FIELD OF INVENTION
The present invention relates to cement composition comprising microbubble suitable
for use in plug back cementing, grouting and other operations in subterranean formation
containing lost circulation zones or depleted, low pressure reservoirs at shallow depth
where normal cement slurry of high density does not meet the requirement of
hydrostatic head.
BACKGROUND OF THE INVENTION
A drilling fluid is circulated from surface down through a drilled out well bore to a
^ j drilling face and back to the surface when drilling into sub-hydrostatic formation to
recover hydrocarbons. Drilling fluids are specifically designed to perform a number of
functions including cooling and lubricating bit, and supporting the formation pressure
by providing the hydrostatic head to maintain the integrity of the wellbore walls and
controlling the flow of fluids across the wellbore face into the wellbore and vice versa.
A common problem encountered during drilling operations is lost circulation which is
excessive flow of drilling fluids into formation and returned on surface is low or no I
returned. This is called circulation loss while drilling. The drilling fluids are either lost
to the formation fractures, fissure and matrix or to voids in direct communication with
the wellbore. Lost circulation is undesirable from an operational and safety standpoint
because it can destabilize permeable formations and damage the pay zone, and in j
^^i extreme cases it can result in a blow out of the hydrocarbon zone followed by a well
fire.
Another problem in petroleum well cementing is the flow of liquid from the cement
slurry into porous earth formations in contact with the cement. This fluid loss is
undesirable since it can result in dehydration of the cement slurry, and it causes thick
filter cakes of cement solids which can plug the well bore. The fluid lost can damage >
sensitive formations. Cement fluid loss is particularly a problem in the process known
as squeeze cementing.
2 :
Lost circulation zones are remediated generally by addition of bridging materials or
sealing materials. Bridging materials generally comprise larger particulate sizes
employed for cavernous or porous formations. Example of bridging materials includes
are plant fibers, nut shells, naturally occurring materials, and marble and sized calcium
carbonate. Sealing materials on the other hand, are generally used to seal smaller
fractures or fissures because the comprise particulates of generally smaller sizes.
Bridging materials and mixtures with sealant products are generally placed in the loss
zone as pill. Once in place, pressure is applied to force the materials into the formation.
- ^ As the pressure is applied the lost circulation materials losses its liquid component,
^** known as dewatering even if the liquid component is substantially organic to form a
plug. If the plug is effective, circulation of the drilling fluid is restored. Multiple
applications of the same or different LCM may be required to restore the circulation.
The more effective the LCM, the more rapidly drilling can resume and the lower the
cost of the drilling operation. Numerous off- the- shelf, proprietary and patented LCM
are currently available to add to the well for delivery to the loss or thief zone but may i
prove deficient or inadequate in regard to specific well requirements since such LCMs
failed to provide sufficient compressive strength to balance the differential pressure
arises during drilling.
Remediation material for lost circulation has been the subject of research and
£>>. development almost since the inception of the industry. Advances in lost circulation
remediation materials continue from a combination of ingenuity and science. Operator
knows that the drilling system be as inexpensive as possible to minimize the cost of
drilling a well. Alternative LCMs are continually being sought to reduce formation
requirements, well operator employee and equipment time, and increase effective over
the broadest range of the thief formations.
Lost circulation treatments known in the art are unsatisfactory at shallow depth because
of operational limitations restricting their utility. The most significant shortcoming of
conventional lost circulation treatments is their inability to effectively control lost
3
circulation encountered when drilling through voids occurring in the formations. Use of
cement plugs of neat slurry is known in the art, however it is difficult to place the
cement plugs at difficult places. Light weight cement plugs are formed by high water
contained / gel cement slurries have also failed to provide the effective barrier to seal
the loss zone. Such cement plugs takes excess time to develop static gel due to diluted
with formation fluids to stop the flow of slurry into loss zone.
When lost circulation of drilling fluid is experienced, cement plugs of neat slurry are
typically used to solve the problem. For example, cement can be washed out around
jp^ cellar pit, may drift away, or the amount of cement placed may not fill the void present.
^"* Such situation may occur at shallow depth having low pore pressure, high slurry
specific gravity and more probability of cross flow resulting washout of conventional
cement plug.
US4 933031 describes gas tight, low density hydraulic cement slurry for cementation of
oil wells in the fields having gas containing formation. The cement slurry contains
microsilica (5-100%, based on the weight of the cement), light weight aggregate with a
real particle density between 0.1 and 1.5g.cm3 (2-200%, based on the weight of
cement), thinner (0-5% based on the weight of cement), fluid loss additive (0-10%,
based on the weight of cement) and water in an amount such that the cement slurry has
a density between 0.8 and 2.0 g/cm3. The slurry is reported to overcome the drawbacks
— of traditional foamed cements of requirement of complicated and costly means for
^ adjusting and controlling gas content in the slurries.
US6997261 describes the additive comprises harden able alkaline mixtures of
diatomaceous earth. However the additive does not provide the use of or the advantage.
UK819229 describes a method and apparatus for cementation to be employed in
pressure grouting fissures in the walls of boreholes and other structures, such as dams.
The invention utilizes addition of increased proportion of surface active agent (0.5 -
2.0% as opposed to the traditional 0.05%) in order to cchieve improved results. The
invention also describes the apparatus employed for the a formulation method which
4
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i
allows one to overcome the problems faced due to foaming produced in the grout on
addition of large proportion of surface active agent.
US3926257 describes a well cementing process where a foaming agent (generally in the
range of 0.1 to 5% by weight) is added to the cement slurry prior to its injection into a
well, which results in a strong reduction of gas permeability and creates a foam barrier.
The foaming agent may be ionic or non-ionic, a mixture containing at least one ionic I
foaming surfactant and at least one non-ionic surfactant in solution is reported to allow
gas tight cementation.
C US4300633 describes a method of cementing wells with foam containing cement
wherein the amount of gas contained in the slurry and the set cement is such that the
density in the cement slurry column and the cement in the annulus increase with
increasing depth. The invention requires a foaming agent active in highly alkaline
environment and resistant to bivalent organic cations. Anionic surfactants with general
formula [CnHm -S03]- and [CnHm --0-S03]- with alkali ions as counter ions, in
particular sodium lauryl sulphonate (Trade Name: Elfan OS 46 by AKZO) has been
found to be particularly suitable.
US120120024527A1 describes a well treatment composition comprising a surfactant
(comprising a substituted ethoxylated phenol having at least one substitute, which may
be alkyl alkene, or alkyne), ethylene oxide (1 to 14 moles), cardanol ethoxylate,
| ^ derivatives thereof and combinations of the foregoing. A method for cementing in a
subterranean formulation is also described.
US5588489 de scribes a compressible, lightweight, fast settling cement composition
which can be utilized in performing a variety of well cementing operations. The
composition comprises slag cement, sufficient water for forming pumpable slurry,
sufficient gas to foam the sluny and a foaming agent.
US6516883 describes a low density cement composition having enhanced compressive,
tensile and bond strengths upon settling. The composition of the invention comprises a
hydraulic cement, water (to form a slurry) and hollow glass microspheres treated with a
5 j
mixture of organosilicate coupling agent, present in an amount to produce a cement
composition density in the range of 6 to about 12 pounds per gallon.
US6562122 describes non-foamed lightweight cement composition and methods of
using the composition for cementing subterranean zones penetrated by well bores. The
cement composition is comprised of coarse particulate hydraulic cement, an ultrafine
particulate hydraulic cement mixture comprised of slag cement and a Portland.
