Page 218 - Air and Gas Drilling Manual

5-60 Air and Gas Drilling Manual
The weight rate of flow of the gas, ˙ w , is
Q
g
g
=
( . )
˙ w ˙ w g = γ . 0 0763 7 87 g
g
˙ w = . 0 601 lb/sec
g
The borehole diameter D h is
.
d h = 12 25 inches
d
D = h
h
12
D = 1 021. ft
h
The estimated drilling rate of penetration is 78.4 ft/hr. From Equation 5-4, the
weight rate of flow of the solid rock cuttings, ˙ w , in the annulus is
s
π
. ) ( . ) 
2
˙ w =   (. 1 021 ) (62 4 2 7  78 .4  
s     (60 ) (60 )  
4
˙ w = . 3 00 lb/sec
s
The temperature of the rock formations near the surface (geothermal surface
temperature) is estimated to be the approximate average year round temperature at
that location on the earth’s surface. Table 4-1 gives 59˚F for the sea level average
year round temperature for the mid latitudes of the North America (also see
Appendix D). Therefore, the absolute temperature of the rock formations at the
surface, T r, is

o
t r = 59 F
T = t + 459 67.
r
r
o
T = 518 67. R
r
The bottomhole temperature is determined from the surface geothermal temperature,
the geothermal gradient, and the depth of the borehole. For this example and the
figures that follow, the geothermal gradient is approximated to be 0.01˚ F/ft. Thus,
T bh is