Field of Invention
This invention relates to a calcium aluminate cement composition containing
a set retarder of an organic acid and a polymeric mixture and a method of cementing
relating thereto. The cement composition includes a set retarder of an organic acid
5 and a polymeric mixture comprising: water; citric acid; a low-molecular weight
polymer of carboxymethyl cellulose; and a low-molecular weight polymer of a
lignosulfonate. The cement composition includes calcium aluminate cement. In
another embodiment, the subterranean formation is a high-temperature well, or a
sour gas or acid gas well.
10
Summary of Invention
According to an embodiment, a cement composition for use in an oil or gas
well, the cement composition comprises: a calcium aluminate cement; water; an
organic acid; and a polymeric mixture comprising: (A) water; (B) citric acid; (C) a
15 first polymer, wherein the first polymer: (i) comprises a cellulose backbone and
carboxymethyl functional groups; and (ii) has a molecular weight of less than
100,000; and (D) a second polymer, wherein the second polymer: (i) comprises a
lignosulfonate; and (ii) has a molecular weight of less than 100,000, wherein a test
composition consisting essentially of: the cement; the water; the organic acid: and
20 the polymeric mixture, and in the same proportions as in the cement composition has
a thickening time of at least 5 hours at a temperature of 300 °F (148.9 °C) and a
pressure of 10,000 psi (68.9 MPa)
According to another embodiment, a method of cementing in a subterranean
formation comprises: introducing the cement composition into the subterranean
25 formation; and allowing the cement composition to set.
Brief Description of Figures
In the accompanying Figure
Figure-1 shows the compressive strength in psi versus time in hours for the
cement composition
- 2 -
Description of the Invention
As used herein, the words "comprise,'* "have,*" "include," and all
grammatical variations thereof are each intended to have an open, non-limiting
meaning that does not exclude additional elements or steps.
5 As used herein, the words "consisting essentially of," and all grammatical
variations thereof are intended to limit the scope of a claim to the specified materials
or steps and those that do not materially affect the basic and novel characteristics) of
the claimed invention. For example, the test composition consists essentially of: the
cement; the water; the organic acid; and the polymer, and in the same proportions as
10 in the cement composition. The test composition can contain other ingredients so
long as the presence of the other ingredients does not materially affect the basic and
novel characteristics of the claimed invention, i.e., so long as the test composition
has a thickening time of at least 5 hours at a temperature of 300 °F (148.9 °C) and a
pressure of 10,000 psi (68.9 MPa).
15 As used herein, a "fluid" is a substance having a continuous phase that tends
to flow and to conform to the outline of its container when the substance is tested at a
temperature of 71 °F (22 °C) and a pressure of one atmosphere "atm" (0.1
megapascals "MPa"). A fluid can be a liquid or gas. A homogenous fluid has only
one phase; whereas a heterogeneous fluid has more than one distinct phase. A
20 colloid is an example of a heterogeneous fluid. A colloid can be: a slurry, which
includes a continuous liquid phase and undissolved solid particles as the dispersed
phase; an emulsion, which includes a continuous liquid phase and at least one
dispersed phase of immiscible liquid droplets; a foam, which includes a continuous
liquid phase and a gas as the dispersed phase; or a mist, which includes a continuous
25 gas phase and liquid droplets as the dispersed phase.
As used herein, a "cement composition" is a mixture of at least cement and
water. A cement composition can include additives. As used herein, the term
"cement" means an initially dry substance that develops compressive strength or sets
in the presence of water. An example of cement is Portland cement. A cement
30 composition is generally a slurry in which the water is the continuous phase of the
- 3 -
slurry and the cement (and any other insoluble particles) is the dispersed phase. The
continuous phase of a cement composition can include dissolved solids.
Oil and gas hydrocarbons are naturally occurring in some subterranean
formations. A subterranean formation containing oil or gas is sometimes referred to
5 as a reservoir. A reservoir may be located under land or off shore. Reservoirs are
typically located in the range of a few hundred feet (shallow reservoirs) to a few tens
of thousands of feet (ultra-deep reservoirs). In order to produce oil or gas, a wellbore
is drilled into a reservoir or adjacent to a reservoir.
A well can include, without limitation, an oil, gas or water producing well, an
10 injection well, or a geothermal well. As used herein, a "well" includes at least one
wellbore. A wellbore can include vertical, inclined, and horizontal portions, and it
can be straight, curved, or branched. As used herein, the term ''wellbore" includes
any cased, and any uncased, open-hole portion of the wellbore. A near-wellbore
region is the subterranean material and rock of the subterranean formation
15 surrounding the wellbore. As used herein, a "well" also includes the near-wellbore
region. The near-wellbore region is generally considered to be the region within
approximately 100 feet of the wellbore. As used herein, "into a well" means and
includes into any portion of the well, including into the wellbore or into the nearwellbore
region via the wellbore.
20 A portion of a wellbore may be an open hole or cased hole. In an open-hole
wellbore portion, a tubing string may be placed into the wellbore. The tubing string
allows fluids to be introduced into or flowed from a remote portion of the wellbore.
In a cased-hole wellbore portion, a casing is placed into the wellbore which can also
contain a tubing string. A wellbore can contain an annulus. Examples of an annulus
25 include, but are not limited to: the space between the wellbore and the outside of a
tubing string in an open-hole wellbore; the space between the wellbore and the
outside of a casing in a cased-hole wellbore; and the space between the inside of a
casing and the outside of a tubing string in a cased-hole wellbore.
