Note: Descriptions are shown in the official language in which they were submitted.
CA 02568358 2006-11-17
IN-SITU METHOD OF PRODUCING OIL AND GAS (METHANE),
ON-SHORE AND OFF-SHORE
Cross-Reference to Related Applications
1 This application claims benefit of U.S. Provisional Application 60/571,183,
filed May
14, 2004, which is incorporated hereby by reference in its entirety.
Statement Regarding Federally Sponsored Research or Development
2 Not applicable.
Background of the Invention
1. Field of the Invention
3 The present invention relates to in-situ methods of producing oil shale and
gas
(methane) hydrates, and more particularly but not by way of limitation, to
methods of forming
fractures in formations by injecting liquified gases into at least one
substantially horizontally
disposed fracturing borehole drilled into the formation. In one aspect the
present invention relates to
methods for in-situ conversion of coal from a solid to a gaseous state by
forming fracturing in
formation by injecting liquified gases into at least one substantially
horizontally disposed fracturing
bore.
2. Brief Description of Related Art
4 Oil shale formations underlie large sections of Western Colorado, Eastern
Utah and
Southern Wyoming. These formations can be several thousand feet thick and
contain more than 500
1
CA 02568358 2006-11-17
billion barrels of oil shale oil. Such oil shale formations consist of rock
minerals combined with
kerogen, a carbonaceous material which is solid material combined with rock
minerals.
Earlier attempts to produce oil shale oil largely consisted of surface mining,
crushing,
and retorting. The efforts proved too costly and environmentally unfriendly.
However, at
temperatures between six hundred and nine hundred degrees Fahrenheit, the
kerogen liquifies and
becomes mobile. This process is referred to as pyrolysis. In pyrolysis,
kerogen is either heated with
hot gases or steam, or undergoes combustion by igniting the kerogen itself and
injecting air or
oxygen to support combustion.
6 After the kerogen beyond the combustion front reaches a temperature of 600
to 900
degrees Fahrenheit, the lighter elements liquify and migrate away. What
remains, is the residual and
less desirable components of the kerogen and it is the residual and less
desirable components that are
consumed in the combustion process.
7 When drilling into gas hydrate zones in subterranean formations problems are
often
encountered because the heat of drilling fluids warms the hydrates near the
wellbore, dissociating
them and creating craters and sink holes against the casing wellbore.
8 Therefore, new and improved methods are being sought for producing oil shale
oil
and gas from gas hydrates in-situ which overcome various problems, including
those described
above. It is to such new and improved methods that the present invention is
directed.
Brief Description of the Drawings
9 Fig. 1 is a pictorial representation of a fractured formation containing oil
shale
wherein the formation has been fractured in accordance with the present
invention.
2
CA 02568358 2006-11-17
Fig. 2 is a pictorial representation of a 40 acre spacing for drilling and
fracturing an
oil shale formation in accordance with the present invention.
11 Fig. 3 is a pictorial representation of a fractured formation containing
gas hydrates
wherein the formation has been fractured in accordance with the present
invention.
12 Fig. 4 is a pictorial representation of a 40 acre spacing for drilling and
fracturing a gas
hydrate zone.
Summary of the Invention
13 In accordance with the present invention, a method for forming fractures in
a
formation to enhance recovery of oil shale oil from shale oil and gas from gas
hydrates is provided.
In one aspect, the method of forming fractures in a formation includes
providing a substantially
vertically disposed borehole (i.e. a motherbore) and a plurality of
substantially horizontally disposed
boreholes extending outwardly from the substantially vertically disposed
borehole. Each of the
substantially horizontally disposed boreholes is provided with a remotely
controlled valve assembly
so that the substantially horizontally disposed boreholes can be selectively
closed off from the
wellbore or selectively opened to provide fluid communication between one or
more of the
substantially horizontally disposed boreholes and the substantially extending
vertically extending
borehole. Of the plurality of substantially horizontally disposed boreholes,
at least one is an
injection borehole, at least one is a fracturing borehole, and at least one is
a production borehole.
14 To fracture the formation so that hydrocarbon products from gas hydrates,
oil shale, or
coal gasification can be recovered, the valve assemblies associated with the
at least one injection
borehole and the at least one is a production borehole are closed and the
remotely controlled valve
assembly associated with the at least one fracturing borehole is opened. An
initial quantity of
3
CA 02568358 2006-11-17
liquified gas is introduced into the at least one substantially horizontally
disposed fracturing borehole
whereby liquified gas is discharged into the formation. The initial quantity
of liquified gas is
allowed to vaporize in a portion of the at least one substantially
horizontally disposed fracturing
borehole whereby a resulting increase in pressure in the at least one
substantially horizontally
disposed fracturing borehole forms fractures in the formation. Once the
initial quantity of liquified
gas has expanded and produced an initial network of fractures in the
formation, an additional
quantity of liquified gas is introduced into the at least one substantially
horizontally disposed
fracturing borehole. The additional quantity of liquified gas is allowed to
vaporize in the fractures in
the formation created by the injection of the initial quantity of liquified
gas into the at least one
substantially horizontally disposed fracturing borehole whereby a resulting
increase in pressure in the
at least one substantially horizontally disposed fracturing borehole forms
additional fractures in the
formation (i.e. a network of cross fractures).
15 Once the formation has been fractured by the introduction of the initial
and additional
quantities of liquified gas, the remotely controlled valve associated with the
at least one substantially
horizontally disposed fracturing borehole is closed and the remotely
controlled valves associated
with the at least one substantially horizontally disposed injection borehole
and the at least one
substantially horizontally disposed production borehole are opened. Heated
gases, heated oxygen or
heated air are then introduced into the at least one substantially
horizontally disposed injection
borehole and distributed across the chimney so that the heated gases, heated
oxygen, heated air, or
direct combustion of adjacent oil shale, gas hydrates, or coal, create the
heat necessary to liquify the
kerogen as same move downward through the fracture system. The heated gases,
oxygen, or air
function to support combustion of the kerogen on the face of the formation.
That is, at each fracture
4
CA 02568358 2006-11-17
face, heating occurs and the kerogen liquifies downward through the fractures
to the substantially
horizontally disposed production borehole along with water and released gases.
In regard to coal
gasification, the heating results in gasification and/or liquidization of the
kerogen whereby the gases
resulting from the coal gasification and the liquids and gases from the
heating of the kerogen travels
through the fractures to the substantially horizontally disposed production
borehole along with water.
16 When the multiple fracture system is provided with more than one
substantially
horizontally disposed injection borehole, more than one substantially
horizontally disposed fracturing
borehole, and more than one substantially horizontally extending production
borehole, the remote
controlled valves associated with each of such boreholes is closed during
introduction of the initial
quantity and the additional quantity of the liquified gas except for the
fracturing borehole into which
the liquified gas is being introduced to provide the desired network of
fractures in the formation. It
should be noted that the multiple fracture system is designed to provide an
effective amount of
overburden formation to insure that the fractures do not penetrate the
surface.
DETAILED DESCRIPTION
17 The method of producing oil shale oil or gas, gas hydrates, or gas via coal
gasification
in accordance with the present invention is to produce the oil shale oil or
conduct the coal
gasification "in-situ" or "in-place". Thus, no mining, crushing or disposal of
spent shale or coal
residue is required.
18 To accomplish in-situ production of oil shale oil, it is necessary to heat
the kerogen,
but since the oil shale has little or no permeability, a multiple fracture
system 10 must be established
in order to heat the oil shale in a timely manner. After the fractures are
created, stream or heated
gases or direct combustion of adjacent oil shale in the fractures will create
the heat needed to liquify
CA 02568358 2006-11-17
the kerogen so that it can travel through the multiple fracture system 10 and
into a vertical borehole
12 (i.e. the "motherbore") whereby the oil shale oil and gas is delivered to
the surface 14 and
recovered in a conventional manner.
19 To accomplish the in-situ production of gases by coal gasification, an
oxidant (air or
oxygen) and steam are pumped down an injection well into the coal seam or
formation containing the
coal which has been fractured to provide the multiple fracture system 10. The
coal is then ignited
and the resulting hot pressurized gases travel through the multiple fracture
system 10 and into the
vertical borehole 12 (i.e. the "motherbore") whereby the gases, that include
methane, hydrogen,
carbon monoxide and carbon dioxide with minor amounts of impurities are
recovered in a
conventional manner.
20 Referring now to Fig. 1, the method of forming fractures 16 in an oil shale
formation
18 to recover oil shale oil and gases from the oil shale formation 18 includes
providing the
substantially vertically disposed borehole 12 (i.e. a motherbore), a supply of
liquified gas 19 and a
plurality of substantially horizontally disposed boreholes 20, 22 and 24
extending outwardly from the
substantially vertically disposed borehole 12.
21 The multiple fracturing system 10 further includes conventional production
equipment (not shown) which is associated with the substantially vertically
disposed borehole 12 for
the recovery of oil shale oil and gas recovered from the oil shale formation
18 in accordance with the
present invention.
22 Each of the substantially horizontally disposed boreholes 20, 22 and 24 is
provided
with remotely controlled valve assemblies 26, 28 and 30, respectively, so that
the substantially
horizontally disposed boreholes 20, 22 and 24 can be closed off from the
substantially horizontally
6
CA 02568358 2006-11-17
disposed borehole 12 or selectively opened to provide fluid communication
between selected
substantially horizontally disposed boreholes 20, 22 and 24 and the
substantially vertically extending
borehole 12. As shown in Fig. 1, at least one of the substantially
horizontally disposed boreholes,
such as borehole 20, is an injection borehole, at least one of the
substantially horizontally disposed
boreholes, such as borehole 22, is a fracturing borehole, and at least one of
the substantially
horizontally disposed boreholes, such as borehole 24, is a production
borehole.
