Williston and Powder River Basins Groundwater Availability Study

 

 

 

-Introduction
-Need for Study
-Purpose, Objective, and Scope of Study
-Background
-Previous and Ongoing Numerical Models of Groundwater Flow
-Selected References
-Related Links
-Publications and Presentations
-Related News Stories and Press Releases
-Research Team

-Project Area Photos
    -Williston Structural basin
    -Powder River Structural basin

 

 

The development of two nationally important energy-producing areas, the Williston structural basin (containing the Bakken Formation) and Powder River structural basin, provide a critical opportunity to study the water-energy nexus within a groundwater context. Large volumes of water are needed for energy development in these basins.   The hydraulically connected aquifers in the regional lower Tertiary and Upper Cretaceous aquifer system are the shallowest, most accessible, and in some cases, the only potable aquifers within the Northern Great Plains.

This study area is part of the USGS Groundwater Resources Program to assess and quantify the availability of the Nation’s groundwater resources. 

Interested in USGS water-quality information for the Williston basin?  See: http://steppe.cr.usgs.gov

Want to know about other USGS projects in the Williston Basin

The Williston and Powder River structural basins contain energy resources of national importance. Coal/lignite, oil, natural gas, and uranium, present in both structural basins in large quantities, currently are extracted from Tertiary-age and older geologic units; however, rapid technological advances (for example, horizontal drilling and hydraulic fracturing), coupled with ever-increasing resource discovery and characterization, are predicted to dramatically increase development of these energy resources in both basins in the near future. Increased extraction of these energy resources will require withdrawal of ever-increasing volumes of groundwater from the lower Tertiary and Upper Cretaceous bedrock aquifer system.

This study will provide the USGS with additional information on important aquifers in the States of Wyoming, Montana, South Dakota, North Dakota, and the Provinces of Saskatchewan and Manitoba in Canada. The study will provide an improved understanding of the lower Tertiary and Upper Cretaceous bedrock aquifer system in the context of a large, hydraulically connected regional aquifer system—an aquifer system undergoing developmental pressure with current and future competing water uses. Simulation of groundwater flow also will allow evaluation of different water-use and energy-development scenarios, as well as evaluation of possible future climatic effects on these aquifers. Perhaps most importantly, the study provides a unique opportunity to understand this regional system prior to large-scale energy development. Data compiled as part of the study will become part of the national USGS water-resources database, and will contribute to the USGS mission by describing and increasing the understanding of the Nation’s groundwater resources.

 

The purpose of the Williston and Powder River Basins groundwater availability study is to quantify the current groundwater resource, as part of a USGS National assessment.

The overall objective of this study is to assess the groundwater resource, particularly as energy resources are developed. This objective will advance tools, information, and conceptual understanding of this areally extensive regional transboundary aquifer system.

The scope includes:

• Williston structural basin. Develop a hydrogeologic framework, estimate hydrologic budget components, refine the conceptual model of groundwater flow, and numerically simulate the regional groundwater flow for the lower Tertiary and Upper Cretaceous aquifer system.

• Powder River structural basin. Develop a hydrogeologic framework, estimate hydrologic budget components, and refine the conceptual model for the lower Tertiary and Upper Cretaceous aquifer system.

Physiography
The Williston and Powder River structural basins underly about 160,000 square miles (mi²) in parts of Montana, North Dakota, South Dakota, and Wyoming and are the shallowest aquifers of the Northern Great Plains aquifer system. Topography in this area is fairly flat with a gently rolling land surface underlain mostly by sedimentary rocks composed of sandstone, coal, and shale. Large river systems such as the Missouri and Yellowstone Rivers erode the relatively soft sedimentary rock and create several hundred feet of local topographic relief. The area is semiarid, with mean precipitation ranging from 12 to 20 inches per year (in/yr) and available precipitation (difference between monthly precipitation and potential evapotranspiration) ranging from 0 to 5 in/yr (Reilly and others, 2008). Pasture and hayland is the predominant land-cover category (70 percent) in the study area (Multi-Resolution Land Characteristics Consortium, 2011).

Hydrogeology
Total thickness of the Quaternary, lower Tertiary, and Upper Cretaceous aquifers range from 2,000 feet (ft) in the Williston structural basin to as much as 8,000 ft in the Powder River structural basin. Lower Tertiary-age geologic units include primarily the Sentinel Butte, Tongue River, and the Slope/Cannonball Members of the Fort Union Formation in the Williston structural basin and the Tongue River, Lebo, and Tullock Members of the Fort Union Formation in the Powder River structural basin. Upper Cretaceous-age geologic units include the Lance Formation, Hell Creek Formation, and the Fox Hills Sandstone. The basal confining units are the Upper Cretaceous-age Lewis Shale, Bearpaw Shale, and Pierre Shale.   

