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Abstract
Traditionally, the Pennsylvanian Tyler Formation has been targeted as a conventional reservoir consisting of barrier island and channel sand deposits in the southwestern Williston basin, North Dakota. The purpose of this study is to investigate the cyclothemic stacking patterns in the Tyler Formation near the depocenter of the basin to improve the petroleum system model. Utilizing one core located in central McKenzie County, the litho-stratigraphy of the cyclothems is characterized. Six facies were identified and described in each cyclothem. A network of six structural and stratigraphic cross sections was constructed. Structural cross sections and structural maps illustrate that the Tyler Formation dips to the northeast. The stratigraphic cross sections illustrate that the Tyler cyclothems were deposited during a period of sea level transgression and high stand. These cross sections and isopach maps also depict a discontinuous sand facies which does not occur in the core studied.
New permeability and porosity data of two carbonate intervals as well as publically available data from several other intervals in the core were used to characterize the reservoir model of these cyclothems. The majority of the identified facies had less than one nanodarcy of permeability, strongly indicating this was a very tight formation.
It is concluded that the overall tight-rock characteristics of the carbonate and siliciclastic rocks within the lower Tyler Formation may indicate an unconventional petroleum play. The sand facies within the upper Tyler Formation might lead to a conventional approach if hydrocarbons are present.
