THREE-DIMENSIONAL STRUCTURE OF MODERN RIVER BEND DEPOSITS: DEVELOPMENT AND ITS IMPLICATIONS ON HYDROGEOLOGIC MODELS

Fluvial deposits play an important role in the formation of petroleum reservoirs and aquifers, and estimation of their heterogeneity is important in many applications. In this study, modern streambed deposits in a channel bend are characterized in three-dimensions using small-scale hydraulic testing and geophysical methods. Previous investigations focused on two-dimensional measurements of permeability on outcrop faces, which yielded statistical properties without delineation of actual three-dimensional (3D) structures. In this research, we infer the 3D structure of the streambed in addition to streambed geostatistical properties by using constant-head injection tests in modern stream sediments.

Estimates of K from hydraulic tests were obtained in 456 points scattered in a 45m x 20m x 1.2m section of Prairie Creek in Central Nebraska. The values ranged from 75 m/d to 0.15 m/d. Geostatistical analysis and 3D visualization of the data indicate the presence of a distinct geometric feature that closely resembles channel deposits along bends as observed in the field, and as predicted by sediment transport models. Ground-penetrating radar surveys also display similar patterns. Both data sets suggest locations of possible scour surfaces. These locations will be compared with empirical and analytical models of the maximum depth of scour along the bend.

The distinct feature can be used to delineate the modern streambed, and separate it from other hydrostratigraphic units. This new 3D approach has significant implications in the development of aquifer models because it constraints the geometric and hydraulic properties of the streambed. This study shows that integration of concepts and principles developed in sedimentology, hydrogeology, geophysics and geostatistics, will allow the verification and improvement of aquifer and streambed models.