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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OLGA has been proven to be a reliable and inexpensive source of information on the composition and spatial distribution of gases at depth - in real time. It is suitable to detect fluid-bearing horizons, shear zones, open fractures, sections of enhanced permeability and methane hydrate occurrences in the subsurface of fault zones [3, 4, 6, 7], volcanoes and geothermal areas [5], permafrost regions [2], and others. Off-site isotope studies on mud gas samples help reveal the origin, evolution, and migration mechanisms of deep-seated fluids [4]. It also has important application to aiding decisions if and at what depth rock or fluid samples should be taken or formation testing should be performed.


  1. Erzinger, J., Wiersberg, T. and Zimmer M. (2006) Real-time mud gas logging and sampling during drilling, Geofluids 6, 225-233
  2. Wiersberg, T., Erzinger, J., Zimmer, M., Schicks, J., and Dahms, E. (2004) Real-time gas analysis at the Mallik 2002 Gas Hydrate Production Research Well; in Scientific Results from Mallik 2002 Gas Hydrate Production Research Well Program, Mackenzie Delta, Northwest Territories, Canada, (ed.) S.R. Dallimore and T.S. Collett; Geological Survey of Canada, Bulletin 585 pp. 15
  3. Erzinger J., Wiersberg T. and Dahms E. (2004) Real-time mud gas logging during drilling of the SAFOD Pilot Hole in Parkfield, CA, Geophys. Res. Lett. 31, L15S18, doi:10.1029/2003GL019395
  4. Wiersberg T. and Erzinger J. (2007) A helium isotope cross-section study through the San Andreas Fault at seismogenic depths, G-cubed 8, No. 1, doi: 10.1029/2006GC001388
  5. Tretner, A., Zimmer, M., Erzinger, J., Nakada, S., Saito, M. (2008) Real-time drill mud gas logging at the USDP-4 drilling, Unzen volcano, Japan. Journal of Volcanology and Geothermal Research, 175(1-2):28-34
  6. Wiersberg T. and Erzinger J. (2008) On the origin and spatial distribution of gas at seismogenic depths of the San Andreas Fault from drill-mud gas analysis, Applied Geochemistry 23, 1675-1690, doi:10.1016/j.apgeochem.2008.01.012
  7. Wiersberg, T. and Erzinger, J. (2011) Chemical and isotope compositions of drilling mud gas from the San Andreas Fault Observatory at Depth (SAFOD) borehole: Implications on gas migration and the permeability structure of the San Anreas Fault,. Chemical Geology, 284, 1-2, 148-159, doi: 10.1016/j.chemgeo.2011.02.016