important function of oil & gas well primary cementing is to isolate the
various zones within the wellbore. In others words, the cement must
prevent fluids or gases in one particular zone from mingling with those
of another. A properly designed and placed cement slurry accomplishes
this by creating the necessary seal between the casing and the
formation. The cement must prevent migration or fluid channeling
throughout the cement.
Today's well cement systems must perform in a variety of down hole
conditions, from 0°C - over 350°C, and at bottom hole pressures in
excess of 30,000 psi.
Chemical Mine WorldCo. is producer of cementing additives
for all its cementing operations here in UAE that has considerable in-house expertise and experience in the
design of cement slurries utilizing Schlumberger products. The technical
manager, laboratory manager, laboratory technician, as well as cementing
supervisors, are trained in the design of, and experienced in the use
of, cement slurries using Schlumberger cementing additives.
The following paragraphs describes the performance of the
cementing additives by functional group, which can be provided
by CMWC (of Chemical Mine WorldCO.):
Accelerators are materials that cause cement to hydrate and develop
strength earlier and faster. They are commonly used to provide improved
strength at low temperatures and to counteract the retarding effects of
other additives. Accelerators shorten the thickening time.
ANTIFOAM AND DEFOM AGENTS :
Antifoam agents prevent or reduce the foaming tendencies of the cement
when it is mixed. This is necessary because the properties of cement
slurries and the set cement depends on the water/cement ratio. Most
flied mixtures determine the ratio by measuring the density of the
slurry, so entrained air causes the slurry to be mixed at improper
ratios. Some materials can be used as antifoam agents, but not as
defoamers. Other materials act as either defoamers or foam preventers.
ANTIGELATION AGENTS :
In some cases gelation is caused by the chemical makeup of the cement.
Many times this gelation can be controlled by dispersants but special
materials may be required.
DEEPCEM ADDITIVES :
DeepCHEM liquid cementing additives were created for short transition
time and early compressive strength development. Such properties are
necessary for isolation and early casing release to ensure successful
cementation in the unconsolidated, low temperature environment of the
surface and conductor casings in deepwater wells. They are also useful
in other low-temperature situations.
Dispersants act to reduce the viscosity of cement by breaking up
aggregates of the fine cement particles. This reduction in viscosity
allows mixing at lower water/cement ratios for higher density, improved
fluid-loss control and pumping at reduced pressures.
EXPANDING ADDITIVES :
Expanding additives react chemically after hydration (setting) to
produce an increase in the bulk volume of the cement. This reaction
provides benefits in zonal isolation and protection of the casing. When
used across soft formations, flexible systems may be required to prevent
Extenders allow the production of a greater volume of slurry from the
powdered cement. This feature can result in reduced cost and where the
extenders are lightweight (or they allow additional water to be used),
lower density. The advantage of reduced cost is obvious. Reduced density
is important where weak formations are to be cemented. Such weak
formations could part and allow loss of the slurry during the cementing
operation. A variety of extenders are available to provide for different
requirements of lower density, lower cost and other performance
FLUID-LOSS CONTROL ADDITIVES :
Fluid-loss control additives minimizes the loss of water from the slurry
into permeable formations. This helps to maintain the properties of the
cement slurry during placement and until the cement sets.
GAS MIGRATION CONTROL ADDITIVES :
Gas migration control additives are used to reduce the risk of gas
invading the cement and migrating into the wellbore.
LOST CIRCULATION CONTROL MATERIALS :
Materials used to prevent or halt losses of slurry from the wellbore are
called LCM. In addition to LCM added to the cement, special lost
circulation control products are available for combining lost
circulation during operations other than cementing.
Retarders are used to lengthen the time that a cement slurry can be
pumped or remains fluid so that other operations (such as pulling pipe
after spotting a cement plug) can be performed. They are required at
elevated temperatures or when large volumes of slurry require a long
time to pump at lower temperatures.
Surfactants are used in chemical washes and spacers with OBM and to
create stable foam when adding a gas to make foamed cement.
SUSPENDING AND ANTISETTLING AGENTS :
Occasionally, segregation can occur in a cement slurry. This segregation
may be in the form of water separation (known as free fluid) or in solid
particle sedimentation. In either case, a material to suspend the solids
is used to maintain slurry integrity.
THIXOTROPIC ADDITIVES :
Thixotropic additives produce an intentional gelation of the cement to
aid in the placement of the cement.
UNISLURRY ADDITIVES :
UniSLUURY additives have unique and synergistic properties. These
additives have been purpose built to perform their function and have
properties that distinguish them from other fluid-loss or set-control
WEIGHTING AGENTS :
Weighting agents are used to increase density of the cement when needed
for well control.
Spacers are generally thickened, weighted fluids used to aid in mud
removal and to separate the mud from the cement to prevent any
CHEMICAL WASHES :
Chemical washes are generally thin fluids with surfactants to aid in mud
removal and to separate the mud from the cement to prevent any
Cement Additives :
Cement Additives, Fluid-Loss Control Additives, Gas Migration
Control Additives, Lost Circulation Control Materials, Antisettling
Agents, Thixotropic Cement Additives, Cementing Equipment, Cementing
Services, Cement Additives, Gas Migration Control.
SPECIAL ADDITIVES :
- There are
number of additives that do not fit neatly into functional
groupings. Fibers are used for controlling lost circulation. Special
types of fibers also improve the impact resistance and tensile
strength of cement.
flexibility of cement can be improved by the use of special
additives. This increase in flexibility provides increased
resistance to failure by mechanical stresses imposed on the cement
during well operation.
salt (sodium chloride) and potassium chloride are used primarily to
change the ionic nature of the water in the slurry, which helps to
minimize adverse formation interactions. In cases where formation is
salt, high concentrations of salt, up to saturation, are commonly
used to prevent leaching salt from the borehole wall.
- Silica is
used to combat strength retrogression. Strength retrogression is a
change in the hydration products that are formed when cement is
exposed to high temperatures (>110°C [ 230°F]). Silica is available
in coarse or fine grades for cementing.