ABOUT GEOSHURR GAS IDEAS GAS LEADS PROSPECTS PUBLICATIONS LINKS



 


Williston Basin

We don’t usually think of the Williston Basin as a gas basin. It has generally been “under the radar” while most of the Rocky Mountain gas basins have been leased up. In central areas where associated gas is produced with deep oil, leasing in the Williston Basin can also be a bit complicated. But around the margins, extensive lease tracts are readily available and existing accumulations demonstrate shallow gas potential.

Our tour of the basin is organized around production clusters on three margins (Leads: Figure 1):
1. northwestern
2. southwestern
3. eastern
Specific fields and structures discussed on each of the three margins are marked by stars and letters on the Williston Basin map. These leads are also all included in the map and tables that constitute the next set of leads in the Rocky Mountains.

NORTHWESTERN MARGIN

The northwestern margin of the Williston Basin is a mature shallow gas province with a long history of production. Initial production was in the early twentieth century; major production was generally established by the 1930’s; modern expansion started in the 1970’s and continues into the 1990’s. The history of production is closely tied to the huge fields on the southeastern margin of the Alberta Basin, CA, Leads: Figure 1). This is also true for exploration models.

Exploration strategies have changed substantially. Initially, buoyancy traps in conventional reservoirs were developed as small sweet spots. Later, more continuous, commodity-type development involved step-out drilling from areas of established production. This phase involved mostly engineering applications with little useful input from geology.

A new exploration model has recently been developed from geologic studies done by the USGS. Aspects of it are included in the “Shallow Gas Ideas” portion of this website. Basically, the gas is thought to be early generation biogenic gas generated shortly after deposition of the Cretaceous clastic rocks. The rocks act as both source beds and as unconventional, “tight” reservoirs. Gas is trapped within paleotectonic lineament blocks and has not migrated significantly through the low permeability rocks. This model needs to be applied in areas away from current production.

Specific accumulations and leads include old established production in the area of the Bearpaw Uplift and Bowdoin Dome and new discoveries and prospects around Poplar Dome.
1. Bearpaw Uplift (BU, Leads: Figure 1)--Numerous small fields (see 11-19, Table 1, in the Rocky Mountain Basin list) in the vicinity of the uplift are generally buoyancy traps in conventional reservoirs of the Cretaceous Eagle Formation. The largest field is Tiger Ridge which has produced more than 76 BCF (Montana Geological Society, 1985).
2. Bowdoin Dome (BD, Leads: Figure 1)--Unconventional reservoirs in the Cretaceous Belle Fourche, Greenhorn, and Carlile Formations cover a large area. More than 700 wells are spread throughout 600 sq mi; cumulative production is grater than 200 BCF (Rice and others, 1990).
3. Poplar Dome (PD, Leads: Figure 1)--Prospects are available on the Ft Peck Reservation (Monson, 1995) in several Cretaceous formations. A shallow gas discovery was reported northeast of the reservation in the spring of 2001, but subsequent development has been limited.

SOUTHWESTERN MARGIN

The southwestern margin of the Williston Basin is an emerging shallow gas province that has had a flurry of recent activity. Like the northwestern margin, clastic Cretaceous rocks are both source beds and reservoirs and the gas has an early generation biogenic origin. The history of development is also similar. Early production emphasized migrated gas in conventional reservoirs in buoyancy traps on specific geologic structures; more recently, in-situ gas in unconventional reservoirs has been targeted with modern stimulation techniques.

Specific leads tend to cluster in two separate areas: Cedar Creek Anticline (CC,Leads: Figure 1) in eastern Montana and western North Dakota and the West Short Pine Hills (WSPH, Leads: Figure 1) area in northwestern South Dakota.

Cedar Creek Anticline is the oldest and largest field on the southwestern Williston Basin margin. Gas was discovered in 1912 and more than 140 BCF has been produced from hundreds of wells (Clement, 1987). Early production was mainly from high porosity sandstones in the Judith River Formation and the Judith River is still a viable economic target. However, most of the recent development work has involved multi-stage frac jobs on unconventional reservoirs in the Eagle Formation.

