CEMENT COMPOSITIONS WITH IMPROVED PROPERTIES FOR OIL AND GAS
WELLS
FIELD OF THE INVENTION
[0001] The present invention relates generally to cement compositions. In particular, the present
invention relates to cement coinpositions with inlproved propel-ties for cementing operations in
oil and gas wells.
BACKGROUND OF THE INVENTION
[0002] Hydraulic cement compositions are commonly utilized in a variety of subterranean
operations. For example, hydraulic cement compositions are used in primary cementing
operations whereby strings of pipe such as casing or liners are cemented in wellbores. Cement
compositions are also used in remedial cementing methods, for example, to seal cracks or holes
in pipe strings or cement sheaths, to seal highly permeable formation zones or fractures, to place
a cement plug, and the like.
[0003] These well cementing operations, however, often suffer structural failures due to stresses
on the set cement. The high fluid pressures and/or temperatures inside the cemented pipe string
during different stages like testing, perforating, fluid injection or fluid production cause both
radial and longitudinal movements of the pipes within the wellbores. These movements of the
pipes exert stresses on the set cement. Because of these stresses on the cement sheath, the
cement bond between the exterior surfaces of the pipe or the wellbore walls, or both, fail. The
failures then allow leakage of formation fluids and so forth.
[0004] Thus, for successful cementing operations, the cement composition or the cement slurry
needs to have several important properties. For instance, the oil well cement composition needs
to have a pumpable viscosity, fluid loss control, minimized settling of particles, good
compressive strength and the ability to set within a practical time. For years silica fume has
been widely used to achieve these properties along with other additives of the oil well ceinent
compositions due to its water consumptive nature, particle size, accelerated pozzolanic
reactivity, chemical composition, and increased rate of hydration.
(00051 However, though silica fume is known to improve durability, in an attempt to increase
the compressive strength of the ceinent compositions with silica fume, the ceinent composition
suffers from various inadequacies. For example, an increase in the compressive strength of the
cement composition is often negated by the increased water ratio and silica fime dosage in the
cement composition. This results in reduced workability and handling propel-ties of the cement
composition for primary and secondary cementing operations. The other demerits of using silica
fume include poor rheology of the cement composition, causing cement composition to become
cohesive, thixotropic, and sticky and thus, making it difficult to be placed fully and efficiently
in wellbores.
[0006] In light of the above, there is a need in the field well cementing operations for cement
compositions which have increased compressive strengths. There is also a need of cement
compositions which have other improved desired parameters like low fluid loss, improved
rheology, increased stability, low permeability and a gas tight behavior.
SUMMARY OF THE INVENTION
[0007] A cement composition has been provided for different cementing operations in
wellbores of oil and gas wells. The cement composition comprises a hydraulic cement, water to
form a slurry, and a reinforcing agent. The water in the composition ranges from 44% to 100%
by weight of the cement. The reinforcing agent is in a range of 5% to 35% by weight of the
cement and is a granulated slag of high glass content with high reactivity. In an embodiment of
the present invention, compressive strength of the composition is increased by at least 7%,
density of the composition is increased by at least 2%, consumption of water in the composition
is reduced by at least 4%, initial consistency of the composition is increased by at least 50%,
fluid loss of the composition is reduced by at least 23%, and rheology of the composition is
increased by at least 22%. Further, in an embodiment of the present invention, the composition
is a light weight cement composition with density ranging from 1.46 gmlcc to 1.62 gmlcc. In
another embodiment of the present invention, the composition is a heavy weight cement
composition with a density of at least 2.2 gmlcc.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
[0008] The present invention is described by way of embodiments illustrated in the
accompanying drawings wherein:
[0009] FIG. 1 is a flow chart illustrating a process for preparing and testing one or more cement
compositions in accordance with an embodiment of the present invention;
[0010] FIG. 2 is a graph illustrating compressive strength measurement results for a cement
composition in accordance with an embodiment of the present invention;
[0011] FIG. 3 illustrates test results for a gas migration test conducted on a cement composition
in accordance with an embodiment of the present invention;
[0012] FIG. 4 illustrates test results for a gas migration test conducted on a cement composition
in accordance with another embodiment of the present invention;
[0013] FIG. 5 illustrates test results for a gas migration test conducted on a lightweight cement
composition in accordance with an embodiment of the present invention;
[0014] FIG. 6 illustrates test results for a gas migration test conducted on a lightweight cement
composition in accordance with another embodiment of the present invention;
[0015] FIG. 7 illustrates test results for a gas migration test conducted on a lightweight cement
composition in accordance with another embodiment of the present invention; and
[0016] FIG. 8 illustrates test results for a thickening time test conducted on a heavy weight
cement composition in accordance with an embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0017] The present invention provides cement compositions with enhanced and superior
performance parameters for different cementing operations in oil and gas wells. The cement
compositions have reduced fluid loss, improved rheological parameters, free water, improved
gas tight property with lower permeability, better thennal stability, and increased compressive
strength.
[0018] The following disclosure is provided in order to enable a person having ordinary skill in
the art to practice the invention. Exemplary embodiments are provided only for illustrative
purposes and various modifications will be readily apparent to persons skilled in the art. The
general principles defined herein may be applied to other embodiments and applications without
departing from the spirit and scope of the invention. Also, the terminology and phraseology
used is for the purpose of describing exemplary embodiments and should not be considered
limiting. Thus, the present invention is to be accorded the widest scope encompassing numerous
alternatives, modifications and equivalents consistent with the principles and features disclosed.
For purpose of clarity, details relating to technical material that is known in the technical fields
related to the invention have not been described in detail so as not to unnecessarily obscure the
present invention.
I00191 The present invention would now be discussed in context of embodiments as illustrated
in the accompanying drawings.
[0020] Various cementing techniques are employed during different phases of wellbore
operations. One cementing technique may be used to secure, fix, plug and/or block various
components, openings, or regions within a wellbore. Another cementing technique may be used
in forming a new wellbore and secure or fix various components including casings, liners,
strings, and the like. Yet another cementing technique may be used for remedial operations to
repair a casing in a wellbore and/or to achieve formation isolation. Yet another cementing
technique may be employed during well abandonment. Broadly, the different cementing
operations may be categorized into primary cementing operations and secondary cementing
operations. Primary cementing is a process of placing a cement sheath around a casing or liner
string. It cai-ries out a zonal isolation to prevent migration of fluids in the annulus, support for
the casing or liner string, and protection of the casing string from corrosive formation fluids.
