Note: Descriptions are shown in the official language in which they were submitted.
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F-4109
LIMITED ENTRY ~ETHOD FOR INDUCING SIMULTANEOUSLY
MULTIPLE FRACTURING IN DEVIATED WELLBORES
This invention is directed to the recovery of
hydrocarbonaceous fluids from a low permeability formation via a
deviated wellbore having multiple vertical fractures therein.
Desired fracture locations are selected along the wellbore. The
wellbore is alternately perforated at the selected locations.
Subsequently, the perforations are hydraulically fractured in a
manner to form simultaneously, multiple fractures.
Low permeability formations generally require significant
stimulation to develop well productivity large enough to be of
commercial value. Hydraulic fracturing, using proppant laden
slurries and/or acid, is most commonly used in these stimulation
applications. While individual well productivity usually is enough
to generate profitable results, effective recovery of a significant
percentage of the hydrocarbon in place is not assure~. For example,
in the Annona Chalk formation of the Caddo Pine Island Field in
northwestern Louisiana, hydraulic fracturing has been utilized as a
part of the initial completion procedure in most wells. While this
results in acceptable profitability for most wells, the proJected
cumulative recovery for the field is only 15~ of -the
original-oil-in-place (OOIP).
One method for increasing the percentage recovery is to
reduce spacing between wells which, when considering that each well
is fractùred, is tantamount to reducing the distance between
fractures. Another method for decreasing the distance between
fractures is described in U.S. Patent No. 3,835,928 issued to
Strubhar et al. Disclosed therein is a method for drilling a
deviated well~ore in a direction substantially normal to the
preferred induced fracture orientation and then creating multiple
vertical fractures from the deviated wellbore. This was
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accomplished ~y selecting individual locations along the wellbore
and alternately perforating and treating each set of perforations
individually. The normal practice in deviated wellbores is to
perforate with a high shot density to create a single, vertical
fracture.
Therefore, what is needed is a method to create
simultaneously, multiple vertical fractures in a deviated wellbore
located in a subterranean formation or reservoir.
This invention is directed to a limited entry method for
inducing simultaneous multiple vertical fractures in a deviated
wellbore which penetrates a subterranean formation. The method
comprises determining the distance the deviated wellbore must travel
to obtain the most effective and efficient recovery of a desired
material; drilling a deviated wellbore through a predetermined
distance to obtain the most effective and efficient recovery of the
desired material; placing a casing in the deviated wellbore;
ascertaining the number and size of perforations to be made in the
casing for forming fractures at desired locations after deciding the
fracture treatment fluid to be used, the fluid's pumping rate, and
the perforation pressure drop necessary to divert the fluid through
alI the holes, pumping conditions being applied to the treating
fluid at a pressure and rate sufficient to create simultaneously
multiple vertical fractures in the formation; perforating the
wellbore to create holes therein of the ascertained number and size
sufficient to create the fractures when a treating fluid is flowed
therethrough at an ascertained pumping rate; and placing a pressure
on the treating fluid in an amount and at a pumpirg rate sufficient
to create simultaneously multiple vertical fractures in the
formation through the holes.
The drawing is a schematic view of a deviated wellbore
having simultaneously induced, multiple vertical fractures emanating
from perforations therefrom where the wellbore is located in a
formation from which it is desired to remove resources therefrom.
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This invention is directed to a method for creating
simultaneously, multiple vertical fractures from a deviated
wellbore. It is often necessary to create multiple vertical
fractures in a formation to recover desired resources therefrom.
This is necessary because often the formation is not as permeable as
is desired. This invention, as disclosed below, can be utilized in
many applications.
One such application is for facilitating the removal of
ores from a formation containing same. Sareen et al. in U.S. Patent
No. 3,896,879, disclose a method for increasing the permeability of
a subterranean formation penetrated by at least one well which
extends from the surface of the earth into the formation. This
method comprises the injection of an aqueous hydrogen peroxide
solution containing therein a stabilizing agent through the well
into the subterranean formation. After injection, the solution
diffuses into the fractures of the formation surroundina the well.
The stabilizing agent reacts with metal values in the formation
which allows the hydrogen peroxide to decompose. The composition of
hydrogen peroxide generates a gaseous medium causing additiona
fracturing of the formation. Sareen et al. utilize a method for
increasing the fracture size to obtain increased removal of copper
ores from a formation. Utilization of the present invention will
increase permeability by creating additional fractures.
In addition to removiny ores, particularly copper ores and
iron ores from a formation, the present invention can be used to
recover geothermal energy more efficiently ~y the creation of more
fractures. ~ method for recovering geothermal energy is disclosed
in U.S. Patent No. 3,863,709 which issued to Fitch on February 4,
197~. Disclosed in this patent is a method and system for
recovering geothermal energy from a subterranean geothermal
formation having a preferred vertical fracture orientatlon. At
least two deviated wells are provided which extend into the
geothermal formation in a direction transversely of the preferred
vertical fracture orientation. ~ plurality of vertical fractures
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are hydraulically formed to intersect the devîated wells. A fluid
is thereafter injected via one well into the fractures to absorb
heat from the geothermal formation and the heated Fluid is recovered
from the formation via another well.
