Date of Award

12-1-1990

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Geology

Abstract

In North Dakota, the Broom Creek Formation CWolfcampian) exists in the subsurface as the upper unit of the Minnelusa Group. The Broom Creek Formation consists of pink quartzarenite with some intervening dolostone beds. The identification of lithofacies, areal distribution* and stratigraphic relationships were determined from oil well logs, mainly the dual laterolog suite and the FDC-CNL log suite, and macroscopic and microscopic core analysis. Cores were examined from four wells.

The major lithofacies identified are: 1) eolian sandstone, 2) nearshore marine sandstone, and 3) marine carbonate. From the sandstone-dolostone distribution, marine predominance existed in the eastern part of the study area and eolian predominance in the west during the deposition of the Broom Creek Formation.

A four-phase depositional model is proposed for the preservation of eolian dunes within the Broom Creek Formation: 1) migration of eolian dunes over a low-relief erosional surface, 2) marine transgression and partial reworking of dunes, 3) carbonate mud deposition and, h) marine regression with accompanying diastem and minor er-osion. At least two such extensive cycles occurred in the Broom Creek Formation. However, many minor transgressive- regressive events deposited most beds as discontinuous lenses across the study area.

The upper Broom Creek contact reflects considerable paleotopography. The overlying Opeche Formation was deposited, in a sufficiently low energy environment such that much of the original paleosurface on top of the Broom Creek Formation is preserved. In the west, the upper seccion of the Broom Creek Formation existed as dune fields with accompanying interdune areas.

The main dlagenetic events in the nearshore marine sandstone lithofacies include iron oxide precipitation* dolorniti zation of carbonate cement* quartz overgrowths, and pressure dissolution. The dlagenetic history of the eollan sandstone lithofacies is similar to the nmrire sandstone lithofacies, with two exceptions; the precipitation of interstitial gypsum (anhydrite) and the absence of carbonate cement. Both sandstone lithofacies exhibit excellent porosity. The marine carbonate lithofacies has been completely clolomi tized and contains minor amounts of vuggy and moldie porosity.

From FDC-CNL logs, the accumulation and distribution of nitrogen gas within the Broom Creek Formation was determined. A volumetric calculation of mapped reserves resulted in an estimate of 2 3 trillion cubic fiet <65 billion cubic, meters) of nitrogen gar. in place. The occurrence of nitrogen in the Broom Creek Formation appears to be related to hydrocarbon gene rati >n in the underlying Amsden and/or Tyler Formations.

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