FIELD OF INVENTION
This invention relates to gravel packing fluids with enhanced
thermal stability for use in subterranean operations. More specifically, the
invention relates to gellable gravel packing fluids that may comprise
5 polysaccharide gelling agents and gel stabilizers to extend the working
temperature range for the polysaccharide gelling agents.
BACKGROUND TECHNICAL INFORMATION
Gravel packing operations are a type of subterranean
10 operation. Typically a gravel packing operation may be used to. reduce the
migration of unconsolidated formation particulates into a well bore. During
gravel packing operations, gravel such as sand/proppant may generally be
carried to a well bore by a gravel packing fluid, which may be gelled to
increase its viscosity and improve its ability to carry gravel. The gravel
15 packing fluid may be pumped into a well bore in which the gravel pack is to
be placed. The base fluid of the gravel packing fluid may leak off into the
subterranean zone and/or return to the surface while the gravel is left in the
zone to form a gravel pack. The resultant gravel pack may act as a filter to
separate formation sands from produced fluids while permitting the
20 produced fluids to flow into the wellbore. Typically, gravel pack operations
may involve placing a gravel pack screen in the wellbore and packing the
surrounding annulus between the screen and the wellbore with gravel
designed to prevent the passage of formation sands through the pack. Such
gravel packs may be used to stabilize the formation while causing minimal
25 impairment to well productivity. Screenless gravel packing operations may
also be performed.
Gravel packing fluids used in gravel packing operations may
typically be a gel formed by viscosifying aqueous-based fluids (e.g., a brine)
with a gelling agent, inter alia, to improve its ability to carry gravel. One
30 example of a common gelling agent includes polysaccharide gelling agents,
such as xanthan and diutan. At elevated temperatures, however, the
viscosity of the gravel packing fluids that use the polysaccharide gelling
agents may be diminished. For example, the gelled gravel packing fluids
may break into lower viscosity fluids before their intended downhole
function is completed. If the gravel starts to settle out of the gravel packing
fluid before completion of the operation, the gravel packing operation may
5 be unsuccessful leaving an incomplete and/or improper gravel pack. The
premature breaking of gelled gravel packing fluids can be particularly
problematic in high temperature subterranean formations, where the
elevated formation temperature decreases the gel stability and accelerates
gel decomposition. Due to premature breakage, xanthan gelling agents may
10 be limited to formations having bottom hole static temperatures ("BHST")
of about 220 °F or lower, while diutan gelling agents may be limited to
BHST's of about 270 °F or lower.
As subterranean operations are being conducted in deeper
wellbores having ever higher formation temperatures, the issues with long-
15 term gel stability are becoming an increasingly common issue as existing,
gels are being pushed to their chemical and thermal stability limits.
BRIEF DESCRIPTION OF THE DRAWINGS
These drawings illustrate certain aspects of some examples
20 of the present invention, and should not be used to limit or define the
invention.
FIG. 1 is a schematic diagram of an example system for
preparation of a gravel packing fluid.
FIG. 2 is a schematic diagram illustrates a placed gravel pack
25 within a subterranean formation.
DESCRIPTION OF INVENTION W.R.T. DRAWINGS
Provided are compositions and methods of use for gravel
packing fluids in subterranean operations, and, more specifically, using
30 gellable gravel packing fluids comprising polysaccharide gelling agents and
gel stabilizers to extend the working temperature range for the
polysaccharide gelling agents. The gravel packing fluids may comprise an
aqueous base fluid. The gravel packing fluids may comprise a
polysaccharide gelling agent and a thermal stabilizer. The gravel packing
fluids may be stable in formations having bottom hole static temperatures up
to 350 °F. The gravel packing fluids may inhibit some crosslinkers, for
example, the gravel packing fluids may inhibit ferric ion crosslinking. The
5 gravel packing fluids may be free or essentially free of crosslinkers. The
gravel packing fluids may be free or essentially free of sulfur. The gravel
packing fluids may be used in wellbore operations of subterranean
formations having bottom hole static temperatures that are prohibitive for
use of polysaccharide gelling agents without thermal stabilizers.
