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Microseeps over Morrow Channels in Southeast Colorado

Seneshen, David M.1; Fontana, John V.1
1 Vista Geoscience, Golden, CO.

Productive, oil- and gas-charged, Pennsylvanian Morrow Sandstone channels are found throughout large areas of southeast Colorado. Production is generally from thin sandstones that are difficult, if not impossible, to see with conventional, compressional P-wave seismic techniques. Various surface geochemical methods were therefore tested to determine if hydrocarbon microseepage could provide an indication of productive channels.

Direct hydrocarbon-based orientation surveys were conducted over the Sorrento, Barrel Springs and Flank fields in Cheyenne, Prowers and Baca Counties respectively. The surveys involved the collection of closely spaced, 5 to 10-foot deep soil samples for headspace and acid-extractable C1-C6 alkanes and alkenes and mono- and poly-aromatic hydrocarbons (C6-C36) by Synchronous Scanned Fluorescence.

The results of the orientation surveys are very encouraging. Acid-extractable C3 to C5 alkanes are anomalous in several samples directly over the Sorrento Field. At the Barrel Springs and Flank fields, acid-extractable C1 through C6 alkanes and 3 to 5-rings aromatics form high contrast anomalies over the channel margins. Aromatic (3- to 5-ring) anomalies are also found directly over the Flank Field.

Hydrocarbon and helium concentrations in free gas from a pending survey over a recently discovered helium- and hydrocarbon-charged Morrow channel will also be presented.



AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009