Page 185 - Air and Gas Drilling Manual

Chapter 5: Shallow Well Drilling Applications 5-27
.
= 903 7
b
a
The bottomhole temperature is determined from the geothermal temperature of
the rock formations at the surface, the regional geothermal gradient, and the depth of
the borehole. The geothermal temperature of the rock formations near the surface is
assumed to be represented by the temperatures given in Table 4-1 (also see Appendix
D). Thus, for a 6,000 ft surface location this temperature is assumed to be 37.6˚F.
For this example the geothermal gradient is approximated to be 0.01˚F/ft. Thus,
T bh, is
o
.
t r = 37 6 F
T = t + 459 67.
r r
T = 497 27. o R
r
T bh = T + 0 01 1 200. ( , )
r
o
T = 509 27 R
.
bh
The average temperature of this borehole is
T + T
T av = r bh
2
o
.
T av = 503 27 R
Using the above values, Equation 5-1 becomes

 2 (. 0 023 ) ( , 1 200 )   . 05

[
. (503 27
P bh =  ( , 1 695 ) 2 + 903 7 . ) 2 ] e 503 .27 − 903 7 . ) 2 
. (503 27
  

2
,
P bh = 5 456 lb/ft abs
P bh
p bh =
144
p bh = 37 9 psia
.
This is the pressure at the bottom of the borehole in the annulus.