During well completion, it is common to introduce a cement composition into
30 an annulus in a wellbore. For example, in a cased-hole wellbore, a cement
composition can be placed into and allowed to set in an annulus between the
- 4 -
wellbore and the casing in order to stabilize and secure the casing in the wellbore.
By cementing the casing in the wellbore, fluids are prevented from flowing into the
annulus. Consequently, oil or gas can be produced in a controlled manner by
directing the flow of oil or gas through the casing and into the wellhead. Cement
5 compositions can also be used in primary or secondary cementing operations, wellplugging,
or squeeze cementing.
During cementing operations, it is necessary for the cement composition to
remain pumpable during introduction into the well and until the composition is
situated in the portion of the well to be cemented. After the cement composition has
10 reached the portion of the well to be cemented, the cement composition ultimately
sets. As used herein, the term "set" and all grammatical variations thereof means the
process of becoming hard or solid through curing. A cement composition that
thickens too quickly while being pumped can damage pumping equipment or block
tubing or pipes, and a cement composition that sets too slowly can cost time and
15 money while waiting for the composition to set.
Often times, a wellbore fluid, such as a cement composition, is modified for
use in challenging wellbores. Examples of challenging wellbores include, but are
not limited to, high temperature and/or high pressure wells, wells containing high
amounts of an acid gas, such as carbon dioxide gas (acid gas wells), steam injection
20 wells, steam production wells, geothermal wells, and wells containing high amounts
of a sour gas, such as hydrogen sulfide gas (sour gas wells). For example, at high
static subterranean temperatures, and in the presence of brines containing carbon
dioxide, conventional cement compositions containing hydraulic cements (e.g.,
Portland cement), particularly those which exhibit high pH (i.e., greater than 11).
25 rapidly deteriorate due to carbonation of alkaline components of the set cement such
as calcium hydroxide. Thus, the use of conventional hydraulic cement compositions,
such as Portland cement, in these types of environments may result in the loss of
wellbore integrity. An alternative to using conventional hydraulic cements in
challenging wellbores is the use of a calcium aluminate based cement (CABC).
30 CABC has a higher temperature resistance compared to Portland cement/silica
mixtures, which can lead to a longer term integrity of the cement sheath. The use of
- 5 -
CABC offers other advantages as it provides resistance to sulfates, corrosion, and
sour gas. Calcium Aluminate Cements (CACs), when combined with a soluble
phosphate salt (e.g., sodium metaphosphate) and a pozzolanic material (e.g.. Class F
fly ash), form cement compositions that upon setting, can exhibit improved physical
5 and mechanical properties. Some of the improved properties include, binding to the
subterranean formation and/or casing and to itself, a higher compressive strength,
carbonation and corrosion resistance, and low permeability.
A variety of CACs are commercially available with varying alumina
contents. While attractive from an economic standpoint, one drawback to the use ol'
10 CACs is their unpredictable thickening times even when set retarders such as citric
acid are used, especially at elevated temperatures, for example at temperatures
greater than 200 °F (93.3 °C). As such, the unpredictable thickening times of CAC
slurries make well cementing with these types of cement a challenge. A need
therefore exists for materials that can retard the CAC slurries so that the CAC slurry
15 may display predictable thickening times and remain pumpable before and during
placement into the desired wellbore location.
It is to be understood that if any test (e.g., thickening time) requires the test
be performed at a specified temperature and possibly a specified pressure, then the
temperature and pressure of the cement composition is ramped up to the specified
20 temperature and pressure after being mixed at ambient temperature and pressure.
For example, the cement composition can be mixed at 71 °F (22 °C) and 1 atm (0.1
MPa) and then placed into the testing apparatus and the temperature of the cement
composition can be ramped up to the specified temperature. As used herein, the rate
of ramping up the temperature is in the range of about 3 °F/min to about 5 °F/min
25 (about 1.67 °C/min to about 2.78 °C/min). The purpose of the specific rate of
temperature ramping during measurement is to simulate the temperature profile
experienced by the cement composition as it is being pumped downhole. After the
cement composition is ramped up to the specified temperature and possibly specified
pressure, the cement composition is maintained at that temperature and pressure for
30 the duration of the testing.
- 6 -
As used herein, the "thickening time" is how long it takes for a cement
composition to become unpumpable at a specified temperature and pressure. The
pumpability of a cement composition is related to the consistency of the
composition. The consistency of a cement composition is measured in Bearden units
5 of consistency (Be), a dimensionless unit with no direct conversion factor to the
more common units of viscosity. As used herein, a cement composition becomes
"unpumpable" when the consistency of the composition reaches 70 Be. As used
herein, the consistency of a cement composition is measured according to API
Recommended Practice 10-B2, First Edition, July 2005 as follows. The cement
10 composition is first mixed according to the following procedure. The water is added
to a mixing container and the container is then placed on a mixer base. The motor of
the base is then turned on and maintained at 4,000 revolutions per minute "rpm" (+/-
200 rpm). The cement and any other ingredients are added to the container at a
uniform rate in not more than 15 seconds (s). After all the cement and any other
15 ingredients have been added to the water in the container, a cover is then placed on
the container, and the cement composition is mixed at 12,000 rpm (+/- 500 rpm) for
35 s (+/- 1 s). The cement composition is then placed in the test cell of a High-
Temperature, High-Pressure (HTHP) consistometer, such as a FANN® Model 290 or
a Chandler Model 8240. Consistency measurements are taken continuously until the
20 cement composition exceeds 70 Be.
