US20130168094A1

US20130168094A1 - Enhanced heavy oil recovery using downhole bitumen upgrading with steam assisted gravity drainage

Info

Publication number: US20130168094A1
Application number: US13/717,894
Authority: US
Inventors: Frank Michael Bayles
Original assignee: ConocoPhillips Co
Current assignee: ConocoPhillips Co
Priority date: 2012-01-03
Filing date: 2012-12-18
Publication date: 2013-07-04
Also published as: WO2013103518A1

Abstract

Methods for recovery of heavy oils use selective catalytic downhole upgrading with SAGD technology. Certain embodiments include extracting heavy oil using a SAGD process and upgrading the heavy oil in a production well with a cracking catalyst. The cracking catalyst is introduced into the production well, allowing the extracted hydrocarbons to interface with the cracking catalyst to upgrade the hydrocarbons. The upgraded hydrocarbons are then separated from the cracking catalyst. This upgraded stream has a lower molecular weight, significantly reducing the viscosity of the produced hydrocarbons. A gasifier is provided to gasify a portion of the slurry containing unconverted heavy oil and cracking catalyst to produce syngas. The syngas may then be used to produce steam for use in the SAGD extraction process, improving energy efficiency of the process. Further, formation catalyst losses are avoided as the catalyst injected into the well is recovered and available for reuse.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a non-provisional application which claims benefit under 35 USC §119(e) to U.S. Provisional Application Ser. No. 61/582,627 filed Jan. 3, 2012, entitled “Enhanced Heavy Oil Recovery Using Downhole Bitumen Upgrading with Steam Assisted Gravity Drainage,” which is incorporated herein in its entirety.

FIELD OF THE INVENTION

The present invention relates generally to methods and systems for enhanced recovery of heavy oils. More particularly, but not by way of limitation, embodiments of the present invention include methods and systems for enhancing recovery of heavy oils using selective catalytic downhole upgrading of a portion of the heavy oil in combination with steam-assisted gravity drainage technology.

