Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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METHOD AND APPARATUS FOR RECOV~RIN~ HIGH VISCOSITY OILS
RELATED PATENT APPLICATIONS
This application is related in ~art to Canadian
Patent Application No. 334,159, filed ~ugust 21, 1979.
(Sec. M-9 - C1. 166- Sub. Cl. 34)
BACKGROUND OF THE INVENTION
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This invention relates to methods and apparatus
for recovering high viscosity oil from subsurface earth
formations, and more particularly relates to improved methods
and apparatus for recovering such oils by employing a large
diameter shaft hole and a plurality of drill holes extending
radially from the shaft hole.
Early disclosures relating to the recovery of
petroleum substances by utilizing a large diameter shaft
hole and a plurality of drill holes are provided in U.S.
Patent Nos. 1,520,737 and 1,634,235, and a paper published
by Ranney in the Petroleum Engineer in 1939 entitled "The
World's First Horizontal Hole." These publIcations propose
the drilling of a large diameter shaft into an oil-bearing
formation and then drilling radial drill holes into the
formation. More recently, U.S. Patent Nos. 4,020,901,
4,099,570, 4,099,783 and 4,160,431 provide improved systems
for recovering petroleum substances employing large diameter
shaft holes and radials. The above processes, however,
suffer limitations relating to restrictions Oil the rate
of introducing the injection fluid, and the overall effi-
ciency of the oil recovery process according to the above
techniques may be so poor that recovery of the oil is not
economically feasible.
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The publication and patents referred to above
teach that steam or other heated fluids can be injected
into horizontal drill holes or laterals extending from
a large diameter shaft hole. The steam or other heated
injection fluid is introduced via laterals into the forma-
tion in order to provide heat to the formation and thus
reduce viscosity of the oil. The heated oil thereafter
flows to recovery laterals, being assisted by gravity.
The above procedure is generally referred to as
a "soak" operation, which should be distinguished from a
"drive" operation. In a "soak" operation, the injected
fluid is intended to lower the viscosity of the oil and
thereby enable the oil to more freely flow toward recovery
lines by gravitational forces. A soak operation may be
enhanced by raising the pressure in the formation and
assisting the recovery of oil by increasing the differen-
tial between the formation pressure and the pressure at
the point of recovery.
It is also common practice to inject fluid into a
conventional vertical well for the purpose of driving oil
within a formation horizontally to be recovered hy a distant
vertical well. In this "drive" operation, injected fluid is
intended to act as a vertical bank or wall in the formation
and push or drive the oil horizontally toward the recovery
well. Although the drive operation may be enhanced by in
jecting either a heated fluid or a solvent to additionally
lower the viscosity of the oil, the injected fluid is ideally
acting as a piston head to move through the formation and
drive the oil toward the point of recovery. ~orizontal drive
often results in viscous fingering and/or gravity override
which are very detrimental to a horizontal drive operation.
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Horizontal drive operations are therefore generally con-
cerned with the "critical velocity" of the injected fluid,
so that the driving force does not break down as a result
of viscous fingering or gravity override. Since the fluid
injected in horizontal drive operations is preferably intro-
duced at rates to keep the driving operation below the
critical velocity, the recovery rate, and the corresponding
economics of this operation, are often unacceptable. Both
phenomena commonly referred to as viscous fingering and
gravity override, as well as the differences between "soak"
and "drive" operations, are more fully discussed in my co-
pending application, Serial No. 334,159.
It is also well-known to inject water via conven-
tional vertical bore holes into the bottom of an oil-bearing
formation, while producing oil from conventional vertical
bore holes near the top of the formation. In this procedure,
often referred to as conventional vertical flooding, the
oil is displaced vertically upward by the injected water.
By using conventional vertical bore holes terminating near
the top of the formation and conventional vertical bore
holes terminating near the bottom of the formation, it is
also known that low viscosity oils can be collected by
injecting a light hydrocarbon in the top of the formation
while recovering the light oil from the vertical bore hole
terminating at the bottom of the formation. In the latter
procedure, the light oil is pushed downward by the lighter
hydrocarbon. The recovery of oil utilizing conventional
vertical wells and drive techniques are often poor, however,
because a limited number of points of recovery are provided
by the vertical wells.
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These conventional techniques have several in-
herent problems. In order to properly "blanket" an area
prior to establishing active horizontal driving displacement
of the oil, the displacing fluid must be injected at a low
rate. Also, if effective blanketing is to be achieved,
the formation must have high permeability and -the difference
in density between the oil and the injected fluid should be
high. If a good blanket of injecting fluid is not formed,
or if a good blanket is formed but the displacing fluid is
injected at too high a rate, viscous fingering can result.
When this condition occurs, the injecting fluid no longer
effectively displaces the oil, and the volumetric sweep
efficiency of the operation falls off drastically.
In order to minimize the likelihood of viscous
fingering when utilizing the prior art techinques, the
injecting fluid is often introduced into the formation at
low injection rates, e.g., 400 barrels of fluid per day
per well. Optimum steam injection rates with vertical
wells are more fully discussed in an article by Messrs.
Bursell and Pittman, appearing in the Journal of Petroleum
Technology, August, 1975, beginning on page 997. Low in-
jection rates, of course, generally result in low production
rates, which significantly increases the cost of production.
The problems and disadvantages of the prior art
are overcome with the present invention. Novel methods in
apparatus are hereinafter provided for recovering high vis-
cosity oils from sub-surface formations, wherein a greater
percentage of the oil can be recovered from the formation
and can be recovered in a more efficient manner.
SUMMARY OF THE INVENTION
In one embodiment of this invention, a vertical
mine shaft of sufficient diameter to accommodate personnel
and equipment is bored to and through a formation containing
a high viscosity oil. The vertical shaft is enlarged near
the top of the formation and near the bottom of the forma-
tion forming chambers to provide increased space for men
and equipment. Substantially horizontal drill holes or
laterals are thereafter bored radially into the formation.
