190079-MS

SPE-190079-MS
Lightweight and Ultra-Lightweight Cements for Well Cementing - A Review
A. Anya, Texas Tech University
Copyright 2018, Society of Petroleum Engineers
This paper was prepared for presentation at the SPE Western Regional Meeting held in Garden Grove, California, USA, 22-27 April 2018.
This paper was selected for presentation by an SPE program committee following review of information contained in an abstract submitted by the author(s). Contents
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Abstract
Lost circulation is a very common and expensive problem during drilling and cementing operations in the
oil and gas industry. The lost circulation problems encountered during drilling or cementing are a result of
one of two factors. These factors are the presence of zones of weak fracture gradients and the presence of
high permeability or thief zones downhole. Light weight cements are an effective solution for curbing lost
circulation caused by the breakdown of weak zones by conventional cement slurries. This paper presents a
discussion of the different methods, additives and technologies that have been and are currently employed
in the formulation of lightweight and ultra-lightweight cement slurries for cementing oil wells as well as
recent developments based on an extensive literature review. This paper also discusses the mechanical
performance, cost effectiveness and field logistical considerations of lightweight slurries formulated using
different methods as these are important factors that impact decision making on what slurry extension
method to choose for any given scenario.
The information presented in this paper is derived from an extensive review of information contained in
papers, journals and books spanning the last 50 years of well cementing and is summarized in such a way
that the paper serves as a quick guide to cement slurry extension technology and techniques.
An extensive review of the literature regarding lightweight cements showed that there are three general
methods of obtaining lightweight cement slurries. These methods include increasing cement slurry water
content (water extension) with the aid of viscocifying agents such as bentonite and sodium metasilicate,
adding lightweight materials like glass microspheres and incorporating foam into slurries. Reported test
data shows that apart from cement slurries containing glass microspheres and foamed cements, lightweight
slurries exhibit lower compressive strength and slower compressive strength development than heavy
slurries. Foamed cements pose the greatest design and field logistics challenge while cement slurries with
glass microspheres have gained more popularity due to the excellent compressive strength values achievable
at ultra-low densities despite their higher cost compared to water-extended slurries and lightweight slurries
containing other lightweight additives like fly ash.
The literature review presented also indicates a need for more research into improving lab mixing and
testing methods that replicate field applications of foam cement. There is also a need for research into more
cost-effective slurry extension additives and technology that exhibit acceptable mechanical performance for
well integrity assurance and rheological properties favorable to proper cement placement in the annulus.
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SPE-190079-MS
Introduction
Lost circulation in drilling and cementing operations is a common problem encountered in the oil and gas
industry. Two main causes of lost circulation are zones of weak fracture gradient that are easily broken
down by drilling fluids and cement slurries and thief zones or high permeability zones that permit the
flow of fluid from the wellbore into vugs and natural fractures in the adjacent formation. Lost circulation
leads to cost increases in the form of increased rig time, fluid replacements, loss circulation treatments,
remedial cementing and in a worst-case scenario, well abandonment. Economics, driven by low oil prices,
are causing operators to look for cost saving measures in drilling and completion operations. Lost circulation
not only increases these costs, but typically causes the implementation of more casing strings or multi-stage
cementing which both contribute to higher costs.
There are generally two methods for combatting lost circulation problems depending on the cause of the
losses. The first method involves the use of bridging agents and gelling agents in drilling fluids. Bridging
agents may be fibrous, flaky, granular or blended to bridge over thief zones. Gelling agents flocculate and
form a spongy mass on contact with water. These spongy masses plug vugs and fractures that may serve as
flow paths for drilling fluid into the formation. The second method used to curb lost circulation problems is
the use of advanced fluid formulations. These include lightweight drilling fluids and cement slurries, cement
slurries with short wait-on-cement times and thixotropic cements. Lightweight drilling fluids and cement
slurries reduce both the amount of overburden on adjacent formations and bottomhole ECD to prevent
breakdown of weak zones in the wellbore. Cements slurries with short wait-on-cement times develop gel
strength quickly enough to prevent significant fluid loss into high permeability zones. Thixotropic cements
gel up as soon as they enter large cavities due to the absence of shear stress acting on the fluid in such
cavities, preventing further inflow from the wellbore.
