| Description |
The Niobrara Formation is an unconventional resource for onshore oil and gas production in the U.S. The Silo Field, located in the Denver-Julesburg Basin in Laramie County, Wyoming, has been producing from the Niobrara since 1981. The Niobrara is an interbedded source-rock marl and low-porosity chalk/limestone deposited during the Late Cretaceous in the Western Interior Seaway. Cumulative production as of July 2013 was ~11 MMBO and 9,997 MMCFG. Despite a long production history, it is not well understood why some wells in Silo are high-volume producers while neighboring wells have poor production. Though the Niobrara has been the attention of much previous research, little quantitative data have been published relating production to geologic variables. The objective of this study is to identify geologic factors that contribute to the most productive wells at Silo Field. Geologic variables analyzed included thickness, resistivity, weight percent calcite, porosity, and fracture intensity. Choke size and perforated length were also compared to production since drilling and production methodologies have a substantial influence on well production. Starting from core description and associated core measurements and working outwards to core-log calibration, cross section construction, and map generation, this study established how geologic factors vary stratigraphically and laterally in Silo Field. Then, relationships between geologic variables, engineering practices, and production were explored. Methods relied heavily on bivariate and multivariate linear regression. Fracture intensity has the strongest correlation to production. Elevated resistivity defines the productive fairway at Silo Field due to the presence of open natural fractures. Fractures in the Niobrara are classified as three types: tectonic, overburden, and microfractures. Correlations between engineering practices and production for horizontal wells drilled since 2005, which are absent for earlier wells, are a testament to improved technology and promising for future field development. |