The numbering and spacing of these laterals will be dis-
cussed in detail below. For the present, it is significant
that one group of laterals is provided near the top of the
formation, and another group of laterals is provided near
the bottom of the formation. Each group or set of boreholes
or laterals effectively blankets a particular portion of
the formation, and the configuration of each blanket may
be rectangular. Thereafter, drill holes are bored into
the face of the formation and radially about the chamber,
through which a suitable fluid is thereafter injected into
the formation by way of a conduit leading to the surface.
Using the above-described apparatus with one set
of laterals near the top of a formation and another set at
the bottom of a formation, oil may be recovered by either
(a) introducing an injected fluid into the bottom set of
laterals while recovering oil from the top set of laterals,
or (b) introducing an injected fluid into the top set
of laterals while recovering oil from the bottom set of
laterals.
The instant invention preferably utilizes a plu-
rality of substantially horizontal laterals which are drilledin the formation for recovery of high viscosity oil through
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"drive" techniques, while the prior art attempts to improve
oil recovery by using boreholes or laterals within the
formation and various "soak" techniques. In the present
invention, the driving force of the injected fluid is sub-
stantially vertical: vertical upward drive toward the top
set of laterals, or vertical downward drive toward the
bottom set of laterals. The advantage of driving vertically
rather than horizontally, as taught by conventional oil
recovery techniques, is that the injected fluid may be
introduced at a much higher rate because the likelihood of
viscous fingering is substantially reduced and detrimental
gravity override is eliminated. A fluid may therefore
be injected according to the present techniques at rates
equivalent to the maximum output of most commercial genera-
tors, without regard to the concept of critical velocity,
fingering, or gravity override.
In conventional oil wells, it is often quite
difficult to establish a blanket of injected fluid, although
the fluid is injected at various points in the plane of the
blanket. According to the present invention, the blanket
of injected fluid may be more easily established since the
fluid is not injected at points in the blanket, but rather
is injected along entire lines lying within the blanket.
These lines effectively provide a multitudinous number of
points of injection so that the blanket for the drive
operation is more easily established.
As previously mentioned, the apparatus described
may be utilized for vertical upward drive or vertical down-
ward drive. This offers a distinct advantage over the
prior art since the injected fluid can be selected for
either upward or downward drive depending on the density of
the oil in the formation, the desirability of using a mis-
cible or an immiscible injected fluid, the availability of
the injected fluid, and the particular characteristics of
the formation. For instance, if the oil in the formation
is a heavy crude oil, e.g., 14 API, and a relatively heavy
injected fluid is available, e.g., carbon disulfide, ver-
tical upward drive of the oil is feasible. Thus, carbon
disulfide, may be injected in the bottom set of laterals,
and, since the injected fluid is heavier than the oil,
it would not tend to rise naturally in the formation. A
blanket of injected fluid may be thereby easily established
in the bottom of the formation. As the injection of carbon
disulfide continues, the injected fluid drives oil upward
in the formation toward the top set of laterals. Fluid may
continue to be injected in the bottom set of laterals while
oil is recovered from the top set of laterals, until the
injected fluid is effectively driven through the entire
formation.
If, on the other hand, the formation pressure is
high and heated water is readily available as an injected
fluid, downward vertical drive may be desirable. Heated
water at 500 F. is less dense than 14 API oil. Thus,
heated water may be injected in the top set of laterals
serving to drive the oil downward for recovery by the bottom
set of laterals. In this manner, a blanket of injected
fluid is established in the upper portion of the formation,
and the oil is driven downward by the continued injection
of fluid.
The particular spacing and arrangement of drill
holes will, of course, depend upon the size and lithology
of the formation of interest, but it is a feature of the
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invention to provide approximately eight different radially
e~tending drill holes for each shaft hole, and to further
extend such drill holes to a location ad~acent the ends of
similar radials extending from an adjacent vertical shaft
hole. As will hereinafter be explained in detail, each
group of radial drill holes will then define a rectangular
pattern within the field, and thus the field may be effec-
tively "covered" with a blanket of such rectangular patterns.
The bore holes or radials may extend from the
large diameter shaft hole in a generally horizontal direc-
tion. Some of the radials, however, may be positioned at
a slight upward angle, e~g., 3 - 7, so that gravity may
assist the flow of oil within the lateral. Also, some for-
mations have generally horizontal barrier zones which are
impermeable to fluid flow. Relatively thin shale deposits
are one example of these impermeable barrier zones. When
such zones exist, the bore holes or laterals may be drilled
at a greater upward angle, e.g., 10 - 18 upward from the
horizontal, so that the bore holes would pass through one
or more of these barrier zones. Thus, the recovery of oil
and the efficiency of the operation will be increased since
oil can be recovered by soak or drive techniques which
would have previously remained within the formation because
of the presence of the impermeable barrier zones.
It is within the concept of the present invention
to locate the radials adjacent the lower limit of the
formation, whereby the fluid injected therefrom will also
tend to rise as well as travel laterally through the forma-
tion, and also to provide additional pluralities of such
radial drill holes at other higher locations within thicker
formations. Furthermore, it is within the concept of this
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invention to inject fluid through only a portion of the
radials, while also recovering oil from one or more of the
other radials extending from the same shaft hole.
The invention is suitable for recovering oil from
subsurface formations, and is particularly suitable for
recovering high viscosity oils. High viscosity oils are
generally inclusive of both medium gravity oils having an
API range of 20to 25, and heavy crude oils having an API
range of 20 or less.
A particular feature of this invention is to pro-
vide methods and apparatus that result in increased produc-
tion rates for recovering high viscosity oil from subsurface
earth formations.
It is another feature of this invention to provide
methods and apparatus for driving oil within a subsurface
earth formation vertically toward recovery laterals extend-
ing radially from a large diameter shaft hole.
It is a further feature of this invention to
provide methods and apparatus that will increase the over-
all efficiency of recovering high viscosity oil from asubsurface earth formation by utilizing vertical drive
techniques.
It is an additional feature of this invention
to provide apparatus for recovering oil from a subsurface
earth formationp comprising a shaft hole extending from
the surface to said subsurface earth formation, a first
plurality of boreholes extending radially from said shaft
hole into said formation at a first elevation, a second
plurality of boreholes extending into said formation at a
second elevation, and injection means introducing a fluid
through said second plurality of said boreholes and into
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said formation for driving said oil vertically for recovery
by said first plurality of boreholes.
