U.S. patent number 3,707,189 [Application Number 05/098,938] was granted by the patent office on 1972-12-26 for flood-aided hot fluid soak method for producing hydrocarbons.
This patent grant is currently assigned to Sell Oil Company. Invention is credited to Michael Prats.
United States Patent |
3,707,189 |
Prats |
December 26, 1972 |
FLOOD-AIDED HOT FLUID SOAK METHOD FOR PRODUCING HYDROCARBONS
Abstract
Relatively viscous liquid hydrocarbons are produced from a
subterranean hydrocarbon reservoir by opening at least one well
borehole into fluid communication with the reservoir at least at
two spaced locations. A relatively mobile hot fluid, such as steam,
is injected through the well borehole and into the earth formation
around one of the locations for a period of time sufficient to form
a hot zone and thermally mobilize liquid hydrocarbons present in
the earth formation. Formation fluids are produced, by backflowing
fluid from the hot zone, while a hydrocarbon-displacing fluid is
being injected into the earth formation around another of the
locations within the reservoir to displace hydrocarbons into the
hot zone.
Inventors: |
Prats; Michael (Houston,
TX) |
Assignee: |
Sell Oil Company (New York,
NY)
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Family
ID: |
22271645 |
Appl.
No.: |
05/098,938 |
Filed: |
December 16, 1970 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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827750 |
May 26, 1969 |
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Current U.S.
Class: |
166/272.3;
166/306; 166/401 |
Current CPC
Class: |
E21B
43/24 (20130101) |
Current International
Class: |
E21B
43/16 (20060101); E21B 43/24 (20060101); E21b
043/24 () |
Field of
Search: |
;166/245,263,272,274,261,303,302,35R,306 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Novosad; Stephen J.
Parent Case Text
CROSS-REFERENCE
This application is a continuation-in-part of copending U.S. Pat.
application, Ser. No. 827,750, filed May 26, 1969, now abandoned.
Claims
What is claimed is:
1. A method of recovering relatively viscous hydrocarbons from a
subterranean reservoir, comprising:
providing at least one fluid conduit that extends from at least one
surface location to at least two locations within the
reservoir;
repetitively flowing relatively mobile hot fluid that is
significantly immiscible with the reservoir hydrocarbon and is
significantly hotter than the reservoir into at least one location
within the reservoir and producing fluid from substantially the
same location, so that a hot zone is formed within the reservoir
and heated hydrocarbons are produced from the reservoir; and
flowing a hydrocarbon-displacing fluid having a mobility
substantially as low as that of the adjacent hydrocarbon containing
reservoir fluid into at least one other location within the
reservoir, so that reservoir hydrocarbons are displaced toward said
hot zone.
2. The method of claim 1 in which said relatively mobile hot fluid
is steam.
3. The method of claim 1 in which said hydrocarbon-displacing fluid
is a thickened aqueous liquid.
4. The method of claim 1 in which the hydrocarbon-displacing fluid
is a relatively low mobility mixture of gas and liquid.
5. The method of claim 1 in which at least one of said fluid
conduits extends to a location near the bottom of said
reservoir.
6. The method of claim 1 in which said location into which
relatively mobile hot fluid is injected and produced and said
location into which hydrocarbon-displacing fluid is injected are
encountered by separate wells.
7. A method for producing liquid hydrocarbons from a
hydrocarbon-bearing subterranean earth formation comprising steps
of:
extending at least one well borehole into fluid communication with
substantially the bottom of said subterranean earth formation;
opening a second well borehole spaced from said first well borehole
into fluid communication with substantially the bottom of said
earth formation;
injecting steam through said first well borehole and into said
earth formation for a period of time sufficient to thermally
mobilize fluids present in said earth formation, thereby forming a
hot soaking zone therein;
producing formation fluids from said hot soaking zone back into
said first well borehole; and
injecting an essentially non-vaporous substantially non-combustible
hydrocarbon-displacing fluid down said second well borehole for a
period of time sufficient to drive a substantial amount of the
hydrocarbons present in said earth formation outside of said hot
soaking zone directly into said hot soaking zone.
8. The method of claim 7 including the step of selectively
injecting steam and producing formation fluids from a plurality of
well boreholes surrounding a single well borehole while injecting
said hydrocarbon-displacing fluid down said single well borehole
during the step of producing formation fluids from said plurality
of well boreholes.
