Method for CAGD recovery of heavy oil

Abstract

A novel method for recovering oil is provided wherein oxygen is injected into a chamber within an oil deposit thereby combusting oil at the chamber walls. The heated oil to drains toward the reservoir floor and is recovered via a production well.

Description

CROSS-REFERENCE

This application is a continuation-in-part of U.S. patent application Ser. No. 11/704,618 filed Feb. 9, 2007; which application in turn claimed the benefit of U.S. Provisional Application Ser. No. 60/773,410 filed Feb. 15, 2006.

FIELD OF THE INVENTION

This invention relates to a method for the recovery of heavy oil. More specifically, this invention relates to reducing the energy inputs required in Steam Assisted Gravity Drainage (SAGD) methods now employed commercially. This invention also relates to improved methods for in-situ combustion.

BACKGROUND OF THE INVENTION

In-situ combustion of heavy oil is a potentially attractive method of mobilizing heavy oil for production. No external source of fuel is required and temperatures can be high enough for oil upgrading. However, few commercial trials have been successful because of the difficulty in controlling combustion. An improvement known as Toe to Heel Air Injection (THAI) is one attempt to solve this issue. Another approach to heavy oil production is heating by steam injection. A recent break-through is Steam Assisted Gravity Drainage (SAGD). SAGD is now widely used to produce heavy oil from oil sands such as are found throughout Alberta.

Although heavy oil can be economically produced, little or no upgrading of the oil is achieved. In SAGD, steam is injected into a heavy oil deposit forming an expanding steam chamber avoiding loss of steam through cracks. Heated oil drains to a production well located under the injection well. Both wells are typically horizontal wells. Typically, the amount of steam required to produce a barrel of oil decreases with time for a period following initial operation. The minimum steam requirement is usually reached after three or four years of operation. Inasmuch as a major cost of such an operation is the cost of providing the steam, there is a need to reduce the amount of steam required to an amount below the minimum now achievable.

It is therefore an object of the present invention to provide a significant reduction in the amount of steam required to produce oil. It is a prime object of the invention to make possible utilization of in-situ combustion to replace at least a portion of the steam required in SAGD production of heavy oil from oil sands. Further it is an object of the invention to provide a method to produce upgraded oil.

SUMMARY OF THE INVENTION

It has now been found that injection of oxygen along with steam into a SAGD steam chamber reduces the amount of steam required to produce a barrel of oil. The resulting in-situ combustion, referred to herein as Combustion Assisted Gravity Drainage (“CAGD”) provides heat to reduce the amount of steam required to produce a barrel of oil and provides for temperatures high enough for oil upgrading.

In-situ combustion in the presence of steam allows control of reaction temperature by control of the oxygen concentration in the gases within the steam chamber. Temperatures at the chamber wall may be well above the saturated steam temperature at the pressure within the chamber. Oil may be upgraded by cracking and high enough temperatures for steam reaction with carbon or hydrocarbons to produce hydrogen are achievable. For existing SAGD operations, oxygen may be mixed with the steam being injected via an injection well. In this case quality of the steam can be limited to eighty or ninety percent to provide a liquid water shield to limit oxidation of the product oil. A separate oxygen injection well may be used to inject the oxygen at a higher elevation than the existing steam injection well. This provides a steam blanket over the production well to limit product oil oxidation.

Injecting oxygen into a SADG steam chamber for in-situ combustion without a continuing supply of steam eliminates the need for a surface fuel supply to produce steam. In this case, air or oxygen-enriched air may be utilized rather than high purity oxygen. For the purpose of this invention, a chamber is a region within a heavy oil deposit bounded by low permeability walls. A steam chamber is a chamber in an oil reservoir formed by injecting steam into the reservoir replacing all or a portion of the chamber oil with steam.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a SAGD steam chamber in a heavy oil deposit operated in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 depicts a SAGD steam chamber 30 in heavy oil deposit 40 operated in accordance with the present invention. As in SAGD, drained oil is withdrawn through production well 33. Oxygen in admixture with steam is injected via well 34 to maximize upgrading of produced oil. Alternatively, oxygen in admixture with steam is injected via optional well 31 into an upper region of chamber 30. In this mode of operation, oxidation and upgrading of oil draining toward production well 33 may be limited by injection of oxygen-free or reduced-oxygen content fluid, as for example steam, via well 34 in sufficient quantity to limit access of oxygen to drained oil being withdrawn through well 33.

Although the present invention has been described in detail with reference to certain preferred versions thereof, other versions are possible. Therefore, the spirit and scope of the invention should not be limited to the description of the preferred versions contained herein.

Claims

1. A method for producing oil comprising:

a) providing a steam chamber within an oil formation wherein the steam chamber defines steam chamber walls;

b) injecting oxygen into the steam chamber and initiating combustion of oil at the steam chamber walls;

c) allowing heated and cracked oil to drain toward a production well; and

d) recovering oil through the production well.

2. The method of claim 1 wherein the steam chamber is a Steam Assisted Gravity Drainage chamber.

3. The method of claim 1 wherein the combustion temperature at the steam chamber wall is higher than the temperature of saturated steam at the steam chamber pressure.

4. The method of claim 1 wherein the oxygen concentration in the steam chamber further comprises a means for controlling the combustion temperature.

5. The method of claim 1 wherein high purity oxygen is injected in admixture with steam having a quality less than 90%.

6. The method of claim 1 wherein the steam chamber walls are maintained at a temperature above that at which oil cracks.

7. The method of claim 5 wherein the combustion temperature of an admixture of oxygen and steam is above the saturated steam temperature at the steam chamber pressure.

8. A method for producing upgraded oil from a heavy oil deposit comprising:

a) injecting oxygen into an enclosed chamber within the deposit wherein the chamber defines chamber walls;

b) combusting fuel at the chamber walls;

c) maintaining the walls at a combustion temperature higher than the temperature of saturated steam; and

d) withdrawing upgraded oil through a production well.

9. The method of claim 8 wherein the oxygen is injected in admixture with steam.

10. The method of claim 8 wherein the oxygen is injected in admixture with nitrogen.

11. The method of claim 8 wherein the oxygen is supplied as air.

12. The method of claim 8 wherein the oxygen is injected above any lower wells.