Approximately 1,400 feet of continuous core was taken .between
800-2,214 feet in depth from USBM/AEC Colorado core hole No. 2. The
drill, site is located in the Piceance Creek basin, Rio Blanco County,
Colorado. From ground surface the drill hole penetrated 1,120 feet
of the Evacuation Creek Member and 1,094 feet of oil shale in the
Parachute Creek Member of the Green River Formation. Oil shale
yielding more than 20 gallons per ton occurs between 1,260-2,214 feet
in depth. A gas explosion near the bottom of the hole resulted in
abandonment of the exploratory hole which was still in oil shale.
The top of the nahcolite zone is at 1,693 feet. Below this depth
the core contains common to abundant amounts of sodium bicarbonate
salt intermixed with oil shale. The core is divided into seven
structural zones that reflect changes in joint intensity, core loss
and broken core due to natural causes. The zone of poor core
recovery is in the Interval between 1,300-1,450 feet.
Results of preliminary geophysical log analyses indicate that
oil yields determined by Fischer assay compare favorably with yields
determined by geophysical log analyses. There is strong evidence
that analyses of complete core data from Colorado core holes No. 1
and No. 2 reveal a reliable relationship between geophysical log
response and oil yield.
The quality of the logs is poor in the rich shale section and
the possibility of repeating the logging program should be considered.
Observations during drilling, coring, and hydrologic testing
of USBM/AEC Colorado core hole No. 2 reveal that the Parachute Creek
Member of the Green River Formation is the principal aquifer water in the Parachute Creek Member is under artesian pressure.
The upper part of the aquifer has a higher hydrostatic head than,
and is hydrologically separated from the lower part of the aquifer.
The transmissibility of the aquifer is about 3500 gpd per foot. The
maximum water yield of the core hole during testing was about 500 gpm.
Chemical analyses of water samples indicate that the content of
dissolved solids is low, the principal ions being sodium and bicarbonate. Although the hole was originally cored, to a depth of
2,214 feet, ,the present depth is about 2,100 feet.
This report presents a preliminary evaluation of core examination,
geophysical log interpretation and hydrological tests from the
USBM/AEC Colorado core hole No. 2. The cooperation of the U.S. Bureau
of Mines is gratefully acknowledged. The reader is referred to
Carroll and others (1967) for comparison of USBM/AEC Col0rado core hole
No. 1 with USBM/AEC Colorado core hole No. 2.
Additional publication details
USGS Numbered Series
Preliminary report on the geology, geophysics and hydrology of USBM/AEC Colorado core hole No. 2, Piceance Creek Basin, Rio Blanco County, Colorado