U.S. patent number RE30,484 [Application Number 05/857,734] was granted by the patent office on 1981-01-20 for zonal fracture treatment of well formations.
This patent grant is currently assigned to Halliburton Company. Invention is credited to Gene C. Broaddus, Sherman E. Fredrickson.
United States Patent |
RE30,484 |
Broaddus , et al. |
January 20, 1981 |
Zonal fracture treatment of well formations
Abstract
Methods are provided for treating an underground well formation
whereby the treatment is confined to a desired zone within the
formation. The methods comprise introducing one or more preflush
fluids into one or more fractures in the formation followed by the
introduction of a treating fluid having a density differing
sufficiently from the density of the preflush fluids whereby the
treating fluid is segregated and caused to flow into a desired zone
within the formation.
Inventors: |
Broaddus; Gene C. (Duncan,
OK), Fredrickson; Sherman E. (Duncan, OK) |
Assignee: |
Halliburton Company (Duncan,
OK)
|
Family
ID: |
25326634 |
Appl.
No.: |
05/857,734 |
Filed: |
December 5, 1977 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
499241 |
Aug 21, 1974 |
03954142 |
May 4, 1976 |
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Current U.S.
Class: |
166/307;
166/308.1 |
Current CPC
Class: |
E21B
43/26 (20130101); C09K 8/72 (20130101) |
Current International
Class: |
C09K
8/72 (20060101); C09K 8/60 (20060101); E21B
43/25 (20060101); E21B 43/26 (20060101); E21B
043/26 (); E21B 043/267 (); E21B 043/27 () |
Field of
Search: |
;166/307,308,281,282,271,259,283,273-275,35R,280
;252/8.55C,8.55R |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
The Condensed Chemical Dictionary, 8th Ed., Van Nostrand Reinhold
Co., New York, N.Y., p. 452. .
Frick et al., "Petroleum Production Handbook," vol. II, McGraw-Hill
Book Co., Inc., New York, 1962, pp. 18-3 and 18-12 relied
on..
|
Primary Examiner: Novosad; Stephen J.
Attorney, Agent or Firm: Tregoning; John H. Weaver; Thomas
R.
Claims
We claim: .[.1. A method for placing an acidic treating fluid into
a desired zone of a fracture in an underground well formation
comprising:
introducing a preflush fluid having a known specific gravity into
said fracture, and therafter
introducing an acidic treating fluid having a specific gravity not
equal to the specific gravity of said preflush fluid into said
fracture, the specific gravity of said acidic treating fluid being
at least about 0.1 less than the specific gravity of said preflush
fluid; whereby said acidic treating fluid having a lower specific
gravity than said preflush fluid is caused to override said
preflush fluid into a desired upper zone of said fracture..]. .].2.
The method of claim 1 wherein said preflush fluid is selected from
the group consisting of hydrocarbon liquids, water, aqueous sodium
chloride solutions, aqueous calcium chloride solutions, and aqueous
potassium chloride solutions..]. .[.3. The method of claim 2
wherein said acidic treating fluid is selected from the group
consisting of hydrochloric acid, hydrochloric acid-organic acid
mixtures and methanol-hydrochloric acid mixtures..]. .[.4. The
method of claim 1 which is further characterized to include the
additional step of:
continuously introducing successive quantities of said preflush
fluid and said acidic treating fluid into said fracture so that the
overriding of said acidic treating fluid into said upper zone is
maintained while said acidic treating fluid is flowed through said
fracture..]. .[.5. The method of claim 4 wherein the apparent
viscosities of said preflush fluid and said acidic treating fluid
at the temperature existing in said fractures are less than about
100 cps..]. .[.6. The method of claim 4 wherein said acidic
treating fluid has a specific gravity in the range of from about
1.02 to about 1.34 at room temperature..]. .[.7. The method of
claim 1 which is further characterized to include the initial step
of inducing one or more of said fractures..]. .[.8. A method for
placing a treating fluid into a desired zone of a fracture in an
underground well formation comprising:
introducing a first preflush fluid having a known specific gravity
into said fracture,
introducing a second preflush fluid into said fracture, said second
preflush fluid having a specific gravity sufficiently lower than
the specific gravity of said first preflush fluid so that said
second preflush fluid overrides said first preflush fluid,
producing an interface between said first preflush fluid and said
second preflush fluid, and thereafter
introducing a treating fluid into said fracture, said treating
fluid having a specific gravity of at least about 0.1 less than the
specific gravity of said first preflush fluid and at least about
0.04 more than the specific gravity of said second preflush fluid;
whereby said treating fluid is caused to override said first
preflush fluid and to underride said second preflush fluid and to
flow along said interface between said first preflush fluid and
said second preflush fluid into a desired zone of said
fracture..]. .[.9. The method of claim 8 wherein the specific
gravity of said second preflush fluid in said fracture is at least
about 0.05 less than the specific gravity of said first preflush
fluid in said fracture..]. .[.10. The method of claim 9 which is
further characterized to include the step of continuously
introducing successive quantities of said first preflush fluid,
said second preflush fluid and said treating fluid into said
fracture so that the flow of said treating fluid along said
interface is maintained while said treating fluid is flowed through
said fracture..]. .[.11. The method of claim 10 wherein said first
preflush fluid and said second preflush fluid are selected from the
group consisting of hydrocarbon liquids, water, aqueous sodium
chloride solutions, aqueous calcium chloride solutions, and aqueous
potassium chloride solutions..]. .[.12. The method of claim 11
wherein said treating fluid is selected from the group consisting
of hydrochloric acid, hydrochloric acid-organic acid mixtures and
methanol-hydrochloric acid mixtures..]. .[.13. The method of claim
12 wherein the apparent viscosities of said first and second
preflush fluids and said treating fluid at the temperature existing
in said fractures are less than about 100 cps..]. .[.14. The method
of claim 13 wherein said first and second preflush fluids are
aqueous solutions having specific gravities in the range of from
about 1 to about 1.4 at room temperature and wherein said treating
fluid is an aqueous acid solution having a specific gravity in the
range of from about 1.075 to about 1.15 at room temperature..].
