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again that although the foams may not be stable at the bottomhole, hole
cleaning can still be achieved with adequate mixture flow velocities in the
annulus.

10.3.3 Handling the Returned Foam
Knowing how to handle the returned foam is important in foam drilling
because it greatly affects drilling costs and impacts the environment.
Returned foam can be either disposed or recycled. Foam disposal
involves dumping the returned foam in an onsite pit if the environment
permits. This option does not require special equipment. It may take a
few days to a few weeks for stiff foams to decompose naturally. There-
fore, in most cases, the returned foams are broken down with acids or
separators before disposal. Engineers have known for years that acid
added to a foam fluid will break down and destabilize the foam. In the
late 1970s and early 1980s, techniques for breaking down foams using
acid were developed to aid in cleaning up reservoir pits full of foam after
foam drilling operations were completed. Lowering the pH of foam acts
to destabilize it and allows the gas phase to break out much more easily.
Foam recycling requires special equipment. The process is illustrated
in Figure 8.5. The procedure serves to greatly reduce the costs associated
with using foam. It is a long process to continually foam, defoam, and
then refoam the drilling fluid for reuse. In cases where containment or
environmental concerns limit the use of foam because of the increased
fluid volume, the foam recycling system eliminates these concerns by
rapidly defoaming the fluid in the blooey line using a special defoamer.
“Rapidly” means the foam half-life goes from 6 minutes to less than 15
seconds. The system results in a volume reduction of 95% within seconds.
The system does not destroy the foaming agent.
The “defoamed” fluid can be cycled through the shale shaker to
remove drill solids and then cycled through the steel pits for complete
settling of the cuttings. An activator is then added to refoam the fluid.
The activator completely counteracts the defoamer. It refoams to its ori-
ginal stability level. The number of foam, defoam, and refoam cycles is
virtually unlimited. At pH levels above 10, the foaming agents, when
agitated with water and air, create a viscous, stable foam. When the pH
is dropped to 3.5 by the addition of sulfuric acid, the foaming potential
of the water is greatly diminished. In fact, the foam is essentially killed by
the addition of the acid.