<->04 F. H. KAY OIL FIELDS OF ILLINOIS 



THE COLMAU FIELD OF WESTERN ILLINOIS 



111 the bottom of the Illinois basin and well up on its sides the Potts- 

 ville rocks are completely saturated with salt water. In the western- 

 central part of the State, however, a few isolated small domes produce 

 commercial quantities of gas and smaller quantities of oil. Of these, the 

 Staunton gas field, the Carlinville oil and gas field, and the old Litchfield 

 oil and gas field are the most important. In these fields the oil and the 

 gas do not occur in continuous sandstone bodies, but are found in sand- 

 stone lenses which are locally discontinuous. As many as four productive 

 horizons have been recognized, separated by a small vertical interval. 

 Theoretically, a tilted, porous sandstone lens should provide conditions 

 for accumulation of oil and gas at its upper end ; but in Illinois the bed- 

 ding planes of the Pottsville do not seem to be impervious enouo^h to pre- 

 vent the lateral movement of oil and gas unless doming of the strata has 

 capped the edge of the porous bed and effectually prevented the escape of 

 the oil. xAt the top of a dome affecting several sandstone lenses accumu- 

 lation will tend to take place independently in each lens, as shown in 

 figure 3, which is a reproduction from a report by Wallace Lee for the 

 State Geological Survey, in cooperation with the ITnited States Geological 

 Survey. 



Since it is impossible in any given area to predict the presence of a 

 porous bed in advance of drilling, it is practical in western Illinois merely 

 to point out the presence of structural domes which may or may not be 

 underlain by beds capable of acting as reservoirs for oil and gas. This 

 method has been successful in locating the only producing fields in west- 

 ern Illinois — namely, the Staunton, the Spanish Needle Creek, and the 

 Colmar fields. 



Great interest has been manifested in the extreme western part of the 

 State since the discovery of oil at the base of the ISTiagaran at Colmar. 

 The existence of a dome was first pointed out by Henry Hinds from levels 

 run to coal number 2, which outcrops at the surface. Commercial oil was 

 found in a sandstone which was probably deposited in depressions on the 

 Maquoketa surface during the encroachment of the Niagaran sea. There- 

 fore the sand exists as lenses separated by areas in which the limestone 

 lies directly on the shale with no intervening sand. No direct connection 

 is apparent between the Hoing pool, where the sand lies 90 feet above 

 sealevel on a terrace at the northeast side of the dome, and the Hamm 

 pool on top of the dome,' where the sand is 70 feet higher. I^ikewise, the 

 pool at the town of Colmar lies on the north side of the dome and prob- 

 ably has no direct connection in the sand with either of the other pools^. 