It is a further feature of this invention to pro-
vide a method of recovering oil from a subsurface earth
formation, comprising establishing a shaft hole extending
from the surface of -the earth to said subsurface earth
formation, drilling a first plurality of boreholes radially
from said shaft hole into said formation at a first eleva-
tion, drilling a second plurality of boreholes into said
formation at a second elevation, and injecting a driving
fluid into said second plurality of boreholes and into said
formation for driving said oil vertically for recovery by
said first plurality of boreholes.
The method of the present invention comprises
establishing a shaft hole extending from the subsurface of
the earth to said subsurface formation, drilling a plurality
of boreholes substantially laterally from the shaft hole
into said subsurface earth formation, drilling a second
plurality of boreholes, all terminated substantially at
another second level, injecting into said formation through
said second plurality of boreholes a displacing fluid to
establish a substantially horizontal stratum of said dis-
placing fluid, injecting into said formation through said
second plurality of boreholes a driving fluid under pressure
to vertically drive said stratum of said displacing fluid
through said formation, and withdrawing oil from said shaft
hole through said first plurality of boreholes while simul-
taneously injecting said driving fluid into said formation.
Also, the present invention provides or an
apparatus that includes a shaft extending from the surface
of the earth to said subsurface earth formation, a first
plurality of boreholes extending radially from said shaft
and lying within a substantially horizontal first plane
within said formation at a first elevation, a second plura-
lity of boreholes all terminated substantially at another
second level and comprising fluid output means for defining
a layer of fluid, injection means introducing a displacing
fluid through said second plurality of boreholes to provide
a layer of displacing fluid, pressurizing means introducing
a driving fluid through second plurality of boreholes for
driving the layer of displacing fluid vertically -toward said
irst plurality of boreholes, and recovery means for with--
drawing oil from said first plurality of boreholes.
These and other features and advantages of the
present invention will become apparent from the following
detailed description, wherein reference is made to the
figures in the accompanying drawings.
IN THE DRAWINGS
Figure 1 is a simplified pictorial representation,
partly in cross-section, of an exemplary installation for
recovering oil from a subsurface earth formation according
to the present invention.
Figure 2 is a cross-sectional representation of a
portion of the apparatus depicted in Figure 1~
Figure 3 is a simplified pictorial representation,
partly in cross-section, of a portion of the apparatus
depicted in Figure 1.
Figure 4 is a graph illustrative of the variations
in specific gravity for fluids, and is referred to in the
description to assist in illustrating the concepts of the
present invention.
Figure 5 is a simplified pictorial representation,
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partly in cross-section, of another form of an exemplary
installation according to the present invention.
Figure 6 is a cross~sectional representation of a
portion of the apparatus depicted in Figure 5.
DETAILED DESCRIPTION
.
In Figure 1, there may be seen a pictorial repre-
sentation of an oil recovery system embodying the concepts
of the present invention. In particular, the apparatus
depicted in Figure 1 may be utilized for recovering high
viscosity oil from subsurface earth formations. A substan-
tially vertical mine shaft 2 is drilled or bored from the
surface 4 to the oil-bearing formation 6. The oil-bearing
formation 6 may typically be hundreds of feet below the
surface 4, and is shown to be bounded by an upper layer 5
and a lower layer 7 of shale deposits, which are generally
impregnable to fluid flow. ~s seen in Figure 1, the mine
shaft 2 is drilled through the oil-bearing formation 6,
and terminates at a sump hole 8~
The shaft 2 is expanded near the top portion of
the formation to form an upper work chamber 10, and is
expanded at the bottom portion of the formation to form a
lower work chamber 12. A plurality of upper laterals 14
and 16 may be drilled into the formation 6 from the upper
work chamber; a plurality of lower laterals 18 and 20 may
likewise be drilled into the formation from the lower work
chamber 12.
A steam generator 22 at the surface floor provides
injection fluid to the upper laterals 14 and 16 by a steam
line 24. If desired, a plurality of steam lines 24 may be
provided, so that the injected fluid to each upper lateral
may be separately controlled at the surface by conventional
. ~ .
valving techniques. The lower laterals 18 and 20 may serve
as recovery lines for oil, which is collected in recovery
tank 26. Each of the lo~er laterals 18 and 20 may be con-
nected to individual recovery lines 28 and 30 which may
terminate at the recovery tank 26, or the recovery lines 28
and 30 may join at a subsurface manifold 32 so that oil from
the various lower laterals 18 and 20 flows to the recovery
tank 26 by a central recovery line 34.
Referring again to Figure 1, it may be seen that
a portion of the radial or lateral 14 extending from the
wall of the upper work chamber 10 may be suitably provided
with a casing 36, with a perforated portion of the lateral
14 thereafter extending from the casing 36. The walls of
the shaft 2 may be conveniently sealed with sections of
bolted or welded steel plates to form a casing 38, or may
be lined with an appropriate material such as gunite, to
prevent caving or other collapse of the walls of the shaft
2. The diameter of the shaft 2 is preferably of a size
sufficient to accommodate the passage of men and equipment
from the surface 4 to the interior of the work chambers 10
and 12. The mine shaft 2 and each of the work chambers 10
and 12 may be constructed in the manner further described
in U.S. Patent 4,160,481.
~ lt'neembodiment of this invention illustrated in
Figure 1, fluid is injected into the formation via radial
drill holes or laterals 14 and 16 which lie entirely within
the formation 6. If the injected fluid is heated water
or steam, heat loss by way of the steel casing 38 therein
is not significant since the heat merely transfers to the
formation. On the other hand, it is desirable for the
injected fluid to enter the formation at a distance from
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the shaft 2 or work chamber 10, so that the fluid will tend
to move outwardly therefrom instead of bypassing back into
the chamber 10. Furthermore, it may be preferable to insert
pre-perforated pipe or casing into the radial drill holes,
rather than to perforate the casing in a conventional manner
after it has been inserted. The upper laterals may contain
the casing 36, but the casing is not necessary according
to the present invention. Thus, although the casing 36 is
only shown for the upper lateral 14, it is within the con-
cept of my invention that the casing be employed with all,some, or none of the injection laterals.
