Page 341 - Air and Gas Drilling Manual

8-24 Air and Gas Drilling Manual
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 44.74˚ F for average year round
temperature for a surface elevation location of 4,000 ft above sea level (for mid
latitudes of North America, or see Appendix D). Therefore, the absolute reference
temperature of the rock formations at the surface, T r, is
o
.
t = 44 74 F
r
T = t + 459 67.
r
r
T = 504 41. o R
r
Blooey Line
The calculation procedure must be initiated with the known atmospheric
pressure at the exit to the blooey line. It is assumed that the air will exit the well
annulus and enter the blooey line with the surface geothermal temperature of 44.74˚
F (or 504.41˚R). It is further assumed that the temperature of the air flow in the
blooey line does not change until it exits the blooey line (i.e., the steel blooey line
will be at nearly the surface geothermal temperature at steady state flow conditions).
The standard isothermal gas pipeline flow equation can be used to determine the
major loss due to pipe wall friction [12]. This equation can be adjusted to also
include the minor loss for the T turn at the top of the annulus into the blooey line
and to include the losses due to the two valves at the entrance end of the blooey line.
Therefore, the equation for the pressure in the air (or gas) flow at the entrance end of
the blooey line, P b, can be approximated as
    w R T   05 .
2
P =   f  b L b + K + Σ K    g 2 r  + P at   (8-3)
2
b
t
v
g 
   D b   gA S   
b
where f b is the Fanning friction factor for the blooey line,
L b is the length of the blooey line (ft),
D b is the inside diameter of the blooey line (ft),
2
A b is the cross-sectional area of the inside of the blooey line (ft ),
K t is the minor loss factor for the T turn at the top of the annulus,
K v is the minor loss factor for the valves in the blooey line.
The loss factor for K t for the single blind Tee at the top of the annulus is
approximately 25 (see Figures 8-5 and 8-6, direct circulation only). These
approximate minor loss values for Tee’s have been obtained from air and gas drilling
operations in the San Juan Basin and in the Permian Basin. The gate valves (with
the gate in the full open position) in a blooey line have a open inside diameter that
is nearly the same as the inside diameter of the blooey line. The loss factor for K v
for gate valves that have an inside diameter slightly less than the inside diameter of
the blooey line is approximately 0.2 [12].