US20080017381A1 - Downhole steam generation system and method - Google Patents

Abstract

The present invention relates generally to a device, system and method for generating steam downhole. More particularly, the present invention relates to an electrical steam generation system that enables efficient production of downhole steam without the heat and pressure losses realized by surface steam generation equipment.

Description

FIELD OF THE INVENTION
• The present invention relates generally to a device, system and method for generating steam downhole. More particularly, the present invention relates to an electrical steam generation system that enables efficient production of downhole steam without the heat and pressure losses realized by surface steam generation equipment.
BACKGROUND OF THE INVENTION
• In heavy oil recovery, the use of steam to assist in oil recovery is well known. For example, it is common to drill parallel horizontal wells into formations at different levels containing heavy oil or bitumen. Such wells have been used in both Steam Assisted Gravity Drainage (SAGD) and Vapor-Extraction (VAPEX) production methods. In the SAGD system, steam is applied to an upper (or injection) well to contact heavy hydrocarbons inherent within the pores of the formation to decrease the viscosity of the hydrocarbons. In the VAPEX system, heated solvents are applied. The steam or solvent increases temperature and pressure within the formation to reduce hydrocarbon viscosity which results in hydrocarbons collecting in a lower production (or recovery) well.
• The current methods of injecting steam downhole are energy and capital intensive. Steam plants on the surface produce steam in boilers usually utilizing natural gas or other fossil fuels as a combustible fuel. The capital costs associated with designing, building and operating a surface steam plant are significant requiring years of production from the formation to make the infrastructure investment worthwhile. As a result, heavy oil recovery using surface steam production is generally only utilized for large scale projects with the result that smaller scale projects that could benefit from steam injection to aid hydrocarbon recovery are not utilized.
• In addition, delivering high pressure steam to the formation is inefficient as the steam must be transported under pressure through lengthy surface and well pipes to the formation. As the horizontal and vertical distances in a typical wellbore can be many thousands of feet, significant losses in steam pressure and temperature result thereby reducing the efficiency of the process.
• As a result, there has been a need for steam production facilities with lower infrastructure costs that can deliver steam more efficiently to downhole formations.
SUMMARY OF THE INVENTION
• In accordance with the invention, there is provided a method of creating in situ steam in a well for hydrocarbon recovery comprising the steps of: positioning a downhole electrical steam generating system in the well adjacent a hydrocarbon bearing formation; continuously forming downhole steam within the well from in situ water; and, maintaining a high intra-well pressure to promote hydrocarbon recovery. In a preferred embodiment, the electrical steam generating system is conveyed to the hydrocarbon bearing formation by coiled tubing.
• In further embodiments, high intra-well pressure is maintained by adding water to the injection well from the surface or is maintained by a sealed wellhead. In other embodiments, steam is generated in an injection well and hydrocarbons are recovered from a recovery well or steam is generated in the well and hydrocarbons are simultaneously recovered from the well. Still further, the system may include at least two generation systems are operatively connected together to enable steam generation at separate locations within the well.
• In accordance with another embodiment, a downhole steam generation system for hydrocarbon recovery is provided comprising: a housing having openings operatively containing an electrical immersion heater, a connector system for connecting the electrical immersion heater to an electrical cable, and, a surface power unit for delivering electrical power to the electrical heater through the electrical cable.
• The electrical immersion heater preferably includes a thermocouple operatively connected to the surface power unit for controlling the surface temperature of the immersion heater.
• Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.
BRIEF DESCRIPTION OF THE DRAWINGS
• Embodiments of the present invention will now be described with reference to the attached Figures, wherein:
• FIG. 1 is a schematic diagram showing a typical deployment of a steam generation system in accordance with one embodiment of the invention;
• FIG. 2 is an isometric view of a steam generation system in accordance with one embodiment of the invention;
• FIG. 3 is a side view of a steam generation system in accordance with one embodiment of the invention;
• FIG. 3A is a cross-sectional view of a steam generation system in accordance with one embodiment of the invention;
• FIG. 3B is a cross-sectional view of a connector system of a steam generation system in accordance with one embodiment of the invention;
• FIG. 3C is a cross-sectional view of a downhole end of a steam generation system in accordance with one embodiment of the invention;
• FIG. 4 is a schematic diagram of the deployment of a steam generation system in accordance with a further embodiment of the invention;
• FIG. 4A is schematic cross-sectional view of a connector system at a downhole end of a steam generation system in accordance with one embodiment of the invention; and
• FIG. 4B is schematic cross-sectional view of a connector system at an uphole end of a steam generation system in accordance with one embodiment of the invention.
DETAILED DESCRIPTION
• Generally, the present invention provides a device, system and method for electrically producing steam downhole.
• With reference to the Figures, a downhole steam generation system and methods of deployment are described. The system includes adownhole heating device10,conductors12 and asurface control unit14. As shown inFIGS. 2, 3,3A,3B,3C and3D, thedownhole heating device10 generally includes ahousing10awith openings10bencasing an immersion heating element (IHE)10cand aconductor connection system10d.
• Downhole Heating Device10
• Housing10a
• Thehousing10 of the downhole heating device is a hollow cylindrical element with openings10bdesigned to allow the passage of fluids into the housing and to contact the IHE where the production of steam occurs. The openings10bare generally of a fixed dimension having sizes and positions designed a) to allow sufficient fluids to enter the housing, b) to provide structural integrity to the housing and c) to protect the immersion IHE downhole. In a preferred embodiment, the housing is constructed of 100% stainless steel and is preferably the same material as the outer surfaces of the IHE so as reduce the risk of deterioration by dissimilar metal and/or galvanic corrosion. Appropriate grades of stainless steel can be used to comply with industry standards enabling use of the system in both sweet and sour gas wells. The housing is adapted for attachment to coiled tubing by any suitable means known to those skilled in the art including specialized connectors and locking systems. In a preferred embodiment, the housing includes a bullnose end10ethat facilitates pushing the downhole heating device to a desired location (discussed below).
