Robert S. Tye, 1991. "Fluvial-Sandstone Reservoirs of The Travis Peak Formation, East Texas Basin", The Three-Dimensional Facies Architecture of Terrigenous Clastic Sediments and its Implications for Hydrocarbon Discovery and Recovery, Andrew D. Miall, Noel Tyler
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Gas production (7.2 Bcf) from low-permeability sandstones in the Early Cretaceous Travis Peak Formation, North Appleby field, Nacogdoches County, Texas, is enhanced through hydraulic fracturing of stacked, blocky to upward-fining sandstones encased in impermeable mudstone interbeds. Pervasive quartz cement in the sandstones decreases porosity and permeability and contributes to formation of the reservoir seal.
Subsurface data indicate that much of this 615-m-thick section represents aggradation of alluvial-valley deposits. Multiple channel belts form a network of overlapping, broad, tabular sandstones having thickness-to-width ratios of 1:850 (2.4 to 13.2 m thick; widths exceed 6.4 to 8 km). Six to eight channel belts, each containing 80 to 90% medium- to fine-grained sandstone, locally occupy a 61 -m-thick interval. In a vertical sequence through one channelbelt sandstone, basal planar cross-bedding grades upward into thinly interbedded sets of planar cross-beds and ripple cross-lamination. Clay-clast conglomerates line scoured channel bases. Adjacent to the channels, fine-grained sediments accumulated in well-drained swamps and lakes. Poorly sorted sandstones represent overbank deposition. During Travis Peak deposition, alluvial styles evolved from dominantly bed-load deposition near the base of the formation to more mud-rich, mixed-load systems at the top.
Sandstone geometry, continuity, and internal heterogeneity influence reservoir performance and well-to-well communication. Small-scale bedforms, biogenic structures, and scour surfaces create fluid-flow barriers and segment reservoirs. Within the channel belts, best-quality reservoir sandstone (high porosity and low-water saturation) exists in narrow bands that are oriented subparallel to depositional dip. Reservoir quality decreases at channelbelt margins (levees) and tops (abandoned channel) and in fine-grained interchannel areas (shadow zones behind longitudinal bars).