--> Quantitative Facies Analysis: A Tool Kit in the Characterization of Eagle Ford Sequence Stratigraphy and Facies Heterogeneity

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Quantitative Facies Analysis: A Tool Kit in the Characterization of Eagle Ford Sequence Stratigraphy and Facies Heterogeneity

Abstract

A methodology of Quantitative Facies Analysis (QFA) was developed and conducted in several cores of the Eagle Ford in South Texas to: 1) determine vertical and regional facies heterogeneity, 2) determine the cumulative thickness of sedimentary facies, and 3) map sequence stratigraphic units regionally. A total of nine Eagle Ford facies were identified on the basis of sedimentary structures, degree of bioturbation, organic content, and textures. By measuring the cumulative thickness of the nine key facies, QFA revealed distinct mappable transgressive and regressive units representing fluctuation in sea level. The base to top sequences in the Eagle Ford are subdivided into: First Transgressive Sequence (TST1), First High Stand Sequence (HST1), Second Transgressive Sequence (TST2), and Second High Stand Sequence (HST2). The stratigraphic distribution of these facies types suggest that the lower Eagle Ford is comprised of the TST1, HST1, and TST2 sequences; whereas, the Upper Eagle Ford is comprised only of the HST2 sequence. Generally, the sequence from TST1 to HST1 is marked by an upward decrease in the organic-rich facies, which then gradually increase from HST1 to TST2. Mapping the spatial distribution of these transgressive and high stand sequences, the Eagle Ford strata can be parsed into proximal, medial, and distal regions based on the relative fluctuation between organic-rich and organic-poor sequences. The proximal region is characterized by relatively large changes between organic-rich and organic-poor facies with thick and frequent intervals of organic poor facies 3 and the lowest cumulative thickness of organic-rich facies at 35-50% of the total Eagle Ford. The medial region is characterized by both equal distribution of the organic-rich and organic-poor facies types with organic-rich facies comprising between 50-65% of the Eagle Ford. Lastly, the distal region is characterized by the largest organic matter comprising 75-95% of the Eagle Ford with organic-poor intervals occurring rarely in thin layers.