US4721160 describes a lightweight cement composition which has styrene-butadiene
latex, a solid extender agent and a density in the range of 1.2 to 1.6. The cement has less
J^. than 70% (preferably 63%) ratio of liquid volume to the slurry volume and was reported
to be the first lightweight homogenous slurry.
US4415366 describes foamed, easily mixing, thixotropic hydraulic cement slurry mixed
by injecting surfactant and a gas or mixture of gases into the prepared slurry. The slurry
may also be prepared by adding a liquid thixotropy imparting agent (made up of a
mixture of Iron (II) sulfate and Aluminium sulfate) to conventional hydraulic cement
' slurry. The invention also describes a method of using the slurry in cementing
subterranean voids.
US7398827 describes methods for performing cementing operations in subterranean
zone under high temperature conditions using a cement composition including calcium
aluminate, water and a light weight additive, and having a specific gravity of less than
^ ^ about 0.70 and a density of less than 10.5 pounds per gallon.
US.2011/0308799 describes a well treatment composition having an activity of atleast
10% and comprising an aqueous liquid, a fluid loss additive (comprising a high
molecular weight, water swellable polymer) and an amphiphilic dispersant. A method
for cementing in a subterranean formation is also described.
US7896076 describes low-density cement slurries which comprise alkali swellable
polymers (preferably carboxylated acrylic copolymer latex) as thickening agents, which
are preferably added as liquid latex dispersions. The slurry may also comprise a
6
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surfactant, present at a concentration below its critical micelle concentration. A method
of increasing the viscosity of low density cement by addition of alkali swellable
polymer to the cement slurry is also described.
US7030184 describes a method of preparation of cement matrix or hydraulic binder
with increased mechanical strength. The method involves preparing an aqueous an
aqueous dispersion comprising a copolymer by radical copolymerization of at least one
alkoxy, aryloxy, alkylaryloxy or arylalkyloxy polyalkylene glycol ethylene urethane
monomer with at least one anionic monomer and at least one non-ionic monomer, and
__ adding the aqueous dispersion to a cement or hydraulic binder. c
The use of foamed cement is still a relatively new technique in the context of oil well
cementing to overcome problems such as low formation fractures and lost circulation
zones. The foamed cement is primarily a mixture of base cement slurry, foaming agent,
and foam stabilizer to produce slurries with ultra light-densities and moderate cement
strength at a relatively low cost (David & Hartog, 1981). When conventional cement is
used, problems such as zonal isolation, formation fracture and lost circulation may be
encountered and the use of foamed cement may be one of the most effective methods to
eradicate such problems which can help in reducing the high cost in cement recovery
work over jobs.
Creating stable foam of the cement slurry is an excellent method of reducing the density '
^K of liquid cement slurry. Nitrogen is normally used as the gaseous phase in foam
cementing. Occasionally compressed air is used, but is limited because delivery
methods are less reliable. Gas-generating solids have been used in the industry, but the
competing chemical reaction with the cementing hydration reaction makes nitrogen the
preferred foaming choice.
7 I
Foam cements using nitrogen are commonly applied to prevent lost circulation in lowpressure
reservoirs, but foam cements have high permeability and low strength,
resulting in cementing failures and higher completion costs. Limitations often exhibited
by foam cements are: higher friction in the well (which can lead to lost circulation),
inconsistency in application, difficulty in controlling the cementing job at the surface,
lack of quality assurance, and the inability to measure bond strengths with sonic and
ultrasonic evaluation tools.
Another option in spite of the growing market, several complications can exist in regard
—K to actually using micro spheres to cement oil and gas wells. Microspheres should be
^* homogeneously distributed throughout the bulk material while it is being delivered to
the mixing head, otherwise viscosity or density-control issues may arise.
While micro sphere cementing is often selected as being the high-tech or premium
lightweight cementing solution, it too can have drawbacks: (1) blending, (2) mixing,
and (3) cost. In all blended cements, homogeneity is required. In micro sphere blends it
is even more important to achieve the highest standards of homogeneity. If the micro
spheres are not evenly distributed, achieving uniform density and/or slurry stability may
be difficult.
Several techniques have been reported in the prior art, varying from mechanical to
chemical treatments, or combinations of both provided desired results in fields. Any
^K type of drilling fluid used in the system will not provide adequate compressive strength;
therefore, a barrier of sufficient compressive strength vv'll not develop to stop further
circulation loss in fragile formation. Thus, there is a need to formulate low /ultra
lightweight cement slurry for shallow wells where temperature range is low and
formulating cement slurry in such typical condition is very difficult
Despite the art for the control of loss circulation which is already known, there exists a
need for novel agents capable of improving control of loss circulation which are not
reduced in utility by the limitations described above. Thus, there is a requirement, for
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materials which, when added to the cement formulation, reduce the loss of fluid from i
the slurry to porous formations.
This requirement can be fulfilled by providing a cement composition such as low/ ultra
low specific gravity cement slurry which can provide sufficient compressive strength to
stop further losses in unconsolidated formation at shallow depth with a good set of
properties and useful in performing cementing operations in shallow wells.
SUMMARY OF THE INVENTION
An aspect of the present invention relates to micro-bubble cement composition
{p,< comprising an aqueous mixture of cement and a non-ionic surfactant as set forth in
Formula I as set forth in Formula I in the amount ranging from 0.5% to 1.5 % (w/w);
R,-(OC2H4)n- OCH2OCH2CH20 R2
Formula I
wherein Rj is Cg-C22 alkyl, R2 is C3-C30 alkyl, and n= 3 to 30
Another aspect of the present invention relates to a process for controlling lost
circulation from a borehole, wherein said process comprises
• providing micro-bubble cement composition comprising an aqueous
mixture comprising a cement and a non-ionic surfactant as set forth in
Formula I in the amount ranging from 0.5% to 1.5 % (w/w);
Ri-(OC2H4)n. OCH2OCH2CH20 R2
Formula I
wherein R| is C8-C22 alkyl; R2 is C3-C30 alkyl, and n= 3 to 30; and
• injecting the aqueous cement composition into the borehole.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The following drawings form part of the present specification and are included to
further illustrate aspects of the present invention. The invention may be better
9
understood by reference to the drawings in combination with the detailed description of
the specific embodiments presented herein.
Figure 1 shows SEM study of 1.20 sp gr cured mold
Figure 2 shows
(a) Thickening time & consistency curve of micro-bubble cement slurry of S. G. 1.30.
(b) Thickening time & consistency curve of neat cement slurry S.G 1.90.
DESCRIPTION OF THE INVENTION
f j Those skilled in the art will be aware that the invention described herein is subject to
variations and modifications other than those specifically described. It is to be
understood that the invention described herein includes all such variations and
modifications. The invention also includes all such steps, features, compositions and
compounds referred to or indicated in this specification, individually or collectively,
and any and all combinations of any two or more of the steps or features.
Definition '
For convenience, before further description of the present invention, certain terms
employed in the specification, examples and appended claims are collected here. These
definitions should be read in light of the remainder of the disclosure and understood as
by a person of skill in the art. Unless defined otherwise, all technical and scientific
%?? terms used herein have the same meaning as commonly understood by a person of
ordinary skill in the art.
The articles "a" and "an" are used to refer to one or to more than one (i.e., to at least (
one) of the grammatical object of the article.