The present invention can also be used to remove thermal
energy produced during in situ combustion of coal by the creation of
additional fractures. A method wherein thermal energy so produced
by in situ combustion of coal is disclosed in U.S. Patent No.
4,019,577 which issued to Fitch et al. on April 26, 1977. Disclosed
therein is a method for recovering thermal energy from a coal
formation which has a preferred vertical fracture orientation. An
injection well and a production well are provided to extend into the
coal formation and a vertical fracture is formed by hydraulic
fracturing techniques. These fractures are propagated into the coal
formation to communicate with both the wells. The vertical fracture
is propped in the lower portion only. Thereafter, a
combustion-supporting gas is injected into the propped portion of
the fracture and the coal is ignited. Injection of the
combustion-supporting gas is continued to propagate a combustion
zone along the propped portion of the fracture and hot production
gases generated at the combustion zone are produced to recover the
heat or thermal energy of the coal. Water may also be injected into
the fracture to transport the heat resulting from the combustion of
the coal to the production well for recovery theref`rom. Both the
injection and production wells can be deviated wells which penetrate
the coal formation in a direction transversely o~ the preferred
fracture orientation.
Recovery of thermal energy from subterranean formations can
also be used to generate steam. A method for such recovery is
disclosed in U.S. Patent No. 4,015,663 which issued to Strubhar on
April S, 1977.
In the practice of this invention, as shown in the drawing,
a deviated wellbore 12 is placed into the pay zone of formation 10.
The wellbore 12 goes through formation 10 from which formation it is
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desired to remove a subterranean resource such as iron, copper ore,
uranium ore! geothermal heat, coal, oil shale or hydrocarbonaceous
fluids. A deviated well is drilled through formation 1~ in a
direction sufficiently normal to the preferred fracture orientation
which is perpendicular to the least principal in-situ horizontal
stress into which it is desired to induce simultaneously, multiple
vertical fractures.
Methods for determining the preferred fracture orientation
are described by Slusser in U.S. Patent No. 3,547,198~ As taught
therein, the preferred fracture orientation exists because of
naturally occurring planes or weakness in the earth's formations.
It is known that the subterranean formations adjoin in a manner
similar to surface rock. Therefore, surface measurements may be
employed as a reasonably close indication of the preferred fracture
orientation. The preferred fracture orientation may also be
determined from measurements taken in wells penetrating a
subterranean earth formation of interest. For example, impression
packer surveys may be run throughout the area to determine the
fracture orientation. Borehole Televiewer surveys offer a
particularly good method of determining the preferred fracture
trends. Borehole Televiewer surveys are discussed in an article by
~. Zemanek et al., entitled "The Borehole Televiewer -- A New
Logging Concept for Fracture ~ocation and Other Types of 80rehole
and Inspection," Journal of Petroleum Technology, Vol. XXI (June,
1969), pp. 762-774. Other methods for determining the preferred
orientation are described in U.S. ~atent No. 3,285,335.
When the position of the fracture plane is determined, the
direction of the slanted hole may be described either in terms of
the angle it makes with the direction of maximum principal stress or
in terms of the angle of incidence which the borehole makes with the
fracture plane, the angle of incidence being the angle between the
line of the slanted borehole and the line parallel to the fracture
plane at the point of intersection of the borehole and the plane.
This angle can be any angle that allows traverse of the
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hydrocarbonaceous formation with a directional component normal to
the preferred fracture orientation. To minimize the amount of hole
drilled to permit the creation of several vertical fractures, this
angle is from 10 to 90, preferably 30 or larger.
Another angle to consider is the angle of deviation from
vertical of the wellbore as it passes through the formation of
interest. This angle is critical to the amount of borehole exposed
to the formation of interest from which multiple fractures can be
simultaneously created. This angle should be lû to ~0. In the
drawing, the angle of deviation is depicted as 70 from vertical as
one example.
Wellbore 12 will have a casing therein. Wellbore 12 is
deviated at least in the lower portion thereof such that it
penetrates the subterranean formation 10 at an angle of at least 10
measured from the vertical and in an azimuth direction transversely
to the preferred fracture orientation. If a casing is utili~ed, it
is cemented into wellbore 12. Thereafter, the casing is selectively
perforated in a manner so that in subseauent fracture treatments,
fluids beino pumped therein will pass through all perforations at a
substantial rate. Thus, limited perforations will be required and
matched to the pump rate to achieve a pressure drop across the
perforations resulting in diversion of fluid through all holes. The
pumping rate should be at least one to 10 barrels per fracture where
each fracture emanates from one or more holes so as to result in a
pressure drop of 1380 kPa (200 psi) or more across the hole(s).
