Following are points about liquid/gas separation.
. Gas and water in a mixture with no solids or emulsifiers separate
naturally and quickly by gravity because gas is lighter, floats up in big
bubbles, and breaks out.
. Water and oil in a mixture with no solids or emulsifiers separate
naturally by gravity because oil is normally lighter than water. Bear in mind, however, that some oil is heavier than water and that some oil is
soluble in water (and all gas is soluble in oil).
. Gas and oil may require extra energy and time to separate. For
example, air and nitrogen separate from diesel oil very quickly. On the
other hand, methane and ethane are soluble in oil and may require a
long time to separate without the addition of heat or chemicals.
. The time required for drilling fluid and gas to separate depends on
the fluid properties. If the drilling fluid approaches water, separation
is quick. If, however, the drilling fluid has high apparent viscosity
(thick), separation can be difficult and time-consuming.
. If emulsifiers are present in the mud system, it is difficult to separate
oil from drillling fluid. In some cases it is simply not practical to work
on line because it requires time, heat, and breaking chemicals.
. Foaming makes it difficult to separate gas from liquid. The best
practical defoamers are aluminum stearate and alcohol.
. In foam, bentonite and some polymers, such as CMCs (ceramic matrix
composites), make such a stable foam that it is time-consuming and
difficult to break them out.
. It is vital to know how the separator and/or degasser in use works,
both mechanically and chemically. Moreover, there must be enough
separators and degassers to handle the anticipated volumes.
. In general, the old rule of simpler is better also holds true for
separators. However, safety considerations offshore or when dealing
with H2S gas are of paramount importance.