WELL CEMENTING
PRESENTED BY S. CHANDA
DY. CED
TECHNOLOGY
PRIMARY
CEMENTING
PRIMARY CEMENTING
PRIMARY CEMENTING
Primary cementing is the first cementing operation performed after the
casing has been run in the hole. This is accomplished by pumping cement
slurry down inside casing and displaced it out into the annular space
between the casing and the borehole. The cement is then allowed to set
before drilling is resumed or the well is completed.
The main function of primary cementation are :(1) To bond and support the casing.
(2) To isolate the drinking water zone
(3) To keep the well safe for drilling oil & gas zones
(4) Protecting the casing from corrosion.
(5) To restrict fluid movements between formations.
(6) Protecting the casing from shock loads during drilling deeper.
(7) Sealing-off problematic zones.
(8) Last and the most important is Complete and durable zonal
isolation for oil and gas production
PRIMARY CEMENTING TECHNIQUES
No. of techniques are used for primary cementing.
Following are the three most commonly used
techniques :1.Single stage cementation
2.Multi stage cementation
3.Liner cementation
API & ISO Classification system
The requirement for well cements(WC) are more rigorous than construction
cements(CC) .WC must perform over a wide range of temp and pressures and
are exposed to subterranean conditions that CC do not encounter .
Oil well cement s are compositions variable concntrations of C3S2,C2S,C3A and
C4AF
There are 8 classes of API-ISO Portland cement designated A-H
Class-A-ordinary Portland Cement
Class-B-medium(MSR) to high (HSR) sulphate resistance Portland Cement
Class-C- Portland Cement wit high early strength in O ,MSR & HSR property
Class-D/E/F-known as retarded cements by reducing fast hydrated phases(C3S
and C3A) with increase in particle size-rarely used
Class-G/H- for use as basic Oil well Cement developed in response improved
technology in slurry acc /returd by chem means
SINGLE STAGE CEMENTING
Single stage cementing is most commonly used for primary
cementing, where there is no complication or lost circulation
and where cement rise in the annulus can be attained in one
stage. The single stage primary cementing is normally
accomplished by pumping one batch of cement down the
casing between two rubber plugs.
The bottom plug is placed in the casing, followed by cement
slurry. When the batch of cement has been pumped into the
casing, a top plug is released The top plug is pumped down
until it lands on the top of float collar. Thus completing the
cement job.
ZONAL ISOLATION
 Complete and durable zonal isolation is the foremost goal of the
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cement job
During the life of a producing oil or gas well, quality of the cement job has a
direct impact on the economic longevity of the well.
From starting of production to abandon the well ,slurry design and placement
technique will effect the well productivity, both physically & economically
If allowed to set undisturbed Portland cement system with 16 ppg density
usually exhibit very matrix permeability.
During the production phase cement is subject to various severe conditions
that effect the longevity of the matrix permeability-termed called cracking
/Debonding is caused by thermal & pressure fluctuations- subsequently
cement integrity is lost resulting secondary cement job for isolation repair
STAGE CEMENTING
Stage cementing consist of placement of cement slurry first around the lower portion
of a casing string using conventional primary cementing technique and then
cementing the successive upper stages through ports in the stage collar. Most stage
cementing is in two stages, although additional stages are possible. Cementation is
required to be done in two or more stages because of the following reasons:-
Down hole formation unable to support hydrostatic pressure exerted by a long
column of cement.
Cement not required between widely separated intervals.
When the volumes of cement cannot be handled with the limited cementing
equipment.
To cement deep wells with high bottom hole temp, where cement slurries of different
thickening time for different stages can be used.
For cementing of high pressure gas zones and water producing horizons.
STAGE COLLAR
Fig. Showing two-stage cementing of a casing string.
The sequence of operation for two stage cementation is
shown in the figure above. After first stage cementing has
been performed in a conventional manner, an opening bomb
is dropped to land in the lower seat of the stage collar. By
pressuring up (1200 to 1500 psi). The retaining pins are
sheared, the sleeve moves down and the ports are opened.
The well is then circulated to clear the ports and condition
the mud. For cementing the second stage, spacers and
slurries are mixed as in any single stage job. The closing plug
is dropped after the slurry pumping and is displaced till it seat
on the upper sleeve in stage collar. After the plug has seated,
a minimum of 1200-1500 psi above the second stage
displacing pressure is required to close the collar ports. And
thus completing the two stage cementing job.
