Madison Group Source Rocks, Williston Basin, USA

Abstract

Madison Group reservoirs have yielded hundreds of millions of barrels of oil since production began in the 1950s. Historically, these oils were thought to be sourced by the Bakken Shale. However, oil fingerprint including light hydrocarbons and biomarker data clearly show these oils not to be related to Bakken Shale source rocks except in special cases in US fields. However, mixing of Madison and Bakken Shale sourced oils in Canadian Williston Basin reservoirs is quite common as a result of lateral migration and trapping of both Madison and Bakken Shale sourced oils. Finally, there can also be differences in stratigraphic nomenclature particularly the Tilston Member of the Mission Canyon formation. The evidence for Madison Group source rocks starts with an inversion of produced oil chemistry that demonstrates the difference from Bakken Shale produced oils and rock extracts in all geochemical properties from bulk analysis (e.g., sulfur contents), light hydrocarbons, pristane/phytane ratios, and traditional extended biomarker data. Review of the depositional setting of various Madison Group intervals demonstrate the occurrence of hypersaline, evaporitic, and highly sulfidic settings. The presence of microbialites further amplifies available biomass for source rock development, although these may be part of the source story as well. The primary source rock for Madison Group reservoirs has been largely focused on the Lodgepole formation, which has been documented as a source rock in both Canada and the USA. However, additional source rock intervals are found throughout the Madison Group from the Ratcliffe Member of the Charles formation to various members of the Mission Canyon formation. Identification of prospective Madison Group source rocks was initiated with a review of available cores as this is a conventionally produced carbonate reservoir. High TOC and hydrogen indices have been now recorded in various members of the Madison Group including the Lodgepole, Mission Canyon (at least three separate source intervals, and the Ratcliffe Member of the Charles formation. Of 38 samples with greater than 1% TOC from 16 wells in North Dakota, restored TOC values range from 3-5 wt.%. Hydrogen indices range from about 300 to over 600 mg HC/g TOC. In order to confirm these rock units as effective source rocks, correlation to produced oils was accomplished verifying the Madison Group source potential.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016