IN-SITU COMBUSTION METHOD FOR RECOVERY OF HEAVY OIL UTILIZING OXYGEN AND CARBON DIOXIDE AS INITIAL OXIDANT

METHODE DE COMBUSTION EN SITE POUR L'EXTRACTION DU PETROLE LOURD, AVEC INTERVENTION D'OXYGENE ET D'OXYDE DE CARBONE POUR L'OXYDATION PRIMAIRE

English Abstract

IN-SITU COMBUSTION METHOD FOR
RECOVERY OF HEAVY OIL UTILIZING
OXYGEN AND CARBON DIOXIDE AS INITIAL OXIDANT
ABSTRACT OF THE DISCLOSURE
An in-situ combustion method for recovering
viscous oil from a subterranean, viscous oil-containing
formation comprising injecting a mixture of essentially
pure oxygen and carbon dioxide into the formation to
initiate an in-situ combustion operation followed by
injecting essentially pure oxygen.

Claims

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WHAT IS CLAIMED IS:
1. A method for recovering oil from a
subterranean; viscous oil-containing formation
penetrated by at least one injection well and a spaced
apart production well comprising:
(a) initiating an in-situ combustion operation
in the formation by injecting a
combustion-supporting gas comprising a
mixture of essentially pure oxygen and
carbon dioxide into the injection well;
(b) thereafter terminating injection of the
mixture of essentially pure-oxygen and
carbon dioxide and injecting essentially
pure oxygen into the injection well to
support in-situ combustion, and
(c) producing oil from the formation via said
production well.
2. The method of Claim 1 wherein the
combustion-supporting gas in step (a) comprises not more
than 80% carbon dioxide.
3. The method of Claim 1 further comprising
terminating injection of the mixture of essentially pure
oxygen and carbon dioxide during step (b) when the
combustion front initiated during step (a) has advanced
away from the injection well a distance of at least 30
feet.

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4. The method of Claim 1 further comprising
gradually decreasing the amount of carbon dioxide in
said combustion-supporting gas following step (a) until
the gas injected comprises essentially pure oxygen.
5. The method of Claim 4 wherein the amount of
carbon dioxide is gradually decreased when the
combustion front has advanced away from the injection
well a distance of at least 30 feet.

Description

SS
1354 ~1-
IN-SITU COMBUSTION METHOD FOR
RECOVERY OF HEAVY OIL UTILIZING
OXYGEN AND CARBON DIOXIDE ~S INITIAL OXIDANT
~ACKGROUND OF THE INVENTION
l. Field o~ The-Invention
This invention pertains to the recovery o~ oil
~rom a subterranean, viscous oil-contain~ng formation
utili2ing an improved in~situ-combustion process.
2. Back~round of the Inventlon
In-situ combustion is a oommon method ~or
reoovering viscous crudes or ta~ sands. The use of high
purity oxygen in place o~ alr signi~icantly improves the
per~ormance o~ the in-situ co~bustion prneess. The
in~ection o~ oxygen into a wellbore, how~ver~ presents
significant hazar~s and requires sa~ety precaut~ons.
Pr~vious work in this regard includes the injection of
2 through a bottom water zone 9 as disclosed in U.S.
~atent No. 3,2089519, and the initiation o~ combustion
with air followed by oxygen as disclosed in an article
by G.Pusch, Erdol und Kohle-Erdgas~Petrochemie combin2d
with Brennstof~-Chemie, Vol. 30, No. l, Jan. 1977, pp.
13-25. All these methods use air to est~blish gas
flow. Howev~r, it has been found that in~ection of air
increases the viscosity o~ the oil by 100 times when the .
oil is contacted by air fcr two days at 210~F. This
increase in viscosity is detrlmental to the recovery
process. In addition, the inert gaseous nltrogen in the
air injected tends to reduce the e~fective permeability
for oil in the reservoir.