The terms "Lightweight cement slurry", "lightweight cement composition", "micro ]
bubble cementing system", "cement slurry", "micro bubble base cement slurry",
"lightweight micro bubble cement slurry", "Micro Bubble Light Weight Cement
10
Slurry", "Micro-bubble cement composition" and "cement composition" used herein
can be used interchangeably.
The present invention relates to a lightweight cement composition comprising
microbubble useful for plug back cementing, grouting and other operations in
subterranean formation containing lost circulation zones or depleted, low pressure
reservoirs at shallow depth where normal cement slurry of high density does not meet
the requirement of hydrostatic head.
The present invention, in particularly provides lightweight cement slurry comprising
4T\ hydraulic cement, water and slurry containing as dispersed, discrete entrained stable
micro bubbles with a specific surfactant poly alkoxy ether as a low foaming agent and a
process of ultra light weight slurry of sp gr 1.0-1.30 for plugging a subterranean void,
fracture and fissure by emplacing the same in the sub-hydrostatic formations void and
then allowing the slurry to therein harden.
Normally neat cement slurries are effective for solving seeping or minor loss, with the
advantage of providing high final compressive strengths. Slurries with a limited degree
of fluid-loss control can be used to solve seepage, partial, or total losses, and contain a
mixture of clays, diatomaceous earth, and LCMs. The size of the LCM is increased as
the losses become more severe. Low-density cement systems can be used for any type
of lost circulation problem. They have the added advantage of reducing the hydrostatic C pressure.
Firstly, to maintain the down hole pressures during the job below the maximum
equivalent mud circulating density, either by reducing the density of the cement slurry,
minimizing the height of the cement column, or limiting the casing and annular friction
pressures during the placement of the cement sluny. The second option is to pump a
plugging material as a spacer in front of the cement slum', add lost circulation materials
to the cement slurry itself or use special additives which impart thixotropic properties
to the cement slurry. When trying to prevent cement losses to highly fractured or
vugular formations, it is often necessary to use a combination of techniques.
Many products and techniques have been used to attempt to restore circulation while
drilling. These include fibrous, flaky and granular materials, as well as techniques such
as gunk and reverse gunk squeezes, high fluid loss squeezes and cement squeezes. The
application of a chemically activated cross-linked pill (CACP) used on challenging
deepwater wells to cure and limit losses when drilling with synthetic-based fluids.
Attempts have been made to restore circulation while drilling and cementing, using
many types of materials. Sometimes sufficiently good results have been obtained simply
by reducing the slurry density, whereas other instances have occurred where bridging
_^ materials were found to be most helpful, but there still remained zones of loss which
^ p ' would not react satisfactorily to either of these methods. Combinations of these two
approaches have also been utilized, but it has been difficult to obtain optimum bridging
and density without sacrificing other desirable slurry properties such as strength and
resistance to corrosive fluids.
The invention discloses lightweight cement composition having micro bubble in
hydraulic cement slurry. The application of the cement slurry composition is applicable
in oil and gas well cementing, more particularly in plug back cementing, grouting and
other operations in subterranean formation containing lost circulation zones; or
depleted, low pressure reservoirs at shallow depth where normal cement slurry of high I
density does not meet the requirement of hydrostatic head. High hydrostatic pressure
may induce the fracture and resultant in breakdown ofthe formation and loss zone will 1
^•^ not seal by conventional gel-cement slurry.
Designing cement slurry at low /moderately low circulating temperature BHCT ranging
from 40°C to 70°C is the area of concern and challenging issues during drilling oil & gas wells. Such temperature range is experienced mostly in shallow wells or well
located in mature/ depleted reservoirs. High hydrostatic pressure may induce the
fracture and resultant in breakdown ofthe formation and loss zone will not seal by gelcement
slurry. Light weight materials such as HGS, micro spheres have been used in
12 ;
the cement composition known in the prior art have drawbacks and could not provide
effective results. The micro spheres are not evenly distributed.
Presence of stable micro bubble in the light weight cement slurry composition helps in
reducing the weight of neat slurry and provides adequate compressive strength in
shortest period of time to seal the loss zone and establishes the circulation in shortest
time. Lightweight cement slurry does not enter in loss zone and prevents water to dilute
the cementing characteristics of formulation.
The cement composition as disclosed in the present invention can be used in shallow
JPs well application to combat severe losses, where designing cement slurry at low
/moderately low circulating temperature BHCT ranging from 40°C to 70°C is the area
of concern and challenging issues during drilling oil & gas wells. Such temperature
range is experienced mostly in shallow wells or well located in mature/ depleted
reservoirs. Further, no additional infrastructure is required as in the case of foamed
slurry and no gas such as air/ nitrogen is required. Furthermore, it is easy to mix
identified surfactant in water or mixed with neat cement slurry at high shear rate. The
cement slurry as disclosed in the present invention can be formed like conventional
slurry and place in well in conventional manner. In aidition, the cement slurry as disclosed in the present invention exhibits excellent performance in compare to
conventional gel slurry and gives thixotropic characteristic.
^K The term "thixotropy" used herein describes the property exhibited by a system that is
fluid under shear, but develops a gel structure when the shear is stopped.
In practical terms, thixotropic systems are fluid during mixing and displacement, but
rapidly form a rigid, self-supporting gel structure when pumping ceases. When i
thixotropic slurry enters a lost circulation zone, the velocity of the leading edge }
decreases and a gel structure starts to form. As the gel strength develops, resistance to
flow increases until the entire zone is plugged. Such systems are very effective for j
solving severe lost circulation to naturally fractured formations.
13
For preparation of microbubble cement composition as disclosed in the present
invention, various non ionic surfactants as density reducing agent were screened. Due
to long carbon chain & low foaming characteristic of non ionic surfactant generation of
dispersed, discrete entrained stable microbubble was achieved. It was observed that
micro bubbles in cement slurry remain stable even after setting of the cement
composition. Laboratory study revealed it's effectively at temperature range 35°C to
70°C.
The microbubble cement composition comprising the non ionic surfactant that is used to
JP*, reduce the density of the cement slurry composition (1.90 SG) to less than water density
^"^ exhibits enhanced properties. The cement composition of the present invention has
reduced density which is up to desired level which is achieved by mixing a specific low
foaming agent surfactant i.e poly alkoxy ether as lightweight material which generates
dispersed, discrete entrained stable micro bubble in harden cement slurry with superior
properties, required for cementing shallow wells.
The set cement mass of the cement slurry of the present invention provides low air
permeability but more porosity which has no significant effect on blocking the loss
zone. Application of micro-bubble light weight cement slurry provides excellent lost
circulation material compare to existing gel cementing systems which more popular.
Thus, the micro bubble cementing system as disclosed in the present invention is a new
- ^ techno-economic LCM pill in curing severe lost circulation while drilling shallow wells.
V
The present invention provides a high performance light weight containing micro
bubble cement slurry having superior compressive strenjth in shortest time span with
low permeability. Further, the micro bubble cement composition of the invention is
useful in plugging a subterranean void by emplacing the cement slurry of the invention
in the subterranean void and allowing the slurry to harden. The slurry is preferably
emplaced in the borehole drilled for an oil or gas well or in the annulus created between
the borehole and the casing of such a well.
14
f »
The cement slurry of the present invention also exhibits excellent properties required for
any operation such as low rheology, fluid loss, free water nil and thickening time as it is
found in the case of neat cement. This is also desirable in shallow depth after
emplacement of cement slurry should immediately set otherwise it will be washed out
in loss zone and more over this gives thixotropic characteristic.
