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A Case Study of a Three Forks (Sanish) Horizontal Well in the U. S. Williston Basin

Eisel, Jacob D. 1, Michael L. Hendricks2 (1) E-M Exploration, Boulder, CO (2) Hendricks and Associates, Inc, Englewood, CO


An upper Three Forks (Sanish) horizontal well in Burke County, North Dakota, provided a model for some of the issues facing exploration in these beds. The “Sanish” reservoir along the eastern flank of the basin is very fine to fine-grained dolomitic sandstone and sandy dolomite and interbedded gray green shale. Porosity within sand-rich beds is principally secondary and a product of dissolution of dolomite cement as shown by cuttings petrography that preceded drilling.


A major problem encountered during horizontal drilling was the inability to delineate the lateral extent of the sandstone reservoir. The well was fracture stimulated and completed as a poor Three Forks producing well with an initial production of 30 BOPD and 100 BWPD. The oil is 42 gravity oil and probably Bakken in origin.


The number of Three Forks horizontal wells is limited in the U. S. Williston Basin and this test demonstrates some of the exploration challenges associated with the Upper Three Forks.


AAPG Search and Discovery Article #90055©2006 AAPG Rocky Mountain Section Meeting, Billings, Montana