FIELD OF INVENTION
This invention relates to a set-delayed cement composition comprising
pumice and a method of cementing related thereto
BACKGROUND TECHNICAL INFORMATION
5 Cement compositions may be used in a variety of subterranean operations.
For example, in subterranean well construction, a pipe string (e.g., casing, liners,
expandable tubulars, etc.) may be run into a well bore and cemented in place.
The process of cementing the pipe string in place is commonly referred to as
"primary cementing." In a typical primary cementing method, a cement
10 composition may be pumped into an annulus between the walls of the well bore
and the exterior surface of the pipe string disposed therein. The cement
composition may set in the annular space, thereby forming an annular sheath of
hardened, substantially impermeable cement (i.e., a cement sheath) that may
support and position the pipe string in the well bore and may bond the exterior
15 surface of the pipe string to the subterranean formation. Among other things, the
cement sheath surrounding the pipe string functions to prevent the migration of
fluids in the annulus, as well as protecting the pipe string from corrosion.
Cement compositions also may be used in remedial cementing methods, for
example, to seal cracks or holes in pipe strings or cement sheaths, to seal highly
20 permeable formation zones or fractures, to place a cement plug, and the like.
A broad variety of cement compositions have been used in subterranean
cementing operations. In some instances, set-delayed cement compositions have
been used. Set-delayed cement compositions are characterized by remaining in a
pumpable fluid state for an extended period of time (e.g., at least about 1 day to
25 about 2 weeks or more). When desired for use, the set-delayed cement
compositions should be capable of being activated whereby reasonable
compressive strengths are developed. For example, a cement set accelerator may
be added to a set-delayed cement composition whereby the composition sets into
a hardened mass. Among other things, the set-delayed cement composition may
30 be suitable for use in well bore applications, for example, where it is desired to
prepare the cement composition in advance. This may allow, for example, the
cement composition to be stored prior to its use. In addition, this may allow, for
- 2 -
example, the cement composition to be prepared at a convenient location and
then transported to the job site. Accordingly, capital expenditures may be
reduced due to a reduction in the need for on-site bulk storage and mixing
equipment. This may be particularly useful for offshore cementing operations
5 where space onboard the vessels may be limited.
While set-delayed cement compositions have been developed heretofore,
challenges exist with their successful use in subterranean cementing operations.
For example, set-delayed cement compositions prepared with Portland cement
may have undesired gelation issues which can limit their use and effectiveness in
10 cementing operations. Other set-delayed compositions that have been
developed, for example, those comprising hydrated lime and quartz, may be
effective in some operations but may have limited use at lower temperatures as
they may not develop sufficient compressive strength when used in subterranean
formations having lower bottom hole static temperatures.
15 SUMMARY OF INVENTION
An embodiment of the present invention provides a method of cementing
in a subterranean formation. The method may comprise providing a set-delayed
cement composition comprising water, pumice, hydrated lime, and a set retarder.
The method may further comprise activating the set-delayed cement composition.
20 The method may further comprise introducing the set-delayed cement
composition into a subterranean formation. The method may further comprise
allowing the set-delayed cement composition to set in the subterranean formation.
Another embodiment of the present invention provides a method of
cementing in a subterranean formation. The method may comprise providing a
25 set-delayed cement composition comprising water, pumice, hydrated lime, and a
set retarder. The method may further comprise storing the set-delayed cement
composition for a period of at least about 1 day. The method may further
comprise adding a cement set accelerator to the set-delayed cement composition.
The method may further comprise introducing the set-delayed cement
30 composition into a subterranean formation. The method may further comprise
allowing the set-delayed cement composition to set in the subterranean formation.
Another embodiment of the present invention provides a set-delayed
cement composition that may comprise water, pumice, hydrated lime, and a set
- 3 -
retarder. The set-delayed cement composition may remain in a pumbable fluid
state for a time period of at least about 1 day.
The features and advantages of the present invention will be readily
apparent to those skilled in the art. While numerous changes may be made by
5 those skilled in the art, such changes are within the spirit of the invention.
DESCRIPTION OF INVENTION
The present invention relates to subterranean cementing operations and,
more particularly, in certain embodiments, to set-delayed cement compositions
and methods of using set-delayed cement compositions in subterranean
10 formations.
Embodiments of the set-delayed cement compositions of the present
invention may generally comprise water, pumice, hydrated lime, and a set
retarder. Optionally, the set-delayed cement compositions may further comprise
a dispersant. Advantageously, embodiments of the set-delayed cement
15 compositions may be capable of remaining in a pumpable fluid state for an
extended period of time. For example, the set-delayed cement compositions may
remain in a pumpable fluid state for at least about 1 day or longer.
