Note: Descriptions are shown in the official language in which they were submitted.
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LOST CIRCULATION COMPOSITIONS AND METHODS OF USING THEM
BACKGROUND OF THE INVENTION
Field of the Invention
This disclosure relates to compositions for servicing a wellbore experiencing
lost
circulation. More specifically, this disclosure relates to introducing
compositions into a
wellbore penetrating a subterranean formation to reduce the loss of fluid to
the formation.
Background of the Invention
A natural resource such as oil or gas residing in a subterranean formation can
be
recovered by drilling a well into the formation. The subterranean formation is
usually isolated
from other formations using a technique known as well cementing. In
particular, a wellbore is
typically drilled down to the subterranean formation while circulating a
drilling fluid through
the wellbore. After the drilling is terminated, a string of pipe, e.g.,
casing, is run in the
wellbore. Primary cementing is then usually performed whereby a cement slurry
is pumped
down through the string of pipe and into the annulus between the string of
pipe and the walls of
the wellbore to allow the cement slurry to set into an impermeable cement
column and thereby
seal the annulus. Subsequent secondary cementing operations, i.e., any
cementing operation
after the primary cementing operation, may also be performed. One example of a
secondary
cementing operation is squeeze cementing whereby a cement slurry is forced
under pressure to
areas of lost integrity in the annulus to seal off those areas.
Subsequently, oil or gas residing in the subterranean formation may be
recovered by
driving the fluid into the well using, for example, a pressure gradient that
exists between the
formation and the wellbore, the force of gravity, displacement of the fluid
using a pump or the
force of another fluid injected into the well or an adjacent well. The
production of the fluid in
the formation may be increased by hydraulically fracturing the formation. That
is, a viscous
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fracturing fluid may pumped down the casing to the formation at a rate and a
pressure
sufficient to form fractures that extend into the formation, providing
additional pathways
through which the oil or gas can flow to the well. Unfortunately, water rather
than oil or gas
may eventually be produced by the formation through the fractures therein. To
provide for the
production of more oil or gas, a fracturing fluid may again be pumped into the
formation to
form additional fractures therein. However, the previously used fractures
first must be plugged
to prevent the loss of the fracturing fluid into the formation via those
fractures.
In addition to the fracturing fluid, other fluids used in servicing a wellbore
may also be
lost to the subterranean formation while circulating the fluids in the
wellbore. In particular, the
fluids may enter the subterranean formation via depleted zones, zones of
relatively low
pressure, lost circulation zones having naturally occurring fractures, weak
zones having
fracture gradients exceeded by the hydrostatic pressure of the drilling fluid,
and so forth. As a
result, the service provided by such fluid is more difficult to achieve. For
example, a drilling
fluid may be lost to the formation, resulting in the circulation of the fluid
in the wellbore being
too low to allow for further drilling of the wellbore. Also, a secondary
cement/sealant
composition may be lost to the formation as it is being placed in the
wellbore, thereby
rendering the secondary operation ineffective in maintaining isolation of the
formation.
Accordingly, an ongoing need exists for compositions and methods of blocking
the
flow of fluid through lost circulation zones in subterranean formations.
BRIEF SUMMARY OF SOME OF THE PREFERRED EMBODIMENTS
According to one aspect of the invention there is provided a lost circulation
composition for use in a wellbore comprising a crosslinkable polymer system
and a filler.
According to another aspect of the invention there is provided a method of
servicing a
wellbore in contact with a subterranean formation, comprising: placing a
wellbore servicing
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fluid comprising a crosslinkable polymer system and a filler into a lost
circulation zone within
the wellbore.
According to another aspect of the invention there is provided a method of
blocking the
flow of fluid through a lost circulation zone in a subterranean formation
comprising placing a
first composition comprising a packing agent into the lost circulation zone,
placing a second
composition comprising a crosslinkable polymer system and a filler into the
lost circulation
zone, and allowing the compositions to set into place.
The foregoing has outlined rather broadly the features and technical
advantages of the
present invention in order that the detailed description of the invention that
follows may be
better understood. Additional features and advantages of the invention will be
described
hereinafter that form the subject of the claims of the invention. It should be
appreciated by
those skilled in the art that the conception and the specific embodiments
disclosed may be
readily utilized as a basis for modifying or designing other structures for
carrying out the same
purposes of the present invention. It should also be realized by those skilled
in the art that such
equivalent constructions do not depart from the spirit and scope of the
invention as set forth in
the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
For a detailed description of the preferred embodiments of the invention,
reference will
now be made to the accompanying drawings in which:
Figure I is a graph of a thickening time test.
Figures 2 -5 are graphs of a static gel strength test.
Figure 6 is a graph of predicted versus observed static gel strength.
Figures 7-11 are pictures of a lost circulation composition.