Secondary cementing or remedial cementing is a cementing operation performed to repair
primary cementing problems and to treat conditions arising after the wellbore has been
constlucted. The remedial cementing can be further categorized into squeeze cementing and the
placing of cement plugs.
[0021] The design of cement compositions for these cementing techniques is a critical task as
often oil and gas wells extend to significant depths where conditions within the well can be
extremely harsh, for example, high temperatures and pressures. In this regard, oil and gas well
cement compositions described herein have been designed and tested for an anticipated broad
range of temperature and pressure conditions that may occur during different cementing
operations in oil and gas wells.
[0022] FIG. 1 is a flowchart illustrating a process for preparing and testing one or more cement
compositions for different cementing operations in oil and gas wells, in accordance with an
embodiment of the present invention. At step 102, one or more cement compositions are
prepared. The one or more cement compositions comprise hydraulic cement, water to form a
slurry, and a reinforcing agent. The hydraulic cement in the cement composition may be selected
from a group consisting of Portland cements, pozzolana cements, gypsum cements, high
aluminum content cements, silica cements, and high alkalinity cements. In an embodiment of
the present invention, the hydraulic cement in the cement composition is American Petroleum
Institute (API) Class G High Sulfate-Resistant (HSR) cement. The water may be selected from
a group consisting of fresh water, tap water, unsaturated salt water, and saturated salt water. In
an embodiment of the present invention, the reinforcing agent in the cement composition is
obtained through controlled granulation of slag of high glass content with high reactivity. In
accordance with the invention, compositions comprising slag of high glass content have
demonstrated surprising and unexpected results. Empirically, compositions of the invention
exhibit, by way of example, higher compressive strength, improved gas tight behaviour,
improved rheological parameters, better densities, improved consistencies, lower fluid loss, and
lower water usage than coinpositions of the art. In another embodiment of the present invention,
the ceinent compositions are prepared with silica fume.
[0023] In an exemplary embodiment of the present invention, the reinforcing agent is based on
slag of high glass content with high reactivity and has a much finer and optimized particle size
than other hydraulic materials like cement, fly ash, silica fume etc. The slag of high glass content
is obtained through a process of controlled granulation. The reinforcing agent enhances
performance of concrete in fresh and hardened stages due to its optimized particle size
distribution. The raw materials of the reinforcing agent are primarily composed of low calcium
silicates. The processing of calcium silicates with other select ingredients results in controlled
particle size distribution (PSD). Preferably, D values of particle size are Dl0 < 2pm, D50 <
5pm and D90 < 20pm. The computed blain value based on PSD is 8000-12000 cm2lgm. This
ultra-fine PSD facilitates in low fluid loss, low rheology, enhanced stability, low permeability,
improved durability, and a gas tight behavior. Preferably, the reinforcing agent of slag of high
glass content comprises 32 to 34% by weight CaO, 18 to 20% by weight A1203, 1.8 to 2.0% by
weight Fe203, 0.3 to 0.7% by weight S03, 8 to 10% by weight MgO, and 33 to 35% by weight
SiOz.
(00241 In one or more embodiments of the present invention, the cement composition further
comprises known in the art chemicals and other additives which may enhance the desired
properties of the cement composition. The chemicals and additives may include, without any
limitation, accelerators, fluid loss control agents, retarders, fluid reducers or dispersants,
weighting materials, extenders, lost circulation control agents, deformer, anti-gas migration
additives, strength retrogression and other miscellaneous additives. The accelerators are the
chemicals that reduce the setting time of a cement composition or slurry and increase the rate
of compressive strength development. The retarders are the chemicals which extend the setting
time of a cement composition. The fluid loss control agents are used to maintain a consistent
fluid volume within a cement composition to ensure that the slurry performance properties
remain within a predetermined range. The fluid reducers or dispersants are used to reduce
viscosity of the cement con~position. The weighting materials may be used to increase the
density of the cement composition. The extenders are added to decrease the density or increase
the yield of the cement con~position.
[0025] Further, it may apparent to a person of ordinary skill in the art that prior to preparing a
cement composition in a laboratory, data pertaining to an oil and gas well where the cementing
operation is to be conducted is collected. The data related to the oillgas well is critical in
designing the cement composition. In embodiments of the present invention, this data
comprises, without any limitation, well name, location of the well, type of cementing operation,
casing size, depth of casing, hole size, Bottom Hole Static Temperature (BHST), Bottom Hole
Circulating Temperature (BHCT), raising time and break, type of mud, mud density and
rheology, and any specific problem associated with the well like lost circulation, kicks, salt
composition etc.
(00261 Based on the data of the oil and gas well, cement compositions or slurries are prepared
and tested for their applicability for different types of cementing operations. It may be apparent
to a person of ordinary skill in the art that the preparation and testing of cement compositions
is done based on API recommendations. In an embodiment of the present invention, one or more
cement compositions are prepared by first placing predefined quantity of water in a waring
blender. The blender is turned on at a slow speed, initially ranging from 3800-4200 for 15
seconds. Then dry hydraulic cement is added to the water along with predefined quantities of
the reinforcing agent and other necessary additives. The mixture is mixed at a high speed
ranging from 1 1500- 12500 RPM for another 35 seconds to obtain the cement composition.
(00271 At step 104, the one or more cement compositions or the obtained mixtures are then
tested on a plurality of parameters to ascertain their applicability for different cementing
operations for oil and gas wells. The plurality of parameters include, without any limitation,
specific gravity or density, thickening time, fluid loss, free fluid, rheology, compressive
strength, stability, and gas migration.
100281 The specific gravity is defined as the ratio between the weight of a given volume of
cement and weight of an equal volume of water. In an exemplary embodiment of the present
invention, the specific gravity of the ceinent composition is tested or measured using pressurized
fluid density scale.
100291 The thickening time of a sluny is calculated to determine the time required to mix and
pump the cement composition for different cementing operations. In an embodiment of the
present invention, it is the time elapsed from the initial application of temperature and pressure
to the time required for the slurry to reach a consistency of 100 Bearden units of consistency
(Bc). The thickening time is a hnction of temperaturelpressure, type of ceinent used, and
various additives added to the ceinent composition and is determined at BHCT conditions. In
an exemplary embodiment of the present invention, the thickening time of the cement
composition is calculated or tested using High-Pressure, High-Temperature (HPHT)
consistometer as it supports elevated pressure and temperature conditions similar to that in oil
and gas wells.