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My invention proposes a rnethod to initlate the
in-situ combustion operation ~nitially using a
combustion supporting gas comprising a mixture of
essentially pure oxygen and carbon dioxide ~ollowed by
the use o~ essent~ally pure oxygen that eliminates the
problem o~ increasing the viscoslty o~ the oil in the
~ormation using conventional combu~tion supporting gases
such as air, air enriched with oxygen, or oxygen.
The invention is a method for recovering oil
~rom a subterranean~ viscous oil-containing formation
penetrated by a~ least one injection well and a spaced
apart production well comprlsing initiating in-situ
cambust~on by injecting a mixture o~ ess~ntially pure
axygen and carbon dioxide lnto the inject-ion well
followed by in~ecting essentially pure oxygen into the
~ormation to supp~rt in-situ combustion either
immediately a~ter the initiation o~ combustion or after
the combustion front has advanced away from the
injection well a distance o~ at least 30 feet~ The
amount o~ carbon dioxide mixed with oxygen for
initiation o~ in-situ combustion is not morz than 80%.
The use o~ an oxygen/carbon diaXide mixture to initiate
in-situ combustion does not promote degradatl-on ln oil
viscosity due to oxidatinn.
DESCRIPTION OF THE PREFERRED EMBODXMENT
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In one embodiment o~ my invention, an in;situ
combustion front is established in a subterranean,
viscous oil-containing formation sueh as tar sand
deposits by injecting a combustion-supporting gas
comprising essentially pure oxygen and carbon dioxide.
The oxygen/carbon dioxide mixture is introduced into the

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1354 -3-
~ormation via at least one injection well to establish
an ln-situ combustion front and oil is produced ~rom the
~or~ation via a spaced apart production well. The
amount o~ carbon dloxide mixed with the oxygen must not
be more than 80% so as not to inter~ere with the in-situ
combustion process. ~he amount o~ carbon dioxide may be
substantially les than ~0%, depending upon the
experienc~ o~ operating p~rsonnel in handling high
purity oxygen. Once an in-situ combustion ~ront is
initiated, or pre~erably a~ter the combustion ~ront has
advanced away ~rom the in~ection well a distance o~ at
least 3n feet r the mixture ~ ~ ~C02 is term~nated
and essentially pure oxygen is injected into the
injection well to support combustion. In a pre~erred
embodiment, a~ter in-sltu combustion has been initiated,
or pre~erably a~ter the c¢mbust~on front:has advanced
away ~ro~ the injection well a distance o~ at least 30
~eet, the amount o~ carbon dioxide in~ected into the
formation along with oxygen iS ~9radually decreased at a
controlled rate until the combu.ction-supporting gas
comprises essentially pure oxygen.
The use o~ a mixture of oxygen and carbon
dioxid~ as the combustion-supporting gas to ~nitiate
in-situ combustion does not pra~ote degradation in oil
viscosity due to oxldation as is the ~ase with mixtures
o~ oxygen and nitrogen in conventional insitu
combustion processes~ In the present process, any
increase in oil viscosity due to oxidation is more than
o~fset by a reduction in viscosity due to carbon dioxide
dlssolution. For example, an Athabasca bitumen with a
viscosity o~ 50,000 cp at 104F. will have a reduction
in viscosity by lOO tim~s, when saturated with carbon
dioxide at 600 psia (see Jacobs, F.A., et al., J. Can.
Pet. Tech., Oct.-Dec. 9 1980, pages 46-50). In the

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lattc~ example7 it is disclosed that it requires only
200 so~ o~ carbon dioxide to saturate a barrel o~ oil at
600 psia. Assuming the oil saturation is 1000
bbls/ac-~t, lt requires only 0.2 x 106 sc~Jac-~t o~
carbon dioxide to saturate the oil. After in-situ
combustion has been initiated, there is a su~icient
a~ount o~ carbon dioxide generated ~n situ to saturate
the oil in the formation so there is no need to
continuously inject carbon dioxlde during the combustion
lo process. It is noted that the dissolution o~ the carbon
dioxide in the oil reduces th~ ~ree gas in the reservoir
and increases e~ective oil permeability. In addition 7
carbon dioxide has a nice ~ire-extinguish~ng
oharacterlstic which can be conveniently applied in the
case o~ an acoidental wellbore ignition.
Th~ oxygen and carbon dinxide may both be
stored in liquid ~orm-near th~ in~ection well or wells,
Both materials may be mor conveniently pumped in liquid
~orm ~rom separate storage tanks into a vaporizer and
then in~ected into the injeotion well. Th~ composltion
of the oxygen/carbon dioxide mlxture supplied to the
inJection well i~ controll~d by sensing and controlling
the ~low rates of the individual oxygen and carbon
dioxide streams by means of a fl'ow controller.