2. Introduction
• Cementing is the process of mixing a slurry of cement, cement additives and water and
pumping it down through casing to critical points in the annulus around the casing or in the
open hole below the casing string.
• The two principal functions of the cementing process are:
-To restrict fluid movement between the formations
-To bond and support the casing
-To provide zonal isolation
3. Wide ranges of cementing solutions
• Heavyweight Cement – heavyweight additives are used to increase slurry density for control of highly
pressured wells.
• Lightweight Cement – situations with lost-circulation and weak formations with low fracture gradients
require the use of low-density cement systems (<15 lb/gal) to reduce the hydrostatic pressure of the fluid
column during cement placement.
• Plug Cementing – cement plugs are set for a variety of reasons, most commonly for abandonment,
temporary abandonment, testing, sidetracking, lost-circulation control, or remedial work.
• Self-Healing Cement – cement that works on the premise that the migrating fluids react with the cement,
causing it to respond by expanding to automatically seal the flow path, helping prevent further fluid
migration.
• Squeeze Cementing – An operation involving the injection of cement into a problematic section of the well
at a desired location.
4. Light weight Cement
• Cementing casing across highly depleted zones and weaker formations requires low-density cement
systems capable of reducing the hydrostatic pressure of the fluid column during cement placement.
• Low-density or lightweight cement systems help achieve the specified of cement by avoiding or
minimizing lost circulation
• Lightweight cement can be achieved in one of three ways: water extended, injection of gas (foamed
cement), or by adding low-specific-gravity microspheres.
• Water extended: adding additional water to the cement slurry is a common means of reducing slurry
density, yet it requires water-extending additives to help maintain slurry stability
• Foamed cement: Injecting gas into the slurry provides the benefit of increased slurry compressibility,
increase set-cement elasticity, and the flexibility to vary density during operations.
• Microspheres: Microspheres are used when slurry densities from 8.5 to 11 lbm/gal are required. They
are hollow spheres obtained as a byproduct from power generating plants
5. Foamed Cement
• Foamed cement is an alternative to conventional cement when lower slurry
densities and moderate compressive strength are required.
• First foamed cement slurry was pumped back in 1979.
• Foamed cement is a mixture of cement slurry, foaming agents, and a gas
(nitrogen).
• When properly executed, the process creates a stable lightweight slurry, with
low permeability and relatively high compressive strength
• Nitrogen is commonly used to foam the base slurry. Hence the foamed cement
slurry density is easily adjustable by varying the nitrogen concentration.
6. Foamed cement is created
when a gas, usually nitrogen, is
injected at high pressure into a
base slurry that incorporates a
foaming agent and foam
stabilizer.
It is possible to make slurries
ranging in density from 4 to 18
lbm/gal using foamed cement.
7. Use of Nitrogen
• Nitrogen gas can be considered inert, and does not react with or modify the cement-
hydration-product formation.
• Under special circumstances, compressed air can be used instead of nitrogen to create
foamed cement.
• In general, because of the pressures, rates, and gas volumes involved, nitrogen-
pumping equipment provides a more reliable gas supply.
• The process forms an extremely stable, lightweight slurry that looks like gray shaving
foam.
• When foamed slurries are properly mixed and sheared, they contain tiny, discrete
bubbles that will not coalesce or migrate.
• Because the bubbles that form are not interconnected, they form a low-density cement
matrix with low permeability and relatively high strength.
8. • When the N2 is introduced into the cement slurry with sufficient energy to create discrete gas
cells, physical stabilization results (the gas is stabilized as small cells, or bubbles, within the
slurry).
The bubbles are not interconnected and do not coalesce (Figure 2), resulting in a low-density
cement matrix with low permeability and relatively high strength.
9. Causes for the Failure of conventional cement
• Mechanical shock from pipe tripping;
• Casing expansion and cement compression during pressure testing;
• Pipe expansion or contraction caused by cycles in production pressures and
temperatures.
Use of Foamed Cement
• The compressible, ductile nature of foamed cement allows it to flex and absorb
stresses that often damage conventional cement.
• The flexibility of foamed cement can help increase the life of a cement job by
maintaining the integrity of hydraulic bonds, preventing the formation of a micro
annulus, and eliminating stress cracking
10. Advantages of foamed cementing
• Although its design and execution can
be more complex than standard jobs,
foamed cement has many advantages
that can overcome these concerns,
because it:
• Is lightweight
• Provides excellent strength-to-density
ratio
• Is ductile
• Enhances mud removal
• Expands
• Helps prevent gas migration
• Improves zonal isolation
• Imparts fluid-loss control
• Is applicable for squeezing and
plugging
• Insulates
• Stabilizes at high temperatures
• Is compatible with non-Portland
cements
• Simplifies admix logistics
• Enhances volume
• Has low permeability
• Is stable to cross flows
• Forms a synergistic effect with
some additives, which enhances
the property of the additive
11. Disadvantages of Foamed Cement
• The disadvantage of foamed cement is the need for
specialized cementing equipment both for field application and for
laboratory testing.
• Nitrogen and Nitrogen equipment
-Using a nitrogen pumping unit on location increases the complexity of
executing a foamed-cement job
-deviations in nitrogen pumping rate can produce foamed cement that is
either too light or too heavy.
12. Comparison with conventional Cement
In direct comparison to conventional cement slurries, foamed cement shows significantly
better resilience and is able to withstand higher wellbore pressures.
Laboratory tests using a tri-axial load-cell revealed a much more favorable Young’s modulus
for foamed cement
13. Foamed Cement has better bonding properties, is more ductile, and shows better
insulating properties, especially for use in geothermal projects.
The insulating capacity of foamed cement is two to ten times higher compared to
conventional cement slurries .
Depending on slurry design, a heat transfer coefficient as low as 0.05 btu/(hr*ft*F) can be
achieved
14. Conclusion
• Overall, foamed cement job costs are comparable in cost to other specialized
slurry designs.
• Because of the success of this foamed-cementing program, the foamed-
cement process has become the first choice for primary cementing where
conventional techniques have failed and where zonal isolation is critical.
• Because foamed cement is more ductile and shows better insulating
properties than non-foamed cement, it is a recommended option in geothermal
applications.
• Foamed cement lost-circulation properties can help enable successful
cementing of geothermal wells in low fracture-gradient zones