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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Disclosed herein are lost circulation compositions (LCC) which may be used to
block
the flow of fluid through lost circulation zones in a subterranean formation.
The LCC may
comprise a crosslinkable polymer system and a filler. Alternatively, the LCC
may comprise a
crosslinkable polymer system, a filler and a packing agent. LCCs such as those
disclosed
herein may be used to block the flow of fluid through pathways such as
fractures filled with
water, voids or cracks in the cement column and the casing, and so forth.
Additionally, LCCs
such as those disclosed herein may be used to improve wellbore pressure
containment ability
when introduced to areas of lost circulation.
In an embodiment, the LCC comprises a crosslinkable polymer system. Examples
of
suitable crosslinkable polymer systems include, but are not limited to, the
following: a water
soluble copolymer of a non-acidic ethylenically unsaturated polar monomer and
a
copolymerizable ethylenically unsaturated ester; a terpolymer or tetrapolymer
of an
ethylenically unsaturated polar monomer, an ethylenically unsaturated ester,
and a monomer
selected from acrylamide-2-methylpropane sulfonic acid, N-vinylpyrrolidone, or
both; or
combinations thereof. The copolymer may contain from one to three polar
monomers and from
one to three unsaturated esters. The crosslinkable polymer system may also
include at least one
crosslinking agent, which is herein defined as a material that is capable of
crosslinking such
copolymers to form a gel. As used herein, a gel is defined as a crosslinked
polymer network
swollen in a liquid medium. The crosslinking agent may be, for example and
without
lunitation, an organic crosslinking agent such as a polyalkyleneimine, a
polyfunctional
aliphatic amine such as polyalkylenepolyamine, an aralkylamine, a
heteroaralkylamine, or
combinations thereof. Examples of suitable polyalkyleneimines include without
limitation
polymerized ethyleneimine and propyleneimine. Examples of suitable
polyalkylenepolyamines
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include without limitation polyethylene- and polypropylene-polyamines. A
description of
such copolymers and crosslinking agents can be found in U.S. Patent Nos.
5,836,392;
6,192,986, and 6,196,317.
The ethylenically unsaturated esters used in the crosslinkable polymer system
may be
formed from a hydroxyl compound and an ethylenically unsaturated carboxylic
acid selected
from the group consisting of acrylic, methacrylic, crotonic, and cinnamic
acids. The
ethylenically unsaturated group may be in the alpha-beta or beta-gamma
position relative to
the carboxyl group, but it may be at a further distance. In an embodiment, the
hydroxyl
compound is an alcohol generally represented by the formula ROH, wherein R is
an alkyl,
alkenyl, cycloalkyl, aryl, arylalkyl, aromatic, or heterocyclic group that may
be substituted
with one or more of a hydroxyl, ether, and thioether group. The substituent
can be on the
same carbon atom of the R group that is bonded to the hydroxyl group in the
hydroxyl
compound. The hydroxyl compound may be a primary, secondary, iso, or tertiary
compound.
In an embodiment, a tertiary carbon atom is bonded to the hydroxyl group,
e.g., t-butyl and
trityl. In an embodiment, the ethylenically unsaturated ester is t-butyl
acrylate.
The non-acidic ethylenically unsaturated polar monomers used in the
crosslinkable
polymer system can be amides, e.g., primary, secondary, and/or tertiary
amides, of an
unsaturated carboxylic acid. Such amides may be derived from ammonia, or a
primary or
secondary alkylamine, which may be optionally substituted by at least one
hydroxyl group as
in alkylol amides such as ethanolamides. Examples of such carboxylic derived
ethylenically
unsaturated polar monomers include without limitation acrylamide,
methacrylamide, and
acrylic ethanol amide.
In an embodiment, the crosslinkable polymer system is a copolymer of
acrylamide and
t-butyl acrylate, and the crosslinking agent is polyethylene imine. These
materials are
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commercially available as the H2ZERO* service providing conformance control
system from
Halliburton Energy Services. The H2ZERO* service providing conformance control
system is
a combination of HZ-10 polymer and HZ-20 crosslinker. HZ-10 is a low molecular
weight
polymer consisting of polyacrylamide and an acrylate ester. The gelation rate
of the H2ZERO*
service providing conformance control system is controlled by the unmasking of
crosslinking
sites on the HZ-20 polymer which is a polyethylene imine crosslinker.
The concentrations of both HZ-10 polymer and HZ-20 crosslinker contribute to
the
LCC reaction time, its final mechanical properties and stability. In an
embodiment, the
crosslinkable polymer system forms a viscous gel in from about 60 mins to
about 300 mins,
alternatively in from about 60 mins to about 300 mins at a temperature of from
about 180 F
to about 320 F, alternatively from about 180 F to about 225 F and,
alternatively from about
250 F to about 320 F. The relative amounts of HZ-10 polymer and HZ-20
crosslinker
suitable for use in the preparation of LCCs of this disclosure will be
described in detail later
herein.
