LAMOTTE SANDSTONE OF SOUTHEASTERN MISSOURI: SEDIMENTARY ARCHITECTURE AND PALEOCHANNEL DIMENSIONS

Planning for CO₂ sequestration requires modeling the flow of injected CO₂. Recent modeling has shown that it is important to represent reservoir heterogeneities at scales ranging from centimeters to kilometers.

Heterogeneity at this range of scales can be determined for target reservoirs by outcrop analogs. For fluvial sandstones, sedimentary structures such as cross-set thickness can be used to infer the dimensions of larger-scale features, such as unit bars, compound bars, and channel belt width and depth. Outcrops of the Lamotte Sandstone in southeastern Missouri were studied in detail to support inferences about heterogeneity in the Mt Simon Sandstone, a sequestration target in the Illinois Basin.

We measured cross-set thicknesses of individual units from three outcrops located within Hawn State Park in southeastern Missouri. Boundaries for unit bars and compound bars were identified within each outcrop and the maximum thicknesses of 39 cross-sets were measured. We also used previously collected data from Yesberger (1982), who measured the thickness of approximately 200 cross-sets within vertical sections. We utilized these data and the approaches from Lunt et al. (2013) and Bridge and Mackey (2003) to estimate mean channel depth, mean channel width, and channel belt width.

For the outcrops we studied, the mean cross-set thickness was 27 cm, whereas for Yesberger’s data it was 14 cm. This difference likely reflects differences in the area studied and in the methods used to measure cross-sets. However, results using both sets of data indicate that mean channel depth ranged from 2 to 8 m, mean channel width ranged from 0.4 to 1.6 km, and channel belt width ranged from 0.6 to 3.3 km.

These results will help constrain geocellular models of fluvial-type reservoirs in ongoing efforts to model CO₂ flow for sequestration.