.[.15. The method of claim 9 which is further characterized to
include the initial step of inducing one or more of said
fractures..]. .Iadd. 16. A method for placing a treating fluid into
a desired zone of a fracture in an underground well formation
comprising:
introducing a preflush fluid having a known specific gravity into
at least one substantially vertically-oriented fracture selected
from the group consisting of natural and induced fractures, said
introducing of said pre-flush fluid being performed via a well bore
penetrating said formation in fluid communication with said
fracture at a treating pressure at least equal to a hydraulic
pressure sufficient to open said fracture and to maintain said
fracture in an open position, and immediately thereafter while
maintaining said treating pressure and ceasing introduction of said
preflush fluid
introducing into said fracture via said well bore a treating fluid
having a specific gravity not equal to the specific gravity of said
preflush fluid, the specific gravity of said treating fluid being
at least about 0.1 less than the specific gravity of said preflush
fluid; whereby said treating fluid having a lower specific gravity
than said preflush fluid is caused to override said preflush fluid
into a desired upper zone of said fracture;
wherein said preflush fluid is selected from the group consisting
of hydrocarbon liquids, water, aqueous sodium chloride solutions,
aqueous calcium chloride solutions, and aqueous potassium chloride
solutions.
.Iaddend. .Iadd. 17. The method of claim 16 wherein said treating
fluid is selected from the group consisting of hydrochloric acid,
hydrochloric acid-organic acid mixtures and methanolhydrochloric
acid mixtures. .Iaddend..Iadd. 18. The method of claim 16 which is
further characterized to include the additional step of:
continuously introducing successive quantities of said preflush
fluid and said treating fluid into said fracture so that the
overriding of said treating fluid into said upper zone is
maintained while said treating
fluid is flowed through said fracture. .Iaddend. .Iadd. 19. The
method of claim 18 wherein the apparent viscosities of said
preflush fluid and said treating fluid at the temperature existing
in said fractures are less than about 100 cps. .Iaddend. .Iadd. 20.
The method of claim 16 which is further characterized to include
the initial step of inducing one or more of said fractures.
.Iaddend. .Iadd. 21. The method of claim 16 wherein said treating
fluid contains propping agents for placement in said desired zone.
.Iaddend. .Iadd. 22. A method for placing an acidic treating fluid
into a desired zone of a fracture in an underground well formation
comprising:
introducing a preflush fluid having a known specific gravity into
at least one substantially vertically-oriented fracture selected
from the group consisting of natural and induced fractures, said
introducing of said preflush fluid being performed via a well bore
penetrating said formation in fluid communication with said
fracture at a treating pressure at least equal to a hydraulic
pressure sufficient to open said fracture and to maintain said
fracture in an open position, and immediately thereafter while
maintaining said treating pressure and ceasing introduction of said
preflush fluid
introducing into said fracture via said well bore an acidic
treating fluid having a specific gravity not equal to the specific
gravity of said preflush fluid, the specific gravity of said acidic
treating fluid being at least about 0.1 less than the specific
gravity of said preflush fluid; whereby said acidic treating fluid
having a lower specific gravity than said preflush fluid is caused
to override said preflush fluid into a desired upper zone of said
fracture; and thereafter while maintaining said treating
pressure
continuously introducing successive quantities of said preflush
fluid and said acidic treating fluid into said fracture so that the
overriding of said acidic treating fluid into said upper zone is
maintained while said acidic treating fluid is flowed through said
fracture wherein said acidic treating fluid has a specific gravity
in the range of from about 1.02 to about 1.34 at room temperature.
.Iaddend..Iadd. 23. A method for placing a treating fluid into a
desired zone of a fracture in an underground well formation
comprising:
introducing a first preflush fluid having a known specific gravity
into at least one substantially vertically-oriented fracture
selected from the group consisting of natural and induced
fractures, said introducing of said first preflush fluid being
performed via a well bore penetrating said formation in fluid
communication with said fracture at a treating pressure at least
equal to a hydraulic pressure sufficient to open said fracture and
to maintain said fracture in an open position, and immediately
thereafter while maintaining said treating pressure and ceasing
introduction of said first preflush fluid,
introducing a second preflush fluid into said fracture via said
well bore, said second preflush fluid having a specific gravity
sufficiently lower than the specific gravity of said first preflush
fluid so that said second preflush fluid overrides said first
preflush fluid, producing an interface between said first preflush
fluid and said second preflush fluid, and immediately thereafter
while maintaining said treating pressure and ceasing introduction
of said second preflush fluid
introducing a treating fluid into said fracture via said well bore,
said treating fluid having a specific gravity of at least about 0.1
less than the specific gravity of said first preflush fluid and at
least about 0.04 more than the specific gravity of said second
preflush fluid; whereby said treating fluid is caused to override
said first preflush fluid and to underride said second preflush
fluid and to flow along said interface between said first preflush
fluid and said second preflush fluid into a desired zone of said
fracture. .Iaddend. .Iadd. 24. The method of claim 23 wherein the
specific gravity of said second preflush fluid in said fracture is
at least about 0.20 less than the specific gravity of said first