Another desirable property of a cement composition is that the composition
exhibit good rheology. Rheology is a measure of how a material deforms and flows.
As used herein, the "rheology" of a cement composition is measured according to
API Recommended Practice 10-B2, First Edition, July 2005 as follows. The cement
25 composition is mixed. The cement composition is placed into the test cell of a
rotational viscometer, such as a FANN® Model 35 viscometer, fitted with a Bob and
Sleeve attachment and a spring number 1. The cement composition is tested at the
specified temperature and ambient pressure, about 1 atm (0.1 MPa). Rheology
readings are taken at multiple rpm's, for example, at 3, 6, 100, 200, 300, and 600.
30 A cement composition can develop compressive strength. Cement
composition compressive strengths can vary from 0 psi to over 10,000 psi (0 to over
- 7 -
69 MPa). Compressive strength is generally measured at a specified time after the
composition has been mixed and at a specified temperature and pressure.
Compressive strength can be measured, for example, at a time of 24 hours.
According to ANSI/API Recommended Practice 10B-2, compressive strength can be
5 measured by either a destructive method or non-destructive method.
The non-destructive method continually measures correlated compressive
strength of a cement composition sample throughout the test period by utilizing a
non-destructive sonic device such as an Ultrasonic Cement Analyzer (UCA)
available from FANN® Instruments in Houston, Texas. As used herein, the
10 "compressive strength" of a cement composition is measured using the nondestructive
method at a specified time, temperature, and pressure as follows. The
cement composition is mixed. The cement composition is then placed in an
Ultrasonic Cement Analyzer and tested at a specified temperature and pressure. The
UCA continually measures the transit time of the acoustic signal through the sample.
15 The UCA device contains preset algorithms that correlate transit time to compressive
strength. The UCA reports the compressive strength of the cement composition in
units of pressure, such as psi or MPa.
The compressive strength of a cement composition can be used to indicate
whether the cement composition has initially set or is set. As used herein, a cement
20 composition is considered "initially set" when the cement composition develops a
compressive strength of 50 psi (0.3 MPa) using the non-destructive compressive
strength method at a temperature of 212 °F (100 °C) and a pressure of 3,000 psi (20
MPa). As used herein, the "initial setting time" is the difference in time between
when the cement and any other ingredients are added to the water and when the
25 composition is initially set.
As used herein, the term "set," and all grammatical variations thereof, are
intended to mean the process of becoming hard or solid by curing. As used herein,
the "setting time" is the difference in time between when the cement and any other
ingredients are added to the water and when the composition has set at a specified
30 temperature. It can take up to 48 hours or longer for a cement composition to set.
Some cement compositions can continue to develop compressive strength over the
- 8 -
course of several days. The compressive strength of a cement composition can reach
over 10,000 psi (69 MPa).
A set retarder can be added to a cement composition to help increase the
thickening time of the cement composition such that the cement composition remains
5 pumpable for a desired time at a specific temperature. The thickening time is
proportional to the setting time, i.e., the longer the thickening time, the longer the
setting time will be. Therefore, a set retarder can be added to a cement composition
to help increase the setting time of the cement composition. However, if a set
retarder is in too-high a concentration, the cement composition may remain in a fluid
10 state for an undesirably long period of time, often referred to as the Waiting-on-
Cement (WOC) time, during which no further operations can be performed on the
wellbore. Therefore, the set retarder also can be used in a concentration such that the
cement composition sets in a desired time.
Set retarders can be a polymer. A polymer is a large molecule composed of
15 repeating units, typically connected by covalent chemical bonds. The number o(
repeating units of a polymer can range from approximately 11 to greater than 10,000.
The number of repeating units of a polymer is referred to as the chain length of the
polymer. A polymer is formed from the polymerization reaction of monomers.
During the polymerization reaction, some chemical groups can be lost from each
20 monomer. The piece of the monomer that is incorporated into the polymer is known
as the repeating unit or monomer residue. The backbone of the polymer is the
continuous link between the monomer residues. The polymer can also contain
functional groups connected to the backbone at various locations along the
backbone. Polymer nomenclature is generally based upon the type of monomer
25 residues comprising the polymer. A polymer formed from one type of monomer
residue is called a homopolymer. A copolymer is formed from two or more different
types of monomer residues. In a copolymer, the repeating units from each of the
monomers can be arranged in various ways along the polymer chain. For example,
the repeating units can be random, alternating, periodic, or block. The conditions of
30 the polymerization reaction can be adjusted to help control the average number of
repeating units (the average chain length) of the polymer.
- 9 -
A polymer has an average molecular weight, which is directly related to the
average chain length of the polymer. The average molecular weight of a polymer
has an impact on some of the physical characteristics of a polymer, for example, its
solubility in water, its viscosity, and its biodegradability. For a copolymer, each o\~
5 the monomers will be repeated a certain number of times (number of repeating
units). The average molecular weight for a copolymer can be expressed as follows:
Avg. molecular weight= (M.W.mi * RU mi) + (M.W.m2 * RU m2). ..