23 Prior to fracturing the formation, the substantially vertically disposed
borehole 12 is
provided with a cemented outer casing 32. After fracturing, a medium or inner
casing 34 is disposed
within the outer casing 32 and lowered to the bottom and tubing 36 is disposed
within the medium
casing 34. A first annulus 38 is formed between the cemented outer casing 32
and the medium or
inner casing 34; and a second annulus 40 is formed between the tubing 36 and
the medium or inner
casing 34. Packers 42, 44, 46 and 48 are selectively positioned within the
first annulus 38 for closing
off portions of the formation 18. Such a configuration permits fluid
communication between the
substantially horizontally disposed injection borehole 20 and the
substantially horizontally disposed
production borehole 24 via the fracture 16 formed in the formation 18.
Further, by running the
uncemented medium or inner casing 34, the tubing 36 and appropriate packers
42, 44, 46 and 48,
heated gases or oxygen or air for direct combustion can be injected into the
upper or injection
borehole 20 and distributed across the chimney for subsequent downward
movement through the
fractures 16. At each face, heating occurs and the kerogen liquifies and
proceeds downward through
the fractures 16 of the formation 18 to the substantially horizontally
disposed production borehole
24.
7
CA 02568358 2006-11-17
24 To fracture the formation 18 so that hydrocarbon products such as oil shale
oil and
gas can be recovered, the valve assemblies 26 and 30 associated with the
substantially horizontally
disposed injection borehole 20 and the substantially horizontally disposed
production borehole 24,
respectively, are closed and the remotely controlled valve assembly 28
associated with the
substantially horizontally disposed fracturing borehole 22 is opened. In
addition the packers 46 and
48 are installed at a desired position in the first annulus 38 at a position
below perforations 50 in the
outer casing 32 so as to provide fluid communication between the first annulus
38 and the
substantially horizontally disposed fracturing borehole 22.
25 Thereafter, an initial quantity of liquified gas is introduced into the
substantially
horizontally disposed fracturing borehole 22 whereby liquified gas is
discharged into the formation
18 via perforations 52 provided at selected positions in a casing 54
surrounding the substantially
horizontally disposed fracturing borehole 22. The casing 54 surrounding the
substantially
horizontally disposed fracturing borehole 22 is provided with a plug catcher
56 which is positioned
at about the midpoint of the casing 54. A plurality of rotating sleeve
assemblies 58 are supported on
the casing 54 for selectively opening and closing off the perforations 52
upstream of the plug catcher
56. When a fracture treatment commences, the rotating sleeve assemblies 58 are
closed and the
liquified gas goes to the farthest set of downstream perforations 52 in the
casing 54. The initial
quantity of liquified gas is allowed to vaporize in a portion of the
substantially horizontally disposed
fracturing borehole 22 whereby a resulting increase in pressure in the
substantially horizontally
disposed fracturing borehole 22 forms fractures 16 in the formation 18. Once
the initial quantity of
liquified gas has expanded and produced an initial network of fractures 16 in
the formation 18, an
additional quantity of liquified gas is introduced into the substantially
horizontally disposed
8
CA 02568358 2006-11-17
fracturing borehole 22. The additional quantity of liquified gas is allowed to
vaporize in the
fractures 16 in the formation 18 created by the injection of the initial
quantity of liquified gas into the
substantially horizontally disposed fracturing borehole 22 whereby a resulting
increase in pressure in
the substantially horizontally disposed fracturing borehole 22 forms
additional fractures 16 in the
formation 18 (i.e. a network of cross fractures).
26 After the first set of perforations 52 is treated, a casing plug 60 is
pumped into the
substantially horizontally disposed fracturing borehole 22 and seats in the
plug catcher 56. While
being pumped into the substantially horizontally disposed fracturing borehole
22, the casing plug 60,
which contains a radio transmitter or other remote control device, activates
the rotating sleeve
assemblies 58. The rotating sleeve assemblies 58 include a rotating sleeve 61
which is perforated on
opposite sides thereof such that upon rotation of the rotating sleeves 61 the
perforations 52 upstream
of the plug catcher 56 and the casing plug 60 are opened. Remote controlled
rotating sleeves are
well known in the art, as are remote control devices capable of activating
such rotating sleeves.
Thus, no further description of such are believed necessary to permit one
skilled in the art to
understand and practice the present invention.
27 To prevent fluids from entering the previously fractured perforations which
will be at
a lower pressure than the breakdown pressure of the upstream perforations, a
packer (not shown) can
be set upstream of the plug catcher 56 in a conventional manner.
28 Once the formation 18 has been fractured by the introduction of the initial
and
additional quantities of liquified gas, the remotely controlled valve assembly
28 associated with the
substantially horizontally disposed fracturing borehole 22 is closed and the
remotely controlled valve
assemblies 26 and 30 associated with the substantially horizontally disposed
injection borehole 20
9
CA 02568358 2006-11-17
and the substantially horizontally disposed production borehole 24,
respectively, are opened.
Further, packers 42 and 44 are installed at a desired position in the first
annulus 38 at a position
below perforations 62 in the cemented outer casing 32 to provide fluid
communication between the
first annulus 38 and the substantially horizontally disposed injection
borehole 20. Perforations 63
are also provided in a casing 64 of the substantially horizontally disposed
injection borehole 20.
Thus, heated gases, oxygen or air can be introduced into the substantially
horizontally disposed
injection borehole 20 via the first annulus 38, the remotely controlled valve
assembly 26 and
distributed across the chimney so that the heated gases, oxygen, air, or
direct combustion of adjacent
oil shale, create the heat necessary to liquify the kerogen as same exits the
substantially horizontally
disposed injection borehole 20 via the perforations 63 in the casing 64 for
downward movement
through the fractures 16 towards the substantially horizontally disposed
production borehole 24. The
heated gases, oxygen, or air function to support combustion of the kerogen on
the face of the
formation 18. That is, at each fracture face heating occurs and the kerogen
liquifies and travels
downward through the fractures 16 to the substantially horizontally disposed
production borehole 24
along with water and released gases.
29 The casings 64, 54 and 66 of the substantially horizontally disposed
boreholes 20, 22
and 24 are not cemented, as is the outer casing 32 of substantially vertically
disposed borehole 12.
Further, the perforations 62, 50 and 68 provided in selected portions of the
cemented outer casing 32
of the substantially vertically disposed borehole 12 provides fluid
communication with the
substantially vertically disposed borehole 12 and each of the substantially
horizontally disposed
boreholes 20, 22 and 24 via the remotely controlled valve assemblies 26, 28
and 30 substantially as
shown in Fig. 1.
CA 02568358 2006-11-17
.'
30 As previously stated, perforations 63, 52, and 70, are provided in the
casings 64, 54
and 66, respectively, of each of the substantially horizontally disposed
boreholes 20, 22 and 24.
Thus, the introduction of the initial quantity of liquified gas and the
additional quantity of liquified
gas into the formationl 8, as well as the network of fractures 16 thereby
produced, is controllable by
the position and number of perforations 52 present in the casing 54 of the
substantially horizontally
disposed fracturing borehole 22. Further, the substantially horizontally
disposed fracturing borehole
22, permits the creation of multiple fractures 16 which enhances recovery of
oil shale oil from oil
shale or gas from gas hydrates in accordance with the present invention.
31 When the multiple fracture system 10 is provided with more than one
substantially
horizontally disposed injection borehole 20, more than one substantially
horizontally disposed
fracturing borehole 22, and more than one substantially horizontally disposed
production borehole
24, the remote controlled valves 26, 28 and 30 associated with each of such
boreholes is closed
during introduction of the initial quantity and the additional quantity of the
liquified gas except for
the fracturing borehole 22 into which the liquified gas is being introduced to
provide the desired
network of fractures 16 in the for,mation 18. It should be noted that the
multiple fracture system 10 is
designed to provide an effective amount of overburden formation 71 to insure
that the fractures 16 do
not penetrate the surface 14.
32 To create the multiple fracture system 10, a liquified gas, such as liquid
nitrogen, is
injected into a substantially horizontally disposed injection borehole 22 via
the vertical borehole 12
at very high rates and a temperature of about -320 Fahrenheit. After cool-
down, the liquid nitrogen
will enter created fractures 16 and then vaporize. At standard temperatures
and pressure a cubic foot
of liquid nitrogen contains 696 SCF of gaseous nitrogen after vaporization.
11
CA 02568358 2006-11-17
y =
33 The critical temperature of liquid nitrogen is -232 R(-228 F) and its
critical
pressure is 492 psi. At standard condition, its temperature is -140 R(-320
F) and pressure is 14.7
psia (pounds per square inch absolute). After the liquid nitrogen enters a
fracture and warms up to
above -232 R(-228 F) it will immediately vaporize and attempt to greatly
increase its volume.
34 As will be described in detail later, liquid nitrogen injected at a
fracturing pressure of
500 psi will increase its volume by 14 fold at a temperature of -75 F. If,
however, no increase in
fracture volume occurs, the expansion pressure would increase to approximately
7,000 psia at a
temperature of -385 R(-75 F). See National Institute Standards Technology
Tables for the
Isothermal Properties For Nitrogen.
35 The fracture would not maintain a constant volume but neither would it
expand
instantaneously to maintain the fracturing pressure at 500 psi. Instead a
fracturing pressure of about
2000-3000 psia could be maintained in an initial major fracture requiring only
500 psia to propagate.
The net effect is to create vertical fractures perpendicular to the initial
major fracture despite
regional stresses both vertical and horizontal. The rapid increase in
expansion pressure coupled
with a very high rate of liquid nitrogen injection results in a continuing low
level explosion that will
create hundreds of cross-hatched or secondary vertical fractures 16 as
illustrated in Fig. 1.