In an embodiment, the LCC comprises a filler. Herein a filler refers to
particulates,
also termed finer filler material, designed to bridge off across the packing
agent of the LCC.
Such fillers may be smaller in size than the packing agent. Details of the
filler and packing
agent size will be disclosed later herein. Such fillers may have a pH of from
about 3 to about
10. In an embodiment, the filler has a specific gravity of less than about 1
to about 5,
alternatively from about 1.5 to about 5, alternatively from about 1.75 to
about 4. Without
wishing to be limited by theory, fillers having a specific gravity in the
disclosed range may
produce a LCC with greater flexibility and ductility.
Examples of suitable fillers include without limitation alkyl quaternary
ammonium
montmorillonite, bentonite, zeolites, barite, fly ash, calcium sulfate, and
combinations
thereof. In an embodiment the filler is an alkyl quarternary ammonium
montmorillonite. In an
* Trademark
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embodiment, the filler is a water swellable or hydratable clay. In an
alternative embodiment,
the filler is an oil-based sealing composition that may comprise a hydratable
polymer, an
organophillic clay and a water swellable clay. Such oil-based sealing
compositions are
disclosed in U.S. Patent Nos. 5,913,364; 6,167,967; 6,258,757, and 6,762,156.
In an
embodiment, the filler material is FLEXPLUG* lost circulation material, which
is an oil-
based sealing composition comprising alkyl quaternary ammonium montmorillonite
commercially available from Halliburton Energy Services.
In an embodiment, the LCC optionally comprises a packing agent. Examples of
packing agents include without limitation resilient materials such as
graphite; fibrous
materials such as cedar bark, shredded cane stalks and mineral fiber; flaky
materials such as
mica flakes and pieces of plastic or cellophane sheeting; and granular
materials such as
ground and sized limestone or marble, wood, nut hulls, formica, corncobs,
gravel and cotton
hulls. In an embodiment, the packing agent is a resilient graphite such as
STEELSEAL* or
STEELSEAL FINE* lost circulation additives which are dual composition graphite
derivatives commercially available from Baroid Industrial Drilling Products, a
Halliburton
Energy Services company.
In another embodiment, the packing agent is a resin-coated particulate.
Examples of
suitable resin-coated particulates include without limitation resin-coated
ground marble,
resin-coated limestone, and resin-coated sand. In an embodiment, the packing
agent is a resin-
coated sand. The sand may be graded sand that is sized based on a knowledge of
the size of
the lost circulation zone. The graded sand may have a particle size in the
range of from about
to about 70 mesh, U.S. Sieve Series. The graded sand can be coated with a
curable resin, a
tackifying agent or mixtures thereof. The hardenable resin compositions useful
for coating
sand and consolidating it into a hard fluid permeable mass generally comprise
a hardenable
* Trademark
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organic resin and a resin-to-sand coupling agent. Such resin compositions are
well known to
those skilled in the art, as is their use for consolidating sand into hard
fluid permeable masses.
A number of such compositions are described in detail in U.S. Pat. Nos.
4,042,032,
4,070,865, 4,829,100, 5,058,676 and 5,128,390. Methods and conditions for the
production
and use of such resin coated particulates are disclosed in U.S. Patents Nos.
6,755,245;
6,866,099; 6,776,236; 6,742,590; 6,446,722, and 6,427,775. An example of a
resin suitable
for coating the particulate includes without limitation SANDWEDGE NT*
conductivity
enhancement system that is a resin coating commercially available from
Halliburton Energy
Services.
In some embodiments, additives may be included in the LCC for improving or
changing the properties thereof. Examples of such additives include but are
not limited to
salts, accelerants, surfactants, set retarders, defoamers, settling prevention
agents, weighting
materials, dispersants, vitrified shale, formation conditioning agents, or
combinations thereof.
Other mechanical property modifying additives, for example, are carbon fibers,
glass fibers,
metal fibers, minerals fibers, and the like which can be added to further
modify the
mechanical properties. These additives may be included singularly or in
combination.
Methods for introducing these additives and their effective amounts are known
to one of
ordinary skill in the art.
In an embodiment, the LCC includes a sufficient amount of water to form a
pumpable
slurry. The water may be fresh water or salt water, e.g., an unsaturated
aqueous salt solution
or a saturated aqueous salt solution such as brine or seawater.
In an embodiment, the LCC comprises a crosslinkable polymer system and a
filler. In
such an embodiment, the crosslinkable polymer system'may be present in an
amount of from
* Trademark
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about 35% to about 90% by volume, and the filler may be present in an amount
of from about
8% to about 40% by volume.