[0030] The fluid loss is a phenomena which occurs when a cement composition or slurry is
placed against permeable formation and water from the cement composition enters into the
formation. If the fluid loss is not controlled it may lead to cement job failure or poor cementation
job. Thus, the fluid-loss test determines the relative effectiveness of a cement slurry to retain its
water phase or to lose a portion of its water phase as a filtrate to the formation. In exemplary
embodiments of the present invention, an atmospheric consistometer and an HTHP filter press
may be used for measuring or testing the fluid loss of the cement composition.
[0031] The rheology measurements become significant as different flow patterns may be
encountered depending on conduit geometry, flow velocity and physical properties of fluid. The
different flow patterns are characterized by the velocity and movement of the particles in
different cross sections of the conduit and accordingly defined as plug flow, laminar flow or
turbulent flow. The rheology of a cement composition is defined by Bingham-Plastic or Power
Law Model or Herschel-Bulkley Model of flow mechanics. In an exemplary embodiment of the
present invention, any known in the art viscoineter or V-G meter may be used to measure
viscosity of the cement composition.
[0032] The compressive strength developed by a cement composition depends on various
factors such as water ceinent ratio, temperature, time and additives used. For testing purposes it
is necessary to define all these conditions. Further, the minimum compressive strength required
to hold the casing and to seal the formation is 500 per square inch (psi). The colnpressive
strength of the set cements mass increases with time and temperature. API recommends a
maximum pressure of 3000 psi, as higher pressures have little effect on compressive strength
during the hydration process of the ceinent composition. In an exemplary embodiment of the
present invention, the compressive strength of the ceinent compositions is measured or tested
using an Ultrasonic Cement Analyser (UCA). In another exemplary embodiment of the present
invention, the compressive strength of the ceinent compositions is measured or tested using
crush method.
100331 Further, the cement composition is conditioned to simulate dynamic placement in a
wellbore. The cement slurry is left static to determine if the cement slurry experiences particle
sedimentation wherein the heavier particles settle at the bottom while the lighter particles
remains on top. These sedimentation results are then analyzed to understand the static stability
of the cement composition in the wellbore conditions. In an exemplary embodiment of the
present invention, to test the stability, the ceinent composition is divided into at least three equal
parts (top/middle/bottom) and their densities are measured individually. The difference in
density between the three sections indicates whether the slurry is stable or unstable.
[0034] The gas migration tests are conducted to determine the resistance to gas invasion or gas
flow into the cement composition or slurry after its placement in the well. In an exemplary
embodiment of the present invention, a gas migration test instrument allows real time
measurement of gas migration during the transition period, when the slurry is changing from a
pumpable liquid state to a solid state.
I00351 After different tests are conducted on the one or more cement compositions, a
comparative analysis ofthe test results in conducted. The comparative analysis of the test results
indicates applicability of the cement compositions for different cementing operations for oil and
gas wells.
[0036] Further, the predetermined temperatures at which the cement compositions are tested
are critical in designing the ceinent compositions for the different cementing operations. In one
or more embodiment of the present invention, the predetermined temperatures include, without
any limitation BHCT and BHST. The BHCT is the temperature to which the ceinent will be
exposed as it circulates past the bottom of the casing. The BHCT controls the tiine that it takes
for the cement to setup (thickening time). It may be apparent to a person of ordinary skill in the
art that BHCT can be measured or estimated using teinperature probes that are circulated with
the drilling fluid or using the temperature schedules of API RP 1 OB. 1. Further, the BHCT may
affect different parameters of the cement con~position which may include, without any
limitation, slurry thickening time, rheology, fluid loss, stability (settling), and set tiine of the
cement slurry. The BHST is generally higher than BHCT and is teinperature of the undisturbed
fonnation at the final depth in a well. It considers a motionless condition where no fluids are
circulating and cooling the wellbore. BHST plays a vital role in the strength development of the
cured cement. The BHST affects compressive-strength development and cement integrity for
the life of the well. The testing of the cement composition at BHST facilitates optimization of
design of the cement composition.
100371 Further, as disclosed in FIG. 1, various cement compositions are prepared and tested for
their applicability for different cementing operations in oil and gas wells. The preparation of the
cement compositions and the tests conducted on the cement compositions have been disclosed
by way of examples.
Example 1
[0038] In exemplary embodiments of the present invention, different cement compositions are
prepared as per oil and gas well cementing operation requirements. The different cement
compositions are prepared by mixing lOOgm of API class G cement HSR (High Sulfate
Resistance) with different percentages (BWOC) of reinforcing agent, different percentages
(BWOC) of water, and different percentages (BWOC) of dispersants. A first cement
composition is prepared by mixing API class G cement HSR and 5% (BWOC) reinforcing
agent. A second cement composition is prepared by mixing API class G HSR ceinent and 10%
(BWOC) reinforcing agent. A third celnent composition is prepared by mixing API class G
cement with 15% (BWOC) reinforcing agent and 0.2% (BWOC) dispersant. A fourth cement
composition is prepared by mixing API class G HSR cement with 20% (BWOC) reinforcing
agent and 0.4% (BWOC) dispersant. A fifth cement composition is prepared by mixing API
class G HSR cement with 25% (BWOC) reinforcing agent and 0.5% (BWOC) dispersant. A
sixth cement composition is prepared by mixing API class G celnent with 30% (BWOC)
reinforcing agent and 0.5% (BWOC) dispersant. Finally, a seventh cement composition is
prepared by mixing API class G HSR cement with 35% (BWOC) reinforcing agent and 0.5%
(BWOC) dispersant. The percentage of water in each cement composition has been disclosed
in Table 1. It may be apparent to a person of ordinary skill in the art that various other chemicals
may be added to the different cement compositions to conduct different tests.
I00391 The different ceinent compositions are then tested to check their applicability for
different cementing operations in wellbores. It may be apparent to a person of ordinary skill in
the art that the cement compositions may be tested according to know in the art techniques,
some of which have been described above. Further, the test conditions comprise BHST at
1 10°C, BHCT at 70°C, and pressure at 3000 psi.
[0040] The cement compositions and their respective test results for different parameters have
been listed in Table 1.
