The Graneros-Greenhorn Petroleum System, a Possible New Resource Play, Rocky Mountain Region, USA

Abstract

High total organic carbon content (TOC) in the Graneros and Greenhorn formations and limestone reservoirs in the Greenhorn suggest potential for a new resource play in the Rocky Mountain region. Operators are currently testing new horizontal wells in the play. The source rocks are dominantly Type II with a mixture of Type III. The Greenhorn is a pelagic carbonate deposit and consists of three members: Bridge Creek, Hartland, and Lincoln. Pelagic constituents consist of nannofossils (coccoliths and calcispheres) and foraminifera (mainly planktonic). The formation ranges in thickness in the northern Denver Basin from 200 to 290 ft. The Bridge Creek and Lincoln are largely chalk units or chalky marl units (40-85 % CaCO3). The Hartland is a chalky marl (20 — 80% CaCO3). TOC in the Bridge Creek, Hartland, and Lincoln members ranges from 0.5 to 5 wt. %. The Hartland contains the high levels of organic carbon and has the lowest levels of fossil diversity and abundance suggesting low oxygen or anoxic conditions during deposition. Depositional depths for the chalk units is probably 100 to 300 ft. The Graneros interval occurs between the Greenhorn and the D Sandstone over much of the Denver basin. Where the D pinches out the Graneros terminology is extended down to the top of the Mowry Shale. The Graneros to Mowry interval ranges in thickness from 150 to 400 ft across the northern Denver basin. TOC in the Graneros ranges from 0.5 to 5.3 wt. %. The overall all distribution of the TOC in the Graneros is more consistent (not as cyclic) than in the Greenhorn. Production from vertical Greenhorn wells has been encountered in the general Denver Basin area. Production comes mainly from the Lincoln member.

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