Silica diagenesis and its pore-scale influence on the characteristics of the upper and lower Bakken shales, Williston Basin, North Dakota and Montana
type: CreativeWork
description: The Bakken Formation has been a major producer of oil and gas in North Dakota and Montana since the advent of horizontal drilling, reaching peak production of over 1.2 million barrels of oil per day. It is Late Devonian and Early Mississippian in age and consists primarily of a dolomitic reservoir member stratigraphically bounded by an upper and a lower organic-rich mudrock member. These bounding shales have been interpreted as depositional sequences of transgression and regression related to eustatic sea level variations and serve as important source rocks in the Williston Basin. The lower and upper Bakken members were deposited in euxinic bottom-water conditions linked to transgressive system tracts and contain a significant portion of biogenic silica in the form of radiolaria. Biogenic silica dissolution and reprecipitation is known to contribute to the development and/or preservation of pore space, ultimately affecting source rock quality and reservoir recoverability. In general, silica diagenesis occurs in multiple stages, beginning with amorphous silica (opal-A) and followed by a sequence of metastable intermediate polymorphs opal-CT, then chalcedony, and finally microcrystalline quartz. The transition from amorphous silica to progressively more orderly crystallographic stages in this sequence is largely controlled by an increase in temperature and a decrease in silica saturation. Recent studies of mudrocks in other high-profile unconventional plays have highlighted the importance of silica diagenesis in the post-depositional development and preservation of porosity, but this sequence remains understudied in the setting of the Bakken Formation’s radiolarian-rich lower and upper shale members. This study describes and characterizes silica in the lower and upper Bakken shales to estimate the extent to which its diagenesis has altered pore networks within the shales. This study incorporates data from three core samples drilled in northwestern North Dakota and one…
abstract: The Bakken Formation has been a major producer of oil and gas in North Dakota and Montana since the advent of horizontal drilling, reaching peak production of over 1.2 million barrels of oil per day. It is Late Devonian and Early Mississippian in age and consists primarily of a dolomitic reservoir member stratigraphically bounded by an upper and a lower organic-rich mudrock member. These bounding shales have been interpreted as depositional sequences of transgression and regression related to eustatic sea level variations and serve as important source rocks in the Williston Basin. The lower and upper Bakken members were deposited in euxinic bottom-water conditions linked to transgressive system tracts and contain a significant portion of biogenic silica in the form of radiolaria. Biogenic silica dissolution and reprecipitation is known to contribute to the development and/or preservation of pore space, ultimately affecting source rock quality and reservoir recoverability. In general, silica diagenesis occurs in multiple stages, beginning with amorphous silica (opal-A) and followed by a sequence of metastable intermediate polymorphs opal-CT, then chalcedony, and finally microcrystalline quartz. The transition from amorphous silica to progressively more orderly crystallographic stages in this sequence is largely controlled by an increase in temperature and a decrease in silica saturation. Recent studies of mudrocks in other high-profile unconventional plays have highlighted the importance of silica diagenesis in the post-depositional development and preservation of porosity, but this sequence remains understudied in the setting of the Bakken Formation’s radiolarian-rich lower and upper shale members. This study describes and characterizes silica in the lower and upper Bakken shales to estimate the extent to which its diagenesis has altered pore networks within the shales. This study incorporates data from three core samples drilled in northwestern North Dakota and one…
author: Rogers, Ryan
language: eng
language: English
keywords: diagenesis, radiolarian, silica, pore, Bakken, shale
identifier: T 9146
date published: 2021
date modified: 2026-07-24T01:41:48Z
provider: Colorado School of Mines
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: Colorado School of Mines. Arthur Lakes Library

PropertyValue
property ID: Handle
value: https://hdl.handle.net/11124/176461