The use of conventional and unconventional lightweight cement to combat wellbore losses due to a
weak formation fracture gradient is a field of research that has seen numerous innovations over the last
four decades. Lightweight cements can be generally classified into water-extended cements, cements with
lightweight particles and foamed cements. Water-extended cements exhibit lightweight by means of an
increased water-cement ratio and typically contain viscosifying agents to prevent excessive free water and
provide slurry stability. Lightweight-particle cements contain solid particles that have specific gravities
lower than that of Portland cement. The idea is that the addition of enough lightweight particles in the
slurry composition will lead to reduced densities. Foamed cements are cements with gas, usually nitrogen
injected to produce a lightweight gas-liquid dispersion with ultralow to low specific gravity and acceptable
mechanical performance.
Certain challenges arise in the design of lightweight slurries for oil and gas applications. The main
concern in cement slurry design is the resulting set cement mechanical properties. The mechanical properties
of set cement determine its ability to support casing, withstand cracking due to thermal and mechanical stress
and maintain zonal isolation through the life of the well. Typically, set cement compressive strength and
compressive strength development have been the main mechanical properties of interest in the petroleum
industry. Lightweight cements compromise strength to achieve a lower density due to the reduced amount
of cementitious material. However, it is important to note that recent studies have shown other mechanical
properties such as hydraulic bond strength, Young's modulus and tensile strength to be more important to
the long-term integrity of a cement sheath (Thiercelin et al., 1998; Bosma et al., 1999). Second, increased
water-cement ratios and improperly dispersed lightweight additives increase the chance for slurry instability
and excessive free water. Third, there is also an increased chance of long wait-on-cement times due to
compromised strength development. Finally, there is a likelihood of ending up with a cement column that
is permeable to formation fluids or susceptible to attack from reactive downhole fluids if the lightweight
system is poorly designed. Lightweight cements can improve the economics of a well by preventing the
need for multiple cementing stages or reducing the amount of stages needed. This paper briefly discusses
SPE-190079-MS
3
the current technology and methods available for formulating low and ultra-low density cement slurries.
The application, advantages and disadvantages of each method will be discussed.
Water-Extended Cements
Water-extended cements are cements that exhibit lower than conventional densities by means of increased
water-cement ratios. API Specification 10A (an outline of standards for the manufacture and testing of oil
well cements published by the American Petroleum Institute) lists the water requirements for neat cements
made from each class of cement.
Table 1—Mix water requirements for neat cements of every class (American Petroleum Institute, Specification 10A).
Cement Class
Mix Water
(%BWOC)
Slurry
Density (ppg)
A
46
15.6
B
46
15.6
C
56
14.8
D
38
16.45
E
38
16.45
F
38
16.45
G
44
15.8
H
38
16.45
The mix water percentages employed in any slurry design will vary from the values shown in table 1
depending on the properties desired. The mix water percentage is a major factor that affects the slurry
density, free water level, solids settling, rheology, fluid loss control, slurry permeability and compressive
strength development of a cement slurry. With the addition of more water to a slurry, the risk of excessive
free water, solids settling and segregation, set cement permeability to formation fluids, slow compressive
strength development, long wait-on-cement time and diminished set cement compressive strength become
much higher. In addition to reduced density, water-extended cement slurries also lead to higher slurry yield
and volume.
To prevent the formation of excessive free water and maintain slurry homogeneity, viscosifying agents are
added to the slurry. The function of these viscosifying agents is to improve the solids suspension capabilities
of the slurry and prevent excessive free water formation through slurry viscosity increase and gelation. The
two most common viscofying agents used in cement slurry formulations are clays and sodium silicates.
The most common clay extender is bentonite and the most common sodium silicate extender is sodium
metasilicate.
