Abstract: Pollen Field, Colorado: Evidence for Vertical Hydrocarbon Migration and Geochemistry Economic Utility

Peter K. H. Groth

Pollen field is thirty five miles east of Denver in the Denver-Julesburg basin. It was the second largest Colorado oil field discovery in 1980. The reservoir existence and exact oil production limit were mapped prior to drilling the initial well which was the greatest oil producer. Confidence to make the bold predictions was based on observing field extension developments after a series of near-surface prospecting methods tests. The effective mapping method was based on dark fossil pollen grains recovered from shallow bore holes. The preservation of pollen color is probably ultimately related to oxidation-reduction conditions. Hydrocarbon microseepage retards or prevents deep oxidative weathering over the oil reservoir. Induced polarization, thermal gradient and elemental soil analysi were also used. The geochemical significance of the Pollen Field discovery is that hydrocarbons migrated vertically for 7,200 feet without deviation to near the surface, where they produced a distinct signature. The migration was so localized that the initial relative production rate of each development well could be predicted. The exploration importance is that hydrocarbon vertical microseepage can affect recognizable changes in the near-surface environment.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994