Seven different cement compositions with reinforcing agent (5% to 35% BWOC)
Water Density Initial Fluid Loss Rheology (Dial Readings) Compressive
% (gmtcc) Consistency (m1/30 300,200, 100, 60, 30, 6,3 Strength
minutes) RPM (psi)
104, 89, 70, 59, 44,20,16
Plastic Viscosity (PV)-55,
44 1.92 10 1900 28 12
Yield Point (YP)-50, Critical
Velocity Vc- 1 0 fps
11 8, 98, 75,62,44,21, 17
46 1.90 15 1700 PV-69, YP-50, 3 125
Vc-10.9 fps
116,96, 70,56,42, 16, 12
46 1.91 15 1252 PV-82,YP-3 8, 3500
VC- 10.7 fps
196, 174, 140, 1 12, 82,40, 26
46 1.94 15 88 1 PV- 107, YP-46, 4250
vc- 9.7 fps
145, 110, 56, 36, 20, 9, 7
46 1.96 20 615 PV-143,YP-38, 4500
Vc- 10.64 fps
188, 140, 94,72, 55, 33,27
46 1.97 20 600 PV- 146 ,YP-42, 4750
VC-12.6 fps
202, 146, 82, 54, 36,20, 16
46 1.98 25 550 PV- 154 YP- 44 , 4800
VC- 13.47 fps
(Table 1)
[0041] Based on test results, various observations can be the drawn from the test results. It may
be apparent to a person of ordinary skill in the art that these observations are merely examples
and several other inferences and observations can be drawn from the test results. The test results
indicate that with the increase of reinforcing agent from 5% to 35% in the ceinent composition,
the compressive strength of the cement composition increases from 28 12 psi to 4800 psi in 24
hours. In an embodiment of the present invention, the compressive strengths of different cement
compositions are tested or measured using crush method and the readings are noted for 24 hours.
In another embodiment of the present invention, the compressive strength of a cement
composition is tested or measured using the UCA technique. FIG. 2 is a graph showing
compressive strength measurement results for a ceinent composition in accordance with an
embodiment of the present invention. The ceinent composition under test is prepared by mixing
100 grams of API Class G cement with 15% (B WOC) reinforcing agent, 46% (BWOC) water,
0.1% (BWOC) tri butyl phosphate (TBP) as defoamer, and 0.2% (BWOC) dispersant. The
compressive strength of the cement composition is then tested using the UCA technique. The
results of the test have depicted in FIG. 2. As shown in graph, curve 'A' depicts the BHST,
curve 'By depicts the compressive strength of the cement composition under test, and curve 'C'
depicts the transit time. The UCA test is conducted for nearly 72 hours with BHST maintained
at 1 10°C. It may be noted by a person of ordinary skill in the art that at 72 hours the compressive
strength of the cement composition with 15% reinforcing agent has reached to a steady level of
2400 psi. It may also be noted that the cement composition has withstood a compressive strength
of 500 psi after 24 hours. Thus, the UCA test indicates that the cement composition successfully
prevents compressive strength retrogression due to addition of reinforcing agent.
[0042] Referring back to Table 1, the test results further indicate that with the increase of
reinforcing agent from 5% to 35% in the cement composition, the API fluid loss of the cement
composition decreases from 1900 milliliter (m1)/30 minutes to 550 m1/30 minutes.
100431 The test results further indicate that with the increase of reinforcing agent from 5% to
35% in the cement composition, the initial consistency of the cement composition increases
from 10 Bearden units of consistency (Bc) to 25 Bc.
[0044] The test results further indicate that with the increase of reinforcing agent fi-om 5% to
35% in the cement composition, the density of the cement composition increases from 1.92
gdcc to 1.98 gmlcc.
100451 The test results further indicate that with the increase of reinforcing agent fi-om 5% to
35% in the cement composition, the rheology of the cement composition increases from 10 feet
per second (fps) to 13.47 fps, the Yield Point (YP) of the cement composition ranges from 38
to 55, and the Plastic Viscosity (PV) of the cement composition ranges from 55 to 154.
[0046] The test results further indicate that a cement composition prepared by mixing cement
with 5% reinforcing agent and 44% of water results in a density of 1.92 ginlcc of the cement
composition, an initial consistency of 10 Bc, an API fluid loss of 1900 m113O min, a compressive
strength of 28 12 psi.
100471 The test results further indicate that a cement composition prepared by mixing cement
with 10% reinforcing agent and 46% of water results in a density of 1.90 gmlcc of the cement
composition, an initial consistency of 15 Bc, an API fluid loss of 1700 m1130 min, and a
compressive strength of 3 125 psi.
[0048] The test results fkrther indicate that a cement composition prepared by mixing cement
with 15% reinforcing agent, 0.2% of dispersant, and 46% of water results in a density of 1.91
gdcc of the cement composition, an initial consistency of 15 Bc, an API fluid loss of 1252
m1130 min, and a compressive strength of 3500 psi.
[0049] The test results further indicate that a cement composition prepared by mixing cement
with 20% reinforcing agent, 0.4% of dispersant, and 46% of water results in a density of 1.94
gdcc of the cement composition, an initial consistency of 15 Bc, an API fluid loss of 88 1 m1/3O
min, and a compressive strength of 4250 psi.
(00501 The test results further indicate that a cement composition prepared by mixing cement
with 25% reinforcing agent, 0.5% of dispersant, and 46% of water results in a density of 1.96
gdcc of the cement composition, an initial consistency of 20 Bc, an API fluid loss of 615 m113O
min, and a compressive strength of 4500 psi.
[0051] The test results fbrther indicate that a cement composition prepared by mixing cement
with 30% reinforcing agent, 0.5% of dispersant, and 46% of water results in a density of I .97
gdcc of the cement composition, an initial consistency of 20 Bc, an API fluid loss of 600 m113O
min, and a compressive strength of 4750 psi.
[0052] The test results fbrther indicate that a cement composition prepared by mixing cement
with 35% reinforcing agent, 0.5% of dispersant, and 46% of water results in a density of 1.98
gmlcc of the cement composition, an initial consistency of 25 Bc, an API fluid loss of 550 m1130
min, and a compressive strength of 4800 psi.
