Note: Descriptions are shown in the official language in which they were submitted.
1 IN SITU OIL SHALE PROCESS
This invention relates to the recovery of
hydrocarbons from subkerranean oil shale formations. A
method is provided for the in situ heating of the
subterranean oil shale formation using two horizontal,
ver~ically spaced metalli.c electrodes formed from
cooling molten metal in fractures of the oil shale
formation. More particularly, the invention relates to
the recovery of hydrocarbons from the formation by
drilling a bore hole, fracturing the oil shale ormation
n~ar the upper and lower boundaries of the formation,
injecting molten metal into the relatively horizontal
lS fractures, all~ing the metal to cool to form vertically
spaced metallic electrodes, providing a radio frequency
transmis~ion line or coaxial cable between the
e].ectrodes, and inducing unterminated standing waves in
the upper and lower metallic electrodes and in the oil
shale formation therebetween by means of a radio
frequency generator.
Subterannean oil shale formations contain relatively
large amounts of valuable hydrocarbons, but the large
scale commercial recovery of these hydrocarbons has been
hindered by economical and environmental constraints.
Deep mining and strip mining techniques such as those
used to mine coal have proved to be an inefficient
method of recovering the hydrocarbons due to the large
amount of bulk shale which must be extracted to produce
the hydrocaxbonsO Additionally, these techniques
negatively affect the environment and a large amount of
unusable rock byproduct must be disposed of.
To avoid these difficulties numerous in situ pro-
cesses of heating the oil shale within the subterranean
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formation have been proposed. Application oE heat to the
oil shale rock increases the porosity and permeabili~y of
the oil shale. Upon pyrolysis, the oil shale yie].ds a
condensable liquid which can be reEined into hydrocarbons
s including petroleum products.
Processes by which super-'neated steam or ho~ liquid
~ad been injected into the oil shale formation have all
proved to be commercia`lly unacceptable since an effective
flow of kerogens from the Eormation could not be readily
achie~ed. These techniques also do not allow ~or the
uniorm heating of the oil ~hale formation due to the low
thermal conductivity of the rock.
Other techniques have also been proposed but these
have met similar disadvanta~es. Partial combustion of the
hydrocarbons within the subterranean oll shale formation
is generally inefficient, environmentaliy damaging, and
difficult to control adequately. Infusion of heat energy
to the oil shale formation by electrical induction heating
likewise fails to provide a commercially adequate recovery
~0 of hydrocarbons due to the limited thermal and electrical
conductivity of the bulk formations.
~ t has been proposed that the uniform heating o~
the rock formation can be achieved by using radio
frequency tR.F.j electrical energy which corresponds to
the dielectric absorption characteristics of the ro~k
formation. An example of such techniques is described
in U.S. Patent Numbers 4,140,180 and 4,144,935 in which
a plurality of vertical conductors are inserted into
the rock formation and bound a particular volume of the
formation. A frequency of electrlcal excitation i5
selected to attain a relatively uniform `neating of the
rock formation.
5imilarlyl U.S. Patent Numbers 4,135~579 and
4,196,329 describe a metho~ and apparatus by which an
alternating electrical field is produced between
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vertical electrode structures lnserted into the
subterranean formation. Temperature gradients within
the rock for~ation result from the electrical field so
as to fracture the rock body. Modification of this
5 technique is described in U.S. Patent Number 4,140,179
in which the amount of liquid water in the rock
formation is reduced prior to supplying the electric
field in order to decrease the temperature needed for
pyrolysis of the hydrocarbons.
The difficulty with the above-described techniques
using 2.F. energy to heat.the formation is the
necessity of implanting an electrode within the
subterranean rock formation at a precise distance. The
electrodes in these processes are described to be
pipes, transmission lines, conductive plates, and
variations thereof. Such an insertion and the proper
spacing thereof has proved to be difficult to achieve,
time consuming, costly, and inef~icient.
There have been some suggestions o~ forming
fractures directly within the rock formation and
applying heat to the ~ormation in order ~o recover
hydrocarbons From the formation. UOS. Patent Number
4,030,549 discloses the injection of a reactive sl~rry
comprising finely divided aluminum and a reactive metal
oxide into a fracture and the subsequent ignition of
the slurry by a thermite reaction to form a molten
metal in the fracture system. U.S. Patent Number
3,149,672 suggests propping fractures in the rock
formation with particles of an electrical conductor,
such as aluminum, iron or copper spheres, and
connecting the Eractures with a source of electric
current. However, these methods lack the ease and
efficiency which results from directly injecting molten
metal into the fracture without the need for a
subsequent chemical reaction within the fracture, or
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1 without uncertainty in obtaining suitable electrical
conduction.
