The Cretaceous reservoirs of the Rockies have become an important component of future unconventional oil growth in the lower 48. Horizontal drilling within the Powder River Basin (PRB), is moving from appraisal towards co-development of horizontal targets within the Niobrara and Turner Sandy member of the Carlile formations (Turner). Here, novel laboratory techniques utilizing drill cuttings as a primary data source were developed to address the following questions: 1) What are the dominant chemofacies in the Niobrara and Turner reservoirs of NE Converse County, WY, and 2) what is the relationship between chemofacies and petrophysical characteristics.
Petrophysical properties in the Niobrara and Turner vary at the field scale, adding complexity to development planning. Additionally, direct measurement of petrophysical properties to calibrate vintage wireline logs prior to development is difficult due to limited core data. Drill cuttings are more abundant and have the advantage of covering a larger stratigraphic section compared to core. However, measuring porosity from drill cuttings with traditional laboratory techniques, specifically Nuclear Magnetic Resonance (NMR), is not widely employed in the industry.
To address these questions, drill cuttings and core from NE Converse County, WY, were analyzed using organic and inorganic geochemical techniques, including handheld X-ray Fluorescence (XRF), X-ray Diffraction (XRD), and LECO TOC (TOC). A new methodology of cuttings preparation for the NMR porosity measurement was used which removes fluid from the surface of the cuttings and focuses the measurement on the pore space fluids. This methodology minimizes surface water signal, which can be misinterpreted as pore volume. Previous attempts to eliminate the surface water signal used pore size distribution cutoffs, which are unreliable due to pore size distribution overlap.
In this study, the NMR Porosity measurements will be paired with geochemical analyses to examine the link between chemofacies and porosity. Integrating this relationship with wireline data will refine understanding of petrophysical characteristics in the Niobrara and Turner, and help validate the new cuttings NMR method.
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