The essential components in preferred slurry composition cement slurry of the invention
are aqueous slurry of hydraulic cement prepared by adding water to a hydraulic cement
component, which preferably comprises API Class G HSR Portland cement, and micro
C bubble which is generated by surfactant is entrained as discrete bubbles in said aqueous
cement slurry. The slurry density is adjusted between 0.97 to 1.5 g/c3 with 44% water
by BWC. The cement slurry, as commonly mixed in the usual practice and thereafter
the Surfactant is added to the slurry in water tank or in batch mixer directly.
The most important part of the slurry of the invention is the role of surfactant. This
quantity of surfactant will vary according to the other components and properties of this
slurry and may be determined for a slurry by first measuring the API Standard RP10B-2
"thickening time" of the slurry and then empirically determining the quantity of
* surfactant needed to maintain the desired stable slurry for that time under the conditions
of temperature and pressure which will be encountered by the cement slurry after it is i
emplaced. To be certain that the stability of the slurry is maintained, |
^ s Surfactant Selection
Number of surfactant samples were collected and studied for generating micro bubble j
characteristic, out of which some are found effective and useful for our applications as i
shown in Table 1. The cement slurry was formulated by mixing surfactant in 100cm3 of I
I
water and cement and stirring the mixture such that the foam should occupy 600cm3 f
f
and half life of the foam is longer than 6 minutes. Such foam should remain stable until I
the cement sets and no bubble should burst. Screened out surfactants were further tested ;
for other characteristics before application for micro fine bubbles in cement slurry {
15 Out of the various surfactants/foaming agents used only Cristol IE AC liquid, supplied
by M/s. Krishna Antioxidants Pvt. Ltd., Mumbai has produced and used in this
invention.
Chemical Name of Cristol IE AC: Poly Alkoxy Ether
Physical Properties of Cristol IE AC:
Physical Appearance: Clear transparent colour less to pale yellow viscous
Liquid
pH of 1 % in distilled water: 6-8
Specific Gravity at 25°C: 1.058 gm/ml
%•* Non ionic surfactant: >99 %
The quantity of the surfactant to be added to the aqueous hydraulic cement needs to be
sufficient to permit the major portion of the gas to remain entrained as discrete bubbles
in the slurry until the slurry has hardened sufficiently so that coalescence or migration
of bubbles is no longer possible. Commonly, by volume, at least about 0.5 to 1.5 % as
per 100 parts of cement preferably at about 1.5 parts will be adequate to serve the
intended purpose.
As is readily discussed, the cement slurry comprises solid, water and the liquid
surfactant. The solid components of the cement slurry primarily comprise hydraulic
cement, preferably, a Portland cement. Examples of cement includes but is not limited
C to various categories of cements such as Class A, C or G, set forth in standards of the
American Petroleum Institute (API) for use in oil and gas well cementing. Other solid
additives commonly incorporated in oil well cement slurries may likewise be added so
long as they do not adversely affect the quality and stability of the bubbles. Such
additives include fluid loss control agents, retarders, accelerators, finely divided silica
fume, calcium chloride & metakaoline and super latex. Similarly, since lightweight
slurry is desired hematite, bariie or other such weighting agents are generally not added.
Also, no dispersant is added as it generally tends to degrade or destabilize the bubble or
cause separation of the liquid in solid phases.
16
The density range from 0.97-1.40 without injecting air or N2 gas
The present invention discloses the cement slurry comprising Cement (100 gm), water
(44%) and surfactant (05-1.5%) of 1.90 sg that was reduced upto 0.97 S.G with suitably
screened surfactant only without adding any other additives or modifications, wherein
only single additive provide all desired characteristics.
The cement slurry disclosed in the present invention exhibits the required compressive
strength which is achieved in shortest time more than 500 psi in 7 to 8 hrs at 40°C. The
slurry was successfully pumped with 1.20 to 1.50 density in three jobs with all adequate
J£*j parameters and able to control severe seepage losses.
The main concern in foamed slurry or any light weight slurry is stability of the cement
slurry composition. The present invention provides the cement slurry having desired
stability. The best result were achieved and shown in SEM analysis which clearly
indicates the uniform distribution pattern of micro bubble in cement slurry which
remain stable even at higher temperature and pressure.
The present invention provides lightweight cement slurry composition having micro
bubble in hydraulic cement slurry comprising entrained gas bubbles generated by
surfactant (foaming agent) selected from certain specific aikyl and aryl non ionic
compounds, is superior to foamed cement slurries prepared from other cationic, anionic
and non ionic surfactants. Designing slurry with the specified foaming agents, stable, !
^ P uniform foam of relatively small bubble size i.e. micro bubble rapidly formed.
Hardened cement prepared from such slurries in many cases exhibits superior strength j
at shortest time and low permeability having density range from 0.97 to 1.40 g/cm3, when compared with hardened foamed cements prepared utilizing other foaming agents. I
The present invention further provides improved lightweight cement slurry as it reduces I
the neat slurry density to a less than water and gives thixotropic characteristic which f
helps of cementing subterranean voids by emplacement of this slurry to give a strong, impermeable seal in applications such as the plugging and grouting of the voids created j
or encountered during the drilling of oil and gas. Because of the light weight of the
17
slurry, the breakdown of weak formations during cementing of such subterranean voids
is avoided. Additionally this invention also provides better stability at temperatures in
excess of about 75°C and even bubbles remain stable, discreet in the hardened set
cement.
Preparation of Base Cement Slurry
For preparation and testing of micro bubble light weight cement slurry the
"Recommended Practice on Preparation and Testing of Foamed Cement Slurries at
Atmospheric Pressure" ANSI/API Recommended Practice 10B-4, reaffirmed, July 2010
J ^ was followed.
All cement slurries were designed as per API standard procedures as: API RP 10B-2,
2005 under simulated conditions and the characteristic properties have been tested for
micro bubble lightweight cement slurries, because of the high volume of gas in Micro
bubble Lightweight (MBLW) cement slurry, it is necessary to modify some of the
standard testing procedures to prevent erroneous test results.
Density
**- The density of the bubble cement slurry in the container was determined by dividing the
slurry mass by the container volume and converting to the appropriate density units.
The density measurement was also done by using mud balance as done in the case of
normal slurries and by calculation as mentioned above, but observed no significant
^ ^ changes in density of MBLW cement slurry due to non-pressurization of lid placed on
the top.
Stability of Surfactants
To check the bubbles stability same methodology with slight modification i.e slurry was
applied under pressures and elevated temperatures. Taking weight immediately after
mixing and kept same slurry for 15 minutes and then noted the Specific gravity, it was
found that weight was same, thus the bubble were intact during static condition and
slurry remained stable.
18
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Determination of compressive strength
Micro bubble cement slurry with varying densities, suitable moulds of 2x2 inch has
been prepared. Compressive strength of the slurry was determined in accordance with
ISO 10426-2:2003, 7.5.3. The sealed mould containing the micro bubble cement slurry
cured into an atmospheric-pressure water bath at BHST-75°C. Compressive strength of
micro bubble lightweight cement slurry with surfactant is quite high and adequate
compressive strength of 500 with density of 1.30 g/cc and slurry prepared with lower
sp.gr as low as 1.0 is between 100-120psi in 24 hrs was observed. This study revealed
jp^ that quite high compressive strength developed in respect to curing different
formulations of high specific gravity slurry (1.25). Moulds cured under elevated
temperature & pressure conditions shown no shrinkage. This further proves stability of
micro-bubbles formed.