10 where M.W.mi is the molecular weight of the first monomer; RU mi is the number
of repeating units of the first monomer; M.W.m2 is the molecular weight of the
second monomer; and RU m2 is the number of repeating units of the second
monomer. Of course, a terpolymer would include three monomers, a tetra polymer
would include four monomers, and so on.
15 It has been discovered that an organic acid and a polymeric mixture can
function effectively as a set retarder for calcium aluminate cement (CAC)
compositions. The cement composition can be used in challenging wellbores. such
as high-temperature wells, or sour gas or acid gas wells. As used herein, a hightemperature
well is a well with a bottomhole temperature of at least 200 °F (93.3
20 °C). As used herein, the bottomhole temperature refers to the downhole temperature,
often referred to as Bottom Hole Circulating Temperature (BHCT), at the portion of
the well to be cemented.
According to an embodiment, a cement composition for use in an oil or gas
well, the cement composition comprises: a calcium aluminate cement; water; an
25 organic acid; and a polymeric mixture comprising: (A) water; (B) citric acid; (C) a
first polymer, wherein the first polymer: (i) comprises a cellulose backbone and
carboxymethyl functional groups; and (ii) has a molecular weight of less than
100,000; and (D) a second polymer, wherein the second polymer: (i) comprises a
lignosulfonate; and (ii) has a molecular weight of less than 100,000, wherein a test
30 composition consisting essentially of: the cement; the water; the organic acid: and
the polymeric mixture, and in the same proportions as in the cement composition has
- 10-
a thickening time of at least 5 hours at a temperature of 300 °F (148.9 °C) and a
pressure of 500 psi (3.4 MPa).
According to another embodiment, a method of cementing in a subterranean
formation comprises: introducing the cement composition into the subterranean
5 formation; and allowing the cement composition to set.
It is to be understood that the discussion of preferred embodiments regarding
the cement composition or any ingredient in the cement composition, is intended to
apply to the composition embodiments and the method embodiments. Any reference
to the unit "gallons" means U.S. gallons.
10 The cement composition includes a calcium aluminate cement (CAC). The
CAC comprises at least calcium, aluminum, and oxygen. According to an
embodiment, the CAC comprises aluminum oxide (AI2O3) and calcium oxide (CaO).
The aluminum oxide can be present in the CAC in an amount in the range of about
30 weight (wt.) % to about 80 wt. %, alternatively from about 40 wt. % to about 70
15 wt. %, or alternatively from about 50 wt. % to about 60 wt. %, based upon the total
weight of the CAC. The calcium oxide can be present in the CAC in an amount in
the range of about 20 wt. % to about 60 wt. %, alternatively from about 30 wt. % to
about 50 wt. %, or alternatively from about 35 wt. % to about 40 wt. %, based upon
the total weight of the CAC. Additionally, the aluminum oxide to calcium oxide
20 (AbCVCaO) weight ratio in the CAC may vary from about 1:1 to about 4:1,
alternatively from about 2:1 to about 1.5:1. An example of a commercially-available
calcium aluminate-based cement is ThermaLock™, marketed by Halliburton Energy
Services.
The cement composition includes water. The water can be selected from the
25 group consisting of freshwater, brackish water, and saltwater, in any combination
thereof in any proportion. The cement composition can also include a salt.
Preferably, the salt is selected from sodium chloride, calcium chloride, calcium
bromide, potassium chloride, potassium bromide, magnesium chloride, and any
combination thereof in any proportion. Preferably, the salt is in a concentration in
30 the range of about 0.1% to about 40% by weight of the water.
- 11 -
According to an embodiment, the cement composition has a density of at
least 9 pounds per gallon (ppg). The cement composition can have a density in the
range of about 9 to about 22 ppg.
The cement composition includes an organic acid. As used herein, an
5 "organic acid" is an organic compound (i.e., containing at least one carbon atom) that
is a proton donor. Examples of organic acids include, but are not limited to,
carboxylic acid, sulfonic acid, lactic acid, acetic acid, formic acid, citric acid, tartaric
acid, oxalic acid, uric acid, ascorbic acid, and peracetic acid. The organic acid can
be selected from the group consisting of citric acid, tartaric acid, lactic acid, ascorbic
10 acid, and combinations thereof. According to an embodiment, the organic acid has a
pKa of less than 7, preferably in the range of about 0 to about 7. Commerciallyavailable
examples of suitable organic acids include, but are not limited to, Fe-2™
and HR®-25, marketed by Halliburton Energy Services, Inc.
The cement composition includes a polymeric mixture. The polymeric
15 mixture includes water. The water can be selected from the group consisting ol~
freshwater, brackish water, and saltwater, in any combination thereof in any
proportion.
The polymeric mixture includes citric acid.