Bentonite is a very common additive for water-extended cement slurries. Bentonite is a water absorbent
which expands when in contact with water, absorbing about 5.3% water for every 1% BWOC (by weight
of cement) added causing an increase in viscosity and gel strength. The addition of bentonite to cement
slurries leads to increased slurry viscosity and solids suspension capacity. Hence, slurry stability and water
retention can be maintained in slurries with higher water-cement ratios. Above bentonite concentrations of
6% BWOC, a dispersant is required to reduce the viscosity and gel strength of the slurry mixture (Nelson
and Guillot, 2008). Bentonite is a more effective extender when it is prehydrated with the mix water as
demonstrated below.
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SPE-190079-MS
Table 2—Comparison between slurry with prehydrated bentonite and slurry with dry-blended bentonite (Nelson and Guillot, 2008).
Prehydrated
Bentonite
(%BWOC)
Dry-Blended
Bentonite
(%BWOC)
Fresh Water
(gal/sk)
Prehydrated
Slurry
Density (ppg)
Dry-Blended
Slurry
Density (ppg)
0.5
2
6.4
14.8
14.8
1
4
7.6
14.1
14.2
1.5
6
8.8
13.5
13.7
2
8
10
13.1
13.3
2.5
10
11.2
12.7
12.9
3
12
12.4
12.4
12.6
4
16
14.8
11.9
12.2
5
20
17.2
11.5
11.8
However, there is no significant difference in the compressive strength obtained from both methods for
preparing the bentonite. Competent cement slurries with density as low as 11.5 ppg can be obtained with
bentonite as an extender (Nelson and Guillot, 2008). However, this density reduction comes with a price in
the form of reduced compressive strength. Figure 1 illustrates the effect of bentonite addition on set cement
compressive strength.
Figure 1—Effect of bentonite on compressive strength of set cement (Nelson and Guillot, 2008).
Bentonite is a relatively cheap clay and offers a cost-effective solution for designing lightweight cement
slurries. High concentrations of bentonite also offer the added benefit of improved fluid loss control. The
salinity of the mix water is a very important factor to be considered with regards to bentonite hydration. High
salinity will inhibit bentonite hydration and consequently reduce slurry extension and cement yield. For high
salinity slurries, the use of attapulgite is suggested as an alternative to bentonite (Nelson and Guillot, 2008).
Another common viscosifier used in the design of cement slurries is sodium metasilicate. Sodium
metasilicate is a white soluble powder manufactured by fusing silica with sodium carbonate at a temperature
of 2552 degree Fahrenheit (Heinold et al., 2002) and is available as a solid or liquid. Sodium metasilicate
viscosifies the slurry by reacting with lime (calcium hydroxide) or calcium chloride in the cement to form
calcium silicate gel. This process permits the addition of more water to increase the water-cement ratio
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without risking the formation of excessive free water. Slurry densities as low as 11.1 ppg (Nelson and
Guillot, 2008) can be obtained with sodium metasilicate at concentrations that vary from 0.1 percent to 4.0
percent (Heinold et al., 2002). Sodium metasilicate can be used as an additive up to a temperature of 200
degrees Fahrenheit. It is important to note that sodium metasilicate can act as an accelerator. This tendency to
accelerate the cement hydration reduces the effectiveness of other additives that may be present in the slurry.
When the solid form of sodium metasilicate is used, it is recommended to dry-blend it with the cement or
else, the addition of calcium chloride may be necessary to cause gel formation (Nelson and Guillot, 2008).
When the liquid form of sodium metasilicate is used, it is added to the mix water before mixing in the slurry.
Typical performance for class G cements with sodium metasilicate is illustrated in Table 3.
Table 3—Performance of class G cement with added sodium metasilicate (Nelson and Guillot, 2008).
