Comparison and Evaluation of Surface Geochemical Methods with Respect to Several Actual Case Histories
Steven A. Tedesco
There are a variety of surface geochemical methods available to the explorationist The literature for many of these methods is lacking in a sufficient number of examples or detailed case histories to allow evaluations under which specific conditions any one particular method is useful. The author evaluated several methods; soil gas, iodine, enzyme leach, magnetic susceptibility, Eh, pH and conductivity over several project areas and under a variety of soil conditions. These project areas comprised surveys of samples over existing fields and in areas prior to drilling of exploration or development wells. Results will be presented from Grant Canyon and Currant Fields, Nevada; Eland Field, North Dakota; Seventy-Six Field, Kentucky; and Cavalier Field, Colorado. The conclusion of the stud was that five of the methods were very dependant upon soil chemistry and stratigraphy in order to be useful. One method was transitory in nature, but when the soils were accurately mapped, was reasonably effective in all survey areas. Only one method was found to function with a significant degree of success in all of the study areas. None of the methods could predict with accuracy, as can seismic, the exact target depth or drillsite location. Nor could they predict quality of production or depth of the reservoir. It was also found that the reliance on statistics, alone, to evaluate a data set could possibly result in the wrong conclusion. Comparison of data sets to well-defined models were more effective than statistics. The presence of subtle anomalies were found to be common rather t an unusual phenomena. It was clear from the study that large data sets were necessary in order to actually determine the presence or absence of an anomaly.
AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California