Referring now to Figure 2, there is illustrated
a cross-sectional view of the laterals shown in Figure 1.
In Figure 2, four upper laterals radiate from the shaft 2
at 90 intervals, and are denoted as 14, 15, 16 and 17.
Four lower laterals are also spaced at 90 intervals, and
the lower laterals 18, 19 r 20 and 21 are shown connected to
their respective vertical recovery lines 28, 29, 30 and 31.
Both the upper set of laterals and the lower set
of laterals depicted in Figures 1 and 2 lie in substantially
horizontal planes. As explained in further detail below,
the upper set of laterals, in combination with an injected
fluid, form a blanket of injected fluid which act as the
driving force for the recovery process. Typically, the
laterals will radiate from the shaft 2 -to enable a substan-
tially horizontal blanket to be established having an area
of 25 acres. In Figure 2, the pattern of the blanket formed
by the injection radials 14, 15, 16 and 17 is circular.
Other configurations are possible, and the particular con-
figuration of the blanket formed by the injection laterals
will depend, in part, on the characteristics of the for-
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mation, the viscosity of the oil in the formation, the
injected fluid, and the possible use of injection laterals
in combination with conventional wells. For instance,
the configuration of the injection laterals may form a
rectangular blanket, as shown in my co-pending patent
application, which i5 Serial No. 334,159. The length of
the laterals will depend on their relative position to one
another, since the injection laterals preferably function
to form a uniform substantially horizontal blanket in a
portion of formation 6~ Further, the diameters of the
laterals will depend primarily upon the type of matrix
composing the formation 6, as well as the viscosity of the
oil sought to be recovered therefrom.
Figure 3 illustrates a portion of the apparatus
generally depicted in Figure 1. A tubular member 40 is
typically inserted into any of the boreholes described,
such as the laterals 14, 15, 16 and 17 in Figure 2. Like-
wise, a tubular member 42 may be inserted into the laterals
18, l9, 20 and 21. The oil-bearing formation 44 is bounded
on the top by a layer of shale or other rock 46, and on the
bottom by a similar impregnable layer of shale or other
rock 48. The layers 46 and 48 are typical of any number of
materials which often exist on the upper and lower portions
of an oil-bearing formation. Generally, these impregnable
layers line a substantially horizontal plane, although
perhaps not as uniform as the layers depicted~
As previously stated, it is preferable according
to the present invention that the upper tubular member 40
be placed near the upper portion of the formation, and that
the lower tubular member 42 be near the bottom portion of
the formation. The exact spacing of the upper and lower
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.
laterals will possibly depend on the configuration of the
layers 46 and ~8. If these layers are uniform and substan-
tially horizontal within the area oE the recovery operation,
the laterals may be drilled very close to the layers. If
the layers are irregular in configuration, the upper laterals
may be drilled in the upper fifth of the formation, and the
lower laterals in the lower fifth of the formation. For
example, if the formation 44 is approximately 60 feet thick
and substantially uniform in configurationr the upper tubular
member 40 is preferably 1 to 5 feet from the bottom of the
top layer 46, and the lower tubular member ~2 is preferably
1 to 5 feet above the top of the bottom layer 48.
A simplified method of operation according to the
present invention will now be described by reference to
Figures 1, 2 and 3. For the present, it will be assumed
that steam has been selected as the injection fluid, and
that both steam and water at the temperature and pressure
within the formation are less dense than the oil in the
formation.
Steam from the generator 22 may be injected into
upper laterals 14, 15, 16 and 17 by a plurality of steam
lines 24. The steam may enter the formation 44 through
a series of perforations in the upper tubular members, such
as the perforations 50 in the tubular member 40. The per-
forations 50 may be formed along the entire length of the
tubular member 40, and are preferably formed along at least
a substantial portion of the length of the tubular members.
Heat from the injected steam will decrease the
viscosity of the oil in the formation adjacent the tubular
member 40. As the formation 44 is heated, condensate may
be formed which will be more dense than the steam, but less
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dense than the oil in the formation. The steam from the
tubular member 40 will, in combination with the steam simul-
taneously injected in the other upper laterals, produce
a blanket of steam generally in the plane of the upper
laterals.
Continued in~ection of steam into the upper lat-
erals will cause a pressure increase in the top of the
formation 44. This pressure increase will drive the oil
in the formation downward toward the lower tubular member
42. Also, the condensate from the injected steam may
serve as a face for the driving Eorce. In other words,
the increase in pressure above the condensate layer will
force the condensate layer downward, thus driving the oil
downward from the formation.
As the steam is injected in the upper tubular
member 40, oil will be simultaneously recovered through
perforations 54 along a substantial portion of the length
of the lower tubular member 52. Referring to Figure 2,
steam injected into the upper laterals 14, 15, 16 and 17
will drive the oil downward for recovery by the lower
laterals 18, 19, 20 and 21. In this manner, the oil from
the formation 44 may be efficiently recovered by the down-
ward drive of the injection fluid.
As stated above, the present invention may be
effectively employed by utili2ing a driving fluid and
driving the oil vertically toward recovery laterals. In a
vertical driving technique, the pressure gradient within
the formation may be altered by the injected fluid to force
the oil toward the recovery lines. Because of the weight
of the oil in the formation, the pressure near the upper
section of the formation will generally be less than the
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pressure in the lower portion of the formation. By way of
illustration and referring to Figure 1, if the formation 6
were 60 feet thick and the pressure at the top of the for-
mation just below the layer 5 was 15 psia, the pressure
near the bottom of the formation above the layer 7 may
typically be 40 psia because of the pressure gradient of
the oil in the formation 6.