Determination of thickening time
To determine the effect of surfactant(s) on thickening time, the thickening-time test is
normally performed using a standard HPHT consistometer on the unfoamed / foamed
:. base cement slurry containing the surfactant(s). Thickening time test was performed on
the unfoamed base cement slurry in accordance with API-RP-10B, and with MBLW
cement slurries as shown in Figure 2. It has been observed that the setting time of the
neat cement slurry and micro-bubble cement slurry has no significant changes. It means »
jt^ no significant effect is observed due to presence of surfactant on thickening time of
cement slurry.
Determination of rheological properties
The flow behavior of cement slurry was determined by using Fann rotational viscometer
resulting separation of the gas from the slurry, causing erroneous results. The rheology
of micro-bubble slurry is complex. It depends mainly on the gas content, gas bubble
size, water to cement ratio, existence of gel forces between solid particles in the foam,
and possibly on surfactant type mixing energy and concentration.
19
A correlation can be used to convert the rheological properties of the un-foamed base
slurry to that of foamed cement slurry with varying foam qualities to simulate the field
conditions. It was concluded that micro bubble cement slurry exhibits a rheological
behaviors similar to that of normal foam cement slurry and formulation can be designed
as per requirements with different cement additives in respect to depth and temperature
of loss zone. To provide more stability to micro bubble, 5% super latex was used (a
product of concrete industry).
All cement slurries were designed as per API standard procedures as: API RP 10B-2,
C 2005 under simulated conditions and the characteristic properties have been tested for
micro bubble lightweight cement slurries. Because of the high volume of gas in
Lightweight micro bubble Lightweight (MBLW) cement slurry, it is necessary to
modify some of the standard testing procedures to prevent erroneous test results.
Number of surfactant samples were collected and studied for micro bubble
characteristic, out of which some are found effective and useful for our applications as
shown in Table-1. Poured surfactant in 100cm3 of the water with all cement additives
and formulated the cement slurry. Stirrer the mixture and the foam should occupy
'•'•: 600cm3and half life of the foam is longer than 6 minutes. Such foam should remain
stable until the cement sets and no bubble should burst. Screened out surfactants were
further tested for other characteristics before application for micro fine bubbles in
cement slurry
^ Table 1: Market survey & Evaluation of surfactants samples
Surfactant Manufactures Type Components Performance
Hostapur M/s Clarient India - - Good
, T . Unitop Chemical PVT . .
Unitop T' XA , . Ionic - Poor
v LTD, Mumbai
P . 4 , i r M/s Krishna XT n . „ •
Cnstol IE . ., ^ „ „. Non Polyalkoxy „
. „ antioxidants Pvt . . ™_ Very Good
AC Lwt.dx,M* umbLa i• ionic Ether
20
Mixing and Emplacement techniques
The cement slurries of the invention are suitably prepared by first mixing the base
aqueous hydraulic cement slurry with any standard cement blending equipment, such as
a paddle mixing tank or a venture-type cement slurry mixer. The slurry can be prepared
as for conventional method the slurry is not a critical element of the instant invention.
Once the neat slurry is prepared, it is suitably transfer to a batch mixer for homogeneous
blending. The slurry transfer means can be a common hydraulic pump such as a triple
cylinder positive displacement pump commonly known as a "triplex" pump. The
#*•= surfactant is added directly into the batch mixer. Such problems in handling may be
avoided by adding the foaming agent directly at the suction of a pump utilized as a
transfer means or immediately downstream from the transfer means to the conduit
containing the aqueous slurry and foaming agent. The specialty of the invention is that
No extra typical equipments or gas is then added to get desired parameters.
Specific Embodiments
By way of examples, the following embodiments of lightweight micro bubble cement
* slurries of the invention are prepared and successfully field implemented. The cement
component is API Class G cement, calcium chloride present in slurry at a level of about
one percent, based on weight of the cement component ("BWOC"). And surfactant is
present at about 0.1 to 0.5 %, gas is entrained in the micro bubble containing slurry ^f prepared from the dry components and water. Resultant slurry densities are described in
the following examples and three runs were performed with lightweight micro bubble
cement slurries while drilling a very complicated well having severe mud loss problems
at shallow depth.
In accordance with the present invention, in one embodiment there is provided a microbubble
cement composition comprising an aqueous mixture of cement and a non-ionic
surfactant as set forth in Formula I in the amount ranging from 0.5% to 1.5 % (w/w); •
Ri-(OC2H4)n-OCH2OCH2CH20 R2
21
Formula I
wherein Ri is Cs-C22 alkyl, R2 is C3-C30 alkyl, and n= 3 to 30
Another embodiment of the present invention provides the micro-bubble cement
composition comprising surfactant having Formula I, wherein Ri is Cio-C]4 alkyl.
Another embodiment of the present invention provides the micro-bubble cement
composition comprising surfactant having Formula I, wherein R2 is C1-C4 alkyl.
Another embodiment of the present invention provides micro-bubble cement
jfc composition comprising an aqueous mixture of cement and a non-ionic surfactant as set
forth in Formula I in the amount ranging from 0.5% to 1.5 % (w/w);
Ri-(OC2H4)n. OCH2OCH2CH2O R2
Formula I
wherein Ri is C8-C22 alkyl, R2 is C3-C30 alkyl, and n= 3 to 30
, wherein specific gravity of the composition is in the range of 0.97 to 1.40g/cc.
Yet another embodiment of the present invention provides micro-bubble cement
composition comprising an aqueous mixture of cement and a non-ionic surfactant as set
forth in Formula I in the amount ranging from 0.5% to 1.5 % (w/w);
Ri-(OC2H4)n- OCH2OCH2CH20 R2
^ ^ Formula I
wherein Ri is C8-C22 alkyl, R2 is C3-C30 alkyl, and n= 3 to 30
, wherein compressive strength of the composition is in th? range of 300 psi to 500 psi.
The micro-bubble cement composition micro-bubble ce.nent composition comprising
an aqueous mixture of cement and a non-ionic surfactant as set forth in Formula I in the J
amount ranging from 0.5% to 1.5 % (w/w);
Ri-(OC2H4)n. OCH2OCH2CH20 R2
22
One embodiment of the present invention provides a cement slurry composition having
micro-bubbles, wherein the composition comprises a cement, water in amount of 44%
by weight of cement, a non-ionic surfactant of the Ri-(OC2H4)n. OCH2OCH2CH20 R2
(Formula I) in amount in the range of 0.5% to 1.5 % by weight of cement, wherein Ri
is C8-C22 alkyl, R2 is C3-C30 alkyl, n is ranging from 3 to 30 and the cement slurry has
specific gravity and compressive strength in the range of 0.97 to 1.40g/cc and 300psi to
500psi respectively.
Another embodiment of the present invention relates to Ri-(OC2H4)n. OCH2OCH2CH20
w* R2 (Formula I), wherein R\ is ranging from C10- C14 alkyl.
Another embodiment of the present invention relates to R--(OC2H4)n- OCH2OCH2CH20
R2 (Formula I), wherein R2 is ranging from C1-C4 alkyl.