BACKGROUND

The production of hydrocarbons from low mobility reservoirs presents significant challenges. Low mobility reservoirs are characterized by high viscosity hydrocarbons, low permeability formations, and/or low driving forces. Any of these factors can considerably complicate hydrocarbon recovery. Extraction of high viscosity hydrocarbons is typically difficult due to the relative immobility of the high viscosity hydrocarbons. For example, some heavy crude oils, such as bitumen, are highly viscous and therefore immobile at the initial viscosity of the oil at reservoir temperature and pressure. Indeed, such heavy oils may be quite thick and have a consistency similar to that of peanut butter or heavy tars, making their extraction from reservoirs especially challenging. As used herein, the term, “heavy oil” includes any heavy hydrocarbons having greater than 10 carbon atoms per molecule. Further, the term “heavy oil” includes heavy hydrocarbons having a viscosity in the range of from about 100 to about 100,000 centipoise at 100° F., and an API gravity from about 5 to about 22° API; or can be a bitumen having a viscosity less than about 100,000 centipoise, and an API gravity less than or equal to about 22° API.
Conventional approaches to recovering heavy oils often focus on methods for lowering the viscosity of the heavy oil or heavy oil mixture so that the heavy oil may be produced from the reservoir. Examples of methods for lowering the heavy oil viscosity include introducing a diluent to the heavy oil or heating the heavy oil. Commonly used heating methods include a number of technologies, such as steam flooding, cyclic steam stimulation, and Steam Assisted Gravity Drainage (SAGD), which require the injection of hot fluids into the reservoir. A 100° F. increase in the temperature of the heavy oil in a formation can lower the viscosity by two orders of magnitude. Thus, heating formation heavy oils can dramatically improve the efficiency of heavy oil recovery.
While diluents, such as solvents or lighter hydrocarbons introduced into a formation, can be effective at reducing the viscosity of the heavy oils therein, solvents can be quite expensive. Indeed, not only are solvents quite expensive, the use of diluents also suffers from costly solvent losses (i.e. solvent lost to the formation that is not subsequently recovered). Thus, the process economics of using diluents are highly sensitive to both solvent cost and solvent losses. Often, the use of solvents to recover heavy oils is prohibitively expensive.
As for the heating methods used to enhance recovery of heavy oils, these methods are highly disadvantageous in that they are all significantly energy intensive. In some cases, these thermal recovery techniques are so inefficient that they are often non-economically viable for recovering heavy crude oil. Indeed, about 2 to 3 barrels of water must typically be vaporized to steam for each barrel of oil produced. Not only must the heavy oil be heated, but the entire mass in the reservoir including rock and sand must also be heated, thus contributing to the inefficiency of these conventional heating methods.
Not only are these energy-intensive processes often economically inefficient, the hydrocarbons produced are usually a lower quality crude oil that requires upgrading either at the production site or at a refinery. Because heavy oils are so viscous, they cannot often be transported from the production site without adding diluents.
Unfortunately, due to the capital intensive nature of an upgrading facility, upgrading facilities only become economical when used to service large quantities of crude oil (e.g. greater than about 100,000 barrels of crude oil a day). Therefore, upgrading facilities are typically not economical for those wells producing less than about 100,000 barrels of crude oil a day.
Certain conventional methods contemplate in-situ upgrading in which an upgrading catalyst is injected into a subterranean formation to allow the crude oil therein to be upgraded. Unfortunately, this conventional method suffers from the disadvantage of large catalyst losses to the formation. Also, it is difficult to control the distribution and contact duration of the catalyst in the formation to maximize the impact of the catalyst with the heavy oil. Further, unlike surface upgrading facilities, this method does not allow reuse of any of the upgrading catalyst injected to the formation.