9. The method of claim 7 including the step of selectively
injecting steam and producing formation fluids from a plurality of
linearly disposed well boreholes displaced adjacent to a plurality
of linearly disposed well boreholes while injecting said
hydrocarbon-displacing fluid down said latter-mentioned well
boreholes during the step of producing formation fluids from said
firstmentioned well borehole.
10. A method for producing liquid hydrocarbons from a
hydrocarbon-bearing subterranean earth formation comprising the
steps of:
extending at least one well borehole into communication with said
subterranean earth formation;
providing fluid communication between said well borehole and at
least two spaced locations within said earth formation;
injecting steam through said well borehole and into one of said
locations in said earth formation for a period of time sufficient
to thermally mobilize fluids present in said earth formation,
thereby forming a hot zone therein;
producing formation fluids from said hot zone;
injecting a hydrocarbon-displacing fluid into the other of said
locations within said earth formation for a period of time
sufficient to displace hydrocarbons in said earth formation into
said hot zone; and
mixing said hydrocarbon-displacing fluid with a gas and sufficient
foaming agent to form a foam having a density below about the
average density of the formation fluids prior to injecting said
hydrocarbon-displacing fluid into the other of said locations
within the formation.
11. A method for producing liquid hydrocarbons from a
hydrocarbon-bearing subterranean earth formation comprising the
steps of:
extending at least one well borehole into communication with said
subterranean earth formation;
providing fluid communication between said well borehole and at
least two spaced locations within said earth formation;
injecting steam through said well borehole and into one of said
locations in said earth formation for a period of time sufficient
to thermally mobilize fluids present in said earth formation,
thereby forming a hot zone therein;
producing formation fluids from said hot zone;
injecting a thickened water containing viscosity-increasing
components into the other of said locations within said earth
formation for a period of time sufficient to displace hydrocarbons
in said earth formation into said hot zone; and
heating said thickened water to a temperature about that at which
said steam is injected into one of said locations in said earth
formation but below the temperature at which the
viscosity-increasing components of the thickened water are
thermally degraded prior to injecting said thickened water into the
other of said locations within said earth formation.
Description
BACKGROUND OF THE INVENTION
The present invention relates to an improved method for recovering
relatively viscous liquid hydrocarbons from subterranean earth
formation. More particularly, the invention is directed to a
thermal recovery process wherein a hydrocarbon-displacing fluid is
injected into one location within the formation while a hot fluid
injection-backflow operation, such as a steam-soak operation, is
being carried out at another location in the same earth
formation.
The term "thermal soak" is used to refer to a recovery process in
which a hydrocarbon-containing formation is heated by injecting and
then back-flowing a relatively mobile hot fluid, such as steam,
into and out of the formation. After a predetermined quantity of
hot fluid has been injected, the well is normally shut in for a
"soaking period". The length of the soaking period is adjusted so
that a substantial quantity of the latent heat of the inflowing
fluid is transferred to the formation to heat the hydrocarbons
contained therein to reduce their viscosity and make them more
mobile. After the soaking period, the formation hydrocarbons are
produced from the heated zone by making substantially any type of
reservoir drainage or other producing mechanism, as for example
gravity drainage, or solution gas drive, and removed from the well
borehole by pumping or other production methods.
Where steam is used as the injected hot fluid, the steam may be
high-quality, substantially dry steam or may be low-quality steam
containing a considerable amount of water in a liquid phase. A
steam soak process using a low-quality steam is more particularly
described and claimed in U.S. Pat. No. 3,193,009. The steam may be
injected into the hydrocarbon-containing formation for a few days
or weeks. The length of time that the steam is injected is
determined by the size to which the heated zone is to be extended,
by the viscosity of the oil and the permeability and other
formation characteristics that affect the efficient transfer of the
latent heat of the steam to the hydrocarbons contained in the
formation. After the soaking period, the well borehole is placed
back on production using conventional producing mechanisms normally
of the depletion type of drive in combination with pumping or
similar lift methods.
Typically, thermal drive oil recovery processes such as steam
drives use spaced injection and production wells completed into an
underground earth formation containing viscous hydrocarbons that
are to be produced. In such processes, steam is injected through
one of the wells while fluid is produced through another of the
wells. The temperature of the steam reduces the viscosity of the
hydrocarbons and the pressure and flow of the steam drives the
heated hydrocarbons towards the producing well. However, during the
initial injection, the hydrocarbons around the production well and
in other areas remote from the injection well remain at original
formation temperature and, therefore, remain relatively immobile.