Another embodiment of the present invention provides a process of preparation of the
cement slurry composition having micro-bubbles and comprising a cement, water in
amount of 44% by weight of cement, a non-ionic surfactant of the Ri(OC2H4)n. OCH2OCH2CH20 R2 (Formula I) in amount in the range of 0.5% to 1.5 % by weight of
cement, wherein R] is Cg-C22 alkyl, R2 is C3-C30 alkyl, n is ranging from 3 to 30,
wherein the process comprises mixing surfactant and water to obtain a fluid, preparing a
C cement blend comprising cement, water and the surfactant and mixing cement blend with the fluid at 12000 rpm for 15 seconds to obtain the cement slurry. j
i
Yet another embodiment of the present invention provides a process for controlling mud f
i'
loss during boring of wells at a depth in the range of 1040m, wherein the process j
comprises placing 7.0m of a cement slurry composition having micro-bubbles and j
comprising a cement, water in amount of 44% by weight of cement, a non-ionic j
surfactant of the Ri-(OC2H4)n- OCH2OCH2CH20 R2 (Formula I) in amount in the range
of 0.5% to 1.5 % by weight of cement at a depth of 35m below the ground at the rate
of 50 SPM; displacing the cement slurry with drilling fluid; cleaning drill string with
24
one cycle drilling fluid; squeezing the cement slurry at 200 psi; closing Blow out
Preventer (BOP) for 3 hrs; starting Running In (R/I) without tagging the cement slurry
at a depth of 973m; and drilling down up to a depth of 1036m and subsequently up to a
depth of 1040m by reaming at the rate of 20m3/hrs.
Further embodiment of the present invention provides a process for controlling mud
loss during boring of wells at a depth of 1042m, wherein the process comprises placing
8.0m3 of a cement slurry composition having micro-bubbles and comprising a cement,
water in amount of 44% by weight of cement, a non-ionic surfactant of the Rj-
^ (OC2H4)n- OCH2OCH2CH2O R2 (Formula I) in amount in the range of 0.5% to 1.5 % j
by weight of cement at a depth of 1038 m below the ground at the rate of 50 SPM;
displacing the cement slurry with drilling fluid; cleaning drill string with one cycle i
drilling fluid; squeezing the cement slurry at 350 psi; closing BOP for 5 hrs, starting R/I
without tagging the cement slurry; and drilling down up to a depth of 1042m and subsequently up to a depth of 1046m by reaming at the rate of 20m3/hrs. * Yet another embodiment of the present invention provides a process for controlling mud
i loss during boring of wells at a depth of 1046m, wherein the process comprise placing
8.0m3 of a cement slurry composition having micro-bubl: les and comprising a cement, I
water in amount of 44% by weight of cement, a non-ionic surfactant of the Rj- f
(OC2H4)n. OCH2OCH2CH20 R2 (Formula I) in amount in the range of 0.5% to 1.5 % j
%J by weight of cement at a depth of 1038m below the ground at the rate of 50 SPM;
displacing the cement slurry with drilling fluid; cleaning drill string with one cycle
drilling fluid; squeezing the cement slurry at 350 psi; closing BOP for 5 hrs; starting
R/I without tagging the cement slurry; and drilling down up to a depth of 1046m by
reaming at the rate of 20m3/hrs.
Although the subject matter has been described in considerable detail with reference to
certain preferred embodiments thereof, other embodiments are possible. As such, the j
spirit and scope of the appended claims should not be limited to the description of the j
preferred embodiment contained therein. I
25 EXAMPLES
The disclosure will now be illustrated with working examples, which is intended to
illustrate the working of disclosure and not intended to take restrictively to imply any
limitations on the scope of the present disclosure.
Example 1
Preparation of Lightweight Micro Bubble Cement Slurry
A blending container with a lid that seals for preparing cement slurry at atmospheric
pressure in the laboratory was used. The blending container is similar to that used for
#** standard slurry preparation, except it has a threaded cap with an O-ring seal. The cap
has a small hole [± 19 mm (± 0, 75 in) diameter] in the centre fitted with a removable
plug with a vent hole. A conventional blending container that does not have a seal
cannot be used for these tests. A blending container may consist either of a single blade
assembly or a mixed blade assembly.
Accurate determination of the volume of the blending container is critical to this
procedure. The calculations for slurry volume, density of above cement slurry-to-gas
« ratio are based on determination of this container volume,, as follows.
The dry blending container has to be weigh (including mixing assembly, screw-on lid
and screw-in plug for the lid). After filling the blending container with water, the lid is
closed. Additional water is poured into hole in the lid until the container is completely
^^ filled. Screw the plug into the lid. The excess water is wiped that exits from the plug's.
The mass of the water inside the container is then divider by the density of the water to
determine an accurate volume of the blending container.
The container is then divided by the density of the water to determine an accurate
volume for the blending container.
The lid is placed on the container and the blending container is sealed. Using the blade
assembly, the slurry was mixed at 12000 rpm for 15 seconds. Because of the increase in
26
' I If
slurry volume and viscosity, the maximum rpm of the blending container blade(s) may
be less than 12000 rpm.
During the mixing a noticeable change in the sound (pitch) from the blending container
was observed. After mixing, there may be some slight pressure in the blending
container, due to temperature increase and energy imparted to the foam during the
foaming process.
Care is to be exercised when removing the top of the blending container. After mixing,
the sampling port or container lid is opened and checked that the slurry completely fills
f j the blending container.
If the slurry does not fill the blending container at the end of the 15 sec. period, it is
doubtful the slurry will foam properly under field conditions. The slurry should be
redesigned. s
The following properties of cement slurries have been tested for micro bubble based j
ultra light weight cement slurries prepared with indigenously available surfactants. j
Example 2
Determination of Lightweight micro bubble Cement Slurry
The density of the foamed cement slurry is determined by pouring the foamed cement slurry into a container with a large open top that has a known volume when completely I
filled. Weigh the container, pour the foamed cement slurry into the container and level !
^^ the top with a straight blade. Wipe the outside of the container clean and again weigh
the container with the slurry. The density of the foamed cement slurry in the container is determined by dividing the slurry mass by the container volume and converting to the
appropriate density units. |
Example 3 I
Application of Lightweight Micro Bubble Cement Slurry
1. 10-40m }
At shallow depth (10-40m), total to partial loss was observed while drilling a well in Cauvery Asset of ONGC. To combat the losses three neat cement slurry plugs were
27
placed and drilled down by slick assembly to 148m. P/O drill string for change of drill
assembly by adding one drill collar but when R/I was in process, total circulation loss
was observed at shallow depth(14m). Pumped 5m3 of neat slurry of sp gr 1.90 keeping
OEDP at 14 M, observed heavy slurry seepage around cellar pit, cement tagged at 11.2
M. Drilled cement and clear hole upto 35m observed circulation loss again. Neat
cement slurry of 7m3 having sp gr 1.90 was placed. After woe, tagged cement at 12 M.
As circulation started, heavy seepage loss was observed and planned to place
lightweight micro-bubble cement slurry of sp gr 1.20-1.23. Therefore, the following
Micro bubble light weight cement slurry was formulated by adding surfactant in slurry
w ' mixing water.
Cement -100 + water -44 % + surfactant -0.1 % (B WOC)
1.5M3 Micro bubble Cement slurry of Average Sp Gr L20 was placed, and kept 5"
* OEDP at 12M. Seepage of slurry was observed near cellar pit area where micro
fractures were created earlier by neat cement slurry. After WOC of 8-10 hrs, R/I was
started and cement was tagged at 11.40 m. Drilled cement upto 25M and hole was
cleared upto drilled depth (148m) and furthermore ?M was drilled without any
circulation loss.