Around the margins of Cedar Creek Anticline there are three small fields located on minor anticlines: Little Missouri (LM), Gaslight (G), and Plevna (PL). In the fall of 2001, a coalbed methane play was reported on the northeastern flank of Cedar Creek Anticline into eastern North Dakota.

West Short Pine Hills (WSPH) Field has produced more than 15 BCF from conventional reservoirs in the Eagle-equivalent Shannon Sandstone. The field is located on an asymmetric anticline draped over a basement fault; the structural motif is thus very similar to Cedar Creek Anticline. There may be a significant component of fracture control in West Short Pine Hills Field (Shurr, 2000), just as documented in the Little Missouri Field (LM) near Cedar Creek (Shurr, 2001). Cady Creek Field is located east of West Short Pine Hills Field on a small anticline. Reservoirs are also in the Shannon Sandstone, but have lower porosity and permeability.

For twenty years after the initial discoveries, there was not much action in the area of West Short Pine Hills. However, during 2000 and 2001 leasing has increased dramatically and half a dozen shallow gas tests were drilled. The geology does explain why there were shows, but no commercial production from these tests. In particular, the exploration model developed on the northwestern margin needs to be applied on the southwestern margin. This means that early generation biogenic gas must be targeted on paleotectonic lineament blocks and not just in buoyancy traps on present day anticlines. The approach should be used in both the West Short Pine Hills and Cedar Creek areas.

GeoShurr prospects on the southwestern margin of the Williston Basin are based on both the new and the old concepts. Descriptions are found in the part of this website that focuses on prospects.

EASTERN MARGIN

The eastern margin of the Williston Basin currently has no shallow gas production and exploration activity is very limited. However, in the early 1900’s, there was extensive production and local consumption. A number of towns in North Dakota and South Dakota had municipal gas systems to provide heat and light.

There are three areas that had extensive historic production: Souris River (SR, Leads: Figure 1) area in north central North Dakota, LaMoure County (LC, Leads: Figure 1) area in southeastern North Dakota, and along the Missouri River near Pierre (P, Leads: Figure 1) in central South Dakota.

The Souris River (SR) area has numerous historic shows, as well as municipal production. The patterns of gas shows correspond with lineament zones mapped on satellite images and suggest that fractures are important (Shurr, 2001). Shallow gas was produced in areas where the Cretaceous Fox Hills and Hell Creek and Tertiary coals subcrop beneath glacial drift. The gas is found in an artesian ground water flow system and may be late generation biogenic gas. Although there is currently no shallow gas exploration, operators drilling for deeper oil have started putting on gas detectors at the grass roots. And, shows of shallow gas have been reported.

LaMoure County (LC) also has historic gas production from an artesian flow system at shallow depths beneath glacial drift. However, the reservoir rocks are in the Cretaceous Dakota Sandstone. The area of historic shows and production covers about 25 townships and is elongate parallel with linear features in a lineament zone. Several recent prospects have been put together south and west of LaMoure County, but exploration activity in the general area is very limited.

Along the Missouri River at Pierre (P) South Dakota there is an area of several thousand square miles that has historic shows of shallow gas. The capital city of Pierre used gas produced from wells within the city limits for more than three decades in the early twentieth century. The gas was produced from the artesian ground water system in the Dakota Sandstone. Lineament blocks mapped on satellite images appear to correspond with patterns of gas shows and local consumption (Shurr, 2000). Exploration programs in the 1970’s targeted objectives in the Niobrara Formation, where a few shows are recorded, as well as in the Dakota Sandstone. Since then, there has been virtually no exploration activity in the area.

GeoShurr prospects on the eastern margin of the Williston Basin combine new exploration concepts and unique data sets and unique data sets in the areas of historic shows. Descriptions of the prospects available are found in the prospect portion of this website.


 

ABOUT GEOSHURR • NATURAL GAS IDEAS • NATURAL GAS LEADS • PROSPECTS • PUBLICATIONS • LINKS • GEOHOME

 


GeoShurr Resources, LLC
1803 - 11th St,
Ellsworth, MN 56129
phone: 507 • 967 • 2156
e-mail: geoshurr@frontiernet.net
© Copyright 2002