preflush fluid in said fracture. .Iaddend. .Iadd. 25. The method of
claim 24 which is further characterized to include the step of
continuously introducing successive quantities of said first
preflush fluid, said second preflush fluid and said treating fluid
into said fracture so that the flow of said treating fluid along
said interface is maintained while said treating fluid is flowed
through said fracture. .Iaddend. .Iadd. 26. The method of claim 24
which is further characterized to include the initial step of
inducing one or more of said fractures. .Iaddend. .Iadd. 27. A
method for placing a treating fluid into a desired zone of a
fracture in an underground well formation comprising:
introducing a first preflush fluid having a known specific gravity
into at least one substantially vertically-oriented fracture
selected from the group consisting of natural and induced
fractures, said introducing of said preflush fluid being performed
via a well bore penetrating said formation in fluid communication
with said fracture at a treating pressure at least equal to a
hydraulic pressure sufficient to open said fracture and to maintain
said fracture in an open position, and immediately thereafter while
maintaining said treating pressure, and ceasing introduction of
said first preflush fluid
introducing a second preflush fluid into said fracture via said
well bore, said second preflush fluid having a specific gravity
sufficiently lower than the specific gravity of said first preflush
fluid so that said second preflush fluid overrides said first
preflush fluid, producing an interface between said first preflush
fluid and said second preflush fluid, and immediately thereafter
while maintaining said treating pressure and ceasing introduction
of said second preflush fluid
introducing a treating fluid into said fracture via said well bore,
said treating fluid having a specific gravity of at least about 0.1
less than the specific gravity of said first preflush fluid and at
least about 0.04 more than the specific gravity of said second
preflush fluid; whereby said treating fluid is caused to override
said first preflush fluid and to underride said second preflush
fluid and to flow along said interface between said first preflush
fluid and said second preflush fluid into a desired zone of said
fracture, wherein the specific gravity of said second preflush
fluid in said fracture is at least about 0.20 less than the
specific gravity of said first preflush fluid in said fracture, and
thereafter while maintaining said treating pressure
continuously introducing successive quantities of said first
preflush fluid, said second preflush fluid and said treating fluid
into said fracture so that the flow of said treating fluid along
said interface is maintained while said treating fluid is flowed
through said fracture, and wherein
said first preflush fluid and said second preflush fluid are
selected from the group consisting of hydrocarbon liquids, water,
aqueous sodium chloride solutions, aqueous calcium chloride
solutions, and aqueous
potassium chloride solutions. .Iaddend..Iadd. 28. The method of
claim 27 wherein said treating fluid is selected from the group
consisting of hydrochloric acid, hydrochloric acid-organic acid
mixtures and methanol-hydrochloric acid mixtures. .Iaddend..Iadd.
29. The method of claim 28 wherein the apparent viscosities of said
first and second preflush fluids and said treating fluid at the
temperature existing in said fractures are less than about 100 cps.
.Iaddend..Iadd. 30. The method of claim 29 wherein said first and
second preflush fluids are aqueous solutions having specific
gravities in the range of from about 1 to about 1.4 at room
temperature and wherein said treating fluid is an aqueous acid
solution having a specific gravity in the range of from about 1.075
to about 1.15 at room temperature. .Iaddend. .Iadd. 31. A method
for placing a treating fluid into a desired zone of a fracture in
an underground well formation comprising:
introducing a first preflush fluid having a known specific gravity
into at least one substantially vertically-oriented fracture
selected from the group consisting of natural and induced
fractures, said introducing of said preflush fluid being performed
via a well bore penetrating said formation in fluid communication
with said fracture at a treating pressure at least equal to a
hydraulic pressure sufficient to open said fracture and to maintain
said fracture in an open position, and immediately thereafter while
maintaining said treating pressure, and ceasing introduction of
said first preflush fluid
introducing a second preflush fluid into said fracture via said
well bore, said second preflush fluid having a specific gravity
sufficiently different from the specific gravity of said first
preflush fluid so that said second preflush fluid and said first
preflush fluid produce an interface between said first preflush
fluid and said second preflush fluid, and immediately thereafter
while maintaining said treating pressure and ceasing introduction
of said second preflush fluid
introducing a treating fluid into said fracture via said well bore,
said treating fluid having a specific gravity of at least about 0.1
less than the specific gravity of one of said preflush fluids and
at least about 0.04 more than the specific gravity of the other of
said preflush fluids; whereby said treating fluid is caused to
override said one preflush fluid and to underride said other
preflush fluid and to flow along said interface between said first
preflush fluid and said second preflush fluid into a desired zone
of said fracture and thereafter while maintaining said treating
pressure
continuously introducing successive quantities of said first
preflush fluid, said second preflush fluid and said treating fluid
into said fracture so that the flow of said treating fluid along
said interface is maintained while said treating fluid is flowed
through said fracture, and wherein
said first preflush fluid and said second preflush fluid are
selected from the group consisting of hydrocarbon liquids, water,
aqueous sodium chloride solutions, aqueous calcium chloride
solutions, and aqueous potassium chloride solutions.