• Immersion Heating Element10c
• The IHE10cis an electric resistance heating element designed to operate between ambient temperatures and a maximum temperature, the maximum temperature being approximately 1400° F. Generally, it is preferred that the maximum temperature can be achieved within a few seconds of applying power to the IHE through power supplied through theconductor12 andsurface control unit14. The IHE is thermatically controlled by an integral thermocouple (not shown) that communicates with thesurface control unit14. Preferably, under normal operating conditions, in order to maximize the operating life of the IHE and to prevent hydrocarbon cracking, the IHE is operated at temperatures in the range of 400-500° F.
• The IHE is preferably powered by a 480 volt alternating current, single phase power source delivering 12,000 Watts or approximately 300 Watts per square inch of IHE surface area. In a typical embodiment, the IHE will be approximately 20-40 inches in length and have an outside diameter of approximately 0.6 inches.
• In various embodiments of the downhole heating element, additional functionality may be incorporated within the IHE such as fluid detection sensors and/or pressure sensors. Over temperature protection may also be provided.
• The resistance heating element is encased within an IHE housing to protect the resistance heating element. The construction is also sealed to prevent contact of fluids with the resistance heating element.
• The IHE is mounted within the housing by any suitable means. As shown inFIG. 3A andFIG. 3B, the IHE is secured to a mounting wall10fby a bushing10g.
• Connectors10d
• As shown inFIGS. 3A and 3B, the system includes connectors that ensure a robust electrical connection between the IHE and conductors for the operating temperatures and downhole conditions. In addition, the connectors must also provide sufficient mechanical strength in tension, compression and torsion for the operating conditions. As shown, the connectors include apin connector10dover which a corresponding female connector (not shown) may be placed. To ensure longevity in operation, the IHE and connectors may also be welded into place.
• Conductors12
• Power is delivered to the IHE throughconductors12. The conductors are designed to deliver power over at least 2500 feet to the IHE while enabling the surface controller to maintain an IHE surface temperature ±1° F. The conductors must provide sufficient mechanical strength to support the weight of the conductors over these distances and have appropriate coverings to provide the appropriate abrasion resistance.
• Surface Control Unit andPower Supply14
• As described above, thesurface control unit14 controls the delivery of power to the IHE through the conductors. Power may be delivered through mains or on-site generated power. In a generator application, the generator is preferablytruck8 or trailer mounted allowing ready delivery of thesurface control unit14 to the well-site. Known diesel generators may be used and should be capable of delivering single and three phase power to within 1% of the desired voltage. A suitable truck- or trailer-mounted genset for a 45 kVA/36 kW generator delivering roughly 12,000 Watts to the IHE will consume roughly 6 liters of diesel fuel per hour.
• Thesurface control unit14 allows the control and delivery of power to the IHE. The SCU will preferably include appropriate displays and switches to enable an operator both to set and monitor power levels.
• Operation
• In operation, the downhole heating device is configured to a coiled tubing12asystem with theconductor12 carried within the coiled tubing in order to protect the conductor and to allow the downhole heating device to be pushed to a desired location within awellbore20. Thesurface control unit14 may be mounted on a truck or trailer for delivery to the well site. After delivery to the well site, the appropriate connections between the coiled tubing, conductor, downhole heating device and surface control unit are made.
• Once attached to the coiled tubing, the downhole heating device is conveyed to the desired location. In various formations, the formation may provide sufficient in situ water to generate the desired temperatures and pressures of steam within the formation for hydrocarbon recovery. Alternatively, additional water may be added to the annular space20abetween the wellbore20 and coiled tubing12a. Downhole pressure may be maintained either by hydrostatic pressure above theheating device10 or by appropriate wellhead systems as is known in the art.
• The methodology is similarly effective in solvent flood methods where hydrocarbon solvents are added to the well.
• Heating losses and hence the cost of downhole heating is reduced significantly over past techniques which lead to significant improvements in sweep efficiency.
• In addition to heavy oil recovery, the system may also be used in the stimulation of conventional vertical wells through alternating steam and production steps, often referred to as “huff and puff”. In this methodology, the downhole heating device is conveyed to the stimulation zone and the formation is stimulated. The downhole heating device may be removed from the well and standard production of the well may follow. In a still further embodiment, specialized well heads may be utilized allowing both pumping equipment and the downhole heating device to be positioned in the same well thereby obviating the need to remove the downhole heating device before production.
• Series Operation
• In further embodiments of the invention, it may be desired to provide stimulation in horizontally or vertically separated zones of the same well bore20. As shown inFIG. 4, separatedownhole heating devices10′ and10″ are shown separated by a section of coiled tubing within awell bore20.Downhole heating device10′ may be a downhole heating device as described above whereas10″ is a distinct assembly. In particular,embodiment10″ is distinct fromembodiment10′ to allow conductors to pass across or through the housing, through coiled tubing section11 todownhole heating device10″. As shown, the uphole ends of10′ and10″ are similar whereas the downhole end of10′ is provided with a bull nose10e. The downhole end of10″ may include a connector system similar to that described above. The housing of10″ is distinct in allowing conductors to pass along or through the housing to the connectors. As shown inFIGS. 4A and 4B, coiled tubing11 may be attached tohousing10a. InFIG. 4A, theconductors12 are attached to aconnector10das described above. Withinconnector10d, the conductors are split and are passed throughappropriate openings10hand alongchannels101. Channels10imay be covered by coverings10j. At the opposite end of the housing, conductors pass through further openings to a downhole connector13 which allow afurther conductor12′ and tubing section11′ to connect to10″ thus permitting10′ to be connected in series with 10″.
• The above-described embodiments of the present invention are intended to be examples only. Alterations, modifications and variations may be effected to the particular embodiments by those of skill in the art without departing from the scope of the invention, which is defined solely by the claims appended hereto.