10 The gravel packing fluids disclosed herein may be linear gels
that comprise an aqueous base fluid, a polysaccharide gelling agent, a
thermal stabilizer, and a prepared gravel of a specific size. Linear gels
provide superior gravel packing to crosslinked gels, and may hot incur the
pumping problems that can affect crosslinked gels, or other highly viscous
15 fluids pumped at low pressure with low shear rates. Further, linear gels may
be used with shunt tubes, without limitation, this may be because shunt
tubes can be narrow and thus crosslinked gels or highly viscous fluids may
cause more friction and potentially damage equipment. Additionally, gravel
packing jobs are typically performed at low shear rates with a low pressure
20 (e.g., below fracture pressure), and in such conditions, linear gels are able to
sufficiently suspend gravel at the desired capacity. Also, and without
limitation, linear gels may perform better in horizontal wells for the
suspension of gravel and may be easier to pump to a desired location in such
operations. In optional examples, gel stabilizers and/or gel breakers may be
25 used. In further optional examples, the gravel packing fluids may be free or
substantially free of added crosslinkers, for example, metal ions such as
ferric ions, titanium (IV) ions, cobalt (III) ions, and the like; with the
potential exception of any crosslinkers which may contact the gravel
packing fluids while in use, for example, metal ions native to or disposed
30 within a subterranean formation. In further optional examples, the gravel
packing fluids may be free or substantially free of sulfur. The linear gravel
packing fluid may have a viscosity of about 5 centipoise to about 1000
centipoise at a shear of 511 sec-1, or about 10 centipoise to about 800
centipoise at a shear of 511 sec-1, or about 10, 15, 20, 25, 30, 35, 40, 45, 50,
55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 200, 300, 500, 700, 900 centipoise at
a shear of 511 sec-1.
The gravel packing fluids disclosed herein may comprise ah
5 aqueous base fluid. The aqueous base fluid may be from any source. In
various examples, the aqueous base fluid may comprise fresh water,
acidified water, salt water, seawater, brine, or an aqueous salt solution. In
some examples, the aqueous base fluid can comprise a monovalent brine or
a divalent brine. Suitable monovalent brines, may include, for example,
10 sodium chloride brines, sodium bromide brines, potassium chloride brines,
potassium bromide brines, and the like. Suitable divalent brines may
include, for example, magnesium chloride brines, calcium chloride brines,
calcium bromide brines, and the like. In some examples, the aqueous base
fluid may be a high density brine. As used herein, the term "high density
15 brine" refers to a brine that has a density of about 8.331bs/gal to about 19.2
lb/gal or greater.
As discussed above, the gravel packing fluids may comprise
a polysaccharide gelling agent. Suitable polysaccharide gelling agents may
include xanthan, scleroglucan, diutan, succinoglycan, guar,
20 hydroxyethylcellulose, and modifications, derivatives, and combinations
thereof. The polysaccharide gelling agent may be present in the gravel
packing fluids in an amount in the range of from about 10 lb/Mgal to about
300 lb/Mgal, alternatively about 25 lb/Mgal to about 100 lb/Mgal, or about
50 lb/Mgal, 75 lb/Mgal, 150 lb/Mgal, 200 lb/Mgal, or 250 lb/Mgal. With the
25 benefit of this disclosure one of ordinary skill in the art should be able to
determine a type and amount of polysaccharide gelling agent for use in a
desired application.
The gravel packing fluids may comprise a thermal stabilizer. The
thermal stabilizers may comprise one or more non-sulfur antioxidants that
30 increase the thermal stability of the polysaccharide gelling agent. The
thermal stabilizers may include, for example, ascorbic acid, any salt of
ascorbic acid (e.g., sodium ascorbate), erythorbic acid, any salt of erythorbic
acid (e.g., sodium erythorbate), tocopherol, any derivative thereof, and any
combination thereof. The thermal stabilizers may be included in the gravel
packing fluids in an amount in a range of about 5 lb/Mgal to about 300
lb/Mgal, alternatively about 10 lb/Mgal to about 50 lb/Mgal, alternatively
about 25 lb/Mgal to about 100 lb/Mgal, or about 150 lb/Mgal, 200 lb/Mgal,
5 or 250 lb/Mgal. Without limitation by theory, the thermal stabilizers may
function by removing oxygen radicals from the gravel packing fluids-
Oxygen radicals may break the ether linkages of the polysaccharide gelling
agents. At higher temperatures, the prevalence of oxygen radicals may be
increased, leading to acceleration in the breakdown of the polysaccharide
10 gelling agents. In contrast to antioxidants that contain sulfur and may be
subject to environmental regulations, the non-sulfur antioxidants may not
damage the environment and thus, their use may be allowed in locations that
are subject to strict environmental regulations, such as the North Sea, Gulf
of Mexico, etc. With the benefit of this disclosure one of ordinary skill in
15 the art should be able to determine a type and amount of thermal stabilizer
for use in a desired application.
