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From Bureau of Economic Geology, The
University of Texas at Austin (www.beg.utexas.edu).
Bureau Seminar, November 30, 2007 New Interpretations of Reservoir Architecture in East Texas Field: Sequence Stratigraphic and Depositional Perspectives andBureau of Economic Geology, Jackson School of Geosciences Abstract: The East Texas Field, located on the west margin of the Sabine Uplift, is the largest oil field in the lower 48 states and produces from a classic stratigraphic trap of Woodbine Group sandstones. Productive units occur within the lower Woodbine, the primary coarse-siliciclastic interval of the Upper Cretaceous in the East Texas Basin. Correlation of fourth-order sequences from the thickest Woodbine in the basin center to the uplift indicates that reservoirs compose the basal three fourth-order sequences of a succession that contains a maximum of 14 such sequences in the basin axis. Analysis of >1,500 ft of 30 whole cores and wireline logs from approximately 500 wells indicates that the sandstone-body architecture is more complex than inferred from previous studies. Moreover, these data, in concert with sequence-stratigraphic analysis, show that the depositional settings of reservoir facies vary considerably from those of earlier investigations. Extreme sandbody heterogeneity is controlled by the fluvial-dominated deltaic depositional architecture. This highstand section is truncated in the northern and western part of the field by a thick (100 to 150 ft), conglomeratic lowstand incised-valley-fill succession, which records as much as 150 to 200 ft of drop in relative sea level. Previous studies of the Woodbine inferred well-connected, laterally continuous sheet sandstones in a wave-dominated deltaic and barrier-strandplain setting. This wave-dominated deltaic model is inappropriate, and a full understanding of reservoir compartmentalization, fluid flow, and unswept mobile oil in East Texas field should consider the fluvial-dominated deltaic and lowstand valley-fill sandbody architecture.
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