Page 219 - Air and gas Drilling Field Guide 3rd Edition

210 CHAPTER 8 Air, Gas, and Unstable Foam Drilling

2
Pressure (N/cm abs)
0 500 1000 1500
12.00

11.50

11.00

% Oxygen 10.50
10.00

9.50

9.00

8.50

8.00
0 500 1000 1500 2000 2500 3000
Pressure (psia)

FIGURE 8-14. Content of oxygen to initiate deflagration or detonation [16].

whereas the mixture of oil and coal creates more of a downhole fire hazard. Fig-
ure 8-13 shows that the hazard of ignition increases with higher pressures
(the wider the region of ignition at the top of Figure 8-13). As the well is drilled
deeper, the bottom hole annulus pressure gets higher. This in turn increases the
ignition probability in the presence of hydrocarbons.
As discussed in Chapter 5, Section 5.8, membrane generated nitrogen technol-
ogy can be used to reduce the percentage of oxygen in the filter output stream to
approximately 5%. This oxygen deprived inert air will not support deflagration
or detonation. Figure 8-14 shows a plot of the approximate minimum percent
of oxygen in a mixture with hydrocarbon (methane) at which deflagration or
detonation will initiate [16]. Deflagration and detonation will not proceed
below these values. This is why membrane filter nitrogen generators are usually
calibrated to keep the percent of oxygen in the stream of filter atmospheric air
at approximately 5%.

8.5 PRIME MOVER FUEL CONSUMPTION
This section discussed the fuel consumption of the prime mover for the compres-
sor system. Illustrative examples of the fuel consumption were discussed in detail