U.S. patent number 3,620,300 [Application Number 05/029,954] was granted by the patent office on 1971-11-16 for method and apparatus for electrically heating a subsurface formation.
This patent grant is currently assigned to The Electrothermic Co., Corpus Christi, TX. Invention is credited to Fred L. Crowson.
United States Patent |
3,620,300 |
|
November 16, 1971 |
METHOD AND APPARATUS FOR ELECTRICALLY HEATING A SUBSURFACE
FORMATION
Abstract
A method and apparatus include providing one or more vertically
spaced electrodes in the borehole in electrical contact with the
formation. Two electrodes in a common borehole may be connected to
a surface source of alternating current voltage to conductive paths
provided respectively by a conductive casing and a conductive
tubing suitably insulated from each other; or the two electrodes
connected to the voltage source may be placed in separate adjacent
boreholes. The flow of current through the formation is guided or
directed by means of insulating barriers which extend laterally
into the formation from the borehole in vertically spaced relation
to the electrode.
Inventors: |
Fred L. Crowson (Portland,
TX) |
Assignee: |
The Electrothermic Co., Corpus
Christi, TX (N/A)
|
Family
ID: |
21851767 |
Appl.
No.: |
05/029,954 |
Filed: |
April 20, 1970 |
Current U.S.
Class: |
166/248;
166/60 |
Current CPC
Class: |
E21B
43/2401 (20130101) |
Current International
Class: |
E21B
43/24 (20060101); E21B 43/16 (20060101); E21b
043/24 () |
Field of
Search: |
;166/248,272,285,294,295,302,57,60,306,292 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Stephen J. Novosad
Attorney, Agent or Firm: Giles C. Clegg, Jr.
Claims
What is claimed is:
1. A method for electrically heating a subsurface formation through
at least one bore hole extending from the surface into said
formation including the steps: establishing an electrode in said
bore hole in electrical communication with said formation;
providing a first relatively low-resistance conductive path in said
bore hole extending from the surface to contact said electrode;
providing a second relatively low-resistance conductive path
extending from the surface to said formation; producing a flow of
electric current from a voltage source through said first and
second conductive paths, said electrode, and said formation to heat
said formation; providing at least one insulating barrier extending
laterally from said bore hole in vertically spaced relation to said
electrode to guide the flow path of electric current through said
formation.
2. A method as set forth in claim 1 including providing said
insulating barrier by producing an annular cavity extending
laterally into said formation from said bore hole; and filling said
cavity with an insulating material
3. A method as set forth in claim 2 wherein said cavity is filled
with an insulating cement.
4. A method as set forth in claim wherein said cavity is filled
with an insulating epoxy.
5. A method as set forth in claim 1 including providing an
insulating liner for said bore hole extending between said
electrode and said barrier.
6. A method as set forth in claim 1 including providing two
insulating barriers extending laterally into said formation from
said bore hole and positioned respectively above and below said
electrode.
7. A method as set forth in claim 6 including providing said second
conductive path within a bore hole spaced laterally from said first
named bore hole.
8. A method as set forth in claim 1 including establishing a second
electrode in said bore hole in electrical communication with said
formation and in vertically spaced relation to said first named
electrode; connecting said second electrode to said second
conductive path; insulating said first and second electrodes from
each other within said bore hole; and providing said insulating
barrier between said vertically spaced electrodes.
9. A method as set forth in claim 8 including providing an
insulating liner in said bore hole between said electrode; and
joining said insulating barrier to said insulating liner.
10. A method as set forth in claim 9 and providing said insulating
barrier by forming a notched interval in said insulating liner,
providing an adjacent annular cavity in said formation, and filling
said notched interval and said cavity with an insulating
material.
11. A method as set forth in claim 1 including providing a
conductive tubing in said bore hole defining said first conductive
path; and providing a conductive casing in said bore hole defining
said second conductive path.
12. A method as set forth in claim 1 including providing an
insulating barrier above said electrode; and providing said second
conductive path within said bore hole terminating at point above
said insulating barrier.
