ABSTRACT: Surface Geochemical Prospecting and Hydrogeology

JONES, VICTOR T., Exploration Technologies, Inc., Houston, TX

It is well established that regional basinal flow patterns and formation water geochemistry are major factors in the establishment of subsurface petroleum accumulations. As basins dewater and compact, vast amounts of water and formation fluids are expulsed. This process not only forms the hydrocarbon reservoirs, it also destroys them, providing the basis for surface geochemical seepage to occur along major fairways, assisted by faults, fracture systems, and other permeable pathways.

Surface geochemical survey techniques merely measure these macro and micro seepages associated with this hydrogeological process, and as such should be thought of as a source rock tool applied at the surface, not as a panacea, or "drill here" tool. Geochemical prospecting can only verify the existence of petroleum hydrocarbons and perhaps identify the potential for oil versus gas. No geochemical method can predict whether an oil or gas deposit will be of economic proportions.

Both exploration and environmental examples will be used to illustrate the influence of hydrological factors on the surface geochemical signal. The importance of migration rates of hydrocarbon gases versus water will be addressed. Global heat flow and geothermal gradients are important factors that allow some measure of this interaction. Shallow heat flow measurements offer a possibility for relating surface seepage to hydrological factors. Examples will show how these concepts may be used in conjunction to study vertical migration and evaluate basins for their elusive hydrocarbons.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)