According to the vertical steam drive techniques
discussed herein, drawing the oil from the recovery lines
and injecting a fluid into the injection lines will produce
a pressure differential sufficient to force or drive the
oil vertically. Preferably, a pressure differential of 100
psia or more is achieved during the driving process between
the pressure at the place of injection and the pressure at
the place of recovery within the formation. The preferred
pressure differential will vary depending on the specific
characteristics of the oil and the formation, and typically
a pressure differential of 200 psia to 400 psia will be
desired. The maximum pressure at the place of injection is
generally limited for safety reasons to 1 psig per foot of
overburden. For instance, if steam is injected into the
laterals 14, 15, 16 and 17 which are ~00 feet below the
surface 4, it may be desired to limit the pressure provided
in the upper portion of the formation 6 to 400 psia.
As previously mentioned, vertical drive may be
properly utilized without concern for gravity override,
even with injection rates far exceeding the injection rate
employed in conventional horizontal drive. In the embodi-
ment described above, the density contrast between the oil
and the injected fluid is deliberately utilized during the
driving operation to increase the efficiency of the recovery
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processes, while the same density contrast ma~v result in
gravity override in horizontal drive operations which is
detrimental to the efficiency of horizontal drive recovery
processes. Also, s-ince the o;l is being driven vertically
downward t the likelihood of viscous fingering during the
driving operation ls substantially eliminated since (a) a
uniform blanket of drlving fluid is initially formed, (b) the
condensate layer 52 acts as a face for driving the oil from
the formation~ and Cc) the oil is being driven vertically
downward, and the injected fluid will not tend to pierce
through the formation 44 because the injected fluid is less
dense than the oil below the injected fluid. Further, as
explained below, vIscous fingering prior to the driving opera-
tion increases the efficiency of th.e recovery process accord-
ing to the present invention, rather than being detrimental
to the recovery eff.iciency as in horizontal drive techni~ues.
Steam may be continually injected into the upper
tubular member 4Q until condensate or steam has been recovered
from the lo~er tubular member 42. At this point, further
injection of steam may not be economical, since little if any
further oil ~ill be recovered from the lower tubular member 42.
If the vertical recovery lines 23 and 3a are used to connect
each lateral to the recovery tank 26, it is possible to monitor
the fluid being recovered at the surface 4 from each lower .`
lateral. In this manner, it may be desirable to discontinue
the injection of steam into the upper laterals which are ad-
jacent the lower laterals in which steam or condensate is being
recovered, whi.le continuing to inject steam into the other upper
lateral.sas long as oil is being produced from their æspective ~Ja-
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cent lower laterals. If the recovered oil is ei~her being
~orwarded to a subsurface manifold 32 or is being taken
from a common sump hole 8, the monitoring of the recovered
fluid from the individual lower laterals may be accomplished
before that fluid is intermingled with fluid from the other
lower laterals. Use of the common sump hole 8 for recover-
ing laterals is more fully described in my co-pending appli-
cation Serial No. 334,159.
Referring again to Figure 2, the following is an
example of the monitoring procedure described above. Steam
may be initially injected into the four la-terals 1~, 15, 16
and 17, forming a substantially horizontal blanket of steam
in the plane of the upper laterals. Continued injection of
the steam will drive the oil in the formation to the lower
laterals. Once steam or condensate has been recovered from
one of the lower laterals, e.g., lateral 21, steam may be
continued to be injected into the upper laterals 15 and
16, while steam is not injected into the upper laterals 14
and 17. Thus, oil recovery would continue from the lower
laterals 18, 19 and 20, but oil recovery from the lower
lateral 21 would be effectively discontinued.
An alternative procedure that may be used when
steam or condensate is recovered in one of the plurality
of lower laterals is to inject cold water into the lower
lateral while continuing steam injection into the upper
laterals. Referring to the example described immediately
above, if water or condensate is being recovered from the
lower lateral 21, cold water may be injected into lower
lateral 21 while continuing to inject steam in either upper
laterals 15 and 16 or all the upper laterals 14, 15, 16 and
17. The introduction of the cold water into the lower
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lateral 21 effectively terminates the recovery of any fluid
from the lateral 21, thus the steam injected into the for-
mation would be effectively used to produce oil from the
laterals 18, 19 and 20.
One of the advantages of the plurality of upper
laterals 14, 15, 16 and 17 is that a blanket can be easily
and rapidly established in the formation which will enhance
the driving efficiency of the in,ected fluid. The rapid
establishment of a blanket in the formation will increase
the thermal efficiency of the recovery process since less
heat and injection fluid will be lost to adjacent beds or
escape from the formation entirely. Conventional vertical
injection wells do not result in the rapid and efficient
establishment of a blanket, since the fluid is injected at
points within the plane of the blanket. According to the
present invention, the laterals lie within the plane of the
blanket to be established, and thus lines of injection are
provided rather than mere points of injection. The parti-
cular number of laterals used will depend on a variety of
factors. It is within the concept of the present invention
that a pluralilty of laterals radiate from the mine shaft
at at least two vertical elevations. The embodiment illus-
trated in Figure 2 shows four upper laterals and four lower
laterals, but any number of upper and lower laterals may
be used. For instance, eight equally spaced upper laterals
could be used in conjunction with eight equally spaced lower
laterals. The efficiency of the recovery process would be
generally enhanced by the increased number of laterals, but
the increased number of laterals also results in increased
drilling and equipment costs.
It is preferable that equal numbers of upper
~18~35~
laterals and lower l~terals be provided, and that the individual
upper laterals and individual lower laterals b.e equally spaced
from each other. Thus, as~ shown in Fîgure 2, each of the upper
laterals is ~0 apart from adjacent upper laterals, and the
lower laterals are 90 apart from ad~acent lower laterals.
In addition, i`t ;s- preferable that lower laterals be spaced
between upper laterals:, as compared to having the lower laterals
directly below the upper laterals. As shown in Figure 2, each
o~ the lower laterals is 45 apart in the horizontal direction
from its adjacent upper laterals; if eight upper laterals were
used in conjunction with eight lower laterals, each lower
lateral would preferably be offset fro~ its adjacent upper
lateral by 22.5. One advantage in offsetting the lower later-
als from th.e upper laterals is that a longer path is there~y
provided between the injection laterals and the recovery later-
als. Thus, the injection fluid tends to spread out evenly
through the formation and increase the swe~p eff.iciency of the
recovery process. If th.e upper laterals were to be placed
directly above the lower laterals, there is less likelihood
that the oil near the bottom of the formation and between the
lower laterals would be recovered.