The polymeric mixture includes a first polymer, wherein the first polymer:
20 comprises a cellulose backbone and carboxymethyl functional groups; and has a
molecular weight of less than 100,000. A polymer comprising a cellulose backbone
and carboxymethyl functional groups is commonly called carboxymethyl cellulose
(CMC). The polymer can be formed from an alkali-catalyzed reaction of cellulose
and chloroacetic acid. The carboxymethyl functional groups can become bound to
25 one or more of the hydroxyl functional groups of the cellulose backbone. The
maximum theoretical hydroxyl groups that could be substituted can be 3. This
number is known as degree of substitution (DS), and represents the average number
of hydroxyl groups that have substituted during the carboxylation reaction. For
optimum solubility, the DS can be greater than 0.40. At lower DS values, the CMC
30 has a tendency to swell rather than dissolve. According to an embodiment, the DS of
hydroxyl groups of the first polymer is in a range from 0.4 to 2.0. preferably from
- 12-
0.90 to 1.30. The first polymer has a molecular weight of less than 100,000,
preferably a molecular weight of less than about 30,000, and more preferably a
molecular weight of less than about 25,000. A commercially-available example of a
suitable first polymer is Ambergum® 3021 carboxymethyl cellulose, available from
5 Ashland Specialty Ingredients in Wilmington, DE.
The polymeric mixture includes a second polymer, wherein the second
polymer comprises a lignosulfonate and has a molecular weight of less than 100,000.
The lignosulfonate can include one or more functional groups. The functional group
can be, without limitation, sodium. The second polymer has a molecular weight of
10 less than 100,000, preferably a molecular weight of less than about 30,000. and more
preferably a molecular weight of less than about 25,000.
The ingredients making up the polymeric mixture can be in a variety of
ratios. According to an embodiment, the ratio of the first polymer, second polymer,
citric acid, and water is in the range from about 35:14:7:44 to about 80:4:2:14.
15 Preferably, the ratio of the first polymer, second polymer, citric acid, and water is
44:13:6:37.
A test composition consisting essentially of: the cement; the water: the
organic acid; and the polymeric mixture, and in the same proportions as in the
cement composition has a thickening time of at least 5 hours at a temperature of 300
20 °F (148.9 °C) and a pressure of 10,000 psi (68.9 MPa). According to an
embodiment, the organic acid and the polymeric mixture are in at least a sufficient
concentration such that the test composition has a thickening time of at least 5 hours
at a temperature of 300 °F (148.9 °C) and a pressure of 10,000 psi (68.9 MPa). The
organic acid and the polymeric mixture can also be in at least a sufficient
25 concentration such that the test composition has a thickening time in the range of
about 5 to about 15 hours at a temperature of 300 °F (148.9 °C) and a pressure of
10,000 psi (68.9 MPa). According to another embodiment, the organic acid and the
polymeric mixture are in at least a sufficient concentration such that the test
composition has a thickening time of at least 5 hours at at least one temperature in
30 the range of about 200 °F to about 370 °F (about 93.3 °C to about 187.8 °C) and a
pressure of 10,000 psi (68.9 MPa). The organic acid and the polymeric mixture can
- 13-
also be in at least a sufficient concentration such that the test composition has a
thickening time in the range of about 5 to about 15 hours at at least one temperature
in the range of about 200 °F to about 370 °F (about 93.3 °C to about 187.8 °C) and a
pressure of 10,000 psi (68.9 MPa).
5 The cement composition can have a thickening time of at least 5 hours at a
temperature of 300 °F (148.9 °C) and a pressure of 10,000 psi (68.9 MPa).
According to an embodiment, the organic acid and the polymeric mixture are in at
least a sufficient concentration such that the cement composition has a thickening
time of at least 5 hours at a temperature of 300 °F (148.9 °C) and a pressure of
10 10,000 psi (68.9 MPa). The organic acid and the polymeric mixture can also be in at
least a sufficient concentration such that the cement composition has a thickening
time in the range of about 5 to about 15 hours at a temperature of 300 °F (148.9 °C)
and a pressure of 10,000 psi (68.9 MPa). According to another embodiment, the
organic acid and the polymeric mixture are in at least a sufficient concentration such
15 that the cement composition has a thickening time of at least 5 hours at at least one
temperature in the range of about 200 °F to about 370 °F (about 93.3 °C to about
187.8 °C) and a pressure of 10,000 psi (68.9 MPa). The organic acid and the
polymeric mixture can also be in at least a sufficient concentration such that the
cement composition has a thickening time in the range of about 5 to about 15 hours
20 at at least one temperature in the range of about 200 °F to about 370 °F (about 93.3
°C to about 187.8 °C) and a pressure of 10,000 psi (68.9 MPa). According to
another embodiment, the organic acid and the polymeric mixture are in at least a
sufficient concentration such that the cement composition has a thickening time of at
least 5 hours at the bottomhole temperature and pressure of the well. The organic
25 acid and the polymeric mixture can be in at least a sufficient concentration such that
the cement composition has a thickening time in the range of about 5 to about 15
hours, alternatively of about 6 to about 10 hours, at the bottomhole temperature and
pressure of the well. One of skill in the art will be able to determine the
concentration of the organic acid and the polymeric mixture needed in order to
30 achieve the desired thickening time, for example, based on the bottom-hole
- 14-
temperature of the well, and other specific conditions of the well, such as the amount
of sour gas or an acid gas present.
According to an embodiment, the organic acid and the polymeric mixture are
in at least a sufficient concentration such that the cement composition has a
5 compressive strength greater than 1,000 psi (6.9 MPa), preferably greater than 2,000
psi (13.8 MPa), at a temperature of 400 °F (204.4 °C), preferably at at least one
temperature in the range of about 200 °F to about 370 °F (about 93.3 °C to about
187.8 °C). According to another embodiment, the organic acid and the polymeric
mixture are in at least a sufficient concentration such that the cement composition
10 has a compressive strength greater than 1,000 psi (6.9 MPa), preferably greater than
2,000 psi (13.8 MPa), at the bottomhole temperature of the well.
