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N orth Dakota G eological S urveyG eological Investigation N o 247 - S heet 3 of 4 K2O Grades of the White Bear Member of the Prairie Formation

Cartographic Compilation: N avin T hapa

Mohall 100K Sheet, North DakotaEdward C. M urphy, S tate G eologistLy nn D. Helms, Director Dept. of Mineral Resources

Ned W. Kruger2020

µ

References:

Mohall Quadrangle, North Dakota Adjoining 100K Maps 2019 Magnetic N orthDeclination at Center of S heet

6o26'

Kenmare BottineauS tanley M inot Velva

Crain, E. R., 2014, Crain’s petrophy sical handbook; U RL, accessed 14 January 2014. Crain, E.R., and Anderson, W .B., 1966, Quantitative log evaluation of the P rairie Evaporite formation in S ask atchewan: Journal of Canadian P etroleum T echnology, vol. 5, p. 145-152. Kruger, N .W ., 2014, The Potash Members of the P rairie Formation in N orth Dakota: N orth Dakota G eological S urvey, Report of Investigation no. 113, 39 p. N elson, P.H., 2007, Evaluation of potash grade with gamma -ray logs: U .S. G eological S urvey, O pen File Report 2007-1292, 14 p.

0 1 2 3 4Miles

0 1 2 3 4Kilometers

M ercator P rojection S tandard P arallel 48°30'0"N

N orth American 1983 Datum Central Meridian 101°30'0"W

S cale 1:100,000

Thickness (ft)01-34-67-910-1213-1516-1819-21S olution edge of P rairie Formation salt

T his series of maps of the Mohall 100K S heet was based on public data from 39 wells gathered by the N orth Dakota Industrial Commission – Department of Mineral Resources, O il & G as Division. T he W hite Bear Member was identified on the geophy sical logs of 24 wells. Isopach contours were generated via PETRA (ver. 3.9.13) geological software. T he contour lines were computer-generated based on well-control data only, with minimal adjustments made by the author. Areas with a geological anomaly may not be accurately portray ed. T he potash member thick ness for each well, and the isopach contours generated from them, were modified from Kruger (2014). All calculations were based on gamma-ray log measurements recorded in AP I units tak en at six-inch increments throughout the potash-containing portion of the log. Corrections for borehole size and drilling mud weight as well as removal of the baseline gamma-ray signal were made (Crain, 2014) (Crain & Anderson, 1966). T he corrected gamma-ray measurements were converted into apparent potassium oxide (K2O ) concentrations. Average K2O concentrations and potash member thick nesses were obtained using the grade-thick ness method described in N elson (2007), where bed thick ness is equal to the distance between the elevations at which the gamma-ray response declines to one-half its maximum value. W hen a potash member display ed multiple gamma-ray log peak s separated by troughs representing salt or insolubles such as clay or anhy drite, thin potash intervals at the upper or lower boundaries of the member were not included in thick ness or average-potash-grade calculations if the corrected gamma-ray measurements were less than 100 AP I or separated by more than four feet from main body of the potash member. T his occurred most frequently in deposits of the W hite Bear Member, which may appear as one or two potash-rich beds underly ing a thin potash-containing zone separated by an interbed of halite. T he volume of potash from the W hite Bear Member as represented on this sheet is approximately 6,040,000 acre feet.

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Avg K2O % / T hick ness (feet)!13.0/14.0W ell Control=

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