Multidisciplinary Analytical Approach to Evaluating the Niobrara Formation Within the Wattenberg Field, Denver-Julesburg Basin

Abstract

Unconventional resources drastically shifted the supply cost and quantity of available hydrocarbon and altered the way geoscientists evaluate these complex geological systems. An innovative, multidisciplinary approach is necessary to unlock the true potential of these resources. Applied data analytics across multiple data sets, including digital wireline logs, production and completion data, can deliver insights into the mechanisms that make an unconventional play successful. This case study analyzes the Niobrara Formation within the Denver-Julesburg (DJ) Basin of eastern Colorado and southeastern Wyoming, with emphasis on the unconventional Wattenberg field and surrounding area.

The DJ Basin is an asymmetric foreland basin formed largely in response to the Laramide orogeny and covers approximately 70,000 square miles. The Wattenberg focus area accounts for approximately 540 Mboe/d of production, 86% of total production from the entire basin. The Niobrara consists of alternating chalk and marl units, ranging in gross thickness of up to 400 feet, with local variations a result of post-depositional faulting. Four chalk units are regionally correlated across the play, referred to in descending stratigraphic order as A-, B-, C-Chalk and the Fort Hays. Operators mainly target the more porous A- through C-Chalks as the interbedded marl units represent the main source intervals for the petroleum system. The reservoir interval is shallow at ~7,000 feet TVD across the core of the play compared to other prolific unconventional plays such as the Wolfcamp core in the Delaware Basin (11,000 feet TVD) and the Eagle Ford core in the Gulf Coast Basin (12,000 feet TVD). Despite their depth, the four chalk intervals are overpressured within core as a result of intense in situ hydrocarbon generation from an anomalous geothermal gradient driven by the underlying Colorado Mineral Belt.

This study synthesizes over 2,000 digital wells logs to characterize the Niobrara interval, with production and completion data drawn from over 4,000 horizontal wells to analyze the impact of completion designs on well productivity within comparable rock types. This work identifies key mechanisms that make the play successful and highlights the multidisciplinary approach required to characterize unconventional plays.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018