Alternatively, the LCC comprises a crosslinkable polymer system, a filler and
a packing
agent. In such an embodiment, the crosslinkable polymer system may be present
in an amount
of from about 30% to about 90% by volume, the filler may be present in an
amount of from
about 8% to about 40% by volume, and the packing agent may be present in an
amount of from
about I% to about 10% by volume.
The components of the LCC may be combined in any order desired by the user to
form
a slurry that may then be placed into a wellbore experiencing lost
circulation. The components
of the LCC may be combined using any mixing device compatible with the
composition, for
example a bulk mixer. In an embodiment, the components of the LCC are combined
at the site
of the wellbore experiencing lost-circulation. Alternatively, the components
of the LCC are
combined off-site and then later used at the site of the wellbore experiencing
lost circulation.
Methods for the preparation of a LCC slurry are known to one of ordinary skill
in the art.
In an embodiment an LCC is prepared by combining the crosslinkable polymer
system
H2ZERO service providing conformance control system with a filler, FLEXPLUG
OBM lost
circulation material. In such an embodiment, the LCC is prepared by combining
from about
35% to about 90% by volume H2ZERO service providing conformance control system
with
from about 8% to about 40% by volume FLEXPLUG OBM lost circulation material.
The H2ZERO service providing conformance control system is prepared by mixing
the
HZ-10 low molecular weight polymer consisting of polyacrylamide and an
acrylate ester with
the HZ-20 polyethylene imine crosslinker. The relative amounts of HZ-10 and HZ-
20 to be
used in the preparation of H2ZERO can be adjusted to provide gelling within a
specified time
frame based on reaction conditions such as temperature and pH. For example,
the amount of
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HZ-20 crosslinker necessary for gelling is inversely proportional to
temperature wherein higher
amounts of HZ-20 are required at lower temperatures to effect formation of a
viscous gel.
Additionally, gel time can be adjusted to compensate for the pH of the filler
material.
Adjustment of the H2ZERO service providing conformance control system to
provide optimum
gelling as a function of temperature and/or pH is known to one of ordinary
skill in the art. The
filler, FLEXPLUG OBM lost circulation material is an oil-based sealing
composition
comprising alkyl quaternary ammonium montmorillonite. Without wishing to be
limited by
theory, such oil-based sealing compositions may function by the hydratable
polymer reacting
with water in the well bore to immediately hydrate and form a highly viscous
gel. The water
swellable clay then immediately swells in the presence of water and together
with the viscous
gel forms a highly viscous sealing mass. The organophillic clay may then react
with an oil
carrier fluid to add viscosity to the composition so that the polymer and clay
do not settle out of
the oil prior to reacting with water in the well bore.
In an embodiment, the LCCs of this disclosure when placed in a lost
circulation zone
produce a permanent plug that is flexible, adhesive and of appreciable
compressive strength. In
an embodiment, the LCCs of this disclosure have an appreciable static gel
strength (SGS).
The LCCs disclosed herein may be used as wellbore servicing fluids. As used
herein, a
"servicing fluid" refers to a fluid used to drill, complete, work over,
fracture, repair, or in any
way prepare a wellbore for the recovery of materials residing in a
subterranean formation
penetrated by the wellbore. Examples of servicing fluids include, but are not
limited to, cement
slurries, drilling fluids or muds, spacer fluids, fracturing fluids or
completion fluids, all of
which are well known in the art. The servicing fluid is for use in a wellbore
that penetrates a
subterranean formation. It is to be understood that "subterranean formation"
encompasses both
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areas below exposed earth and areas below earth covered by water such as ocean
or fresh
water.
The LCCs may be introduced to the wellbore to prevent the loss of aqueous or
non-
aqueous drilling fluids into lost circulation zones such as voids, vugular
zones, and natural or
induced fractures while drilling. In an embodiment, the LCC is placed into a
wellbore as a
single stream and activated by downhole conditions to form a barrier that
substantially seals
lost circulation zones. In such an embodiment, the LCC may be placed downhole
through the
drill bit forming a composition that substantially eliminates the lost
circulation. In yet another
embodiment, the LCC is formed downhole by the mixing of a first stream
comprising one or
more LCC components and a second stream comprising additional LCC components.
For
example, the LCC may be formed downhole by the mixing of a first stream
comprising a
packing agent and a second stream comprising a crosslinkable polymer system
and a filler.
