Liquid Hydrocarbon Fluorescence Applications in Geochemical Exploration.
Gary K. Rice
GeoFrontiers Corporation, Rowlett, TX
Fluorescence measures emissions caused by ultraviolet light in solvent extracts of soil or sediment. Fluorescence can be measured at selected wavelengths or using single-scan, synchronous scan, or total (multiple) scan techniques. Previous presentations emphasized the composition discriminating capabilities of fluorescence data. Fluorescence spectra of shallow soil samples can be similar to fluorescence spectra of the reservoir oil. A 3-ring/2-ring fluorescence intensity ratio reduces a fluorescence spectrum to a single number and offers a simple way to differentiate oil reservoirs from surface signatures. Since the 3-ring/2-ring ratio tends to reflect amounts of “heavier” versus “lighter” hydrocarbons, fluorescent ratios are proportional to reservoir API gravity. This presentation explores structural information obtained from fluorescence data. Fluorescent hydrocarbon concentrations were highest over faults and fractures in Navigator and Iron Bridge fields Dickens County, Texas, which was important information during development of these fields. Dare I (Hope) field, Concho County, Texas, also exhibit patterns of high fluorescence concentration, but not along verifiable fault traces. Nevertheless, it was determined Dare I (Hope) fluorescence was indicating migration up fractures, possibly caused by differential compaction near sandstone reservoir edges. Fluorescence information also was very important during development of Dare I (Hope). Land sample collection requires only a shovel and plastic bag. Easy to collect samples, low-cost analysis, structural information, and the ability to identify and differentiate oil reservoirs are compelling reasons for using geochemical exploration fluorescence data.
AAPG Search and Discovery Article #90152©2012 AAPG Southwest Section Meeting, Fort Worth, Texas, 19-22 May 2012