PIERRE GAS FIELD REVISITED

High quality methane gas has been known in the central part of South Dakota, centering on Pierre since the late 1800s. The gas was discovered while drilling water wells that were developed in the Upper Cretaceous Dakota Sandstone at depths ranging from 1,250 to 1,700 feet below land surface.

Well drilling proved that the volume of gas was enough to be utilized commercially for cooking and lighting in Pierre and Fort Pierre, and on a number of farms and ranches in the surrounding ten county region, for about 25 years from 1910 to 1935, when the volumes gradually diminished below the commercial level. State Geological Survey records show more than 1,341 million cubic feet of gas was produced from the Pierre gas field during the 55 year period from 1899 to 1953. Many farm and ranch water wells in the Pierre region continue to produce small volumes of gas, some of which is still used. The gas is either biogenic that has accumulated in situ, or thermogenic that has migrated from underlying Paleozoic rocks that almost certainly are in contact with the Mesozoic section by means of a great angular unconformity that occurs in the central part of South Dakota. Or the gas may be from both sources.

Only minimal exploration for Dakota Sandstone gas has been done in the region. A knowledge of the stratigraphy from lithologic and electric logs from water wells and oil test holes allows suppositions to be made as to the structure of the rocks in the region. Enough is known to show that the Paleozoic section thins from more than 4,000 feet in the northwest part of the state to a few hundred feet in the vicinity of the Pierre gas field. Likewise, the Mesozoic rocks thin toward the east from about 4,000 feet thick to several hundred feet, but these rocks continue over all older rocks into eastern South Dakota and beyond. A massive Precambrian high feature, 20 miles southwest of Pierre, probably represents the westernmost nose of the Sioux Quartzite Ridge, underlies most of Stanley County and extends westward into Haakon County. This structural high probably has some effect on the older rocks in the section, but the influence gradually diminishes upward.

The updip pinchout of the Paleozoic rock section beneath the overlapping Mesozoic rocks seem to be the best bet for prospecting for oil and natural gas in the Dakota Sandstone and possibly other potential reservoir rocks in the region.