U.S. patent number 3,682,246 [Application Number 05/107,833] was granted by the patent office on 1972-08-08 for fracturing to interconnect wells.
Invention is credited to Philip Joseph Closmann.
United States Patent |
3,682,246 |
Closmann |
August 8, 1972 |
FRACTURING TO INTERCONNECT WELLS
Abstract
Wells in a substantially impermeable subterranean earth
formation that tends to fracture along non-intersecting vertical
planes of natural weakness are interconnected by initially
fracturing at least one of the well boreholes along its vertical
plane of natural weakness, filling the fracture with a granular
material, and refracturing the well borehole by pumping in a
viscous fluid at a rate causing the pressure to rise above the
pressure at which the first fracture was formed. The last-mentioned
fracture is extended into communication with an adjacent well or a
fracture extending from the adjacent well.
Inventors: |
Closmann; Philip Joseph (The
Hague, NL) |
Family
ID: |
22318714 |
Appl.
No.: |
05/107,833 |
Filed: |
January 19, 1971 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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850712 |
Aug 18, 1969 |
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Current U.S.
Class: |
166/271; 166/259;
166/272.2 |
Current CPC
Class: |
E21B
43/17 (20130101); F24T 10/20 (20180501); E21B
43/247 (20130101); Y02E 10/10 (20130101); Y02E
10/14 (20130101) |
Current International
Class: |
F24J
3/00 (20060101); F24J 3/08 (20060101); E21B
43/16 (20060101); E21B 43/247 (20060101); E21B
43/17 (20060101); E21b 043/24 (); E21b
043/26 () |
Field of
Search: |
;166/271,308,252,256,254,298,259,245 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Novosad; Stephen J.
Parent Case Text
CROSS-REFERENCE TO RELATED PATENT APPLICATION
This application is a continuation-in-part of patent application,
Ser. No. 850,712, filed Aug. 18, 1969, now abandoned.
Claims
1. A method for interconnecting at least a pair of well boreholes
extending into a substantially impermeable subterranean earth
formation wherein fractures formed therein tend to form along
non-intersecting planes of natural weakness, said method comprising
the steps of:
initially fracturing the formation adjacent at least one of said
well boreholes along its plane of natural weakness;
filling the fracture formed along the plane of natural weakness of
said formation with a permeable mass of a relatively fine granular
material;
refracturing said formation adjacent said first well borehole by
pumping through said well borehole and into said first-mentioned
fracture a viscous fluid at a rate sufficient to cause the pressure
in said well borehole and in at least some of said first-mentioned
fracture to rise above the pressure at which said first-mentioned
fracture was formed whereby a second fracture is formed along a
plane which intersects said plane of natural weakness; said viscous
fluid having a viscosity such that the pressure in said
first-mentioned fracture adjacent said well borehole as said
viscous fluid flows at said rate through said permeable mass of
granular material in said first-mentioned fracture is sufficient to
provide a region of high compressive stress adjacent said well
borehole; and
providing communication with at least a second well borehole
between said latter-mentioned fracture and said second well
borehole.
2. The method of claim 1 wherein the step of providing
communication with at least a second well borehole includes the
step of extending said latter-mentioned fracture into communication
with said second well borehole.
3. The method of claim 1 wherein the step of providing
communication with at least a second well borehole includes the
steps of:
fracturing the formation adjacent said second well borehole along
its natural plane of weakness; and
extending the last two mentioned fractures until communication is
provided between said well boreholes.
4. The method of claim 3 wherein the step of extending said last
two fractures includes the step of extending said fractures by
pumping a fluid therein.
5. The method of claim 3 including the step of flowing through said
fractures interconnecting said well boreholes a fluid adapted to
remove solid materials from the walls of said fractures
interconnecting said well boreholes.
6. The method of claim 5 including the step of injecting an acid
adapted to react with the solid material forming the walls of said
fractures through said fractures after flowing said fluid
therethrough.
7. The method of claim 5 including the step of recovering from the
fluid being flowed through said well borehole interconnecting
fractures, at least some of the components of solid materials
removed from the wells of said fractures by said fluid.
8. The method of claim 1 wherein the step of filling said fracture
with granular material includes the step of filling said fracture
with dissolvable granular material over a distance of about one
hundred feet from said first-mentioned well borehole.
9. The method of claim 1 including the step of pumping fluid into
said last-mentioned fracture thereby extending said last-mentioned
fracture within said subterranean earth formation.