36 As will be described later herein, a 1-~ length fracture of 220 feet in
length and height
and 0.2 inches wide will contain 806 cubic feet of void space. An injection
rate of 5 BPM of liquid
nitrogen will result in 393 cubic feet of vaporized nitrogen being injected at
an expansion rate of 14
fold. Therefore, approximately 2 minutes of injection would be required to
fill the fracture.
However, during this time period the fracture may grow to full length. Thus,
during the 2 minute
time period an additional 5 barrels of liquid nitrogen is injected.
12
CA 02568358 2006-11-17
37 Also to be considered, a 220 foot fracture could not be created in just 2
minutes of
injection. The net effect is a buildup in pressure well beyond the fracturing
pressure of 500 psia
which would be in the range of a low level explosion. Normally, because of its
low Reynold's
Number, vaporized nitrogen will not attain significant friction losses even at
very high rates of
injection because it will still be in laminas flow. However, significant
friction pressure might occur
because as liquid nitrogen in a fracture vaporizes, it rapidly builds volume
and this "churning" could
destroy the laminar flow streamlines and could result in friction against the
fracture faces. If friction
pressure occurs, it would only add to the pressure of expansion of the liquid
nitrogen. In addition, as
the cryogenic vaporized nitrogen gas proceeds down a fracture a continuous
expansion will occur
because of the significant increase in temperature.
38 The process of the present invention will create hundreds of cross-hatched
fractures
16 as indicated in Fig. 1. Because of the extensive fracturing, where
fractures could be as close as 6
feet apart, and because of the explosive nature of the nitrogen expansion it
is believed that no
propping of the fractures will be necessary. If, however, closure does occur,
the fractures can be re-
opened by the injection pressure necessary to inject heating or combustion
gases into the fracture
system 10.
39 In addition, water released by the combustion process will vaporize to
steam and
expand to double its water volume. The combustion residue gases will also
expand. These expansion
forces should offset the narrowing of the fractures because of heat related
expansion.
40 For illustration purposes, a forty acre spacing wel172 is drilled in a
manner shown in
Fig. 2. The substantially vertically disposed borehole 12 is first drilled to
provide at least 600 feet of
overburden formation 71 (Fig. 1) above the top of the oil shale zone or deeper
in the oil shale zone
13
CA 02568358 2006-11-17
for adequate coverage so that vertical fractures do not penetrate to the
surface. The substantially
vertically disposed borehole 12 is then cased with the cemented outer casing
32 herein before
described.
41 Two boreholes 73 and 74 are drilled opposite each other from the
substantially
vertically disposed borehole 12 in a direction perpendicular to the direction
of the least regional
stresses. Four connecting boreholes 76, 78, 80 and 82 are drilled
perpendicular to the boreholes 73
and 74 and the four connecting boreholes 76, 78, 80 and 82 extend a distance
of 440 feet (for a 40-
acre spacing) from the substantially vertically disposed borehole 12. Four ~
radius boreholes 84, 86,
88 and 90 are drilled and connect with the connecting boreholes 76, 78, 80 and
82 substantially as
shown. That is, the borehole 84 is connected to the end of the connecting
borehole 76 and the
borehole 86 is connected to the end of the connecting borehole 78 so that the
boreholes 84 and 86 are
substantially parallel to the borehole 73. Similarly, the borehole 88 is
connected to the end of the
connecting borehole 80 and the borehole 90 is connected to the end of the
connecting borehole 82 so
that the boreholes 88 and 90 are substantially parallel to the borehole 74.
Thus, the boreholes 73, 84
86 and 74, 88 and 90 would be at the midpoint of a 220 foot section of oil
shale.
42 Since each %~ fracture would have to extend 220 feet horizontally to meet
up with a
fracture of an adjacent borehole, the vertical fracture will also extend 220
feet in height. In practice,
the injection of volumes of liquid gas, such as liquid nitrogen, beyond the
necessity of creating 220
feet %~ length fractures will extend the fracturing deeper than 220 feet into
the oil shale. Further, each
of the fracturing boreholes is perforated as herein described. (see Fracture
Creation Section).
43 In thicker sections (some oil shales are 2000 feet thick) it may be
advantageous to
drill additional wells to exploit the deeper sediments rather than to drill
additional boreholes in the
14
CA 02568358 2006-11-17
same well which would take years to heat. Additional horizontal boreholes in
the same configuration
may also be drilled at the top of the oil shale zone to distribute air, steam,
oxygen or heated gasses to
the top of the herein described chimney. Other boreholes at the bottom of the
oil shale zone may be
drilled to act as production boreholes. However, the injection and production
boreholes may not be
needed because of over extensive fracturing.
Fracture Creation
44 The greater the number of fractures, the greater the recovery efficiency
because oil
shale formations conduct heat very slowly. Thus, the closer the fractures are
to each other the greater
will be the oil and gas production rate and the greater the efficiency of heat
conduction and the
shorter the producing life of the project.
45 To create this fracturing program for a vertical fracture system, the large
diameter
vertical borehole or motherbore 12 is drilled and six substantially
horizontally disposed boreholes,
i.e. fracturing boreholes) 73, 74, 84, 86, 88, and 90, along with four
connecting substantially
horizontally disposed connecting boreholes 76, 78, 80, and 82, are drilled in
the middle of a 220 foot
thick oil shale zone as shown in Fig. 2.
46 The six substantially horizontally disposed boreholes 73, 74, 84, 86, 88,
and 90, are
drilled such that any vertical fractures created will be perpendicular to the
direction of the least
regional stress. Each of the substantially horizontally disposed boreholes 73,
74, 84, 86, 88, and 90,
is cased with an uncemented casing which contains perforations in the same
manner as the
substantially horizontally disposed fracturing borehole 22 herein before
described, and each of such
substantially horizontally disposed fracturing boreholes is fractured
separately with multiple fractures
in each borehole.
CA 02568358 2006-11-17
47 A borehole orientation drilled to conform to a vertical azimuth is believed
desirable
even if the regional stresses favor a horizontal fracture. If the fracturing
pressure is maintained
above the fracturing pressure of a horizontal fracture, even if formed first,
a vertical fracture will
occur in the previously created horizontal fracture and afterwards a
horizontal fracture in the
previously created vertical fracture. In some situations a vertical fracture
will occur in the original
vertical fracture parallel to the least regional stresses if it is lower than
the stresses in a horizontal
fracture.
48 For illustration purposes, assume the 40 acre spacing well 72 is drilled as
shown in
Fig. 2 and 42 inch perforated, uncemented casing is run in the substantially
horizontally disposed
fracturing boreholes (also referred to hereinafter as boreholes) with the
perforations spaced 30 feet
apart. The perforations in each of the uncemented casings of the substantially
horizontally disposed
fracturing boreholes 73, 74, 84, 86, 88, and 90 are indicated in Fig. 2 by the
numerals 92a, 92b, 92c,
92d, 92e and 92f, respectively. If a single borehole is fractured separately,
each borehole will
contain 20 separate sets of perforations. By use of a packer set halfway down
the borehole (see Fig.
1), 10 sets of perforations can be treated simultaneously.
49 If the injection rate is 100 barrels of liquid nitrogen per minute (BPM)
each 2 length
borehole would fracture at 50 BPM rate or 5 BPM per separate fracture.
50 At -75 Fahrenheit, this rate after vaporization expands 14 fold to an
equivalent rate
of 70 BPM. Although this is a very high rate, a method of fracturing and
repressuring subsurface
geological formations employing liquified gas which may be employed is
disclosed in U.S. Patent
No. 3,822,747, the entire contents of which is incorporated herein. It should
be noted that the above
16
CA 02568358 2006-11-17
referenced method, does not depend on frictional pressures to create secondary
fractures but rather
the secondary fractures will be created by the expansion forces of the
vaporizing nitrogen gases.
51 It will be shown later that a rate of 5 BPM of liquid nitrogen translates
to 210 GPM.
This volume will occupy the void space of a 220 foot 1,,~ fracture in just 2
minutes of pumping. If the
entire fracture is not created in 2 minutes, the result will be a build up in
pressure well beyond the
fracturing pressure and as a result numerous secondary horizontal and vertical
fractures will be
created.
52 For purposes of calculations, assume that 20 separate vertical 2 fractures
220 feet in
length are created in a single borehole. This will result in a one "fold"
volume of liquid nitrogen. In
practice, secondary fractures will be occurring before the 220 foot extension
is reached therefore
more than one "fold" volume of liquid nitrogen will be required.
53 A one "fold" volume of liquid nitrogen "theoretically" would result in 20,
220 foot 1'~
fractures 30 feet apart. The injection of a 5 "fold" volume of nitrogen would
result in the "equivalent"
of 1200 1~ fractures averaging 6 feet apart. This is important for two
reasons:
54 1. The fracturing of all six (6) boreholes in a 40 acre spacing well may
create the
equivalent of 1,200 separate 1~ fractures. In reality, the fracture system
consists of vertical fractures
perpendicular to each other both with and against the regional stresses and
also the horizontal
fractures. This occurs because the injection pressure can be maintained at
2000 to 3000 psi, well
above the fracturing pressure of 500 psi.
55 The fracturing system is not confined to 220 foot fractures. Some fractures
will
extend into adjacent producing units. However, upon their treatment an
equivalent number of
fractures will occur in the first units. As a result of all this "cross
fracturing" and the creation of
17
CA 02568358 2006-11-17
1,200, 1-~ fractures, the regional stresses overburden pressure can be
nullified so that closure of the
fractures does not occur.