[0053] Further, FIG. 3 shows test results for a gas migration test conducted on a cement
composition in accordance with an embodiment of the present invention. The cement
composition is prepared by mixing 100 grams of API Class G cement with 15% (BWOC)
reinforcing agent, 46% (BWOC) water, 0.1% (BWOC) TBP, and 0.2% (BWOC) dispersant. In
an embodiment of the present invention, the cement composition is tested at 95OC and the test
results have been depicted in form of a graph in FIG. 3. In FIG. 3, curve 'A' depicts hydraulic
pressure, curve 'B' depicts lower pore pressure, curve 'C' depicts upper pore pressure, curve
'D' depicts gas pressure, curve 'E7 depicts balance, curve 'F' depicts gas flow, curve 'G' depicts
BHCT temperature, curve 'H' depicts the travelling of the piston in the gas migration test
instrument. Based on the curve 'F', it may be apparent to a person of ordinary skill in the art
that the cement composition shows a gas tight behaviour at anticipated temperature and pressure
conditions. Further, a person of ordinary skill in the art may note that during test when a gas
valve is opened i.e. when lower pore pressure (B) goes below to gas pressure (D), at around 425
minutes, the gas is allowed to flow through the cement composition by opening the valve. It is
then checked whether the cement composition is allowing gas to pass or not. It may be noted
that the cement composition continues to show a gas tight behaviour for further test period of
475 minutes. Thus, the test results indicate that with the addition of reinforcing agent, the
cement composition would show resistance to gas invasion or gas flow into the cement
composition or slurry after its placement in the well for a time period of 475 minutes.
Example 2
[0054] Further in exemplary embodiments of the present invention, various cement
coinpositions are prepared as per oil and gas well cementing operation requirement. These
cement coinpositions are prepared by mixing different percentages of silica hrne as reinforcing
agent with the 1 OOgln of API class G cement. The cement compositions further include different
percentages of water and dispersants. A first cement composition is prepared by mixing API
class G cement and 5% (BWOC) silica hme. No dispersant is added to this cement composition.
A second cement composition is prepared by mixing API class G cement with 8% silica fume
and 0.2% (BWOC) dispersant. A third cement composition is prepared by mixing API class G
cement with 10% (BWOC) silica fume and 0.2% (BWOC) dispersant. A fourth cement
composition is prepared by mixing API class G cement with 12% (BWOC) silica hrne and
0.4% (BWOC) dispersant. A fifth cement composition is prepared by mixing API class G
cement with 15% (BWOC) silica hrne and 0.4% (BWOC) dispersant. A sixth cement
composition is prepared by mixing API class G cement with 20% (BWOC) silica hme and
0.8% (BWOC) dispersant. A seventh cement composition is prepared by mixing API class G
cement with 20% (BWOC) silica hrne and 0.6% (BWOC) dispersant. An eighth cement
composition is prepared by mixing API class G cement with 25% (BWOC) silica fume and 1%
(BWOC) dispersant. A ninth cement composition is prepared by mixing API class G cement
with 25% (BWOC) silica fume and 1% (BWOC) dispersant. A tenth cement composition is
prepared by mixing API class G cement with 25% (BWOC) silica fume and 0.6% (BWOC)
dispersant. An eleventh cement composition is prepared by mixing API class G cement with
30% (BWOC) silica fume and 0.8% (BWOC) dispersant. Finally, a twelfth cement composition
is prepared by mixing API class G cement with 35% (BWOC) silica hrne and 1% (BWOC)
dispersant. The percentage of water in each cement composition has been disclosed in Table 2.
It may be apparent to a person of ordinary skill in the art that various other chemicals may be
added to the different cement compositions to conduct different tests.
100551 The different silica fume based cement compositions are then tested to check their
applicability for different cementing operations. The test conditions comprise BHST at 11 O°C,
BHCT at 70°C, and pressure at 3000 psi. The cement compositions and their respective test
results for different parameters have been listed in Table 2.
Twelve different cement compositions with Silica Fume
Rheology (Dial
Fluid Loss
Water Density Initial Readings)
(m1130
'YO (gmlcc) Consistency 300, 200, 100, 60,30, 6,3
minutes)
RPM
84 ,70, 52,44,38, 18, 14
46 1.88 10 1700 PV-45,YP-36, VC -7.5fps
-
87,73, 56,48,40,21, 16
46 1.87 10 1560 PV-5 1 ; YP-37,
Vc-8.03 fps
171, 155, 134, 120, 87,38,
46 1.89 10 1420 20 PV-63, YP-110,
Vc-13.8 fps
122, 99, 72, 57,46, 20, 16
46 1.90 10 1187 PV-84, YP-39,
VC-10.5 fps
178, 155, 121, 81,65, 30,
46 1.91 10 1047 23 PV-134, YP-57,
VC- 14.2 fps
231,210, 187, 172, 142,
46 1.91 10 512 50,42 PV-72, YP-160,
Vc- 1 6 fps
140, 110,78, 62, 50,22,
4 8 1.84 10 1154 18 PV-100, YP-41,
Vc-10.6 fps
Compressive
Strength
(psi)
2625
2735
2812
3015
3 187
Slurry highly
viscous
3500
Could not Could not
Could not be Could not be
48 be be Slurry highly viscous
determined determined
determined detennined
Could not Could not
Could not be Could not be
50-54 be be Slui-ry highly viscous
determined determined
determined determined
90,78,58,51,46,23,20
55 1.82 10 1229 3600
PV-5 1, YP-4 1, vc-9.3 fps
150, 124,96, 84, 62, 35,
55 1.83 10 93 5 2 1 3675
PV-82 , YP-67, VC-12 fps
55 1.84 10 Could not be Could not be determined 3725
determined
(Table 2)
[0056] Further, FIG. 4 shows test results for a gas migration test conducted on a cement
composition in accordance with an embodiment of the present invention. The cement
composition is prepared by mixing 100 grams of APl Class G cement with 35% (BWOC) silica
fume, 46% (BWOC) water, 0.1% (BWOC) TBP, and 0.5% (BWOC) dispersant. In an
embodiment of the present invention, the cement composition is tested at 75OC BHCT and the
test results have been depicted in form of a graph in FIG. 4. In FIG. 4, curve 'A' depicts
hydraulic pressure, curve 'By depicts lower pore pressure, curve 'C' depicts upper pore pressure,
curve 'D' depicts gas pressure, curve 'E' depicts balance, curve 'F' depicts gas flow, curve 'G'
depicts BHCT temperature, curve 'H' depicts the travelling of the piston in the gas migration
test instrument. Based on the graph in FIG. 4, it may be apparent to a person of ordinary skill
in the art that the cement composition fails to show a gas tight behavior at anticipated
temperature and pressure conditions. Further, a person of ordinary skill in the art may note that
during test when gas valve is opened i.e. when lower pore pressure (B) goes below gas pressure
(D), at around 375 minutes, the cement composition fails to show a gas tight behavior for further
test period. The same can be observed with a surge in the curve 'F', also shown with a dotted
oval shape. Thus, the test results indicate that even with addition of 35% silica fume, the cement
composition would not show a resistance to gas invasion or gas flow into the cement
coinposition or slul~yaf ter its placement in the well.