13. A method as set forth in claim 12 including providing a
conductive tubing defining said first conductive path; providing a
conductive casing defining said second conductive path; and
insulating said conductive tubing from said conductive casing.
14. Apparatus for electrically heating a subsurface formation
through at least one bore hole extending from the surface into said
formation comprising: means defining an electrode in said bore hole
communicating with said formation; means in said bore hole defining
a first relatively low-resistance conductive path extending from
the surface to said formation and connected to said electrode;
means defining a second relatively low-resistance conductive path
extending from the surface to said formation; a source of
alternating current supply voltage; means at the surface connecting
one terminal of said voltage source to said first conductive path,
and means connecting another terminal of said voltage source to a
second conductive path for completing an electric circuit through
said first and second conductive paths and said electrode through
said formation; and means defining at least one insulating barrier
extending laterally from said bore hole into said formation; said
barrier means being spaced vertically from said electrode to guide
the flow of current through said formation.
15. Apparatus as set forth in claim 14 wherein said insulating
barrier means is defined by a mass of insulating material urged
into an annular cavity extending laterally from said bore hole.
16. Apparatus as set forth in claim 15 wherein said insulating
material is an insulating cement.
17. Apparatus as set forth in claim 15 wherein said insulating
material is an epoxy material.
18. Apparatus as set forth in claim 14 said first conductive path
being defined by a conductive tubing; and said second conductive
path being defined by a conductive casing.
19. Apparatus as set forth in claim 14 said insulating barrier
being disposed vertically above said electrode; and said second
conductive path being disposed within said bore hole, terminating
at a point above said insulating barrier.
20. Apparatus as set forth in claim 14 first and second insulating
barriers disposed respectively above and below said electrode; said
second conductive path being provided in a bore hole spaced
laterally from said first named bore hole.
21. Apparatus as set forth in claim 14 means defining first and
second vertically spaced electrodes; said first electrode being
connected to said first conductive path; said second conductive
path being disposed within said bore hole and being connected to
said second electrode; said insulating barrier being disposed
vertically between said first and second electrodes.
22. Apparatus as set forth in claim 21 means defining an insulating
liner for said bore hole between said first and second electrodes;
and said insulating barrier extending laterally from said
insulating liner.
Description
This invention relates to a method and apparatus for heating an
oil- or mineral-bearing formation to stimulate the flow of the oil
or mineral; and more particularly to a method and apparatus for
guiding the flow of electric current in the oil- or mineral-bearing
formation.
It is estimated that a large percentage of the known petroleum
reserves in the United States cannot be recovered using
conventional pumping methods. Known methods for effecting secondary
recovery include techniques known as water flood, steam injection
and fire flood. All of these techniques require extensive and quite
expensive surface installations for their implementation.
An object of this invention is to provide an improved method and
apparatus for the recovery of oil or minerals through the use of
electric current for heating the formation to encourage the flow of
the oil or mineral from the formation.
Another object of this invention is to provide a simple and
efficient method and apparatus for electrically heating the
formation including means for guiding the path of current flow
through the formation.
The method according to the invention includes providing at least
one electrode in the bore hole of the producing well in electrical
contact with the formation, providing a first conductive path in
the bore hole contacting the electrode, providing a second
conductive path from the surface to the formation, providing a flow
of electrical current through said conductive paths and through
said formation to heat the formation, and provide insulating
barriers extending into the formation from the producing bore hole
positioned relative to the electrode to guide the flow of current
through the formation.
The apparatus of the invention includes at least one electrode in
the producing bore hole in contact with the formation, means within
the bore hole defining a first conductive path from the surface to
the electrode, means defining a second conductive path from the
surface to the formation, which second conductive path may include
a second electrode in the producing bore hole or in another bore
hole, a source of alternating current voltage connected to the two
conductive paths at the surface to effect the flow of current
through said conductive paths and said formation, and means
defining one or more insulating barriers extending laterally from
the bore hole in spaced relation to the electrodes to guide the
flow of current within the formation.
