Page 382 - Air and Gas Drilling Manual

κ is the actual drilling rate used in the well,
S fw is the specific gravity of the formation water.
For this illustrative example Equation 8-7 becomes
)
π Chapter 8: Air, Gas, and Unstable Foam Drilling 8-65
(62 4 .
) (2 7 .
2
.
q fw = (0 656 ) ( 320 − )
60
.
.
4 (833 ) (107 )
q fw = 1 663 gal/hr
,
or
,
q fw = 1 663 = 40 bbl/hr
42
The influx of formation water into the annulus can increase the bottomhole
pressure in the annulus and injection pressure into the top of the drill string. If
water is injected into the injected gas flow to the well, the gas entering the annulus
will be saturated and the injected water and the formation water in the annulus can be
assumed to be carried as droplets (or as a particle mass). Also, the injected water can
be assumed to be carried as droplets in the inside of the drill string. Therefore, in
order to assess the effects of injected water and lifted formation water in the annulus,
Equation 6-52 is altered to include the weight rates of flow of injected water, ˙ w ,
iw
and the lifted formation water, ˙ w fw . Equation 6-52 becomes
 S    ˙ w + w ˙  
w + ˙
g
a =   1 +  s iw fw   (8-8)
a
 R     w ˙ g  
where ˙ w is the weight rate of flow of injected water (lb/sec),
iw
˙ w is the weight rate of flow of formation water (lb/sec).
fw
For flow in the inside the drill string, Equation 6-69 becomes
 S    w ˙  
a =  g  1 +  iw   (8-9)
i
 R     w  
˙
g
The values of ˙ w and ˙ w fw are, respectively,
iw
q ( ) . (8 33 )
42
˙ w = iw (8-10)
iw )
, (3 600