.Iaddend..Iadd. 32. The method of claim 31 wherein said treating
fluid is selected from the group consisting of hydrochloric acid,
hydrochloric acid-organic acid mixtures and methanol-hydrochloric
acid mixtures. .Iaddend..Iadd. 33. The method of claim 32 wherein
the apparent viscosities of said first and second preflush fluids
and said treating fluid at the temperature existing in said
fractures are less than about 100 cps. .Iaddend..Iadd. 34. The
method of claim 32 wherein said first and second preflush fluids
are aqueous solutions having specific gravities in the range of
from about 1 to about 1.4 at room temperature and wherein said
treating fluid is an aqueous acid solution having a specific
gravity in the range of from about 1.075 to about 1.15 at room
temperature. .Iaddend. .Iadd. 35. A method for placing a treating
fluid into a desired zone of a fracture in an underground well
formation comprising:
introducing a first preflush fluid having a known specific gravity
into at least one substantially vertically-oriented fracture
selected from the group consisting of natural and induced
fractures, said introducing of said preflush fluid being performed
via a well bore penetrating said formation in fluid communication
with said fracture at a treating pressure at least equal to a
hydraulic pressure sufficient to open said fracture and to maintain
said fracture in an open position, and immediately thereafter while
maintaining said treating pressure, and ceasing introduction of
said first preflush fluid
introducing a second preflush fluid into said fracture via said
well bore, said second preflush fluid having a specific gravity
sufficiently lower than the specific gravity of said first preflush
fluid so that said second preflush fluid overrides said first
preflush fluid, producing an interface between said first preflush
fluid and said second preflush fluid, and immediately thereafter
while maintaining said treating pressure and ceasing introduction
of said second preflush fluid
introducing a treating fluid into said fracture via said well bore,
said treating fluid having a specific gravity of at least about 0.1
less than the specific gravity of said first preflush fluid and at
least about 0.04 more than the specific gravity of said second
preflush fluid; whereby said treating fluid is caused to override
said first preflush fluid and to underride said second preflush
fluid and to flow along said interface between said first preflush
fluid and said second preflush fluid into a desired zone of said
fracture, and wherein
said treating fluid contains propping agents for placement in said
desired zone. .Iaddend. .Iadd. 36. A method for placing a treating
fluid into a desired zone of at least one vertically oriented
fracture induced in an underground well formation, the
vertically-oriented fracture extending laterally outwardly from a
well bore penetrating the formation, which method comprises
while applying sufficient hydraulic pressure to open said fracture
and to maintain the vertical fracture in an open position,
introducing a first preflush fluid having a known specific gravity
into said vertical fracture via said well bore and thereafter
while applying sufficient hydraulic pressure to maintain the
vertical fracture in an open position, and ceasing introduction of
said first preflush fluid introducing a second preflush fluid into
said vertical fracture via said well bore, said second preflush
fluid having a specific gravity sufficiently different from the
specific gravity of said first preflush fluid so that said second
preflush fluid and said first preflush fluid produce an interface
between said first preflush fluid and said second preflush fluid,
and thereafter
while applying sufficient hydraulic pressure to maintain the
vertical fracture in an open position, and ceasing introduction of
said second preflush fluid introducing a treating fluid into said
vertical fracture via said well bore, said treating fluid having a
specific gravity of at least about 0.1 less than the specific
gravity of one of said preflush fluids and at least about 0.04 more
than the specific gravity of the other of said preflush fluids;
whereby said treating fluid is caused to override said one preflush
fluid and to underride said other preflush fluid and to flow along
said interface between said first preflush fluid and said second
preflush fluid into a desired zone of said vertical fracture, said
treating fluid being forced by said hydraulic pressure to flow
outwardly in the fracture from the well bore, extending the
fracture and simultaneously treating the desired zone therewithin.
.Iaddend..Iadd. 37. The method of claim 36 which is further
characterized to include the initial step of inducing one or more
of said vertical fractures, and wherein said treating fluid is an
acidic treating fluid having a specific gravity in the range of
from about 1.02 to about 1.34 at room temperature. .Iaddend. .Iadd.
38. The method of claim 36 wherein said treating fluid contains
propping agents for placement in said desired zone. .Iaddend.
.Iadd. 39. A method for placing an acidic treating fluid into a
desired zone of at least one vertically-oriented fracture induced
in an underground well formation, the vertically-oriented fracture
extending laterally outwardly from a well bore penetrating the
formation, which method comprises:
while applying sufficient hydraulic pressure to open said fracture
and to maintain the vertical fracture in an open position,
introducing a preflush fluid having a known specific gravity into
said vertical fracture via said well bore, and thereafter
while applying sufficient hydraulic pressure to maintain the
vertical fracture in an open position, and ceasing introduction of
said preflush fluid introducing into said fracture via said well
bore an acidic treating fluid having a specific gravity not equal
to the specific gravity of said preflush fluid, the specific
gravity of said acidic treating fluid being at least about 0.1 less
than the specific gravity of said preflush fluid, whereby said
acidic treating fluid having a lower specific gravity than said
preflush fluid is caused to override said preflush fluid into a
desired upper zone of said vertical fracture, said acidic treating
fluid etching flow channels in faces of the vertical fracture in
the formation, said flow channels after said hydraulic pressure is
lessened and said fracture closes, remaining in the formation to
allow desired fluid contained in the formation to flow relative to
the well bore wherein said acidic treating fluid has a specific
gravity in the range of from about 1.02 to about 1.34 at room
temperature, and wherein the hydraulic pressure is sufficient to
extend the vertical fracture laterally from the well bore.
.Iaddend. .Iadd. 40. A method for placing a treating fluid into a
desired zone of a fracture in an underground well formation
comprising:
introducing a first preflush fluid having a known specific gravity
into at least one substantially vertically-oriented fracture
selected from the group consisting of natural and induced
fractures, said introducing of said preflush fluid being performed
via a well bore penetrating said formation in fluid communication
with said fracture at a treating pressure at least equal to a
hydraulic pressure sufficient to open said fracture and to maintain
said fracture in an open position and immediately thereafter while
maintaining said treating pressure, and ceasing introduction of
said first preflush fluid,
introducing a second preflush fluid into said fracture via said
well bore, said second preflush fluid having a specific gravity
sufficiently different from the specific gravity of said first
preflush fluid so that said second preflush fluid and said first
preflush fluid produce an interface between said first preflush
fluid and said second preflush fluid, and immediately thereafter
while maintaining said treating pressure, and ceasing introduction
of said second preflush fluid
introducing a treating fluid into said fracture via said well bore,
said treating fluid having a specific gravity of at least about 0.1
less than the specific gravity of one of said preflush fluids and
at least about 0.04 more than the specific gravity of the other of
said preflush fluids; whereby said treating fluid is caused to
override said one preflush fluid and to underride said other
preflush fluid and to flow along said interface between said first
preflush fluid and said second preflush fluid into a desired zone
of said fracture
continuously introducing successive quantities of said first
preflush fluid, said second preflush fluid and said treating fluid
into said fracture so that the flow of said treating fluid along
said interface is maintained while said treating fluid is flowed
through said fracture.