Water in the regional lower Tertiary and Upper Cretaceous aquifer system occurs mostly under confined conditions except along basin margins and in aquifers in the upper part of the lower Tertiary-age geologic units, which are characterized by local flow systems (Whitehead, 1996). Where aquifers in the lower Tertiary and Upper Cretaceous aquifer system are covered by thin unconsolidated glacial or alluvial deposits, water percolates downward through the deposits to the aquifers. Most of the recharge to the lower Tertiary and Upper Cretaceous aquifer system is from precipitation that falls on outcrop areas or from snowmelt that runs into ephemeral and perennial streams that cross aquifers or aquifer boundaries (Whitehead, 1996). Discharge is primarily to large perennial streams that dissect the aquifer system and to withdrawals for irrigation, public-supply, energy production, and self-supplied industrial uses. In 2000, the Northern Great Plains aquifer system provided 101 million gallons per day (Mgal/day) of water to irrigation (66.6 Mgal/day), public-supply (33 Mgal/day), and self-supplied industrial (1.62 Mgal/day) uses (table 1 from Maupin and Barber, 2005). Most of this water is from the regional lower Tertiary and Upper Cretaceous aquifer system (Wesolowski, 1991) because relatively thick Cretaceous-age shale that underlies these aquifers hampers deeper drilling.

The Williston structural basin has been a leading domestic oil and natural gas producing region for more than one-half century. To meet future, and ever-growing needs, oil and gas development from deep geologic units such as the Bakken Formation is rapidly increasing due to recently improved hydraulic fracturing methods that require substantial volumes of freshwater from shallow aquifers or streams, rivers, and lakes. Other potential sources of energy in the Williston structural basin include coal/lignite and coal bed natural gas (CBNG). Both of these energy sources are present primarily in the lower Tertiary-age and Upper Cretaceous-age geologic units. Coal/lignite extraction commonly requires strip mining that removes large volumes of the host rock and aquifer material. CBNG development requires removal of substantial volumes of groundwater to allow degasification of the energy resource. Development of these energy resources can affect groundwater availability in the lower Tertiary and Upper Cretaceous aquifer system through water and rock mining.



Since the late 1880s, the Powder River structural basin has been an important mineral and energy-producing region to the States of Wyoming and Montana and to the Nation. Until recently, the Powder River structural basin was known primarily for oil, coal, and uranium production; natural gas production from conventional resources was a small component of overall energy development in the structural basin. However, the development of unconventional natural gas (that is, CBNG) in the basin beginning in the late 1980s, and widespread development in the late 1990s, has rapidly transformed the basin into a nationally important natural-gas producing region.

Previous and Ongoing Numerical Models of Groundwater Flow

Williston structural basin

• Northern Great Plains (Downey, 1986). Grouped the lower Tertiary- and Upper Cretaceous-age geologic units as a single model aquifer layer. Finite-difference cell size of about 50 mi on a side.
• Lower Tertiary- and Upper Cretaceous- age units in SW part of Williston structural basin (Hotchkiss and Levings, 1982). Modeled as five layers.  Cell size of 6 mi on a side.
• Fox Hills aquifer in Canada and central United States (Anna, 2011). This aquifer was the upper layer in a regional model.
• Fox Hills-Hell Creek aquifer in the center of the Williston structural basin (Fischer, North Dakota State Water Commission, ongoing).
• Fox Hills-Hell Creek aquifer in the center of the Williston structural basin (Fischer, North Dakota State Water Commission, WRI No 54, 2013).

Powder River structural basin

• Lower Tertiary- and Upper Cretaceous- age units (Hotchkiss and Levings, 1986). Modeled as five layers.  Cell size of 6 mi on a side.
• Lower Tertiary Wasatch and Fort Union aquifers in southeastern Montana (ALL Consulting and CH2M Hill, 2001).  Modeled as 17 layers with 0.5-mi cell size.
• Lower Tertiary Fort Union aquifers in Southeastern Montana (Wheaton and Metesh, 2002). Modeled as 6 layers with 0.25-mi cell size.
• Lower Tertiary Wasatch and Fort Union aquifers in the Powder River structural basin in Wyoming (Applied Hydrology Associates and Greystone Environmental Consultants, 2002). Modeled as 17 layers with 0.5-mi cell size.
• Fort Union Formation in Powder River structural basin in Montana (Myers, 2009).  Modeled as nine layers with 0.8-kilometer cell size.

Related Links

Publications and Presentations

Related News Stories and Press Releases

Research Team