10. The method of claim 1 wherein the step of initially fracturing
at least one of the formation adjacent said well boreholes includes
the step of injecting a heated fluid through said earth formation
at a pressure above the breakdown pressure of said subterranean
earth formation but below the overburden pressure thereof until a
substantially vertical fracture is formed therein.
11. A method for interconnecting a plurality of well boreholes
extending into a substantially impermeable subterranean earth
formation wherein fractures formed therein tend to form along
non-intersecting planes of natural weakness, said method comprising
the steps of:
initially fracturing the formation adjacent said well boreholes
along planes of natural weakness to form non-intersecting
fractures;
filling the fracture formed along the plane of natural weakness in
said formation adjacent at least a first of said well boreholes
with a permeable mass of a relatively fine granular material;
refracturing the formation adjacent said first well borehole by
pumping through said first well borehole and into said granular
material filled fracture a viscous fluid at a rate sufficient to
cause the pressure in said well borehole and in at least some of
said first-mentioned fracture to rise above the pressure at which
said first-mentioned fracture was formed, whereby a second fracture
is formed in said formation adjacent said first well along a plane
which intersects said plane of natural weakness; said viscous fluid
having a viscosity such that the pressure drop as said viscous
fluid flows at said rate through said permeable mass of granular
material in said first-mentioned fracture is sufficient to provide
a region of high compressive stress adjacent said first well
borehole;
providing communication between said first well borehole and at
least a second well borehole of said plurality of well boreholes
through said second fracture.
12. The method of claim 11 wherein communication between said first
well borehole and at least a second well borehole is provided
by:
filling the fracture formed along the plane of natural weakness in
said formation adjacent said second well borehole with a permeable
mass of a relatively fine granular material;
refracturing the formation adjacent this second well borehole by
pumping into said granular material filled fracture in the
formation adjacent said second well borehole said viscous fluid at
a rate sufficient to cause the pressure to rise above the pressure
at which said granular material filled fracture was formed, whereby
a second fracture is formed in the formation adjacent said second
well borehole along a plane which intersects said plane of natural
weakness; and
extending the fractures formed in the formation adjacent said first
and second well boreholes in planes which intersect said plane of
natural weakness until said extended fractures intersect and
thereby provide communication between said first and second well
boreholes.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the method of interconnecting a pair of
well boreholes; and, more particularly, interconnecting well
boreholes by means of fractures that extend through a substantially
impermeable subterranean earth formation.
2. Description of the Prior Art
It is known that it is extremely difficult to recover liquifiable
components from deposits of various substantially impermeable
subterranean formations such as oil shale, coal, coral beds,
deposits of cinnabar, etc. under conditions in which the deposits
are normally present in these formations. Various proposals have
been made, such as described in a U.S. Pat. No. 3,284,281, to
recover oil from oil shale. Therein shale oil is produced from an
oil shale formation through fractures interconnecting wells. It has
been well established that at depths greater than, say, a few
hundred feet, most subterranean earth formations will fracture
vertically upon the application of sufficient fluid pressure to a
well borehole extending into such formations. It is not easy,
however, to generate vertical fractures that communicate between
adjoining well boreholes in the same subterranean earth
formation.
In a U.S. Pat. No. 3,431,977 to East et al., a vertical fracture is
extended in a selected direction within a subterranean earth
formation by notching the formation communicating with a well
borehole extending into the earth formation, vertically fracturing
the formation, sealing the fracture with cement or finely divided
solid particles that form an impermeable solid mass, and then
renotching and refracturing the formation along the selected
direction. The renotching and refracturing steps are proposed as an
improvement to a series of certain prior art methods for notching
to guide the initiation of a fracture and extending the fracture
along a selected direction. Such retreatment is proposed in order
to overcome the tendency of fractures to form along a natural plane
of weakness and force a fracture to extend along a selected
direction. This prior art method and similar prior art methods seek
to accomplish the necessary adjusting of the compressive stresses
in the earth formations surrounding a well borehole by forming both
notches and impermeable plugs in the earth formation in the
immediate vicinity of the well borehole.
SUMMARY OF THE INVENTION
It is an object of this invention to provide an improved method for
interconnecting wells extending into a substantially impermeable
subterranean earth formation wherein fractures formed in the
formation tend to form along non-intersecting vertical planes of
natural weakness.
It is a further object of this invention to provide an improved
method for establishing well-interconnecting flow paths through
fractures formed in a substantially impermeable subterranean earth
formation.