It is an object of the present invention to provide
an in situ pyrolysis process of heating hydrocarbons
contained in subterranean oil shale formations, in such
a manner that relatively large amounts of hydrocarbons
are recovered.
A further object of the present invention is the
provision of a method by which relatively horizontal
metallic electrodes vertically spaced apart are formed
in the subterranean formation between which unterminated
standing waves induced by a radio frequency generator
can be passed.
It is an object of the present invention to recover
vaporized hydrocarbons from the in situ heating of a
subterranean oil shale formation in an economical and
efficient manner which may require only a single bore
hole, with a minimum of adverse environmental impacts.
Further objects and advantage of this invention will
become apparent in study of the following portion of the
specifications, claims, and the attached drawings.
According to the invention there is provided a method
for the recovery of hydrocarbons from subterranean oil
shale formations, including the steps of drilling a bore
hole from the surface substantially to the bottom of the
oil shale formation, inserting a metallic casiny
therein, fracturing the oil shale generally horizontally
in at least two vertically spaced locations, propping
the fractures with an electrically conductive material
and applying electromagnetic energy between these
fractures for inductive heating of the oil shale
formation, the improvement comprising injecting molten
metal into a lower generally horizontal fracture,
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providing a n~nconductive spacing material in the
casing above the fracture, and injecting molten metal
into an upper generall~ horizontal fracture above the
spacer, there~y forming a pair of vertically spaced,
metallic electrodes in the upper and lower fracture.s.
Applicant in one embodiment of the invention has
devised a method for the recovery of hydrocarbons from
subterranean oil shale formations in which a bore hole
is drilled from the surface to the lowér region of the
oil shale formation; a metallic casing is inserted into
the bore hole; the oil shale formation is fractured
generally horizontally adjacent to the lowermost end of
the casing; molten metal is injected into ~he generally
horizontal fracture to form a me~allic electrode in the
fracture; the oil shale formation is again Eractured
generally horizontally adjacent to the upper boundary
of the oil ~hale formation; molten metal is injected
into this fracture to form a second metallic electrode;
a passage is ~ormed through the ~econd electrode within
the casing; the oil shale formation is fractured
generally horizontally intermediate between the first
and second electrodes and this intermediate fracture is
propped with nonconductive granular materials; the
casing is severed in at least one location intermediate
the electrodes; a metallic tubing is inserted centrally
in the casing to form an electrical connection bet~een
the lower metallic electrode and the surface and this
tubing is insulated ~rom the casing; unterminated
standing waves are induced in the upper and lower
metallic electrodes and in the oil shale formation
therebetween by means of a radlo frequency generator,
the oil shale formation is heated su~ficiently to
vaporixe hydrocarbons therein; and the vaporized
hydrocarbons are recovered at the surface through the
.35 intermediate racture and tubing.
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1 BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a vertical sectional view of a bore hole
entering a subterranean oil ~hale formation illustrating
the formation of a lower metallic electrode.
Figure 2 is a vertical sectional view o a bore hole
p~netrating a subterranean oil ~hale formation
illustrating the production of an upper metallic
electrode.
Figure 3 illustrates a vertical sectional view of a
bore hole penetrating a subterranean oil shale formation
in completed condition for recovery of hydrocarbons from
the shale.
DETAILED DESCRIPTIO~
Referring now to Figure 1, a cross-sectional view of
an oil shale ormation indicated generally at 1 is shown
below the surface of the earth 2. The extent of the oil
shale formation 1 is defined by boundaries 3 and 4 at
the top and bottom of the oil shale formation
respectively.
A bore hole 5 is drilled through the oil shale
formation 1 by using conventional rotary drilling
techniques to reach a depth in the underburden 7 below
the bottom boundary 4. A metallic casing 6 of high
t~mperature and pressure rating is inserted into the
bore hole 5 along the entire length of the bore hole. A
cement outer coating 8, especially formulated to with-
stand high temperatures, is injected between the casing
6 and the bore hole along the entire length or the
casing. This ~ementing of the casing may be achieved by
conventional oil well cementing techniques. A cement
base 9 fills the bottom of the bore hole 5 at a position
in the underburden 7 just below the bottom boundary 4 of
the oil shale formation 1. A rotatable high pressure
tubing 10 is inserted into the casing 6 with an
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annular space 11 therebetween.
