Note: Descriptions are shown in the official language in which they were submitted.
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METHOD AND SYSTEM FOR FRACTURE STIMULATION BY FORMATION
DISPLACEMENT
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional Application
No.
61/407,249, filed October 27, 2010 entitled METHOD AND SYSTEM FOR FRACTURE
STIMULATION, and also claims the benefit of U.S. Provisional Application No.
61/544,766, filed October 7, 2011 entitled METHOD AND SYSTEM FOR FRACTURE
STIMULATION BY FORMATION DISPLACEMENT. This application is related to
concurrently filed International Patent Application, Attorney Docket No.
2010EM298-A,
entitled "Method and System for Fracture Stimulation by Cyclic Formation
Settling and
Displacement".
FIELD OF THE INVENTION
[0002] Exemplary embodiments of the present techniques relate to a method
and system
for fracture stimulation of subterranean formations to enhance the recovery of
hydrocarbons.
Specifically, an exemplary embodiment provides for creating fractures and
other flow paths
by delamination and rubblization of formations.
BACKGROUND
[0003] This section is intended to introduce various aspects of the art
that may be
topically associated with exemplary embodiments of the present techniques.
This discussion
is believed to assist in providing a framework to facilitate a better
understanding of particular
aspects of the present techniques. Accordingly, it should be understood that
this section
should be read in this light, and not necessarily as admissions of prior art.
[0004] As hydrocarbon reservoirs that are easily harvested, such as
reservoirs on land or
reservoirs located in shallow ocean water, are used up, other hydrocarbon
sources must be
used to keep up with energy demands. Such reservoirs may include any number of
unconventional hydrocarbon sources, such as biomass, deep-water oil
reservoirs, and natural
gas from other sources.
[0005] One such unconventional hydrocarbon source is natural gas produced
from rocks
that form unconventional gas reservoirs, including, for example, shale and
coal seams.
Because unconventional gas reservoirs may have insufficient permeability to
allow
significant fluid flow to a wellbore, many of such unconventional gas
reservoirs are currently
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not considered as practical sources of natural gas. However, natural gas has
been produced
for years from low permeability reservoirs having natural fractures.
Furthermore, a
significant increase in shale gas production has resulted from hydraulic
fracturing, which can
be used to create extensive artificial fractures around wellbores. When
combined with
horizontal drilling, which is often used with wells in tight gas reservoirs,
the hydraulic
fracturing may allow formerly unpractical reservoirs to be commercially
viable.
[0006] The fracturing process is complicated and often requires numerous
hydraulic
fractures in a single well and numerous wells for an economic field
development. Thus,
more efficient fracturing processes may provide a more productive reservoir.
In other words,
a greater amount of the gas or other hydrocarbon, trapped in a relatively non-
porous
reservoir, such as a tight gas, tight sand, shale layer or even a coal seam
may be harvested.
Accordingly, numerous researchers have explored ways to improve fracturing.
[0007] For example, U.S. Patent No. 3,455,391, to Matthews, et al.,
discloses a process
for horizontally fracturing subterranean earth formations. The process is
performed by
injecting a hot fluid at high pressure, until vertical fractures are formed
and then closed due to
thermal expansion of the earth formation. A fluid is then injected at a
pressure sufficient to
form horizontal fractures.
[0008] A similar process is disclosed in U.S. Patent No. 3,613,785, to
Closman and
Phocas. In this process a wellbore is extended into the formation and a
vertical fracture is
generated by pressurizing the borehole. A hot fluid is injected into the
formation to heat the
formation, until thermal stressing of the formation matrix material causes the
horizontal
compressive stress in the formation to exceed the vertical compressive stress
at a location
selected for a second well. Hydraulically fracturing the formation through
this second well
can form a horizontal fracture extending into the formation.
[0009] Other approaches have focused on relieving stress in the formation,
for example,
by cavitation of the formation. For example, U.S. Patent No. 5,147,111, to
Montgomery,
discloses a method for cavity induced stimulation of coal degasification
wells. The method
can be used for improving the initial production of fluids, such as methane,
from a coal seam.
To perform the method, a well is drilled and completed into the seam. A tubing
string is run
into the hole and liquid carbon dioxide is pumped down the tubing while a
backpressure is
maintained on the well annulus. The pumping is stopped, and the pressure is
allowed to build
until it reached a desired elevated pressure, for example, 1500 to 2000 psia.
The pressure is
quickly released, causing the coal to fail and fragment into particles. The
particles are
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removed to form a cavity in the seam. The cavity can allow expansion of the
coal, potentially
leading to opening of cleats within the coal seam.
[0010] A similar concept has been described in Ukraine Patent No. 35282,
which
discloses another method for coal degasification, but through subsurface
gasification of an
underburden coal seam (a coal seam that underlies the gas-containing
formation). In this
process, wellbores are drilled through an underburden coal bed so that a
gasification catalyst
can be applied. Once gasification occurs and lowers the underburden pressure
due to
depletion, subsidence of the overburden (e.g., the layer containing the gas)
occurs due to
gravitational loading. The subsidence can potentially create microfractures
within the
overburden reservoir, thereby allowing improved gas migration to the degassing
wells.
[0011] It has also been noted that vertical wells and mining processes can
lower stress
points on coal seams, leading to increases in the production of coal bed
methane. For
example, S. Sang, et al., "Stress relief coalbed methane drainage by surface
vertical wells in
China," International Journal of Coal Geology, Volume 82, 196-203 (2010),
presents a
summary of studies on improved coalbed methane production by stress relief The
paper
summarizes the status of engineering practice, technology, and research
related to stress relief
coalbed methane (CBM) drainage using surface wells in China during the past 10
years.
Comments are provided on the theory and technical progress of this method. In
high gas
mining areas, such as the Huainan, Huaibei and Tiefa mining areas,
characterized by heavily
sheared coals with relatively low permeability, stress relief CBM surface well
drainage has
been successfully implemented and has broad acceptance as a CBM exploitation
technology.
The fundamental theories underpinning stress relief CBM surface well drainage
include
elements relating to: (1) formation layer deformation theory, vertical zoning
and horizontal
partitioning, and the change in the stress condition in mining stopes; (2) a
theory regarding an
Abscission Circle in the development of mining horizontal abscission fracture
and vertical
broken fracture in overlaying rocks; and (3) the theory of stress relief
inducing permeability
increase in protected coal seams during mining; and the gas
migration¨accumulation theory
of stress relief CBM surface well drainage.
[0012] Other techniques for increasing production from coal beds, and other
reservoirs,
have focused on in-situ pyrolysis of hydrocarbons in a reservoir, followed by
production of
hydrocarbons from the reservoir. All of these techniques above have focused on
the
treatment of the hydrocarbon reservoir itself Further, some techniques have
taught that
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relieving a stress on a reservoir may enhance the production of hydrocarbons,
for example, by
allowing cleats to open up in coal seams.
[0013] Related information may be found in S.E. Laubach, et al.,
"Characteristics and
origins of coal cleat: A review," International Journal of Coal Geology 35
(1998), 175-207;
Ian Palmer, "Coalbed methane completions: A world view," International Journal
of Coal
Geology 82 (2010), 184-195; Jack A. Pashin, "Stratigraphy and structure of
coalbed methane
reservoirs in the United States: An overview," International Journal of Coal
Geology 35
(1998), 209-240; Pablo F. Sanz, et al., "Mechanical models of fracture
reactivation and slip
on bedding surfaces during folding of the asymmetric anticline at Sheep
Mountain,
Wyoming," Journal of Structural Geology 30 (2008), 1177-1191; V. Palchik,
"Localization
of mining-induced horizontal fractures along formation layer interfaces in
overburden: field
measurements and prediction," Environ. Geol. 48 (2005), 68-80; and Stephen P.
Laubach, et
al., "Differential compaction of interbedded sandstone and coal," from:
Cosgrove, J.W. and
Ameen, M.S. (eds.), Forced Folds and Fractures, Geological Society of London,
Special
Publications, 169,51-60 (The Geological Society of London 2000).
SUMMARY
[0014] An embodiment of the present techniques provides a method for
fracturing a
hydrocarbon-bearing (HC-bearing) subterranean formation, more particularly by
directly
effecting either increasing stress and strain, or decreasing stress and strain
upon or within a
formation or portion of a formation that is proximately adjacent to a HC-
bearing formation
that provides the primary hydrocarbon source for desired HC production. The
directly
applied stress and strain (whether increased, decreased, or cycled through
both effects) is
applied in a method that indirectly translates or effects the stress and
strain upon the targeted
HC-bearing formation, thereby effecting structural or stratagraphic
alterations, fractures,
rubblization, or other desired effects that increases effective permeability
within the HC-
bearing formation to enable movement of at least a portion of the previously
flow-restricted
hydrocarbons toward a wellbore. The method includes causing a bulk volumetric
increase or
deformation in a zone or formation proximate to the subterranean formation so
as to apply or
affect a resultant mechanical stress and induced strain or deformation to the
proximately
adjacent HC-bearing subterranean formation. In another embodiment, the present
techniques
may comprise cyclically increasing and decreasing the applied stress to
facilitate imparting in
the HC-bearing formation, the desired permeability change. Some methods may
also create a
formation matrix distortion hysteresis in the HC-bearing formation structure
that yields
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improved effective permeability. For simplicity purposes, all such formation
changes,
subductions, deformations, distortion, cleaving, fracturing, rubblization,
microfracturing, or
other formation shape or strain changes may be referred to generally as a
volumetric
"decrease" or volumetric "increase" in bulk formation volume (or volumetric
"increase," as
appropriate, such as in a cyclic operation) of both the directly treated
formation and the
indirectly affected HC-bearing formation, even when an actual volumetric
decrease or
increase is not actually affected, but is merely facilitated by plastic or
elastic formation
displacement or compression of the treatment and/or HC-bearing formations
and/or
compression or displacement of remote compressible or incompressible strata
and/or fluid.
[0015] In one aspect, the inventive methods include a method for fracturing
a
subterranean formation, comprising causing a volumetric increase in a zone
proximate to the
subterranean formation so as to apply a mechanical stress to the subterranean
formation. In
another aspect, the improved technology provides a method for fracturing a
subterranean
formation, comprising applying stress in a zone proximate to the subterranean
formation to
indirectly translate a mechanical stress to the subterranean formation and
effect a
permeability increase within the subterranean formation. For consistency and
simplicity of
explanation purposes, the zone that is initially treated, stressed or other
wise affected with the
applied stress may be referred to as the zone proximate, while the zone that
contains the
desired hydrocarbons or other fluids, may be referred to as the subterranean
formation. The
zone proximate and the subterranean formation may be immediately adjacent or
in contact
with each other, or may be subset of the same general formation, or may be
separated by
intermediate formations, layers, or lenses of strata.
