Integrated Subsurface and Outcrop Sedimentological, Mineralogical, and Geochemical Characterization of Late Cretaceous Mancos Shale, SouthwesternPiceance Basin, Southern Douglas Creek Arch, and Southeastern Uinta Basin, Colorado and Utah

Abstract

In early 2013, a study of the Mancos Shale was initiated at Colorado Mesa University with initial funding from the CMU Unconventional Energy Center and industry donations. The goal of this project is to generate a stratigraphically calibrated mineralogical, geochemical, radiometric, and sedimentological dataset for the total Mancos in the southwest Piceance Basin, southern Douglas Creek Arch, and southeast Uinta Basin. The total project area is about 4,185 mi 2 , extending from Cisco, UT, to Delta, CO. Input comes from four sources: 1) publicdomain well-log data; 2) public-domain organic and inorganic geochemical data; 3) spectral gamma-ray, mineralogical, and inorganic geochemical analyses of cuttings from a well about 16 mi north of Fruita, CO; and 4) measured sections from the outcrop belt near Grand Junction, CO. In the project area, the Mancos is 3,697 to 4,751 feet thick (average = 4,059 ft) and is subdivided into four assessment/inventory intervals: Upper Mancos, Prairie Canyon, Niobrara, and Lower Mancos. These intervals are clearly defined on well logs and in outcrop, and have average thicknesses of 865, 1,231, 1,656, and 329 feet, respectively. Currently, public-domain data have been harvested from 38 wells in the project area, including 559 total-organiccarbon (TOC), 513 RockEval, 95 vitrinite-reflectance (VR), 175 total-carbonate (TC), 12 x-ray diffraction (XRD for bulk mineralogy), and 596 x-ray fluorescence (XRF) analyses (El Attar, 2013). Most analyses (~95%) come from the lower Mancos and Niobrara equivalent. New data generated from cuttings in the Fees Federal 2-6-8-101 (API 05-045-07432), include 169 XRD, TC (calcimeter), and spectral gamma-ray (SGR) analyses. These samples span the total Mancos and part of the overlying Mesaverde Group and underlying Dakota Sandstone. Outcrop work includes 16 measured sections (2,245 ft) with foot-by-foot gamma-ray measurements (total count and SGR) for about half of the sections. It is anticipated that when completed, the results will provide a platform that will enhance exploration and exploitation of the Mancos, plus allow researchers to better understand its depositional history, stratigraphy, and sedimentology. Additionally, the inorganic-geochemical data will allow environmental studies on Mancos intervals that could influence disposal of produced water and drill cuttings. Data on mineralogic characteristics will also contribute to a better understanding of the mechanical-stratigraphy of the Mancos, which will aid well completions. Introduction The Mancos Shale is present over much of western Colorado and eastern Utah. In western Colorado, it exceeds 4,000 feet in thickness and has an outcrop width that can reach 17 miles (Whitney, 1981; Gaultieri, 1988). The Mancos has a long history of oil and gas production in the western Piceance Basin, Douglas Creek Arch, and eastern