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Brief Summary of Oil and Gas in
South Dakota
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by Fred V. Steece Oil and Gas
Supervisor, South Dakota Geological Survey, December 18, 2003
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Stucture--The tectonic or structural framework of South Dakota dates to the Precambrian Period, at least 2 billion years ago. The surface of the basins began to subside as sedimentary rocks accumulated in them as the higher lands were weathered and worn away, during the Paleozoic, Mesozoic and Cenozoic Eras. As much as 10,000 feet of rocks have built up in Williston Basin, the largest in South Dakota (see map), while only about 3,000 to 4,000 feet were deposited in the South Dakota part of the Kennedy Basin. Oil and gas, began to form shortly after deposition of organic material in the sedimentary rocks, and migrated, along with trapped sea water, through the permeable pathways in these rocks until they were trapped by anticlines, synclines, updip pinchouts or other stratigraphic traps. Oil in the Williston Basin is trapped by smaller structures in the Basin or by stratigraphic traps. Traps in most of South Dakota can fit these two styles. Other areas with basinal sediments are the southern fringe of the Black Hills, and the extreme northern part of the Forest City Basin in the southeasternmost corner of the state.
Exploration--Early well drilling in the eastern and central parts of the state resulted in the discovery of high quality natural gas, largely methane, that was produced along with large volumes of water, much of this from free flowing wells, particularly at lower surface elevations. About 1,350 million cubic feet of gas was produced from this reservoir between 1898 and 1953. The search for oil and gas in the state has focused at various times on the Newcastle or "Muddy" sands on the western margin of the Williston Basin and the eastern fringe of the Black Hills. No oil has yet been found here, but the potential is still favorable. Natural gas was discovered in this reservoir in the 1940's but has not proved to be commercial. The Niobrara Chalk produces natural gas in several Rocky Mountain states and has been explored in central South Dakota without success to date. Gradually thinning and rising to the east and south out of the Williston Basin are rocks of the Paleozoic Era, that are overlain unconformably by younger Mesozoic and Cenozoic rock. This angular unconformity is a striking feature that may hold great potential for the discovery of oil and gas. The Paleozoic and Mesozoic sequence of sedimentary rocks in the Forest City Basin may have oil and gas potential. Exploration for oil and gas has been stimulated in recent years by the development of horizontal drilling. This technique has resulted in the recovery of oil and gas - even in 40-year old oil fields - where primary oil recovery was nearing depletion. Also adding to the state's total oil production has been enhanced oil recovery by means of in situ recovery and by water flooding. Oil was first discovered at Harding County in 1954. At present South Dakota has 19 oil fields in 3 counties and 2 gas fields in 1 county. The cumulative production from the state's fields at the end of 2002 was 37.3 million barrels oil and 116.7 billion cubic feet of gas. Much of the gas is utilized as lease gas and only about 20 percent is sold as marketable gas.
Future Development -- Oil and gas exploration, development and production will continue in the established regions of the state into the foreseeable future. Because there have been less than 2,000 oil and gas test holes and wells drilled in the state in its history, large regions are relatively unexplored. For example, the Paleozoic/Mesozoic unconformity that covers the north-south middle one third of South Dakota is relatively untested and may hold considerable potential for both gas and oil. The Niobrara Chalk and the Greenhorn Limestone offer shallow (less than 3,000 feet) potential for natural gas in the central and maybe even the eastern part of the state. The sand know as the Dakota in central and eastern South Dakota has already given up immense volumes of gas in the so-called "Pierre Gas Field," and this horizon may have some future potential. The stratigraphically equivalent rocks, called Newcastle or "Muddy,"in the northwest one-fourth and the southwest corner of the state, produce hugh volumes of oil in Montana, Wyoming, Colorado and Nebraska. So far only some non commercial gas has been found in these rock in South Dakota. Limestones and dolomites of the Madison Group (Mississippian age) in the Williston Basin, produce more than half of all the oil in North Dakota, but other than oil shows, no significant oil has been found in these rocks in South Dakota. Another rock layer worth mentioning, lying deep in the Williston Basin, is the Deadwood sand and limestone sequence, that has great potential as it is a porous and permeable on the order of hundreds of feet thick. Several gas shows have been recovered in this unit. One deterrent to exploring this rock unit is its greater depth compared to any other sedimentary rock in the state, thus adding to exploration costs.
