New Advances in Field Collection and Analyses of Low-Molecular-Weight Hydrocarbon Gas Samples

VERSECKES, MICHAEL S., Halliburton Geophysical Services, Inc., Dallas, TX

Low-molecular-weight hydrocarbon (LMWHC) gas exploration has been around for more than 50 yr. Recent improvements and advances in sample collection, analysis, and interpretation have enabled explorationists to use LMWHC in more applications than were previously possible. One such use is in the search for subtle stratigraphic traps like those found along the Texas Eastern shelf. Many new fields have been discovered there using LMWHC surveys. One of the most notable of these is the Lonesome Dove II field in Concho County, discovered by Marshall and Winston, Inc., using a Halliburton Geophysical Services, Inc. (HGS) interstitial soil gas survey as a lead tool.

HGS's LMWHC land exploration incorporates many innovations in soil gas collection and analysis. A unique sample design and a 10-ft depth capability provide a more sensitive and less noisy data set. On-site analysis with a field-adapted gas chromatograph with a flame ionization detector provides a sensitivity of approximately 30 parts per billion, which is several orders of magnitude better than many hot-wire detectors that have sensitivities of only several parts per thousand. A field computer also removes much of the operator variable because it operates the chromatograph and digitally transcribes the concentration data onto floppy diskettes.

This same field computer also improves the efficiency and quality of the surveys in other ways. The data quality can be checked on site, and collection or analysis problems can be discovered early and corrected. Computer plotting and graphing software is available to perform field interpretations, which can have an immediate impact on sampling design or drilling decisions.

All of these improvements in LMWHC collection and analysis mean that explorationists now have a new proven exploration tool to help find their increasingly elusive targets. Areas like Concho County with its Lonesome Dove II field have already shown the value of near-surface geochemical exploration.

AAPG Search and Discovery Article #91011©1991 AAPG Southwest Section Meeting, Abilene, Texas, February 9-12, 1991 (2009)