Dimensions and quality of reservoirs originating in low and high sinuosity channel systems, Lower Cretaceous Travis Peak Formation, East Texas, USA

Abstract

Abstract Quantification of the dimensions and quality of fluvial reservoirs requires knowledge of channel style, depositional environment and diagenesis. Two styles of fluvial channel co-existed during the rapid aggradation of >600 m of Lower Cretaceous, Travis Peak sediments in East Texas: (1) high sinuosity (meandering) channels, and (2) low sinuosity (straight) channels. Each was restricted to a specific geographic area, the result of long-term, geomorphic stability. In both channel systems, reservoir sandstones originated principally in channel and crevasse splay environments. Reservoir models developed through sedimentological analysis are similar to those developed independently through reservoir simulation studies. Reservoir sandstones originating as point bars in high sinuosity channel systems are relatively small (1.2 km 2 or less), thin (3.6 m), heterogeneous, and isolated within non-pay mudrocks. Reservoir sandstones originating as medial and transverse/oblique bars in the low sinuosity system are areally extensive (>20 km 2 ) thick (3.6 to 13.7 m), homogeneous, and display complex pressure relationships due to avulsion of long stream segments, and the lateral and vertical stacking of successive channels in well-defined channel belts. The greatest volume of channel sandstone occurs in the low sinuosity channel system. The high sinuosity system is dominated by overbank deposits. Travis Peak sandstones have been extensively modified by compaction and cementation. Despite extensive diagenesis, permeability values reflect original depositonal environment and bedding style, even in rocks which have lost more than 80% of their original, depositional porosity. Channel sandstones have higher permeability than associated splay sandstones. Within a channel sandstone, the highest values of permeability occur in destratified, and flat- to low-angle cross-bedded sandstones: planar cross-bedded and ripple-bedded sandstones have the lowest values of permeability. Original depositional environment and bedding style exercise important control on permeability (particularly potential gas flow) even in rocks in which the pore systems have been modified significantly by diagenesis. A knowledge of depositional environment and bedding style is therefore important in predicting potential producibility in tight, gas sandstones such as the Travis Peak formation.