To further increase temperature stability, the thermal stabilizers may
be optionally combined with an antioxidant stabilizer. Examples of
antioxidant stabilizers may include hydroxylamines, for example,
20 alkylhydoxylamines such asisopropylhydroxylamine. The antioxidant
stabilizers may have a molecular weight of less than about 400. When used,
a ratio of the antioxidant stabilizers to the thermal stabilizers may range, for
example, between about 1:1 and about 3:1 .The antioxidant stabilizers may
• be included in the gravel packing fluids in an amount in a range of about 2
25 lb/Mgal to about 100 lb/Mgal, alternatively about 5 lb/Mgal to about 25
lb/Mgal, alternatively about 10 lb/Mgal to about 20 lb/Mgal, or about 50
lb/Mgal, 70 lb/Mgal, or 90 lb/Mgal. Without limitation by theory,, it is
believed that the antioxidant stabilizers may increase the effective working
temperature range of the thermal stabilizers, thus allowing the thermal
30 stabilizers to stabilize the polysaccharide gelling agents at higher
temperatures. With the benefit of this disclosure one of ordinary skill in the
art should be able to determine a type and amount of antioxidant stabilizer
for use in a desired application.
The gravel packing fluids may comprise a gravel. As used herein,
"gravel" may be any particulate manner used to filter sand or other similar
particulate solids from the production fluid or other such produced fluids.
Examples of gravel may include, sand, ceramics, any type of proppant, or
5 any type of sized solid particulate. Optionally, the gravel may be used with a
screen to aid in filtration if desired, as well as to assist in placement of the
gravel in loosely consolidated or unconsolidated formations. The gravel
may be pre-sized to a specific desirable size. If a screen is used, the gravel
may be sized at a size greater than the screen apertures. The gravel may
10 have a size in the range of about 0.0083 inch to about 0.0661 inch.
Alternatively, the gravel may have a size of 12/18, 16/30, 20/40, 30/50, or
40/70 US mesh. The gravel may be included in the gravel packing fluids in
an amount of in a range of about 0.5 pounds added per gallon to about 10
pounds added per gallon, alternatively about 1 pound added per gallon to
15 about 7 pounds added per gallon, alternatively about 2 pounds added per
gallon to about 4 pounds added per gallon, or about 6 pounds added per
gallon, 7 pounds added per gallon, or 8 pounds added per gallon. The gravel
may be carried to a subterranean formation location wherein filtration (e.g.,
sand control) is needed via the gravel packing fluid and placed in said
20 location. If the gravel packing fluids do not possess a sufficient viscosity
and/or break prematurely, the gravel may settle out of the gravel packing
fluids and a gravel pack may not be formed. With the benefit of this
disclosure one of ordinary skill in the art should be able to determine a type,
amount, and size of gravel for use in a desired application.
25 In optional examples, agel breaker may be added to the gravel
packing fluids when it is desirable to break the gravel packing fluids. In
some example, the gel breaker may be added to the gravel packing fluids
within a separate fluid. A wide variety of suitable gel breakers are well
known to one having ordinary skill in the art. Examples of which include,
30 but are not limited to oxidizers such as sodium bromate, sodium chlorate, or
manganese dioxide. In other examples the breaker can comprise a treatment
fluid having a pH of about 7 or greater, which may cause the gelled gravel
packing fluids to break. In some examples, the gel breaker may be present in
the gravel packing fluid as a delayed-release gel breaker. For example, a gel
breaker may be prepared for delayed release by encapsulating the gel
breaker in a material that is slowly soluble or slowly degradable in the
gravel packing fluid or the gel formed therefrom. Examples of encapsulation
5 materials may include, for example, porous materials (e.g., precipitated
silica, alumina, zeolites, clays, hydrotalcites, and the like), EPDM rubber,
polyvinylidene chloride, polyamides, polyurethanes, crosslinked and
partially hydrolyzed acrylate polymers, and the like. In some examples,
degradable polymers can be used to encapsulate a gel breaker. The gel
10 breaker may be included in the gravel packing fluids in an amount in a range
of aboutO.001% to about 0.5% by volume of the gravel packing fluids,
alternatively about 0.01% to about 0.3% by volume of the gravel packing, or
further alternatively, about 0.1% to about 0.2% by volume of the gravel
packing. With the benefit of this disclosure one of ordinary skill in the art
15 should be able to determine a type and amount of gel breaker for use in a
desired application.
