Deposited during the late Cretaceous, the Eagle Ford formation found in the Maverick basin from Dimmit, Webb, and Maverick counties is a fine grained rock with variable lithological and organic content. Characterizing and predicting this variability is an important factor in being able to commercially develop this unconventional resource. Information about the elemental make up of rock, which can be obtained by using wavelength dispersive X-ray fluorescence (WDX-XRF), was used to characterize the vertical variability of the Eagle Ford formation in this area based on trace metals such as Mo, Ni, V, U, Th, and Rb which are impacted by oxygen level, organic productivity, and clay content. Samples were collected and measured every 4ft along the length of a ∼300ft core. These data allowed for the creation of a frame work to better understand the geologic processes which gave rise to variability in total organic carbon (TOC) and lithology. Energy dispersive X-ray fluoresces (EDX-XRF) was then performed using a hand held XRF device making a measurement on five cores across the basin at 2 ft. intervals including the core characterized with a laboratory based WDX-XRF which helped to quality control the data collected by the hand held device. The XRF results from these five cores were correlated and compared which allowed for better characterization of the variation in the Eagle Ford within this basin and provided some insight into how these elements predict the geologic processes which help to give rise to this variability. However, the elemental data alone were challenged in predicting well performance. This is because the elemental data are not materially impacted by the maturity or pressure of a formation. As a result, it is clear that these data represent just one component of formation evaluation and can be useful for improving the geologic understanding of an area only when integrated with other reservoir parameters such as fluid viscosity and phase.

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