2. OUTLINE
• INTRODUCTION
• CLASSIFICATION OF CEMENTING ADDITIVES
• ACCELERATORS
• WEIGHTING AGENTS
• EXTENDERS
• RETARDERS
• LOSS CIRCULATION
• FLUID LOSS ADDITIVE
• DISPERSANTS
• ANTI – SETTING ADDITVES
• ANTI- FOAM
• SPECIAL ADDITIVES
• RECOMMENDATION
• CONCLUSION
3. INTRODUCTION
cementing additives are added to different
slurry systems to achieve an excellent
environment bond. Due to varying pressure and
temperature ranges, which may be too low or
too high, these additives are added to modify
the cement for Individual well requirements.
The additives are developed to control the
major cement properties i.e thickening time,
consistency, fluid loss rate, free water etc.
4. CLASSIFICATION OF CEMENT ADDITIVES
• Accelerators
• Retarders
• Heavy weight additives (weighting agents)
• Light weight additives (extenders)
• Loss circulation control agents
• Filtration- control agents
• Friction reducers (dispersants)
• Special additives.
5. ACCELERATORS (Cacl2)
Cement slurries to be used on shallow, low temperature formations require
accelerator to shorten thickening time and increase early strength development,
particularly at formation temperature below 100oF. Basic cement and good
mechanical practises, in as little as 4hrs, a strength of 500psi can be developed. This
strength is generally accepted as the minimum for bonding and supporting pipe.
Accelerator commonly used ;
a. Calcium chloride – normally 2-4% BWOC
b. Nacl - --1.5-5% BWOW. Low percent of it accelerate
c. WE-IX --- accelerates cement slurries containing carboxymethyl hydroxyethyl
cellulose (CMHEC) retarder
d. Sea water --- contain 23000ppm of chlorides which acts as an accelerator used for
mixing cement slurries in marine locations.
6. WEIGHTING AGENTS
High pressures are frequently encountered in deep wells, hence cement slurries of high density are required . To
increase cement slurry density, an additive which has a specific gravity in the range of 4.5-5.0, having low water
requirement not significantly reduce the strength of the cement, and have little effect on pumping, be inert chemically
and compatible with other additives is added , Barite and hematite are commonly used for this purpose.
LIGHT WEIGHT ADDITIVES (EXTENDERS)
These additives are used to reduce the weight of the slurry, make the slurry cheaper, increase yield and sometimes
lower filter loss.
Light weight additives includes ; - bentonite (2-16%) , diatomaceous earth –(10-40%)
Bentonite
• decreases compressive strength
• Increases permeability
• Viscosifies the slurry
WE-IX
• Forms viscous gelatiinous silicate gel
• Binding extra water
• Low free fluid separation
Acts as an accelerator at low temperature (˂ 185oF)
No inherent fluid loss control
ADVANTAGES OF WE –IX OVER BENTONITE
• Low rheology for mixing and turbulent flow
• Higher compressive strength
7. RETARDERS
In the present day drilling, hydrocarbon –bearing formations are encountered
at great depth (deep) at these depths, the bottom hole static temperature
(BHST) may range from 170oF-500oF
To prevent the cement from setting too quickly, retarders must be added to
the cement slurries. Increasing temperature hastens thickening more than
increasing pressure.
Retarders are lignosulphates extracted from plants.
Retarders have dispersion effects.
They increase fluid loss.
Incompatibility
Slow development of compressive strength.
Marabond-21 (low temperature retarder)
Kelig-32 (high temperature retarder)
8. LOSS CIRCULATION CONTROL
Loss circulation is defined as the loss to induced
fractures of either whole drilling fluid or cement
slurries used I drilling or completing a well. To
check this bridging or plugging materials are
utilized. Example of such materials are mica,
cellophane, walnut shells etc.
This materials reduces density and friction
pressure.
9. FLUID LOSS ADDITIVES
The filter loss of cement slurries is lowered with
additives to prevent premature dehydration or loss of
water to porous zones, protect sensitive formations.
These filtration control additives function in the
following ways:-
(a) Forms films which control the flow of water from
the cement slurry and prevent rapid dehydration
(b) To improve particle size distribution, which
determines how liquid is held or trapped in the
slurry. In WEAFRI Diacel –FL is used for this purpose.
10. DISPERSANTS ORFRICTION REDUCER
Dispersing agents are added to cement slurries to improve their
flow properties. Dispersed slurries have lower pressures, thereby
minimizing the horsepower required and lessening the chances
of the lost circulation and premature dehydration. Dispersants
lowers the yield point and gel strength of the slurry. They re
added in conjuction with fluid loss control additives. In WEAFRI
we use lomar’d for this purpose.
REASON FOR USE
• Reduce viscosity and yield point
• Reduce friction pressure
• Improve cement slurry mixability /pumpability
• Improve efficiency of fluid loss control additives
11. ANTI- SETTLING ADDITIVES
This additives reduces sedimentation, slurry
instability ,compatible with all cement products
and cement, No significant effect on slurry
properties except rheology, in WEAFRI we use
HEC-10 for this purpose.
12. ANTI FOAM (ASP-742)
Prevent slurry gelation and prevent poor hydration. The
anti foam forms a thin coating above the slurry. It is
insoluble in the foaming fluid.
A good anti foam should be oil based.
Prevents pump cavitation
Allow true slurry density to be mixed and pumped
PROPERTIES
Insoluble in the foaming fluid
Have more surface active than the foaming fluid
13. SPECIAL ADDITIVES
a) Gas check:- this checks gas migration/ chanelling
from the formation to the slurry. WLS-2L is used
in WEAFRI
b) Strength retrogression:- ensures that set cement
does not loose their compressive strength at
high temperatures in the well.
for temperature (BHST) greater than 230oF,
strength retrogression agents are used. This loss
of strength is accompanied by an increase in
permeability. Silica flour (WE-SF-3/SF-4) is used for
this purpose in WEAFRI
14. RECOMMENDATION
I recommend that cement additives be used in
slurry designs due to it’s efficiency in controlling
slurry behaviours especially in deep formations.
15. CONCLUSIONN
Additives are very necessary in slurry designs.
They modify the behaviour of the cement
system, ideally allowing successful slurry
placement between the casing and the
formation, rapid compressive strength
development and adequate zonal isolation
during the lifetime of the well.