Thus, the energy inefficiencies of SAGD processes combined with the limitations of conventional upgrading technologies limit the efficiency under which heavy oil can be produced. Accordingly, there is a need for enhanced heavy oil recovery methods that address one or more of the disadvantages of the prior art.

SUMMARY

The present invention relates generally to methods and systems for enhanced recovery of heavy oils. More particularly, but not by way of limitation, embodiments of the present invention include methods and systems for enhancing recovery of heavy oils using selective catalyst downhole upgrading scheme in combination with steam-assisted gravity drainage technology.
One example of a method for enhancing heavy oil recovery from a subterranean formation comprises the steps of: providing a production well intersecting a subterranean formation, wherein the production well is in fluid communication with an injection well to form a well pair among one or more steam-assisted gravity drainage production well pairs for recovering heavy oil from a bitumen formation; (a) providing a cracking catalyst; (b) heating the cracking catalyst to a catalyst pre-heated temperature; (c) introducing the cracking catalyst into the production well at a catalyst injection point above a producing interval; (d) allowing the heavy oil to be produced through the production well; (e) allowing the heavy oil to be upgraded in the production well in the presence of the cracking catalyst to form an upgraded mixture; wherein the catalyst pre-heated temperature is sufficient to provide a reaction temperature of about 500° F. to about 550° F. during step (e); (f) introducing the upgraded mixture to a separator to separate the upgraded mixture into a hydrocarbon-enriched stream and a catalyst slurry; (h) separating the catalyst slurry into two streams, a gasification feed and recovered catalyst; (i) recycling the recovered catalyst to the catalyst injection point; (j) introducing the gasification feed to a gasifier to gasify the gasification feed to produce a syngas and a waste stream; (k) producing steam using the syngas in a steam generator for use in the one or more steam-assisted gravity drainage production well pairs; (l) introducing the steam into the one or more steam-assisted gravity drainage production well pairs.
One example of a method for enhancing heavy oil recovery from a subterranean formation comprises the steps of: providing a production well intersecting a subterranean formation, wherein the production well is in fluid communication with an injection well to form a well pair among one or more steam-assisted gravity drainage production well pairs for recovering heavy oil from a bitumen formation; (a) providing a cracking catalyst; (b) heating the cracking catalyst; (c) introducing the cracking catalyst into the production well at a catalyst injection point above a producing interval; (d) allowing the heavy oil to be produced through the production well; (e) allowing the heavy oil to be upgraded in the production well in the presence of the cracking catalyst to form an upgraded mixture; (f) introducing the upgraded mixture to a separator to separate the upgraded mixture into a hydrocarbon-enriched stream and a catalyst slurry; (h) separating the catalyst slurry into two streams, a gasification feed and recovered catalyst; (i) recycling the recovered catalyst to the catalyst injection point; (j) introducing the gasification feed to a gasifier to gasify the gasification feed to produce a syngas and a waste stream; (k) producing steam using the syngas in a steam generator for use in the one or more steam-assisted gravity drainage production well pairs; (l) introducing the steam into the one or more steam-assisted gravity drainage production well pairs.
The features and advantages of the present invention will be apparent to those skilled in the art. While numerous changes may be made by those skilled in the art, such changes are within the spirit of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present disclosure and advantages thereof may be acquired by referring to the following description taken in conjunction with the accompanying figures, wherein:

FIG. 1 illustrates an example of an enhanced heavy oil recovery system using a downhole upgrading catalyst in combination with a SAGD process in accordance with one embodiment of the present invention.

While the present invention is susceptible to various modifications and alternative forms, specific exemplary embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION

The present invention relates generally to methods and systems for enhanced recovery of heavy oils. More particularly, but not by way of limitation, embodiments of the present invention include methods and systems for enhancing recovery of heavy oils using selective catalytic downhole upgrading of heavy oil in combination with steam-assisted gravity drainage technology.
In certain embodiments, methods and systems for enhancing recovery of heavy oils comprise the steps of extracting heavy oil using a SAGD process and upgrading the heavy oil in a production well with a cracking catalyst. In this way, cracking catalyst is introduced into the production well, allowing the extracted hydrocarbons to intimately interface with the cracking catalyst so as to upgrade the hydrocarbons in the production well. The upgraded hydrocarbons thus produced are separated from the cracking catalyst in a separator. This upgraded stream has a lower molecular weight which significantly reduces the viscosity of the produced heavy oil at similar temperatures.
A gasifier is provided to gasify a portion of the slurry that contains unconverted heavy oil and cracking catalyst. The produced syngas is then used to produce steam for use in the SAGD extraction process. In this way, the energy efficiency of the SAGD process is improved by leveraging syngas produced from the gasifier to produce steam. Further, this enhanced process avoids catalyst losses to the formation as the catalyst that is injected into the production well is recovered and available for reuse. The specific activity of the catalyst can be controlled by mixing the recycled catalyst with fresh catalyst. Other features, embodiments, and advantages will be apparent from the disclosure herein.
Reference will now be made in detail to embodiments of the invention, one or more examples of which are illustrated in the accompanying drawings. Each example is provided by way of explanation of the invention, not as a limitation of the invention. It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used on another embodiment to yield a still further embodiment. Thus, it is intended that the present invention cover such modifications and variations that come within the scope of the invention.
FIG. 1 illustrates an example of an enhanced heavy oil recovery system using a selective catalyst downhole upgrading scheme in combination with a SAGD process in accordance with one embodiment of the present invention. In this example, enhanced heavy oil recovery system 100 comprises SAGD well pair 122, separator 130, slurry catalyst tank 140, fresh catalyst tank 150, process heater 160, gasifier 170, and steam generator 180.
Production well 112 and steam injection well 120 intersect subterranean formation 105 for extracting heavy oil from production interval 114. Portions of production well 112 and steam injection well 120 together forms a SAGD well pair 122, which traverses through production interval 114. Typically, SAGD well pairs comprise a pair of horizontal wells drilled into an oil reservoir, one a few meters above the other (e.g. about 4 to about 6 meters). The upper well injects steam, possibly mixed with solvents, and the lower one collects the heated crude oil or bitumen that flows out of the formation, along with any water from the condensation of injected steam. The basis of the process is that the injected steam forms a “steam chamber” that grows vertically and horizontally in the formation. The heat from the steam reduces the viscosity of the heavy crude oil or bitumen which allows it to flow down into the lower wellbore. The steam and gases rise due to their low density compared to the heavy crude oil below, ensuring that steam is not produced at the lower production well. Production as high as 70% to 80% of oil in place is common in suitable reservoirs. In this way, the SAGD process may be used to extract heavy oil for production to surface 110 via production well 112. It is recognized that a plurality of SAGD well pairs may be used to extract heavy oil from subterranean formation 105 as desired.
Often, the heavy oil thus produced is of low quality and requires additional viscosity reduction, usually around an API of at least about 19 to about 22°, to allow transportation of the heavy oil to its final destination. While this can be accomplished by adding diluent to the extracted hydrocarbons, this method is often not economical. Additionally, as described in the Background Section, upgrading facilities are capital intensive and therefore may not always be economical, especially for smaller production wells. Accordingly, the methods herein contemplate introducing heated cracking catalyst 162 to production well 112 at catalyst injection point 116. In this way, extracted heavy oil may be upgraded in the presence of heated cracking catalyst 162 as the heavy oil and cracking catalyst 162 flow through downhole reaction interval 118. In certain embodiments, the ratio of heated cracking catalyst 162 to heavy oil varies from three to seven on a weight basis.
Cracking catalysts suitable for use with this invention include any catalysts capable of upgrading the heavy oil to lighter compounds at production temperatures and pressures. To achieve adequate cracking at temperatures found in production systems, a high activity catalyst is required. Examples of suitable cracking catalysts include high surface area catalysts, such as, nanocatalysts. In some embodiments, the cracking catalyst includes particle sizes ranging from about 50 micrometers to about 100 micrometers. In some embodiments, the particle size of the cracking catalyst is selected to maximize surface area for enhanced upgrading reaction of the heavy oil.
Catalyst injection point 116 may be located at any distance from producing interval 114 to prevent catalyst loss to the formation. Examples of suitable distances include, but are not limited to, about 50 feet from producing interval 114 and about 40 feet to about 100 feet from producing interval 114. In certain embodiments, the length and diameter of the production well is preferably of dimensions to provide a sufficient reaction residence time to allow the extracted hydrocarbons to be sufficiently upgraded. Downhole reaction interval 118 may be any length suitable for providing sufficient reaction residence time to allow the heavy oil to be upgraded as desired.