[0016] In other aspects, the methods may include steps whereby the
permeability
increase is effected by creation of a fracture network in the subterranean
formation. In some
embodiments, the applied stress in the zone proximate effects a volumetric
increase in the
within the zone proximate. In some instances, the stress in the zone proximate
causes at least
a portion of the zone proximate to arch against at least a portion of the
subterranean
formation, producing a fracture network in at least a portion of the arched
portion of the
subterranean formation. In still other methods, the applied stress in the zone
proximate
produces a stress reduction in the in-situ stress of the zone proximate and
enables the
subterranean formation to arch toward at least a portion of the zone
proximate, producing a
fracture network in the arched at least a portion of the subterranean
formation. In most
instances, the effected permeability increase results from creation of a
fracture network
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within an arched portion of the subterranean formation, whereby the
subterranean formation
may be cause to arch toward or away from the zone proximate.
[0017] In another aspect, the inventive methods include a method for
production of a
hydrocarbon from a reservoir, comprising: penetrating a hydrocarbon bearing
subterranean
formation and a zone proximate with a wellbore; applying stress to the zone
proximate to the
subterranean formation to indirectly affect a mechanical stress to the
subterranean formation
to arch at least a portion of the subterranean formation and thereby effect
enhanced
permeability within the arched portion of the subterranean formation; and
extracting
hydrocarbons from the enhanced permeability subterranean formation into the
wellbore.
[0018] In yet another embodiment, the present methods include a hydrocarbon
production
system, comprising: a hydrocarbon bearing subterranean formation; a zone
proximate to the
hydrocarbon bearing subterranean formation; a stimulation well drilled to the
zone
proximate; and a stimulation system configured to applying stress in the zone
proximate to
the subterranean formation to indirectly affect a mechanical stress to the
hydrocarbon bearing
subterranean formation and effect a volumetric increase within the hydrocarbon
bearing
subterranean formation.
[0019] Another embodiment of the present techniques provides a method for
production
of a hydrocarbon from a reservoir. The method includes expanding a zone below
a
hydrocarbon reservoir to mechanically stress the hydrocarbon reservoir and
create an arch in
the hydrocarbon reservoir. A relative movement may be created across a
fracture surface to
enhance conductivity.
[0020] Another embodiment provides a hydrocarbon production system that
includes a
hydrocarbon bearing subterranean formation, a zone proximate to the
hydrocarbon bearing
subterranean formation, a stimulation well drilled to the zone, and a
stimulation system
configured to create a volumetric increase in the zone.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] The advantages of the present techniques are better understood by
referring to the
following detailed description and the attached drawings, in which:
[0022] Fig. 1 is a diagram of a hydraulic fracturing process;
[0023] Fig. 2 is a drawing of a local stress state for an element in a
hydrocarbon bearing
subterranean formation;
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[0024] Fig. 3 is a drawing of a first mode of fracture formation, commonly
resulting from
a standard hydraulic fracturing process;
[0025] Fig. 4 is a schematic of a hydraulic fracturing process, wherein a
zone below a
reservoir is subjected to a volumetric increase, placing stress on an adjacent
reservoir layer;
[0026] Fig. 5 is a block diagram of a method for stimulation of a
hydrocarbon bearing
subterranean formation by treating a formation outside of the reservoir;
[0027] Fig. 6 is a more detailed schematic view of a delamination fracture
stimulation;
[0028] Fig. 7 is a drawing of two modes of fracture formation that may
participate in
delamination fracture stimulation as discussed herein;
[0029] Fig. 8 is a drawing of rubblization during shearing at a fracture
boundary;
[0030] Fig. 9 is a drawing of an azimuthal rotation of fracture planes
within a formation
that may occur as a result of cyclic treatment of the formation; and
[0031] Fig. 10 is a drawing of a delamination fracturing process
illustrating the use of a
separate production well and treatment well.
DETAILED DESCRIPTION
[0032] In the following detailed description section, the specific
embodiments of the
present techniques are described in connection with exemplary embodiments.
However, to
the extent that the following description is specific to a particular
embodiment or a particular
use of the present techniques, this is intended to be for exemplary purposes
only and simply
provides a description of the exemplary embodiments. Accordingly, the present
techniques
are not limited to the specific embodiments described below, but rather, such
techniques
include all alternatives, modifications, and equivalents falling within the
true spirit and scope
of the appended claims.
[0033] At the outset, and for ease of reference, certain terms used in this
application and
their meanings as used in this context are set forth. To the extent a term
used herein is not
defined below, it should be given the broadest definition persons in the
pertinent art have
given that term as reflected in at least one printed publication or issued
patent. Further, the
present techniques are not limited by the usage of the terms shown below, as
all equivalents,
synonyms, new developments, and terms or techniques that serve the same or a
similar
purpose are considered to be within the scope of the present claims.
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[0034] "Cavitation completion" or "cavitation" is a process by which an
opening may be
made in a formation. Generally, cavitation is performed by drilling a well
into a formation.
The formation is then pressurized in the vicinity of the well. The pressure is
suddenly
released, causing the material in the vicinity of the well to fragment. The
fragments and
debris may then be swept to the surface through the well by circulating a
fluid through the
well.
[0035] "Cleat system" is the system of naturally occurring joints that are
created as a coal
seam forms over geologic time. The cleat system allows for the production of
natural gas if
the provided permeability to the coal seam is sufficient.
[0036] "Coal" is a solid hydrocarbon, including, but not limited to,
lignite, sub-
bituminous, bituminous, anthracite, peat, and the like. The coal may be of any
grade or rank.
This can include, but is not limited to, low grade, high sulfur coal that is
not suitable for use
in coal-fired power generators due to the production of emissions having high
sulfur content.
[0037] "Coalbed methane" (CBM) is a natural gas that is adsorbed onto the
surface of
coal. CBM may be substantially comprised of methane, but may also include
ethane,
propane, and other hydrocarbons. Further, CBM may include some amount of other
gases,
such as carbon dioxide (CO2) and nitrogen (N2).
[0038] A "compressor" is a machine that increases the pressure of a gas by
the
application of work (compression). Accordingly, a low pressure gas (for
example, 5 psig)
may be compressed into a high-pressure gas (for example, 1000 psig) for
transmission
through a pipeline, injection into a well, or other processes.
[0039] "Directional drilling" is the intentional deviation of the wellbore
from the path it
would naturally take. In other words, directional drilling is the steering of
the drill string so
that it travels in a desired direction. Directional drilling can be used for
increasing the
drainage of a particular well, for example, by forming deviated branch bores
from a primary
borehole. Directional drilling is also useful in the marine environment where
a single
offshore production platform can reach several hydrocarbon bearing
subterranean formations
or reservoirs by utilizing a plurality of deviated wells that can extend in
any direction from
the drilling platform. Directional drilling also enables horizontal drilling
through a reservoir
to form a horizontal wellbore. As used herein, "horizontal wellbore"
represents the portion of
a wellbore in a subterranean zone to be completed which is substantially
horizontal or at an
angle from vertical in the range of from about 15 to about 75 . A horizontal
wellbore may
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have a longer section of the wellbore traversing the payzone of a reservoir,
thereby permitting
increases in the production rate from the well.
[0040] "Exemplary" is used exclusively herein to mean "serving as an
example, instance,
or illustration." Any embodiment described herein as exemplary is not to be
construed as
preferred or advantageous over other embodiments.
[0041] A "facility" is tangible piece of physical equipment, or group of
equipment units,
through which hydrocarbon fluids are either produced from a reservoir or
injected into a
reservoir. In its broadest sense, the term facility is applied to any
equipment that may be
present along the flow path between a reservoir and its delivery outlets,
which are the
locations at which hydrocarbon fluids either leave the model (produced fluids)
or enter the
model (injected fluids). Facilities may comprise production wells, injection
wells, well
tubulars, wellhead equipment, gathering lines, manifolds, pumps, compressors,
separators,
surface flow lines, and delivery outlets. In some instances, the term "surface
facility" is used
to distinguish those facilities other than wells.
[0042] "Formation" refers to a body or section of geologic strata,
structure, formation or
other subsurface solid or collected material that is sufficiently distinctive
and continuous with
respect to other geologic strata or characteristics that it can be mapped, for
example, by
seismic techniques. A formation can be a body of geologic strata of
predominantly one type
or a combination of types, or a fraction of strata having substantially common
set of
characteristics. A formation can contain one or more hydrocarbon-bearing
zones. Note that
the terms formation, hydrocarbon bearing subterranean formation, reservoir,
and interval may
be used interchangeably, but may generally be used to denote progressively
smaller
subsurface regions, zones, or volumes. More specifically, a geologic formation
may
generally be the largest subsurface region, a subterranean formation may
generally be a
region within the geologic formation and may generally be a hydrocarbon-
bearing zone (a
formation, reservoir, or interval having oil, gas, heavy oil, and any
combination thereof), and
an interval may generally refer to a sub-region or portion of a reservoir. A
hydrocarbon-
bearing zone can be separated from other hydrocarbon-bearing zones by zones of
lower
permeability such as mudstones, shales, or shale-like (highly compacted)
sands. In one or
more embodiments, a hydrocarbon-bearing zone may include heavy oil in addition
to sand,
clay, or other porous solids.
[0043] A "fracture" is a crack, delamination, surface breakage, separation,
crushing,
rubblization, or other destruction within a geologic formation or fraction of
formation not
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related to foliation or cleavage in metamorphic formation, along which there
has been
displacement or movement relative to an adjacent portion of the formation. A
fracture along
which there has been lateral displacement may be termed a fault. When walls of
a fracture
have moved only normal to each other, the fracture may be termed a joint.
Fractures may
enhance permeability of rocks greatly by connecting pores together, and for
that reason,
joints and faults may be induced mechanically in some reservoirs in order to
increase fluid
flow.
[0044] "Fracturing" refers to the structural degradation of a treatment
interval, such as a
subsurface shale formation, from applied thermal or mechanical stress. Such
structural
degradation generally enhances the permeability of the treatment interval to
fluids and
increases the accessibility of the hydrocarbon component to such fluids.
