Niobrara Chalk

Core analysis is challenged when physically measuring permeability, capillary pressure, “irreducible” water saturation, and relative permeability for rocks with permeability of 0.000001-0.1 millidarcies (mD). Measurements are complicated by stress-dependency, high capillary pressure, microcracks, differing PHI-K-Sw measurement methods, and controlling fluid distributions. Image-based digital rock physics provides independent complimentary measurements. The objective of this study was to develop an integrated CA-DRP workflow and measure these properties. Using a workflow integrating CA and DRP, we characterized the Niobrara Formation chalks and marls, Denver Basin, Colorado. CA was performed on representative chalk/marl samples and high resolution 3D microscope images were acquired using focused ion beam scanning electron microscopy. Carefully cross-validated digital rock physics and core analysis is an extremely powerful tool for microdarcy rocks, and digital rock physics provides unique data particularly in assessing permeability relationships and saturation/bound water influences. Properties computed herein have been used in reservoir- and well-scale numerical flow modeling to support exploration, completion and production management decisions.


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Left: Niobrara Chalk Surface SEM Image, Right: Niobrara Chalk FIB-SEM Image