Advantageously, the set-delayed cement compositions may develop reasonable
compressive strengths after activation at relatively low temperatures. While the
20 set-delayed cement compositions may be suitable for a number of subterranean
cementing operations, they may be particularly suitable for use in subterranean
formations having relatively low bottom hole static temperatures, e.g.,
temperatures less than about 200°F or ranging from about 100°F to about 200°F.
The water used in embodiments of the set-delayed cement compositions
25 of the present invention may be from any source provided that it does not contain
an excess of compounds that may undesirably effect other components in the setdelayed
cement compositions. For example, a set-delayed cement composition
may comprise fresh water or salt water. Salt water generally may include one or
more dissolved salts therein and may be saturated or unsaturated as desired for a
30 particular application. Seawater or brines may be suitable for use in
embodiments of the present invention. Further, the water may be present in an
amount sufficient to form a pumpable slurry. In certain embodiments, the water
may be present in the set-delayed cement composition in an amount in the range
- 4 -
of from about 33% to about 200% by weight of the pumice. In certain
embodiments, the water may be present in the set-delayed cement compositions
in an amount in the range of from about 35% to about 70% by weight of the
pumice. One of ordinary skill in the art with the benefit of this disclosure will
5 recognize the appropriate amount of water for a chosen application.
Embodiments of the set-delayed cement compositions may comprise
pumice. Generally, pumice is a volcanic rock that can exhibit cementitious
properties, in that it may set and harden in the presence of hydrated lime and
water. The pumice may also be ground, for example. Generally, the pumice may
10 have any particle size distribution as desired for a particular application. In
certain embodiments, the pumice may have a mean particle size in a range of
from about 1 micron to about 200 microns. The mean particle size corresponds
to d50 values as measured by particle size analyzers such as those manufactured
by Malvern Instruments, Worcestershire, United Kingdom. In specific
15 embodiments, the pumice may have a mean particle size in a range of from about
1 micron to about 200 micron, from about 5 microns to about 100 microns, or
from about 10 micron to about 50 microns. In one particular embodiment, the
pumice may have a mean particle size of less than about 15 microns. An
example of a suitable pumice is available from Hess Pumice Products, Inc.,
20 Malad, Idaho, as DS-325 lightweight aggregate, having a particle size of less than
about 15 microns. It should be appreciated that particle sizes too small may have
mixability problems while particle sizes too large may not be effectively
suspended in the compositions. One of ordinary skill in the art, with the benefit
of this disclosure, should be able to select a particle size for the pumice suitable
25 for use for a chosen application.
Embodiments of the set-delayed cement compositions may comprise
hydrated lime. As used herein, the term "hydrated lime" will be understood to
mean calcium hydroxide. The hydrated lime may be included in embodiments of
the set-delayed cement compositions, for example, to form a hydraulic
30 composition with the pumice. For example, the hydrated lime may be included in
a pumice-to-hydrated-lime weight ratio of about 10:1 to about 1:1 or 3:1 to about
5:1. Where present, the hydrated lime may be included in the set-delayed cement
compositions in an amount in the range of from about 10% to about 100% by
- 5 -
weight of the pumice, for example. In some embodiments, the hydrated lime
may be present in an amount ranging between any of and/or including any of
about 10%, about 20%, about 40%, about 60%, about 80%, or about 100% by
weight of the pumice. In some embodiments, the cementitious components
5 present in the set-delayed cement composition may consist essentially of the
pumice and the hydrated lime. For example, the cementitious components may
primarily comprise the pumice and the hydrated lime without any additional
components (e.g., Portland cement, fly ash, slag cement) that hydraulically set in
the presence of water. One of ordinary skill in the art, with the benefit of this
10 disclosure, will recognize the appropriate amount of the hydrated lime to include
for a chosen application.