.Iaddend. .Iadd. 41. The method of claim 40 which is further
characterized to include the intial step of inducing one or more of
said fractures. .Iaddend.
Description
The present invention relates to the zonal fracture treatment of
well formations, and more particularly, but not by way of
limitation, to an improved method of fracture treating underground
well formations whereby the treatment is confined to a desired zone
within the formations.
Many various methods have been developed and used for increasing or
stimulating the production of oil, gas and the like from an
underground well formation penetrated by a well bore. One commonly
used method of well stimulation where the producing formation to be
stimulated is formed of relatively low permeability material
consists of exerting fluid pressure on the formation to create one
or more fractures therein and then extending the created fractures
outwardly from the well bore. After the fractures have been created
and extended, a propping agent such as sand, glass beads, etc., can
be placed therein to maintain the fractures open after fluid
pressure on the formation is withdrawn and the fractures close.
Another commonly used well stimulation method involves a technique
known in the art as fracture acidizing which consists of creating
and extending one or more fractures in a well formation and then
etching the fracture faces with acid so that when the formation is
returned to production and the fractures close, flow channels
remain therein through which desired fluids contained in the
formation flow to the well bore.
In fracture treatment procedures used heretofore, less than desired
results have often been achieved due to the fractures extending
into undesirable zones in the formation. While most wells are
completed in the zone of best possible production, it is often
difficult to prevent a created fracture from extending vertically
above or below the desired zone or both, resulting in increased
production of unwanted fluids or gases. For example, barren zones
or zones producing excessive water or undesirable gases may lie in
close proximity to a preferred production zone and when a fracture
treatment procedure is carried out to stimulate production from the
preferred zone, flow channels extending into the undesirable zones
are simultaneously created causing an undesirable increase in the
flow of gases or water therefrom as well as a desirable increase in
the production of oil or gas from the preferred zone.
By the present invention an improved method of treating a well
formation is provided wherein the treatment is confined to a
desired zone within the formation. While the invention is
particularly suitable for carrying out fracture acidizing
treatments of well formations to increase the production of desired
fluids therefrom, it will be readily understood by those skilled in
the art that the invention can be utilized for carrying out a
variety of fracture related treatments in well formations such as
the placement of propping agents in a particular zone, etc.
The present invention broadly comprises treating an underground
well formation containing one or more fractures so that the
treatment is confined to a desired zone within the fractures
comprising the steps of first introducing a preflush fluid into the
fracture or fractures and then introducing a treating fluid
therein, the treating fluid having a density differing sufficiently
from the density of the preflush fluid whereby the treating fluid
is segregated and caused to flow into a desired zone within the
fracture or fractures by the preflush fluid.
The methods of the present invention can be carried out in
formations including natural fractures or in formations wherein
artificial fractures are created therein and extended by exerting
fluid pressure thereon. Further, where fractures are induced in a
formation, the preflush fluids of the present invention can be
utilized as the fracturing fluid for creating the fractures and the
fractures can be extended simultaneously with the carrying out of
the treatment methods.
In the accompanying drawings forming a part of this disclosure:
FIG. 1 is a schematic illustration of a fracture in an underground
well formation after a preflush fluid of the present invention has
been introduced therein;
FIG. 2 is a schematic illustration of the fracture of FIG. 1 after
a light treating fluid of the present invention has been introduced
therein;
FIG. 3 is a schematic illustration of the fracture of FIG. 1 after
additional preflush fluid has been introduced therein;
FIG. 4 is a schematic illustration of the fracture of FIG. 1 after
additional light treating fluid has been introduced therein;
FIG. 5 is a schematic illustration of a fracture in an underground
well formation after a preflush fluid of the present invention has
been introduced therein;
FIG. 6 is a schematic illustration of the fracture of FIG. 5 after
a heavy treating fluid of the present invention has been introduced
therein;
FIG. 7 is a schematic illustration of a fracture in an underground
well formation after a heavy preflush fluid of the present
invention has been introduced therein;
FIG. 8 is a schematic illustration of the fracture of FIG. 7 after
a light preflush fluid of the present invention has been introduced
therein;
FIG. 9 is a schematic illustration of the fracture of FIG. 7 after
a treating fluid of the present invention has been introduced
therein;
FIG. 10 is a schematic illustration of the fracture of FIG. 7 after
additional heavy preflush fluid has been introduced therein;
FIG. 11 is a schematic illustration of the fracture of FIG. 7 after
additional light preflush fluid has been introduced therein;
and
FIG. 12 is a schematic illustration of the fracture of FIG. 7 after
additional treating fluid has been introduced therein.
In treating underground well formations penetrated by well bores,
particularly those formed of relatively impermeable and fracturable
materials, it has become common practice to induce fractures in the
most productive zone of such formations and extend the fractures
laterally outwardly from the well bore whereby desired fluids
contained in the formation more freely flow from the formation into
the well bore. In most formations, induced fractures are vertically
oriented, i.e., the fracture or fractures produced lie in a
substantially vertical plane paralleling the axis of the well bore.
The induction of such fractures is generally accomplished by
pumping a fracturing fluid through the well bore into the formation
thereby exerting hydraulic pressure on the formation at a point in
the most productive and desired zone of the formation. Once parting
of the formation is achieved, continued pumping of the fracturing
fluid at high pressures into the formation extends the fracture or
fractures outwardly from the well bore. However, in addition to
extending the fractures outwardly, they are often also extended or
enlarged in directions upwardly or downwardly, or both, from the
point of initiation. If undesirable zones lie above or below the
desired zone, and if during the fracture treatment of the desired
zone conductive fractures are also formed into the adjacent
undesirable zones, fluids from the undesirable zones are produced
along with fluids from the desired zone into the well bore. For
example, zones containing excessive quantities of water or unwanted
gas can lie adjacent oil producing zones and stimulation of the
production of water and unwanted gas with the oil is an undesirable
result.