Claims (12)

1. A method of creating in situ steam in a well for hydrocarbon recovery comprising the steps of:

positioning a downhole electrical steam generating system in the well adjacent a hydrocarbon bearing formation;

continuously forming downhole steam within the well from in situ water; and,

maintaining a high intra-well pressure to promote hydrocarbon recovery.

2. A method as inclaim 1 wherein the electrical steam generating system is conveyed to the hydrocarbon bearing formation by coiled tubing.

3. A method as inclaim 1 wherein the high intra-well pressure is maintained by adding water to the injection well from the surface.

4. A method as inclaim 1 wherein the high intra-bore pressure is maintained by a sealed wellhead.

5. A method as inclaim 1 wherein steam is generated in an injection well and hydrocarbons are recovered from a recovery well.

6. A method as inclaim 1 wherein steam is generated in the well and hydrocarbons are simultaneously recovered from the well.

7. A method as inclaim 1 wherein at least two generation systems are operatively connected together to enable steam generation at separate locations within the well.

8. A downhole steam generation system for hydrocarbon recovery comprising:

a housing having openings operatively containing an electrical immersion heater,

a connector system for connecting the electrical immersion heater to an electrical cable, and,

a surface power unit for delivering electrical power to the electrical heater through the electrical cable.

9. A downhole steam generation system as inclaim 8 wherein the housing is adapted for operative connection to coiled tubing.

10. A downhole steam generation system as inclaim 9 wherein the electrical cable is contained within the coiled tubing.

11. A downhole steam generation system as inclaim 10 wherein the electrical immersion heater includes a thermocouple operatively connected to the surface power unit for controlling the surface temperature of the immersion heater.

12. A downhole steam generation system as inclaim 8 wherein the housing and connector system enable two or more downhole steam generation systems to be operatively connected together across one or more sections of coiled tubing to enable simultaneous steam production at one or more locations within the well.

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