Embodiments of the set-delayed cement compositions may comprise a set
retarder. A broad variety of set retarders may be suitable for use in the setdelayed
cement compositions useful in the present invention. For example, the
15 set retarder may comprise phosphonic acid, phosphonic acid derivatives,
lignosulfonates, salts, organic acids, carboxymethylated hydroxyethylated
celluloses, synthetic co- or ter-polymers comprising sulfonate and carboxylic acid
groups, borate compounds, derivatives thereof, or mixtures thereof. In certain
embodiments, the set retarders used in the set-delayed cement compositions
20 useful in the present invention are phosphonic acid derivatives, such as those
described in U.S. Pat. No. 4,676,832, the disclosure of which is incorporated
herein by reference. Examples of suitable set retarders include, among others,
phosphonic acid derivatives available from Halliburton Energy Services, Inc.. of
Duncan, Oklahoma, as Micro Matrix® cement retarder. Generally, the set
25 retarder may be present in the set-delayed cement composition used in the present
invention in an amount sufficient to delay the setting for a desired time. In some
embodiments, the set retarder may be present in the set-delayed cement
compositions in an amount in the range of from about 0.01% to about 10% by
weight of the pumice. In specific embodiments, the set retarder may be present
30 in an amount ranging between any of and/or including any of about 0.01 %, about
0.1%, about 1%, about 2%, about 4%, about 6%, about 8%, or about 10% by
weight of the pumice. One of ordinary skill in the art, with the benefit of this
- 6 -
disclosure, will recognize the appropriate amount of the set retarder to include for
a chosen application.
As previously mentioned, embodiments of the set-delayed cement
compositions may optionally comprise a dispersant. Examples of suitable
5 dispersants include, without limitation, sulfonated-formaldehyde-based
dispersants and polycarboxylated ether dispersants. One example of a suitable
sulfonated-formaldehyde-based dispersant that may be suitable is a sulfonated
acetone formaldehyde condensate, available from Halliburton Energy Services,
Inc., as CFR™-3 dispersant. One example of a suitable polycarboxylated ether
10 dispersant that may be suitable is Liquiment® 514L dispersant, available from
BASF Corporation, Houston, Texas, that comprises 36% by weight of the
polycarboxylated ether in water. While a variety of dispersants may be used in
accordance with embodiments of the present invention, polycarboxylated ether
dispersants may be particularly suitable for use in some embodiments. Without
15 being limited by theory, it is believed that polycarboxylated ether dispersants
may synergistically interact with other components of the set-delayed cement
composition. For example, it is believed that the polycarboxylated ether
dispersants may react with certain set retarders (e.g., phosphonic acid derivatives)
resulting in formation of a gel that suspends the pumice and hydrated lime in the
20 composition for an extended period of time.
In some embodiments, the dispersant may be included in the set-delayed
cement compositions in an amount in the range of from about 0.01% to about 5%
by weight of the pumice. In specific embodiments, the dispersant may be present
in an amount ranging between any of and/or including any of about 0.01%, about
25 0.1%, 0.5%, about 1%, about 2%, about 3%, about 4%, or about 5% by weight of
the pumice. One of ordinary skill in the art, with the benefit of this disclosure,
will recognize the appropriate amount of the dispersant to include for a chosen
application.
Other additives suitable for use in subterranean cementing operations also
30 may be included in embodiments of the set-delayed cement compositions.
Examples of such additives include, but are not limited to, weighting agents,
lightweight additives, gas-generating additives, mechanical-property-enhancing
additives, lost-circulation materials, filtration-control additives, fluid-loss-control
-7-
additives, defoaming agents, foaming agents, thixotropic additives, and
combinations thereof. In embodiments, one or more of these additives may be
added to the set-delayed cement composition after storing but prior to placement
of the set-delayed cement composition into a subterranean formation. A person
5 having ordinary skill in the art, with the benefit of this disclosure, will readily be
able to determine the type and amount of additive useful for a particular
application and desired result.
Those of ordinary skill in the art will appreciate that embodiments of the
set-delayed cement compositions of the present invention generally should have a
10 density suitable for a particular application. By way of example, the set-delayed
cement compositions may have a density in the range of from about 4 pounds per
gallon ("lb/gal") to about 20 lb/gal. In certain embodiments, the set-delayed
cement compositions may have a density in the range of from about 8 lb/gal to
about 17 lb/gal. Embodiments of the set-delayed cement compositions may be
15 foamed or unfoamed or may comprise other means to reduce their densities, such
as hollow microspheres, low-density elastic beads, or other density-reducing
additives known in the art. In embodiments, the density may be reduced after
storing the composition, but prior to placement in a subterranean formation.
Those of ordinary skill in the art, with the benefit of this disclosure, will
20 recognize the appropriate density for a particular application.