Methods for introducing compositions into a wellbore to seal subterranean
zones are
described in U.S. Patent Nos. 5,913,364; 6,167,967; and 6,258,757
The LCC may form a non-flowing, intact mass inside the lost circulation zone
which
plugs the zone and inhibits loss of subsequently pumped drilling fluid, which
allows for
further drilling. It is to be understood that it may be desired to hasten the
viscosification
reaction for swift plugging of the voids. Alternatively, it may be desired to
prolong or delay
the viscosification for deeper penetration into the voids. For example the LCC
may form a
mass that plugs the zone at elevated temperatures, such as those found at
higher depths within
a wellbore.
In an embodiment, the LCCs may be employed in well completion operations such
as
primary and secondary cementing operations. The LCC may be placed into an
annulus of the
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wellbore and allowed to set such that it isolates the subterranean formation
from a different
portion of the wellbore. The LCC thus forms a barrier that prevents fluids in
that subterranean
formation from migrating into other subterranean formations. In an embodiment,
the wellbore
in which the LCC is positioned belongs to a multilateral wellbore
configuration. It is to be
understood that a multilateral wellbore configuration includes at least two
principal wellbores
connected by one or more ancillary wellbores.
In secondary cementing, often referred to as squeeze cementing, the LCC may be
strategically positioned in the wellbore to plug a void or crack in the
conduit, to plug a void or
crack in the hardened sealant (e.g., cement sheath) residing in the annulus,
to plug a relatively
small opening known as a microannulus between the hardened sealant and the
conduit, and so
forth. Various procedures that may be followed to use a sealant composition in
a wellbore are
described in U.S. Patent Nos. 5,346,012 and 5,588,488.
In other embodiments, additives are also pumped into the wellbore with LCC.
For
example and without limitation, fluid absorbing materials, resins, aqueous
superabsorbers,
viscosifying agents, suspending agents, dispersing agents, or combinations
thereof can be
pumped in the stream with the LCCs disclosed.
The LCCs of this disclosure may provide lost circulation control in a
sufficiently short
time period to prevent the operator from pulling out of the hole and thus
reducing
nonproductive rig time. Without wishing to be limited by theory, the packing
agent may
immediately pack off into the lost circulation zones in the subterranean
formation. The filler
may then squeeze into the lost circulation zones forming a bridge between the
larger sized
packing agent. Finally, the thermally activated crosslinkable polymer system
may gel into
place to produce a permanent plug that is flexible, adhesive and of
appreciable compressive
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strength. In addition, due to the filler within the slurry the amount of
crosslinkable polymer
system squeezed into the matrix of the surrounding rock may be minimized thus
providing a
finite layer of rock adjacent to the plug that has negligible permeability and
avoids formation
damage.
EXAMPLES
The invention having been generally described, the following examples are
given as
particular embodiments of the invention and to demonstrate the practice and
advantages
thereof. It is understood that the examples are given by way of illustration
and are not intended
to limit the specification of the claims in any manner.
COMPARATIVE EXAMPLE
The ability of H2ZERO service providing conformance control system to produce
a
suitable LCC was evaluated. H2ZERO service providing conformance control
system is a
crosslinkable polymer system commercially available from Halliburton Energy
Services. An
H2ZERO service providing conformance control system slurry was designed for
temperatures
in the range of 120 F to 190 F, which contained an extremely high percent of
HZ-20, Table 1.
Table 1
Component Percent of Slut? Weight
HZ-10 35.5%
HZ-20 48.2%
Water 16.3%
Two samples of the base H2ZERO service providing conformance control system
product were mixed and placed in a water bath at 130 F overnight to confirm
the recipe would
gel within a reasonable time at the lower temperature. Both samples made a
clear ringing gel
that was strong but did not hold up to impact and did not exhibit
qualitatively detectable
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flexibility. Further, when the product was over-stressed its failure mode was
akin to bursting.
The product easily broke apart.
EXAMPLE 1
The ability of H2ZERO service providing conformance control system to form an
LCC
with FLEXPLUG OBM lost circulation material was evaluated. FLEXPLUG OBM lost
circulation material is an oil-based sealing composition commercially
available from
Halliburton Energy Services. The H2ZERO service providing conformance control
system had
an adverse effect on the latex contained within the FLEXPLUG OBM lost
circulation material
slurry. The FLEXPLUG OBM lost circulation material was then used as a drymix
filler in the
H2ZERO service providing conformance control system slurry. A 9.3 ppg slurry
was targeted
as this is the density of the typical FLEXPLUG OBM lost circulation material
slurry. Table 2
lists the components and amounts used to design the H2ZERO/FLEXPLUG OBM
slurry.
Table 2
Component Percent of Sluny Weight
Water 6.9%
HZ-10 15.0%
HZ-20 59.3%
FLEXPLUG OBM Drymix lost circulation material 18.9%
The samples were heated overnight in a water bath at 130 OF, The final gelled
product
was much different than the gelled product of the base H2ZERO service
providing
conformance control system described in the Comparative Example. The
H2ZERO/FLEXPLUG OBM gelled product exhibits great flexibility, increased
toughness,
improved resilience and increased durability to impact. In addition, the
H2ZERO/FLEXPLUG
OBM gelled product remained "tacky" unlike the original H2ZERO service
providing
conformance control system gelled product.