Fracturing may also
be performed by degrading rocks in treatment intervals by chemical means.
"Fracture
network" refers to a field or network of interconnecting fractures.
[0045] "Fracture gradient" refers to an equivalent fluid pressure
sufficient to create or
enhance one or more fractures in the subterranean formation. As used herein,
the "fracture
gradient" of a layered formation also encompasses a parting fluid pressure
sufficient to
separate one or more adjacent bedding planes in a layered formation. It should
be understood
that a person of ordinary skill in the art could perform a simple leak-off
test on a core sample
of a formation to determine the fracture gradient of a particular formation.
[0046] "Geomechanical stress" (including a change related thereto) or
similar phrase,
refers generally to the forces external to and/or interior to a formation
acting upon or within
such formation, which may define a stress state, condition, or property of a
formation, zone,
or other geologic strata, and/or any fluid contained therein.
[0047] "Heat source" is any system for providing heat to at least a portion
of a formation
substantially by conductive or radiative heat transfer. For example, a heat
source may
include electric heaters such as an insulated conductor, an elongated member,
or a conductor
disposed in a conduit. Other heating systems may include electric resistive
heaters placed in
wells, electrical induction heaters placed in wells, circulation of hot fluids
through wells,
resistively heated conductive propped fractures emanating from wells, downhole
burners,
exothermic chemical reactions, and in situ combustion. A heat source may also
include
systems that generate heat by burning a fuel external to or in a formation.
The systems may
be surface burners, downhole gas burners, flameless distributed combustors,
and natural gas
distributed combustors. In some embodiments, heat provided to or generated in
one or more
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heat sources may be supplied by other sources of energy. The other sources of
energy may
directly heat a formation, or the energy may be applied to a transfer medium
that directly or
indirectly heats the formation. For example, an "electrofrac heater" may use
electrical
conductive propped fractures to apply heat to the formation. In an electrofrac
heater, a
formation is hydraulically fractured and a graphite proppant is used to prop
the fractures
open. An electric current may then be passed through the graphite proppant
causing it to
generate heat, which heats the surrounding formation.
[0048] "Hydraulic fracturing" is used to create single or branching
fractures that extend
from the wellbore into reservoir formations so as to stimulate the potential
for production. A
fracturing fluid, typically a viscous fluid, is injected into the formation
with sufficient
pressure to create and extend a fracture, and a proppant is used to "prop" or
hold open the
created fracture after the hydraulic pressure used to generate the fracture
has been released.
When pumping of the treatment fluid is finished, the fracture "closes." Loss
of fluid to
permeable formation results in a reduction in fracture width until the
proppant supports the
fracture faces. The fracture may be artificially held open by injection of a
proppant material.
Hydraulic fractures may be substantially horizontal in orientation,
substantially vertical in
orientation, or oriented along any other plane. Generally, the fractures tend
to be vertical at
greater depths, due to the increased mass of the overburden. As used herein,
fracturing may
take place in portions of a formation outside of a hydrocarbon bearing
subterranean formation
in order to enhance hydrocarbon production from the hydrocarbon bearing
subterranean
formation.
[0049] "Hydrocarbon production" refers to any activity associated with
extracting
hydrocarbons from a well or other opening. Hydrocarbon production normally
refers to any
activity conducted in or on the well after the well is completed. Accordingly,
hydrocarbon
production or extraction includes not only primary hydrocarbon extraction but
also secondary
and tertiary production techniques, such as injection of gas or liquid for
increasing drive
pressure, mobilizing the hydrocarbon or treating by, for example chemicals or
hydraulic
fracturing the wellbore to promote increased flow, well servicing, well
logging, and other
well and wellbore treatments.
[0050] "Hydrocarbons" are generally defined as molecules formed primarily
of carbon
and hydrogen atoms such as oil and natural gas. Hydrocarbons may also include
other
elements, such as, but not limited to, halogens, metallic elements, nitrogen,
oxygen, and/or
sulfur. Hydrocarbons may be produced from subterranean formations through
wells
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penetrating a hydrocarbon containing formation. Hydrocarbons derived from a
hydrocarbon
bearing subterranean formation may include, but are not limited to, kerogen,
bitumen,
pyrobitumen, asphaltic or tar oil, crude oils, natural gases, and/or
combinations thereof
Hydrocarbons may be located within or adjacent to mineral matrices within the
earth.
Matrices may include, but are not limited to, sedimentary rock, sands,
silicilytes, carbonates,
diatomites, and other porous media.
[0051] A "hydraulic fracture" is a fracture at least partially propagated
into a formation,
wherein the fracture is created through injection of pressurized fluids into
the formation.
While the term "hydraulic fracture" is used, the techniques described herein
are not limited to
use in hydraulic fractures. The techniques may be suitable for use in any
fractures created in
any manner considered suitable by one skilled in the art. Hydraulic fractures
may be
substantially horizontal in orientation, substantially vertical in
orientation, or oriented along
any other plane. Generally, the fractures tend to be vertical at greater
depths, due to the
increased mass of the overburden.
[0052] "Hydraulic fracturing" is a process used to create fractures that
extend from the
wellbore into formations to stimulate the potential for production. A
fracturing fluid,
typically viscous, is generally injected into the formation with sufficient
pressure, for
example, at a pressure greater than the lithostatic pressure of the formation,
to create and
extend a fracture. A proppant may often be used to "prop" or hold open the
created fracture
after the hydraulic pressure used to generate the fracture has been released.
Parameters that
may be useful for controlling the fracturing process include the pressure of
the hydraulic
fluid, the viscosity of the hydraulic fluid, the mass flow rate of the
hydraulic fluid, the
amount of proppant, and the like.
[0053] "Imbibition" refers to the incorporation of a fracturing fluid into
a fracture face by
capillary action. Imbibition may result in decreases in permeation of a
formation fluid across
the fracture face, and is known to be a form of formation damage. For example,
if the
fracturing fluid is an aqueous fluid, imbibition may result in lower transport
of organic
materials, such as hydrocarbons, across the fracture face, resulting in
decreased recovery.
The decrease in hydrocarbon transport may outweigh any increases in fracture
surface area
resulting in no net increase in recovery, or even a decrease in recovery,
after fracturing.
[0054] "In-Situ" or "insitu" refers to a state, condition, or property of a
geologic
formation, strata, zone, and/or fluids therein, prior to changing or altering
such state,
condition, or property by an action effecting the formation and/or fluids
therein. Changes to
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the insitu properties may be effected by substantially any action upon the
formation, such as
producing or removing fluids from a formation, injecting or introducing fluids
or other
materials into a formation, stimulating a formation, causing a collapse such
as permitting a
wellbore collapse or dissolving supporting strata, removing adjacent formation
or fluid,
heating or cooling the formation, or other action that effects change in the
state, condition or
property of the formation. The insitu state may or may not be the virgin or
original state of
the formation, but is a relative term that may in fact merely reference a
state that exists prior
to undertaking some action upon the formation.
[0055] As used herein, "material properties" represents any number of
physical constants
that reflect the behavior of a rock. Such material properties may include, for
example,
Young's modulus (E), Poisson's Ratio ( ), tensile strength, compressive
strength, shear
strength, creep behavior, and other properties. The material properties may be
measured by
any combinations of tests, including, among others, a "Standard Test Method
for Unconfined
Compressive Strength of Intact formation Core Specimens," ASTM D 2938-95; a
"Standard
Test Method for Splitting Tensile Strength of Intact formation Core Specimens
[Brazilian
Method]," ASTM D 3967-95a Reapproved 1992; a "Standard Test Method for
Determination
of the Point Load Strength Index of Rock," ASTM D 5731-95; "Standard Practices
for
Preparing formation Core Specimens and Determining Dimensional and Shape
Tolerances,"
ASTM D 4435-01; "Standard Test Method for Elastic Moduli of Intact formation
Core
Specimens in Uniaxial Compression," ASTM D 3148-02; "Standard Test Method for
Triaxial
Compressive Strength of Undrained formation Core Specimens Without Pore
Pressure
Measurements," ASTM D 2664-04; "Standard Test Method for Creep of Cylindrical
Soft
formation Specimens in Uniaxial Compressions," ASTM D 4405-84, Reapproved
1989;
"Standard Test Method for Performing Laboratory Direct Shear Strength Tests of
formation
Specimens Under Constant Normal Stress," ASTM D 5607-95; "Method of Test for
Direct
Shear Strength of formation Core Specimen," U.S. Military formation Testing
Handbook,
RTH-203-80, available at "http://www.wes.army.mil/SL/MTC/handbook/RT/RTH/203-
80.pdf' (last accessed on June 25, 2010); and "Standard Method of Test for
Multistage
Triaxial Strength of Undrained formation Core Specimens Without Pore Pressure
Measurements," U.S. Military formation Testing Handbook, available at
http://www.wes.army.mil/SL/MTC/ handbook/RT/RTH/204-80.pdf '(last accessed on
June
25, 2010). One of ordinary skill will recognize that other methods of testing
formation
specimens may be used to determine the physical constants used herein.
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[0056]
"Natural gas" refers to various compositions of raw or treated hydrocarbon
gases.
Raw natural gas is primarily comprised of light hydrocarbons such as methane,
ethane,
propane, butanes, pentanes, hexanes and impurities like benzene, but may also
contain small
amounts of non-hydrocarbon impurities, such as nitrogen, hydrogen sulfide,
carbon dioxide,
and traces of helium, carbonyl sulfide, various mercaptans, or water. Treated
natural gas is
primarily comprised of methane and ethane, but may also contain small
percentages of
heavier hydrocarbons, such as propane, butanes, and pentanes, as well as small
percentages
of nitrogen and carbon dioxide.
[0057]
"Overburden" refers to the subsurface formation overlying the formation
containing one or more hydrocarbon-bearing zones (the reservoirs). For
example,
overburden may include rock, shale, mudstone, or wet/tight carbonate (such as
an
impermeable carbonate without hydrocarbons). An overburden may include a
hydrocarbon-
containing layer that is relatively impermeable. In some cases, the overburden
may be
permeable.
