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Using Soil Gas Composition to Distinguish Previous HitHydrocarbonNext Hit Type in Areas of Multiple Petroleum Producing Horizons 

RICE, GARY K., JOHN Q. BELT, JR.,  HARVEY H. HOWELL and LANCE HARWERTH, and CHAD A. BOWERMAN

Soil gas data is frequently used to detect near-surface Previous HithydrocarbonNext Hit seepage. It can also be used to calculate measures of soil gas composition. Composition Previous HitindicatorsNext Hit include Ethane/Propane ratios (EPR) and a new Ethane Composition Index (ECI). ECI is one of several related composition measurements derived from "common mode" reduction of Previous HithydrocarbonNext Hit data.

Previous HitHydrocarbonNext Hit composition data exhibits unique properties: 1. Composition is independent of concentration. 2. Composition data is normally distributed. The first property attenuates large spatial variations in Previous HithydrocarbonNext Hit concentrations caused by vertical migration pathways. Therefore, composition data is more evenly distributed over a reservoir. The second property allows Previous HitdirectNext Hit application of statistical data analysis. Histograms, duster analysis, and discriminate analysis detect and separate multiple compositions into distinct groups.

This project tested EPR, ECI, and other composition measures in a Study Area at the southern end of the Eastern Shelf of the Midland Basin. The Study Area included southern Concho, northern Menard and eastern McCulloch Counties and is a complex multiple petroleum horizon area. Composition data spanning 12 years were evaluated for effectiveness in discriminating among known Previous HithydrocarbonTop reservoirs to target specific petroleum reservoirs with commercial viability. Resulting composition information proved successful in refining geologic models that yielded several new field discoveries.

AAPG Search and Discovery Article #91021©1997 AAPG Annual Convention, Dallas, Texas.