The present invention provides methods of fracture treating
underground well formations utilizing a treating fluid whereby the
treating fluid is confined to a desired zone within fractures in
the formation, and as a result, the effects of the treatment do not
reach undesirable zones. While as stated above, the methods of the
present invention can be adapted for carrying out a variety of
treatments or procedures in well formations, they are particularly
well adapted for carrying out fracture acidizing procedures whereby
high capacity flow channels are formed in a formation.
Referring now to the drawings and particularly to FIGS. 1 through
4, a vertical fracture 10 in an underground well formation is
schematically illustrated extending laterally outwardly from a well
bore 12 penetrating the formation. A casing or liner 14 is shown
positioned in the well bore 12 having perforations 16 disposed
therein positioned adjacent a desirable production zone of the
formation. The fracture 10 can be natural or induced, and in either
case, a preflush fluid is introduced into the fracture by pumping
the fluid under pressure through the conduit 14 into the fracture
by way of the perforations 16. As will be understood, if the
fracture 10 is induced, the preflush fluid can be utilized for
inducing the fracture. Assuming that an undesirable zone lies
directly below the zone in which it is desired to carry out a
treatment utilizing a treating fluid, in accordance with the
present invention, a treating fluid having a density differing
sufficiently from the density of the preflush fluid is utilized
whereby the treating fluid is segregated and caused to flow into
the desired upper zone by the preflush fluid as shown in FIG. 2.
After pumping the preflush fluid into the fracture 10 in an amount
at least sufficient to fill the lower portion thereof, the light or
less dense treating fluid is introduced into the fracture 10. Due
to the density difference between the treating fluid and the
preflush fluid, the lighter treating fluid overrides the preflush
fluid and is segregated into the top portion of the fracture. After
the light treating fluid has been pumped into the fracture in a
quantity sufficient to fill the top portion and extend the
fracture, additional preflush fluid is introduced into the fracture
in order to maintain the treating fluid in the upper desired zone
as shown in FIG. 3. After the additional preflush fluid has been
introduced into the fracture, additional treating fluid is
introduced therein which is also maintained in the desired upper
zone as shown in FIG. 4 by overriding the preflush fluid.
Successive quantities of preflush fluid and treating fluid can be
continuously introduced into the fracture 10 while applying
sufficient hydraulic pressure to maintain the fracture in an open
position thereby forcing the treating fluid outwardly in the
fracture from the well bore 12 extending the fracture and
simultaneously treating the desired zone therewithin.
Referring now to FIGS. 5 and 6, when it is desired to treat a lower
zone in a formation and prevent upper portions of a fracture
therein from receiving treating fluid, a light preflush fluid is
introduced into the fracture as shown in FIG. 5. After introduction
of the preflush fluid, a treating fluid having a density greater
than the density of the preflush fluid whereby the treating fluid
is segregated and caused to flow into the lower zone in the
fracture by the preflush fluid is introduced into the fracture as
shown in FIG. 6. Additional quantities of light preflush fluid and
heavy treating fluid can be successively introduced into the
fracture while maintaining the fracture open so that the treating
fluid is confined to the desired lower zone therein and caused to
flow through the fracture as the fracture is extended.
Referring now to FIGS. 7 through 12, when it is desired to confine
a treating fluid to an intermediate zone of a formation penetrated
by a fracture, i.e., prevent the treating fluid from entering the
uppermost or lowermost portions of the fracture which may extend
into undesirable zones, a heavy preflush fluid is first introduced
into the fracture as shown in FIG. 7. After introduction of the
heavy preflush fluid in an amount at least sufficient to fill the
lower portion of the fracture, a light preflush fluid having a
density differing sufficiently from the density of the heavy
preflush fluid so that the light preflush fluid is segregated into
the upper portion of the fracture along an interface is introduced
into the fracture as shown in FIG. 8. After placement of the light
and heavy preflush fluids in the fracture, a treating fluid is
introduced therein having a density substantially intermediate to
the densities of the light and heavy preflush fluids whereby the
treating fluid is segregated and caused to flow along the interface
between the light and heavy preflush fluids in the desired treating
zone as shown in FIG. 9.
As shown in FIGS. 10 through 12, additional quantities of heavy
preflush fluid, light preflush fluid and treating fluid can be
successively introduced into the fracture thereby maintaining the
segregation of the treating fluid in the desired zone as the
fracture is extended.
Thus, in accordance with the methods of the present invention, the
densities of preflush fluids and treating fluid utilized are
controlled to cause separation and segregation of the treating
fluid into a desired zone within a fracture. While any of a variety
of fluids can be utilized in carrying out the methods of the
present invention, hydrocarbon liquids, water, and aqueous
solutions are preferred because of their availability and general
compatibility with well formations.
In order to achieve separation and segregation between the fluids
used, the densities thereof must be such that a difference in the
specific gravities of the fluids of at least about 0.025 exists at
the conditions existing in the well formation to be treated.
