Note: Descriptions are shown in the official language in which they were submitted.
365~
This invention relates to the recovery of oil from
tar sands.
There are in Western Canada huge deposits of tar
sands containing useful oil fractions. However, recovery of
the oil is complex, difficult and costly.
A principal surface process for the recovery of
oil from tar sands is by hot water immersion followed by
extraction of the oil fractionO In the case of subterranean
deposits, high pressure steam, at a temperature of about
300C, is injected into the oil-bearing formation for a
period of several months, following which the steam is cut
off and oil from the heated formation flows to a s~np, whence
it is raised to the surface. This is known as the "huff and
puff" system. In a variation of this system, steam may be
introduced into an injection well and after heating the tar
sands to 300C to 400C, the oil fraction, separating from
the sand, is driven towards a connecting production well.
These processes are complicated by the fact that,
where steam is used, it has to be conveyed from a source,
through insulated piping. Also, its thermal efficiency is
not more than about 30%, A further complication is that
residual water mixes with the oil fraction to form an
emulsion from which it is hard to separate the oil.
It is an aim of the present invention to provide
a process for recovering oil from tar sands which avoids
these disadvantages and provides certain positive advantages
as will be selen from the ~ollowing description.
A process according to the invention comprises
causing a gas, heated to a temperature within the range
r
~ 1 ~ ~
;5~9L
from 300C to 600C, -to flow downward through an enclosed
mass of tar sands to cause an oil fraction to separate from
the mass by gravitational flow~ The oil fraction i8 re-
covered after being forced from the bottom of the retort by
the pressure of the incoming gas.
~ Gases which may be used are inert gases, for
,i`, ~/ffo9c~
'~` example, hyd~ogc~, argon, helium, carbon dioxide, or
active gases, for ~x~mple, hydrogen or oxygen. In the case
of the use of an inert gas, the mixture of gases formed
within the mass and emanating therefrom are recovered and
the inert gas stripped from the product gases combined with
makeup gas, heated and recycled through the mass. Where a
hydrocarbon gas is used, it dissolves the hydrocarbon fluid
within the tar sands to provide a fluid of lower density,
which is recovered.
In the case where oxygen is used, heat is gener-
ated by the ensuing combustion of some of the hydrocarbon
within the mass, the resulting oil fraction is recovered
together with carbon dioxide and water from the reaction.
The latter are separated from the oil fraction.
The invention will be described in more detail,
by reference to the accompanying drawings, which illustrate
preferred embodiments and in which:
Figure 1 is a diagram showing a typical recovery
plant employing an inert gas;
Figure 2 is a graph showing the results of
uslng an lnert gas.
~e~erring more particularly to Figure 1, the
preferred process illustrated proceeds as follows. A
mass of tar sands, from the Athabasca Tar Sand Fiel.ds, is
placed in a retort B (or this may be a number of retorts
in seri.es or in parallel) Hot nitrogen, at a temperature
of ~50C is introduced into the retort B from the line J.
Passage of the hot gas through the retort B first heats up
the mass of tar sands to operating temperature and then
causes a gravitational flow of the tar sands assisted by
the downward flow of the inert gas~ The oil fraction is
forced from the bottom of the retort by the pressure of the
10 incoming gas and passes to an oil-gas separator D. The oil
is removed from the separator D and the gas conveyed through
a line F.
Off gases coming from the tar sands are bled off
at G, while the nitrogen passes through the line H, which
is also supplied with fresh hydrogen and flows into the ga.s
re~enerator I. The nitrogen is heated in the regenerator I
and passes through the line J and back into the top of the
retort B.
The spent tar sand, which is a fine particled
relatively dry siliceous mass, is then removed from the
retort B and replaced by additional mass of tar sands.
Alternatively, the invention contemplates an in-
situ procedure, either to treat surface or subterranean
tar sand deposits, specially the latter.
It is seen that, according to the process, des-
cribed, the gas is heated to a predetermined temperature
and is then circulated through the tar sands. The e~fect
is to warm the tar sands to the point where the oil
separates. It then drains by gravity to a sump heated by
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the circulating hot gas or gases which flow in the same
gravitational direction.
In selecting a gas, suitable for this process, one
must consider the results to be achieved. For example, where
it is desired to extract the oil from the sand without any
reaction, then there may be selected an inert gas, for
~x~mpl e, nitrogen, argon, helium, or CO2.
Nitrogen has proved specially effective when
applied to tar sands of the Athabasca typeO Where a tar
sand formation is extremely dense and, therefore, qui~e
impervious, helium would be preferable to nitrogen.
Under other circumstances, where it is desirable
to lower the density of the oil, before pumping to the
surface, carbon dioxide would be a preferable gas because
of its miscibility in oil.
Under other circumstances, it may be desirable to
achieve a partial cracking of the hydrocarbon in order to
generate heat. In this case, various concentrations of
oxygen, above 70%, and including pure oxygen (99.5%~ may
be introduced into the tar sands to provide heat through
partial combustion.
Further, one might wish to use hydrogen because
of its good heat transfer properties and low density. The
introduction of hydrogen may, under suitable conditions,
produce hydroforming.
Other suitable gases for oil extraction are re-
lated hydrocarbon gases, for example, methane, ethane,
propane, or butane.
The optimum temperature is that which extracts
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I
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the greatest amount of vil. The applicants have found that
a temperature between about 300C and 600C, preferably 400C
and 500C, makes it possible to extract up to 85% of the oil
contained in the sand. Surprisingly, the oil fraction has
a viscosity, at 20~C, comparable to that of llibricating oil.
This product has the advantage over the heavy bltumen pro-
duct extracted by steam methods which, at room temperature,
is not fluid and requires spec:ial insulating precautions
to keep it fluid.
The process may be applied to tar sands which are
mined at the surface, for ~x~mple~ the Athr~basca Tar Sands.
It may also be used for in-situ recovery where the oil- ~
bearing formation is located 500 metres or more beneath the
surface, for ~x~mpl e at Cold Lake, Alberta.
The invention will be further illustrated by
reference to the accompany non-limiting example.
~x~mple
A mass of 600 grams of Athabasca tar sands con-
taining about 14% volatiles by wei~ht, was treated with hot
nitrogen (400C) substantially as described above by
reference to Figure 1~! The amount of oil extracted was
71.4 grams. This represents a yield of about 85%. This
was achieved in not more than 30 minutes, including the
initial heating of the mass to extraction temperature.
