--> --> Using pXRF to Identify Pay Zones in Hydrocarbon-Rich Shales: A Litho-Geochemical Analysis of the Eagle Ford Shale

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Using pXRF to Identify Pay Zones in Hydrocarbon-Rich Shales: A Litho-Geochemical Analysis of the Eagle Ford Shale

Abstract

Finding the pay zones of potential hydrocarbon-rich shales is vital to the success of the oil companies and investors. In this work, we identify key zones in the Eagle Ford shale (South Texas) by using geochemical data obtained with a pXRF (portable X-ray fluorescence) spectrometer.

Litho-geochemistry is important in interpreting where pay zones are because slight changes in lithology chemistry can indicate changes in hydrocarbon potential. Our goal in this research is to use a pXRF spectrometer to quantify certain elements in the shale samples that were provided by Pioneer Drilling. Shales trap hydrocarbons along with certain elements such as molybdenum, vanadium and chromium, allowing us to correlate the two.

We received three wells worth of powdered drill cuttings (approximately 3000 feet total) at increments of 5 to 15 feet through the Eagle Ford formation to scan with the pXRF and quantify the elemental data. Using this data we constructed a detailed log of each element of interest. We focused on some major elements (e.g., calcium and aluminum) to identify lithology and trace elements (e.g., molybdenum and chromium) to identify emplacement oxidation-reduction (paleoredox) facies and the proper lithology for hydrocarbon production. Our hypothesis is that key elements that correlate to hydrocarbon potential in the Eagle Ford may apply to finding pay zones in other shale plays. Unconventional wells and hydraulic fracturing are expensive, so why not pinpoint where you would like to produce from and reduce the cost of completing the well? With this research we show that there are several elements such as molybdenum and vanadium that have a high correlation with hydrocarbon potential. With rapid expansion in shale plays both here in Texas and around the globe, the implications for this technique are becoming more important, and a simple, reliable method to identify pay zones is needed.