As a consequence, when using economically feasible injection
pressures, increased production of viscous hydrocarbons is not
significant during the early stages of a thermal drive process. A
significant increase in the production is not attained until
sufficient hot fluid has been injected into the injection well to
heat substantially all of the portion of the formation that is
located between the injection and production wells.
Steam soak process, as for example those described in U.S. Pat.
Nos. 3,259,186 and 3,292,702, are generally effective in producing
hydrocarbons from viscous hydrocarbon reservoirs that are
relatively thick and generally uniformly permeable. However, since
steam is lighter than the oil and water which is normally present
in the pores of such a reservoir, the injected steam tends to rise.
This effect, known as "gravity layover" or "gravity segregation",
causes the steam zone to expand radially along the top of the
reservoir to a much greater extent than it does along the bottom of
the reservoir.
It is well known in the oil production art to inject an
oil-displacing fluid into an oil reservoir to move the oil present
in the reservoir toward a well borehole or a zone from which fluid
is to be or is produced. This oil production operation is commonly
referred to as a "flooding" or "displacing" process. Such a process
generally uses an inexpensive oil-displacing fluid such as water or
an aqueous solution, which may contain a viscosity enhancer of the
type described in U.S. Pat. Nos. 2,827,964 and 3,039,529.
Alternatively, such process may use soluble oils of the type
described in U.S. Pat. No. 3,254,714. Where the viscosity of the
oil present in the formation is relatively high, the oil-displacing
fluid must have a comparable viscosity in order to avoid bypassing
much of the oil. The rates at which relatively viscous fluids can
be moved through hydrocarbon-bearing reservoirs, without applying a
pressure that fractures the reservoir rock, are often too low for a
commercially feasible oil production process.
SUMMARY OF THE INVENTION
It is an object of this invention to provide an improved method of
producing liquid hydrocarbons from a hydrocarbon-bearing
subterranean earth formation by combining a hot fluid soak process
with a viscous oil displacement process while avoiding the
disadvantages inherent in the individual processes.
It is a further object of this invention to provide such a method
which produces hydrocarbons at a relatively rapid rate during the
backflow cycle of a hot fluid soak operation.
These and other objects are preferably accomplished by opening at
least one well borehole into fluid communication with a
hydrocarbon-bearing subterranean earth formation at least at two
spaced locations (preferably separated vertically) in the
formation. A relatively mobile hot fluid is injected into the earth
formation around one of the locations for a period of time
sufficient to thermally mobilize fluids present in the earth
formation and form a hot zone. Formation fluids are produced from
the hot zone while a substantially non-bypassing
hydrocarbon-displacing fluid is injected into the earth formation
around another of the locations within the earth formation to
displace hydrocarbons into the hot zone. Hydrocarbons are recovered
from the fluid produced from the hot zone.
The relatively mobile hot fluid that is injected can comprise
substantially any fluid that is or becomes significantly hotter and
more mobile than the reservoir hydrocarbon at the normal reservoir
temperature. Such a fluid is injected into the reservoir so that it
moves around or bypasses, at least some of the reservoir
hydrocarbon, transfers heat to the bypassed hydrocarbon, and
subsequently, entrains and/or displaces the heated hydrocarbon when
fluid is flowed back into the well during a backflow or production
cycle of a hot fluid soak oil recovery process. Such a fluid can
comprise steam or hot water or substantially any hot mobile fluid
that is not extensively miscible with the reservoir hydrocarbon.
Such a fluid can be heated at a surface or downhole location in or
near the borehole of a well; for example, steam or hot water can be
generated or heated in a surface-located boiler or heater or in a
downhole boiler or heater or by means of an in situ combustion
within the reservoir; or, a mobile reactive fluid such as an oil
reactant of the type described in U.S. Pat. No. 3,250,328 can be
injected at ambient temperature and heated chemically within the
reservoir; or the like.
