Date of Award


Document Type


Degree Name

Master of Science (MS)



First Advisor

R.D. LeFever


The Spearfish oil play is unconventional requiring the use of horizontal wells that are fracture stimulated to deliver economic flow rates. However, fraccing into the underlying water has been a source of significant production problems for operators. The key to developing the area is to keep the individual fracs large enough to stimulate the tight Spearfish sands but not to let them propagate into the underlying water zone.

The Spearfish Formation of the Black Hills has been traced into the subsurface of the Williston Basin in western North Dakota from bore holes at the northern margin of the outcrop area in extreme eastern Wyoming. In the Williston Basin, the Spearfish can be divided into three lithologic units; in ascending order these are; a lower gray shale and red siltstone unit (Belfield Member), a middle salt unit (Pine Salt Member) and an upper siltstone unit (Saude Member).

The lower two units are considered to be Permian, while the overlying Saude Member is predominantly Triassic. In North Dakota, the Saude is considered to be an onlapping transgressive unit, probably supplied by a source area to the west and becoming younger to the east and north where it rests with angular discordance on progressively older Paleozoic rocks. Lack of fossil evidence makes it difficult to assign a definite age to the upper part of the Saude although it is possible that the upper part of the Saude in northwestern North Dakota and southern Saskatchewan and Manitoba crosses the Triassic-Jurassic time boundary.

The petroleum production potential of the Spearfish Formation was analyzed using decline curves on the cumulative oil production from 90 wells chosen from North Dakota and Manitoba. A comparison was made on these wells based on field locations and drilling method employed.

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