For years, wells in central and western Kansas have produced oil from a deep underground rock layer called the Drum Limestone.
By studying the Drum in southeastern Kansas, where it is near the surface, geologists from the Kansas Geological Survey, based at Kansas University, hope to provide clues about its makeup, and lead to increased oil production.
Their study, funded by the U.S. Department of Energy, has involved geophysical research and well-drilling in Montgomery County during the past two years. Local landowners Jesse Clarkson, Warren Ferrell, William Brothers Pipeline and Heartland Cement Co. have cooperated with researchers by providing access to land. Survey geologists plan to return to the area in mid-August for more drilling.
According to the geologists, the Drum Limestone named after Drum Creek, near Independence was deposited during the Pennsylvanian Period, about 300 million years ago, when a shallow sea covered eastern Kansas. The sea level fluctuated, sometimes reaching as much as 300 feet in depth. At the edge of the sea, where the water was shallowest, only a few feet deep, it deposited the limestone layers.
"WHEN THE sea level was the lowest, it deposited the rock that makes the best reservoir of oil," survey geologist Lynn Watney said.
The Drum Limestone is one of those layers deposited by shallow sea water. Survey geologists studied the rock where it crops out at the surface, drilled new wells bringing up cores from several hundred feet below the ground and examined records of previous wells drilled in the area.
They also used seismic methods, similar to those in the oil industry in which a vibration is set off at the ground surface and sound waves travel underground, reflect off underground rocks and bounce back to the surface, where they are analyzed to provide an image of the underground geology.
"TO UNDERSTAND a layer like the Drum Limestone, we use all types of methods, like seismic and drilling, then piece the information together," survey geologist Evan Franseen said. "We now understand the geometry of the formation better."
For example, the Drum Limestone differs considerably from place to place around Independence. At one point, it is as thick as 75 feet; less than a mile away, it is only 3 feet thick. Similar trends in the Drum Limestone may occur in western and central Kansas, where the formation produces substantial amounts of oil.
"The cores from wells show that the formation thickens, then thins to the north and south," Franseen said. "That ties into the records of other wells and to the seismic lines and helps us understand the geometry of the formation."
Some of the findings about the Drum Limestone in southeastern Kansas also may be applicable to the western part of the state, and maybe beyond.
"EVEN THOUGH the rocks are 300 miles apart, they are very similar," said Watney. "The events that led to the deposition of the rocks are regional.
And the cycles that led to these rocks high sea-level followed by shallow sea level followed again by high sea level are found in rocks in Russia, in South America, all over the place. Studying them in Kansas has application throughout the world."