In optional examples, the gravel packing fluids may comprise a nonemulsifier,
or any such additive used to control emulsion formation in the
gravel packing fluids. Examples of non-emulsifiers may include, but are not
20 limited to ionic and nonionic surfactants, foaming agents, and the like.
Commercial examples of non-emulsifiers includeNEA-96M' surfactant,
PEN-5M™foaming agent, and LoSurf-300M™ surfactant, all available from
Halliburton Energy Services, Inc. of Houston, Texas. The non-emulsifiers
may be included in the gravel packing fluids in an amount in a range of
25 about 0.1% v/v to about 10% v/v. For example, the non-emulsifiers may be
included in the gravel packing fluids in an amount in a range of about 1 %
v/v to about 9% v/v, alternatively about 2% v/v to about 8% v/v, or further
alternatively, about 3% v/v, about 4% v/v, about 5% v/v, about 6% v/v, or
about 7% v/v. With the benefit of this disclosure one of ordinary skill in the
30 art should be able to determine a type and amount of non-emulsifier for use
in a desired application.
In optional examples, the gravel packing fluids may comprise an
iron control agent, or any such additive used to reduce the precipitation of
iron. Examples of iron control agents may include reducing agents and
chelates; specific examples may include but are not limited to citric acid,
sodium citrate, potassium citrate, acetic anhydride. The iron control agents
may be included in the gravel packing fluids in an amount in a range of
5 about 0.01% w/v to about 1% w/v. For example, the iron control agents may
be included in the gravel packing fluids in an amount in a range of about
0.1% w/v to about 0.9%o w/v, alternatively about 0.2% w/v to about 0.8%
w/v, or further alternatively, about 0.3% w/v, about 0.4%-w/v, about 0.5%
w/v, about 0.6% w/v, or about 0.7% w/v. With the benefit of this disclosure
10 one of ordinary skill in the art should be able to determine a type and
amount of iron control agent for use in a desired application.
As discussed above, the gravel packing fluids may be used in a
subterranean formation having a bottom hole static temperature of up to
about 350 °F. For example, the gravel packing fluids may be used in a
15 subterranean formation having a bottom hole static temperature of up to
about 325 °F. Alternatively, the gravel packing fluids may be used in a
subterranean formation having a bottom hole static temperature of up to
about 300 °F. Further alternatively, the gravel packing fluids may be used in
a subterranean formation having a bottom hole static temperature of up to
20 about 275 °F. By way of example, the gravel packing fluids may be used in
subterranean formations having a bottom hole static temperature of from
about 275 °F to about 350 °F. With the benefit of this disclosure one of
ordinary skill in the art should be able to produce a gravel packing fluid for
use in a subterranean formation with a bottom hole static temperature up to
25 about 350 °F.
Those of ordinary skill in the art will appreciate that the gravel
packing fluids generally should have a density suitable for a particular
application. By way of example, the gravel packing fluids may have a
density in the range of from about 8 pounds per gallon ("lb/gal") to about 20
30 lb/gal. In certain examples, the gravel packing fluids may have a density in
the range of from about 10 lb/gal to about 17 lb/gal. Those of ordinary skill
in the art, with the benefit of this disclosure, will recognize the appropriate
density for a particular application.
The gravel packing fluids disclosed herein may be free of or
essentially free of crosslinkers. Examples of crosslinkers may include, but
are not limited to metal ions such as titanium (IV) ions, zirconium (IV) ions,
chromium (III) ions, cobalt (III) ions, aluminum (III) ions, hafnium (III)
5 ions, and the like; as well as metal ion-releasing compounds such as
coordination compounds; organic crosslinkers such as diamines, dithiols, or
diols; organic polymers such as polyesters, polyalkyleneimines (e.g.,
polyethyleneimine), or polyalkylenepolyamines. In some examples, the
gravel packing fluids may encounter crosslinkers within a subterranean
10 formation, said crosslinkers being present in the subterranean formation
previously as either a native component Of the subterranean formation or
being introduced by a prior pumped fluid. In these examples the gravel
packing fluids may be free or substantially free of "added" crosslinkers,
wherein "added" is defined as the addition of crosslinkers to the gravel
15 packing fluids during preparation of the gravel packing fluids and prior to
introduction of the gravel packing fluids in the subterranean formation.