These and other objects are preferably accomplished by initially
fracturing along its natural vertical plane of weakness at least
one well borehole extending into a substantially impermeable
subterranean earth formation wherein fractures formed therein tend
to form along non-intersecting planes of natural weakness, filling
the fracture with granular material, and refracturing the well
borehole by pumping therein a viscous fluid at a rate causing the
pressure to rise above the pressure at which the first fracture was
formed. If the last-mentioned fracture is horizontal, it is
extended into communication with an adjacent well borehole. If it
is vertical, an adjacent well borehole is fractured along its
natural vertical plane of weakness and this fracture and the
second-mentioned fracture are extended until they intersect thus
providing communication between the well boreholes.
Thus, the method of my invention compressively stresses the earth
formations at a significant distance from the well borehole as
opposed to prior art methods. It is particularly applicable to the
formation of a well-interconnecting path of fluid communication
within a subterranean earth formation that is normally
substantially impermeable, such as a subterranean oil shale
formation. My method utilizes the fact that, in such a formation,
substantially none of the fluid which enters the fracture is lost
by leakage through the walls of the fracture. Within a fracture
that has been conditioned by filling it with a permeable mass of
solid granules, the resistance to flow through the interstices
between the granules provides a means for producing a high
compressive stress in regions many feet away from the borehole of a
well. This extensively distributed pressurization is then increased
until a new fracture is formed throughout this relatively extensive
region of applied compressive stress. The new fracture is initially
formed along the borehole, where the fluid pressure is highest, and
is extended throughout the stressed region along a plane that may
be either vertical or horizontal but is generally perpendicular to
the plane of natural weakness within the earth formations. If the
reformed fracture (which is generally perpendicular to the natural
plane of weakness) is horizontal, its extension is likely to
provide a flow path to an adjacent well borehole. Alternatively, if
it is vertical, its extension is likely to provide an
interconnection with a fracture (along the natural plane of
weakness) that is formed within a adjacent well borehole. If the
well interconnection is not provided by the conditioning and
refracturing within one well borehole, nor by fracturing an
adjacent well borehole along the natural plane of weakness, the
conditioning and refracturing are repeated, preferably in the
initially refractured well borehole, until well-interconnecting
flow paths are formed.
In a normally impermeable earth formation, the well-interconnecting
flow paths formed by the method of my invention are unobviously
advantageous. The fracture, which was conditioned by filling it
with a permeable mass of granules through which a viscous liquid
was injected at a high rate in order to induce the refracturing,
provides an alternately directed flow path through which fluid can
be injected into the earth formation, at the option of the well
operator. For example, by throttling the outflow through the well
boreholes, a less viscous fluid may be injected to displace the
viscous fluid through the mass and into a further extension of the
fracture. Alternatively, the composition of the viscous fluid used
in the refracturing step may be one having a time-breaking,
temperature-breaking, or chemically breakable viscosity.
Alternatively, the granules with which the fracture is packed may
comprise selectively soluble particles such as carbonates, metals,
etc., which may be dissolved in order to increase the permeability
of the porous mass within the fractures.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a top plan view of a preferred arrangement of well
boreholes extending into a subterranean earth formation;
FIG. 2 is a vertical sectional view of two of the well boreholes of
FIG. 1; and
FIGS. 3 and 4 are plan views similar to that of FIG. 1 showing
further applications of the teaching of my invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawing, FIG. 1 shows a plurality of well
boreholes 11 through 13 extending into an earth formation 14
overlying a normally impermeable subterranean earth formation such
as an oil shale formation (Not shown). The underlying oil shale
formation is one in which fractures formed therein tend to form
along non-intersecting vertical planes of natural weakness.
Thus, a generally vertical fracture 15 is first formed along a
substantially vertical plane by initially fracturing well borehole
11 along its plane of natural weakness thus forming vertical
fracture 15. Such a fracture may be formed by any technique for
applying a fluid pressure above the breakdown pressure of earth
formation 14 but below the overburden pressure of earth formation
14. Of course, although three such well boreholes 11 through 13 are
illustrated in FIG. 1, obviously a plurality of such well boreholes
may be opened into the selected earth formation and treated
simultaneously or sequentially, in any order.
Thus, in a preferred procedure for interconnecting well boreholes
11 through 13, vertical fracture 15 is extended from well borehole
11 for a significant distance along a natural vertical plane of
weakness within the subterranean earth formation. Conventional
subterranean stress analysis techniques and/or techniques for
measuring the orientation of fractures may be utilized to determine
the direction along which the fracture 15 is extended. Vertical
fracture 15 is then propped open by pumping therein a relatively
fine granular material, such as sand particles, at a pressure
sufficient to fill fracture 15 over a considerable distance, as for
example, at least 100 feet.