A lower casing slot 12 o 360~ is cut completely
through the casing 6 and cement 8 to the oil shale
formation 1~ A standard technique to effectuate this
S cutting is a process by which Eine sand particles are
entrained in water and pumped down the tubing 10.
After the casing slot 12 has been cut, the water~sand
mixture is returned to the surface 2 through the
annulus 11 circumscribing the tubing 10. A lower
fracture 20, whic~ is generally horizontal relative to
the surface 2, is formed by standard techniques used in
the oil industry. To form the fracture 20, pressure is
applied down through ~he casing slot 12 so as to
fracture the oil shale formation 2 adjacent to the
casing slot 12. Once the formation is parted, a
sufficient a~ount of water is injected into the widening
fracture to cause the lower fracture 20 to extend
approximately to a 100 foot radius from the casing slot
12. However, various other radius lengths can be achieved
depending upon the extent of such deposi~s. ~fter the
fracture 20 is formed, bore hole 5 is opened at the
surface 2 to allow some of the injected water to flow back
from the fracture 20 to the surface 2.
The lower ~racture 20 may be further cleansed of water
by injecting gas or steam supplied at 21 through the
tubing 10 into the Eracture. The bore hole 5 is se~led at
the surface Z by a high pressure temperature seal 22~ The
pressure resulting from the injection of gas or steam
3n cleanses the fracture by forcing the remaining water out
of the casing 6 and by displacing the water remaining near
the casing slot 12 to distant points in the periphery o
the expanding fracture 20. Air, nitrogen, or any other
suitable gas at low temperature may be used as the
injected gas in this technique.
The fracture 20 is preferably preheated to or above
the melting point of the molten metal which is to be used
by further injecting hot gas or superheated steam vapor
through the tubing 10 into the fracture 20. Preferably a
metal or alloy is used having a melting point ranging
between about 300 and 700 C. Little heat loss occurs
~rom the bore hole 5 during this procedure du~ both to ~
reflective coating which may be placed on the casing 6 and
the tubing 10 and- to the static vapor or gas in the
annulus 11 acting as an insulatorO The high temperature
pressure seal 22 allows pressure to- build within the
casing 6 so as to Eorce the hot gas or vapor into the
fracture 20 and further ex~and the fracture. Since the
oil shale f~rmation 1 conducts heat poorly, this technique
allows the racture 20 to be readily heated outwardly.
The ~elting point isotherms 23 of the oil shale formation
1 are formed by this injection of gas or vapor.
During or subsequent to the heating of the casing 6 and
the fracture 20 by the above process~ molten metal from a
co~taine~ 24 is allowed to Elow gravitationally
down tubing 10 toward the fractu}e 20. PreerablyJ the
metal may be aluminum, aluminum alloys, lead, lead alloys,
zinc, or zinc alloys. When the hydrostatic head 25 of the
column of molten metal in the tubing 10 exceeds the
formation fracture pressure of the oil shale formation,
the molten metal flows and extends radially into the
fracture 20. During the injection of the molten metal
into the fracture 20, ~he metal remains molten since the
oil shale formation 1 surrounding the fracture 20 ha~ been
previously heated to a temperature above the melting point
of the metai by the injection of hot gas or vapor into the
fracture 20.
After the fracture 20 has been filled by the molten
metal~ hot gas is injected into the tubing 10 to displace
the metal remaining in the tubing into the
fracture 20. Sufficient pressure is maintained in the
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tubing 10 to sustain a level 26 of the molten metal in
the tubing 10 a short distance above the casing slot 12.
~fter a period of time, the molten metal in the
fracture 20 will cool and solidify into a lower metallic
electrode 30. The electrode 30 i5 connected to casing 6
by a solidified metal plug 31 positioned on top of the
cement base 9.
Referring now to figure 2, in like manner, an upper
fracture 33 is formed at a distance just below the upper
boundary 3 which separates the oil shale formation from
the oYerburden between the surface 2 and upper boundary
3. An upper casing slot 34 of 360 is cut through both
the casing ~ and cement 8 to allow for the passage of
gas, water, and molten metal. After the slot 34 is cut,
the sand used in the cutting process is allowed to
accummulate in the bore hold 5 below the slot 34. The
sand acts as a nonconductive spacer 35 although other
nonconductive material may be used to fill the s~ace
below slot 34. The spacer 35 prevents the flow oE gas,
vapor, or molten metal down the bore hole 5. The
preferred injection of hot gas or vapor into the
fracture 33 establishes a melting isotherm 36 oE the oil
shale formation 1.