Borehole 12 is perforated to provide a plurality of perforations at
preselected intervals therein. These perforations are spaced 3-to
3û meters (10 to lûû feet) apart so the desired fracture spacing can
be obtained. Such perforations may at each level comprise two sets
of perforations which are simultaneously formed on opposite sides of
the borehole 12. A set can be one or more perforations.
Preferably, these perforations should have diameters between ~.4 mm
and 12.7 mm (1/4 and 1/2 of an inch) and should be placed
circumferentially about the casing in the anticipated plane of the
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F-4109
induced fracture. Other perforating techniques that will achieve
limited entry conditions while permitting simultaneous creation of
multiple, vertical fractures may be employed and will be apparent to
those skilled in the art.
Perforations will be placed in borehole 12 in a manner such
as to obtain the predetermined proper distance between fractures
based upon reservoir characteristics. This determination is made in
order to balance the effective reservoir drainage with the highest
degree of profitability.
lo To create the desired simultaneous, multiple vertical
fractures, wellbore 12 is perforated such that the horizontal
distance between individual or clusters of perforations is
equivalent to the preferred distance between fractures. The number
and size of perforations are determined by the fracture treatment
pumping rate and the pressure drop neoessary to divert fluid through
all holes.
Qeferring to the drawina, the distance between vertical
fractures i6 determined to be 6 meter~ (20 faet). ~he formation
thiaknese 1~ 30 meters (100 feet). The horizontal distanoe the
deviated wellbore 12 w~ll travel 1~ determlned to b~ 91 meters(30o
feet). ~ wellbore is drilled into the pay zone of formation 10
which is approximately 70 from vertical, permitting approximately
16 fractures to be induced from the wellbore intersecting formation
10. Assuming that a pumping rate of 795 liters/minute (five barrels
per minute9 BPM) per fracture is a minimum rate suitable to achieve
adequate fracture growth, the total pump rate for the 16 fractures
would be 12720 liters/minute (80 BPM~. By utilizing 12.7 mm (0.5
inch) perforations, two perforations per fracture (a total of 32
holes) would result in a 1793 kPa (260 psi) pressure drcp across
perforations according to Figure 7-1~, page 104, SPE Monograph 1 by
G. C. Howard and C. R. Fast This pressure drop is sufficient to
successfully divert fracturing fluid through all perforations. Upon
application of the determined pressure at the determined rate
through the perforations, simultaneous, multiple vertical ~ractures
are produced in formation 10.
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Fracturing fluids which can be utilized include simple
Newto,nian fluids, gels described as Power Law fluids, and acids.
Use of acids for a fracturing fluid is discussed in U~S. Patent No.
4,249,609 issued to Haafkens et al. on February 10, 1981.
Usq of a gel as a fracturing fluid is disclosed in U.S.
Patent No. 4,415,035 i~sued to Medlin et al. on
November 15, 1983.
In a preferred mode of operation? perforations 14 as shown
in the drawing can be treated, or "broken down" prior to pumping the
main fracture treatment. A suitable "breakdown" treatment can
consist of pumping an acid such as hydrochloric acid of a
concentration of 7. 5 vol. % at 3180 llter~/minute (20 ~PM). B~ll
sealers can be included in the acid to plug off perforations 14
receiving the acid. This would allow other perforations to be
lS opened.
Following the breakdown treatment~ the main ~racturing
treatment would be pumped into wellbore 12 starting with a pre-pad
or pad volume prior to pumping a fluid laden with proppant. Acid,
such as hydrochloric acid, could be used in place of a proppant
laden fracturing fluid to achieve fracture conductivity by ~ormation
etching in a carbonate reservoir. It can also be used as a means
for substantially opening up perforations to accept fracturing
fluids. The acid can also be used as a carrier for the proppant
should a proppant be desired. Treatment volumes for utilization can
be selected on the basis of the design specification to achieve the
specific ~racture dimensions desired.
Use of this limited entry fracture treatment in a deviated
wellbore can achieve close fracture spacing without drilling
individual wells. It can also result in effective reservoir
drainage even in very low permeability reservoirs.
Another application of this technology can be utili7ed in
reservoirs that contain natural fractures upon which well
productivity is highly dependent. This would result because the
deviated wellbore itself can likely intersect more natural fractures
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than a vertical well. Equally important, multiple induced vertical
fractures would greatly increase the number of intersections with
the natural fracture network. Spacing of the induced fractures can
be selected on the basis of apparent distribution of the natural
fractures.
Vertical simultaneous fractures induced in the deviated
wellbore of the present invention would permit secondary and
tertiary recovery techniques to be used effectively in low
permeability reservoirs where use of current technology is
impractical. Utilization of the present invention in combination
with the injection of secondary and tertiary recovery fluids would
result in the production of reservoir fluids from alternate pairs of
fractures in an effective manner within practical time limits.
Although the present invention has been described with
preferred embodiments, it is to be understood that modifications and
variations may be resorted to without departing from the spirit and
scope of this invention, as those skilled in the art would readily
understand.
