THICK PRE-SILURIAN SECTIONS POSTULATED IN WESTERN ILLINOIS

Exploration of horizons beneath the main Illinois basin producing sands is proceeding in western Illinois, where few deep tests have been drilled. Nyvatex Oil Corp., Billings, Mont., is waiting on a mud rotary rig to deepen 16-1 Kearby, SE SE 16-2n-4w, in Schuyler County, to Cambro-Ordovician Knox from present depth of 1,210 ft. The closest control well to the Schuyler County wildcat is the Cardinal Petroleum Co. 1 Billingsly, in 2-2n-4w, 3 miles northeast. The dry hole was drilled in 1983 to

Feb. 4, 1991

2 min read

Exploration of horizons beneath the main Illinois basin producing sands is proceeding in western Illinois, where few deep tests have been drilled.

Nyvatex Oil Corp., Billings, Mont., is waiting on a mud rotary rig to deepen 16-1 Kearby, SE SE 16-2n-4w, in Schuyler County, to Cambro-Ordovician Knox from present depth of 1,210 ft.

The closest control well to the Schuyler County wildcat is the Cardinal Petroleum Co. 1 Billingsly, in 2-2n-4w, 3 miles northeast. The dry hole was drilled in 1983 to 895 ft in Ordovician St. Peter sandstone, a major aquifer in the area.

Based on well site examination of drill cuttings, the 161 Kearby ran about 50 ft low to the 1 Billingsly on all lithologic markers from St. Peter upward.

The Hunton limestone megagroup (Devonian Cedar Valley and Silurian Kankakee) was extraordinarily thin at the Kearby location, 4 ft vs. 27 ft at the Billingsly.

St. Peter was topped at 1,124 ft (-229) in the Kearby, 87 ft low to the same marker in the Billingsly, indicating thickening in the Galena and Platteville groups.

WELLSITE ANALYSIS

St. Peter, regionally about 200 ft thick, had thinned to 16 ft at the Kearby location, and examination of cuttings indicated the test went directly into the Knox dolomite megagroup.

"The thin St. Peter found in the Kearby 16-1 indicates the possibility of a deep seated structure with vertical closure that could be measured in the hundreds of feet," said Barry W. Koch, the well site geologist.

He noted that Knox contains several formations that have the potential of being excellent reservoirs and said it may be more than 1,000 ft thick. He expects to encounter 500 ft or more of Cambrian Mount Simon sandstone below the Knox.

Nyvatex spudded the Kearby well Nov. 27, 1990. An air rig on the well could not deep through St. Peter past 1,210 ft because of water inflow.

The operator encountered minor shows of oil through a long interval of Ordovician Trenton and a slight rainbow of oil during drilling in the top of St. Peter.

The well is the most recent in a western Illinois drilling program (OGJ, Jan. 21, p. 45).