100571 Based on the test results in Table 1 and Table 2, the improvements may include, without
any limitation, increase in coinpressive strength of the cement composition by at least 7%,
increase in density of the cement composition by at least 2%, reduction in consumption of water
by at least 4%, increase in initial consistency of the ceinent composition by at least 50%,
reduction of fluid loss by at least 23%, and increase in rheological parameters by at least 22%.
Table 3 shows improvement in different properties of the cement coinpositions of the present
invention in comparison to the ceinent compositions with silica fume. It may be apparent from
Table 3 that the cement compositions of the present invention have achieved improvement in
almost all the properties or parameters. Furthermore, cement compositions with reinforcing
agent show better gas tight behavior than cement compositions with silica fime. Furthermore,
for few silica fume based ceinent compositions the density, initial consistency, fluid loss,
rheology, and compressive strengths could not be tested as the cement slurries under test became
highly viscous. Thus, the comparative test results indicate that cement compositions with
reinforcing agent are more suitable for different cementing operations of oil and gas wells.
Property of cement Cement
con~position composition with
Silica fume
Compressive strength 2625
(psi)
Density (grnlcc)
Water Consumption
(BWOC)
Initial consistency (Bc) 10
Fluid loss (m1130 1154
minutes) I
Rheology I PV-45
Cement
composition of
present invention
Percentage
increasetdecrease
in property
Table 3
20
[0058] Further in an embodiment of the present invention, a lightweight cement composition is
designed and tested for cementing operations for Coalbed Methane (CBM) wells. Light weight
cements are used when there is a weak subterranean fornlation as a lightweight cement exerts a
lower hydrostatic pressure on the formation than regular cements. For CBM well cementing
operations, the lightweight cement needs to possess a low density and a high colnpressive
strength. The density of the cement compositions can be lowered by mixing known in the art
lightweight additives including, but not limited to, sealed micro balloons, and borosilicate glass.
The lightweight cements can also be created by injecting the cement with a gas, such as nitrogen,
in order to create a foam. Thus, while the density of cement composition can be controlled by
various known in the art methods, there are limitations which restricts use of these methods.
Thus, to overcome the limitations, in one or more embodiments of the present invention, one or
more lightweight cement cornpositions are prepared with the reinforcing agent and silica hlne
and are tested at different conditions including anticipated BHST, BHCT, and pressure ratings
in the CBM wells. The preparation of the cement compositions and the tests conducted on the
cement compositions have been disclosed by way of examples.
Example 3
[0059] In one or more embodiments of the present invention, two different types of lightweight
cement compositions are prepared. A first lightweight cement colnposition is prepared by
mixing 100 gm of API class G cement with 100% (BWOC) water. The first lightweight cement
colnposition also comprises 35% (BWOC) silica hme, 70% (BWOC) Polyvinyl chloride
(PVC), 1.2% (BWOC) Cement Friction Reducer- 3 (CFR-3) dispersant, and 0.1% (BWOC)
TBP. Further, a second lightweight cement composition is prepared by mixing 100 gm of API
class G cement with 100% (BWOC) water and 15% (BWOC) of reinforcing agent. The second
lightweight cement composition also comprises 70% (BWOC) PVC, and 0.1 % (BWOC) TBP.
The second lightweight cement composition does not comprise any dispersant. The two
lightweight cement compositions are then tested on various parameters including, without any
limitation, density, thickening time, fluid loss, rheology, gas tight behavior, and compressive
strength. The test conditions comprise BHST at 55OC, BHCT at 40°C, and pressure at 1 100 psi.
[0060] The test results for the lightweight first cement co~npositionsh as been listed in Table 4.
The test results for the second light weight cement compositions has been listed in Table 5.
First lightweight cement composition with Silica Fume (35% BWOC) for use in CBM
Density Thickening Fluid Loss Rheology (Dial Readings) Compressive
(gmlcc) Time (m1130 300, 200, 100, 60, 30, 6, 3 Strength (psi)
(minutes) minutes) RPM
1.46 235 406 124, 92, 60,48,47,26,24 1500 at 24 hours
PV - 88, YP - 37, Vc - 1 lfps 1750 at 48 hours
(Table 4)
[0061] In an embodiment of the present invention, the first lightweight cement composition
with silica fume (35% BWOC) is further tested for its gas migration properties. FIG. 5 shows
test results for a gas migration test conducted on the first lightweight cement composition in
accordance with an embodiment of the present invention. Apart from the above composition,
the first lightweight cement composition further comprises 0.2% (B WOC) gas stop additive. In
an embodiment of the present invention, the first lightweight cement composition is tested at
BHST and BHCT equal to 70°C and 45°C respectively and the test results have been depicted
in form of a graph in FIG. 5. In FIG. 5, curve 'A' depicts hydraulic pressure, curve 'By depicts
lower pore pressure, curve 'C' depicts upper pore pressure, curve 'D' depicts gas pressure, curve
'E' depicts balance, curve 'F' depicts gas flow, curve 'G' depicts BHCT temperature, curve 'H'
depicts the travelling of the piston in the gas migration test instrument. Based on the graph in
FIG. 5, it may be apparent to a person of ordinary skill in the art that the cement composition
fails to show a gas tight behavior at anticipated temperature and pressure conditions. Further, a
person of ordinary skill in the ai-t may note that during test when gas valve is opened i.e. when
lower pore pressure (B) goes below gas pressure (D), at around 296 minutes, the cement
composition fails to show a gas tight behavior for further test period. The same can be observed
with a surge in the curve 'F', also shown with a dotted oval shape at 300 minutes. Thus, the test
results indicate that even with addition of 35% silica fume, the cement composition would not
show a resistance to gas invasion or gas flow into the cement composition or slurry after its
placement in the oil and gas well.
