Sequence Stratigraphy of the Upper Cretaceous Niobrara Formation, A Bench, Wattenberg Field, Denver Julesburg Basin, Colorado

The Niobrara, like the Barnett Shale in Texas, forms a complete hydrocarbon system, as the rock itself acts as the source, reservoir, and seal. The formation contains a mix of low-permeability organic-rich chalks, marls, and shales. The lower limestone within the Niobrara is known as the Fort Hays. Overlying units are grouped together as the Smoky Hill member, which contain limestone beds named and recognized as “A”, B”, and “C” intervals or benches, in increasing depth order.

Much of the focus on oil and gas production coming out of the Niobrara has been from development of the limestone units in the middle Niobrara, or “B Bench” of the Smoky Hill member. However, production from the A, C, and Fort Hays chalk intervals in older vertical wells suggest that they may be future targets of horizontal drilling, as well.

Good well control and an abundance of digital geophysical well logs allowed for the ability to recognize and correlate several distinctive mappable units within the A bench of the Niobrara. The focus of this study was to integrate information gleaned from gamma -ray, spontaneous potential and deep resistivity logs, scout tickets, production and completion data to construct correlations, cross sections and isopach maps of these distinctive units within the A bench of the Niobrara.

By using major flooding surfaces and parasequence boundaries to build a stratigraphic framework to base our interpretation on, we were able to identify fault patterns that impacted the A bench both during and after deposition. Production patterns were then matched with the depositional units interpreted during this study.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California