As previously mentioned, the set-delayed cement compositions may have
a delayed set in that they remain in a pumpable fluid state for an extended period
of time. For example, the set-delayed cement compositions may remain in a
pumpable fluid state for a period of time from about 1 day to about 7 days or
25 more. In some embodiments, the set-delayed cement compositions may remain
in a pumpable fluid state for at least about 1 day, about 7 days, about 10 days,
about 20 days, about 30 days, about 40 days, about 50 days, about 60 days, or
longer. A fluid is considered to be in a pumpable fluid state where the fluid has a
consistency of less than 70 Bearden units of consistency ("Be"), as measured on a
30 high-temperature high-pressure consistometer at room temperature (e.g.. about
80°F) in accordance with the procedure for determining cement thickening times
set forth in API RP Practice 10B-2, Recommended Practice for Testing Well
Cements, First Edition, July 2005. As set forth in Example 4 below, an example
- 8 -
composition was prepared that comprised pumice, 20% hydrated lime, 1.4%
dispersant (Liquiment® 514L), 1.26% set retarder (Micro Matrix® cement
retarder), and 62% water (all % by weight of pumice). After 45 days of storage at
ambient conditions, the example composition was mixed with 6% calcium
5 chloride by weight of the pumice. At 140°F, the example composition had a
thickening time (time to 70 Be) of 2 hours and 36 minutes and developed 50 psi
compressive strength in 9 hours and 6 minutes as measured on an Ultrasonic
Cement Analyzer ("UCA"), available from Fann Instrument Company, Houston,
TX, while maintained at 3000 psi. After 48 hours, the sample was crushed and
10 had a compressive strength of 2,240 psi.
When desired for use, embodiments of the set-delayed cement
compositions may be activated (e.g., by combination with a cement set
accelerator) to thereby set into a hardened mass. By way of example,
embodiments of the set-delayed cement compositions may be activated to set to
15 form a hardened mass in a time period in the range of from about 2 hours to about
12 hours. For example, embodiments of the set-delayed cement compositions
may set to form a hardened mass in a time period ranging between any of and/or
including any of about 2 days, about 4 days, about 6 days, about 8 days, about 10
days, or about 12 days. After activation, the set-delayed cement composition
20 may develop a 24-hour compressive strength in the range of from about 50 psi to
about 5000 psi, alternatively, from about 100 psi to about 4500 psi, or
alternatively from about 500 psi to about 4000 psi. In some embodiments, the
set-delayed cement composition may develop a compressive strength in 24 hours
of at least about 50 psi, at least about 100 psi, at least about 500 psi, or more.
25 The compressive strengths may determined in accordance with API RP I0B-2.
Recommended Practice for Testing Well Cements, First Edition, July 2005, using
an UCA at 140°F while maintained at 3000 psi.
Embodiments of the present invention may include addition of a cement
set accelerator to the set-delayed cement compositions. Examples of suitable
30 cement set accelerators include, but are not limited to, calcium chloride,
triethanolamine, sodium silicate, zinc formate, calcium acetate, sodium
hydroxide, sodium sulfate, and combinations thereof. The cement set accelerator
should be added to embodiments of the set-delayed cement composition in an
- 9 -
amount sufficient to activate the extended settable composition to set into a
hardened mass. In certain embodiments, the cement set accelerator may be added
to the set-delayed cement composition in an amount in the range of about 1 % to
about 20% by weight of the pumice. In specific embodiments, the cement set
5 accelerator may be present in an amount ranging between any of and/or including
any of about 1%, about 5%, about 10%, about 15%, or about 20% by weight of
the pumice. One of ordinary skill in the art, with the benefit of this disclosure,
will recognize the appropriate amount of the cement set accelerator to include for
a chosen application.
10 As will be appreciated by those of ordinary skill in the art, embodiments of
the set-delayed cement compositions of the present invention may be used in a
variety of subterranean operations, including primary and remedial cementing. In
some embodiments, a set-delayed cement composition may be provided that
comprises water, pumice, hydrated lime, a set retarder, and optionally a
15 dispersant. The set-delayed cement composition may be introduced into a
subterranean formation and allowed to set therein. As used herein, introducing
the set-delayed cement composition into a subterranean formation includes
introduction into any portion of the subterranean formation, including, without
limitation, into a well bore drilled into the subterranean formation, into a near
20 well bore region surrounding the well bore, or into both. Embodiments of the
present invention may further include activation of the set-delayed cement
composition. The activation of the set-delayed cement composition may
comprise, for example, addition of a cement set accelerator to the set-delayed
cement composition.
