Evaluation of the Tyler Formation, Williston Basin, western North Dakota

Stevanovic, Ivana M.

The Williston Basin is a large oval-shape intracratonic sedimentary basin in southern Saskatchewan, eastern Montana, and western North and South Dakota. The marginal marine depositional environment of the Tyler Formation (Pennsylvanian age) can be very challenging for petroleum exploration and production particularly on the barrier islands in the transgressive sequence. Depending on the subsidence rate and sediment supply, these environments can range from very thick sand deposits with uniform strike orientation to very thin discontinuous sand bodies with small reservoirs displayed in any number of orientations, which are correspondingly high risk reservoirs. The Tyler Formation represents the later type of deposition and hence the importance to evaluate all aspects and make detail mapping of this source and reservoir formation. The rare earth elements (REE's) and trace elements are an excellent indicator of depositional environments. Determination of REE's chemical composition coupled with total organic content and biomarkers show petroleum migration pathways from source to reservoir rocks within the Tyler Formation.

The Tyler Formation, which has produced 84 million BBLS over the past 50 years out of estimated 1.5 billion BBLS reserve is also represents its own hydrocarbon source and reservoir. The study used cores and oil samples from the Tyler Formation within the Williston Basin of western North Dakota. Samples were examined for geochemical composition primarily rare earth elements (REE), trace elements, and total organic content, as well as biomarkers, atomic ratios of hydrogen/carbon, oxygen/carbon, and maturity by using pyrolysis, inductively-coupled plasma - mass spectrometry (ICP-MS), and gas chromatography-mass spectrometry (GC-MS). The geochemical data has been mapped and analyzed using Arc GIS with RockWare geochemical software. Thin sections from the cores were examined for microsedimentary structures, porosity and permeability. The data from the geochemical analysis, thin sections and the geophysical logs will be used to model potential drilling sites using Schlumberger's Petrel® simulation software.

Utilizing rare earth elements, trace elements and total organic content in innovative and standardized geochemical techniques coupled with the computer modeling will enhance our understanding of the depositional environments, source and reservoir rocks, and petroleum migration pathways, which will enable for better drilling decision making.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013