Abstract |
For this study, the sandstones were divided into three stratigraphic units. In the western two-thirds of South Dakota, where Skull Creek Shale separates the Dakota and Fall River Formations from the overlying Newcastle-Dakota Formations, separate estimates have been made for each unit. East of the Skull Creek Shale pinchout, the formations merge into the Dakota Formation and have been treated as a third unit. Thickness of effective sandstone within each unit were determined from resistivity and spontaneous potential logs. Data from about 380 wells were used. An isopach map of effective sandstone thickness was prepared for each unit. A total of 1.3 billion acre-feet of water storage capacity was determined for the Fall River-Lakota interval, 977800 acre-feet for the Newcastle-Dakota sandstones, and 360 million acre-feet for the sandstones of the Dakota Formation. (Modified author abstract) |