Sodium Metasilicate
(%BWOC)
Slurry Density (ppg)
Mix Water (%BWOC)
24 hr Compressive
Strength at 120°F (psi)
0
15.8
44
4770
0.15
14.5
60
1746
1
14.5
60
1896
0.25
14
68
1420
1
14
68
1640
0.5
13.5
78
946
2
13.5
78
1327
0.5
13
90
750
2
13
90
120
0.75
12.5
> 100
382
2
12.5
> 100
633
1
12
> 100
265
2
12
> 100
420
1.5
11.5
> 100
147
3
11.5
> 100
271
2
11
> 100
102
3
11
> 100
145
Water-extended cements have the advantage of being relatively easier to design because the standard API
testing methods can be used without any modification. This means that the prediction of slurry behavior and
properties downhole is straight forward and adjustments on the well site are easy to implement if required.
Cements with Lightweight Particles
Various lightweight substances have been applied to the design of lightweight cement slurries. These include
pozzolans, gilsonite, ceramic microspheres and hollow glass microspheres. These materials have a specific
gravity less than that of Portland cement. Mixing a calculated amount of these substances with cement can
yield low density slurries suitable for weak fracture gradient zones.
Pozzolans
Pozzolans are one of the most common cement slurry extenders in use today. They exist naturally as volcanic
ashes and diatomaceous earth for example, and artificially as fly ash. Fly ash is the most common form of
pozzolan and is obtained as a by-product of coal combustion in power plants. It has a particle size that is
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SPE-190079-MS
close to that of Portland cement and is mainly composed of silica and alumina. The specific gravity of fly
ash varies from 2 to 2.7 (Hewlett, 2001) and slurries with density as low as 13.1 ppg (Nelson and Guillot,
2008) can be designed with acceptable properties. An interesting property of pozzolans is that when used
in cement slurries, they react with calcium hydroxide produced as a by-product of the cement hydration
process. This reaction produces a cementitious material that contributes positively to the compressive
strength development of the slurry. This means that pozzolan slurries not only provide weight reduction
but also provide better set cement strength than slurries extended with bentonite alone. The reaction with
calcium hydroxide prevents degradation of the cement due to free calcium hydroxide in the cement that
can be attacked by exterior chemical agents. The permeability of set pozzolan cements is very low which is
desirable with regards to the zonal isolation objectives of cementing (Nelson and Guillot, 2008). A major
challenge with using pozzolan cements is the inconsistency in particle size and specific gravity that exists
from one batch to another. It is important to measure every batch of pozzolan used in the field and adjust
the cement mixing operations to ensure that laboratory design parameters are adhered to. Another challenge
regarding the use of pozzolans in cement is the decreasing number of coal-fired plants because of the move
towards more environmentally friendly power generation methods. Because of this trend, a shortage in
the future supply of fly ash for cement extension is anticipated. Cement slurries can be extended with a
combination of pozzolans and bentonite to obtain more density reduction than that which would be obtained
with pozzolan alone as well as incorporate some of the benefits of bentonite such as fluid loss reduction. For
higher temperature applications above 200 °F, an appropriate amount of silica can be added to maintain the
effectiveness of the pozzolan additive. If the cost of shipping is minimized or the supply source is nearby,
pozzolans offer an economical solution for lightweight slurries with good strength performance. Table 4
shows typical properties for different blends of cement and pozzolan.
Table 4—Performance of Cement Slurries with Class H and Fly Ash (Jangid and Marjason, 2013).
Slurry
Density
(ppg)
Poz:ClassH (% by volume of blend)
Compressive Strength (psi)
12.0
75:25
392
12.0
50:50
555
13.0
75:25
1050
13.0
50:50
1378
13.5
75:25
1294
13.5
50:50
1452
13.5
75:25
1349
14.5
75:25
1796
14.5
50:50
2270
14.5
25:75
1611
Expanded Perlite
Expanded perlite is made by heating crushed volcanic glass to its melting point. It has a very low bulk
density of about 1.03 ppg and can be used to formulate slurries with densities as low as 12 ppg (Nelson
and Guillot, 2008). Bentonite is usually added to the slurry mix to prevent segregation of the perlite. It is
important to note that perlite becomes significantly denser under pressure, hence its applications are limited
to shallow wells where the variation between the downhole slurry density and the surface mixing density is
kept to a minimum. Cements formulated with expanded perlite exhibit decent performance. For example,
a 10.60 ppg slurry with cement-perlite ratio of 1:2 (by volume), 15.5 gal/sk of mix water and 4% bentonite
SPE-190079-MS
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will yield a compressive strength of 520 psi after 24 hours under a curing pressure of 3000 psi (Nelson and
Guillot, 2008). In addition to density reduction and slurry yield increase, the inert nature of perlite helps to
render the set cement more durable due to increased resistance to external chemical attack from corrosive
environments.
