2014 Rocky Mountain Section AAPG Annual Meeting

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Fourier Analysis of the Laminated Facies of the Middle Bakken Member, Sanish-Parshall Field, Mountrail County, North Dakota


The Bakken Formation is a significant hydrocarbon source and reservoir within the Williston Basin. The Middle Bakken, which is the main horizontal target zone, is subdivided into several facies, including a laminated facies consisting predominately of 1 mm to 5 mm thick lamina pairs of very fine grained light gray sandstone and very fine grained dark gray siltstone. Additionally, each well in the eight well data set contained several laminations up to 1.2 cm thick. This study examines the origin of the laminated facies focusing on the origin of the parallel lamination. Recent hypotheses for the origin of the laminated facies include tidal, algal and hyperpycnal gravity flows. The resulting sedimentary structures are similar but are deposited in different shoreline configurations and water depths, which may result in different reservoir characteristics including lateral continuity. The primary analysis method utilizes Fast Fourier Transform (FFT) and periodograms of lamina sets to determine if an underlying tidal signature is present. Results of the spectral analysis show the parallel laminations were deposited in a lower intertidal environment with tidal periodicity ranging from a semi-diurnal to mixed tidal system and synodically driven tidal forces. A number of thick laminations indicated non-tidal influence in laminations such as storm events. Non-sinusoidal lamination pattern resulted from a low sediment influx and probably was the result of eolian transport. Low sediment influx and low tidal range resulted in thin lamination with lack of preservation with the tidal cycles.