The earth formations at a significant distance from well borehole
11 are compressively stressed by pumping a relatively viscous
fracturing fluid, such as a viscous oil or a chemical polymer
solution, into well borehole 11 and through the permeable mass of
granular material in fracture 15. The viscous fluid inflow rate is
then increased until the injection pressure exceeds the pressure at
which the first fracture 15 was formed and a new fracture 16 is
formed along a direction generally vertical and substantially
perpendicular to that of fracture 15, probably close to 90.degree.
to fracture 15. The viscous fluid may be pumped into the second
fracture 16 in order to extend it a considerable distance in the
subterranean earth formation.
If the second formed fracture 16 is horizontally extending, it may
be extended into communication with well borehole 12 by continuing
the injection of viscous fluid until communication is established
between the horizontally extending fracture 11 and well borehole
12. However, if the fracture 16 is vertically extending, such as
illustrated in FIG. 1, communication may be established between
well boreholes 11 and 12 by fracturing well borehole 12 along its
natural plane of weakness thus forming vertical fracture 17 which
is generally parallel to fracture 15. The fracture 17 is then
extended, such as by injecting a viscous fluid therein, until
fractures 16 and 17 intersect as illustrated in FIG. 1.
In like manner, inter-communication may be provided between well
boreholes 12 and 13 by fracturing well borehole 13 along its
natural plane of weakness thus forming vertical fracture 18, and
subsequently filling fracture 19 in the manner discussed
hereinabove with respect to well borehole 11.
The method described hereinabove may be repeated at other well
boreholes extending into the subterranean earth formation. By this
method, all the fractures so formed eventually intersect at some
point in the earth formation, thus providing intercommunication
between all the well boreholes. It is not necessary to notch the
earth formations surrounding the well boreholes, either vertically
or horizontally. Since it is desired to establish multiple paths of
fluid communication through the formation, it is not desirable to
seal the fractures. It is simpler, and generally more economical,
than any permanent sealing method to inject therein a coarse sand,
as for example, coarser than about 150 mesh, and allow this sand to
fill the initial fracture 15. A very viscous liquid (e.g., more
than about 100 centipoises) then develops sufficient pressure drop
in the first fracture 15 to enable generation of the second
vertical fracture 16. Both fractures 15 and 16 are then permeable.
In a consolidated material, such as oil shale, the fractures once
formed tend to remain open. Other propping materials which may be
used are granular limestone or marble chips, or aluminum filings.
These materials, after being injected into the first fracture 15,
may then be dissolved by acid, to increase their permeability,
subsequent to forming the second and any later fractures, thus
establishing a good path of communication. By conducting these
steps at other well boreholes, it is possible to establish
interwell communication.
The fluid used to form the initial fractures 15, 17 and 18 at each
of well boreholes 11 through 13 may be hot or unheated water or any
gas and/or liquid that is heated, if desired, at the surface of
earth formation 14, in the respective well boreholes and/or in
situ, e.g., by underground combustion, in the subterranean earth
formation.
Once inter-well communication has been established, a reacting
fluid may be flowed there-through. The composition of the reaction
fluid is preferably adjusted to the extent required to circulate
fluid that removes solid materials from the walls of the
interconnecting fractures without a significant reduction in the
average rate of flow between well boreholes 11 through 13, so that
the effective permeability of the interconnecting fractures, as for
example fractures 16 and 17, is increased relative to fluid flowing
between well boreholes 11 and 12. Solid-material-removing
components may be incorporated into the reacting fluid being
circulated through the interconnecting fractures without
interrupting the flow to an extent that permits the fractures to
close and reseal. In treating a subterranean oil shale formation,
such components may comprise hot benzene, steam, or other solvent,
or nitric acid, of a lower temperature than the hot fracturing
fluid. Nitric acid has the advantage of reacting with the organic
matter as well as the carbonate present in the subterranean earth
formation. The injection of such a reacting fluid leaches out part
of the kerogen adjoining the faces of the interconnecting
fractures. The injection at a lower temperature and at
substantially the same injection pressure permits the fractures to
open slightly for better passage of the fluids. The temperature of
the solid-material-removing fluid may be increased as the
permeability of the interconnecting fractures, fractures 16 and 17,
for example, is increased until the circulating fluid becomes hot
enough to liquefy the liquefiable components of the subterranean
earth formation.
Following or during the hot solvent injection as discussed
hereinabove, acid may be injected to react with part of the rock
matrix along the fracture walls. This acid injection renders the
channels even more permeable.