[0058]
"Overburden stress" refers to the load per unit area or stress overlying an
area or
point of interest in the subsurface from the weight of the overlying sediments
and fluids. In
one or more embodiments, the "overburden stress" is the load per unit area or
stress overlying
the hydrocarbon-bearing zone that is being conditioned or produced according
to the
embodiments described. In general, the magnitude of the overburden stress may
primarily
depend on two factors: 1) the composition of the overlying sediments and
fluids, and 2) the
depth of the subsurface area or formation. Similarly, underburden refers to
the subsurface
formation underneath the formation containing one or more hydrocarbon-bearing
zones
(reservoirs).
[0059]
"Permeability" is the capacity of a formation to transmit fluids through the
interconnected pore spaces of the rock. Permeability may be measured using
Darcy's Law: Q
= (k AP A) / (p. L), where Q = flow rate (cm3/s), AP = pressure drop (atm)
across a cylinder
having a length L (cm) and a cross-sectional area A (cm2), p. = fluid
viscosity (cp), and k =
permeability (Darcy). The customary unit of measurement for permeability is
the millidarcy.
The term "relatively permeable" is defined, with respect to formations or
portions thereof, as
an average permeability of 10 millidarcy or more (for example, 10 or 100
millidarcy). The
term "relatively low permeability" is defined, with respect to formations or
portions thereof,
as an average permeability of less than about 10 millidarcy. An impermeable
layer generally
has a permeability of less than about 0.1 millidarcy. By these definitions,
shale may be
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considered impermeable, for example, ranging from about 0.1 millidarcy (100
microdarcy) to
as low as 0.00001 millidarcy (10 nanodarcy).
[0060] "Porosity" is defined as the ratio of the volume of pore space to
the total bulk
volume of the material expressed in percent. Although there often is an
apparent close
relationship between porosity and permeability, because a highly porous
formation may be
highly permeable, there is no real relationship between the two; a formation
with a high
percentage of porosity may be very impermeable because of a lack of
communication
between the individual pores, capillary size of the pore space or the
morphology of structures
constituting the pore space. For example, the diatomite in one exemplary
formation type,
Belridge, has very high porosity, at about 60%, but the permeability is very
low, for example,
less than about 0.1 millidarcy.
[0061] "Pressure" refers to a force acting on a unit area. Pressure is
usually shown as
pounds per square inch (psi). "Atmospheric pressure" refers to the local
pressure of the air.
Local atmospheric pressure is assumed to be 14.7 psia, the standard
atmospheric pressure at
sea level. "Absolute pressure" (psia) refers to the sum of the atmospheric
pressure plus the
gauge pressure (psig). "Gauge pressure" (psig) refers to the pressure measured
by a gauge,
which indicates only the pressure exceeding the local atmospheric pressure (a
gauge pressure
of 0 psig corresponds to an absolute pressure of 14.7 psia).
[0062] As previously mentioned, a "reservoir" or "hydrocarbon reservoir" or
"hydrocarbon bearing subterranean reservoir" is defined as a pay or
hydrocarbon bearing
zone (for example, hydrocarbon-producing zones) that includes sandstone,
limestone, chalk,
coal, and some types of shale. Pay zones can vary in thickness from less than
one foot
(0.3048 m) to hundreds of feet (hundreds of m). The permeability of the
reservoir formation
provides the potential for production.
[0063] "Reservoir properties" and "Reservoir property values" are defined
as quantities
representing physical attributes of rocks containing reservoir fluids. The
term "reservoir
properties" as used in this application includes both measurable and
descriptive attributes.
Examples of measurable reservoir property values include impedance to P-waves,
impedance
to S-waves, porosity, permeability, water saturation, and fracture density.
Examples of
descriptive reservoir property values include facies, lithology (for example,
sandstone or
carbonate), and environment-of-deposition (EOD). Reservoir properties may be
populated
into a reservoir framework of computational cells to generate a reservoir
model.
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[0064] A
"rock physics model" relates petrophysical and production-related properties
of
a formation (or its constituents) to the bulk elastic properties of the
formation. Examples of
petrophysical and production-related properties may include, but are not
limited to, porosity,
pore geometry, pore connectivity volume of shale or clay, estimated overburden
stress or
related data, pore pressure, fluid type and content, clay content, mineralogy,
temperature, and
anisotropy and examples of bulk elastic properties may include, but are not
limited to, P-
impedance and S-impedance. A formation physics model may provide values that
may be
used as a velocity model for a seismic survey.
[0065]
"Shale" is a fine-grained clastic sedimentary formation with a mean grain size
of
less than 0.0625 mm. Shale typically includes laminated and fissile siltstones
and claystones.
These materials may be formed from clays, quartz, and other minerals that are
found in fine-
grained rocks. Non-limiting examples of shales include Barnett, Fayetteville,
and Woodford
in North America. Shale has low matrix permeability, so gas production in
commercial
quantities requires fractures to provide permeability. Shale
gas reservoirs may be
hydraulically fractured to create extensive artificial fracture networks
around wellbores.
Horizontal drilling is often used with shale gas wells.
[0066]
"Stimulated Rock Volume" (SRV) describes a relatively large formation volume
that has experienced increased permeability and associated hydrocarbon
production potential
through the use of applied (volumetric increasing) or reduced (volumetric
decreasing) stress
and strain adjusting techniques, such as but not limited to hydraulic
fracturing or other
related reservoir stimulation or stressing techniques. In one potential SRV
scenario, a
network of hydraulic fractures could be in communication with fractures that
naturally occur
in the formation so that the formation volume outside of one specific
hydraulic fracture
experiences improved reservoir properties.
[0067]
"Strain" is the fractional change in dimension or volume of the deformation
induced in the material by applying stress. For most materials, strain is
directly proportional
to the stress, and depends upon the flexibility of the material. This
relationship between
strain and stress is known as Hooke's law, and is presented by the formula: =
E -
[0068]
"Stress" is the application of force to a material, such as a through a
hydraulic
fluid used to fracture a formation. Stress can be measured as force per unit
area. Thus,
applying a longitudinal force f to a cross-sectional area S of a strength
member yields a stress
which is given by f/S.
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[0069] "Substantial" when used in reference to a quantity or amount of a
material, or a
specific characteristic thereof, refers to an amount that is sufficient to
provide an effect that
the material or characteristic was intended to provide. The exact degree of
deviation
allowable may in some cases depend on the specific context.
[0070] The force f could be compressional, leading to longitudinally
compressing the
strength member, or tensional, leading to longitudinally extending the
strength member. In
the case of a strength member in a seismic section, the force will typically
be tension.
[0071] "Thermal fractures" are fractures created in a formation caused by
expansion or
contraction of a portion of the formation or fluids within the formation. The
expansion or
contraction may be caused by changing the temperature of the formation or
fluids within the
formation. The change in temperature may change the pressure of fluids within
the
formation, resulting in the fracturing. Thermal fractures may propagate into
or form in
neighboring regions significantly cooler than the heated zone.
[0072] "Tight oil" is used to reference formations with relatively low
matrix permeability
and/or porosity where liquid hydrocarbon production potential exists. In these
formations,
liquid hydrocarbon production may also include natural gas condensate.
[0073] "Underburden" refers to the subsurface formation below or farther
downhole than
the formation containing one or more hydrocarbon-bearing zones (the
reservoirs). For
example, underburden may include rock, shale, mudstone, or wet/tight carbonate
(such as an
impermeable carbonate without hydrocarbons). An underburden may include a
hydrocarbon-
containing layer that is relatively impermeable. In some cases, the
underburden may be
permeable. The underburden may be a formation that is distinct from the HC-
bearing
formation or may be a selected fraction within a common formation shared
between the
underburden portion and the HC-bearing portion. Intermediate layers may also
reside
between the underburden layer and the HC-bearing zone.
[0074] The "Young's modulus" of a formation or rock sample is the stiffness
of the
formation sample, defined as the amount of axial load (or stress) sufficient
to make the
formation sample undergo a unit amount of deformation (or strain) in the
direction of load
application, when deformed within its elastic limit. The higher the Young's
modulus, the
harder it is to deform. It is an elastic property of the material and is
usually denoted by the
English alphabet E having units the same as that of stress.
Overview
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[0075] Exemplary embodiments of the present techniques provide techniques
for fracture
stimulation of reservoirs, or portions of a reservoir, on a large scale, up to
stimulating an
entire reservoir at once. The techniques may be used with any type of
hydrocarbon bearing
subterranean formation, such as oil, gas, or mixed reservoirs and may also be
used to fracture
other types of formations, such as formations used for the production of
geothermal energy.
In exemplary embodiments, the techniques can be used to enhance production of
natural gas
from unconventional (i.e., low permeability) gas reservoirs.
[0076] The stimulation is generally based on changes to formations other
than the target
formation itself, for example, by changing a volume of a proximate formation,
which places a
stress on the target formation. The applied stress can cause delamination of
layers and other
forms of non-hydraulic fracturing in the target formation, leading to the
formation of cracks
over a broad area. The cracks or fractures may result from a residual or
"hysteresis"
displacement of the formation components due to the strain displacement that
remains, both
while the stress is applied and after the stress is relaxed. The hysteresis
effect results from
the failure of the crack or fracture to heal completely, in the event further
fracturing happens
and/or the applied stress is reduced. Thereby, the permeability may be at
least somewhat
permanently improved. Ideally, the stress (applied initially in the zone
proximate and then
translated or otherwise promulgated into the hydrocarbon containing subsurface
formation)
creates some residual permeability in at least a portion of the targeted
subterranean formation.
The treatment duration may range from seconds, such as if explosives are used,
to months,
such as if waste tailings are used to fracture and prop open the fractures in
the zone proximate
formation. The ultimate goal is to effect fracturing within the near,
hydrocarbon-bearing
subterranean formation.
[0077] At the delaminated fractures, the formation surfaces or rock strata
within the
formation can be destroyed, forming a rubble layer or interface between the
surfaces, or the
formation surfaces offset from their original position, forming open apertures
between the
surfaces. If the volume changes in the proximate formation are repeated, the
rubblization
may be increased, forming channels through which natural gas, other
hydrocarbons, or heated
water, may be harvested. The use of an applied mechanical stress may be
considered
counterintuitive; as such stress would normally tend to close fractures or
cleats, leading to
lower production. However, in exemplary embodiments, the application of stress
may
provide increased permeability and production rates, due to delamination along
weak layers
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and rubblization within the target reservoir, as mentioned above and discussed
in further
detail below.
