--> Abstract: Exploration Applications of Hydrogeology in the Great Basin, Nevada, by B. C. Reinsborough; #91012 (1992).

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ABSTRACT: Exploration Applications of Hydrogeology in the Great Basin, Nevada

REINSBOROUGH, BRIAN C., Mobil Oil Corp., Denver, Denver, CO

The Great Basin exhibits a highly dynamic gravity-driven flow system. The present-day hydrogeologic regime within the half-grabens of east-central Nevada were established in Miocene time, during Basin and Range development. Hydrocarbon generation within the valleys is suggested to be late Tertiary to present in age, which is concurrent with and influenced by the present-day hydrogeologic systems. The localized Tertiary basin-fill sections are underlain by a thick Paleozoic carbonate platform aquifer that facilitates the regional transport of groundwater and possibly long distance migration of hydrocarbons.

Two-dimensional numerical modeling within the Pine Valley area indicates that groundwater flow velocities are in the range of 5-20 cm/yr. The presence of only fresh meteoric waters (<2000 NaCl equil.) within marine sediments suggests a dynamic system. Surficial evidence such as the presence of hot springs, oil seeps, artesian wells, playa lakes, and salt marshes in discharge areas also indicates the dynamics of the system.

Hydrogeologic modeling indicates that two flow cells have evolved during Tertiary time: a lower Paleozoic carbonate system and an upper Tertiary valley-fill system. The thrusted allochthonous Ordovician shale unit acts as an insulating aquitard for direct fluid migration and heat transfer between the two cells. More direct communication is established via extensional faulting creating vertical conduits through the thick shale unit.

A conceptual model is developed to explain the current surficial and subsurface physical phenomena seen within a productive valley. Hydrogeologic conditions are seen to greatly affect the positioning, thermal character, and physical signature of oils within the Railroad Valley system.

 

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