According to an embodiment, the organic acid and the polymeric mixture are
in a concentration equal to or less than a sufficient concentration such that the
cement composition has an initial setting time of less than 48. preferably less than
15 24, hours at a temperature of 300 °F (148.9 °C), preferably at at least one
temperature in the range of about 200 °F to about 370 °F (about 93.3 °C to about
187.8 °C). According to another embodiment, the organic acid and the polymeric
mixture are in a concentration equal to or less than a sufficient concentration such
that the cement composition has an initial setting time of less than 48, preferably less
20 than 24, hours at the bottomhole temperature of the well.
According to an embodiment, the organic acid and the polymeric mixture are
in a concentration equal to or less than a sufficient concentration such that the
cement composition has a setting time of less than 48, preferably less than 24, hours
at a temperature of 300 °F (148.9 °C), preferably at at least one temperature in the
25 range of about 200 °F to about 370 °F (about 93.3 °C to about 187.8 °C). According
to another embodiment, the organic acid and the polymeric mixture are in a
concentration equal to or less than a sufficient concentration such that the cement
composition has a setting time of less than 48, preferably less than 24, hours at the
bottomhole temperature of the well.
- 15-
The organic acid can be in a concentration of at least 0.2% by weight of the
cement (bwoc). The organic acid can also be in a concentration in the range of about
0.2% to about 4% bwoc, preferably about 0.5% to about 3% bwoc.
The polymeric mixture can be in a concentration of at least 0.05% by weight
5 of the cement (bwoc). The polymeric mixture can be in a concentration in the range
of about 0.05%o to about 10% bwoc, preferably in the range of about 0.1% to about
l%bwoc.
The cement composition can be used in a variety of wells. Examples of wells
the cement composition can be used in include, without limitation, high-temperature
10 and/or high-pressure wells, geothermal wells, sour gas wells, and acid gas wells.
The subterranean formation can have a bottomhole temperature of at least 200 °F
(93.3 °C). The subterranean formation can have a bottomhole temperature in the
range of about 200 °F to about 370 °F (about 93.3 °C to about 187.8 °C).
The cement composition can further include other additives. Examples of
15 other additives include, but are not limited to, a filler, a fluid loss additive, a friction
reducer, a light-weight additive, a defoaming agent, a high-density additive, a
mechanical property enhancing additive, a lost-circulation material, a filtrationcontrol
additive, a thixotropic additive, and combinations thereof.
The cement composition can include a filler. Suitable examples of fillers
20 include, but are not limited to, fly ash, sand, clays, and vitrified shale. Preferably,
the filler is in a concentration in the range of about 5% to about 50% by weight of
the cement (bwoc).
The cement composition can include a fluid loss additive. The fluid loss
additive can be a cationic starch as described in US Patent No. 6.846,357, issued on
25 Jan. 25, 2005 to Reddy et al., and US Patent No. 6,796,378, issued on Sep. 28. 2004
to Reddy et al., or polymers capable of viscosifying an aqueous acid as described in a
pending US patent application No. 12/961,234, filed on Dec. 6, 2010 and having for
named inventors Trissa Joseph et al., each of which is incorporated by reference
herein in its entirety. Preferably, the fluid loss additive is in a concentration in the
30 range of about 0.05% to about 10% bwoc.
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The cement composition can include a friction reducer. Suitable examples of
commercially-available friction reducers include, but are not limited to, CFR-2™,
CFR-3™, CFR-5LE™, CFR-6™, and CFR-8™, marketed by Halliburton Energy
Services, Inc. Preferably, the friction reducer is in a concentration in the range of
5 about 0.1 % to about 10% bwoc.
Commercially-available examples of other additives include, but are not
limited to, and are marketed by Halliburton Energy Services, Inc. under the
tradenames HIGH DENSE® No. 3, HIGH DENSE® No. 4, BARITE™, and
MICROMAX™, heavy-weight additives; SILICALITE™, extender and
10 compressive-strength enhancer; WELLLIFE® 665, WELLLIFE ® 809. and
WELLLIFE ® 810 mechanical property enhancers.
The method embodiments include the step of introducing the cement
composition into the subterranean formation. The step of introducing can be for the
purpose of at least one of the following: well completion; foam cementing; primary
15 or secondary cementing operations; well-plugging; squeeze cementing; and gravel
packing. The cement composition can be in a pumpable state before and during
introduction into the subterranean formation. In an embodiment, the subterranean
formation is penetrated by a well. The well can be, without limitation, an oil. gas. or
water production well, or an injection well. According to this embodiment, the step
20 of introducing includes introducing the cement composition into the well. According
to another embodiment, the subterranean formation is penetrated by a well and the
well includes an annulus. According to this other embodiment, the step of
introducing includes introducing the cement composition into a portion of the
annulus.
25 The method embodiments also include the step of allowing the cement
composition to set. The step of allowing can be after the step of introducing the
cement composition into the subterranean formation. The method embodiments can
include the additional steps of perforating, fracturing, or performing an acidizing
treatment, after the step of allowing.
30
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Examples
To facilitate a better understanding of the present invention, the following
examples of certain aspects of preferred embodiments are given. The following
examples are not the only examples that could be given according to the present
5 invention and are not intended to limit the scope of the invention.
