Online Gas Analysis

Continuous mud gas loggings during drilling as well as offline mud gas sampling are standard techniques in oil and gas exploration, where they are used to test reservoir rocks for hydrocarbons while drilling.

Online Gas Monitoring at SAFOD


ICDP’s Online Gasmonitoring OLGA extends this technique for scientific drilling in hydrocarbon and non-hydrocarbon formations to sample and study the composition of crustal gases [1]. Online-Gasmonitoring of drilling mud is a three-step process, comprising:


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Gas analysis

N2, O2, Ar, CO2, CH4, He, and H2 are determined by a quadrupole mass spectrometer (QMS). A complete QMS analysis with detection limits between 1 and 20 ppmv (parts per million by volume) is achieved with this setup after an integration time of less than 30 s. However, a sampling interval of one minute is mostly chosen to reduce the amount of data produced. Hydrocarbons (CH4, C2H6, C3H8, i-C4H10, and n-C4H10) are analyzed at 10 min intervals with an automated standard field GC, which is equipped with a flame ionization detector. Detection limits for the hydrocarbons are at about 1 ppmv. Gas samples for further studies e.g. of isotopes are taken automatically when a given threshold level at the QMS is exceeded.