Second lightweight cement composition with reinforcing agent (15% BWOC) for use
in CBM
Density
(gm/cc)
Rheology I Thickening Compressive -
Time
(minutes)
Fluid Loss
(m1130
minutes)
RPM I
(Dial Readings)
300, 200, 100, 60, 30, 6, 3
Strength (psi)
I
100621 Further, FIGS 6 and 7 depict gas migration test conducted on the second lightweight
cement composition in accordance with different embodiments of the present invention. For
conducting the gas migration test, the second lightweight cement composition further comprises
0.2% (BWOC) gas stop additive. In one embodiment of the present invention, the second
lightweight cement composition is tested at BHST and BHCT equal to 70°C and 45°C
respectively and the test results have been depicted in form of a graph in FIG. 6. In another
embodiment of the present invention, the second lightweight cement composition is tested at
BHST and BHCT equal to 1 10°C and 70°C respectively and the test results have been depicted
in form of a graph in FIG. 7. In Figs. 6 and 7, curve 'A' depicts hydraulic pressure, curve 'B'
depicts lower pore pressure, curve 'C' depicts upper pore pressure, curve 'D' depicts gas
pressure, curve 'E' depicts balance, curve 'F' depicts gas flow, curve 'G' depicts BHCT
temperature, curve 'H' depicts the travelling of the piston in the gas migration test instrument.
Based on the graphs in Figs. 6 and 7, it may be apparent to a person of ordinary skill in the art
that the second light weight cement composition shows a gas tight behavior at anticipated
temperature and pressure conditions. Further, a person of ordinary skill in the art may note that
during test when gas valve is opened i.e. when lower pore pressure (B) becomes less to gas
pressure (D), at 575 minutes in FIG. 6 and 300 minutes in FIG. 7, the second light weight cement
composition continues to show a gas tight behavior for further test period. The test results
indicate that with the addition of reinforcing agent, the second light weight cement composition
shows a resistance to gas invasion or gas flow into the cement composition or slurry after its
68,52,33,23, 16,8,6 RPM
PV - 55, YP - 13, Vc - 7fps
1700 at 24 hours
2000 at 48 hours
(Table 5)
placement in the oil and gas well for a time period of 750 minutes (as shown in FIG. 6) and for
a time period of 375 minutes (as shown in FIG. 7).
[0063] Further, the test results from Table 4 and Table 5 indicate that with the use of 15%
reinforcing agent, the lightweight ceinent composition gives better test results as compared to
with addition of 35% silica fume. While the density of both the first and second lightweight
cement composition remains similar, the compressive strength of the lightweight ceinent
composition with reinforcing agent is higher at 24 hours when compared to compressive
strength of the lightweight cement composition with silica fume. Similarly, the compressive
strength of the lightweight cement composition with reinforcing agent is higher at 48 hours
when compared to compressive strength of lightweight cement composition with silica fume
for the same time period. The test results further indicate that the lightweight cement
composition with reinforcing agent has better rheological parameters when compared to the
lightweight cement composition with silica fume as reinforcing agent. Furthermore, the test
results indicate that cement composition with reinforcing agent shows better gas tight behavior
than cement composition with silica fume. Further, due to large volume of silica fume (35%
BWOC), difficulties in mixing were observed when the cement composition was prepared with
silica fume. On the other hand, no such mixing difficulties were encountered with reinforcing
agent as only 15% (BWOC) reinforcing agent was sufficient to provide an improved cement
composition. Thus, the comparative test results indicate that lightweight cement compositions
with the reinforcing agent are more suitable for different cementing operations in CBM wells.
Example 4
(00641 In one or more embodiments of the present invention, one or more lightweight ceinent
compositions are prepared and tested at conditions comprising BHST equal to 55OC, BHCT
equal to 40°C, and pressure at 1 100 psi. The one or more lightweight cement compositions are
tested for meeting the desired compressive strength requirements. Firstly a gel slurry is prepared
and tested on various parameters which are critical for cementing CBM wells. In an exemplary
embodiment of the present invention, the gel slurry is prepared by 2% (BWOC) pre hydrated
Bentonite clay which is kept overnight and mixed with the hydraulic cement.
[0065] Further, a lightweight cement composition is prepared by mixing 100 gm of API class
G cement with 90% (BWOC) water, 35% (BWOC) silica fume, and 0.1% (BWOC) TBP.
Another lightweight cement composition is prepared by mixing 100 gm of API class G cement
with 100% (BWOC) water, 35% (BWOC) reinforcing agent, and 0.1 % (BWOC) TBP. The three
compositions are then tested and the test results been listed in Table 6, Table 7 and Table 8. The
test results indicate that with addition of reinforcing agent, compressive strength of the
lightweight cement composition increases by a huge margin with a stability in the density of the
composition. Thus, the comparative test results indicate that lightweight cement compositions
with the reinforcing agent are more suitable for different cementing operations in CBM wells.
I Gel slurry for use in CBM
Fluid Loss
(m1/30
minutes)
Density
(gmlcc)
Thickening
Time
(minutes)
Rheology
(Dial Readings)
300, 200, 100, 60, 30, 6, 3
RPM
(Table 6)
Compressive
Strength (psi)
69, 56, 50,48,44, 12 ,8
PV-26.5, YP-41, VC-8.20fps
I Lightweight cement composition with Silica fume (35% BWOC) for use in CBM I
230 at 24 hours
(minutes)
Fluid Loss
(m1/30
minutes)
Rheology
(Dial Readings)
300, 200, 100, 60, 30, 6, 3
RPM
Compressive
Strength (psi)
240 at 24 hours
(Table 7)
Second lightweight cement composition with reinforcing agent (35% BWOC) for use
in CBM well
Density
(gdcc)
Thickening
Time
Fluid Loss Rheology
(Dial Readings)
Compressive
Strength (psi)
(minutes) (m1/30
minutes)
300,200,100,60,30,6,3 RPM
I I
(Table 8)
Example 5
100661 In an embodiment of the present invention, a cement composition is prepared and tested
for desired compressive strengths at 1 day, 3 days and 7 days of curing. The ceinent composition
is prepared by mixing 100 gm of API class G cement with 100% (BWOC) water, 35% (BWOC)
reinforcing agent, 0.1% (BWOC) deformer, and 0.5% (BWOC) dispersant. The ceinent
composition is then tested at BHST in the range of 160°C-200°C and a pressure of 3000 psi.
The test results show a compressive strength of 1350 psi after 1 day, 1875 psi after 3 days and
2200 psi after 7 days of curing. The desired increase in compressive strength of the cement
composition, with the reinforcing agent, at high temperature and pressure conditions indicates
applicability of the cement composition for different cementing operations in oil and gas wells.
With the unique particle size distribution and inbuilt CaO, the reinforcing agent results in
formation of a dense pore structure, which facilitates improved workability and its retention,
and better compressive strength at all ages.
