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High-Resolution Elemental Chemostratigraphy of the Three Forks Formation Using Energy Dispersive X-Ray Fluorescence


The Three Forks Formation of the Williston Basin in North Dakota is an upper Devonian stratigraphic unit unconformably overlain by the Bakken Formation. It consists primarily of dolostone, dolomitic mudstone, siltstone and shale. Sandy, pyritic, and anhydritic zones occur at intervals throughout the formation. The Three Forks is a productive tight oil resource play, which in recent years has been increasingly targeted and developed as part of the unconventional Bakken Petroleum System. The absence of biozones, in addition to lithologic complexity and variability, act as challenges to detailed stratigraphic analysis of the Three Forks Formation. Core analysis via energy dispersive x-ray fluorescence (EDXRF) allows for a non-destructive, efficient, and relatively inexpensive chemostratigraphic data collection method. Elemental data collected in this manner has been used to produce concentration logs which reflect both subtle changes in rock composition and complex interbedding. Correlation of such logs on a local, and then regional scale, combined with the mapping of elemental concentrations, should contribute to a more complete understanding of the Three Forks Formation and its role in the larger Bakken Petroleum System.