Page 62 - Air and gas Drilling Field Guide 3rd Edition

3.4 Flow Line from Rig 53

3.4.1 Blooey Line
Figure 3-1 shows a blooey line exiting from the drilling rig annulus for direct cir-
culation operations. Blooey lines (or equivalent) are required for all air and gas
drilling operations and are needed to keep drilling rock dust and cuttings away
from the drilling rig and rig personnel. Blooey lines must be secured to the
ground surface with tie-downs (see Figure 3-1). The high velocity of the air or
gas flow from the well will interact with the flexible blooey line to set up an
aerodynamic flutter situation, which is very similar to the motion of a water
hose on the ground when the water valve is turned on. This flutter situation
can result in high dynamic forces and resulting blooey line movement. This
potential movement must be constrained along its length by tie-downs to the
ground.
The blooey line should be designed with an inside cross-sectional area greater
(by a factor of 1.1) than the annulus cross-sectional area at the top of the well.
In general, this is not practical when drilling shallow larger diameter borehole
sections. This requirement applies to the drilling of the deep smaller diameter
borehole sections. Therefore, the inside diameter of the blooey line, d b (inches,
or mm), should be approximately
h i 0:5
2
d b 1:1 d d 2 ;
c p
where d c is the inside diameter of the casing at the top of the well (inches, or
mm) and d p is the outside diameter of the drill pipe at the top of the well (inches,
or mm).
The typical length of the blooey line for large drilling rigs is from 100 to
300 ft (30 to 90 m). This line is run from the annulus to a burn pit (see Figure 3-1).
The air or natural gas drilling fluid with the entrained rock cuttings flows
from the annulus down the blooey line and exits at the burn pit. The rock cut-
tings are dropped in the burn pit as the air flow with the natural gas exits the
blooey line.
In some operations the single blooey line is often replaced with two parallel
smaller diameter lines. In this situation the inside cross-sectional area of the
two lines should also be designed to be greater (by a factor of 1.1) than the
annulus cross-sectional area at the top of the well.
All blooey lines should be equipped with two high pressure gate valves. These
valves are located on the horizontal blooey line at its entrance (just downstream
from the tee turn where the return flow from the annulus turns to horizontal flow
in the blooey line). Figure 3-13 shows these two valves on the horizontal
flow line (blooey line) just below the rotating (control) head. During drill-
ing operations these valves are in the full open position to prevent erosion.
These valves are an added safety feature allowing the well to be closed when
the surface pressure in the well is low. However, the valves can also be used
to carry out some rudimentary well testing operations (e.g., static wellhead
pressure, wellhead flowing pressure, and volumetric flow rate).