The main criteria for determining upgrading success are reduction in viscosity. The degree of viscosity reduction is based on the economics of the cost of upgrading versus the decrease in cost of any diluent necessary to allow pipeline transportation of the heavy oil. The range is from maximum diluent (traditional approach) to no diluent. At maximum diluent, up to one part light condensate—natural gas liquids—may be added to two parts bitumen.
Examples of suitable selective catalytic downhole reaction interval lengths include, but are not limited to, at least about 500 feet and lengths from about 500 feet to about 1,200 feet. Examples of suitable reaction residence times include, but are not limited to, about two seconds to about 2 minutes to several minutes.
Upgraded mixture 129 exits subterranean formation via production well 112 at surface 110. Upgraded mixture 129 comprises both upgraded hydrocarbons combined with catalyst slurry. Upgraded mixture 129 is introduced to separator 130 to separate upgraded mixture 129 into hydrocarbon-enriched stream 132 and recovered catalyst 134. In certain embodiments, separator 130 is any process equipment suitable for separating hydrocarbon-enriched stream 132 from recovered catalyst 134. Examples of suitable separators include, but are not limited to, fractionators, flash drums, or any combination thereof. From separator 130, recovered catalyst 134 flows to optional slurry catalyst tank 140. The recovered catalyst may be split into recycled catalyst 142 a and gasification feed 144. Now that hydrocarbon-enriched stream 132 has a higher API (i.e. a lower viscosity) than the heavy oil in-situ in the formation, hydrocarbon-enriched stream 132 may be transported to a final destination, for example, to storage or to a refinery for further processing.
Recycled catalyst 142 a combines with fresh catalyst 152 from fresh catalyst tank 150 to form cracking catalyst mixture 154 and is fed to process heater 160. In certain embodiments, process heater 160 heats cracking catalyst mixture 154 to form heated cracking catalyst 162. Process heater 160 heats heated cracking catalyst 162 to a temperature to achieve an overall reaction temperature of about 500° F. to about 550° F. In some alternative embodiments, all or a portion of recycled catalyst 142 a may bypass process heater 160 via diverted catalyst 142 b. In this way, catalyst slurry may be recycled to allow catalyst reuse for upgrading the extracted heavy oil from subterranean formation 105. This recycling of catalyst avoids the catalyst losses inherent to those conventional methods that inject catalyst directly into the subterranean formations. Moreover, introducing the catalyst in the confined space of production well 112 allows the catalyst to be actively concentrated on the extracted heavy oil and further allows the reaction conditions to be more precisely controlled or varied, which is not possible when injecting catalyst directly into a formation.
Returning to separator 130, gasification feed 144 comprises a portion of recovered catalyst 134. Gasification feed is introduced to gasifier 170. Gasification is a process that converts organic or fossil based carbonaceous materials into carbon monoxide, hydrogen, carbon dioxide and methane. This process is achieved by reacting material at high temperatures (e.g. greater than about 700° C.), without combustion, with a controlled amount of oxygen and/or steam. The resulting gas mixture is often referred to as syngas (from synthesis gas or synthetic gas) or producer gas and is itself a fuel. One of the advantages of gasification is that using the syngas is potentially more efficient than direct combustion of the original fuel, because it can be combusted at higher temperatures, so that the thermodynamic upper limit to the efficiency defined by Carnot's rule is higher or not applicable. In addition, the high-temperature combustion refines out corrosive ash elements such as chloride and potassium, allowing clean gas production from otherwise problematic fuels.
Thus, gasification of gasification feed 144 in gasifier 170 produces syngas 172 and waste stream 174. Syngas 172 may be used as a fuel to produce steam in steam generator 180 or to produce heat in process heater 160 by combusting syngas 172. Steam generator 180 may comprise a direct steam generator, an indirect steam generator, or a combination thereof for generating steam 182. By leveraging syngas 172 for steam production in the SAGD process, energy savings are realized and the efficiency of the SAGD process is enhanced. Waste stream 174 is also produced by gasifier 170. Waste stream 174 is typically disposed of.
In certain optional embodiments, a portion of syngas 170 may be diverted for use in process heater 160 to reduce energy requirements needed to heat cracking catalyst mixture 154 to form heated cracking catalyst 162. This use of syngas 170 in process heater 160 reduces the overall energy required to heat cracking catalyst mixture 154 and therefore further economizes energy usage of the upgrading process.
A higher quality upgraded product can be produced by separating the hydrogen from the syngas and directing it to the well bore. Introducing hydrogen in the catalytic upgrading will result in a more stable product than with non-hydrogen upgrading.
It is recognized that any of the elements and features of each of the devices described herein are capable of use with any of the other devices described herein without limitation. Furthermore, it is recognized that the steps of the methods herein may be performed in any order except unless explicitly stated otherwise or inherently required otherwise by the particular method.
Therefore, the present invention is well adapted to attain the ends and advantages mentioned as well as those that are inherent therein. The particular embodiments disclosed above are illustrative only, as the present invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular illustrative embodiments disclosed above may be altered or modified and all such variations and equivalents are considered within the scope and spirit of the present invention. Also, the terms in the claims have their plain, ordinary meaning unless otherwise explicitly and clearly defined by the patentee.