Gilsonite
Gilsonite is a naturally occurring mineral with a specific gravity of 1.05. It has a low water requirement
and hence will result in lightweight cements with relatively good set cement compressive strength. While
the primary use of gilsonite is as a bridging agent for lost circulation control, it can be used to obtain
slurry densities as low as 12 ppg. When high concentrations of gilsonite are used in cement slurries, it
is necessary to add an appropriate amount of bentonite or another viscosifier to minimize or eliminate
particle segregation. Finally, it is recommended that gilsonite not be used in wellbores with bottomhole
temperature greater than 300 degrees Fahrenheit. Gilsonite will start to melt at 385 degrees Fahrenheit and
above 240 degrees Fahrenheit, the gilsonite particles begin to fuse and the downhole slurry density becomes
significantly heavier than the surface slurry density (Nelson and Guillot, 2008).
Powdered Coal
Powdered coal has a specific gravity of 1.3 and a wide particle size distribution. It can be used to obtain
slurry densities as low as 11.9 ppg. It is also very well suited for thermal wells due to its high melting point
of 1000 degrees Fahrenheit. Use appropriate amounts of bentonite with powdered coal extended cements
to prevent particle segregation (Nelson and Guillot, 2008).
Ceramic Microspheres
Ceramic microspheres also known as cenospheres are hollow spheres filled with nitrogen or carbon dioxide,
consisting mainly of silica and alumina and produced as a by-product of coal combustion in coal-firing
power plants. Ceramic microspheres have a wide range of specific gravity and particle size depending on
the source. The crush rating for ceramic microspheres are generally close to 3000 psi (Sarmah et al., 2015).
The variation in specific gravity and particle size poses a challenge to field mixing because each batch must
be tested to ensure consistency with the properties of the slurry as designed in the lab. Competent slurries
with density as low as 9 ppg are obtainable with ceramic hollow spheres (Dajani and Curtis, 2009). In field
applications, a certain percentage of the cenospheres in the slurry will break under downhole pressures.
When this happens, the slurry density downhole becomes higher than the slurry density on the surface and in
wellbores with a narrow pressure window, the lost circulation prevention function of the slurry may be lost.
Proper testing is necessary to simulate downhole conditions in the lab and determine the crush resistance of
the cenospheres to be used so that the density variation can be accounted for. A class G slurry with ceramic
microspheres and 1% calcium chloride with a density of 8.5 ppg yielded a 24-hour compressive strength of
215 psi under a curing pressure of 3000 psi (Nelson and Guillot, 2008).
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SPE-190079-MS
Figure 2—Sample of ceramic microspheres showing imperfections
and size variation between spheres (Dajani and Curtis., 2009).
Glass Microspheres
Glass microspheres are gas filled hollow spheres manufactured from borosilicate glass with an appearance
of fine white powder. They have an average specific gravity of 0.32 (Olutimehin et al., 2015) but specific
gravity can vary between 0.2 and 0.4. Glass microspheres have a particle size that is generally larger than
that of Portland cement but smaller than that of silica flour ranging from 0.5 to 2 microns (Smith et al.,
1980), and they can be used to obtain slurries with densities as low as 7.5 ppg (Nelson et al., 2008).