The substantially non-bypassing hydrocarbon-displacing fluid that
is injected may comprise substantially any fluid that: (1) is
sufficiently mobil to flow into the hydrocarbon-bearing
subterranean earth formation at a significant rate (e.g., at at
least about 100 barrels per day), in response to an injection
pressure of less than the fracturing pressure of the earth
formation; and (2) has a mobility at least substantially as low as
that of the hydrocarbon-containing fluid in the earth formation
near the location at which the hydrocarbon-displacing fluid is
injected. For example, such a hydrocarbon-displacing fluid may
comprise (a) a foam or relatively low mobility mixture of gas and
liquid, (b) a relatively low mobility thickened aqueous liquid
(i.e., an aqueous solution or dispersion of a thickening agent such
as a partially hydrolyzed polyacrylamide), (c) an oil solvent that
dissolves sufficient earth formation hydrocarbon to form a solution
having a frontal portion mobility substantially as low as that of
the reservoir fluid, (d) a combination of a chemical slug such as
an aqueous or oil external dispersion or micellar solution of
surfactant material followed by a slug of thickened water, or the
like.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a vertical sectional view of a well borehole producing
formation fluids from a subterranean earth formation in accordance
with the teachings of the present invention;
FIG. 2 is a vertical sectional view of a plurality of well
boreholes producing formation fluids from the formation of FIG. 1
in accordance with the teachings of the invention;
FIG. 3 is a graphical illustration of one feature of the present
invention; and
FIGS. 4 and 5 are schematic illustrations of examples of preferred
well borehole patterns for producing formation fluids from a
subterranean earth formation in accordance with the teachings of
the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In a conventional steam soak process, or other thermal soak
process, the "gravity layover" effect, as discussed hereinabove,
tends to produce a poor sweep efficiency. In a substantially
non-bypassing viscous oil displacement process, the slow rate of
fluid movement often results in an economically unattractive
process. In the method of this invention, however, the viscous oil
present in the formation is moved by a non-bypassing displacement
for only a relatively short distance before it enters a
steam-heated zone where the oil is thermally mobilized. The hot oil
is then produced at a relatively rapid rate, during the backflow
cycle of a hot fluid soak operation. Thus, although the viscous oil
moves at a slow rate, since it moves across a collection zone
boundary (such as the boundary of a steam-heated zone) having a
relatively large area, the rate of oil production from the
collection zone is relatively high, due to the large volume of oil
that enters the collection zone and becomes heated so that its
viscosity and its resistance to flow into the well borehole are
greatly reduced.
Thus, as illustrated in FIG. 1, a well borehole 10 is shown
extending into communication with a hydrocarbon-bearing
subterranean earth formation 11. Well borehole 10 is preferably
cased by casing 12 with casing 12 cemented therein, as is well
known in the art. A tubing string 13 is disposed in casing 12,
preferably extending to a point substantially adjacent to the
bottom of formation 11. Tubing string 13 is packed off at two
locations in casing 12. Thus, tubing string 13 is packed off at
packing means 14, a relatively short distance above the bottom of
tubing string 13, and at packing means 15, at substantially the
upper portion of formation 11, for reasons to be discussed further
hereinbelow. Casing 12 is perforated, as at perforations 16, below
packing means 14 so as to establish fluid communication between the
bottom of tubing string 13 and the lower portion of formation 11.
Casing 12 is also perforated, as at perforations 17, above packing
means 15 so as to establish fluid communication between the annulus
18 formed between tubing string 13 and casing 12 and the upper
portion of formation 11.
An annulus outlet 19 is associated with the upper end of tubing
string 13 for introducing fluids into annulus 18, through
perforations 17 and into the upper portion of formation 11. In like
manner, fluids may be injected down tubing string 13, out
perforations 16 and into the lower portion of formation 11.
A hot fluid soak, such as a steam-soaking operation, is preferably
carried out through the openings (i.e., perforations 16) which are
confined within the lower portion of formation 11, as indicated by
the double-ended arrows in FIG. 1. A suitable process for injecting
steam into a limited zone of an oil-producing reservoir and
subsequently recovering reservoir fluids through this limited
injection zone to enhance the production of oil from the reservoir
is described in a U.S. Pat. No. 3,358,762. The steam which is
injected down tubing string 13 may be low quality, wet, dry, or
superheated steam. The steam is preferably injected under pressure
and temperature conditions that are near the minimum required for
adequate rates of flow and extents of reduction in the viscosity of
the oil. The steam generation can be conducted by or supplemented
by the initiation of an underground combustion, for example, as
described in U.S. Pat. 3,409,083. Such an underground combustion
steam generation can be conducted at a relatively high temperature
under conditions that are conducive to a thermal conversion of
water-sensitive clay components to materials which are more
resistant than the untreated clays to the effects of aqueous
liquids that are substantially free of dissolved electrolytes.