Since surfactant has no significant effect on thickening time, therefore laboratory
simulation was compared with neat slurry. Cement slurry of sp gr 1.25-1.35 can be
JK formulated with less dosages of surfactant (0.08%) and will provide compressive
strength 300-500psi in 8-10 hrs which is sufficient to create a barrier to minimize the
circulation loss across the loss zone. Slurry volume will be based on severity of loss
zone and normally it is taken 4-6m3 to cover the 50-70m whole volume. After
placement and displacement of slurry, P/O in shoe and squeeze cement slurry slowly for
60-100 psi pressure. Under pressure allow WOC for 6-8hrs, it depends on bottom whole f
temperature conditions of the well.
2. 1038m depth At 1038m depth observed mud loss of 1.5m3 / hrs and started R/I with bit without
28
nozzle and reached to depth 1034m without tagging the LCM pill. No circulation was
carried out. Another LCM pill of micro bubble cement slurry of low weight was
planned. Circulation was carried out and removed the cross linked LCM pill which was
remained in hole as semi-mass. Started P/O for cement plug and reached bottom with
OEDP at 1034m.
Cement slurry of 5m3 API Class G cement with 44% water was prepared and the
cement slurry was collected into batch mixer to form homogeneous slurry and added 60
liter surfactant into batch mixer and reduced the density of cement slurry upto 1.50 g/cc.
f;; Prepared 6m3 lightweight cement slurry having the density of 1.50 g/cc and displaced
with drilling fluid. Reversed wash below kick off point. P/O upto Casing shoe and
squeeze cement at lOOpsi, but pressure was not built-up. Kept BOP closed at 40psi.
WOC for 6 hrs cement tagged at 1001m top, R/I with bit and reached at 1034m. no
static loss was observed. At depth 1038m observed circulation loss of 4-5m3/hrs.
Drilling was continuing upto 1046m and circulation loss remained 4-5m3/hr. Further
drilled down to 1053m Due to very low ROP, it was planned to place light weight micro
bubble cement plug to strengthen the loss zone.
Prepared neat cement slurry with 5mt cement of sp gr 1.90 and transferred into batch
mixer to form the slurry. Added 0.5% surfactant and agitated the slurry for 10-
15minutes to induce the micro bubbles into slurry to achieve the sp gr 1.45. Kept OEDP
^ \ at 1043m and placed cement slurry. Cement was tagged at 1021m. No static and
dynamic loss at 1034m was observed. Well drilled further smoothly. It has been
observed and recommended also for effective sealing across the loss zone Keep OEPD
3-5 M below loss zone.
Example 4
Determination of Density of Light Weight & Ultra Light Weight Cement Slurry
(SG<1)
The density of the bubble cement slurry in the container is determined by dividing the
slurry mass by the container volume and converting to the appropriate density units.
29
The density measurement was also done by using mud balance as done in the case of
normal slurries and by calculation as mentioned above, but observed no significant
changes in density of MBLW cement slurry due to non-pressurization of lid placed on
the top.
Table 2 shows the density of micro bubble cement slurry achieved, when the various
dose of surfactant Cristol IE AC-liquid was added to cement slurry having different %of
water, BWOC.
Table 2: Determination of Density
^ I Cement, gm I Water, % BWOC I FAL %, BWOC 1 Sp. Gr. I
W 100 44 04% K50 ;
100 44 05 L40
100 44 08 L30
100 44_ L0^ L20_
100 " 50 1.5 097
0 97
100 50 2 0
| I | No further reduction in density.
The micro bubble cement slurry samples of Sp. Gr. 1.20 &. 0.97 respectively were cured
for 24 hours at 75°C and atmospheric pressure in water bath using stability tube as per
the methodology described at 7.4(B) (ii). Very little variation (less then ± 0.05) in the
density of set foamed cement slurry samples (top, middle and bottom) were observed, |
indicating that the micro-bubble cement slurries prepared using 44 % & 50 %water,
(§J BWOC to achieve Sp. Gr. <1.2 & <1.0 are also stable, when set.
Example 5
Determination of Stability of Surfactants
To check the bubbles stability same methodology with slight modification i.e. slurry
was applied under pressures and elevated temperatures. Taking weight immediately j
after mixing and kept same slurry for 15 minutes and then noted the Specific gravity, It
was found that weight was same, it means no bubble were broken during static
condition and slurry remained stable.
30
Table 3: Stability studies of set micro-bubble cement slurry
Specific Composition of micro Stability Test „ .... n
Gravity bubble cement slurry Condition _
C-100%+W-44%+ Temperature: 75°C M i d d l e : M7
'•20 CA i , no/ m i / n r Pressure: Atmospheric _ _ , ._
FAL-1.0%BWOC _ . _. fI
r Bottom: 1.17
Curing-24 Hours 0i ., Stable
T nroC Top: 0.96
C-100%+W-50%+ iemperature:o e Middle: 0.97
0 9 7 FAl+1.5%BWOC ^ssure: A^osohenc Bottom. a 98
1 | Curing-24 Hours | ^
The micro bubble cement slurry samples of Sp. Gr. 1.10 & 0.95 respectively were cured
w ' for 24 hours at 75°C and atmospheric pressure in water bath using stability tube as per
the methodology described at 7.4(B) (ii). Very little variation (less then ± 0.05) in the
density of set foamed cement slurry samples (top, middle and bottom) were observed,
indicating that the micro-bubble cement slurries prepared using 44 % & 50 %water,
B WOC to achieve Sp. Gr. <1.2 & <1.0 are also stable after it became harden.
Example 6
s" Determination of Permeability, Porosity & Microscopic Structure of Micro bubble
Cement Slurry
Table 4 shows the porosity and permeability data obtained of micro bubble ultra light
weight cement slurries of SG 1.50 to 1.20. The formulations show permeability less
than 1 md.
Table 4: Permeability and Porosity of set micro-bubble cement slurry
Sp. Gr. Composition,0/*) BWOC 0/
S ^ Air Permeability md
/o
1.90 C-100+W-44 1 30.0 I 0.07
1.50 C-100+W-44+FAL-0.4 30(5 0JM
1.30 " " C-100+W-44,FAL-0.8 | 31.1 [ 0J2.
1 2 0 ^ C - I 0 0 +W-44,FAL-10MK ~ ^ ;
I 10,Suppcr Latex-5.0 | |
31
The crushed samples of the moulds were analyzed by Scanning Electron Microscope for
the microscopic structure of micro bubble ultra light weight cement. Figures show that
micro bubbles are uniformly distributed within the cement matrix.
As surfactants can affect the thickening time, the thickening time test is performed on
the un-foamed base cement slurry as per the methodology described in 7.5(A). It has
been observed that the setting time of neat cement and micro bubble based ultra light
weight cement slurries are almost identical i.e. it means no significant effect is observed
due to surfactant on the thickening time of the slurry.
f^ Table 5: Thickening Time data of light weight micro-bubble cement slurry
Test Conditions .
Sp. Composition „, „ Raising _,. 8
r< o/ nwrnr-* Temperature Pressure lime
L»r. /o BWUL r Time /»»• * i ime (Minutes)
1.90 C+W-44 75°C ~ 2500 psi 25 min~ 120
1.64 • o 0 ? 1 ? ' " ? 7 ( Bentonite ba sed.), 75°C 2500 p_s i 25 min 297
1.0 C+W-44+ +FA L-0.5 75°C 2500 psi 25 min 130
, _. C+W-44++FA L-0.5 _„_ __.. __ . oon
1.30 +nxnn 0 ? 2500 psi 25 min 290
Example 7
Determination of Rheological Properties
The rheology of micro bubble base cement slurry was determined as per the
^r methodology described in 7.5(B). PV & Yp were calculated using Bingham's Plastic
Model. The rheological behavior of micro bubble base cement slurry is similar to that of
normal cement slurry & formulations can be designed as per requirements using cement
dispersants.
