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Oil production in the Mid-Continent began in 1860 with a discovery near Kansas City. The initial find was in rocks of Pennsylvanian age, and reservoirs in that system are still the most important in the region. Hundreds of pools produce from it at depths which range from the surface "tar sands" of western Missouri and southern Oklahoma to sandstones 3 mi or more deep. Several major fields produce mainly from Pennsylvanian rocks.
The geologic history which accounts for this prolific production is punctuated by 3 distinct orogenic episodes: the widespread post-Morrowan Wichita orogeny, the early Desmoinesian Ouachita orogeny, and the Late Pennsylvanian Arbuckle uplift. Activity centered in a belt extending from southern Arkansas across Oklahoma and into the Texas panhandle. Between the major orogenic pulses there were lesser and somewhat more localized movements. Repeated folding is common in the area.
Orogeny actually began in Late Mississippian time with the uplift of an area in northern Texas and southern Oklahoma and the development of a foredeep on the north. Earliest Pennsylvanian rocks are a flysch laid down in this southern Oklahoma geosyncline. In the beginning of the Pennsylvanian most of the Mid-Continent was above sea level and subject to erosion, but by Desmoinesian time shallow seas had spread across the shelf as far north as central Nebraska. Two large topographic highs in Kansas were the last to be submerged.
Cyclic sedimentation characterized the entire period so that alternating marine and nonmarine rocks occupy most of the region north of the geosyncline. Relatively thin and persistent carbonate rocks and shale are most abundant on the north, siliceous clastic rocks predominate and attain great thicknesses on the south. A shelf-edge zone of marine banks and algal reefs occupies the boundary between the two regions. Redbeds and some evaporites are present in Upper Pennsylvanian strata.
Oil and gas are produced from all types of stratigraphic and structural traps. Reservoirs include conglomerate, arkose, sandstone, siltstone, limestone, dolomite, and shale. To date, only dry gas has been found in the southeast Oklahoma-western Arkansas part of the province; elsewhere gas and oil generally are found in close association. Liquids range from nearly solid hydrocarbons to very light naturally refined oils.
Prospecting in the region uses all the conventional techniques but subsurface geology is the most popular and most effective in the more densely drilled parts. Success for exploratory wells in recent years has been as high as 26% in Oklahoma and Kansas where virtually all wildcat drilling is based on geologic advice.
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