In the embodiment shown in FIG. 1, an oil-displacing fluid is
injected into annulus outlet 19 and out perforations 17 into the
upper portion of formation 11. Preferably, particularly in those
cases where formation 11 is relatively thick, the oil-displacing
fluid is a relatively low density fluid, such as a liquid mixed
with a gas and sufficient foaming agent to form a foam having a
density of less than the average density of the fluids in the pores
of the reservoir. In this manner, a driving and soaking pattern is
provided whereby hydrocarbons present in formation 11 in the
driving zone 20 surrounding well borehole 10 are driven or
displaced into the hot soaking zone 21 from whence formation fluids
are to be or are being produced back through perforations 16 and up
tubing string 13 (as indicated by the double-ended arrows in FIG.
1) for example, by fluid production procedures well known in the
oil production art. Hydrocarbons are recovered from the fluid being
produced from hot soaking zone 21, for example by hydrocarbon
recovery procedures well known in the oil production art. Thus,
conventional heat exchanging, pumping, separating and heating
equipment is shown associated with the upper portion of well
borehole 10. A steam inlet 10a is provided, controlled by valve
means 10b. An inlet 10c is provided for introducing the
oil-displacing fluid into annulus outlet 19. A valve means 10d is
provided between the separator and inlet 10c for controlling the
injection of the fluid into well borehole 10.
Preferably, however, a pair of well boreholes 22 and 23 are
extended into communication with hydrocarbon-bearing formation 11
as illustrated in FIG. 2. Well boreholes 22 and 23 are preferably
cased, as by casing 24 and 25, respectively, with the casing
cemented therein, as is well known in the art. Tubing strings 26
and 27 are disposed in well boreholes 22 and 23, respectively, as
is also well known in the art. Packing means 28 and 29 are disposed
a short distance above the bottom of tubing strings 26 and 27,
which are disposed adjacent to the bottom of formation 11 in the
manner discussed hereinabove with respect to the well borehole 10
of FIG. 1. Both casings 24 and 25 are perforated, as at
perforations 30 and 31, respectively, so as to establish fluid
communication between the lower ends of casings 24 and 25 (and thus
the bottom of tubing strings 26 and 27) and the bottom portion of
formation 11.
A third well borehole 32 is also extended into communication with
formation 11 at a location spaced from well boreholes 22 and 23.
Well borehole 32 is extended to the lower portion of formation 11
and is preferably cased, as by casing 33, with casing 33 cemented
therein as is well known in the art. A tubing string 34 is disposed
in well borehole 32 extending adjacent to the bottom of formation
11 and packed off from casing 23 as at packing means 35. Packing
means 35 is disposed a short distance above the bottom of tubing
string 34 in the manner of packing means 28 and 29 of well
boreholes 22 and 23, respectively. Casing 33 is perforated below
packing means 35, as at perforations 36, thus establishing fluid
communication between the bottom of tubing string 35 and the lower
portion of formation 11, as discussed hereinabove with respect to
well boreholes 22 and 23.
A conventional steam soak operation is then carried out in the
manner discussed hereinabove with respect to well borehole 10.
Thus, steam is injected down well boreholes 22 and 23 and into
formation 11, thus forming hot steam soaking zones 37 and 38,
respectively. Formation fluids are then flowed from zones 37 and 38
within formation 11 back into well boreholes 22 and 23, as is well
known in the art.
The oil-displacing fluid is injected down tubing string 34 of well
borehole 32 and into the lower portion of formation 11, thus
forming a driving zone 39 surrounding well borehole 32. In this
manner, hydrocarbons in zone 39 are driven or displaced into hot
zones 37 and 38 as indicated by the arrows in FIG. 2.
Conventional heat exchanging, separating, pumping, heating, valving
and inlet means are also associated with well boreholes 22, 23 and
32 for recovering hydrocarbons therefrom in the manner discussed
hereinabove with respect to the well borehole 10 of FIG. 1.