Unless otherwise stated, each of the cement compositions had a density of
15.0 pounds per gallon (ppg) (1.797 kilograms per liter "kg/L") and contained at
least the following ingredients: tap water at a concentration of 40% by weight of the
cement "bwoc"; ThermaLock™ cement comprising calcium aluminate; and D-Air
10 3000L™ defoamer at a concentration of 0.02 gallons per sack of the cement "gal/sk".
The cement compositions also included, in varying concentrations, a polymeric
mixture and Fe-2™ organic acid. The polymeric mixture included a first polymer of
Ambergum® 3021 carboxymethyl cellulose having a molecular weight of 25.000, a
second polymer of sodium lignosulfonate having a molecular weight of less than
15 30,000, citric acid, and water. The ratio of the first polymer, second polymer,
organic acid, and water was 43.5:13:6.5:37.
All of the cement compositions were mixed and tested according to the
procedure for the specific test as described in The Detailed Description section
above. The thickening time tests were conducted at a variety of temperatures and a
20 pressure of 10,000 psi (68.9 MPa).
Table 1 contains thickening time data for the cement compositions at various
temperatures and varying concentrations of the organic acid and polymeric mixture.
As can be seen in Table 1, regarding composition numbers 1 - 3, the compositions
that did not contain both, the organic acid and the polymeric mixture had thickening
25 times of less than 2 hours; whereas, composition #1 containing both ingredients had
a thickening time of greater than 7 hours. This indicates that at a temperature of 300
°F, the organic acid and the polymeric mixture are needed in order to increase the
thickening time of the cement composition. As can also be seen with reference to
composition numbers 4 - 1 0 , the organic acid and the polymeric mixture function
30 effectively as a set retarder from temperatures ranging from 200 °F to 370 °F.
Moreover, with reference to composition numbers 11 - 13, for a given concentration
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of the organic acid, the concentration of the polymeric mixture may need to be
increased in order to increase the thickening time of the cement composition.
Table 1
Composition
#
1
2
3
4
5
6
7
8
9
10
11
12
13
Cone, of
organic acid
(% bwoc)
1
0
1
0.5
1
2
2
2
2
2
1
1
1
Cone, of
porymeric mixture
(gal/sk)
0.3
0.3
0
0.2
0.3
0.3
0.3
0.3
0.3
0.3
0.3
0.25
0.2
Temperature
(°F)
300
300
300
200
300
350
360
370
380
400
300
300
300
Thickening
Time
(hrsxnins)
728
0:30
1:55
528
728
9:30
10:12
1020
1:00
0:55
728
327
2:58
5 Table 2 contains rheology data for a cement composition containing: the
polymeric mixture at a concentration of 0.3 gal/sk and Fe-2™ organic acid at a
concentration of 2% bwoc at temperature of 71 °F (21.7 °C). As can be seen in
Table 2, the cement composition exhibited good rheology. This indicates that the
organic acid and the polymeric mixture did not adversely affect other desirable
10 properties of the composition.
Table 2
RPM
3
6
30
60
100
200
300
600
Values
4
6
14
26
39
74
114
218
Figure 1 is a graph of compressive strength in psi versus time in hours for a
cement composition having a density of 15.0 ppg (1.797 kg/L) and containing the
following ingredients: tap water at a concentration of 40% bwoc; ThermaLock™
cement comprising calcium aluminate; the polymeric mixture at a concentration of
5 0.2 gal/sk and Fe-2™ organic acid at a concentration of 1% bwoc as the set retardcrs:
and D-Air 3000L™ defoamer at a concentration of 0.02 gal/sk. Compressive
strength was measured at a temperature of 400 °F (204.4 °C) and a pressure of
10,000 psi (68.9 MPa) from a time of zero to 96 hours (4 days).
As can be seen in Figure 1, the cement composition developed a compressive
10 strength of greater than 1,750 psi (12.1 MPa) at a time of 12 hours. Moreover, the
composition had a compressive strength of greater than 2,500 psi (17.2 MPa) at a
time of 96 hours. This data indicates that the presence of the set retarders does not
adversely affect the compressive strength of the cement composition. The cement
composition also had an initial setting time of 2 hours and 14 minutes. This
15 indicates that the presence of the set retarders does not unnecessarily delay the initial
setting or final setting of the cement composition.
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
20 modified and practiced in different but equivalent manners apparent to those skilled
in the art having the benefit of the teachings herein. Furthermore, no limitations are
intended to the details of construction or design herein shown, other than as
described in the claims below. It is, therefore, evident that the particular illustrative
embodiments disclosed above may be altered or modified and all such variations are
25 considered within the scope and spirit of the present invention. While compositions
and methods are described in terms of "comprising," "containing," or "including"
various components or steps, the compositions and methods also can "consist
essentially of or "consist of the various components and steps. Whenever a
numerical range with a lower limit and an upper limit is disclosed, any number and
30 any included range falling within the range is 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 to b") disclosed
herein is to be understood to set forth every number and range encompassed within
the broader range of values. Also, the terms in the claims have their plain, ordinary
meaning unless otherwise explicitly and clearly defined by the patentee. Moreover,
5 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. 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.