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The above slurry was then tested for pumpability in an HPHT Consistometer at a
constant pressure of 1000 psi. The temperature was programmed to initiate the
test at 80 IF,
ramp to 130 IF over a one-hour period, and then ramp to 190 IF over a two-hour
period. Table
3 contains the consistency readings from this test which is also graphed in
Figure 1.
Table 3
Test Time (hh:mm) Test Temperature F Consistency (Be)'
0:00 80 30
3:09 190 70
3:43 190 100
Bearden consistency
Typically, a fluid is considered "non-pumpable" once it exceeds 70 Bc. The
results
demonstrate that the compositions remain pumpable until they reach the desired
temperature at
which point they rapidly form a highly flexible, durable and adhesive product.
EXAMPLE 2
A slurry was prepared as described in Example 1 and the SGS determined as a
function
of temperature. The static gel strength development test requires specialized
equipment, such
as the MACS Analyzer or the MINIMACS Analyzer. This equipment measures the
shear
resistance of a slurry under downhole temperature and pressure while the
slurry remains
essentially static. The test is conducted by mixing the slurry and placing
into the specialized
testing device. The slurry is then stirred and heated to a bottomhole
circulating temperature
(BHCT) and downhole pressure according to the same schedule as the thickening
time test.
After the slurry reaches the BHCT, stirring is stopped and the slurry is
allowed to essentially
remain static. The stirring paddle is rotated at a rate of about 0.5 '/rain
while the shear
resistance on the paddle is measured. The shear resistance is correlated to
the SGS (units are
lbf/100 ft) and a plot of SGS development is made as a function of time.
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Figure 2 is a graph of the results of an SGS test conducted at 80 IF, Figure 3
is a graph
of results of an SGS test conducted at 130 F; Figure 4 is a graph of results
of an SGS test
conducted at 160 IF, and Figure 5 is a graph of results from an SGS test
conducted at 190 IF.
The results demonstrate the formation of static gel strength more rapidly at
increased
temperatures.
EXAMPLE 3
An additional FI2ZERO/FLEXPLUG OBM formulation was prepared according to
Table 4.
Table 4
Component Volume (cc)
Tap Water 47
HZ-10 97
HZ-20 38
FLEXPLUG OBM Drymix lost circulation material 74(129g)
The materials in Table 4 were mixed in a MINIMACS for 25 minutes at 1000 psi
until
it reached the preset temperature of 80 IF, 130 IF, 160 IF or 190 IF. Then the
MIMMACS set
static at t=30 minutes and SGS (lbf/100 sq. ft.) recorded v. time. Four tests
were conducted,
one at each of the temperatures given. Raw SGS data are given in Table 5.
Analysis of the
data revealed the need to model SGS as a function of a "shifted time" defined
as follows:
Shifted time = t - toffser,T
(1)
Where: t = time of mixing, with t = 0 materials added to mixing container; t =
30 min
went to static conditions; and tofse1,T = offset time (min) at the set point
temperature of T (F).
The room temperature (80 F) tests never exceeded 40 lbf/100 sq.ft., thus
indicating that some
initial minimum temperature is required to initiate the kinetic reaction(s)
that produce the
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rheological changes resulting in substantial gel strength. It is assumed that
SGS is a direct
indicator of yield point of the LCC.
Figure 6 contains the SGS vs time data for the 130 IF, 160 IF and 190 IF
samples along
with the prediction fit of the generalized model in Eq (2).
SGS = (t -- toffset,T )aT (2)
where: aT is the "psuedo reaction rate constant" which is a function of
temperature.
Table 5
Static Gel Stren h, SGS, lbf./100 s .ft.
Time 130 OF 160 OF 190 OF
(mins.)
154 1
160 30
166 50
170 70
177 100
185 125
190 150
194 200
200 233
205 275
210 325
214 350
220 395
227 450
230 470
235 515
390 1
420 5
480 20
540 35
570 75
600 160
630 290
660 410
690 470
100 1
105 8
110 22
115 50
120 82
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Static Gel Strength, SGS, lbf./100 s .ft.
Time 130 OF 160 OF 190 OF
mires.
130 190
140 295
150 410
155 475
Table 6
Parameters:
aT toffset T
Time To Reach
Temp (F) (Mill) SGS=500
130 1.2 520 710
160 1.43 153 230
190 1.53 99 160
The results demonstrate that deploying the "time shift" concept resulted in a
simple but
very accurate model for all three temperatures tested. Best-fit values of the
parameters in Eq
(2) are given in Table 6. Note how the reaction rate exponent, aT, is a
function of temperature,
as well as the "time shift" parameter tofset,T . Also given in Table 6 is the
"time to reach SGS =
500 lbf/100 sq.ft.," and note its sensitivity to temperature as well.