DRAWINGS
The novel features of the invention, as well as additional objects
and advantages thereof, will be understood more fully from the
following description when read in connection with the accompanying
drawings in which:
FIG. 1 is a diagrammatic illustration of one form of the invention
including one electrode, one insulating barrier, and two conductive
paths in a common bore hole;
FIG. 2 is a diagrammatic illustration of another form of the
invention including one electrode, two insulating barriers, and a
single conductive path in the common bore hole; and
FIG. 3 is a diagrammatic illustration of still another form of the
invention including two electrodes, a single insulating barrier,
and two conductive paths in a common bore hole.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to the drawing, there is illustrated in FIG. 1 the lower
portion of a producing well bore hole 10 which extends downwardly
through the overburden 11, through the producing formation 12, and
terminates at the boundary between the producing formation 12 and
the underburden 13. A casing for the bore hole extends from the
surface and into the producing formation 12 to a depth somewhat
below the upper surface of the formation, the casing including an
upper conductive portion 14, which may be conventional steel casing
for example, and a lower insulating portion 15 which may be
fabricated of fiberglass or ceramic for example. The upper
conductive portion extends to a depth somewhat above the producing
formation 12.
A lower portion 16 of the bore hole 10 may be of reduced diameter,
being produced through coring, for example, to ascertain the nature
of the producing formation. The bottom of the bore hole may be
provided with a cement plug 17 to support a conventional steel
screen 18 provided with slots or other openings to permit the flow
of oil into the well. An insulating packer 19 positions the screen
relative to the lower end of the insulating casing 15 and
physically seals the annular opening between the upper end of the
screen and the lower end of the conductive casing.
A string of tubing 21 extends from the surface to the bottom of the
bore hole, terminating within the screen 18, to carry the oil to
the surface. This tubing is of conductive material to provide a
path for the flow of electric current from the surface to one or
more electrodes within the bore hole contacting the producing
formation 12. An electrode 22 is defined within two annular
cavities 23 and 24 which are cut into the formation 12, extending
laterally from the lower portion 16 of a bore hole 10. These
cavities, and the annulus between the walls of the bore hole
portion 16 and the exterior surface of the screen 18, are filled
with electrically conductive particles 25 which may be metallic
pellets of steel or aluminum, carbon pellets, or metallic pellets
coated with carbon, for example. These particles are retained in
the cavities by the conductive screen 18 and the packer 19. The
conductive tubing 21 is electrically connected to the screen 18 by
a pair of conventional centralizers 26 fixed to the tubing and
having bands which bow outwardly into engagement with the inner
walls of the screen.
As illustrated diagrammatically, a source of alternating current
voltage 29 has one terminal connected to the upper end of the
conductive tubing 12 and another terminal connected to the upper
end of the conductive casing 14. Current flows then from the
voltage source 29 through the tubing 22, the centralizers 26, the
screen 18 and the conductive particles 25 into the formation 12,
then through the formation 12 and the overburden 11 and returning
through the conductive portion 14 of the casing. To prevent any
short circuit current paths, the tubing 22 is insulated from the
conductive casing 14 by means of vertically spaced insulating
spacers 27; and the screen 18 is insulated from the conductive
casing by the intervening nonconductive casing portion 15.
In order to increase the extent of the formation 12 which may be
effectively heated by the above described electrical circuit, the
flow path of current through the formation 12 may be guided to
extend further in a radial direction from the bore hole 10. For
this purpose, an insulating barrier 30 is provided, consisting of
generally disc-shaped shield of insulating material which extends
radially from the bore hole and having an effective radius greater
than that of the electrode. This barrier is formed by providing a
notched interval 31 in the insulating portion 15 of the casing and
in the adjacent cement, and forming an adjacent annular cavity 32
in the formation 12 of the desired radial extent. The notched
interval and cavity are then filled with an insulating material 33,
such as an insulating cement or an insulating epoxy, with the
insulating material being retained by an insulating sleeve 34
confined between the packer 19 and an upper packer 35.