As previ.ously-described, the use of upper and lower
laterals within a formation enables a blanket to be easily
formed for the driving process. It is possible to use conven-
tional vertical injection wells instead of the injection
laterals, although the blanket of driving fluid may not
be established as:readiL~ as if horizontal boreholes or
laterals were used for the injectors. Referring to Figure
5, there is illustrated another form of my invention which
employs the use of conventional vertical wells 60
- 23 -
,~,. . .
and 62. It will be seen that these conventional vertical
wells 60 and 62 are drilled from the surface 64 through the
top rock layer 66 and terminate in the upper portion of the
formation 68. Fluid may be injected into the vertical
wells from a common generator, or separate generators 70
and 74 may be employed for each vertical well. Valves 72
and 73 may be used to control the flow of fluid from the
generators to the formation.
The laterals 76 and 78 extend radially from the
work chamber 80 in the lower portion of the mine shaft 82.
The lower set of laterals preferably "blanket" a portion of
the formation, as previously described. Valves 83, 84 and
86 may be used to control the recovery of oil from the
laterals to the recovery tank 88. In Figure 5, both the
laterals 76 and 78, and the work chamber 80 are entirely
within the lower portion of the formation 88, and lie above
the rock layer 90.
It is also within the concept of my invention to
utilize conventional vertical boreholes in combination with
both upper and lower laterals, if desired, to assist the
formation of a blanket and the driving process. Thus, in
Figure 5 there is illustrated vertical injection wells 60
and 62 plus horizontal laterals 92 and 94. By controlling
valves 96, 98 and 100, the injection of fluid from the
generator 70 to each of the horizontal injection laterals
92 and 94 may be controlled.
Referring now to Figure 6, there is shown a cross-
sectional view of a portion of the apparatus depicted in
Figure 5. The vertical injection wells are designed as 102,
103, 104, 105, 106, 107, 108 and 109, with wells 103 and
108 corresponding to the wells 60 and 62 shown in Figure 5.
The horizontal recovery laterals form a generally rectangular
blanket, and are designated as ~aterals 112, 113, 114, 115,
~ 24 -
~ t~t~ ~
116, 117, 118 and 119, with latera:Ls 113 and 117
corresponding to laterals 76 and 78 in Figure 5.
It will be seen that the vertical wells may be spaced be-
tween the horizontal laterals, and that the injection wells
are spaced geographically to cover the area to be blanketed.
If desired, other injection wells may be spaced inwardly to
the vertical mine shaft from the injection wells shown in
Figure 6.
If horizontal injection laterals are utilized, it
is anticipated that vertical injection wells would generally
not be necessary. On the other hand, if vertical injection
wells are utilized, it generally may not be necessary to
drill horizontal injection laterals. However, it is pos-
sible to use both vertical and horizontal injections, and
this may be desirable if only a relatively few number of
injection laterals are utilized.
To assist in establishing a horizontal blanket if
vertical injectors are used in combination with recovery
laterals, fluid may be initially injected into a portion
of the vertical boreholes while oil is recovered from the
remaining vertical boreholes. Thus, fluid may initially
be inserted into the odd-numbered vertical wells, and the
oil may be driven horizontally and recovered by the adja-
cent even-numbered vertical boreholes until the injection
fluid is recovered in the adjacent even-numbered vertical
boreholes. At this point, a horizontal blanket of injec-
tion fluid is established, and ~luid may be injected in
all the vertical boreholes 102 through 109 to drive the oil
downward for recovery by the lower laterals 112 through
119. In this embodiment, the vertical boreholes are preEer-
ably spaced between the injection laterals and toward the
periphery of the blanketed zone to increase the efficiency
of the recovery operation. As previously described, it is
-25-
.~ `?
~.
within the concept oE this inventicn to drive vertically
upward or vertically downward, and the conventional vertical
boreholes herein described may terminate near the top of
the formation if downward drive is desired, or may terminate
near the bottom of the ormation if upward drive is desired.
It is within the concept of this invention to
employ a plurality of substantially horizontal laterals and
inject fluid to drive the oil in the formation vertically
toward recovery laterals. Oil may be driven vertically
upward or downward, and thus the upper laterals and lower
laterals may function either as injection laterals or
recovery laterals. For instance, steam may be effectively
used in many operations wherein the steam i5 injected into
the upper laterals, since bo~h the steam and the condensate
at the temperature and pressure within the formation may be
less dense than the oil. However, some miscible fluids
which are more dense than the oil in the formation can also
be effectively used as a driving fluid. If the injected
fluid chosen, e.g., carbon disulfide, is more dense than
the oil, it may be advantageous to inject the fluid in the
lower laterals 18, 19, 20 and 21 while recovering oil from
the upper laterals 14, 15, 16 and 17. In this case, the
heavier injected fluid would easily and rapidly form a
blanket in the lower portion of a formation, and continued
injection would drive the oil upward toward the recovery
laterals. Also, neither gravity override or viscous finger-
ing is a problem in this case during the driving operation,
since the heavier injected fluid is below the oil to be
displaced.
It may therefore be seen that the present inven-
tion is applicable with both miscible and immiscible injec-
-26-
tion fluids. Also, it is within the concept of my invention
to inject a liquid lighter than the oil in a formation into
the upper laterals, and thereafter to drive the oil downward
toward the lower laterals by injecting a gas or a gas/liquid
mixture in the upper laterals as the driving force. More
particularly, a solvent less dense than the oil may be
injected into the upper laterals to form a blanket of fluid
to act as the face of the driving force. ~uccessively
lighter slugs of fluid, each slug having a lower density
than the previous slug, may thereafter be injected into the
formation. Finally, a gas may be injected. The injection
slugs of fluid and gas produce a driving force, and the
solvent first injected acts as the face of the driving
force. This technique, which may be referred to as graded
miscible displacement, may be highly effective, permit much
higher injection rates, and yield higher production rates
than possible according to the prior art.