Following are some of the points to be considered
before primary cementing job.
Hole condition
a) Well bore shall be preferably 3” larger than casing diameter
(absolute minimum 1.5) inch.
b)It shall be as near gauge as possible without washouts and
severe dog legs.
c) It shall be stabilize and properly conditioned, free from
lost circulation, tight pull, caving and activity.
d)Tally the casing and total depth such that the casing can be
landed within 1.5 m (5 ft.) of the bottom (floor).
e) Caliper logs must be taken to determine hole volume to
achieve desired cement rise.
Mud conditioning.
a. Adjust Plastic Viscosity (Pv) and Yield Point (Y ) to
the lowest possible values without dropping Solids.
p
b. Condition hole with good surface conditioned mud
at a rate anticipated for cement pumping rate for 1.5
to 2 cycles (minimum).
c. Use carbide pills, oats or other fluids caliper that
indicate at least 90% of the hole mud is being
circulated.
Cement slurry design
a)Determine the maximum allowable down hole density
to prevent fracturing. The density of cement should be
at least 1 ppg (preferable 2 to 3 ppg) heavier than the
drilling mud.
b) Determine BHCT from logs and API temperature
data/tables.
n
d)Water separation:
For:- 1) Normal slurries ------- 1.0% or less
2) Prevention of gas channeling – Nil
e) Determine cement slurry thickening time at BHCT
and BHP. Minimum thickening time should be job
time plus one hour thickening time to a consistency of
50 Bc.
f) Use 33% to 40% silica at static temperature above 110
degree C
a
g) For cement slurries to be placed across salt
formations, use 20% to 37%(saturation) sodium
chloride.
h)Use the same mix water in lab as that will be used on
the location.
I) Analyze water on the location prior to mixing
j) Check slurry consistency in lab mixed 0.5 ppg heavier.
Slurry consistency(Initial)
For:- 1) Turbulent flow
: 10 Bc or less
2) Plug flow
: 30 Bc (approx)
3) other slurries
: 2o Bc or less
4) Scavenger slurries : No measurement applicable
Preflush/Spacer
Check compatibility of preflush/spacer, drilling mud
and cement slurry at room temperature and BHCT.
Design preflush/spacer to be displaced ahead of
cement slurry in turbulent flow (if not possible, then
in plug flow) with minimum 10 minutes contact time.
Compressive strength
 The minimum compressive strength required to hold the
casing and to seal the formation is 500 psi. compressive
strength of cement stone increases with time and
temperature. API recommends a maximum pressure of
3000 psi. For the increase of compressive strength, the
water cement ratio of cement slurry is reduced or
accelerators, like CaCI2 are used at low temperature and
silica flour above 110 degree C.
CEMENT ADDITIVES
ACCELERATORS
 Accelerating a slurry means shortening the
Thickening Time or reducing the time required
to gain Compressive Strength or both.
 In general an in-organic material will act as an
accelerator.
Examples:
Calcium Chloride, Sodium Chloride, Sea water,
potassium Chloride, Sodium Silicate, Gypsum
etc
RETARDERS
 A material that allows sufficient time for slurry
placement by delaying the set of the cement is
called a retarder.
 In general, any organic material will retard the
setting time of a cement slurry.
Examples:
Calcium Lignosulfonates, Calcium
Lignosulfonates, Organic acids etc.
sodium
FLUID LOSS ADDITIVES
 Reduces the rate at which filtrate is lost to a
permeable formation.
 Works by viscosifying the mix water or by
plugging the pore throat in the filtrate cake
with long polymer chains.
Examples:
 Organic polymers (Cellulose)
 Organic polymers (Dispersants)
 CMHEC.
DISPERSANTS
 Also called friction reducers, these materials
make cement slurries easier to mix and pump.
 Act on surface charges of the cement grains.
 Secondary retardation
 Enhances fluid loss control.
Examples;
Polynapthalene sulfonate(PNS),
Non lignosulfonate.
EXTENDERS
 Additives that reduce slurry density and
increase slurry yield are called extenders.
 Cement may be lightened to protect the weak
formations or slurry yield may be increased to
reduce the cost.
Examples:
water, Bentonite, Pozzolan, Gilsonite etc.
Heavy weight Additives
These are required to counter high formation pressures.
Common high density materials are:a) Haematite
b) Ilmenite
c) Barytes
Thank You
For your time.