56 2. The creation of 1,200, ii~ length fractures result in each fracture
being the
equivalent of six (6) feet apart. This means the combustion front will have to
penetrate only three (3)
feet to consume all the kerogen in a particular fracturing block. It also
creates a very large surface
area for the combustion front.
57 It is desirable that each of the six separate substantially horizontally
disposed
fracturing boreholes 73, 74, 84, 86, 88, and 90, be cased with 41,~" inch
casing. The farthest half of
the casing strings having pre-perforated holes or perforations 92 grouped
together and spaced 30 feet
apart or 10 sets for 1.~ of the borehole. The 41I~" casing is not cemented as
the casing pressure will be
so high (2000 to 3000 psi plus friction losses) that all perforated intervals
will be fractured.
58 The closer half of the casing, which contain rotating sleeve assemblies, as
herein
before described with reference to Fig. 1, are spaced 30 feet apart. Each
rotating sleeve assembly
will contain sets of perforations along with a battery operated rotating
sleeve. The rotating sleeve
assemblies are run with the rotating sleeve covering the perforations.
59 A two-stage treatment can be performed by installing an open hole plug
catcher
midway down the casing string to separate the farthest 10 sets of perforations
from the closer sliding
sleeve assemblies as herein before described with reference to Fig. 1.
60 When a fractured treatment commences, the rotating sleeve assemblies are
closed and
all of the fracture treatment goes into the farthest set of perforations 92 in
one of the substantially
horizontally disposed fracturing boreholes, such as the borehole 72. Also in
the midway point is a
"plug catcher". After the first sets of perforations 92 are treated, a casing
plug is pumped down the
18
CA 02568358 2006-11-17
hole and seats in the "plug catcher". While being pumped down the hole, the
"casing plug", which
also contains a radio transmitter, will activate the battery operated rotating
sleeves and the sleeves
will rotate and open the upper sets of perforations. With the casing plug in
place the upper sets of
perforations can be treated. This procedure is repeated for each borehole
separately.
61 A packer is set below the plug catcher to prevent fluids from entering the
previously
fractured perforations which is at a lower pressure than the breakdown
pressure of the upper set of
perforations.
62 The rotating sleeves are pre-perforated with four (4) 1 inch holes
approximately 2
inches apart on one side and four (4) holes on the other. This arrangement
requires that the rotating
sleeves be rotated only 3 inches to open.
Larger Spacing Units
63 Because of the mountainous terrain it may be necessary to drill certain
wells on
spacing units greater than 40 acres. Also, field operations may indicate the
feasibility of a larger
spacing on a nominal basis. The drilling of additional connecting boreholes
can be made to the 40
acre spacing well illustrated in Fig. 2. This will allow the drilling of
another fracturing borehole
parallel to the original off well fracturing borehole at another 440 feet
distance. Doing this and
extending all fracturing boreholes to a distance of 1100 feet as compared to
660 feet for a 40 acre
well will increase the unit spacing to 111 acres.
64 Further, the drilling of a third fracturing borehole would extend the
fracturing
borehole to 1540 feet and the unit spacing to 217 acres. Since each borehole
will be fractured
separately, the fracturing of these additional boreholes will be similar to
what has been described for
40 acre spacing except for additional stages required for the added borehole
length.
19
CA 02568358 2006-11-17
65 The injection boreholes will be extended from 660 feet at 40 acres to 1100
feet for
111 acres and 1540 feet for 217 acre spacing. The extended injection distance
for combustion gases
will be more than compensated for by running one or two strings of tubing with
packers and utilizing
the annulus to separate injection intervals to less than that in a 40 acre
well.
66 In very mountainous territory it will be impossible to drill straight down
with a
"motherbore@ hole. In such cases a long inclined and horizontal borehole can
be drilled to a point
above the oil shale zone before diverting to a vertical "motherbore" hole.
Methods Of Heat Conduction
67 There are several methods available which can be applied to conduct heat to
the oil
shale kerogen, such as steam injection, air injection for direct combustion or
injection of pure oxygen
for direct combustion. However, a preferred method utilizes injection of pure
oxygen for direct
combustion for the following reasons:
68 1. The oil and gas production rate is directly a function of the rate of
combustion
of the oil shale. Comparing air to oxygen injection, air injection would
require almost 5 times as
much volume of injection as pure oxygen for a given production rate. Because
of this large ratio of
injection, oxygen injection would require fewer wells to obtain the same rate
of production.
69 2. The cost to provide 71,000,000 SCFD of air compression compared to a
15,000,000 SCFD on-site oxygen plant would be 25% to 50 % higher. In addition,
the operating cost
for air compression would be considerably higher. Further, the air emissions
from the compressors
would far exceed those from an on-site oxygen plant which is largely electric
driven.
70 3. The flue gas emissions from air combustion is a serious and costly
problem as
compared to combustion with pure oxygen. It would also be far easier and less
costly to reclaim the
CA 02568358 2006-11-17
methane produced in the oil shale process for generation of electricity which
would be needed as fuel
in the liquid nitrogen and liquid oxygen on-site plants and for other fuel
use.
71 4. Other possible advantages for oxygen over air are the increased
production of
hydrogen needed for refinery upgrading of the raw oil shale and possibly a
lower pour point of the
oil.
72 5. The use of pure oxygen in the combustion process would assure a better
rate
of combustion and a more sustainable burn front as compared to air.
73 6. Because of the danger of corrosion using air or oxygen for combustion,
it is
recommended that all tubulars be made from high pressure aluminum or coated
steel. The larger
casing size may pose a problem because these sizes are probably not
manufactured, but could be. In
that event a coating on the casings may suffice.
Production Rate
74 As 28 gal. per ton oil shale requires approximately 1630 SCF of pure oxygen
for
combustion to generate one barrel of raw oil but this is reduced to 1086
SCF/bbl, by preheating the
inj ected oxygen. The pre-heating is done by heat exchanging the oxygen with
the hot produced oil,
gas, water and combustion gases. If an on site oxygen plant had a capacity of
15,000,000 SCFD, the
production rate would be approximately 13,8 12 BOPD and a gas production rate
of 27,624 millions
of BTU's. If this volume of nitrogen is injected into 4 separate wells, the
average production rate per
well would be over 3000 BOPD and 6,000 millions of BTU's of gas.
75 Based on an injection rate of 3,750,000 SCFD it is believed that a spacing
of 40 acres
would be an optimum well density.
21
CA 02568358 2006-11-17
76 The above calculations are based on a rate of combustion and subsequent
production
rate resulting from the combustion. Not included in the additional production
rate resulting from the
migration of very hot oil vapors, is hot natural gas and combustion gases that
heat up the fracture
faces downstream of the combustion front.
Generation of Liquid Nitrogen
77 As shown hereinafter, the cost to generate a gallon of liquid nitrogen is
approximately
16 cents per gallon. This cost is based on $40 per ton for a 544 ton plant or
$21,760 per day. The
plant would require one (1) 1,000 Kw/hr or $10,560 per day of electricity or
nearly one half the daily
operating costs. Since the oil shale process will produce approximately
2,000,000 BTU's of fuel for
each barrel of produced oil, excess fuel will be available to produce on-site
electricity which will
substantially reduce the indicated 4 cents/Kw-h cost of plant electricity.
78 Also included in the cost estimate of $40 per ton is a 39% corporate income
tax which
would not apply to the direct cost. Therefore the estimated direct cost of
generating on-site liquid
nitrogen could be approximately 10 cents per gallon if electricity is
generated for production gases.
For a 40 acre well requiring 400,000 gallons of liquid nitrogen the cost of
the liquid nitrogen @ 16
cents per gallon would be approximately $64,000.
Calculation of Production Rate
79 Approximately 260 BTU's per lb. of raw shale are required to raise a pound
of 28 g/t
shale to 900 Fahrenheit (Ref 2).
80 Required BTU's per ton = 2000 x 260 = 520,000 BTU's
81 Barrels of oil in ton = 28/42 = 0.67 bbls.
82 Required BTU's per barrel of oi1= 520,000/0.67 = 776,119 BTU's
22
CA 02568358 2006-11-17
83 One SCF of air liberates 100 BTU's (Ref 3).
84 SCF of air required to produce one bbl. of oil = 776,119/100
85 =7,761 SCF/ bbl.
86 SCF of oxygen required = SCF of air x 21% oxygen = 7,761 x .21
87 = 1630 SCF oxygen /bbl oil.
88 Oil production from 15,000,000 SCF oxygen plant = 15,000,000/1630
89 =9209 bbls. oil per day.
90 If injected oxygen is heat exchanged with the hot water, oil and gases of
production,
the heat generated in the process would transfer to the raw shale in addition
to the heat of
combustion. This would reduce the oxygen need by at least 1/3 to 1086 SCF/bbl.
91 Oil production from 15 million SCF oxygen plant = 13,812 BOPD. The plant
capacity could be injected into 4 wells.
Calculation of Required Liquid Nitrogen
92 Assume for a 40 acre spacing well (See Fig. No. 1) the creation of 6
separate
horizontal fracturing boreholes 73, 74, 84, 86, 88, and 90, with an initial
vertical fracture being
created every 30 feet in each borehole.
93 As seen in Fig. 2, each 1-~ length "major" fracture would extend 220 feet
before linking
up with the %~ length fracture of the adjoining borehole, and it is assumed
each fracture would be 220
feet in height.
94 Therefore:
95 (220 feet)(220 feet)( 0.2 inch)
12in/ft
96 = 806 cubic feet of void space per single 1-~ length fracture.
