STANDARD HANDBOOK OF PETROLEUM & NATURAL GAS ...

Air and Gas Drilling 861
log,,p,,, = 0.4327
p, = 2.708 psia
The volumetric flowrate of injected water is determined from Equation 4-136,
which yields
qi = 269.17( 68.0-2.708 2*708 )(2.556) = 28.5gallhr
The approximate volumetric rate of foaming agent q, (lb/hr) injected will be
q, = 0.002(28.5)
= 0.06 gal/hr
However, this foaming agent injected is only a small part of what should be
injected to foam the anticipated formation water which may enter the annulus.
This will be covered in the next Example.
If the circulating air has been saturated, then any formation water entering
the annulus will be carried to the surface as droplets and will not reduce the
temperature of the air and thereby reduce kinetic energy of the air as it expands
in the annulus. The amount of formation water that can be carried from the
borehole annulus by the real amount of air circulating Q is directly related to
the additional air that is being circulated above that minimum value Q.,
necessary to clean the hole of rock cuttings.
To calculate the amount of water that can be carried from the hole, Q is
substituted into Equation 4-123 and the potential drilling rate such an air
volumetric flowrate can support. The additional drilling rate that can be
supported by Q is actually the weight of formation water (per hour) that can
be removed from the borehole. Therefore, once the potential drilling rate is
obtained for Q, then the formation water that can be taken in the borehole
annulus per hour q, (gal/hr) while maintaining the normal drilling rate will be
x (62.4)( 2.7)
qw =-Di(K 4 p - k )
8.33
(4137)
where KP = potential drilling rate for Q in ft/hr
Ka = actual drilling rate in ft/hr
Using the data and results from the previous Examples, determine the
approximate volumetric flowrate of formation water into the annulus of the well
that can be removed by the actual air circulation rate of 2,400 actual cfm. Also,
determine the total amount of foaming agent which should be injected into the
circulating air.
Substitute into Equations 4-122, 4123, and 4124 the previous example values
and let
Q = Q = 2,400 actual cfm