Chemostratigraphic and depositional characterization of the Niobrara Formation: Techniques for assessing lateral heterogeneity, CEMEX Quarry, Lyons, Colorado, Denver-Julesburg Basin

Abstract

The Late Cretaceous (89–82 Ma) Niobrara Formation is the primary target for unconventional horizontal well activity in the Denver Basin. With an abundance of horizontal activity, the question of well-length scale lateral heterogeneity becomes paramount addressing steering practices, completion, and ultimately well performance. We have incorporated detailed core description, high-resolution chemostratigraphy, and petrophysical logs from four near-surface cores taken at the CEMEX Lyons Quarry to assess lateral heterogeneity. Cores were originally intended to determine the geochemistry and areal extent of the Fort Hays Limestone Member of the Niobrara Formation, CEMEX’s primary target for cement production. However, due to the cores’ proximity to one another (91.4–609.6 m [300–2000 ft]) and the presence of not only the Fort Hays Limestone but also the petroliferous chalks and marls of the Lower Smoky Hill Member (including the D Chalk, C Marl, and a portion of the C Chalk), the data set can also be used as a proxy to model changes along a pseudohorizontal wellbore. Observations include lateral bentonite discontinuity, trace element and organic carbon variations, and distinct changes in sedimentary structures. Well-length sedimentological and stratigraphic changes may have unique implications for unconventional oil and gas development.