25 In some embodiments, a set-delayed cement composition may be
provided that comprises water, pumice, hydrated lime, a set retarder, and
optionally a dispersant. The set-delayed cement composition may be stored, for
example, in a vessel or other suitable container. The set-delayed cement
composition may be permitted to remain in storage for a desired time period. For
30 example, the set-delayed cement composition may remain in storage for a time
period of about 1 day or longer. For example, the set-delayed cement
composition may remain in storage for a time period of about 1 day, about 2
days, about 5 days, about 7 days, about 10 days, about 20 days, about 30 days.
- 10-
about 40 days, about 50 days, about 60 days, or longer. In some embodiments,
the set-delayed cement composition may remain in storage for a time period in a
range of from about 1 day to about 7 days or longer. Thereafter, the set-delayed
cement composition may be activated, for example, by addition of a cement set
5 accelerator, introduced into a subterranean formation, and allowed to set therein.
In primary cementing embodiments, for example, embodiments of the setdelayed
cement composition may be introduced into a space between a wall of a
well bore and a conduit (e.g., pipe strings, liners) located in the well bore, the
well bore penetrating the subterranean formation. The set-delayed cement
10 composition may be allowed to set to form an annular sheath of hardened cement
in the space between the well bore wall and the conduit. Among other things, the
set cement composition may form a barrier, preventing the migration of fluids in
the well bore. The set cement composition also may, for example, support the
conduit in the well bore.
15 In remedial cementing embodiments, a set-delayed cement composition
may be used, for example, in squeeze-cementing operations or in the placement
of cement plugs. By way of example, the set-delayed composition may be placed
in a well bore to plug an opening, such as a void or crack, in the formation, in a
gravel pack, in the conduit, in the cement sheath, and/or a microannulus between
20 the cement sheath and the conduit.
To facilitate a better understanding of the present invention, 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 scope of the
invention.
25 EXAMPLE 1
The following series of tests was performed to evaluate the force
resistance properties of comparative cement compositions comprising pumice
and hydrated lime. Three different comparative sample settable compositions,
designated Samples 1-3, were prepared using pumice (DS-325 lightweight
30 aggregate), hydrated lime, Liquiment 514L dispersant, and water, as indicated in
the table below. After preparation, the samples were placed in an UCA and cured
at 140°F and 3,000 psi for 24 hours. The cured cement was then removed from
- 11 -
the UCA and crushed to yield the compressive strength values provided in Table
1 below.
TABLE 1
Compressive Strength Tests
Sample
Density
Pumice:Lime Wt Ratio
Pumice
Lime
Dispersant
Water
24-Hr Crush Strength
lb/gal
g
g
g
g
psi
1
14.3
3:1
400
134
12
196
2,240
2
14.3
4:1
400
103
4
187
1,960
3
14.3
5:1
400
100
13
220
2,130
5 Example 1 thus indicates that cement compositions that comprise pumice
and lime in a weight ratio ranging from 3:1 to 5:1 may develop compressive
strengths suitable for particular applications.
EXAMPLE 2
A sample set-delayed cement composition, designated Sample 4, having a
10 density of 13.3 lb/gal was prepared that comprised 500 grams of pumice (DS-325
lightweight aggregate), 100 grams of hydrated lime, 13 grams of Liquiment*
514L dispersant, 24 grams of Micro Matrix® cement retarder, and 300 grams of
water. The rheological properties of the sample were measured after storing at
room temperature and pressure for periods of 1 day and 6 days. After
15 preparation, the rheological properties of the sample were determined at room
temperature (e.g., about 80°F) using a Model 35A Fann Viscometer and a No. 2
spring, in accordance with the procedure set forth in API RP Practice 10B-2,
Recommended Practice for Testing Well Cements. The results of this test are set
forth in the table below.
- 12-
TABLE 2
Viscosity Tests
Age of Sample
(days)
1
6
Fann Readings
600
560
498
300
322
310
200
244
228
100
170
136
6
46
24
3
38
20
Yield
Point
(lb/lOOft2*
84
122
Plastic
Viscosity
(centi poise)
238
188
Example 2 thus indicates that set-delayed cement compositions that
comprise pumice, hydrated lime, a dispersant, a set retarder, and water can
5 remain fluid after 6 days.
EXAMPLE 3
A sample set-delayed cement composition, designated Sample 5, having a
density of 13.4 lb/gal was prepared that comprised 500 grams of pumice (DS-325
lightweight aggregate), 100 grams of hydrated lime, 7 grams of Liquiment* 514L
10 dispersant, 6.3 grams of Micro Matrix® cement retarder, and 304 grams of water.