FIG. 2 is a diagrammatic illustration of another form of producing
well bore hole 40 which includes a single electrically conductive
path to an electrode within the producing formation which is
included in an electric circuit including a second conductive path
to the formation and which is spaced laterally from the bore hole
40, possible in an adjacent well bore hole which may or may not be
another producing well. In this arrangement, the well bore hole
extends from the surface through the overburden 11 and the
producing formation 12 to the lower boundary between the producing
formation 12 and the underburden 13. The bore hole includes a lower
cored portion 41, similar to the bore hole of FIG. 1. This bore
hole is cased, for example, with an insulating casing 42 which
extends from the surface to a point below the upper surface of the
producing formation 12; and a screen 43 is positioned in the lower
bore hole portion 41 and physically connected to the lower end of
the casing 42 by means of a packer 44.
A low resistance electrically conductive path is provided from the
surface to the bottom of the bore hole by a string of conductive
tubing 45 which is also the production tubing for carrying the
production fluid to the surface.
An electrode 47 is identical to that of FIG. 1 including
centralizers 48 affixed to the lower end of the tubing and
contacting the screen 43; the screen 43 retaining conductive
particles 49 with upper and lower annular cavities 50 and 51
extending laterally from the bore hole portion 41, with the screen
maintaining electrical contact with these particles.
With the arrangement of FIG. 2, an alternating current voltage
source 53, at the surface, has one terminal connected to the upper
end of the tubing 45, and another terminal connected at the surface
through a conductor 54 to the upper end of a conductive path
defining tubing or rod extending toward the formation in an
adjacent bore hole, for example. The flow of current then is
through the tubing 45 centralizer 48 screen 43 particles 49, and
through the producing formation 12 to the other conductive path
defining means.
The conductive tubing 45 is insulated from the walls of the bore
hole, above the formation, by the insulating casing 42. Since the
bore hole 40 contains only a single conductive path, and since the
conductive tubing is a much lower resistance path than would be the
walls of the formation, it may not be necessary to provide
particular means to insulate the tubing from the bore hole walls of
the formation 12 in this configuration. Accordingly, the casing
may, in the alternative, consist of an upper conductive portion and
a lower insulating portion as in the arrangement of FIG. 1.
It may be desirable, in this situation, to prevent too rapid a
vertical diffusion of the current flow path as it moves away from
the electrode 47, in order to concentrate the power absorption of
the electrical current and therefore the heating effect within an
effective area adjacent to the producing well bore.
To prevent the too rapid diffusion of the current flow path through
the formation 12 adjacent to the electrode 47, there are provided
two insulating barriers or shields 55 and 56 disposed respectively
above and below the electrode 47. The upper barrier 55 is similar
to that illustrated in FIG. 1 consisting of a disclike mass 57 of
insulating material disposed in a notched interval 58 in the lower
end of the insulating casing 42 and an adjacent cavity 49. The
insulating cement or epoxy 57 is again retained by an insulating
sleeve 60 confined between a lower packer 44 and an upper packer
51. The lower insulating barrier 56 is defined by a disclike mass
62 of insulating cement or epoxy, for example, which defines the
bottom of the bore hole portion 41 and which extends laterally from
the bore hole in an annular cavity 63.
The radial extent of the insulating barriers 55 and 56 is
preferably greater than that of the electrode 47.
FIG. 3 is a diagrammatic illustration of still another producing
well arrangement wherein electric current flows between electrodes
vertically spaced in a common bore hole, and a bore hole containing
means defining separate conductive paths for the respective
electrodes. Referring to FIG. 3, there is shown a production bore
hole 70 extending from the surface through the overburden 11 and
the producing formation 12 to the boundary between the producing
formation and the underburden 13. In this configuration, the bore
hole is cased from the surface to the bottom thereof, with an upper
insulating portion 71 extending from the surface to a point below
the upper surface of the producing formation 12, and with an
insulating portion 72 extending from the conductive portion to the
bottom of the bore hole. Preferably, the casing is cemented in the
bore hole with an insulating cement, at least in the portion of the
bore hole which extends through the producing formation 12. The
insulating cement may also define a base or bottom plug for the
bore hole 70.