Preferably, fluids are utilized having a specific gravity
difference of about 0.10 at the conditions in the formation which
creates a pronounced vertical movement of one fluid with respect to
the other. In treatments where an extreme overriding or underriding
of one fluid with respect to another is required, a specific
gravity difference of 0.20 between the fluids is preferred. To
create the above mentioned difference of 0.025 between specific
gravities of fluids in the situation where it is desired that the
treating fluid can be confined to an intermediate zone of a
fracture, as described in connection with FIGS. 7 through 12, it is
necessary that the minimum difference between the specific
gravities of the heavy preflush fluid and the light preflush fluid
be at least about 0.05. Accordingly, in these situations, the
difference between the specific gravities of the heavy preflush
fluid and the light preflush fluid is equal to the sum of the
differences between the heavy preflush fluid and the treating fluid
and the treating fluid and the light preflush fluid. In this
connection, reference should be made to Table III, below, where the
differences between the specific gravities of the heavy preflush
fluids and the light preflush fluids can be readily observed. As
will be understood, the greater the difference in density between
the fluids, the more pronounced will be the overrunning or
underrunning result.
High viscosity fluids tend to move through a fracture in a well
formation as a mass with less tendency to be affected by differing
densities than low viscosity fluids. Low viscosity fluids on the
other hand readily override and underride fluids of differing
density. Therefore, preflush and treating fluids having apparent
viscosities of less than about 100 cps at the temperatures existing
in the fractures into which they are to be introduced are generally
preferred for use in accordance with this invention. However,
higher viscosity treating and preflush fluids can be used if the
circumstances dictate and overriding or underriding can be
accentuated by utilizing fluids of differing viscosity. More
specifically, the segregation and separation ofthe preflush and
treating fluids can be enhanced by using a preflush fluid having a
higher viscosity than the treating fluid. Preferably, when preflush
and treating fluids of different viscosity are used, the preflush
fluid viscosity is in the range of from about 5 to about 80 times
the viscosity of the treating fluid.
The most preferred light preflush fluids for use in accordance with
this invention are oil, kerosene, or water. Most preferred heavy
preflush fluids are aqueous sodium chloride solutions, aqueous
calcium chloride solutions, and aqueous potassium chloride
solutions. The most preferred treating fluids are those in the form
of aqueous solutions.
Specific preferred aqueous preflush fluids for fracture acidizing
are solutions ranging in specific gravity from about 1.0 to about
1.4 at room temperature (room temperature is used herein to mean a
temperature in the range of from about 15.degree. C. to about
20.degree. C.). Aqueous acid solutions having specific gravities in
the range of from about 1.02 to about 1.34 at room temperature are
particularly suitable for use with the preflush fluids. Aqueous
solutions of hydrochloric acid and hydrochloric acid-organic acid
mixtures, e.g., hydrochloric-acetic acid mixtures are most
preferred for carrying out fracture acidizing procedures, but
alcohol-hydrochloric acid solutions are also suitable in cases
where an extra light acid treating fluid is required.
In carrying out fracture acidizing procedures to stimulate
production from a desired zone within a formation using the methods
of the present invention, hydrocarbon liquids, water or aqueous
solutions are particularly suitable and are preferred for use as
preflush fluids. Any of a variety of acidizing treating fluids can
be utilized, but aqueous hydrochloric acid solutions, aqueous
solutions of hydrochloric-organic acid mixtures and
alcohol-hydrochloric acid solutions are particularly suitable and
are preferred.
As stated above, successive quantities of preflush fluid and acid
treating fluid can be continuously pumped or otherwise introduced
into a fracture to extend the fracture while maintaining the acid
segregated in a desired zone therein.
As is well understood by those skilled in the art, the acid is
moved through the fracture while the fracture is maintained in an
open position by fluid pressure exerted thereon so that the
fracture is extended and channels are etched in the faces of the
fracture by the reaction of the acid therewith. When the fractures
have been extended to the desired extent and the acid has become
spent, the fluid pressure exerted on the formation is withdrawn
causing the fractures to close, but high capacity flow channels
remain therein.
As the acid treating fluid reacts with the material forming the
fracture faces, it increases in density. This density change must
be taken into consideration when calculating the required densities
of preflush fluids used.
When a single preflush fluid is used in carrying out a fracture
acidizing treatment, the use of equal quantities of acid generally
achieves satisfactory results. When two preflush fluids of
differing density are used, equal quantities of the preflush fluids
and acid can generally be used.
A variety of conventional additives can be incorporated with the
preflush and treating fluids utilized to vary their physical
characteristics, e.g., fluid loss additives, viscosity increasing
agents, wetting agents, etc.
In order to more clearly illustrate the present invention in
carrying out fracture acidizing procedures, the following examples
are presented.
EXAMPLE 1
In applications where it is desired to confine an acid treating
fluid to an upper zone in a fractured formation, i.e., the acid
must override the preflush fluid, the acid used should preferably
be at least about 0.8 pounds per gallon less dense than the
preflush fluid used at room temperature, or stated another way, the
acid should have a specific gravity less than the preflush fluid by
at least about 0.10.
In Table I below the minimum required preflush fluid densities for
various hydrochloric acid treating solutions are given:
TABLE I
__________________________________________________________________________
MINIMUM PREFLUSH FLUID DENSITIES REQUIRED FOR TREATING AN UPPER
ZONE WITH VARIOUS HYDROCHLORIC ACID SOLUTIONS Acid Acid Acid
Treating Preflush Fluid Treating Strength, Acid Fluid Density,
Density, Fluid By Treating Fluid Pounds Per Specific Pounds Per To
Be Used Weight Specific Gravity Gallon Gravity Gallon
__________________________________________________________________________
Aqueous Hydrochloric Acid Solution 15% 1.075 8.95 1.17 9.75 Aqueous
Hydrochloric Acid Solution 20% 1.1 9.17 1.2 10.0 Aqueous
Hydrochloric Acid Solution 25% 1.127 9.39 1.25 10.42 Aqueous
Hydrochloric Acid Solution 28% 1.14 9.5 1.3 10.83
Methanol-Hydrochloric Acid Solution 22.4% 1.04 8.67 1.2 10.0
__________________________________________________________________________
EXAMPLE 2
In applications where it is required that an acid treating fluid be
confined to a lower zone in a fractured formation, i.e., the acid
must underride the preflush fluid, the acid used should preferably
be at least about 0.32 pounds per gallon greater in density than
the preflush fluid at room temperature, or stated another way, the
acid should have a specific gravity greater than the preflush fluid
by at least about 0.04.