The rheological properties of the sample were measured after storing at room
temperature and pressure for periods of from 1 day to 19 days. The rheological
properties were measured at room temperature (e.g., about 80°F) using a Model
35A Fann Viscometer and a No. 2 spring, in accordance with the procedure set
15 forth in API RP Practice 10B-2, Recommended Practice for Testing Well
Cements. The results of this test are set forth in the table below.
Table 3
Viscosity Tests
Age of Sample
(Days)
1
2
5
8
12
19
Fann Readings
300
462
458
420
446
420
426
200
300
282
260
270
252
248
100
130
122
106
110
100
94
6
12
6
3
4
3
2
3
8
4
2
1
2
1
After 7 days, calcium chloride in the amount indicated in Table 4 below
was added to a separately prepared sample of the same formulation as above.
The sample was then placed in an UCA and the initial setting time, which is the
5 time for the composition to reach a compressive strength of 50 psi while
maintained at 3,000 psi was determined in accordance with API RP Practice 10B-
2, Recommended Practice for Testing Well Cements. The initial setting time of
the sample was also determined without addition of the calcium chloride. The
samples with and without the calcium chloride were heated to a temperature of
10 140°F in 30 minutes and then maintained at that temperature throughout the test.
TABLE 4
Compressive Strength Tests
Age of
Sample
(Days)
7
7
Test
Temperature
(op)
140
140
CaCl2
(% by wt of
Pumice &
Lime)
0
10
Initial Setting
Time
(hnmin)
no set after 4
days
5:11
Example 3 thus indicates that the set-delayed cement compositions that
comprise pumice, hydrated lime, a dispersant, a set retarder, and water will not
15 set for a period of at least 19 days at ambient temperature and over 4 days at
140°F. Example 3 further indicates that sample set-delayed cement compositions
may be activated at a desired time by addition of a suitable activator.
EXAMPLE 4
A sample set-delayed cement composition, designated Sample 6, having a
20 density of 13.4 lb/gal was prepared that comprised pumice (DS-325 lightweight
aggregate), 20% hydrated lime, 1.4% Liquiment® 514L dispersant, 1.26% Micro
Matrix® cement retarder, and 62% of water (all by weight of pumice, referred to
in the table below as "% bwop"). After 45 days in storage at ambient conditions,
the sample was mixed with 6% calcium chloride. At 140°F, the sample had a
25 thickening time (time to 70 BC) of 2 hours and 36 minutes and an initial setting
- 1 4 -
time (time to 50 psi) of 9 hours and 6 minutes as measured using an UCA while
maintained at 3000 psi. After 48 hours, the sample was crushed with a
mechanical press which gave a compressive strength of 2,240 psi. The
thickening time and initial setting time were both determined in accordance with
5 API RP Practice 10B-2, Recommended Practice for Testing Well Cements. The
results of this test are set forth in the table below.
TABLE 5
Age of
Sample
(Days)
45
Test
Temperature
(°F)
140
Calcium
Chloride
(% bwop)
6
Thickening
Time
(hr:min)
2:36
Initial
Setting
Time
(hr:min)
9:36
48 Hr
Crush
Strength
(psi)
2,240
Example 4 thus indicates that the set-delayed cement compositions that
comprise pumice, hydrated lime, a dispersant, a set retarder, and water will not
10 set for a period of at least 45 days at ambient temperature. Example 4 further
indicates that sample set-delayed cement compositions may be activated at a
desired time by addition of a suitable activator.
EXAMPLE 5
This example was performed to evaluate the ability of sodium hydroxide
15 and sodium sulfate to activate a set-delayed cement composition that comprised
pumice (DS-325 lightweight aggregate), hydrated lime, Liquiment® 514L
dispersant, Micro Matrix® cement retarder, and water. Four sample set-delayed
cement compositions, designated Samples 7-10, were prepared having
concentrations of components as indicated in the table below. The samples were
20 monitored via an UCA. After the samples were placed in the UCA, the pressure
was increased to 3,000 psi, and the temperature was increased to 100°F over a
15-minute time period and held for the duration of the test. A portion of the
slurry was retained and poured into a plastic cylinder to monitor the slurry
behavior at room temperature and pressure. These procedures were repeated for
25 all samples.
- 15-
Sample 7 was monitored for 72 hours over which time no strength was
developed and the slurry was still pourable when removed from the UCA. The
portion kept at room temperature and pressure was likewise still pourable after 72
hours.
5 Sample 8 was prepared using the same slurry design as Sample 7 except
that sodium hydroxide was added as an activator. The sodium hydroxide was
added in solid form directly to the mixing jar that contained the prepared sample.