23
CA 02568358 2006-11-17
97 The volume of liquid nitrogen required after vaporizing at fracturing
pressure of 500
psi is as follows:
98 A SCF of liquid nitrogen will expand to 20.07 cubic feet (see attached
tables of
Isometric Properties of Nitrogen from NIST) assuming an injection pressure of
the liquid nitrogen of
500 psia and -140 R(-320 F) to 520 R(60 F) temperature change.
99 A gallon of liquid nitrogen after vaporization would occupy 2.68 cubic feet
@ 500
psia 20.07 ft3
7.48g/ft3
100 Therefore one single 1~ fracture length would require 301 gallons nitrogen
806
2.68 of liquid nitrogen.
101 Since it is desirable to create numerous secondary, cross-hatched
fractures, additional
liquid nitrogen is needed to create secondary fractures. The initial 301
gallons of liquid nitrogen
needed to create a "major" fracture is hereby referred to as one "fold"
volume. A 5 "fold" volume is
recommended to reverse the effects of fracture healing and to decrease the
distance the combustion
front must travel in each fracture block.
102 A one "fold" treatment would result in major fractures occurring every 30
feet. A 5
"fold" treatment would create the equivalent of a "major" fracture every 6
feet which would require
the combustion front to advance only 3 feet for complete combustion for each
block.
103 In actual practice at least one "major" fracture of 220 foot length would
be created and
numerous "cross-hatched" vertical and horizontal fractures would occur;
however, a 5 "fold"
treatment would be the equivalent of 6 "major" fractures.
24
CA 02568358 2006-11-17
104 As to the total volume of liquid nitrogen required consider: 6, II~
fractures to connect
clear across a 40 acre spacing unit (1 320 feet) (6 fractures) (301
gal/fracture) = 1806 gals. of liquid
nitrogen with "connecting" fractures running every 30 feet a total of 40 would
result.
105 Therefore: (40)(1806) = 72,240 gals/"fold" at 5 "folds"
106 (73,240 gals)(5) = 361,200 gal of liquid nitrogen.
107 Since each gallon of liquid nitrogen can be produced at about 16 cents per
gallon
additional "fold" would only cost $11,558 each, however, 5 "folds" should be
sufficient unless field
experience indicates an increase in recoverable reserves would result from
increased fracturing or the
healing of fractures would be prevented.
108 The parameters herein before described the successful in-situ production
of oil shale
are "off the shelf' procedures; that is, liquefaction, nitrogen, and
vaporization of liquid nitrogen,
horizontal drilling, in-site combustion of hydrocarbons, treatment of produced
water and flux gas and
refining upgrading.
109 The successful production of oil shale is the creation of hundreds of
vertical and
horizontal, cross-hatched fractures which will allow a vast surface area for
the heating of oil shale
kerogen and alleviate the need to prop open the fractures created. If 1200 +
fractures are created in a
40 acre well this should prevent the healing of cross-hatched fractures. If
not, the pressure necessary
to inject combustion gases and the expansion of water to steam will hold open
the fractures. But
equally important is the creation of the fractures by vaporizing large volumes
of liquid nitrogen
which will create very large "expansion pressures" well in excess of regional
fracture stresses. The
creation of 1200 or more fractures will also.
CA 02568358 2006-11-17
110 Although the in-situ production of oil shale will have many treating
problems such as
low pour point of oil, water treating, flux gas treating and up-grading before
refining, these problems
and costs appear to be less than those associated with athabasca oil sands and
tar sands in Canada
which are being produced at a profit and at increasingly large volumes.
111 Although a single 40 acre spacing well, 220 feet in thickness has been
described, it
should be understood that as many as 6 wells can be drilled on a 40 acre unit
with approximately
1500 feet of oil shale thickness with 4 of those wells being drilled
concurrently using countercurrent
flow in two of the wells. This could result in the possible recovery of
100,000,000 barrels of oil
equivalent (BOE) and a potential profit of $1,000,000,000 per 40 acre
location.
112 Gas Hydrates (Methane) are sources of methane and in some cases heavier
hydrocarbons, that are present in vast areas of continental ocean slopes deep
enough to cause
freezing. They are also present in some areas of the Arctic and can be several
thousand feet thick.
113 These gas hydrates and associated water are frozen in place and exist in
huge volumes
that well exceed all other forms of carbon existing in oil, gas, oil shale and
coal reserves. They exist
worldwide and represent a very valuable energy source for the future. Since a
unit of gas hydrate in
place can contain as much as 160 units at standard conditions, their
exploitation can change the
world's energy future.
114 Gas hydrates are gas molecules surrounded by water molecules in a cage-
like lattice
network existing in a permafrost area or in continental ocean slopes deep
enough to cause freezing.
Like oil shales, these gas hydrates in place are solid with little or no
permeability and must be heated
to cause this dissociation.
26
CA 02568358 2006-11-17
115 To accomplish in-situ production of gas hydrates, it is necessary to heat
the hydrates
to cause dissociation. Thus, heated water or steam is injected into a multiple
fracture system 110 so
that the dissociated gases can travel through the multiple fracture system 110
and into a vertical
borehole 112 (via the mother borehole) whereby the gas is delivered to the
surface 114 and recovered
in a conventional manner.
116 The utilization of steam or heated water is important because water can
replace the
void spaces created by dissociation of the gas hydrate and the shrinking of
the hydrate ice and
prevent possibly slumping of the hydrate beds.
117 As shown in Fig. 3, the method of forming fractures 116 in a hydrate
formation 118 to
recover disassociated gas from the hydrate formation 118 includes providing
the substantially
vertically disposed borehole 112, a lightweight drilling barge 119 containing
an air drilling rig, liquid
nitrogen plant and associated cryogenic storage tanks, and a plurality of
substantially horizontally
disposed boreholes 120, 122 and 124, extending outwardly from the vertically
disposed borehole
112. The multiple fracture system 110, further includes conventional
production equipment (not
shown) which is associated with the vertically disposed borehole 112 for the
recovery of gases
recovered due to disassociation of the gas hydrates. The vertically disposed
borehole 112 and the
substantially horizontally disposed boreholes 120, 122 and 124 are similar to
the vertically disposed
borehole 12 and the plurality of substantially horizontally disposed boreholes
20, 22 and 24,
hereinbefore discussed with reference to the method for forming fractures in
the oil shale formation
18 to recover oil shale oil and gases from the oil shale formation heretofore
described with reference
to Fig. 1, except in the method for recovering gas from gas hydrates, the
production borehole is
preferably the substantially horizontally disposed borehole 120 and the
injection borehole is the
27
CA 02568358 2006-11-17
, . ,
substantially horizontally disposed borehole 124. However, it should be
understood that the
production borehole can be the lower most borehole such as heretofore
described with reference to
Fig. 1.
118 That is, the uppermost substantially horizontally disposed borehole 120 is
a
production borehole, the intermediate substantially horizontally disposed
borehole 122 is a fracturing
borehole and the lower most substantially horizontally disposed borehole 124
is an injection
borehole. However, it should be understood that the location of the production
borehole and the
injection borehole can be reversed so that such boreholes are positioned
relative to the fracturing
borehole 122 in the same manner as hereinbefore described with reference to
Fig. 1.
119 Except for the location of the production borehole 120 relative to the
injection
borehole 124 of the multiple fracturing system 110, the multiple fracturing
system 110 is similar in
construction and function to that heretofore described with reference to the
multiple fracturing
system 10. That is, each of the substantially horizontally disposed boreholes
120, 122 and 124, is
provided with a remotely controlled valve assemblies 126, 128 and 130,
respectively, so that the
substantially horizontally disposed boreholes 120, 122 and 124, can be closed
off from the vertically
disposed borehole 112 or selectively opened to provide fluid communication
between selected
substantially horizontally disposed boreholes 120, 122 and 124 and the
vertically extending borehole
112.
Drilling Method Off-Shore Well
120 It is believed desirable to drill off-shore gas hydrates wells utilizing
the light weight
drilling barge 119 containing an air drilling rig, a liquid nitrogen plant and
associated cryogenic
storage tanks.
28
CA 02568358 2006-11-17
, , .
121 A serious problem exists in drilling into gas hydrate zones because the
heat of drilling
fluids warms the hydrates near the wellbore, dissociating them and creating
craters and sinkholes
against the casing wellbore. To avoid this, it is believed desirable to employ
a cryogenic drilling
method disclosed in U.S. Patent 3,612,192 entitled "Cryogenic Drilling
Method", the entire contents
of which is expressly incorporated herein by reference.
122 In process disclosed in U.S. Patent 3,612,192, high pressure air is passed
through a
turbo-expander and exited at a much lower pressure and in the process can
lower the temperature of
the air to as low as -200 F. Such a process is used extensively in gas
processing plants.
123 By drilling with cryogenic air in conjunction with an electric driven
downhole motor,
the bit can be rotated many times faster than normal air drilling because of
the bit being cooled by
cryogenic temperatures near -200 F. The results will be vastly increased
penetration rates. It may be
desirable to augment the turbo-expander temperature with partial injection of
liquid nitrogen to lower
the temperature below -200 F.
124 To prevent possible slumping of gas hydrate beds after their exploitation,
it is
believed desirable that adjacent acreage be left alone so that if slumping
occurs in one 40 acres unit it
will encounter a frozen undisturbed unit and slumps no further.