Table II below presents the preflush fluid densities which are
preferred for use with various hydrochloric acid treating
solutions.
TABLE II
__________________________________________________________________________
PREFLUSH FLUID DENSITIES FOR TREATING A LOWER ZONE WITH VARIOUS
HYDROCHLORIC ACID SOLUTIONS Acid Acid Acid Treating Preflush Fluid
Treating Strength, Acid Fluid Density, Density, Fluid By Treating
Fluid Pounds Per Specific Pounds Per To Be Used Weight Specific
Gravity Gallon Gravity Gallon
__________________________________________________________________________
Aqueous Hydrochloric Acid Solution 15% 1.075 8.95 1.0 8.3 Aqueous
Hydrochloric Acid Solution 20% 1.1 9.17 1.0 8.3 Aqueous
Hydrochloric Acid Solution 25% 1.127 9.39 1.0 8.3 Aqueous
Hydrochloric Acid Solution 28% 1.14 9.5 1.0 8.3
Methanol-Hydrochloric Acid Solution 22.4% 1.04 8.67 0.8 6.7
__________________________________________________________________________
EXAMPLE 3
In applications where it is required that an acid treating fluid be
confined to an intermediate zone in a fractured formation, i.e.,
the acid must override the heavy preflush fluid used and underride
the light preflush fluid used, the acid should preferably be at
least about 0.8 pounds per gallon less dense than the heavy
preflush fluid and at least about 0.32 pounds per gallon more dense
than the light preflush fluid used.
Table III below presents the light and heavy preflush fluid
densities which are preferred for use with various hydrochloric
acid solutions.
TABLE III
__________________________________________________________________________
LIGHT AND HEAVY PREFLUSH FLUID DENSITIES FOR TREATING AN
INTERMEDIATE ZONE WITH VARIOUS HYDROCHLORIC ACID SOLUTIONS Acid
Acid Acid Treating Heavy Preflush Fluid Light Preflush Fluid
Treating Strength, Acid Fluid Density, Density, Density, Fluid By
Treating Fluid Pounds Per Specific Pounds Per Specific Pounds Per
To Be Used Weight Specific Gravity Gallon Gravity Gallon Gravity
Gallon
__________________________________________________________________________
Aqueous Hydrochloric Acid Solution 15% 1.075 8.95 1.17 9.75 1.0 8.3
Aqueous Hydrochloric Acid Solution 20% 1.1 9.17 1.2 10.0 1.0 8.3
Aqueous Hydrochloric Acid Solution 25% 1.127 9.39 1.25 10.42 1.0
8.3 Aqueous Hydrochloric Acid Solution 28% 1.14 9.5 1.30 10.83 1.0
8.3 Methanol-Hydrochloric Acid Solution 22.4% 1.04 8.67 1.20 10.0
0.8 6.7
__________________________________________________________________________
In Table IV below the densities at room temperature of various
preferred preflush acid treating fluids are given:
TABLE IV ______________________________________ DENSITIES OF
VARIOUS PREFLUSH AND ACID TREATING FLUIDS Concen- Density, tration,
Pounds By Con- Specific Per Fluid Weight dition Gravity Gallon
______________________________________ Aqueous Hydrochloric Acid
Solution 5% Live 1.025 8.50 Aqueous Hydrochloric Acid Solution 10%
Live 1.050 8.75 Aqueous Hydrochloric Acid Solution 15% Live 1.075
8.96 Aqueous Hydrochloric Acid Solution 15% 1/4 Spent 1.1 9.17
Aqueous Hydrochloric Acid Solution 15% 1/2 Spent 1.125 9.38 Aqueous
Hydrochloric Acid Solution 15% 3/4 Spent 1.15 9.59 Aqueous
Hydrochloric Acid Solution 15% Spent 1.175 9.79 Aqueous
Hydrochloric Acid Solution 20% Live 1.1 9.17 Aqueous Hydrochloric
Acid Solution 20% Spent 1.233 10.28 Aqueous Hydrochloric Acid
Solution 25% Live 1.127 9.39 Aqueous Hydrochloric Acid Solution 25%
Spent 1.295 10.79 Aqueous Hydrochloric Acid Solution 28% Live 1.14
9.5 Aqueous Hydrochloric Acid Solution 28% 1/4 Spent 1.19 9.9
Aqueous Hydrochloric Acid Solution 28% 1/2 Spent 1.24 10.34 Aqueous
Hydrochloric Acid Solution 28% 3/4 Spent 1.29 10.75 Aqueous
Hydrochloric Acid Solution 28% Spent 1.34 8.67
Methanol-Hydrochloric Acid Solution 22.4% Live 1.04 8.67 Water --
Fresh 1.0 8.3 Aqueous Potassium Chloride Solution 2% -- 1.011 8.44
Aqueous Sodium Chloride Solution 2% -- 1.012 8.45 Aqueous Sodium
Chloride Solution 5% -- 1.034 8.63 Aqueous Sodium Chloride Solution
10% -- 1.07 8.93 Aqueous Sodium Chloride Solution 15% -- 1.11 9.25
Aqueous Sodium Chloride Solution 20% -- 1.15 9.58 Aqueous Sodium
Chloride Solution 26% -- 1.2 10.0 Aqueous Calcium Chloride Solution
Saturated -- 1.4 11.6 ______________________________________
It will be apparent from the foregoing that many widely different
embodiments of this invention may be made without departing from
the spirit and the scope thereof and the invention should be
limited only by the lawful scope of the appended claims.
* * * * *