[0078] Fig. 1 is a diagram of a hydraulic fracturing process 100. The
traditional method
of fracture stimulation utilizes "hydraulic" pressure pumping and is a proven
technology that
has been used since the 1940s in more than 1 million wells in the United
States to help
produce oil and natural gas. In typical oilfield operations, the technology
involves pumping a
water-sand mixture into subterranean layers where the oil or gas is trapped.
The pressure of
the water creates tiny fissures or fractures in the rock. After pumping is
finished the sand
props open the fractures, allowing the oil or gas to escape from the HC-
bearing formation and
flow to a wellbore.
[0079] For example, a well 102 may be drilled through an overburden 104 to
a
hydrocarbon bearing subterranean formation 106. Although the well 102 may
penetrate
through the hydrocarbon bearing subterranean formation 106 and into the
underburden 108,
perforations 110 in the well 102 can direct fluids to and from the hydrocarbon
bearing
subterranean formation 106. The hydraulic fracturing process 100 may utilize
an extensive
amount of equipment at the well site. This equipment may include fluid storage
tanks 112 to
hold the fracturing fluid, and blenders 114 to blend the fracturing fluid with
other materials,
such as proppant 116 and other chemical additives, forming a low pressure
slurry. The low
pressure slurry 118 may be run through a treater manifold 120, which may use
pumps 122 to
adjust flow rates, pressures, and the like, creating a high pressure slurry
124, which can be
pumped down the well 102 to fracture the rocks in the hydrocarbon bearing
subterranean
formation 106. A mobile command center 126 may be used to control the
fracturing process.
[0080] The goal of hydraulic fracture stimulation is to create a highly-
conductive fracture
zone 128 by engineering subsurface stress conditions to induce pressure
parting of the
formation in the hydrocarbon bearing subterranean formation 106. This is
generally
performed by injecting fluids with a high permeability proppant 116, such as
sand, into the
hydrocarbon bearing subterranean formation 106 to overcome "in-situ" stresses
and
hydraulically-fracture the reservoir rock. The fracture zone 128 may be
considered a network
or "cloud" of fractures generally radiating out from the well 102. Depending
on the depth of
the hydrocarbon bearing subterranean formation 106, the fractures may often be
predominately perpendicular to the bedding planes, e.g., vertical within the
subsurface.
[0081] After the fracturing process 100 is completed, the treating fluids
are flowed back
to minimize formation damage. For example, contact with the fracturing fluids
may result in
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imbibement of the fluids by pores in the hydrocarbon bearing subterranean
formation 106,
which may actually lower the productivity of the reservoir. Further, a
carefully controlled
flowback may ensure proper fracture closure, trapping the proppant 116 in the
fractures and
holding them open. Stimulation is generally effective at near-well scale, for
example, in
which the fracture dimensions are in the 100s of feet. Treating and production
are often
conducted in the same interval, e.g., the portion of the hydrocarbon bearing
subterranean
formation 106 reached by the well 102. The fracturing process 100 may use
significant
amounts of freshwater and proppant materials. The orientation of the fractures
is controlled
by the local stresses in the hydrocarbon bearing subterranean formation 106 as
discussed
further with respect to Fig. 2.
[0082] Fig. 2 is a drawing of a local stress state 200 for an element 202
in a hydrocarbon
bearing subterranean formation. The state of stress in the earth is defined by
the mass of the
overburden, the pressure in the pores of the rock, the tectonic stresses
governing boundary
conditions, and the basic mechanical properties of the rock, such as Young's
modulus or
stiffness. The in-situ earth stresses determine the predominant orientation of
hydraulic
fractures. The presence of natural fractures, the configuration of the
completion itself, and
the characteristics of the treating fluids may alter the earth stresses near
the well and thereby
influence growth of hydraulic fractures for a relatively short distance away
from the well.
[0083] The earth stresses can be divided into three principal stresses
where uz is the
vertical stress in this drawing, umax is the maximum horizontal stress, while
um, is the
minimum horizontal stress, where uz> Gmax> Gmin= However, depending on
geologic
conditions, the vertical stress could be the intermediate (un,ax) or minimum
stress (a.).
These stresses are normally compressive and vary in magnitude throughout the
reservoir,
particularly in the vertical direction and from layer to layer. The magnitude
and direction of
the principal stresses are important because they control the pressure
required to create and
propagate a fracture in the reservoir, the shape of the fracture, the vertical
extent of the
fracture, the direction of the fracture, and the stresses trying to crush or
embed the propping
agent during production. Fractures in a horizontal direction, e.g.,
perpendicular to a vertically
drilled well or parallel to a horizontally drilled well, may be more effective
at conducting
hydrocarbons back to the well for production. However, in deeper wells, the
vertical stresses
may often force fractures to be predominately vertical, e.g., perpendicular to
a horizontally
drilled wellbores. As pressure on the hydrocarbon bearing subterranean
formation drops, for
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example, during production, further fracturing may be horizontal. This is
discussed in further
detail with respect to Fig. 9.
[0084] In other exemplary aspects or descriptions, the earth stresses can
be divided into
three principal stresses where uv is the vertical stress, uHmax is the maximum
horizontal stress
(similar to umax in the paragraph above) and uhmm is the minimum horizontal
stress.
Typically, these stresses are normally compressive and vary in magnitude
throughout the
reservoir, particularly in the vertical direction and from layer to layer. The
vertical stress uv,
is typically the most compressive stress, i.e., Gv> >1min.
However, depending on
geologic conditions, the vertical stress could be less compressive than the
maximum
horizontal stress, uHmax, or than the minimum horizontal stress, uhm,n.
[0085] Fractures in a horizontal direction, e.g., perpendicular to a
vertically drilled well
or parallel to a horizontally drilled well, may be more effective at
conducting hydrocarbons
back to the well for production. In deeper wells, the higher vertical stress
from the
overburden may often force fractures to be predominately vertical, e.g.,
perpendicular to a
horizontally drilled wellbore.
[0086] Fig. 3 is a drawing of a first mode (mode I) 300 of fracture
formation, commonly
resulting from a standard hydraulic fracturing process. Fractures generally
propagate in one
or more of three primary modes as discussed with respect to Figs. 3 and 7.
While, each mode
is capable of propagating a fracture, standard hydraulic fracture stimulation
predominantly
utilizes mode I 300, resulting from "direct" fluid pressure parting of the
rock. In mode I 300,
the pressure of the hydraulic fracturing fluid either creates fractures or
advances pre-existing
fractures. The fractures are propagated by tensile breaking of the formation
at the crack tip.
[0087] As noted herein, the fractures may often be nearly vertical and
approximately
perpendicular to bedding planes. At shallow depths, the fractures produced may
be
horizontal, in which case they likely will be parallel to bedding planes. In
standard hydraulic
fracturing, the hydraulic pressure and fluids directly contact the formation
being fractured or
treated. Application of the traditional hydraulic fracturing method to
unconventional
hydrocarbon resources, such as tight gas or shale gas reservoirs, requires
both large numbers
of wells and large numbers of fracture treatments in each well. These
requirements are
largely driven by the relatively small "effective" area that is created during
the hydraulic
fracturing process due to inherent limitations in the treating fluids,
proppants, reservoir
stratigraphy, and in-situ stresses. In exemplary embodiments of the present
techniques, a new
fracturing concept can be used to achieve massive fracture stimulation of
wells, particularly
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for unconventional hydrocarbon resources. In these embodiments, a volumetric
increase in a
layer adjacent to the hydrocarbon bearing subterranean formation can be used
to place a
stress on the reservoir, leading to fracturing in the reservoir.
[0088] Fig. 4 is an exemplified drawing of a well treatment system such as
a hydraulic
fracturing system 400, wherein a zone 402 below a hydrocarbon bearing
subterranean
formation 404 is subjected to a volumetric expansion 406, which can place
stress on the
hydrocarbon bearing subterranean formation 404 leading to fracturing. The
techniques are
not limited to a hydrocarbon bearing subterranean formation 404, but may be
used in any
number of situations where fracturing a formation layer would be useful, such
as in the
production of geothermal energy. In the hydraulic fracturing system 400, all
like units are as
discussed with respect to Fig. 1. In this exemplary embodiment, the drilling
and production
wastes from the field may be used for the hydraulic fracturing of the zone
402, lowering the
requirements for freshwater over standard hydraulic fracturing. Further, the
drilling cuttings
may be used to provide a proppant to maintain the fractures open in the zone
402. The
present techniques are not limited to hydraulic fracturing of the zone 402. In
embodiments,
thermal expansion may be used to create the volumetric expansion 406. Further,
a
pressurized liquid may be used to cause the volumetric expansion 406 of the
zone 402
without fracturing. The volumetric expansion 406 may be cycled by successive
thermal
heating and cooling cycles. In other embodiments, a chemical treatment may be
applied in
the zone 402 to create an area of cavitation. The present techniques are not
limited to a
chemical treatment of the zone 402. In embodiments, the volumetric contraction
406 may be
provided through production of fluids from non-hydrocarbon productive zone 402
to create
subsidence in both the non-hydrocarbon-bearing zone and in the adjacent
hydrocarbon
bearing subterranean formation 404, thereby creating a network of conductive
fractures in
both zones, including any intermediate zones, such that hydrocarbon can flow
from the HC-
bearing reservoir to the non-hydrocarbon bearing zone and finally to the
wellbore. In some
embodiments, the network of conductive fractures may facilitate production of
the
hydrocarbons directly from the HC-bearing zone directly to the wellbore or
another wellbore
that is separate from the wellbore used for the treatment process. Further, a
borehole could
be drilled in the zone 402 to induce the volumetric contraction 406. The
volumetric
contraction 406 may be enhanced by alternately injecting (for example, hours,
days, weeks,
months, even years) and then producing fluid in successive cycles.
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[0089] In some embodiments, the formation layers of interest are
mechanically damaged
or "delaminated," for example, by arching, or bending flexure, of the
hydrocarbon bearing
subterranean formation 404. The method used to treat the hydrocarbon bearing
subterranean
formation 404 would need to create the stress state to impose delamination
fracturing along
preferred layers of interest. This may occur from dilating, enlarging, or
uplifting formations
in the zone 402 from below. The delamination fractures may be created without
pressurizing
the fracture surfaces of the hydrocarbon bearing subterranean formation 404
with treating
fluids. As stimulation fluids do not need to contact the surfaces of the
formation, the
hydrocarbon bearing subterranean formation 404 may not be damaged by
imbibement of the
treating fluids. The stimulation may be effective at reservoir scale, i.e.,
the fracture
dimensions may be on the order of 1000s of feet. Further, the treating and the
production
may be conducted in different intervals, using the same or separate wells.