A conductive tubing 75 for carrying the produced fluid to the
surface also defines a low-resistance conductive path for a lower
electrode 76 disposed adjacent to the bottom of the bore hole. This
lower electrode consists of a mass of conductive particles 77, such
as metallic carbon-coated pellets, disposed in a notched interval
in the lower end of the insulating casing 72 and adjacent cement
73, and an adjacent cavity 78 in the producing formation 12. The
particles are retained in the cavity by a conductive sleeve or
screen 79, positioned in the bottom of the bore hole by a packer
80, the sleeve 79 being electrically engaged by a conductive
centralizer 81 fixed to the lower end of the tubing 75.
An upper electrode 84 is positioned adjacent to the upper surface
of the producing formation 12 and consists of a mass of conductive
particles 85 confined within a notched interval provided in the
lower end of the conductive casing 71 and the adjacent cement and
in an adjacent annular cavity 86 extending into the formation 12.
The particles are retained within a cavity by a conductive sleeve
87, confined between a lower insulating packer 88 and an upper
packer 89.
The conductive casing 71 defines a conductive path from the surface
to the electrode 84, and must be insulated from the conductive
tubing 75. This insulation is provided by a string of insulating
tubing 91 which extends from the surface to a depth sufficient to
overlap the upper end of the insulating casing 72. The insulating
packer 88 mechanically couples these insulating members, and seals
the annulus between them to obviate any conductive path between the
electrodes 76 and 84 within the casing. Similarly, the insulating
casing 72 and the insulating cement 72 obviate any low-resistance
conductive path between the electrodes, so that the current flowing
between the electrodes necessarily flows through the formation 12.
The terminals of the alternating current source 92 are connected at
the surface to the conductive tubing and the conductive casing so
that the current flows through the tubing and associated electrode
76, through the formation 12, then through the electrode 84 and
associated conductive casing 71.
In order to expand the area of the formation which is effectively
heated by the current flowing therethrough, an insulating barrier
93 is formed within the formation between the electrodes. This
barrier takes the form of a disc-shaped mass of insulating material
94, such as insulating cement or epoxy, confined in an annular
cavity 95 formed in a formation 12 through a notched interval 96
provided in the insulating casing 72 and the adjacent cement 73.
The insulating material is retained in a cavity by means of an
insulating sleeve 96 supported on a packer 97.
The insulating barrier 93 preferably has a radial extent greater
than that of the electrodes 76 and 84, and serves to deflect the
current flow path through the formation outward relative to the
bore hole to effect heating of the formation at radial distance
greater from the bore hole than would otherwise be effected, and
thereby increase the amount of formation which may be produced. The
produced fluid flows from the formation into the well through
perforations 98, formed in the insulating casing and the adjacent
cement by conventional techniques; and the production tubing 75 may
include slots or other openings 99 to effect the flow of fluid into
the tubing to be transported to the surface.
A method of the invention which may be practiced by the above
described producing well configurations, or by other
configurations, includes the steps: establishing an electrode in
the producing well bore hole in electrical contact with the
formation to be produced; providing a first low-resistance
conductive path contacting the electrode, which is preferably
provided by a conductive tubing which is also the tubing for
transporting the produced fluid to the surface; providing a second
low-resistance conductive path from the surface to the formation,
which may be provided by a conductive path from the surface to the
formation, which may be provided by a conductive casing either
alone or in conjunction with a second electrode, or a conductive
pipe or rod in an adjacent bore hole; producing a flow of electric
current through the two conductive paths and the formation. The
current being carried in the connate water in the formation to heat
the formation and providing one or more insulating barriers
extending radially from the producing bore hole into the formation
to guide, direct or concentrate the flow path of current through
the formation to provide more efficient or more extensive heating
of the formation.
* * * * *