Upper Jurassic Reef Play, East Texas Basin: An Updated Overview Part 2--Inboard Trend

Abstract

This paper is the second part of a two-part paper summarizing new data on the Upper Jurassic play in the East Texas basin. Information presented in this paper focuses on carbonate buildups of the inboard trend. Inboard buildups represent significant backstepping of reefal facies from the ramp margin-outboard trend to more updip sites along a developing shelf margin. Inboard features resemble pinnacles that can be identified with two-dimensional seismic data, but that require three-dimensional data to properly image. Such pinnacles represent stacked features that resulted from three to five cycles of reef growth. The general upward progression of facies within each cycle exhibits a shallowing trend, with the overall proportion of shallow-water facies also increasing upward among these cycles. Most inboard buildups possess a low-porosity micritic cap immediately overlying vuggy, coral-bearing facies with good-to-excellent porosity. Evidence of both primary and secondary porosity exists, with some correlation between porosity and permeability development. Log and rock sample data from the Frost buildup (Freestone County) confirm the existence of diverse microfacies in these buildups, with complex lateral variation in porosity/permeability distribution. Two models of buildup occurrence in the basin are presented.