Reservoir characterization and tertiary recovery improvement of the Weber sandstone, northwest Colorado

This doctoral dissertation constitutes a reservoir characterization and tertiary recovery improvement of the Weber Formation, northwest Colorado. The Weber formation was deposited in an ancient desert environment and consists of intertonguing eolian dunes and fluvial deposits. Similar reservoirs are increasingly important to the petroleum industry, well known examples are in the Rotliegende in the North Sea oil fields and newly discovered Pennsylvanian strata in Saudi Arabia. This study gives scientists the first example that shows how eolian reservoirs are compartmentalized in three dimensions. Previous studies have concentrated on anisotropy in the eolian sands caused by the foreset dips of the eolian dunes, but these studies assumed that the eolian sands were relatively continuous and internally homogenous. This study shows that soils, ponds and discontinuous fluvial deposits can effectively compartmentalize a reservoir unit. The dissertation consists of three studies, each addressed in a separate chapter, and each of which will be submitted to different scientific journals for publication. The first paper describes the different facies in the Weber sandstone and shows which form reservoir and which are potential barriers to fluid flow. The different depositional facies in the core were classified as a function of their depositional environment. Cross-sections and depositional models were developed to characterize the environment of deposition during the Lower and Upper Weber Formation ages. Finally, the different depositional facies were classified as a function of their potential reservoir quality. The depositional model allows us to extrapolate the geometries of reservoir and non-reservoir sandstones in three dimensions. The second paper used well-logs and rock physics to quantify the permeabilities and porosities of the different depositional facies as a function of their rock properties. And correlated the potential reservoir and non-reservoir facies to well logs. This allows scientists to infer depositional environment and reservoir quality in other similar oil fields. Secondly, reservoir and non-reservoir rocks were distinguished based on their compressional and shear wave velocities. This allows scientists to infer reservoirs on seismic images, even where no wells are present. Those velocities have been employed to calculate compressional to shear wave ratios, Poisson\u27s ratio, and acoustic and elastic impedance, which help to distinguish the rocks bearing oil from the water saturated rocks. (Abstract shortened by UMI.