stokes: the boys are back , page-10

When monitoring ditch gas a Gas Unit refers to 200pm of total gas (methane equivalent in air).

Its used mainly because it means when gas reading sget high youre dealing with smaller numbers. The other commonly used unit is %.....1% = 10,000ppm.

Mudlogging Companies usually operate a gas monitoring system consisting of a degasser which sits at the shale shakers and stirs up the mud returning out of the hole. The gas liberated from the mud is sucked down a gas line to the mudlogging unit and is run through a Total Gas Detector to measure Total Gas and also through a gas chromatograph which gives measurements of the component alkane gases methane through to pentane. Most companies operate total gas detectors and chromatographs which use Flame Ionisation Detectors (FID). Theyre fairly accurate down to about 10ppm or in some cases less.

The ratios of the different alkanes measured by the chromatograph can usually give an indication of type of hydrocarbons being intersected by the well. Eg high proportion of ligther alkanes like methane would indicate dry gas (or coal) and a high proportion of the heavier alkanes would indicate oil.