Page 67 - Air and Gas Drilling Manual

is released to the atmosphere as the fluid exits the flow line. Foam drilling return
flow lines are large diameter pipelines and are unique in that they must be equipped
with valves to allow the choking of the return flows.
2.4.1 Blooey Line Chapter 2: Surface Equipment 2-17
Figure 2-1 shows the blooey line exiting from the drilling rig annulus for direct
circulation 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 2-1). 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 a 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 the 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),
should be approximately
d ( [ 2 p)] 05 .
2
.
d b ≥ 11 c − d (2-1)
where d c is the inside diameter of the casing at the top of the well (inches) and d p is
the outside diameter of the drill pipe at the top of the well (inches).
The typical length of the blooey line for large drilling rigs is from 100 ft to 300
ft. This line is run from the annulus to a burn pit (see Figure 2-1). 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 cuttings are dropped in the
burn pit and any natural gas is ignited by the pilot flame at the blooey line exit.
In some operations the single blooey line is replaced by 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 2-13 shows these two valves on the horizontal flow line
(blooey line) just below the rotating (control) head. During drilling 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. But 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, etc.).