[0090] Fig. 5 is a block diagram of a method 500 for stimulation of a
hydrocarbon
bearing subterranean formation by treating a formation outside of the
reservoir. The method
500 begins at block 502, with the drilling and completing of a well to the
treatment interval.
The treatment interval may be a formation under the hydrocarbon bearing
subterranean
formation, as generally discussed with respect to Fig. 4. In other
embodiments, the treatment
interval may be beside or above the hydrocarbon bearing subterranean
formation, for
example, if the hydrocarbon bearing subterranean formation is in a deviated
formation. At
block 504, the treatment interval may be treated. For example, a chemical,
thermal, physical,
biological, and/or other treatment may be injected or introduced into the
treatment interval.
For further example, fracturing fluids may be injected into the treatment
interval. The
fracturing fluids may or may not include solids for proppants, such as crushed
drilling
cuttings from wells. In some embodiments, the treatment may be performed by
successively
inflating and deflating the treatment interval to cause rubblization of the
hydrocarbon bearing
subterranean formation. The treatment may be performed by reducing underburden
support
and/or pressure and thereafter providing an expansive force such as pressure
or a heat source
into the treatment interval to cause inflation of the treatment interval such
as by thermal
expansion. Such deflation and inflation may be cyclically performed.
[0091] At block 506, a production well is completed to the reservoir to
produce
hydrocarbons. The production well may be drilled after stimulation from the
treating well,
thereby reducing the potential for subsequent well integrity or reliability
issues. In
embodiments, the production well may be the same as the treatment well, for
example, by
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creating perforations in the well at the interval of the hydrocarbon bearing
subterranean
formation, or by drilling production wells from the treatment well. At block
508,
hydrocarbons may be produced from the production well. It will be clear that
the techniques
described herein are not limited to the production of hydrocarbons, but may be
used in other
circumstances where a subterranean formation is fractured to aid in the
production of fluid.
For example, in embodiments, the techniques may be used to fracture a hot dry
formation
layer for use in geothermal energy production. Water or other fluids may then
be circulated
through the fractures, collected in a production well, and returned to the
surface for
harvesting heat energy. The wells are not limited to the conformations
discussed above. In
embodiments, various treating, and producing well patterns and operational
schemes may be
considered to concurrently optimize reservoir stimulation, gas production,
waste disposal,
and well operability.
[0092] Fig. 6 is a more detailed schematic view of a delamination fracture
stimulation
600 showing the physics that may lead to delamination fracturing. A well 602
may be drilled
through a hydrocarbon bearing subterranean formation 604, and into a treatment
interval or
zone 606 below the hydrocarbon bearing subterranean formation 604. The
treatment interval
or zone 606 does not have to be adjacent to the hydrocarbon bearing
subterranean formation
604, but may have one or more intervening layers 608. These layers 608 may
lower the
chance that a treatment fluid, if used, will leak into the hydrocarbon bearing
subterranean
formation 604. Further, if waste tailing are used as proppants, the layers 608
may assist in
fixing the tailings in place, lowering the probability that material may
migrate into the
hydrocarbon bearing subterranean formation 604 or other locations, such as
aquifers.
[0093] As the treatment progresses, a volumetric expansion 610 occurs in
the treatment
interval or zone 606, which presses upwards on the layers 608, forming an arch
or dome 612
in the hydrocarbon bearing subterranean formation 604. In the embodiment
shown, fluids
and/or particulate solids are injected into the treatment interval or zone 606
to dilate, uplift,
"arch," and shear fracture the hydrocarbon bearing subterranean formation 604.
The
distance, or vertical distance, between the zone 606 and the hydrocarbon
bearing
subterranean formation 604 may control the size of the area over which the
treatment affects
the hydrocarbon bearing subterranean formation 604. A layer that is further
from the
hydrocarbon bearing subterranean formation 604 may affect a wider area, but
with a lower
total movement. For example, if a treatment of a zone 606 located around 50 m
under the
hydrocarbon bearing subterranean formation 604 caused a vertical motion of
about 2 cm over
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a distance of about 500 m, treatment of a zone 606 located about 100 m under
the
hydrocarbon bearing subterranean formation 606, using the same contaction
and/or expansion
conditions, may cause a vertical motion of about 1 cm over a horizontal
distance of about
1000 m. In addition to separation distance, the choice of the treatment zone
606 may be
made on the basis of formation properties, both in the zone 606 and in the
hydrocarbon
bearing subterranean formation 604.
[0094] In addition to separation distance, the choice of the treatment zone
606 may be
made on the basis of formation properties, both in the zone 606 and in the
hydrocarbon
bearing subterranean formation 604. A relatively impermeable formation may be
useful for
treatment using hydraulic fracturing techniques, as the zone 606 may have
lower leak-off,
making the treatment more efficient. If waste tailings are going to be used,
this may be less
of an issue, as the zone 606 may be propped open and expanded, even after
pressure has
leaked off If thermal expansion is going to be used, the zone 606 may be
selected to have a
higher coefficient of thermal expansion than other surrounding zones.
[0095] In addition to the properties of the formation within the zone 606,
the properties of
the material in the hydrocarbon bearing subterranean formation 604 may also
influence the
choice of expansion techniques and location. For example, if the hydrocarbon
bearing
subterranean formation 604 is shale, a slow expansion may not open sufficient
cracks, as a
ductile shale may have enough plastic deformation to reseal the cracks. Thus,
an explosive
deformation may cause a fast enough deformation, such as on the order of
seconds, to shatter
the shale without plastic flow resealing the cracks. In this case, the zone
606 may be selected
to have a hard rock, such as granite, that can transfer the energy of
expansion to the
hydrocarbon bearing subterranean formation 604.
[0096] A hydrocarbon bearing subterranean formation 604 may often have
weaker layers
614, or even inherent fracture planes 616. The arching can cause shear stress
in the
hydrocarbon bearing subterranean formation 604, leading to sliding or breaking
of the
hydrocarbon bearing subterranean formation 604 along these layers 614 and
fracture planes
616, as indicated by the arrows 618, creating delamination fractures 620.
Thus, the
delamination fracture stimulation 600 can create a highly-conductive multi-
fracture / dual-
porosity reservoir system by delaminating formation layers, parting formation
within layers,
and rubblizing the formation "in-situ." The injection operations may also
create relative
movement or displacement between the fracture surfaces along the layers 614
and fracture
planes 616 to achieve fracture conductivity, for example, by creating
delamination fractures
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620 that contain enhanced permeability formation debris. Vertical fractures
622 may also be
created during the delamination process. The control of stresses in the
formation may be
used to control the direction of the fractures, as discussed with respect to
Figs. 9 and 10.
[0097] In
addition to the injection of fluids, embodiments may induce delamination
fractures in the hydrocarbon bearing subterranean formation 604 using in-situ
techniques,
such as thermal heating, explosive detonations, and the like to enlarge the
volume of the
treatment interval or zone 606 and thereby increase the stresses at the target
formation
intervals such that shear-dominated fractures delaminate along, and possibly
normal to, the
bedding planes.
[0098] The
flow conductivity of the delamination fractures may be enhanced by
cyclically inflating and deflating the treatment interval or zone 606 such
that the delaminated
formations "rubblize" due to frictional contact and relative sliding motion
between formation
surfaces, creating an in-situ propped bed of failed formation material. This
is discussed
further with respect to Fig. 8.
[0099] In
contrast with the direct hydraulic fracture stimulation of a hydrocarbon
bearing
subterranean formation 604, the delamination fracture stimulation 600
minimizes direct fluid
contact with the formation fracture face, thereby reducing the potential for
formation damage
and the need for flowback clean-up. Further, fracture "conductivity" is
created in-situ over
the full fracture dimensions, thereby enhancing productivity and eliminating
the need for
transporting proppants. The fractures 620 may also extend beyond geologic
drainage
boundaries, such as faults, pinchouts and the like, reducing the number of
wells required for
economic development. The fracture delamination may be created using "waste
disposal"
products, such as drill cuttings, produced brines, and the like, to enhance
volumetric strain,
reducing the need for customized fracturing formulations and large volumes of
freshwater.
The fracture delamination or other permeability improvement also may be
created with non-
aqueous techniques to enhance volumetric strain, reducing the need for
customized fracturing
formulations and large volumes of freshwater.
[0100] In
summary, the delamination fracture stimulation 600 is based on three physical
components, including delamination, rubblization, and stress control. The
relative
importance of each of these components is dependent on the parameters of the
particular
application, for example, the depths of treatment interval or zone 606 and
hydrocarbon
bearing subterranean formation 604, the thicknesses of each interval 604 and
606, the
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formation properties, the pore pressures, the in-situ stress environments, and
the like. These
parameters are discussed in more detail with respect to Figs. 7-10.
[0101] Fig. 7 is a drawing 700 of two modes of fracture formation that may
participate in
delamination fracture stimulation as discussed herein. Both of these modes are
based on
shearing the rock, rather than tensile parting of the rock. An in-plane shear
mode 702
develops a fracture 704 that is aligned (i.e., in the same two-dimensional
plane) with the
applied shear stress 706. The in-plane shear mode 702, also termed mode II,
may develop as
an arch or bend that distorts a reservoir. Further, the in-plane shear mode
702 may develop
horizontal fractures, for example, as some layers 708 are placed under
compressive stress,
while other layers 710 are released from compressive stress. Additional mode I
300 "non-
hydraulic" tensile fractures also may be incurred from stress arching of the
reservoir.
Another mode of fracture formation is an anti-plane shear mode 712, also
termed mode III.
Similarly, the anti-plane shear mode 712 develops a fracture 714 that also is
aligned in the
same two-dimensional plane with the applied shear stress 716. This mode may
also
participate in both vertical and horizontal fractures as adjacent layers are
moved in opposite
directions. In embodiments, both mode II 702, and mode III 712, or any
combinations
thereof, may propagate damage and fractures perpendicular or parallel to
bedding planes
through the use of a volumetric increase in layers outside of a reservoir
interval. The
shearing modes may cause material to disaggregate.