125 Prior to fracturing the formation, the vertically disposed borehole 112 is
provided
with a cemented outer casing 132. After fracturing, a medium or inner casing
134 is disposed within
the cemented outer casing 132 and lowered to the bottom and tubing 136 is
disposed within the
medium casing 134. A first annulus 138 is formed between the cemented outer
casing 132 and the
medium or inner casing 134; and a second annulus 140 is formed between the
tubing 136 and the
medium or inner casing 134. Packers 142, 144, 146 and 148 are selectively
positioned within the
29
CA 02568358 2006-11-17
first annulus 138 for closing off portions of the formation 118. Such a
configuration permits fluid
communications between the substantially horizontally disposed injection
borehole 124 and the
substantially horizontally disposed production borehole 120 via the fractures
116 formed in the
formation 118. Further, by running the uncemented medium or inner casing 134,
the tubing 136 and
appropriate packers 142, 144, 146 and 148, heated gases, steam or the like,
can be injected into the
injection borehole 124 for disassociating the gas hydrate and permitting the
gas disassociated
therefrom to move upwardly through the fractures 116 and into the production
borehole 120.
126 To fracture the formation 118 so that the disassociated gas can be
recovered, the valve
assemblies 126 and 130 associated with the substantially horizontally disposed
production borehole
120 and the substantially horizontally disposed injection borehole 124,
respectively, are closed and
the remotely controlled valve assembly 128 associated with the substantially
horizontally disposed
fracturing borehole 122 is opened. In addition, the packers 146 and 148 are
installed at a desired
position in the first annulus 138 at a position below perforations 150 in the
cemented outer casing
132 so that fluid communication can be established between the first annulus
138 and the
substantially horizontally disposed fracturing borehole 122 when the remotely
controlled valve
assembly 130 is opened. Thereafter, an initial quantity of liquified gas is
introduced into the
substantially horizontally disposed fracturing borehole 122 whereby liquified
gas is discharged into
the formation 118 via perforations 152 provided at selected positions in a
casing 154 surrounding the
substantially horizontally disposed fracturing borehole 122. The casing 154
surrounding the
substantially horizontally disposed fracturing borehole 122 is provided with a
plug catcher 156 which
is positioned at about the midpoint of the casing 154. A plurality of rotating
sleeve assemblies 158,
which are similar in construction and function to the rotating sleeve
assemblies 58 hereinbefore
CA 02568358 2006-11-17
described, are supported on the casing 154 for selectively opening and closing
off the perforations
152 upstream of the plug catcher 156. When a fracture treatment commences, the
rotating sleeve
assemblies 158 are closed and the liquified gas goes to the furthermost set of
or downstream
perforations 152 in the casing 154. The initial quantity of liquified gas is
allowed to vaporize in a
portion of the substantially horizontally disposed fracturing boreholes 122
whereby a resulting
increase in pressure in the substantially horizontally disposed borehole 122
forms the fractures 116 in
the formation 118. Once the initial quantity of liquified gas has expanded and
produced an initial
network of fractures 116 in the formation 118, an additional quantity of
liquified gas is introduced
into the substantially horizontally disposed fracturing borehole 122. The
additional quantity of
liquified gas is allowed to vaporize in the fractures 116 in the formation 118
created by the injection
of the initial quantity of liquified gas into the substantially horizontally
disposed fracturing borehole
122 whereby a resulting increase in pressure in the substantially horizontally
disposed fracturing
borehole 122 forms additional fractures 116 in the formation 118 (i.e. a
network of cross fractures).
127 After the first set of perforations 152 is treated, a casing plug 160 is
pumped into the
substantially horizontally disposed fracturing borehole 122 and seats in the
plug catcher 156. While
being pumped into the substantially horizontally disposed fracturing borehole
122, the casing plug
160, which contains a radio transmitter or other remote control device,
activates the rotating sleeve
assemblies 58.
128 As with the rotating sleeve assemblies 58 of the multiple fracture system
10
hereinbefore described with referenced to Fig. 1, each of the rotating sleeve
assemblies 158 includes
a rotating sleeve 161 which is perforated on opposite sides thereof such that
upon rotation of the
rotating sleeve 161 the perforations 152 upstream of the plug catcher 156 and
the casing plug 160 are
31
CA 02568358 2006-11-17
. ~+..
opened. As previously stated, remote control rotating sleeves are well known
in the art as are remote
control devices capable of activating such rotating sleeves. Thus, no further
description of such are
believed necessary to prevent one skilled in the art to understand and
practice the invention.
129 Once the formation 118 has been fractured by the introduction of the
initial and
additional quantities of liquified gas, the remotely controlled valve assembly
128 associated with the
substantially horizontally disposed fracturing borehole 122 is closed and the
remotely controlled
valve assemblies 126 and 130 associated with the substantially horizontally
disposed production
borehole 120 and the substantially horizontally disposed injection borehole
124, respectively, are
opened. Further, packers 146 and 148 are installed at a desired position in
the first annulus 138 so
that the packers 146 and 148 are positioned above perforations 162 in the
cemented outer casing 132
and perforations 163 in the medium or inner casing 134 to provide fluid
communication between the
second annulus 140 and the substantially horizontally disposed injection
borehole 124. Perforations
164 are also provided in a casing 165 of the substantially horizontally
disposed injection borehole
124. Thus, heated gases, steam, and the like, can be introduced into the
substantially horizontally
disposed injection borehole 124 for movement upward through the fractures 116
of the fractured
formation 118 to the substantially horizontally disposed production borehole
120.
130 Each of the substantially horizontally disposed injection borehole 124,
the
substantially horizontally disposed fracturing borehole 122, and the
substantially horizontally
disposed production borehole 120, is cased with casings 165, 154, and 166,
respectively, but the
casings 165, 154 and 166 of such substantially horizontally disposed boreholes
124, 122 and 120, are
not cemented as is the outer casing 132 of the vertically disposed borehole
112. Perforations 162,
150 and 168 are provided in selected portions of the cemented outer casing 132
of the vertically
32
CA 02568358 2006-11-17
. , .~,
disposed borehole 112 so that fluid communication can be established between
the vertically
disposed borehole 112 and each of the substantially horizontally disposed
boreholes 124, 122, and
120 as shown in Fig. 3. In addition, the medium casing 134 is provided with
perforations 163 so that
fluid communication is established between the second annulus 140 and the
substantially vertically
disposed injection borehole 122 via perforations 162 in the cemented outer
casing 132 and the
perforations 163 in the inner casing 134 substantially as shown in Fig. 3.
131 Perforations 164, 152, and 170 are provided in the casings 165, 154 and
166,
respectively, of each of the substantially horizontally disposed boreholes
124, 122, and 120. Thus,
the introduction of the initial quantity of liquified gas and the additional
quantity of liquified gas into
the formation 118, as well as the network of fractures 116 thereby produced,
is controlled by the
position and number of perforations 152 present in the casing 154 of the
substantially horizontally
disposed fracturing borehole 122. Further, the use of the substantially
horizontally disposed
injection borehole 124, the substantially horizontally disposed fracturing
borehole 122, and the
substantially horizontally disposed production borehole 120, permit the
creation of the multiple
fractures 116 which enhance recovery of gas once the gas is disassociated from
the gas hydrate.
132 When the multiple fracturing system 110 is provided with more than one
substantially
horizontally disposed injection borehole 124, more than one substantially
horizontally disposed
fracturing borehole 122, and more than one substantially horizontally disposed
production borehole
120, the remotely controlled valve assemblies 130, 128 and 126 associated with
each of such
boreholes, is closed during introduction of the initial quantity and the
additional quantity of the
liquified gas except for the fracturing borehole 122 through which the
liquified gas is being
introduced to provide the desired network of fractures 116 in the hydrate
formation 118. It should be
33
CA 02568358 2006-11-17
noted that the multiple fracturing system 110 is designed to provide an
effective amount of
overburden formation 171 to ensure that the fractures 116 do not penetrate the
surface, such as the
ocean floor.
133. As with the production of oil shale oil to recover oil shale oil from a
shale oil
formation as hereinbefore described with reference to Fig. 2, a 40 acre
spacing well can be drilled in
the same manner as disclosed in Fig. 2 for the recovery of gas from a gas
hydrate formation. In such
instance, the same procedures hereinbefore described with reference to Fig. 2
and the 40 acre spacing
well drilled into the oil shale zone will be carried out to form the 40 acre
spacing for the gas hydrate
zone. However, as hereinbefore described, in drilling into gas hydrate zones
it is believed desirable
to employ the cryogenic drilling method disclosed in U.S. Patent No. 3,612,192
entitled, "Cryogenic
Drilling Method" which is heretofore been incorporated in its entirety by
reference.
134 With reference to Fig. 4, a method for drilling off-shore gas hydrate
wells is
illustrated. The vertically disposed borehole 112 is first drilled and cased
with the cemented outer
casing 132. The well 112 is drilled to provide at least 600 feet of overburden
formation 171 above
the top of the gas hydrate zone (Fig. 3) so that vertical fractures do not
penetrate to the surface.
135 Then two additional boreholes 172 and 174 are drilled opposite each other
from the
vertically disposed borehole 112 in a direction perpendicular to the direction
of the least regional
stresses. Four other "connecting" boreholes 176, 178, 180 and 182 are drilled
perpendicular to the
first from the vertically disposed borehole 112 for a distance of 440 feet
(for a 40 acre spacing) then
from the end of these connecting boreholes four more %~ radius boreholes 184,
186, 188 and 190 are
drilled parallel to the boreholes. All of these fracturing boreholes 184, 186,
188 and 190 are at the
midpoint of a 220 foot section of gas hydrate.
34
CA 02568358 2006-11-17
136 Since each1-t fracture extends 220 feet horizontally to meet up with a1~2
fracture of an
adjoining borehole, it is believed that the vertical fracture will also extend
220 feet in height. In
practice, the injection of volumes of liquid nitrogen beyond the necessity of
creating 220 feet'-~
length fractures will extend the fracturing deeper than 220 feet into the gas
hydrate. In thicker
sections (some gas hydrates are 2000 feet thick) it would be advantageous to
drill additional wells to
exploit the deeper sediments rather than to drill additional boreholes in the
same well which would
take years to heat. Each fracturing borehole is to be perforated in a number
of separate intervals as
hereinafter discussed.
