Radon-Thoron Isotope Ratios:
a new method of geochemical exploration for oil and gas

  • Reports listed in the annotated bibliography (below) describe the success of surface and airborne radiometric surveys in exploration for oil and gas. Most of these papers refer to gamma radiation, but some refer to radon. Radon geochemistry can be more sensitive than gamma, because it is based on alpha radiation which has a lower background count.
  • Our Lucas cells provide radon-thoron ratios, which are more sensitive still. These ratios have been successful in uranium exploration and should prove useful in oil and gas exploration as well. Link We have a formula to resolve radon from thoron giving on-the-spot results with our field instruments.
  • Like all exploration methods, radon and thoron geochemistry will benefit from a thorough understanding of the geological setting of the reservoir.
What causes these radon anomalies? Some possibilities:

Upward migrating non aqueous-phase formation fluids
  • Radon geochemistry in soil gas and groundwater has been widely used by environmental scientists in the search for hydrocarbon contamination (NAPL or non aqueous-phase liquids). Link Radon has an affinity for organic liquids, and in the presence of NAPL the radon concentration in groundwater or soil gas is reduced due to partitioning into the organic NAPL phase. This results in lower radon values over hydrocarbon contamination and we expect similar low values over natural hydrocarbon sources such as a reservoir or reservoir edge.
  • Matolin et al. (see annotated bibliography below) noted increased levels of radon and thoron over an oil productive zone, which they attribute to enhanced radon gas emanation from U- and Th-bearing minerals decomposed by hydrocarbon-generated groundwater acids ("enhanced emanation power").
Upward migrating aqueous-phase formation fluids (formation water)
  • Aqueous-phase formation fluids can carry upward dissolved members of the uranium decay series (radium etc.), which are leached out of formations with normal background levels. These elements are then deposited near surface.
  • Near surface enrichments of radium result in recognizable anomalies of radon and possibly gamma radiation. Our radon-thoron ratios allow us to correct for local variability in soil permeability and weather conditions.
  • The impermeable structure which traps the oil and gas into a commercial reservoir can deflect the upward migration path of these formation fluids, resulting in a recognizable pattern of radon and gamma radioactivity at surface. In this case we can expect a concentration above the field boundary, ideally in the form of a halo or part halo.
  • Another possible cause of radon anomalies over reservoir edges is the development of fractures due to differential compaction, resulting in increased permeability. This process, in the case of reef structures, is described by Sikka and Shives, 2002 (see annotated bibliography below).
Fractures and shale gas
  • Ghahremani (see below) hypothesized that shale gas yields will be optimized where natural fracturing of the shales is greatest, and that such fracturing will allow radon to migrate to surface causing radon anomalies in soil gas.
Click here for annotated bibliography
  • We measure: radon - radium - thoron - radon daughters - alpha radiation.
  • The Lucas cell is recognized as the most sensitive and reliable method for these elements.
  • Our instruments are used around the world in exploration for uranium, oil & gas, groundwater and hydrothermal, and in environmental protection, health physics, earthquake prediction, and evaluation of hydrocarbon and NAPL contamination.
  • In the radon business since 1968, our latest major instrument update was 2015.
  • Modern, low-power, field-rugged electronics. Some earlier versions still working after 35 years.
  • Continuous real-time monitoring and data recording.
  • Winter and summer, from the Sahara Desert to the Canadian Shield, our instruments have faced up to severe field conditions.
  • Intrinsically safe functions.
  • Sensitive to geochemical trace levels necessary for radon in lake water and for radon-thoron isotope ratios.
  • Can work in a tent without electricity or be carried from point to point in the field.
  • 50 readings per day. Results available immediately.
  • Rechargeable battery pack good for a long day in the field and recharges in a few hours.
  • Can be operated by junior personnel if carefully supervised.
  • Same instruments used for radon and radium in soil, sediment, plant parts, rocks, water, soil gas, air, and snow, and for radon daughters in air.
  • EPA compliant.
  • Click here for more details of instruments.
  • Click here for or other instruments, components and accessories we provide
  • Technical specification sheets and pictures of our instruments provided on request.
  • Multilingual consulting and training (if required).
For instruments contact
R.H. Morse & Associates Ltd.
skype: robert.morse.toronto

Robert H. Morse, Ph.D., P.Eng.
April 15, 2011
Click here for studies of radon in uranium exploration

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