Glass microspheres are more crush resistant than ceramic microspheres and are manufactured at fixed
crush resistance ratings up to 18000 psi (Dajani and Curtis, 2009). Because glass microspheres are
manufactured in a precise fashion, the batch to batch variations that exist with ceramic cenospheres are
minimized or absent with glass microspheres. The uniformity in the particle size and consistency in specific
gravity from one batch to another result in more predictable slurry mixtures. Glass microsphere cements
are especially suited for situations that require low to ultra-low density but high set cement strength as
well. A glass microsphere-based slurry with a density of 9.65 ppg yielded a compressive strength of 1755
psi after 24 hours and 2069 psi after 48 hours (Sarmah et al., 2015). Cement slurries extended with glass
microspheres also exhibit fast compressive strength development due to the low water requirement for
achieving a pumpable slurry. Glass microsphere cements also retain their strength at high temperatures and
exhibit insignificant permeability to water. These characteristics have made them one of the most popular
means of extending cement slurries for combatting lost circulation problems today.
Glass microspheres like every other extender are not without their drawbacks. Very much like ceramic
microspheres, a certain percentage of the spheres will break under pressure. This breakage will lead to higher
slurry densities downhole. Thus, as in the case of cenospheres, sphere breakage should be accounted for in
the design of the slurry. Slurry instability is another challenge that arises in the use of glass microspheres.
This is caused by segregation of the microspheres in the cement due to their low density. Slurry design with
glass microspheres must minimize segregation to prevent excessive free water and subsequent loss of zonal
isolation in the borehole.
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9
Figure 3—Sample of glass microspheres showing more homogeneity
compared to ceramic microspheres (Dajani and Curtis, 2009).
Foamed Cements
Foamed cement can best be described as a gas-liquid dispersion of nitrogen stabilized as microscopic
bubbles in a base cement slurry (Kutchko et al., 2016). Nitrogen is injected into a base slurry containing
a foaming agent and foam stabilizer along with other required additives under pressure during mixing on
the surface and is then pumped into the wellbore. Foamed cements can be designed with densities as low
as 6.0 −7.0 ppg (Nelson and Guillot, 2008). They offer good fluid loss control, cement columns with low
hydrostatic pressure, better strength than water-extended slurries, high tensile strength and ductility, efficient
mud displacement and hole cleaning performance (Mariott et al., 2005).
Even though foamed cements can yield ultra-low density slurries, a maximum of 33 percent – 35 percent
foam quality is recommended for the slurry to be competent (Bybee K., 2006; Mariott et al., 2005). The
resulting permeability and porosity of a typical foamed cement slurry is higher than that of conventional
lightweight cement and is determined by the foam quality (gas volume divided by slurry volume) (Kutchko
et al., 2016). According to Dusterhoft (2003), the cement permeability rapidly increases below a slurry
density of 8 ppg. The surface treating pressure and prevailing wellbore pressure are also important factors
that determine the set cement permeability and porosity (Kutchko et al., 2015).
The compressive strength of the set cement is determined by the bubble size and bubble distribution
through the cement, the compressive strength of the base slurry and the nitrogen content or foam quality.
Minimum contact between the bubbles in the slurry is desirable for ensuring structural integrity in the set
cement. Lab tests should be used to determine the appropriate design parameters to optimize the bubble
distribution in the slurry (Mariott et al., 2005). Table 5 on the next page shows the compressive strength
and cement permeability for foamed cements of different densities and bubble size distributions for a base
slurry comprised of class G cement cured for 72 hours at 80 degrees Fahrenheit.
Table 5—Performance of Foamed Cements (de Rozières and Ferrière, 1991).
