CA1196855A - In-situ combustion method for recovery of heavy oil utilizing oxygen and carbon dioxide as initial oxidant - Google Patents

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.

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.

1354 ~2-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
-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 ~ >8 5~

~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 1354 _l~

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.

Claims (5)

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.

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.