Claims

What is claimed is:

1. A method for enhancing heavy oil recovery from a subterranean formation comprising the steps of:

(a) providing a production well intersecting a subterranean formation, wherein the production well is in fluid communication with an injection well to form a well pair among one or more steam-assisted gravity drainage production well pairs for recovering heavy oil from a bitumen formation;

(b) providing a cracking catalyst;

(c) heating the cracking catalyst to a catalyst pre-heated temperature;

(d) introducing the cracking catalyst into the production well at a catalyst injection point above a producing interval;

(e) allowing the heavy oil to be produced through the production well;

(f) allowing the heavy oil to be upgraded in the production well in the presence of the cracking catalyst to form an upgraded mixture;

(g) wherein the catalyst pre-heated temperature is sufficient to provide a reaction temperature of about 500° F. to about 550° F. during step (f);

(h) introducing the upgraded mixture to a separator to separate the upgraded mixture into a hydrocarbon-enriched stream and a catalyst slurry;

(i) separating the catalyst slurry into two streams, a gasification feed and recovered catalyst;

(j) recycling the recovered catalyst to the catalyst injection point;

(k) introducing the gasification feed to a gasifier to gasify the gasification feed to produce a syngas and a waste stream;

(l) producing steam using the syngas in a steam generator for use in the one or more steam-assisted gravity drainage production well pairs;

(m) introducing the steam into the one or more steam-assisted gravity drainage production well pairs.

2. The method of claim 1 further comprising the step of heating at least a portion of the recovered catalyst after step (i) and before step (j).

3. The method of claim 2 wherein a portion of the syngas produced in step (j) is used to heat the recovered catalyst.

4. The method of claim 1 wherein the injection point is about 40 to about 100 feet above the producing interval.

5. The method of claim 1 wherein the production well has a length of at least about 500 feet or from about 500 to about 1,200 feet.

6. The method of claim 1 wherein the production well has a length sufficient to provide a reaction residence time from the catalyst injection point to the surface of about 20 seconds to about 2 minutes.

7. The method of claim 1 wherein the cracking catalyst is high activity, high surface area catalyst.

8. The method of claim 7 wherein the cracking catalyst comprises a nanocatalyst.

9. The method of claim 1 wherein the ratio of cracking catalyst introduced into the production well to the heavy oil produced through the production well is about three to about seven on a weight basis.

10. The method of claim 1 wherein the cracking catalyst has a particle size of about 50 μm to about 100 μm

11. The method of claim 1 wherein the hydrocarbon-enriched stream has an API from about 5° to about 22°.

12. The method of claim 1 wherein the separator is a flash tower or a fractionator.

13. The method of claim 1 wherein the separator comprises a fractionator.

14. The method of claim 1 wherein the one or more steam-assisted gravity drainage production well pairs comprises a plurality of steam-assisted gravity drainage production well pairs.

15. The method of claim 1 wherein the steam generator is a direct steam generator or an indirect steam generator; wherein the steam is generated in step (1) by combustion of the syngas.

16. A method for enhancing heavy oil recovery from a subterranean formation comprising the steps of:

(b) providing a cracking catalyst;

(c) heating the cracking catalyst;

(e) allowing the heavy oil to be produced through the production well;

(g) introducing the upgraded mixture to a separator to separate the upgraded mixture into a hydrocarbon-enriched stream and a catalyst slurry;

(h) separating the catalyst slurry into two streams, a gasification feed and recovered catalyst;

(i) recycling the recovered catalyst to the catalyst injection point;

(j) introducing the gasification feed to a gasifier to gasify the gasification feed to produce a syngas and a waste stream;

(k) producing steam using the syngas in a steam generator for use in the one or more steam-assisted gravity drainage production well pairs;

(l) introducing the steam into the one or more steam-assisted gravity drainage production well pairs.

17. The method of claim 16 further comprising the step of heating at least a portion of the recovered catalyst after step (h) and before step (i);

18. The method of claim 17 wherein a portion of the syngas produced in step (j) is used to heat the recovered catalyst.