In both embodiments it is preferable to heat the injected
oil-displacing fluid to a temperature which is near that at which
the steam is injected in the steam-soaking operation but is below
the temperature at which the viscosity-increasing components of the
oil-displacing fluid are thermally degraded. The advantages of such
a step are illustrated in FIG. 3. Portions of the arrangement of
FIG. 2 have been eliminated for simplification. The graph
illustrates that, when the oil-displacing fluid is hot, it heats
the first-contacted oil to a temperature at which it has a
relatively low viscosity. In zones near the oil-displacing fluid in
the injection well borehole 32, as for example in the
cross-hatched, near-borehole portion of zone 39, the temperature
tends to remain high and the resistance to flow is relatively low.
As the fluids move away from well borehole 32, the temperature
falls and the viscosity of the displaced oil increases as it
becomes cooler. In these zones, as for example near the steam
soaked zones 37 and 38, the oil temperature tends to become lower
and the flow rate decreases as the injected fluid spreads over
areas of larger diameters; but, as the displaced oil is moved into
the steam heated zones, it is heated to a temperature at which its
mobility is relatively high.
Furthermore, the region near the injection well which has been
heated as a result of the heated injection fluid will result in a
region of relatively low resistance to the injection of fluids.
This will allow an increase in injection rate at the permissable
injection pressures, which results in a shortening of the operating
life of the process (lower operating costs); or in injecting the
pump capacity at relatively low injection pressures, which results
in lower injection costs. The use of hot water to precede the
viscous drive would be advantageous in accelerating the heating of
the formation near the injection well.
In both arrangements of FIGS. 1 and 2, the rate at which the
oil-displacing fluid is injected into formation 11 may be varied
widely and the injection may be continuous or intermittent. In
general, the average rate of oil-displacing fluid injection is less
than that conventionally used for waterflooding or miscible
displacement. Where the viscosity of the drive-fluid approximates
that of the formation fluids at reservoir temperature, the
injection rate of the oil-displacing fluid is preferably that which
occurs at a pressure slightly below the fracturing pressure of
formation 11. For example, oil-displacing fluid injection rates of
from about 100 to 1000 barrels per day have been found suitable for
use in the method of the present invention. Where the injection of
the oil-displacing fluid is intermittent, the inflow of the fluid
is preferably sustained throughout each production cycle of the
steam soaking and fluid production operation. The injected
oil-displacing fluid is preferably a thickened water injected hot
relative to the formation temperature. The hot injection of
thickened water is advantageous in reducing the viscosity of the
formation fluids adjacent to the injection point of the
oil-displacing fluid.
Referring once again to the drawing, FIGS. 4 and 5 show examples of
well borehole patterns which may be used in accordance with the
teachings of the present invention. Thus, in FIG. 4, a "five-spot"
pattern of well boreholes is shown, whereby four production well
boreholes 40 (similar to well boreholes 22 and 23 of FIG. 2) are
shown surrounding a single injection well borehole 41 (similar to
well borehole 32 of FIG. 2). This "five-spot" pattern is repeated
throughout the entire pattern of well boreholes. The inner dotted
lines surrounding each production well borehole indicate the lower
steam zone boundaries created utilizing the method of this
invention with the outer dotted lines indicating the upper steam
zone boundaries.
A "line-drive" pattern of well boreholes is shown in FIG. 5. Here,
the production well boreholes 42 are disposed in a linear
arrangement with injection well boreholes 43 disposed adjacent
thereto in a similar linear arrangement. The dotted lines
surrounding the production well boreholes 42 are similar to the
dotted lines of FIG. 4. The linear arrangement of well boreholes is
repeated throughout the entire pattern.
The cooperating hot fluid soak and oil-displacing operations as
discussed hereinabove materially enhance the sweep efficiency of
the hot fluid soaks at the production well boreholes. The
intervening portions of formation 11 between the injection well
borehole and the production well borehole are heated and depleted,
thus increasing both the rate at which hydrocarbons are produced as
a result of the substantially non-bypassing viscous fluid drive and
the ultimate recovery. By soaking the formation 11 at the
production well boreholes, relatively vast effective production
well borehole diameters are provided and the viscous fluid drive
(i.e., the substantially non-bypassing hydrocarbon-displacing fluid
injection) operates at a relatively high rate and efficiency due to
the reduction in pressure over the path between the injection and
production well boreholes. The method of this invention as
discussed hereinabove thus increases the potential profitability of
a hydrocarbon-bearing formation, particularly one that is
relatively thick and uniformly permeable.
* * * * *