2014 Rocky Mountain Section AAPG Annual Meeting

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Utilizing Hydrocarbon Yield Determinations to Evaluate Source/Reservoir Relationships in the Bakken/Three Forks of the Williston Basin, ND


The Bakken/Three Forks Petroleum System hosts variable source/reservoir relationships throughout different portions of the Williston Basin. While some of these relationships are easily discernible from production and wireline log data, others most readily become evident by comparing production results to geochemical data of the Upper and Lower Bakken Shales. In order to better identify and characterize these relationships a series of “Hydrocarbon Yield” maps were created for the Upper and Lower Bakken Shales using a method recently described in a paper by Ruble and Lewan (2013). The method computes a volume of hydrocarbon yield (MBOE/640 acres) by multiplying the thickness of the shales by the amount of S2 that has been converted into hydrocarbons. The generated maps are then compared to production data for both the Middle Bakken and Three Forks formations. Four distinct trends have been identified in this study: -The bulk of the data fits in a highly correlative trend of lower water cuts in areas with increasing hydrocarbon yield, typical of “basin centered oil accumulations.” -A smaller subset shows a group of high water cut in areas of significant hydrocarbon yield.” Wells in this subset consist primarily of good reservoir quality in the Middle Bakken, which suggests that these areas have poor trap integrity. -Another subset shows a trend of wells with low water cut in areas of low hydrocarbon yield. Wells in these areas exhibit extremely good reservoir quality in the Middle Bakken and show evidence of a possible charge contribution from migrated oil. -The bulk of the Three Forks wells tend to show a typical “basin centered oil” trend, with a small subset of wells with low water cut and minor hydrocarbon yield from the presumed source (Lower Shale). The small subset occurs in areas where the Lower Shale and Middle Bakken have pinched out, placing the Three Forks in direct contact with the oil generating Upper Shale. While this approach does provide a new understanding of the Bakken/Three Forks source/reservoir relationships, it can also prove beneficial when used in the evaluation of other basins and formations.