U.S. Geological Survey Open-File Report 02-417
2002

Characterization of core extracted from the Olmos Formation (Cretaceous), Southwest Texas
Alex W. Karlsen, Peter D. Warwick, Robert W. Hook*, John R. SanFilipo , Charles E. Barker, Jennifer M. Klein*
U.S. Geological Survey, Reston, VA
U.S. Geological Survey, Denver, CO
*Contractor to the U.S. Geological Survey

This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards and stratigraphic
nomenclature. Any use of trade names is for descriptive purposes only, and does not imply endorsement by the U.S. Government.

INTRODUCTION
This preliminary report presents data from ongoing activities of the U.S. Geological Survey (USGS),
Energy Resources Program, Gulf Coast Framework Studies Project (GCFSP). The purpose of the GCFSP is
to conduct geologic framework studies that will aid in the evaluation of all fossil fuel energy
commodities (coal, gas, and oil) in the Gulf Coast Region. The project will: (1) define the petroleum
systems of the region; (2) conduct specific geologic framework studies and petroleum system analyses
on selected priority intervals; (3) study the coal-bearing intervals to evaluate coal distribution and
quality, and coal-bed methane, and source rock potential; (4) work in cooperation with the National Oil
and Gas Assessment (NOGA) Project to conduct a focused assessment of the Gulf Region; and (5)
contribute to the next phase of the National Coal Resource Assessment.
The USGS, through a Cooperative Research and Development Agreement (CRADA) with The
Exploration Company (TXCO) of San Antonio, has drilled a series of wells to assess the coalbed methane
potential in the South Texas portion of the Gulf Coast Region. This report presents lithologic
descriptions, photographs, and x-ray prints of cored intervals from the Olmos Formation (Cretaceous)
from two wells, 1-117CR and 1-613CR, located in Maverick County (Figure 1) . The cored interval for 1-
117CR (from 1090.0 feet to 1212.5 feet below the surface) is 122.5 feet in length. For the 1-613CR well,
the cored interval (from 1390.0 feet to 1525.7 feet below the surface) is 135.7 feet in length. The depths
and lithology thicknesses for 1-117CR and 1-613CR were corrected based on comparison with borehole
e-logs from the well locations. Due to depth correction of intervals for 1-613CR, information on cardboard
or wood block labeled markers used in the core photographs to denote portions of the cores that were
removed or missing, at the time of photography, do not reflect the corrected depth intervals.
X-ray radiographs were taken of the coal and carbonaceous shale portions of the cores to determine
internal structural properties such as, partings, cleats, and burrows. For conversion to digital format
the x-ray prints were scanned and, as a result, they appear as reversed images in this report.
Additionally, in the scanned x-ray prints, carbonaceous shales or clays appear white and coals are black.
Initial analyses of sample data from cores 1-117CR and 1-613CR show average as-received ash yield
values of 61.09 percent and 58.94 percent, respectively. Less than 50 percent ash yield occurs for five of
the samples from 1-117CR and four of the samples from 1-613CR. Based on these initial results,
intervals described as coal in 1-117CR and 1-613CR, in some cases, would be classified as carbonaceous
shales and not coal (Wood and others, 1981).
REFERENCES
Wood, G.H. and others. 1983, Coal resource classification system of the U.S. Geological Survey: U.S.
Geological Survey Circular 891, 65 p.
ACKNOWLEDGEMENTS
We wish to acknowledge The Exploration Company for their continuing assistance and collaboration.
The radiographs were performed with the assistance of Jeff Halka and William Panageotou of the
Maryland Geological Survey and we would like to thank them for their cooperation in this study. In
addition, we wish to acknowledge Bryan Williams of Stata Log for his assistance in the field.

This report is visual in nature. It consists of a location map, two stratigraphic logs, 25 photographs of cores, and 36 X-ray radiographs of the cores. For more-detailed information, contact Alex Karlsen at the email address akarlsen@usgs.gov.

Stratigraphic Logs:

1-117CR
28°35.714 N
100°17.622 W

Borehole: TXCO/USGS 1-117CR Comanche Ranch
Company or Agency: TXCO The Exploration Company/U.S. Geological Survey
Location: Comanche Ranch, Maverick County, TX
Coordinates: 28°35.714 N, 100°17.622 W (GPS)
Ground Elevation: 766 ± 25 ft. (GPS)
Coring Depth: 1090.0-1212.5' (122.5')
Total Borehole Depth: 1214.0'
Driller: A. Clark, U.S. Geological Survey
Drill Rig: Truck-mounted mobile drill rig
Drilling Method: Continuous wireline coring, 10 ft spring loaded push tube with shoe
Bit type: Tungsten-carbide/diamond HC 4.75" OD, 3" ID core
Drilling Medium: Bentonite mud
Casing: None (PVC to 6ft)
Geophysical Logs: Natural gamma, caliper, gamma-gamma density, conductivity, resistivity
Dates Drilled: 6/2/01-6/10/01
Rock Descriptions by: P. Warwick, A. Karlsen
Stratigraphic Log Scale: 1 inch = 2.50 feet

1-613CR
28°36.294 N
100°09.927 W

Borehole: TXCO/USGS 1-613CR Comanche Ranch
Company or Agency: TXCO The Exploration Company/U.S. Geological Survey
Location: Comanche Ranch, Maverick County, TX
Coordinates: 28°36.294 N, 100°09.927 W (GPS)
Ground Elevation: 721 ± 25 ft. (GPS)
Coring Depth: 1390-1525.7' (135.7')
Total Borehole Depth: 1649.6'
Driller: A. Clark, U.S. Geological Survey
Drill Rig: Truck-mounted mobile drill rig
Drilling Method: Continuous wireline coring, 10 ft spring loaded push tube with shoe
Bit type: Tungsten-carbide/diamond HC 4.75" OD, 3" ID core
Drilling Medium: Bentonite mud
Casing: None (PVC to 6ft)
Geophysical Logs: Natural gamma, caliper, gamma-gamma density, conductivity, resistivity
Dates Drilled: 4/28/01-5/6/01
Rock Descriptions by: J.SanFilipo, R. Hook, P. Warwick
Stratigraphic Log Scale: 1 inch = 2.50 feet