As can be seen from Table 6, Sample 8, reached 50 psi of compressive strength at
16 hours and 36 minutes. The strength continued to build, reaching a maximum
10 of 1,300 psi, when the test was stopped at 72 hours. The cured cement was
removed from the UCA and crushed with a mechanical press which gave a
compressive strength of 969 psi. The portion kept at room temperature and
pressure was crushed after 7 days resulting in a compressive strength of 143 psi.
Sample 9 was prepared using the same slurry design as Sample 8 except
15 that sodium sulfate was added as an activator. The sodium sulfate was added in
solid form directly to the mixing jar that contained the prepared slurry. Sample
9 reached 50 psi of compressive strength at 67 hours and 29 minutes. The
strength continued to build, slowly, reaching a maximum of 78 psi, when the
test was stopped at 72 hours. The cured cement was removed from the UCA
20 and crushed with a mechanical press which gave a compressive strength of 68.9
psi. The portion kept at room temperature and pressure was still too soft to be
crushed after 7 days.
Sample 10 was prepared using the same slurry design as Sample 8 except
that equal amounts of sodium hydroxide and sodium sulfate were added as an
25 activator. The sodium hydroxide and sodium sulfate were added in solid form
directly to the mixing jar that contained the prepared slurry. Sample 10 reached
50 psi of compressive strength at 22 hours and 40 minutes. The strength
continued to build, reaching a maximum of 900 psi, when the test was stopped at
72 hours. The cured cement was removed from the UCA and crushed with a
30 mechanical press which gave a compressive strength of 786 psi. The portion
kept at room temperature and pressure was crushed after 7 days resulting in a
compressive strength of 47.9 psi.
- 16-
The results of these tests are set forth in the table below. The abbreviation
"% bwop" refers to the percent of the component by weight of the pumice. The
abbreviation "gal/sk" refers to gallons of the component per 46-pound sack of the
pumice. The abbreviation "RTP" refers to room temperature and pressure.
$ TABLE 6
gam pie
Density
Water
Pumice
Hydrated Lime
Dispersant
get Retarder
Sodium Hydroxide
Sodium Sulfate
UCA
Temp/Press
Initial Set (50 psi)
Final Set (100 psi)
24 Hr Comp. Strength
48 Hr Comp. Strength
72 Hr Comp. Strength
72 Hr Crush Strength (UCA)
7-Day Crush Strength (RTP)
lb/gal
% bwop
% bwop
% bwop
gal/sk
% bwop
% bwop
% bwop
F/Psi
hnmin
hnmin
psi
psi
psi
psi
psi
7
13.38
61.97
100
20
0.07
0.06
-
-
100/3000
>78
-
--
~
-
-
-
8
13.38
63.60
100
20
0.07
0.06
4
~
100/3000
16:36
21:08
138.74
711.35
1300
969
143.20
9
13.38
64.62
100
20
0.07
0.06
-
4
100/3000
67:29
-
-
-
78
68.90
0.00
10
13.38
64.11
100
20
0.07
0.06
2
2
100/3000
22:40
32:44
59.60
331.48
900
786
47.90
Example 5 thus indicates that sodium hydroxide, sodium sulfate, and
combinations of the two can activate the set-delayed cement compositions, but to
varying degrees. The testing showed that both sodium hydroxide and
combinations of sodium hydroxide with sodium sulfate activated the cement
- 17-
compositions to an acceptable level. When compared to the non-activated
composition, sodium sulfate activated the cement compositions, but much less so
than the sodium hydroxide or combination of sodium hydroxide and sodium
sulfate.
5 It should be understood that the compositions and methods are described
in terms of "comprising," "containing," or "including" various components or
steps, the compositions and methods can also "consist essentially o f 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
10 the element that it introduces.
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
15 the same way, ranges from any upper 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,
20 equivalently, "from 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 upper
25 limit, to recite a range not explicitly recited.
Therefore, the present invention is 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, as the present invention may
be modified and practiced in different but equivalent manners apparent to those
30 skilled in the art having the benefit of the teachings herein. Although individual
embodiments are discussed, the invention covers all combinations of all those
embodiments. Furthermore, no limitations are intended to the details of
construction or design herein shown, other than as described in the claims below.
- 18-
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 variations are considered within the scope and spirit of the present
5 invention. 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.
- 19-

B (. 7 09W- ^ 5 ^ t
We Claim:
1. A method of cementing in a subterranean formation, comprising:
providing a set-delayed cement composition comprising water,
pumice, hydrated lime, and a set retarder;
5 activating the set-delayed cement composition;
introducing the set-delayed cement composition into a
subterranean formation; and
allowing the set-delayed cement composition to set in the
subterranean formation.
