Guane
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eological Consulting
How do Guane scientists determine oil is present? To answer this, some basic Geology is needed:
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Centered in and underlying most of the state of Illinois is a large geologic structure or province known as the Illinois Basin. It is a geologically old, depositional and structural basin with the deepest part beneath southern Illinois. The basin is surrounded by structural uplifts that formed highlands of the past, from which ancient rivers flowed south towards the lowest part of the basin. On the map below the brown coloring represents low elevation and yellow, high. The basin’s outline is a dotted black line. Orange triangles represent ancient highlands, and blue rivers can be seen flowing south.
The rivers carved valleys and channels into the ground. These channels were then filled with a particular type of mud, carbonate mud. Over millions of years since then, the mud filled channels were buried to a present day depth of about 600 feet. Weight and pressure from the overlying sediment changed the mud into rock. The particular chemical make-up of the mud allowed for the development of small pore spaces within the rock. If oil then moves through the area, the pores can become filled with oil.
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These carbonate filled river channels are our drilling targets.
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We find the channels through Subsurface geology. By this method a geologist studies information gained from wells that have already been drilled in an area. After each well is drilled to total depth, an electrical instrument is lowered down the well. This instrument is an electric log and the process is known as "logging a well." The log shows the depth of the formations and, to some degree, if any of the rocks are oil bearing. Geologists use this information to draw geologic maps in order to determine where to drill future wells.
If oil is on my land, then how much?
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In the Brown County oil producing area a rule of thumb is: ~1100 barrels of oil per acre.
There are many factors which control the amount of oil a well will make. Two of the most important are the thickness of the reservoir and the location of the well within the reservoir. The above rule of thumb agrees very closely with other, published rules. Very roughly speaking, if a well is drilled on 10 acre spacing and has 5 feet of oil reservoir present, it will produce about 12,500 barrels of oil….10 feet will produce 25,000 barrels of oil…. 20 feet will produce 50,000 barrels of oil, etc. (modified from Scoper, 1980). This “rule of thumb” agrees with Illinois State reported production numbers for the Buckhorn Consolidated Oil Field where the average reservoir thickness is between 4 and 5 feet. 2.3 million barrels produced from 217 wells equals 10,600 barrels per well and 1060 barrels per acre.