The density of the injection fluid may vary with
temperature changes to a different extent than the oil in
the formation. It is possible, therefore, to inject a par-
ticular fluid in the top laterals as a driving force when
that fluid is lighter than the oil, and to inject the same
fluid in the lower laterals as a driving force when the
fluid is heavier than the oil in the formation. Referring
now to Figure 4, there is depicted a chart which illustrates
the approximate density of the water, 10 API oil, 12 API
oil, and 14 API oil as a function of temperature. It will
be noted that at 100 F., water is denser than 12 API oil,
but that at 500 F., 12 API oil is denser than water.
The principle of different density changes for
fluids can be fully utilized according to the present
-27-
invention. For example, high temperature steam can be
in jected into the upper laterals, and 12 API oil can be
recovered by the lower laterals. At the pressure within
the formation, the condensate from the high temperature
steam may form a layer oE water at 500 F. In this case,
both the steam and the condensate are lighter than the oil,
and can be efficiently used to drive the oil downward.
After steam or condensate has been recovered from one of
the lower laterals, the injection of steam may be continued
in the upper laterals that are not adjacent the lower lat-
eral from which the condensate was recovered, as previously
described. tAlternatively, steam may be injected in all
the upper laterals while cold water is injected in the
lower lateral from which condensate or steam has been
recovered). If the formation were at a relatively shallow
depth and therefore correspondingly lower formation pres-
sures existed, it is within the concept of my invention to
inject superheated steam to achieve the high temperature
desired to maximize the efficiency of the recovery process.
After the downward steam drive has been completed,
the driving process may be reversed and cold water may be
injected in the lower laterals while oil is recovered from
the upper laterals. From the graph in Figure 4, it may
be seen that at a temperature of 100 Fo~ water is more
dense than 1~ API oil, and thus the injection of water
will now drive some of the remaining oil in the formation
upward toward the upper laterals. Thus, during both the
vertically upward driving stage and the vertically downward
driving stage, the density of the injected fluid enables an
effective blan~et to be established, and the likelihood of
viscous fingering is substantially eliminated.
-28-
~ 3~BB5~
Although driving vertically in one direction ac-
cording to the present invention will effectively sweep the
formation, it is understood that the oil recovery process
will not be 100~ ef~ective. Driving in both directions,
i.e., driving downward and thereafter driving upward, will
increase the percent of oil recovered. This increased
recovery is due, in part, to the fact that formations are
not completely homogeneous, and thus driving in the reverse
direction will cause the driving fluid to invade some areas
that may have been sheltered from the forward driving fluid.
Also, the injection of cold water in the lower laterals, as
described above, may cause some water to flash to steam
because of the residual heat in the formation, and the
steam may lower the viscosity of some remaining oil to
enhance the effectiveness of the upward driving process.
In the methods described above, oil recovery is
based on a vertical drive process, which may be simplicity
described as injecting the fluid in one set of boreholes
while recovering oil from another set of laterals. It is
within th~ concept of my invention, however, to improve
the efficiency of the vertical driving process by providing
or a limited soak cycle for each of the sets of laterals.
For instance, if a vertical downward drive of the oil is to
be achieved, it may be initially desirable to inject steam
in the lower laterals to soak the formation directly adja-
cent the lower laterals and thus improve the subsequent
driving process. Also, the upper laterals may be thereafter
injected with steam to soak the formation adjacent the upper
laterals and therefore enhance the uniformity of the driving
blanket. After the lower laterals have been opened and oil
begins to flow in the lower laterals, steam may thereafter
-29-
~ 3~
be injected in the upper laterals to drive the oil toward
the lower laterals.
Soaking the formation about the upper and lower
laterals prior to establishing the driving process, as de-
scribed above, may be beneficial in most applications. If
a high viscosity oil is to be efficiently driven, it may
be desirable, if not essential, to establish a flow path
between the point of injection and the point of recovery
prior to the driving cycle. The heavy oil in many forma-
tions has such a high viscosity that it is very difficultto displace the oil by an injection fluid supplied from
commercial generators.
If steam is to be used as the injection fluid
in the application depicted in Figure 1, the efficiency of
the downward driving process may be substantial]y increased
by first injecting steam in the lower set of laterals 18,
19, 20 and 21. As the lower portion of the formation 6
is being soaked, viscous fingering and gravity override
will readily occur since the injected fluid is lighter
than the oil, and is being introduced in the lower portion
of the formation. As viscous fingering and gravity over-
ride occur, heated communication paths will be established
between the lower set of laterals and the upper set of
laterals. Thus, the formation may be subjected to repeated
steam soak cycles from steam supplied through the lower
set of laterals, wherein steam is injected into the lower
laterals, the laterals are stopped off or shut in, and the
laterals are opened for recovery of oil as a result of the
soaking process.
When the repeated soaking from the lower laterals
results in steam fingering to the top of the formation 6,
~30-
the soaking process may be discontinued and steam thereafter
injected into the upper set oE laterals 14, 15, 16 and 17
for driving the oil downward while recovering oil from the
lower set of laterals. The steam soak cycle therefore
results in communication paths between the injection loca-
tions and the production locations which may have a greater
area than that commonly associated with horizontal driving
techin~ues. For instance, when conventional horizontal
drive between vertical wells is utilized in a formation 60
feet thick, the area of face of the driving formation is
typically approximately 12,500 square feet per acre. If
vertical drive is practiced between horizontal laterals
according to the present invention, the area or face of
the driving front increases to approximately 43,000 square
feet per acre. Thus, if the same injection rate per area
of driving front is utilized, fluid is injected at approx-
imately 3.5 times the rate as in conventional horizontal
drive. Moreover, since the oil is being driven vertically
rather than horizontally, the injection rate per area of
the driving ~ront may be substantially increased since
viscous fingering is substantially eliminated during the
driving operation.
