Subsurface Mapping and Preliminary Compaction Analysis of the Lower Cretaceous Bow Island Formation, North-Central Montana

摘要

The Bow Island Formation is an Albian age sequence of shales to sandstones deposited insouthern Alberta and north-central Montana during the Early Cretaceous transgressions andregressions of the Western Interior Seaway that flooded the interior of North America. It is ashallow, low pressure gas producer in Montana, produces oil further north around Calgary, and isequivalent with the Muddy Formation in Wyoming and Colorado. Extensive mapping usingboth well logs and dozens of cores has been completed throughout Alberta. Mapping andstratigraphic correlations in Montana are very incomplete, consisting of two published crosssections, very little sedimentology, and no subsurface mapping.This work provides the first publically available detailed mapping of the Bow Islandthroughout north central Montana and preliminary stratigraphic correlations that show thickeningand thinning across the study area. De-compaction analysis was performed along one crosssection to determine if the relative thickening could be attributed to differing rates of compactionas lithologies change across the study area. This study also touches on the major geologicfeatures in the mapping area that are controlling production in the numerous gas fields, andattempts to de-conflict the different formation nomenclature that has been used in studiescompleted in this area in the past 30 years.