10
-21 -

w.cu.: fV?!^' k
1. A method of cementing in a subterranean formation comprising: *£ « °
introducing a cement composition into the subterranean formation, wherein
5 the cement composition comprises:
(A) a calcium aluminate cement;
(B) water;
(C) an organic acid; and
(D) a polymeric mixture comprising:
10 (i) water;
(ii) citric acid;
(iii) a first polymer, wherein the first polymer:
(a) comprises a cellulose backbone and
carboxymethyl functional groups; and
15 (b) has a molecular weight of less than 100,000:
and
(iv) a second polymer, wherein the second polymer:
(a) comprises a lignosulfonate; and
(b) has a molecular weight of less than 100,000,
20 wherein a test composition consisting essentially of: the cement: the
water; the organic acid; and the polymeric mixture, and in the same
proportions as in the cement composition has a thickening time ol' at
least 5 hours at a temperature of 300 °F (148.9 °C) and a pressure of
10,000 psi (68.9 MPa); and
25 allowing the cement composition to set.
2. A method as claimed in Claim 1, wherein the water is selected from the
group consisting of freshwater, brackish water, and saltwater, in any combination
thereof in any proportion.
30
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3. A method as claimed in Claim 1, wherein the organic acid is selected from
the group consisting of citric acid, tartaric acid, lactic acid, ascorbic acid, and
combinations thereof.
5 4. A method as claimed in Claim 1, wherein the first polymer, the second
polymer, or the first and the second polymers have a molecular weight of less than
about 30,000.
5. A method as claimed in Claim 1, wherein the first polymer, the second
10 polymer, or the first and the second polymers have a molecular weight of less than
about 25,000.
6. A method as claimed in Claim 1, wherein the organic acid and the polymeric
mixture are in at least a sufficient concentration such that the test composition has a
15 thickening time of at least 5 hours at at least one temperature in the range of about
200 °F to about 370 °F (about 93.3 °C to about 187.8 °C) and a pressure of 10,000
psi (68.9 MPa).
7. A method as claimed in Claim 1, wherein the cement composition has a
20 thickening time of at least 5 hours at a temperature of 300 °F (148.9 °C) and a
pressure of 10,000 psi (68.9 MPa).
8. A method as claimed in Claim 7, wherein the organic acid and the polymeric
mixture are in at least a sufficient concentration such that the cement composition
25 has a thickening time in the range of about 5 to about 15 hours at at least one
temperature in the range of about 200 °F to about 370 °F (about 93.3 °C to about
187.8 °C) and a pressure of 10,000 psi (68.9 MPa).
9. A method as claimed in Claim 1, wherein the organic acid and the polymeric
30 mixture are in a concentration equal to or less than a sufficient concentration such
-23-
that the cement composition has a setting time of less than 48 hours at a temperature
of300°F (148.9 °C).
10. A method as claimed in Claim 1, wherein the organic acid is in a
5 concentration in the range of about 0.2% to about 4% by weight of the cement.
11. A method as claimed in Claim 1, wherein the polymeric mixture is in a
concentration in the range of about 0.05% to about 10% by weight of the cement.
10 12. A method as claimed in Claim 1, wherein the cement composition further
comprises other additives.
13. A method as claimed in Claim 12. wherein the other additives are selected
from the group consisting of a filler, a fluid loss additive, a friction reducer, a light-
15 weight additive, a defoaming agent, a high-density additive, a mechanical property
enhancing additive, a lost-circulation material, a filtration-control additive, a
thixotropic additive, and combinations thereof.
14. A method as claimed in Claim 1, wherein the cement composition has a
20 density in the range of about 9 to about 22 ppg.
15. A method as claimed in Claim 1, wherein the subterranean formation has a
bottomhole temperature in the range of about 200 °F to about 370 °F (about 93.3 °C
to about 187.8 °C).
25
16. A method as claimed in Claim 15, wherein the organic acid and the
polymeric mixture are in at least a sufficient concentration such that the cement
composition has a thickening time in the range of about 5 to about 15 hours, at the
bottomhole temperature and pressure of the well.
30 17. A method as claimed in Claim 1, wherein the subterranean formation is
penetrated by a well.
-24-
...,-^ 77 AUG M«
0 / 1 >? /
18. A method as claimed in Claim 17, wherein the well is a high-temperature
well, a high-pressure well, a geothermal well, a sour gas well, or an acid gas well.
5 19. A method as claimed in Claim 1, further comprising at least one of the
following steps: perforating, fracturing, or performing an acidizing treatment.
wherein the step is performed after the step of allowing.
20. A cement composition for use in an oil or gas well, the cement composition
10 comprising:
a calcium aluminate cement;
water;
an organic acid; and
a polymeric mixture comprising:
15 (A) water;
(B) citric acid;
(C) a first polymer, wherein the first polymer:
(i) comprises a cellulose backbone and carboxymethyl
functional groups; and
20 (ii) has a molecular weight of less than 100,000; and
(D) a second polymer, wherein the second polymer:
(i) comprises a lignosulfonate; and
(ii) has a molecular weight of less than 100,000,
wherein a test composition consisting essentially of: the cement; the water; the
25 organic acid; and the polymeric mixture, and in the same proportions as in the
cement composition has a thickening time of at least 5 hours at a temperature of 300
°F (148.9 °C) and a pressure of 10,000 psi (68.9 MPa).
Dated: this.2-6 day of August, 2014 @£lJD^f < _
30 (VD GULWAN1)
Patent Attorney of Applicant, Dua Associates
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