A method for placing a gravel pack in a subterranean formation may
comprise: providing a gravel packing fluid in the form of a linear gel and
comprising an aqueous base fluid, a polysaccharide gelling agent, a thermal
20 stabilizer, and a gravel; placing the gravel packing fluid into the
subterranean formation; and allowing the gravel packing fluid to form a
gravel pack in the subterranean formation. The aqueous base fluid may
comprise a monovalent or divalent brine. The polysaccharide gelling agent
may comprise a polysaccharide gelling agent selected from the group
25 consisting of xanthan, scleroglucan, diutan, succinoglycan, guar,
hydroxyethyl cellulose, and combinations thereof. The thermal stabilizer
may be selected from the group consisting of ascorbic acid, salts of ascorbic
acid, erythorbic acid, salts of erythorbic acid, tocopherol, and combinations
thereof. The thermal stabilizer may be present in the gravel packing fluid in
30 an amount of about 5 lb/Mgal to about 300 lb/Mgal. The gravel may
comprise sand. The gravel packing fluid may further comprise an
antioxidant stabilizer, wherein the antioxidant stabilizer comprises a
hydroxylamine. The gravel packing fluid may further comprise a gel
breaker. The gravel packing fluid may be essentially free of added
crosslinkers. The bottom hole static temperature of the subterranean
formation may be greater than 200 °F.
A gravel packing fluid may comprise: an aqueous base fluid, a
5 polysaccharide gelling agent, a thermal stabilizer, and a gravel. The aqueous
base fluid may comprise a monovalent or divalent brine. The polysaccharide
gelling agent may comprise a polysaccharide gelling agent selected from the
group consisting of xanthan, scleroglucan, diutan, succinoglycan, guar,
hydroxyethyl cellulose, and combinations thereof. The thermal stabilizer
10 may be selected from the group consisting of ascorbic acid, salts of ascorbic
acid, erythorbic acid, salts of erythorbic acid, tocopherol, and combinations
thereof. The thermal stabilizer may be present in the gravel packing fluid in
an amount of about 5 lb/Mgal to about 300 lb/Mgal. The gravel may
comprise sand. The gravel packing fluid may further comprise an
15 antioxidant stabilizer, wherein the antioxidant stabilizer comprises a
hydroxylamine. The gravel packing fluid may further comprise a gel
breaker. The gravel packing fluid may be essentially free of added
crosslinkers.
A gravel packing system may comprise: a gravel packing fluid
20 comprising an aqueous base fluid, a polysaccharide gelling agent, a thermal
stabilizer, and a gravel; a production tubing; a screen coupled to the
production tubing; and a pumping system fluidically coupled to the
production tubing, wherein the pumping system is capable of pumping the
gravel packing fluid through the production tubing. The polysaccharide
25 gelling agent may comprise a polysaccharide gelling agent selected from the
group consisting of xanthan, scleroglucan, diutan, succinoglycan, guar,
hydroxyethyl cellulose, and combinations thereof. The thermal stabilizer
may be selected from the group consisting of ascorbic acid, salts of ascorbic
acid, erythorbic acid, salts of erythorbic acid, tocopherol, and combinations
30 thereof. The thermal stabilizer may be present in the gravel packing fluid in
an amount of about 5 lb/Mgal to about 300 lb/Mgal. The gravel may
comprise sand. The gravel packing fluid may further comprise an
antioxidant stabilizer, wherein the antioxidant stabilizer comprises a
hydroxylamine. The gravel packing fluid may further comprise a gel
breaker. The gravel packing fluid may be essentially free of added
crosslinkers.
Referring now to FIG. 1, the preparation of a gravel packing
5 fluid in accordance with the examples described herein will now be
described. FIG. 1 illustrates a system 2 for the preparation of. a gravel
packing fluid and subsequent delivery of the gravel packing fluid to a
location within a subterranean location. As shown, the gravel packing fluid
may be mixed in mixing equipment 4, such as a jet mixer, re-circulating
10 mixer, or a batch mixer, for example, and then pumped via pumping
equipment 6 tq the cementing application site. Mixing equipment 4 may be
used to mix the aqueous base fluid, the polysaccharide gelling agent, the
thermal stabilizer, and the gravel. In optional embodiments, the mixing
equipment 4 may be used to also mix an antioxidant stabilizer with the
15 gravel packing fluid. In some embodiments, a jet mixer may be used, for
example, to continuously mix the gravel with the aqueous base fluid as it is
being pumped to the wellbore. Additionally, batch mixer type units for the
gravel packing fluid may be plumbed in line with a separate tank containing
one or more additives. In some examples, mixing equipment 4 may be
20 coupled to pumping equipment 6.
