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HELIUM EXPLORATION

Petro-Find Geochem Ltd provides geochemical soil gas surveys to reduce high risk in the exploration for helium reservoirs. In the past, most helium reservoirs have been found by accident in the drilling for petroleum. This technology was developed in the exploration for uranium over a six-year period. It was found that helium concentrations in soil gas can be related to underlying uranium deposits. In the the radioactive decay process uranium generates alpha particles which convert to helium with the pick up of two electrons. Hydrogen, produced by the radiolysis of water by radioactivity, is also a useful pathfinder. However, water must be in contact with uranium. Helium and hydrogen migrate by diffusion and mass flow vertically to the surface soils unless short-circuited by fractures/faults. See paper "Cost-Effective Helium/Hydrogen/Neon Soil Gas Surveys in Uranium Exploration" Link...  helium exploration principles

Helium in natural gas is the main source for helium supply worlwide, an important commodity for scientific purposes; it is too expensive to separate helium from ambient air because it contains only 5.4 ppm helium. Although the helium content of gas reservoirs far exceeds that for uranium deposits, salt and anhydrite formations can reduce the surface signal. Natural gas reservoirs that are produced for their helium contain normally 1- 2 % helium. CO2 and nitrogen reservoirs also contain helium but are usually less attractive economically because there is no co-product natural gas. The high price of helium, which is many times that of natural gas, relates to the expensive separation and purification processes required to achieve the desired high grades. The United States is the largest producer with the largest reserves but many of the reservoirs are rapidly depleting. Other countries with large reserves and production include Qatar, Algeria, Poland, Russia and China.

Helium surveys have been underused and even ignored in geochemistry notwithstanding their proven worth. Helium surveys are important principally for:(1) Uranium exploration using helium and hydrogen as pathfinders; (2) Exploration for petroleum associated with helium; (3) Exploration for helium in reservoirs associated with hydrocarbons, CO2 or nitrogen; and (4) Exploration for gold and base metals associated with uranium. Industry attempts to use helium as a pathfinder have been mostly unsuccessful because of poor sampling equipment and methods; too large a sample; inability to sample wet sediments; leakage problems with long-distance transport in containers or vials from field to laboratory; and inappropriate analyzers for helium. While the major difficulty in measuring helium in soils is its volatility, its inertness is a plus factor. Fast sampling methods and extraction of too large a sample can lead to the exhaustion of soil gas at the tip of the probe thus causing dilution of the sample with ambient air drawn down from around the annulus of the probe. Sampling depth must be at least three feet to avoid the pumping action of ambient air pressure. analysis by micro-gc for helium in field office

Helium exploration principles are outlined in the accompanying picture. For substantial helium gas to develop, three important geological events must be present: production of helium from the decay of uranium in crystalline basement rocks; adequate fractures and faults to allow helium to escape into the overlying Phanerozoic sedimentary rocks; and a caprock tight enough to hold any helium in commercial quantities. In Saskatchewn helium is usually found in formations close to bedrock where helium is generated. However, as helium migrates continuously upward it could be found in commercial quantities in formations in the upper Phanerozoic if a suitable trap is found.

Soil gas surveys can find natural gas reservoirs associated with helium using helium as a pathfinder. Helium produced by the decay of uranium migrates from the crystalline basement rocks to sedimentary strata where it is trapped by overlying shales and anhydrites. However, some of the helium escapes throught the cap rock and thence to the surface where it is trapped temporarily in the interstices of soils before it finally escapes to ambient air. Soil gas surveys using light hydrocarbons as pathfinders would be able to locate the associated gas reservoirs as well. It is well known that fractures/faults provide fast flow paths for helium and hydrogen to reach the surface (see accompanying picture of a hydrogen survey). Correlation of helium gas anomalies with structural traps found by seismic provides valid targets for exploration drilling. Helium gas anomalies without confirmation of seismic structural traps could indicate stratigraphic trapping.

 hydrogen contours showing structures

HYDROGEN AS A PATHFINDER

Hydrogen can also be a useful pathfinder in helium exploration. As noted above, hydrogen can only be produced (i.e. by radiolysis) if water is in direct contact with uranium. This limits its usefulness as a pathfinder for helium reservoirs that do not contain uranium but could be extremely useful in tracing the underlying source rocks containing both water and uranium (see accompanying picture).

METHODOLOGY

The same sampling methodolgy is used as in petroleum and uranium exploration. However, like in uranium exploration where both helium and hydrogen are used as pathfinders, analysis is conducted by a micro-gas chromatograph specially designed for this purpose. For methodology refer to the following Link... Also refer to a paper entitled "Cost-Effective Helium/Hydrogen/Neon Soil Gas Surveys in Uranium Exploration" Link.... In general, the basic approach to any exploration program is to use methods that provide the maximum information at the lowest cost possible. For large areas, reconnaissance surveys can be conducted first to establish anomalous trends. In follow-up, higher-density surveys are conducted to define the aerial extent and configuration of the anomalies. The latter survey is a target-generating mechanism.


PETRO-FIND GEOCHEM LTD

215 Mallin Crescent
Saskatoon, Saskatchewan, Canada S7K 7X3
Contact: Paul Lafleur, President
View Paul Lafleur's profile on LinkedIn
Phone: (306)931-3156 Fax: (306)931-9773
E-Mail: plafleur@sasktel.net