EXAMPLE 4
Preliminary measurements of the mechanical properties of the H2ZERO/FLEXPLUG
OBM gelled product were conducted. For the base slurry recipe given in Tables
2 and 4,
rudimentary testing for the purpose of capturing gross compressive strength
estimates and
visual depictions of flexibility and resilience were performed on three
samples of the resultant
product. These tests were performed by placing the samples on a Tinius-Olsen
machine and
gradually increasing the compressive load, while measuring the change in
height. The Tinius-
Olsen machine is used to test compressive strength. The compressive load was
increased until
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the sample exhibited failure in the form of permanent tears in the axial
direction. Resilience
was exhibited by the product returning to near its original height and
diameter when loads were
released. In all three cases, the sample returned to its original shape until
the point of failure.
As can be seen by the photographs taken of one failed sample in Figure 11,
even at this time
the sample returns to near its original shape.
Figure 7 shows a sample with original dimensions of 3 inch diameter and 2 inch
height
with a 50 lb compressive load applied. The sample, under this load, had
deformed to a height
of approximately 1 inch and a diameter of approximately 4-1/4 inches. Figure 8
shows this
same sample under a 100 lb compressive load. The sample, under this load, had
deformed to a
height of approximately 1/2 inch and a diameter of approximately 6 inches.
Figure 9 shows
this same sample after the 100 lb load has been removed. The sample has
returned to its
original dimensions and shape with no discernible permanent deformation. A
similar result
was obtained when the sample was subjected to a 150 lb compressive load (not
shown). Figure
10 shows this same sample under a 200 lb compressive load. As can be seen by
the presence of
cracks along the diameter of the specimen, the sample has now failed. Since
failure detection
was purely through visual confirmation, it can only be stated the specimen
failed between 150
and 200 lbs of compressive force. Figure 11 shows the failed sample after it
is taken from the
Tinius-Olsen. As can be seen in this photograph, the sample returns to near
its original shape
even after the "starburst" shaped rupture.
EXAMPLE 5
The compression tests described in Example 4 were repeated with two smaller
samples
with a height of 1 inch and a diameter of 2 inches. The results were similar
to those seen with
the larger sample. In general, all three tests showed that a sample can be
deformed to
approximately 27% of its original height and 2 times it original diameter
before the repeatable
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starburst rupture failure occurs. Failure appears to be dependent more on the
limitations of
deformation the specimen can undergo, rather than the pressure applied. For
instance, on the
smaller diameter samples it again took between 150 and 200 lbs of compressive
load before
the sample failed. For the smaller sample this equates to more than twice the
pressure at
failure than the larger sample, but both samples appeared to fail at
approximately the same
percent reduction in height.
EXAMPLE 6
In addition to compressive loading tests, two 6 inch long synthetic rock cores
with
fractures tapering from 4.5 mm to 1.5 mm were packed with the H2ZERO*/FLEXPLUG
OBM slurry containing a mixture of STEELSEAL FINE* and BARACARB 600* products
as
the packing agent, Table 7. BDF-391 and BDF-393 are lost circulation additives
with a d50
particle size distribution of approximately 725 and 1125 microns respectively.
The d50
particle size distribution specifies a size for which 50% of the total volume
of particles is
smaller in size than the value. Packing agent particulates were added to
achieve an 80 ppb
loading. STEELSEAL FINE* lost circulation additive is a resilient graphite
material
commercially available from Halliburton Energy Services. BARACARB 600*
bridging agent
is a sized calcium carbonate commercially available from Halliburton Energy
Services.
Table 7
Material Liquid Volume Solid
(CO Weight
Water 113
HZ-10 75
HZ 20 26
FLEXPLUG OBM lost circulation material 65
BDF-391 6
BDF-393 17
BARACARB 606bridging Mont 29
STEELSEAL FINInost circulation additive 8
* Trademark
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The cores were packed in the Extrusion Rheometer on a Tinius-Olsen machine.
Both
cores were packed at a pressure of approximately 280 psi. The cores were then
heated in a
water-bath at 190 F overnight. Each core was then placed in the Hassler sleeve
Dislodgment
Apparatus and pressured until the fracture plug failed. The first core
dislodged at 820 psi and
the second dislodged at 640 psi. In comparison, FLEXPLUG OBM lost circulation
material
tends to fail at pressures of 150 psi or less in this same fracture geometry.