As illustrated in FIG. 2, subterranean formation 8may
produce sand which may reduce or block flow of producing fluids. In a
subterranean formation 8 which produces sand or other undesirable solids, a
gravel packing fluid may be used to filter the sand from any produced
25 fluids. FIG. 2 illustrates a gravel pack 10, comprising gravel that has been
pre-sized to a specific size. Gravel pack 10 has been placed into a targeted
area within a subterranean formation 8. The gravel pack 10 was placed
using a gravel packing fluid as described herein. For example, the gravel
packing fluids described herein may be mixed with mixing equipment 4,
30 and then pumped into the production tubing 12 within the wellbore 14 of the
subterranean formation 8 by pumping equipment 6 (as shown in FIG. 1). As
illustrated a gravel pack 8 may then be placed into a specific target area of
the subterranean formation 8. This may be accomplished by pumping the
gravel packing fluid to the specific target area and breaking the gravel
packing fluid (e.g., with a gel breaker) and/or leaving the gravel packing
fluid in the specific target area until it breaks and/or the gravel settles out of
the gravel packing fluid. The remaining components of the gravel packing
5 fluid may then disperse into the subterranean formation 8 and/or be pumped
back Lo the surface. It is to be understood that that it is important to select
components which do not damage the subterranean formation 8 should any
of the remaining components of the gravel packing fluid disperse into the
subterranean formation 8.
10 As discussed above, the gravel packing fluids disclosed
herein allow for placement of a gravel pack 10 in subterranean formations 8
with bottom hole static temperatures of up to about 350 °F. This is
accomplished by the gravel packing fluids comprising thermal stabilizers as
disclosed herein. As illustrated by FIG. 2, once the gravel pack is in place, a
15 screen 16 may be inserted at the bottom of the production tubing 12. The
screen 16 may be optional. Screen 16 may be a wire-wrapped screen and
may aid in the filtration of sand or other solids from any of the produced
fluids. Once the gravel pack 10 is in place, produced fluids may flow out of
the subterranean formation 8 and through perforations 18 in the cement 20
20 and casing 22. The produced fluids may have sand or any other type of
solid, filtered out of the produced fluids by the gravel pack 8. The produced
fluids may flow through screen 16, should optional screen 16 be in place,
and into production tubing 12 where the produced fluids may be pumped to
the surface and collected.
25 The exemplary gravel packing fluids disclosed herein may
directly or indirectly affect one or more components or pieces of equipment
associated with the preparation, delivery, recapture, recycling, reuse, and/or
disposal of the disclosed gravel packing fluids. For example, the disclosed
gravel packing fluids may directly or indirectly affect one or more mixers,
30 related mixing equipment, mud pits, storage facilities or units, composition
separators, heat exchangers, sensors, gauges, pumps, compressors, and the
like, used to generate, store, monitor, regulate, and/or recondition the
exemplary gravel packing fluids. The disclosed gravel packing fluids may
i«»s»
also directly or indirectly affect any transport or delivery equipment used to
convey the gravel packing fluids to a well site or downhole such as, for
example, any transport vessels, conduits, pipelines, trucks, tubulars, and/or
pipes used to compositionally move the gravel packing fluids from one
5 location to another, any pumps, compressors, or motors (e.g., topside or
downhole) used to drive the gravel packing fluids into motion, any valves or
related joints used to regulate the pressure or flow rate of the gravel packing
fluids, and any sensors (i.e., pressure and temperature), gauges, and/or
combinations thereof, and the like. The disclosed gravel packing fluids may
10 also directly or indirectly affect the various downhole equipment and tools
that may come into contact with the gravel packing fluids such as, but not
limited to, wellbore casing, wellbore liner, completion string, insert strings,
drill string, coiled tubing, slickline, wireline, drill pipe, drill collars, mud
motors, downhole motors and/or pumps, cement pumps, surface-mounted
15 motors and/or pumps, centralizers, turbolizers, scratchers, floats (e.g., shoes,
collars, valves, etc.), logging tools and related telemetry equipment,
actuators (e.g., electromechanical devices, hydromechanical devices, etc.),
sliding sleeves, production sleeves, plugs, screens, filters, flow control
devices (e.g., inflow control devices, autonomous inflow control devices,
20 outflow control devices, etc.), couplings (e.g., electro-hydraulic wet
connect, dry connect, inductive coupler, etc.), control lines (e.g., electrical,
fiber optic, hydraulic, etc.), surveillance lines, drill bits and reamers, sensors
or distributed sensors, downhole heat exchangers, valves and corresponding
. actuation devices, tool seals, packers, cement plugs, bridge plugs, and other
25 wellbore isolation devices, or components, and the like.
