New Exploration Techniques and Opportunities, Denver Basin

By

W. Richard Moore

Independent Geologist, Crawford, CO

The distribution of Cretaceous oil fields in the northern Denver Basin is explained, at least in part, by a combination of gravity, magnetic, and geothermal gradient maps. The area studied includes Banner, Kimball, and portions of surrounding counties in southwestern Nebraska.

A geothermal gradient map of the area was constructed using bottom hole temperatures recorded by wireline logs. Gravity and magnetic data were acquired from public sources. Comparison of the maps show that areas of high geothermal gradient coincide with areas of Bouguer gravity minimums, magnetic positives, and concentrations of oil fields. Few fields exist in areas of low gradient and gravity positives. It is believed that the areas of high geothermal gradient reflect areas of fractured basement rock that have conducted more heat into the sedimentary section. From modeling it can be shown that the fracture zones have reduced the density of the basement rocks, as well as localized the emplacement of granitic intrusions into the basement, which explains the Bouguer gravity and magnetic anomalies.

These fracture zones have localized D and J Sandstone oil fields by causing abrupt changes in the environment of deposition of the sandstones, thus forming stratigraphic traps. Adjacent areas of limited basement fractures have a paucity of traps and production. Not only can existing producing trends in the D and J Sandstones be explained, but other areas in the northern Denver Basin can be shown to have a high potential for production from the Cretaceous sandstones as well as deeper and shallower objectives.

AAPG Search and Discovery Article #90004©2002 AAPG Rocky Mountain Section, Laramie, Wyoming