Gas detectors (gas sniffers) are used only in air drilling operations directed at the recovery of oil and natural gas. Figure 2-14 shows the position of the gas detector on the blooey line. This detector can detect very small quantities of hydrocarbons that might enter the blooey line from the annulus. As the drill bit is advanced and hydrocarbon producing formations are drilled, the hydrocarbons are entrained in the return air flow to the surface with entrained rock cuttings. The detector alerts the drilling rig crew that hydrocarbons are in the annulus. This alert allows rig personnel to take safety precautions against subsurface and surface fires or explosions.
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