EXAMPLES
To facilitate a better understanding of the disclosure, the
following examples of certain aspects of some embodiments are given. In
no way should the following examples be read to limit, or define, the entire
30 scope of the embodiments.
Example 1
The following series of tests were performed to evaluate the
rheology of comparative gravel packing fluids comprising a thermal
stabilizer. Four different comparative sample gravel packing fluids,
designated Samples 1-4, were prepared using at least some of the following
components as indicated in Table 1 below.
After preparation, the viscosity (cP) of the five samples was
10 determined at310°F using a Chandler Engineering® Model 5550 HTHP
Viscometer at 511 sec"'withBl bob and Rl rotor under nitrogen pressure.
The data is presented in Table 2 below. The Chandler Engineering Model
5550 HTHP Viscometer is available from Chandler Engineering® of Broken
Arrow, Oklahoma.
Example 1 thus indicates that the addition of a thermal
stabilizer to a polysaccharide gelling agent increases the stability of the
polysaccharide gelling agent at high temperatures.
Example 2
5 Sand settling tests were performed on the formulations
identified as Samples 1 and 2 as described above, such Samples having a
density of 70 lb/Mgal. For these tests, a slurry of sand and 16/30
CARBOLITE proppant (at 4 pounds of proppant added per gallon) was
filled in a marked glass liner, and then the liner was transferred to an
10 autoclave and heated under nitrogen pressure to reach the testing
temperature of 310 °F.CARBOLITE proppant is available from Carbo
Ceramics of Houston, Texas. After the test temperature was reached, the
sample was cooled for 10 minutes and depressurized. The glass liner was
then removed and the level of settled sand was noted.
As shown, the presence of a thermal stabilizer reduces sand
settling at elevated temperatures, therefore illustrating that the thermal
stabilizer improves the fluid suspension of gravel in gravel packing fluids
20 comprising polysaccharide gelling agents.
The preceding description provides various embodiments of
the systems and methods of use disclosed herein which may contain
different method steps and alternative combinations of components. It
should be understood that, although individual embodiments may be
discussed herein, the present disclosure covers all combinations of the
disclosed embodiments, including, without limitation, the different
component combinations, method step combinations, and properties of the
system. It should be understood that the compositions and methods are
5 described in terms of "comprising," "containing," or "including" various
components or steps, the compositions and methods can also "consist
essentially of or "consist of the various components and steps. Moreover,
the indefinite articles "a" or "an," as used in the claims, are defined herein to
mean one or more than one of the element that it introduces.
10 For the sake of brevity, only certain ranges are explicitly
disclosed herein. However, ranges from any lower limit may be combined
with any upper limit to recite a range not explicitly recited, as well as,
ranges from any lower limit may be combined with any other lower limit to
recite a range not explicitly recited, in the same way, ranges from any upper
15 limit may be combined with any other upper limit to recite a range not
explicitly recited. Additionally, whenever a numerical range with a lower
limit and an upper limit is disclosed, any number and any included range
falling within the range are specifically disclosed. In particular, every range
of values (of the form, "from about a to about b," or, equivalently, "from
20 approximately a to b," or, equivalently, "from approximately a-b") disclosed
herein is to be understood to set forth every number and range encompassed
within the broader range of values even if not explicitly recited. Thus, every
point or individual value may serve as its own lower or upper limit
combined with any other point or individual value or any other lower or
25 upper limit, to recite a range not explicitly recited.
Therefore, the present embodiments are well adapted to
attain the ends and advantages mentioned as well as those that are inherent
therein. The particular embodiments disclosed above are illustrative only,
and may be modified and practiced in different but equivalent manners
30 apparent to those skilled in the art having the benefit of the teachings herein.
Although individual embodiments are discussed, the disclosure covers all
combinations of all of the embodiments. Furthermore, no limitations are
intended to the details of construction or design herein shown, other than as
described in the claims below. Also, the terms in the claims have their
plain, ordinary meaning unless otherwise'explicitly and clearly defined by
the patentee. It is therefore evident that the particular illustrative
embodiments disclosed above may be altered or modified and all such
5 variations are considered within the scope and spirit of those embodiments.