EXAMPLE 7
Filler materials other than FLEXPLUG OBM drymix lost circulation material were
used to produce slurries similar to that listed in Table 4 for the purpose of
qualitative
comparison of such discernable characteristics as flexibility, gel time and
firmness. The fillers
investigated, and the relative rating of the resultant product characteristics
are listed in Table
8. FLEXPLUG OBM drymix appeared to produce the most favorable end product due
to its
extreme flexibility, durability, resilience and tackiness. FLEXPLUG W lost
circulation
material is a sealing composition, FLY ASH retarder is a coal combustion
product, CAL
SEAL* gypsum additive is a gypsum cement, FDP-C661-02 additive and FDP-C661VA-
02
accelerating component are compressive strength accelerants, all of which are
commercially
available from Halliburton Energy Services. BAROID* weighting material is
barium sulfate,
which is commercially available from Baroid Industrial Drilling Products a
Halliburton
Energy Services company. FLEXPLUG OBM lost circulation material was the only
filler
tested that produced an end product with an appreciable 'tackiness'.
Table 8
Filler Gel Time Flexibility St=Rth
FLEXPLUG OBM lost circulation Excellent Excellent Good
material
FLEXPLUG W lost circulation Excellent Excellent Good
material
FDP-C661-02 additive Excellent Fair Fair
* Trademark
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Filler Gel Time Flexibility Stren
FDP-C661 VA-02 accelerating Excellent Good Excellent
component
BAROID weighting material Excellent Fair to Poor Fair
FLY ASH retarder Excellent Fair Excellent
CAL SEAL gypsum additive Poor Fair Good
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EXAMPLE 8
Several traditional particulate packing agent products were used to produce
slurries
similar to that listed in Table 4 for the purpose of qualitative comparison of
such discernable
characteristics as flexibility, gel time and firmness. HYDROPLUG lost
circulation plug is a
self-expanding lost circulation material commercially available from
Halliburton Energy
Services. For each packing agent or packing material, the slurry recipe listed
in Table 4 was
loaded to an equivalent of 80 ppb of the packing agent. Table 9 lists the
observations of the
final products with these various packing agents. Packing quality was
determined by how
distinct (segregated) the pack layer was. If the packing agent remained
dispersed it was given a
Fair rating where a packing agent that created a thick, delineated packing
layer was given an
excellent rating.
Table 9
Packing Material Tackiness Firmness Packing
Quality
BARACARB 600 bridging agent Good Fair Excellent
HYDROPLUG lost circulation plug Fair Good Good
STEELSEAL lost circulation Fair Good Good
addditive
FLEXPLUG OBM lost circulation Excellent Fair Poor
material
EXAMPLE 9
A base slurry as described in Tables 2 and 4 was prepared. To this base
slurry, 100g of
SANDWEDGE conductivity enhancement system coated gravel was added as the
packing
agent. The resultant material displayed enhanced resiliency and flexibility
when compared to
the composition without the resin-coated gravel.
It has been found that by adding the filler FLEXPLUG OBM lost circulation
material
drymix to the crosslinkable polymer system H2ZERO service providing
conformance control
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system in combination with any one of a number of particulate packing agent
products, a
highly flexible, durable and adhesive product is formed. This product, via the
particulate
packing agent, provides an immediate short-term plug so that the driller can
continue to drill
ahead. In addition, the thermally activated FLEXPLUG*/ H2ZERO* gel produces a
long-term
plug that also creates a limited invasion zone within the matrix of the nearby
rock, creating a
greatly reduced permeability zone to further strengthen the plug.
While preferred embodiments of the invention have been shown and described,
modifications thereof can be made by one skilled in the art without departing
from the spirit
and teachings of the invention. The embodiments described herein are exemplary
only, and
are not intended to be limiting. Many variations and modifications of the
invention disclosed
herein are possible and are within the scope of the invention. Where numerical
ranges or
limitations are expressly stated, such express ranges or limitations should be
understood to
include iterative ranges or limitations of like magnitude falling within the
expressly stated
ranges or limitations (e.g., from about 1 to about 10 includes, 2, 3, 4, etc.;
greater than 0.10
includes 0.11, 0.12, 0.13, etc.). Use of the term 'optionally' with respect to
any element of a
claim is intended to mean that the subject element is required, or
alternatively, is not required.
Both alternatives are intended to be within the scope of the claim. Use of
broader terms such
as comprises, includes, having, etc. should be understood to provide support
for narrower
terms such as consisting of, consisting essentially of, comprised
substantially of, etc.
Accordingly, the scope of protection is not limited by the description set out
above but
is only limited by the claims which follow, that scope including all
equivalents of the subject
matter of the claims. The discussion of a reference
* Trademark
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herein is not an admission that it is prior art to the present invention,
especially any reference
that may have a publication date after the priority date of this application.