Broad Bubble Size Distribution
Density (ppg)
Compressive Strength (psi)
Permeability (md)
14.8
3016.78
0.05
12.2
2030.52
0.0076
Narrow Bubble Size Distribution
Compressive Strength (psi)
Permeability (md)
1189.31
1.25
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Broad Bubble Size Distribution
Narrow Bubble Size Distribution
Density (ppg)
Compressive Strength (psi)
Permeability (md)
Compressive Strength (psi)
Permeability (md)
10.2
1363.35
0.017
986.26
5.7
9.0
1305.34
0.054
826.72
25.7
7.5
1087.78
89
464.12
1.99
5.1
739.69
58890
232.06
6800
Density variation of the pumped slurry from surface to bottomhole is also a challenge in foamed cement
application. As the wellbore pressure increases, the slurry density increases due to the compression of the
nitrogen gas. Proper design and testing of the slurry at simulated wellbore conditions is necessary to account
for this problem. Software simulation can be used to model the hydrostatic pressure profile to be expected
for any job. Such models can then be factored into the operational parameters of the cement job to ensure
that the cement placed in the borehole maintains the properties it was designed for.
Cementing a wellbore with foamed cement is a technically challenging process because of the special
equipment required for the injection of nitrogen gas into the base cement slurry as it is pumped downhole.
Field results for foamed cementing may be vastly different from results obtained in the lab. Part of the
problem is due to the difficulty in characterizing foamed slurry behavior in the lab under downhole
conditions in a way that yields accurate and reliable results. Foamed slurries consisting of the same
components in the same composition can have different properties based on the mode of preparation. This is
because the preparation parameters such as mixing speed (shear rate), and mixing pressure greatly affect the
bubble size distribution and as mentioned earlier, bubble size distribution affects the compressive strength
and permeability. For example, Davies et al. (1981) showed that foamed cement prepared in the field under
high shear rate and high pressure conditions are more stable than their laboratory-prepared counterparts.
Conclusions
Various methods are used for the extension of cement slurries for combatting lost circulation in wellbores
where the formation pressure gradient is too weak to support the hydrostatic pressure imposed by
conventional slurry mixes. The method chosen should be decided based on the prevailing conditions and
challenges in the well of interest, additive availability, logistical considerations and cost of implementation.
Table 6 is a comparison of the average cost range of each lightweight additive discussed in this paper
obtained from publicly available vendor information on the internet.
Table 6—Average Price Range of different Additives.
Material
Average Cost Range
(US$ / Metric Ton)
Bentonite
60 – 150
Sodium Silicate
150 – 300
Fly Ash
40 – 60
Ceramic
Microsphere
600 – 1350
Glass
Microsphere
5000 – 5500
Expanded Perlite
98 – 205
Gilsonite
1000 – 1300
SPE-190079-MS
11
Interest in the use of glass microspheres and foamed cement have especially garnered a lot of renewed
interest due to improved technology, their effectiveness in highly critical situations across the globe and a
better technical understanding of the processes that govern the behavior of such slurries.
It is of great research interest in well cementing to understand and quantify the relationship between
the various mechanical properties of cement and zonal isolation performance and wellbore integrity.
Compressive strength has been the main mechanical property used to evaluate the capacity of oilwell
cements to provide adequate zonal isolation. However, as mentioned previously, other factors like tensile
strength and Young's Modulus have been shown to be at least just as important for maintaining wellbore
integrity under stresses induced by completion, stimulation and production activities. A better understanding
of the significance of the above mentioned mechanical properties with regards to wellbore integrity will be
critical to formulating more reliable advanced lightweight slurries that will be specifically optimized for the
prevalent scenario expected in any given well.
Nomenclature
°F
API
BWOC
ECD
gal/sk
hr
md
ppg
psi
= Degrees Fahrenheit
= American Petroleum Institute
= By Weight of Cement
= Equivalent Circulating Density
= Gallons per Sack
= Hour
= Millidarcy
= Pounds per Gallon
= Pounds per Square Inch
SI Metric Conversion Factors
(°F – 32) * (5 / 9)
= °C
psi * 6.894757 E+02 = bar
ppg * 1.1982639 E+02 = kg/m3
References
Bosma, M., Ravi, K., van Driel, W., & Schreppers, G. J. (1999, January 1). Design Approach to Sealant Selection for the
Life of the Well. Society of Petroleum Engineers. doi:10.2118/56536-MS
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