Table 6: Rheological properties of micro-bubble cement slurry
1 Dial Reading, 8 I p . 7 | ^Z I
Sp. Gr. 3 0 0 | 2 0 0 [ l O O | 6 0 | 3 0 p J T j c p ,bs/100Ft2
T20 91 72 48 36 27 l8~~T2~ 72 21 ~
0.97 [78 J 62 I 40 J 30 I 22 1 14 1 12 I 62" 1 16 |
32 Example 8
Determination of Compressive Strength
Micro bubble cement slurry with varying densities, suitable moulds of 2" has been
prepared. Compressive strength was determined in accordance with ISO 10426-2:2003,
7.5.3. The sealed mould containing the Micro bubble cement slurry cured into an
atmospheric-pressure water bath at BHST-75°C. Compressive strength of micro bubble
light weight cement slurry with surfactant exhibits quite high and adequate compressive
strength of 500 with density of 1.30 g/cc and slurry prepared with lower sp.gr as low as
1.0 is between 100-120psi in 24 hrs was observed. This study revealed that quite high
w compressive strength developed in respect to curing different formulations of high j
specific gravity slurry (1.25). Moulds cured under elevated temperature & pressure j
conditions shown no shrinkage. This further proves stability of micro-bubbles formed.
Compressive strength of Micro bubble cement slurries respectively were determined as
per the methodology described at 7.4(C). Table shows the compressive strength
achieved after 24 and 48 hours, when molds were cured in water bath at 75°C & j
atmospheric pressure. Table also shows the compressive strength of the micro bubble j
cement slurry when cured in HTHP curing chamber at 110°C & 1500 psi for 24 hours. Table 7: Compressive stiength data of set micro-bubble cement slurry
l>pe^ficT~ ~n Z P Curing Condition 1 Compressive I I
Gravity Composition Temperature Pressure Time/hours S t r e n g t h ( P s i)
0~^^-m%+WHO%^^dQG^\ — ~^~ 24 600 j
_ I-slurry ; • i
1.40" C-i00%+W44%+(BWOC)FAL-0.5 " 75°C Atm 24 I 680 I
" 1.40* C-I00r.+W44%+(BWOC)D800 - ~ [ |000 j
0.2%+FAL -0.5 s
1.30 C-10Q%+W44%+(BWOC)FAL-0.8 75°C Atm 24 670 j
1.20 C-100%+W44%+(BWOC)FAL-1.0 75°C Atm 24 500 '
K20- C-,00%:W70%+(BWOC)FAL-1.0+ 750C 24 " j
S Fume-35% 0.97 I C-100%+W50%+(BWOC)FAL-1.5 [ 75°C | Atm | 24 [ 100 [ 1
33
Compressive Strength of micro bubble ultra light weight cement slurry of SG <1.0 is
giving compressive strength more than 250 psi, which is adequate to control the losses
during drilling by plugging the formation.
** The slurry density showing range of 1.20 is achieved with compressive strength
1500psi in 24 hrs can be utilized this formulation in casing cementation where more
compressive strength is required.
ABBREVIATIONS
API American Petroleum Institute
jp*. Be Bearden Unit
BHCT Bottom Hole Circulating Temperature
BHST Bottom Hole Static Temperature
BWOC By Weight of Cement
CCM Cementing & Cementing Material
IDT Institute of Drilling Technology
ONGC Oil & Natural Gas Corporation Limited
psi Pounds per square inch
PV Plastic Viscosity
Sp. Gr. Specific Gravity
SPE Society of Petroleum Engineers
UCA Ultrasonic Cement Analyser
W WOC Waiting on Cement
YP Yield Point
OWC Oil well cement
MBLWCS Micro bubble light weight cements slurry
FA Foaming Agent (Surfactant)
ND Not determined
REFERENCES
34
ASTM C 109, Standard test method for compressive strength of hydraulic Cement
mortars (using 2- Minor [50-mm] cube specimens) API Recommended Practice 10B-4 /
ISO 10426-4. I
Mc Elfresh, P. M and Boncan, V.C. "Applications of Foam Cements" SPE 11203. Sept.
1982.
Foamed Cement Characterization Under Down hole conditions and its Impact on Job f
Design Rozierrs and R.F Ferrire, Dowell Schlumberger.
Applications of Foam Cement by Paul M. McElfresh and Virgilio C. Go Boncan BJ
Hughes Services.
^ ^ Peters, J., Nanda, R. K., Formulation of Low Weight Slurries of specific Gravity less
than 1.5., Report No IDT/ CCM/7/ 80 -PR-I CCM Deptt. Institute of Drilling
Technology, ONGC, India.
New Ultra Lightweight cement with supper Strength. SPE 8256.By Robert C. Smith,
Charles A. Powers, and Terrell A. Dobkins, Members. 5
API Recommended Practice 10B-4 / ISO 10426-4, 2010 recommended procedure [
preparation and testing of foamed cement slurries at atmospheric pressure i
Well Cementing, Edited by Erik B. Nelson, Elsevier Science Publisher B. V
Netherlands.

We Claim:
1. Micro-bubble cement composition comprising an aqueous mixture of cement
and a non-ionic surfactant as set forth in Formula I in the amount ranging from
0.5% to 1.5%(w/w);
R,-(OC2H4)n. OCH2OCH2CH2O R2
Formula 1
wherein Ri is C8-C22 alkyl, R2 is C3-C30 alkyl, and n= 3 to 30
# ^ 2. The micro-bubble cement composition as claimed in claim 1, wherein Ri is C10-C14
alkyl.
3. The micro-bubble cement composition as claimed in claim 1, wherein R2 is C1-C4
alkyl.
4. ri;e micro-bubble cement composition as claimed in claim 1, wherein specific
gravity of the composition is in the range of 0.97 to 1.40g/cc.
5. The micro-bubble cement composition as claimed in claim 1, wherein compressive
strength of the composition is in the range of 300 psi to 500 psi.
6. The micro-bubble cement composition as claimed in claim 1, wherein the
lf% composition further comprises one or more additives selected from a group
consisting of fluid loss control agents, retarders, accelerators, finely divided silica
fume, calcium chloride, metakaoline and super latex.
7. A process for controlling lost circulation from a borehole, wherein said process
comprises
• providing micro-bubble cement composition comprising an aqueous
mixture of cement and a non-ionic surfactant as set forth in Formula I in
the amount ranging from 0.5% to 1.5% (v//w);
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• •» ^
Rl-(OC2H4)n- OCH2OCH2CH2O R2
Formula I
wherein Rj is C8-C22 alkyl; R2 is C3-C30 alkyl, and n= 3 to 30; and
• injecting the aqueous cement composition into the borehole.
8. The process as claimed in claim 7, wherein Ri is C10-C14 alkyl.
9. The process as claimed in claim 7, wherein R2 is Cj-Ca alkyl.
10. The process as claimed in claim 7, wherein, wherein the micro-bubble cement
composition further comprises one or more additives selected from a group
consisting of fluid loss control agents, retarders, accelerators, finely divided silica
fume, calcium chloride, metakaoline and super latex.