Example 6
[0067] In an embodiment of the present invention, the effect of reinforcing agent on thickening
time of a heavy weight cement composition is tested. FIG. 8 shows test results for a thickening
time test conducted on a heavy weight ceinent in accordance with an embodiment of the present
invention. The thickening time test is used to simulate pumping conditions in order to determine
a length of time before the heavy weight cement composition becomes difficult or impossible
to pump. A cement composition is prepared by mixing 100 grams of API Class G cement with
35% (BWOC) reinforcing agent, and 46% (BWOC) water. The heavy weight cement
composition also comprises 0.5% (BWOC) CFR-3 dispersant, 0.1% (BWOC) tli butyl
phosphate (TBP), 1.3% (BWOC) Synthetic Cement Retarder (SCR), and 1.3% (BWOC) known
in the art co-retarder, for example COMPONENT RTM. The cement composition hrther
contains 40% (BWOC) known in the art weight additive like MICROMAXTMw hich makes the
cement composition a heavy weight cement composition with a density of 2.2 grnlcc. Further,
as depicted in FIG. 8 curve 'A' shows thickening time of the heavy weight cement composition,
curve 'B' shows pressure, and curve 'C' shows BHCT as testing conditions. Based on the
readings from the graph, it may be noted by a person of ordinary skill in the art that the initial
consistency of the cement composition is 25 Bc and continues to be in a pumpable range i.e. 10
Bc after 2 hours and 30 minutes and at 170°C. The cement con~positiont hen starts getting thick
and shows a consistency of 100 Bc at 2 hours 53 minutes. It may also be noted by a person of
ordinary skill in the art that with the addition of Reinforcing agent, the heavy weight cement
composition gives desired thickening time test results and is applicable for different cementing
operations in oil and gas wells. In an exemplary embodiment of the present invention, the
thickening time test is conducted using a pressurized consistometer.
[0068] Thus, based on test results for various cement compositions, it may be apparent to a
person of ordinary skill in the art, that cement compositions comprising slag of high glass
content have demonstrated surprising and unexpected results. With addition of the reinforcing
agent, the cement compositions have shown higher compressive strength, improved gas tight
behaviour, improved rheological parameters, better densities, improved consistencies, lower
fluid loss, and lower water usage than cement compositions prepared with silica fume.
[0069] While the present invention has been shown and described with reference to preferred
embodiments, it will be understood by those skilled in the art that various changes in form and
detail may be made therein without departing from or offending the spirit and scope of the
invention as defined by the appended claims.
We claim:
1. A cement composition for wellbores, the composition comprising:
a hydraulic cement;
water to form a slurry, wherein the water ranges from 44% to 100% by weight of the
cement; and
a reinforcing agent in a range of 5% to 35% by weight of the cement, wherein the
reinforcing agent is a granulated slag of high glass content with high reactivity.
2. The composition as claimed in claim 1, wherein the reinforcing agent comprises 32% to
34% by weight CaO, 18% to 20% by weight A1203, 1.8% to 2.0% by weight Fe203, 0.3%
to 0.7% by weight S03, 8% to 10% by weight MgO, and 33% to 35% by weight SiO2.
3. The composition as claimed in claim 1 or 2, wherein compressive strength of the
composition is increased by at least 7%.
4. The composition as claimed in claim 1 or 2, wherein compressive strength of the
composition ranges from 28 12 per square inch (psi) to 4800 psi in 24 hours.
5. The composition as claimed in claim 1 or 2, wherein the composition has a compressive
strength of at least 1350 psi at day 1, at least 1875 psi at day 3, and at least 2200 psi at day
7 of curing at a Bottom Hole Static Temperature (BHST) in a range of 160°C-200°C, and
at a pressure of at least 3000 psi, wherein the reinforcing agent is in the amount of 35% by
weight of cement.
6. The composition as claimed in claim 1 or 2, wherein density of the composition is increased
by at least 2%.
7. The composition as claimed in claim 1 or 2, wherein density of the composition ranges from
1.92 gm/cc to 1.98 gm/cc.
8. The composition as claimed in claim 1 or 2, wherein consumption of water in the
composition is reduced by at least 4%.
9. The composition as claimed in claim 1 or 2, wherein initial consistency of the composition
is increased by at least 50%.
10. The con~positiona s claimed in claim 1 or 2, wherein initial consistency of the composition
ranges from 10 Bearden units of consistency (Bc) to 25 Bc.
1 1. The composition as claimed in claim 1 or 2, wherein fluid loss of the composition is reduced
by at least 23%.
12. The composition as claimed in claim 1 or 2, wherein fluid loss of the composition ranges
from 1900 milliliter (m1)/30 minutes to 550 m1/30 minutes.
13. The composition as claimed in claim 1 or 2, wherein rheological parameter of the
composition is increased by at least 22%.
14. The composition as claimed in claim 1 or 2, wherein Critical Velocity (Vc) of the
composition ranges from 10 feet per second (fps) to 13.47 fps, Yield Point (YP) of the
composition ranges from 38 to 55, and Plastic Viscosity (PV) of the composition ranges
from 55 to 154.
15. The composition as claimed in claim 1 or 2, wherein the composition has a gas tight behavior
for a time period of 475 minutes at Bottom Hole Circulating Temperature (BHCT) of 95°C.
16. The composition as claimed in claim 1 or 2, wherein the composition has a gas tight behavior
for a time period in a range of 375 minutes to 750 minutes at BHST in the range of 70°C to
1 10°C and BHCT in a range of 45°C to 70°C.
17. The colnposition as claimed in claim 1 or 2, wherein the composition is a light weight
cement composition.
18. The composition as claimed in claim 17, wherein density of the composition ranges from
1.46 gidcc to 1.62 gmlcc.
19. The composition as claimed in claim 17, wherein compressive strength of the composition
is increased by at least 13%.
20. The composition as claimed in claim 17, wherein compressive strength of the composition
is at least 1700 psi at 24 hours and at least 2000 psi at 48 hours.
21. The composition as claimed in claim 1 or 2, wherein the composition is a heavy weight
cement composition.
22. The composition as claimed in claim 2 1, wherein density of the composition is at least 2.2
gmlcc.
23. The composition as claimed in claim 21, wherein the composition has a consistency of at
least 25 Bc at 2 hours and 45 minutes, a consistency of at least 70 Bc at 2 hours and 51
minutes, and a consistency of at least 100 Bc at 2 hours and 53 minutes.