The larger driving face area, therefore, enables
more driving fluid to be injected into the formation while
maintaining a relatively low, stable driving velocity across
the formation. Also, as previously mentioned, the driving
velocity may be substantially increased when compared to
horizontal drive since vertical driving minimizes the like-
lihood of viscous fingering. Further, the fluid may be
injected at higher pressures and at higher rates than
realized in the prior art, which improves the efficiency of
31-
the recovery process. For instance, steam which may have
been injected at 25~ quality in hori~ontal drive operations
may effectively be injected at the higher rates and with
greater steam quality, e.g., 80%, than in the prior art.
Also, as previously mentioned, superheated steam may be
used as the injection fluid.
Although this invention has principally been de-
scribed with steam or water as the injection fluid, both
heated and unheated fluid may be used as a driving force
within the concept of my invention. For example, water,
solvents, gas, oil, distillate, LPG, and naptha, or a com-
bination of liquids and gases may be utilized as the driving
fluid according to the present inventionO Examples of
gases that may be used in this invention are air, oxygen,
hydrogen, carbon dioxide, inert gas, stack gas, steam,
anhydrous ammonia, natural gas, ethane, propane and butane.
Also, although no additives must be combined with the fluid
to be injected, the addition of additives may enhance the
recovery process. Less heat is lost through condensation,
and the average temperature of the formation is raised at
a faster rate than in the prior art. Thus, the increased
injection rates yield higher production rates, which improve
the economics of the recovery operation.
It is also within the concept oE this invention
to utilize in situ combustion to achieve or enhance vertical
drive of the oil toward horizontal recovery laterals. For
instance, if horizontal laterals are placed near the bottom
of the formation, in situ combustion near the top of the
formation will tend to drive the oil downward. Air or oxygen
for the combustion process may be injected via either con-
ventional vertical injection wells from the surface to the
-32-
,
upper portion of the formation or horizontal laterals from
the mine shaft. Referring to Figures 5 and 6, if desired
air or oxygen may be injected via the odd-numbered vertical
wells, and in situ combustion used to recover oil from the
even-numbered vertical wells as the combustion process
drives the oil in the upper portion of the formation hori-
zontally. After in situ combustion has progressed in a
horizontal direction and the producing even-numbered ver-
tical wells become heated, all the conventional vertical
wells 102 through 109 may be used to inject air or oxygen.
Thus, in situ combustion may thereafter be utilized to drive
the oil downward for recovery by the laterals or boreholes
112 through 119. If desired, this latter operation may be
conducted in rotating segments, rather than exploiting the
entire area at one time, which would reduce the capital
investment required for the air or oxygen compressors.
Alternatively, in situ combustion may be conducted
in the upper portion of the formation between conventional
vertical wells, as previously described, and thereafter
another fluid such as water, steam, inert gas or mixtures
thereof injected into all the vertical wells for driving
the oil downward for recovery by the horizontal laterals.
If desired, the lower horizontal laterals may be initially
steam soaked or soaked at intervals during the driving pro-
cess to maintain the desired recovery flow. The in situ
combustion between the conventional vertical wells may be
conducted until enough heat has been added to the formation
for an efficient oil recovery by subsequent vertical drive
techniques. If water is injected into the formation as the
driving fluid from the vertical conventional wells, the
residual heat from the "burned out" zones may generate
-33-
f~'5~
steam in situ whîch may efficiently drive the remaining
oil downward for recovery by the laterals.
The above operation is especially attractive from
an economic standpoint since little or no sur~ace fuel is
used to heat the formation. Temperatures in the combustion
zone may be 800 F. to 1000 F. or more, and very good drive
of heavy oil can be achieved if the oil in the formation
is heated to 250 to 300 F. Also, creating a blanket of
combustion-cleaned matrix establishes extremely high verti-
cal downward transmissibility for the injected fluids usedin the subsequent driving cycle. In situ combustion further
dehydrates and breaks down any shale layers or lenses with-
in the combustion zone.
The recovery of oil when utilizing vertical drive,
as described according to my invention, may be further
enhanced by reducing the pressure at the recovery laterals
to a sub-atmospheric value by connecting the recovery lat-
erals to suction-type pumps. In this manner, oil recovery
may be enhanced regardless of whether the vertical drive is
propagated by in situ combustion, steam injection, solvent
injection, gas injection, or injection of any number of
fluids commonly used to enhance the driving operation.
The injection ]aterals in the embodiments de-
scribed are preferably positioned in a substantially horizon-
tal plane. The laterals may be inclined to conform to ~he
inclination of the barrier layer, but the injection laterals
with the injected fluid principally serve to establish a
uniform, substantially horizontal blanket to be driven
vertically through the formation. The recovery laterals
are generally positioned in a similar substantially hori-
zontal plane so that the formation may be efficiently swept
-34-
t,9~
of oil. Some deviation of the laterals is expected, and
in that sense the upper and lower laterals may not lie
precisely in flat planes. Further, the laterals typically
lie in relatively thin discs approximately five feet thick,
and these discs or "planes" may be inclined slightly to
conform to the barrier layers.
It may also be seen that the present invention
may be profitably employed by installing a plurality of
vertical mine shafts and laterals, as described herein.
Also, by operating such multiple installations in a simul-
taneous manner, as more fully described in my co-pending
patent application, Serial No. 334,159, an entire field may
be drained in a systematic manner.
It may be that two or more oil bearing formations
exist at different elevations. In such a case, it is within
the concept of my invention that a vertical mine shaft may
be employed, and upper and lower laterals may extend from
the mine shaft into each of the oil bearing formations.
As hereinbefore described, the techniques of the
present invention are principal]y directed to recovery of
relatively heavy oils. However, it should be noted that
these techniques are not limited to heavy oils only, but
can be used with substantial affect in recovering hydro-
carbons of various weights and gravities.
Other alternate forms of the present invention
will suggest themselves from a consideration of the appara-
tus and practices hereinbefore discussed. Accordingly, it
should be clearly understood that the systems and techniques
depicted in the accompanying drawings, and described in the
foregoing explanation, are intended as exemplary embodiments
of my invention, and not as limitations thereto.
-35-