137 Additional horizontal boreholes in the same configuration could be drilled
at the
bottom of the gas hydrate zone to inj ect heated water or steam. Other
boreholes at the top of the gas
hydrate zone could be drilled to act as production boreholes.
Optional 80 Acre Spacing
138 Drilling on 80 acre spacing is a viable option and will reduce the
necessary drilling
and thus the total cost. A possible disadvantage is the minimum major =~
length fracture would
increase from 220 feet to 311 feet. A 41 % increase.
139 Since the sudden vaporization of liquid nitrogen will result in a low
level explosion,
one would expect a tendency of fractures to occur in the earlier portion of
the major fracture and the
longer this fracture is, the more difficult it would appear to create
fractures in an orderly manner.
140 Consider, however, that the fracture creation is a matter of breakdown
pressure at a
particular part of a fracture and this would be the controlling factor. That
is, a weaker section would
break down first even if it is a long way down a fracture.
CA 02568358 2006-11-17
141 Also, additional injection of nitrogen at pressures below fracturing
pressure would
propagate the fractures near the fracturing borehole to lengths that would
exceed the 311 feet major
fracture length.
142 An alternative to increase spacing units beyond 80 acres is to drill an
additional
fracturing borehole parallel to the original borehole. This will require a new
connecting borehole
and because of the longer length of the fracturing borehole, additional
fracturing stages will be
required.
Fracture Creation
143 The greater the number of fractures in the impermeable gas hydrate
formation, the
greater the recovery efficiency.
144 Gas hydrate formations can conduct heat very slowly so the closer the
fractures are to
each other the greater will be the gas hydrate production rate and the greater
the efficiency of heat
conduction and the shorter the producing life of the project.
145 To create a fracturing program for a vertical fracture system it is
believed desirable to
first drill a large diameter vertical "motherbore" hole as herein before
stated and drill six horizontal
"fracturing" boreholes from the "motherbore" hole as illustrated in Fig. 2 in
the middle of a 220 foot
thick gas hydrate zone and also four connecting horizontal boreholes to
distribute the fracturing
fluid.
146 The boreholes are drilled such that any vertical fractures created will be
perpendicular
to the direction of the least regional stress. Each borehole is fractured
separately with multiple
fractures in each borehole.
36
CA 02568358 2006-11-17
~
147 It is desirable that the borehole orientation drilled to conform to a
vertical azimuth
even if the regional stresses favor a horizontal fracture. If the fracturing
pressure is maintained
above the fracturing pressure of a horizontal fracture, even if formed first,
a vertical fracture will
occur in the previously created horizontal fracture and afterwards a
horizontal fracture in the
previously created vertical fracture.
148 In some situations a vertical fracture will occur in the original vertical
fracture parallel
to the least regional stresses if it is lower than the stresses in a
horizontal fracture.
149 For illustration purposes, assume a 40 acre spacing well is drilled as
shown in Fig. 2
and 41,~ perforated, uncemented casing is run in the fracturing boreholes with
the perforations spaced
30 feet apart. If a single borehole is fractured separately, each borehole
would contain 20 separate
sets of perforations. By use of a cased hole packer, set halfway down the
borehole, 10 sets of
perforations can be treated simultaneously.
150 If the injection rate is 100 barrels of liquid nitrogen per minute (BPM)
each =~ length
borehole would fracture at 50 BPM rate or 5 BPM per separate fracture.
151 At -75 Fahrenheit, this rate after vaporization at 1200 psia, would
expand 5.59 fold
to an equivalent rate of 28 BPM down each separate fracture. Although this is
a very high rate, the
"Maguire Process" does not depend on frictional pressures to create secondary
fractures but rather
the secondary fractures will be created by the expansion forces of the
vaporizing nitrogen gases.
152 As hereinafter described, a rate of 5 BPM of liquid nitrogen translates to
210 GPM.
This volume at 1200 psia pressure will occupy the void space of a 220 foot %~
fracture in just 4.32
minute of pumping. It is believed that the entire fracture is not created in
4.32 minutes and an
37
CA 02568358 2006-11-17
additiona122 BPM is injected, the result of which is a build up in pressure
well beyond the fracturing
pressure, and as a result numerous secondary horizontal and vertical fractures
will be created.
153 For purposes of calculations, assume that 20 separate vertical 1-~
fractures 220 feet in
length are created in a single borehole. This will result in a one "fold"
volume of liquid nitrogen.
154 In practice, secondary fractures occur before the 220 foot extension is
reached.
Therefore more than one "fold" volume of liquid nitrogen will be required.
155 A one "fold" volume of liquid nitrogen "theoretically" would result in
20,200 foot 1-~
fractures 30 feet apart. The injection of a 5 "fold" volume of nitrogen would
result in the
"equivalent" of 1200 1-~ fractures averaging 6 feet apart. This is important
for two reasons:
156 1. The fracturing of all 6 boreholes in a 40 acre spacing well creates the
equivalent of 1,200 separate 1-i~ fractures. In reality, the fracture system
will
consist of vertical fractures perpendicular to each other both with and
against
the regional stresses and also the horizontal fractures. This occurs because
the
injection pressure is maintained at 3500 to 5000 psi, well above the
fracturing
pressure of 1200 psi.
157 In particular, the fracturing system in practice will not be confined to
220 foot
fractures. Some fractures will extend into adjacent producing units. However,
upon
their treatment an equivalent number of fractures will occur. As a result of
all the
"cross fracturing" and the creation of 1,200 1,~ fractures, it is believed
that the regional
stresses and overburden pressure can be nullified so that closure of the
fractures does
not occur. If, however, closure does occur, the injection of the heated water
or steam
38
CA 02568358 2006-11-17
will keep open the fracture system and also the expansion of the heated
hydrate
water.
158 2. The creation of 1,200, 1-~ length fractures will result in each
fracture being the
equivalent of 6 feet apart. This means the heating front has to penetrate only
3 feet to consume all the gas hydrate in a particular fracturing block. It
also
creates a very large surface area for the heating front.
159 It is believed desirable that each of the six separate horizontal
fracturing boreholes be
cased with 41-~ casing strings. The farthest half will have pre-perforated
holes grouped together and
spaced 30 feet apart or 10 sets for 1,~ of the borehole. The 41.~ casing will
not be cemented as the
casing pressure will be so high (2000 to 3000 psi plus friction losses) that
all perforated intervals will
be fractured.
160 The closer half will contain rotating sleeve assemblies also spaced 30
feet apart. Each
assembly will contain sets of perforations with a battery operated rotating
sleeve. The assemblies are
run with the rotating sleeve covering the perforations.
161 A two stage treatment can be performed by installing an open hole packer
midway
down the casing string to separate the farthest 10 sets of perforations from
the closer rotating sleeve
assemblies.
162 When a fractured treatment commences, the sliding sleeve assemblies are
closed and
all of the fracture treatment goes into the farthest set of perfs. Also in the
midway point is a "plug
catcher." After the first sets of perforations are treated, a casing plug is
pumped down the hole and
seats in the "plug catcher". While being pumped down the hole, the "casing
plug" which also
contains a radio transmitter will activate the battery operated rotating
sleeves and the sleeves will
39
CA 02568358 2006-11-17
rotate and open the upper sets of perforations. With the casing plug in place
the upper sets of
perforations can be treated. This procedure will be repeated for each borehole
separately.
163 After treatment, the casing plug can be retrieved by fishing operations.
The rotating
sleeves will have four (4), one inch openings separated by 2 inches with
another set of 4 on the
opposite side of the sleeve. It will only be necessary to rotate the sleeves
about 2 inches to open the
perfs.
164 Instead of using radio controlled plugs, direct wireless control can be
employed to
actuate the small battery controlled electric motors.
Method of Heat Conduction
165 Heat necessary to dissociate the gas hydrates is supplied by injecting
heated water
down the insulated injection line going from the production barge to the
subsea wellhead and thence
down the gas hydrate zone as indicated in Fig. 3. The water would normally be
converted to steam
but because of the pressure remains fluid.
166 The utilization of water as the heating agent is important because the
injection of the
water will replace the void spaces created by the dissociation of the gas
hydrate and the shrinking of
the hydrate ice and will also prevent possible slumping of the hydrate beds.
167 After injection, the heated water will dissociate the gas hydrate and the
gas will
migrate downward through the created fracture system to the lower production
borehole and into the
casing annulus and thence to the surface.
168 The required heat to heat the water is supplied by combustion of produced
gas to fuel
steam generators. This would amount to approximately 10% of the produced gas
including heat
losses. These figures are based on pure methane which contain 911 BTU's per
SCF.
CA 02568358 2006-11-17
169 It is believed desirable that the injection of hot water should occur into
the top of the
gas hydrate zone to permit the injected water to migrate downward so that no
"old" water would steal
heat from the "new" water being injected as would occur if injection was
instigated from the lower
zone.
170 The hydrostatic pressure and increased injection pressure, with a lower
production
borehole pressure would force the liberated gas to flow downward rather than
upward from the
buoyancy factor.
Calculation of Gas Production Rate
171 BTU's required to raise one SCF of injected water from 60 F. to 212 F.
plus BTU's
required to vaporize the water to saturated vapor or 100% quality steam.