As disclosed for the lower fracture, molten metal
is injected into the tubing 10 and it enters into the
fracture 33 when the hydrostatlc head 37 on the column
of molten metal in the tubing 10 exceeds the formation
fracture pressure o the oil shale. Whan the molten
metal solidifies within the upper fracture 33, an upper
metallic electrode 40 generally horizontal to the
surface 2 is formed. The electrode 40 is connected to a
solidified metal plug 41 within the casing 60
Now referring to figure 3, after formation of the
electrode 40, the metal plug 41 is drilled through to
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1 form a central passage while leaving intact a sheath 42
connected to the casing 6 and electrode 40. Spacer
material 35 is removed dcwnwardly, by drilling and
washing, to a point approximately intermediate the upper
electrode 40 and the lawer electrode 30~
In the same manner as slots 12 and 34 were cut, a
360 casing slot 44 is cut through the casing 6 and
cement 8 intermediate the upper and lower metallic
electrodes. A fracture 45 is formed by injecting
hydraulic pressure through slot 44. The pressure can be
appli.ed directly dcwn the bore hole 5 or through a tubing
similar to 10 inserted into the casing 6.
Using standard oil well techniques, a propping
agent 46 of nonconductive granular material such as sand
is suspended in gelled water and placed into fracture 45.
After the gel breaks, the water ret~.~rns to the bore hole
5 and leave~ the propping agent 46 within the fracture 45
to hold the fracture 45 open and to provide a permeable
path back to the bore hole 5.
By the same ~echnique that slots 12, 34 and 44
were cut, two or more slots 47 are cut 360~ around the
casing 6 so as to prevent electrical connection through
the casing 6 between the upper electrode 40 and the lower
electrode 30.
As shown in Fig. 3, a metallic tubing 50 is
positioned centrally in the casing 6 so as to act as a
central conductor electrically connecting the lower
electrode 30 with the surface 2. The tubing 50 is
drilled into the metal plug 31 by a self-tapping thread
51. A spring centrali~er 52, which may be manufactured
from metal, centers the tubing 50 within the bore hole 5
and establishes electrical contact between the casing 6
and the tube 50. A series of low dielectric loss
centralizers 53 centers the upper part of the tubing 50
in bore hole 5. A lcw 109s dielectric pressure seal 54
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is positioned around tube 50 at the mouth oE the bore
hole 5. The seal 54 maintains sufficient gas pressure
within the casing 6 to cause a flow of products from
the oil shale formation through the tubing 50.
An alternating current power supply 60 is led into
a generator 61 which produces eadio frequency (R.F.)
energy waves. The terminals 62 of the generator are
connected by wires or cables 65 to the casing 6 and the
central tubing 50 which comprise electrically an R.F.
transmission line or coaxial cable. The transmission
line terminates at the electrodes 30 and 40,
resp~ctively. Thus the R.F. energy produced by the
generator 61 is carried to the electrodes 30 and 40
with little loss of ener~y.
Because the electrodes are unterminated~ s~anding
waves are induced in the upper electrode 40, lower
electrode 30 and in the shale formation 1 therebetween.
- The waves generate sufficient heat in the oil shale
formation 1 as to vaporize the kero~en contained
therein. These pyrQlysis products migrate through the
microfractures and pores of the shale toward the
inter~ediate fracture 45. Gravitationally the
pyroly~is products move down the paths shown by arrows
66 in the casing 6 to the ports 67 at the bottom o the
~5 tubing 50, The pyrolysis products come up through the
tubing 50 to the surface 2 due to the vapor pres~ure in
the tubing 50. At the surface 2, the vapori~ed
products are conducted away by conduit 70 and are
condensed and separated into the various components by
conventional apparatus (not shown).
The unterminated standing waves from the R.F.
energy generator are induced by introducing electricial
excitation to the oil shale formation 1 to establish
alternating electrical fields within the oil shale
formation~ The frequency of ~he excitation is selected
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12
as a function of the volume dimensions between the
electrodes 30 and 40 50 as to confine the electrical
field generated to the volume between the electrodes.
.