Exploration in the Eagle Ford Formation relies on systematic analysis of the elemental, mineralogical, petrological, and organic content of the rock to characterize petrofacies and select horizons at which to effectively land horizontal wells. Previous work on road-cut outcrops located along US Highway 90 (Val Verde and Terrell Counties, Texas) of the Eagle Ford Formation shows that vertical trends exist but have not been quantified. Understanding these variations is crucial when selecting a horizon for horizontal well landing. Our study investigates lateral and vertical trends in ∼100-m-long outcrop of the transgressive systems tract of the Eagle Ford Formation, which is the principal productive interval. The results of this study yield an integrated reservoir analysis through the combination of (1) lithologic outcrop analysis, (2) thin-section petrography, (3) Rock-Eval pyrolysis, (4) x-ray diffraction, (5) x-ray fluorescence, and (6) porosity and permeability measurement. Our results show that significant vertical and lateral variations of the reservoir facies exist on a small scale (50 m), which would not be detectable at the well scale. Therefore, a better understanding of these petrofacies variations and, most importantly, their range and variance must be taken into consideration to enhance well completion. The best approach for quantifying and predicting the range and variance of physical and chemical properties of the transgressive systems tract of the Eagle Ford Formation may be to rely upon geostatistical analysis of nearby well or outcrop data combined with a robust sedimentary model for such unconventional mudrock reservoirs.

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