172 (62.5#/SCF)(152 F) + (6,25#/SCF)(97OBTU/#)
173 =9500 BTU/SCF + 60,625 BTU/SCF
174 =70,125 BTU/SCF
175 =(70,125 BTU/SCF)(5.6 1 SCF/bbl)
176 =393,401 BTU's/ bbl injected
177 BTU's to dissociate one SCF of gas hydrate from 28 F to 38 F:
178 (6.25#/SCF)(.5specific heat)(10 F)
179 +(6.25#/SCF)(144BTU/#)
180 =313 +9000 = 9313 BTU/SCF
181 Since only the BTU's required to offset the heat of fusion, and since a
SCF of hydrate
consists of 0.9 water and 0.1 methane, the total BTU's to dissociate a SCF of
hydrate is:
182 (93 13 BTU/SCF - 313BTU/SCF)(0.9)
41
CA 02568358 2006-11-17
183 = 8100 BTU/SCF of hydrate
184 Since each BTU/SCF of hydrate will release 160 SCF of produced gas then:
185 8100BTU/SCF = 50.63 BTU/SCF
160 SCF/SCF of produced gas
186 For a production rate of 50,000,000 SCFD the required BTU's would be
(50,000,000
SCFPD)(50.63 BTU/SCF)
187 = 2,531,500,000 BTU/D
188 Since each barrel of 100% quality steam contains 393,401 BTU/bbl, then the
required
injection rate would be:
189 2,531,500,000/D = 6434 B/D
393,401 BTU/bbl of injected water.
190 However, void spaces created by the produced gas and the shrinkage of the
hydrate
water could result in slumping of the gas hydrate zones particularly after
sustained production.
191 To alleviate this problem, the volume of void spaces created by a
production rate of
50,000,000 SCFD is as follows:
192 Since each SCF of hydrate releases 160SCF of produced gas then:
50,000,000 SCF = 312,500 SCF of hydrate
160 SCF/SCF
193 Since each SCF of hydrate consists of 0.9 SCF of H20 and 0.1 SCF of
methane the
void space created by the gas production is:
194 (312,500 SCF)(0.1SCF) = 30,500 SCF
195 then: 30,500 SCF = 5436 bbl.
5.61 SCF/bbl.
196 The void space created by the shrinkage of the hydrate ice to water is
42
CA 02568358 2006-11-17
(0.9)(312,500 SCF) ) 5.61 SCF/bb1.
197 =5014 bbl. of shrinkage.
198 Total space = 5436 bbl. + 5014 bbl.
199 = 10,452 bbls. per day.
200 Since the heat required to produce 50,00,000 SCFD was 6434 B/D of 100%
quality
steam and the void space requirement is 10452 bbls. Then, 10,452 bbls. of 62%
quality steam should
be injected.
201 For higher rates of production appropriate increases in injection would be
required.
The actual rate of production would be increased above 50MMSCF because of the
vacuum effect of
the hydrate water and injected water as they cool.
202 Although the production rate would be reduced by the loss of heat down the
insulated
flow line and insulated tubing, over time the heat retained in the hydrate
water (2 12 F) after
dissociation of the gas (1 4% injected heat) would, after heat conduction to
surrounding frozen
hydrate molecules increase the production rate. This heat of retention would
more than make up for
the injection heat losses.
203 These production rates are based on gas hydrate zones occupying 100% of
the
sediments. This is necessary because there is great uncertainty at this time
regarding total thickness
and continuity of gas hydrate zones. It is expected, however, that early
exploitation will be made in
zones of high production rates.
Total Gas Reserves Per 40 Acre Well
43
CA 02568358 2006-11-17
204 An accurate estimation of hydrate gas reserves are difficult because of
lack of
knowledge of the hydrate continuity, thickness, hydrate concentration and
porosity in various areas
of the world.
205 Biogenic source hydrates which originate from the action of bacteria on
carbon
sediments contain nearly pure methane at about 911 BTU's per SCF. On the other
hand, thermogenic
source hydrates originate from conventional source gas deposits and thru
structure or other means
migrate upward until they encounter cold regions that result in the creation
of gas hydrates.
206 These non-biogenic hydrates appear to be very prevalent in the Gulf of
Mexico and
therefore initial attempts to exploit them using the "Maguire Process" should
be attempted here.
207 There are also indications that since these natural gases originate from
conventional
sources below the present hydrate zones, they also contain heavier
hydrocarbons of C2 thru C5 and
thus their BTU content could be 30% to 40% higher than the biogenic methane
hydrates.
208 Realizing that reserves parameters are difficult to estimate, an attempt
to do so will be
made using reasonable numbers that would be consistent with a rich area of the
Gulf of Mexico
sediments.
209 These calculations are as follows:
210 (43,560 SCF/acre)(40 acres)(40 porosity)(330 feet thickness)
211 = 36,800,000 SCF per 40 acre location, 330 feet in thickness.
212 Where the hydrate reserves are perhaps 1000 feet thick, 3 separate wells
could be
drilled on a single 40 acre unit, increasing the reserves to approximately 100
billion SCF/40 acres.
On Shore - Gas Hydrate Wells
44
CA 02568358 2006-11-17
213 Gas hydrates located in the land based areas of the arctic, notably
Russia, Canada,
Norway and Alaska can be recovered in a manner similar to that described for
ocean hydrates, except
of course, it is much easier and less expensive to drill on land than at sea.
214 An immediate problem to exploitation is the present lack of a gas
pipeline. One is
now planned for the future and should not lag too far behind the large scale
production of arctic
hydrates.
215 The parameters hereinbefore described of the in-situ method of producing
gas
hydrates are "off the shelf' procedures, that is liquefaction, pumping and
vaporization of liquid
nitrogen, horizontal drilling, offshore drilling and production platforms.
216 The successful production of gas hydrates is the creation of cross-hatched
vertical and
horizontal fractures which will allow a vast surface area for the heating of
gas hydrate lattice works.
Equally important is the creation of these fractures by vaporizing large
volumes of liquid nitrogen,
which will create very large "expansion pressures" well in excess of regional
fracture stresses.
217 The creation of perhaps 1,200, 1,~ length fractures in a 40 acre well has
a high
probability of preventing the closure of created fractures, but in any event
the pressures necessary to
inject steam for heating should hold open the fractures created.
218 The creation of 1,200,1-~ length fractures would result in these fractures
being the
equivalent of 6 feet apart. It is possible that the injection of additional
"folds" of liquid nitrogen
causing even closer spacing of fractures would result in higher rates of
recovery or to ensure that
fractures will stay open.
219 The drilling of the horizontal borehole using cryogenic air is especially
significant.
The cooling of the bit with cryogenic temperatures will permit much faster bit
rotation than normal
CA 02568358 2006-11-17
and result in much faster penetration rates. The bit would be driven by a
downhole electric motor
whose power would be increased by the cryogenic temperatures.
Geothermal Wells
219 Geothermal areas where above normal heat is located near the surface are
usually
associated with volcanic areas.
220 In areas where geothermal wells are drilled, for instance, California,
exist wet
formations from which steam flows when penetrated by boreholes. This steam is
usually contained in
the pore spaces, that is porosity, of these formations. Their rate of flow is
controlled by the porosity
and permeability of the formations.
221 The "Maguire Process" could enhance this process by creating hundreds of
cross-
hatch fractures in a manner similar to that recommended for oil shale
production.
222 In the geothermal process, all that would be necessary is to fracture the
"wet"
formations with liquid nitrogen and produce back the vaporized nitrogen in the
fractures as rapidly as
possible.
223 Because of the temperature disparity between liquid nitrogen and the steam
temperature formations, the fracturing process would be more violent than
would occur in the oil
shale process. Accordingly smaller volumes of liquid nitrogen would be
required.
224 By creating hundreds of fractures in a geothermal well as opposed to a
single vertical
borehole or limited horizontal boreholes, the production rate and possible
recovery factor would be
greatly increased.
225 Another type of geothermal area is referred to as "dry" areas. These are
areas where
the formations have little or no permeability. To extract the heat from these
formations, it is
46
CA 02568358 2006-11-17
proposed to fracture them in a manner similar to that used in the "Maguire
Process" in fracturing oil
shale.
226 It is proposed to drill a well in a similar manner and inject water from
the surface into
the top of the chimney, allow the water to encounter the hot fracture faces,
turn to steam and produce
it through the bottom borehole and thence to the surface through the vertical
borehole.
227 In both areas, wet or dry, the steam will be utilized to create
electricity.
Tar Sands and Heavy Oil Reserves
228 Tar sands in Canada and heavy oil reserves in Venezuela are successful
operations.
However, their cost and recovery efficiency can be greatly enhanced by use of
this "Maguire
Process."
229 Most of the tar sands production in Canada is done through surface mining
and
crushing. Some newer production is being done by drilling horizontal boreholes
of less density than
the "Maguire Process" with steam being injected into the borehole, heating the
tar sands oil with the
oil migrating to bottom through gravity.
230 The "Maguire Process" could greatly enhance this current process by
drilling the
horizontal borehole in a configuration similar to Fig. 1 and by fracturing in
a manner identical to that
described for oil shale development.
231 The net result is a much more extensive area for steam to heat up the sand
oil and thus
create much higher production rates and probably increased oil recovery.
232 It may be more practical to inject oxygen and ignite the tar sands as what
the
"Maguire Process" recommends for oil shale development.
Burning Coal Formations
47
CA 02568358 2006-11-17
233 Currently there are thousands of underground fires throughout the world.
It is
proposed to use the "Maguire Process" to eliminate these fires by drilling a
vertical "motherbore"
down past the bed of coals, drill horizontal boreholes as in Fig. 2 and then
fracture these beds
extensively using liquid nitrogen. The fracture system will distribute the
vaporized nitrogen over a
very extensive area and permit the injection of additional volume of normal
temperature nitrogen to
reduce or eliminate the oxygen needed to feed the coal fires.
48
