle layer has similar carbon