Niobrara EUR Estimates for the Powder River and DJ Basins

Abstract

Estimated Ultimate Recoveries (EURs) were made for approximately 600 productive wells from the geopressured Niobrara Formation in the Denver-Julesburg (DJ), 520 wells, and Powder River, 80 wells, basins. EUR estimates were calculated using Drillinginfo's web based EUR calculator and all wells were normalized to a 9,000 foot horizontal length. This approach was used because many of the well's perforated intervals were missing from available databases. The normalization was done using the difference between the well's listed measured depth (md) and true vertical depth (tvd) values. A ratio for each well was made to gain up (many) or down (few) the calculated EUR values. Range distributions for the EURs (P10-Pmn-P90) where calculated using the Rose & Associates Toolbox distribution program. The Niobrara Pmn for the DJ Basin is 245,000 BO & 0.53 BCF and for the Powder River Basin Pmn is 277,500 BO & 1.31 BCF. The largest Niobrara EURs develop over structural trends that have thermally mature Niobrara source lying over them such as the Wattenberg High, the Colorado Mineral Belt (CMB), Silo and Hereford in the DJ Basin and more thermally mature parts of the southern Powder River Basin. EURs for wells drilled away from those trends decline drastically. From a selection of 104 wells, Wattenberg Field has a Pmn of 305,000 BO & 1.15 BCF. Silo Field has a Pmn of 247,300 BO & 0.32 BCF and Hereford Field has a Pmn of 195,600 BO & 0.29 BCF. The CMB has a Pmn of 245,400 BO & 0.42 BCF. Sweeter areas within each of those trends exist, but are often areally limited as open natural fractures acting as reservoir wax and wane through the section. As the Niobrara source rock becomes more mature, it is possible that added porosity and permeability from the conversion of organic matter to hydrocarbons would increase well EURs, however as most of the Niobrara source is only in the oil window in both of the DJ and Powder River basins, this would only have a limited effect over all.

AAPG Datapages/Search and Discovery Article #90266 © 2016 AAPG Pacific Section and Rocky Mountain Section Joint Meeting, Las Vegas, Nevada, October 2-5, 2016