If there is any conflict in the usages of a word or term in this specification
and one or more patent(s) or other documents that may be incorporated
herein by reference, the definitions that are consistent with this specification
should be adopted. •

We claim:
1. A method for placing a gravel pack in a subterranean formation
comprising:
providing a gravel packing fluid in the form of a linear gel and comprising
5 an aqueous base fluid, a polysaccharide gelling agent, a thermal stabilizer, and a gravel;
placing the gravel packing fluid into the subterranean formation; and
allowing the gravel packing fluid to form a gravel pack in the
subterranean formation.
10 2. A method as claimed in claim 1 wherein the aqueous base fluid comprises
a monovalent or divalent brine.
3. A method as claimed in claim 1 or 2 wherein the polysaccharide gelling
agent comprises a polysaccharide gelling agent selected from the group consisting of
15 xanthan, scleroglucan, diutan, succinoglycan, guar, hydroxyethyl cellulose, and
combinations thereof.
4. A method as claimed in any of claims 1 to 3 wherein the thermal
stabilizer is selected from the group consisting of ascorbic acid, salts of ascorbic acid,
20 erythorbic acid, salts of erythorbic acid, tocopherol, and combinations thereof.
5. A method as claimed in any of claims 1 to 4 wherein the thermal
stabilizer is present in the gravel packing fluid in an amount of about 5 lb/Mgal to about
300 lb/Mgal.
25
6. A method as claimed in any of claims 1 to 5 wherein the gravel comprises
sand.
7. A method as claimed in any of claims 1 to 6 wherein the gravel packing
30 fluid further comprises an antioxidant stabilizer, and wherein the antioxidant stabilizer
comprises a hydroxylamine.
8. A method as claimed in any of claims 1 to 7 wherein the gravel packing
fluid further comprises a gel breaker.
9. . A method as claimed in any of claims 1 to 8 wherein the gravel packing
fluid is essentially free of added crosslinkers.
5 10. A method as claimed in any of claims 1 to 9 wherein the bottom hole
static temperature of the subterranean formation is greater than 200 °F.
11. A gravel packing fluid comprising:
an aqueous base fluid,
10 a polysaccharide gelling agent,
a thermal stabilizer, and
a gravel.
12. A gravel packing fluid as claimed in claim 11 wherein the polysaccharide
15 gelling agent comprises a polysaccharide gelling agent selected from the group
consisting of xanthan, scleroglucan, diutan, succinoglycan, guar, hydroxyethyl cellulose,
and combinations thereof.
13. A gravel packing fluid as claimed in claim 11 or 12 wherein the thermal
20 stabilizer is selected from the group consisting of ascorbic acid, salts of ascorbic acid,
erythorbic acid, salts of erythorbic acid, tocopherol, and combinations thereof.
14. A gravel packing fluid as claimed in any of claims 11 to 13 wherein the
thermal stabilizer is present in the gravel packing fluid in an amount of about5 lb/Mgal to
25 about 300 lb/Mgal.
15. A gravel packing fluid as claimed in any of claims 11 to 14 wherein the
gravel packing fluid further comprises an antioxidant stabilizer, and wherein the
antioxidant stabilizer comprises a hydroxylamine.
30
16. A gravel packing fluid a as claimed in any of claims 11 to 15 wherein the
gravel packing fluid is essentially free of added crosslinkers.
17. A gravel packing system comprising:
a gravel packing fluid comprising an aqueous base fluid, a
polysaccharide gelling agent, a thermal stabilizer, and a gravel;
a production tubing;
a screen coupled to the production tubing; and
5 a pumping system fluidically coupled to the production tubing,
wherein the pumping system is capable of pumping the gravel packing fluid through the
production tubing.
18. A gravel packing system as claimed in claim 17 wherein the
10 polysaccharide gelling agent comprises a polysaccharide gelling agent selected from the
group consisting of xanthan, scleroglucan, diutan, succinoglycan, guar, hydroxyethyl
cellulose, and combinations thereof.
19. A gravel packing system as claimed in claim 17 or 18 wherein the thermal
15 stabilizer is selected from the group consisting of ascorbic acid, salts of ascorbic acid,
erythorbic acid, salts of erythorbic acid, tocopherol, and combinations thereof.
20. A gravel packing system as claimed in any of claims 17-19 wherein the
gravel packing fluid further comprises an antioxidant stabilizer, and wherein the
20 antioxidant stabilizer comprises a hydroxylamine.