[0102] Fig. 8 is a drawing of rubblization 800 during shearing 802 at a
fracture boundary
804. Direct hydraulic fracturing of a reservoir generally causes tensile
fracturing of reservoir
rocks as discussed with respect mode I shown in Fig. 3. In contrast, the
shearing 802 that
takes place in embodiments, as discussed with respect to Fig. 7, can force
formation surfaces
to slide against each other at a fracture boundary 804. Frictional engagement
of features on
the surfaces may cause the formation to break, leading to the formation of a
rubblized layer
within the fracture boundary 804.
[0103] As mentioned previously, the flow conductivity of delamination
fractures may be
enhanced by cycling the induced flexures such that the delaminated formations
"rubblize" at
the fracture boundaries 804 due to frictional contact and relative movement
between
formation surfaces. This process may create a propped bed of failed formation
material in-
situ. Based on measurements of formation debris fields created during
movements of faults,
the thickness of the rubblized zone adjacent to the delamination fractures may
up to about 20
% of the cumulative linear or transverse movement of the fracture surfaces.
Although the
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amount of formation debris created may be lower with each subsequent cycle,
significant
porosity may be created in fracture debris zones through the cyclic movement.
The failed
formation is referred to herein as Cyclic Rubblized Material ("CRM"). CRM
results in
secondary permeability, i.e., dual porosity. The cycling of the induced
flexures may also
relieve stress in the hydrocarbon bearing subterranean formation, which may
allow the
fracture planes to rotate from vertical to horizontal, as discussed with
respect to Fig. 9.
[0104] Fig. 9 is a drawing of an azimuthal rotation 900 of fracture planes
902 within a
formation that may occur as a result of cyclic treatment of the formation. The
in-situ earth
stresses determine the predominant orientation of hydraulic fractures. At
shallow depths,
hydraulic fractures generally are horizontal and easily create arching, uplift
and delamination
fractures in formation layers above. However, at deeper depths, hydraulic
fractures generally
are vertical and the horizontal stresses must be increased to locally re-
orient hydraulic
fractures.
[0105] As discussed above with respect to Fig. 2, the earth stresses can be
divided into
three principal stresses. In this case, uz is the vertical overburden stress
and is initially the
highest stress in the system. Further, (3 max is the maximum horizontal
stress, while um,. is the
minimum horizontal stress, where uv > 6max > Gmin. Although, at all depths,
injection of fluids
creates volumetric increases due to pore dilation or formation thermal
expansion, the initial
fracture plane 904 that forms with the treatment zone may be vertical, which
may not place
an effective amount of stress on the hydrocarbon bearing subterranean
formation. Specially
engineered stress conditions may shift the position of the overburden stress
to the
intermediate (max) or minimum stress (umm), especially in regions near the
well.
As a result, the axis of each successive fracture plane 902 in a cyclic
fracturing process may
be slightly shifted or rotated from the last fracture plane 902, as indicated
by an arrow 906.
This may continue until a final fracture plane 908 may be horizontal. Fracture
re-orientation
is dependent on the characteristics of the pumping treatment (i.e., fluid
rheology,
temperature, pressure, rate, solids content, treatment duration, shut-down
schedule), and
generally occurs initially about the "azimuth" axis and subsequently about the
"inclination"
axis until turning horizontal.
[0106] Fig. 10 is a drawing of a delamination fracturing process 1000
illustrating the use
of a separate production well 1002 and treatment well 1004. The techniques
described herein
are not limited to using a single well for both treatment and production. In
some
embodiments, the treatment interval 1006 may be accessed by one or more
treatment wells
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1004 other than the production well 1002 accessing the reservoir interval
1008. Furthermore,
more than one treatment well 1004 may be utilized to achieve a desired degree
of stimulation
in a production well 1002. Similarly, more than one production well 1002 may
be utilized for
a single treatment well 1004. Further, various combinations of treatment wells
1004 and
production wells 1002 may be located in sufficient proximity to create
synergistic
enhancement in their interactions.
[0107] To recap, in one embodiment, the inventive methods include a method
for
fracturing a subterranean formation, comprising applying stress in a zone
proximate to the
subterranean formation to indirectly translate a mechanical stress to the
subterranean
formation and effect a permeability increase within the subterranean
formation. A single
wellbore may be used to reach both the zone proximate and the hydrocarbon
bearing
subterranean formation, or separate wellbore may be used for access to each of
the zone
proximate and the subterranean formation. Similarly, a set of wells may be
used for
application of the principles and methods disclosed and provided herein, such
as in a field-
wide plan that utilizes numerous wellbores to effect the techniques provided
herein. The
inventive methods and systems provided herein may also be applied using any of
a variety of
wellbore configurations, such as substantially vertical wells, horizontal
wells, multi-branch
wells, deviated wellbores, and combinations thereof Similarly, the zone
proximate and
hydrocarbon bearing subterranean formation may be substantially parallel or
coplanar with
respect to each other, or situated in non-parallel planes, and each may
comprise a single
geologic formation, zone, lens, or structure, or multiple formations, zones,
lenses, or
structures. The zone proximate and hydrocarbon bearing subterranean formation
may also be
oriented substantially horizontal, vertical, deviated, folded, originally
arched, faulted, or
irregularly positioned with respect to the wellbore and each other.
[0108] In many embodiments, the desired permeability increase is effected
by creation of
a fracture network in the subterranean formation, such as by delamination
fracturing during
uplifting, down-folding or other affected movement of the subterranean
formation. The
desired permeability may also be the result of other types of fracturing, but
is noted that for
simplification purposes, all such fracturing and displacements may be referred
to herein
generally as fracturing.
[0109] The volumetric increase in the zone proximate is created by
introducing a stress-
inducing force into the zone proximate, such as via hydraulic fluid,
explosively generated
gases or pressure, thermal expansion, proppant or cuttings introduction, or
other means of
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effecting such forces. The introduced force may be residual and long lasting
or maintained
such as via hydraulic fluid introduction, or short in duration such as via
explosives. Either
such action may introduce residual volume increases, even though at least a
portion of the
volume increase may be lost when the force is removed. The action in the zone
proximate is
then translated or transferred into the objective formation, the subterranean
formation,
whereby a fracture or rubblization network is created within the subterranean
formation.
[0110] In some embodiments, stress may be introduced into the zone
proximate in the
form of, or so as to effect a reduction in, a reduction of structural support
within the zone
proximate that is then translated into at least a partially corresponding
reduction in stability in
the hydrocarbon bearing subterranean formation, resulting in creation of a
fracture or
rubblization network within the subterranean formation. Examples of effecting
a stress
reduction in the zone proximate may include freshwater dissolution of salt
from a zone
proximate, production of water or other fluids from a zone proximate to reduce
structural
support in the subterranean formation, chemical dissolution of the rock
material within the
zone proximate, physical removal of portion of the zone proximate, such as via
a network of
relatively large or underreamed wellbores within the zone proximate, and
similar actions or
treatments to reduce structural strength of the zone proximate with respect to
the in-situ, pre-
treatment, or pre-action strength. In some embodiments, application and
removal of the
stress and strain on the zone proximate may be cycled to cause subsequent
rubblization and
fracturing within the subterranean formation.
[0111] As discussed in the above paragraphs, applying stress changes to the
zone
proximate may cause the zone proximate to either arch (expand, bow, collapse,
settle, or
otherwise displace or experience growth or reduction in volume, with the
effect of such
action generally being most prominent in the vicinity of the wellbore or point
of application
or introduction, and then radiating or diffusing outwardly from the point of
such application
or introduction) toward or away from the subterranean formation, whereby the
subterranean
formation may arch compliantly as a result of such actions in the zone
proximate and as
translated through any intermediate formations. Stated differently, the
applied stress in the
zone proximate produces a stress reduction or increase in the in-situ or pre
action stress level
in the zone proximate, producing strain in the zone proximate, and enables at
least a portion
(the affected portion) of the subterranean formation to arch toward or away
from, as
appropriate, at least a portion of the zone proximate, producing a fracture
(including
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rubblization) network in at least a portion of the arched or affected portion
of the
subterranean formation.
[0112] It is noted that the techniques and methods disclosed herein are
described
generally from two different standpoints, although both are closely related.
In one
standpoint, the techniques are described in terms of creating or effecting
"volumetric
changes" (increase or decrease, or both) in the zone proximate and/or in the
subterranean
formation. As discussed herein, many of the methods used to accomplish the
objectives and
techniques disclosed herein (e.g., to fracture, rubblize, delaminate a
geologic formation
objective to create improved permeability within a hydrocarbon or other
reservoir or
formation), may effect a volumetric change in such formations or zones,
relative to an insitu
or pre-treatment state. From another standpoint, the methods herein are
described in terms of
altering the geomechanical stresses of a formation (including external and/or
internal
stresses), such alterations including volumetric changes, but also including
dislocation,
displacement, strain changes, and/or fracturing of a zone proximate or
subterranean
formation, without substantial volumetric change therein, but which otherwise
none-the-less
effect translation of force, stress, and/or energy (either applied or reduced,
as compared to
pretreatment levels) from a zone proximate to an objective subterranean
formation, The
common steps include, generally, treating a zone proximate to effect a stress
change therein
or thereupon, to effect permeability increases in a hydrocarbon bearing
subterranean
formation. Both such descriptions are within the scope of the present
inventive methods and
techniques.
[0113] As discussed herein, embodiments of the present techniques can
increase well
productivity, lessen environmental impact, enhance well integrity &
reliability, and improve
well utilization and hydrocarbon recovery. Further, production rates and the
recovery factor
may be enhanced by cyclic "rubblization" over the full formation thickness. In
contrast to
hydraulic fracturing, which is generally halted by geological drainage
boundaries, such as
faults and pinchouts, delamination fractures may extend beyond geologic
drainage
boundaries, thereby reducing the number of wells and associated environmental
footprint
required for economic development. For example, the delamination may cover an
area of
about nine times the area of the volumetric expansion.
[0114] Still other embodiments of the claimed subject matter may include:
A. A method (500) for fracturing a subterranean formation (404,
604),
comprising causing (504) a volumetric increase (406, 610) in a zone (402, 606)
proximate to
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the subterranean formation (404, 604) so as to apply a mechanical stress to
the subterranean
formation (404, 604).
B. The method of paragraph 1, wherein the zone (402, 606) is below the
subterranean formation (404, 604).
C. The method of paragraph 1, wherein the mechanical stress is applied to
only a
portion of the zone (402, 604) so as to create a bending motion in the
subterranean formation
(404, 604) and cause fractures (614, 620, 622) to form through delamination
(618).
