# Box 9.4

Mathematical calculations of separation ability for the various
separation methods have a number of variables that make it
impractical to mathematically predict separation of gas or oil
from the drilling fluid.
Basic variables:
. Liquid flow rate
. Gas volume
. Fluid properties, plastic viscosity, gel strength, density, etc.
. Residence time
. Centrifugal force
. Vacuum
. Gas bubble size
. Gas bubble film strength
. Emulsifiers (for drilling fluid and oil)

Some basic ideas and numbers are:

. Retention time in the vessel
. Tr = Ve / Q×k, where
. Tr = retention time, sec
. Ve = effective volume of the vessel, ft³
. Q = flow rate, gpm
. k = units constant, 7.48 gal/ft³
. Vacuum measurements:
. Atmospheric pressure = 14.7 psia
. = 29.9 Hg
. = 33.94 water
. = 1 atm absolute
. = 101.3 kPa
. Hydraulic horsepower (Hhp):
. Hhp = P×Q/1714, where
. P = gage pressure, psi
. 1714 = units constant, psi/gpm.

Electrical or mechanical equivalent hp is at least twice the theoretical
Hhp (see Box 9.1).