10 2. A method as claimed in claim 1 wherein the pumice has a mean
particle size in a range of about 1 micron to about 200 microns.
3. A method as claimed in claim 1 wherein the pumice and the
hydrated lime are present in a weight ratio of pumice to hydrated lime of about
10:1 to about 1:1.
15 4. A method as claimed in claim 1 wherein the set retarder comprises
at least one retarder selected from the group consisting of a phosphonic acid, a
phosphonic acid derivative, a lignosulfonate, a salt, an organic acid, a
carboxymethylated hydroxyethylated cellulose, a synthetic co- or ter-polymer
comprising sulfonate and carboxylic acid groups, a borate compound, and any
20 mixture thereof.
5. A method as claimed in claim 1 wherein the set-delayed cement
composition further comprises a dispersant.
6. A method as claimed in claim 5 wherein the dispersant comprises
at least one dispersant selected from the group consisting of a sulfonated-
25 formaldehyde-based dispersant, a polycarboxylated ether dispersant, and any
combination thereof.
7. A method as claimed in claim 1 wherein the set retarder comprises
a phosphonic acid derivative, and wherein the set-delayed cement composition
further comprises a polycarboxylated ether dispersant.
20
8. A method as claimed in claim 7 wherein the set-delayed cement
comprise has a pumice-to-hydrated-lime weight ratio of about 3:1 to about 5:1,
wherein set retarder is present in an amount of about 0.01% to about 2% by
weight of the pumice, and wherein the polycarboxylated ether dispersant is
5 present in an amount of about 0.01% to about 2% by weight of the pumice.
9. A method as claimed in claim 1 wherein the set-delayed cement
composition further comprises at least one additive selected from the group
consisting of a weighting agent, a lightweight additive, a gas-generating additive,
a mechanical-property-enhancing additive, a lost-circulation material, a filtration-
10 control additive, a fluid-loss-control additive, a defoaming agent, a foaming
agent, a thixotropic additive, and any combination thereof.
10. A method as claimed in claim 1 wherein the set-delayed cement
composition remains in a pumpable fluid state for a time period of at least about 7
days prior to the activating.
15 11. A method as claimed in claim 1 wherein the set-delayed cement
composition remains in a pumpable fluid state for a time period of at least about
30 days prior to the activating.
12. A method as claimed in claim 1 wherein the activating comprises
adding a cement set accelerator to the set-delayed cement composition.
20 13. A method as claimed in claim 1 wherein the set-delayed cement
composition sets to develop a 24-hour compressive strength of at least about 50
psi as measured using an Ultrasonic Cement Analyzer at 140°F while maintained
at 3,000 psi.
14. A method as claimed in claim 1 wherein the set-delayed cement
25 composition is introduced into a well bore penetrating the subterranean
formation, the well bore having a bottom-hole static temperature of less than
about 200°F.
21
15. A method as claimed in claim 1 wherein the set-delayed cement
composition is introduced into an annulus between a wall of a well bore and a
conduit disposed in the well bore.
16. A method as claimed in cementing in a subterranean formation.
5 comprising:
providing a set-delayed cement composition comprising water,
pumice, hydrated lime, and a set retarder;
storing the set-delayed cement composition for a period of at least
about 1 day;
10 adding a cement set accelerator to the set-delayed cement
composition;
introducing the set-delayed cement composition into a
subterranean formation; and
allowing the set-delayed cement composition to set in the
15 subterranean formation.
17. A method as claimed in claim 16 wherein the pumice and the
hydrated lime are present in a weight ratio of pumice to hydrated lime of about
10:1 to about 1:1.
20 18. A method as claimed in claim 16 wherein the set retarder
comprises a phosphonic acid derivative, and wherein the set-delayed cement
composition further comprises a polycarboxylated ether dispersant.
19. A method as claimed in claim 16 wherein the set-delayed cement
composition further comprises a dispersant.
25 20. A method as claimed in claim 16 wherein the set-delayed cement
composition is stored for a time period of at least about 30 days.
21. A set-delayed cement composition comprising
water;
pumice;
30 hydrated lime; and
22
#
•> IV
"5A\J\N J
a set retarder, \| *
v orv r, wherein the set-delayed cement composition will remain in a
pumbable fluid state for a time period of at least about 1 day.
22. A composition as claimed in claim 21 the set-delayed cement
5 composition further comprises a dispersant.