D. The method of paragraph 1, further comprising:
reversing the volumetric increase (406, 610); and
repeating the volumetric increase (406, 610) for one or more cycles to cause
rubblization (800) along a delaminated joint (804).
E. The method of paragraph 1, wherein the subterranean formation (404, 604)
comprises a hydrocarbon formation.
F. The method of paragraph 1, wherein creating the volumetric increase
(406,
610) comprises pumping a fracturing fluid into the zone (402, 604).
G. The method of paragraph F, wherein the fracturing fluid comprises a
suspension of a proppant.
H. The method of paragraph G, wherein the proppant comprises waste product
tailings.
I. The method of paragraph 1, wherein creating the volumetric increase
(406,
610) comprises thermally expanding the zone (402, 604).
J. A hydrocarbon production system (400), comprising:
a hydrocarbon bearing subterranean formation (404);
a zone (402) proximate to the hydrocarbon bearing subterranean formation
(404);
a stimulation well (102) drilled to the zone (402); and
a stimulation system configured to create a volumetric increase (406) in the
zone
(402).
K. The hydrocarbon production system of paragraph J, wherein the
hydrocarbon
bearing subterranean formation (404) comprises an unconventional gas layer.
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L. The hydrocarbon production system of paragraph J, wherein the zone (402)
comprises a formation layer in an underburden.
M. The hydrocarbon production system of paragraph J, comprising a
production
well drilled into the hydrocarbon bearing subterranean formation (404).
N. The hydrocarbon production system of paragraph J, comprising a
production
well drilled into the hydrocarbon bearing subterranean formation (404) from
the stimulation
well (102).
[0115] Still other embodiments may include the methods disclosed in the
following
paragraphs:
1. A method for fracturing a subterranean formation, comprising applying
stress
in a zone proximate to the subterranean formation to indirectly translate a
mechanical stress
to the subterranean formation and effect a permeability increase within the
subterranean
formation.
2. The method of paragraph 1, wherein the permeability increase is effected
by
creation of a fracture network in the subterranean formation.
3. The method of paragraph 1, wherein the applied stress in the zone
proximate
affects a volumetric increase in the within the zone proximate.
4. The method of paragraph 1, wherein the stress in the zone proximate
causes at
least a portion of the zone proximate to arch against at least a portion of
the subterranean
formation, producing a fracture network in the arched at least a portion of
the subterranean
formation.
5. The method of paragraph 1, wherein the applied stress in the zone
proximate
produces a stress reduction in the in-situ stress of the zone proximate and
enables the
subterranean formation to arch toward at least a portion of the zone
proximate, producing a
fracture network in the arched at least a portion of the subterranean
formation.
6. The method of paragraph 1, wherein the effected permeability increase
results
from creation of a fracture network within an arched portion of the
subterranean formation.
7. The method of paragraph 6, wherein at least a portion of the fracture
network
results from delamination fracturing within the arched portion of the
subterranean formation.
8. The method of paragraph 1, wherein the zone proximate is below the
subterranean formation, with respect to the wellbore path.
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9. The method of paragraph 1, applying the stress to a near-wellbore
portion of
the zone proximate to the subterranean formation to bend the subterranean
formation and
cause fractures to form in the subterranean formation.
10. The method of paragraph 1, further comprising:
thereafter reducing the applied stress to reversing at least a portion of the
volumetric
increase and effect rubblization within the subterranean formation; and
thereafter reapplying the applied stress to repeat the volumetric increase to
cause
further rubblization within the subterranean formation.
11. The method of paragraph 1, wherein the subterranean formation comprises
a
hydrocarbon-bearing formation and the method further comprises extracting at
least a portion
of the hydrocarbons from the subterranean formation into a wellbore.
12. The method of paragraph 1, wherein the zone proximate comprises an
underburden formation layer.
13. The method of paragraph 1, wherein creating the volumetric increase
comprises pumping a fluid into the zone proximate.
14. The method of paragraph 13, wherein the pumped fluid comprises a
suspension of a proppant.
15. The method of paragraph 14, wherein the proppant comprises waste
product
tailings.
16. The method of paragraph 1, wherein applying the stress in the zone
proximate
comprises thermally expanding the zone proximate.
17. The method of paragraph 1, wherein applying the stress to the zone
proximate
comprises expanding the zone proximate by a pressurized fluid without
hydraulically
fracturing the zone proximate.
18. The method of paragraph 1, wherein applying the stress to the zone
proximate
comprises expanding a cavity or tunnel in the zone proximate by a pressurized
fluid.
19. The method of paragraph 1, wherein applying the stress to the zone
proximate
comprises expanding the zone proximate by a chemical reaction.
20. The method of paragraph 1, wherein applying the stress to the zone
proximate
comprises expanding the zone proximate by a pressurized fluid.
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21. The method of paragraph 1, wherein applying the stress to the zone
proximate
comprises expanding the zone proximate with explosives.
22. The method of paragraph 1, further comprising applying stress to the
zone
proximate so as to cause at least a portion of the subterranean formation to
arch in a direction
away from the zone proximate.
23. The method of paragraph 1, further comprising applying stress to the
zone
proximate by reducing the in-situ geomechanical stress in the zone proximate
so as to cause
at least a portion of the subterranean formation to arch in a direction toward
the zone
proximate.
24. A method for production of a hydrocarbon from a reservoir, comprising:
penetrating a zone proximate a hydrocarbon bearing subterranean formation with
a
wellbore;
applying stress to the zone proximate to the subterranean formation to
indirectly
translate a mechanical stress change to the subterranean formation to arch at
least a portion of
the subterranean formation and thereby effect enhanced permeability within the
arched
portion of the subterranean formation; and
extracting hydrocarbons from the enhanced permeability subterranean formation
into
the wellbore.
25. The method of paragraph 24, further comprising penetrating both the
zone
proximate and the hydrocarbon bearing subterranean formation with the
wellbore.
26. The method of paragraph 24, wherein the enhanced permeability results
from
creation of a fracture network within the arched portion of the subterranean
formation.
27. The method of paragraph 26, wherein at least a portion of the fracture
network
results from delamination fracturing within at least a portion of the arched
portion of the
subterranean formation.
28. The method of paragraph 24, wherein the hydrocarbon bearing
subterranean
formation comprises a tight gas reservoir.
29. The method of paragraph 24, wherein the hydrocarbon bearing
subterranean
formation comprises a shale gas reservoir.
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30. The method of paragraph 24, wherein the hydrocarbon bearing
subterranean
formation comprises a coal bed methane reservoir.
31. The method of paragraph 24, wherein the hydrocarbon bearing
subterranean
formation comprises a tight oil reservoir.
32. The method of paragraph 30, wherein a cleat system within the coal bed
methane reservoir is opened to enhance conductivity.
33. The method of paragraph 24, further comprising drilling a stimulation
well to
the zone proximate and applying the stress to the zone proximate from the
stimulation well;
and
extracting the hydrocarbons from a wellbore other than the stimulation well.
34. The method of paragraph 33, comprising drilling a production well from
the
stimulation well into the hydrocarbon bearing subterranean formation.
35. The method of paragraph 24, further comprising applying stress to the
zone
proximate so as to cause at least a portion of the subterranean formation to
arch in a direction
away from the zone proximate.
36. The method of paragraph 24, further comprising applying stress to the
zone
proximate by reducing the in-situ stress in the zone proximate so as to cause
at least a portion
of the subterranean formation to arch in a direction toward the zone
proximate.
37. The method of paragraph 24, further comprising drilling a production
well into
the hydrocarbon bearing subterranean formation after applying the stress to
the zone
proximate.
38. The method of paragraph 24, further comprising drilling a production
well into
the hydrocarbon bearing subterranean formation before the step of applying the
stress to the
zone proximate is completed.
39. The method of paragraph 24, further comprising cycling applying the
stress
and relieving the applies stress to cause a cycle of an expansion of the zone
proximate and a
contraction of the zone proximate to effect rubblizing a layer of material
within the
hydrocarbon bearing subterranean formation.
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40. The method of paragraph 24, further comprising:
injecting waste product tailings into the zone proximate to prop open any
fractures
within the zone proximate.
41. A hydrocarbon production system, comprising:
a hydrocarbon bearing subterranean formation;
a zone proximate to the hydrocarbon bearing subterranean formation;
a stimulation well drilled to the zone proximate; and
a stimulation system configured to applying stress in the zone proximate to
the
subterranean formation to indirectly affect a mechanical stress to the
hydrocarbon bearing
subterranean formation and effect a volumetric increase within the hydrocarbon
bearing
subterranean formation.
42. The hydrocarbon production system of paragraph 41, wherein the
hydrocarbon
bearing subterranean formation comprises a tight gas layer.
43. The hydrocarbon production system of paragraph 41, wherein the
hydrocarbon
bearing subterranean formation comprises a shale gas layer.
44. The hydrocarbon production system of paragraph 41, wherein the
hydrocarbon
bearing subterranean formation comprises a coal bed methane layer.
45. The hydrocarbon production system of paragraph 41, wherein the
hydrocarbon
bearing subterranean formation comprises a tight oil layer.
46. The hydrocarbon production system of paragraph 41, wherein the zone
comprises a formation layer in an underburden.
47. The hydrocarbon production system of paragraph 41, comprising a
production
well drilled into the hydrocarbon bearing subterranean formation.
48. The hydrocarbon production system of paragraph 41, comprising a
production
well drilled into the hydrocarbon bearing subterranean formation from the
stimulation well.
49. The hydrocarbon production system of paragraph 41, further comprising
applying stress to the zone proximate so as to cause at least a portion of the
subterranean
formation to arch in a direction away from the zone proximate.
50. The hydrocarbon production system of paragraph 41, further comprising
applying stress to the zone proximate by reducing the in-situ stress in the
zone proximate so
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as to cause at least a portion of the subterranean formation to arch in a
direction toward the
zone proximate.
51. A
method for fracturing a subterranean formation, comprising causing a
volumetric increase in a zone proximate to the subterranean formation so as to
apply a
mechanical stress to the subterranean formation.
[0116] While
the present techniques may be susceptible to various modifications and
alternative forms, the exemplary embodiments discussed above have been shown
only by
way of example. However, it should again be understood that the present
techniques are not
intended to be limited to the particular embodiments disclosed herein. Indeed,
the present
techniques include all alternatives, modifications, and equivalents falling
within the true spirit
and scope of the appended claims.
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