After all the steps discussed hereinabove are carried out, an
underground combustion process, as is well known in the art, which
develops considerably higher temperatures, may be undertaken. The
steps of leaching out part of the kerogen and the rock generally
make closure of the fracture paths during combustion very unlikely.
In this manner, it is possible to treat a substantial part of the
formation by underground combustion.
Thus, as illustrated in FIG. 1, uniform temperature zones 21
through 23 may be seen surrounding well boreholes 11 through 13,
respectively. Also, advancing combustion fronts 24 through 26,
initiated and alternatingly advanced, for example, by means well
known in the art, may be formed about well boreholes 11 through 13,
respectively.
FIG. 2 shows permeable channel 27 formed in the subterranean earth
formation of FIG. 1 by the foregoing method of this invention. Only
two of the well boreholes of FIG. 1 are shown in FIG. 2 for
convenience of illustration. Injection well borehole 11 is
preferably equipped with casing 28 cemented therein and sealed with
cement, as at cementing 29. A tubing string 30 is disposed in well
borehole 11 and packed off at packer 34. Conventional heating,
pumping, heat exchanging and separating equipment are associated
with well boreholes 11 and 12 for injecting fluid from well
borehole 11 through perforations 31 in well borehole 11, through
the permeable channel 27 created by intersecting fractures, such as
16 and 17, into well borehole 12 through perforations 33 therein.
Well borehole 12 is preferably cased with casing 34 surrounded by
cement 35. Since certain subterranean earth formations, such as oil
and shale deposits in Colorado, Utah, and Wyoming, are practically
impermeable except for certain natural vertical fractures, the
method of this invention improves injectivity and fluid
communication between two or more wells from a succession of
vertical fractures.
Referring now to FIG. 3, the techniques of my invention may be used
to provide fluid communication between substantially parallel
fractures. Thus, well boreholes 36 through 39, extending into an
earth formation 40 overlying a subterranean earth formation, are
fractured initially, by conventional fracturing techniques, thereby
forming fractures 41 through 44, respectively. The fractures 41
through 44 will most likely be substantially vertical and will be
oriented along the natural plane of weakness of the formation 40,
as indicated. A coarse propping agent is now pumped into all
fractures 41 through 44, and a viscous liquid is injected into
them. The pressure in well boreholes 38 and 39 is limited to
approximately the initial fracturing pressure. The pressure in well
boreholes 36 and 37 is raised until well boreholes 36 and 37 again
fracture. Due to the presence of the stress field set up in
formation 40 due to pressure from the parallel fractures 41 through
44, the second set of fractures 45 and 46, at well boreholes 36 and
37 respectively, tends to be substantially perpendicular to the
first set at the respective fracturing well boreholes. As liquid is
injected into well boreholes 36 and 37 at this higher fracturing
pressure, the fractures from these well boreholes tend to seek the
regions of higher stress near the respective opposite well
boreholes, i.e., the fracture from well borehole 36 tends toward
well borehole 37, and similarly for the fracture from well borehole
37. As these approach each other, as indicated by the dotted lines
in FIG. 3, the stressed regions near the growing fractures will
tend to orient these fractures to connect with each other. If
necessary to maintain the injection pressure at sufficient levels,
this second set of fractures 45 and 46 may also be propped open.
Any fractures which propagate from well boreholes 36 and 37 towards
the fractures from well boreholes 38 and 39 eventually reach the
latter fractures if the well borehole spacing is not too large
(e.g., 50-100 feet). This procedure may be repeated at well
boreholes 38 and 39 and any other adjacent well boreholes (not
shown).
Rather than propagate into regions of comparatively high stress as
illustrated in FIG. 3, the fractures may tend towards the adjoining
original fracture system, possibly tending toward alignment
parallel to this latter set until they are close to it. Thus, as
illustrated in FIG. 4, initial fractures 47 through 50 are formed
at well boreholes 51 through 54, respectively, in the manner
discussed hereinabove. Then the second set of fractures are formed,
that is, fractures 55 and 56 at well boreholes 51 and 52,
respectively, they tend towards the initial fractures (i.e.,
fracture 55 tends toward initial fractures 48 and 49 and fracture
56 tends toward fractures 47 and 50). Thus, the formation of
interconnecting flow paths is created between adjoining fractures
when fractures 55 and 56 are extended as indicated by the dotted
lines in FIG. 4. This type of well intercommunication becomes
feasible when the initially formed fractures, as for example,
fractures 47 through 50, are close enough to each other. In the
well arrangements of both FIGS. 3 and 4, production of fluids may
be obtained in the manner discussed hereinabove with respect to the
well arrangement of FIGS. 1 and 2.
* * * * *