One way scientists can see back into the geologic past is by drilling a deep borehole and capturing a core of the rocks encountered during drilling. Boreholes are often referred to as "wells" because they are most often drilled as part of a well to recover oil, natural gas, or water. A core is a cylinder of rock about two to four inches in diameter and hundreds or thousands of feet long (although it comes out in segments, not one continuous tube).
Rocks commonly found in Kansas drill cores are limestone, shale, and sandstone. Each core, from top to bottom, contains a section of several different rock layers that formed during several different geologic periods over millions of years. The rock layers in cores can be analyzed to determine their ages and whether they were formed in a harsh desert climate, tropical marshes, large inland seas, or other ancient environment.
Companies searching for oil and natural gas are the main source of cores, which they bring up to help them identify which underground rocks may contain petroleum. For safe storage, companies often donate the cores to the Kansas Geological Survey. If a well isn't cored, bits of underground rock are broken up during drilling and flushed to the surface. Although these pieces, called cuttings, are a much less reliable source of information than solid cores, coring is expensive so done sparingly.
The Kansas Geological Survey and other government agencies and organizations sometimes drill boreholes to remove cores purely for research purposes. In 2009, the KGS drilled and cored a half-mile deep well in Douglas County through limestones, sandstones, and shales deposited during the Pennsylvanian subperiod, about 300 million years ago. The final few hundred feet of the well drilled into Precambrian-age rocks that are as much as 1.67 billion years old. The deep Precambrian igneous and metamorphic rocks are especially rare and important discoveries because they are at depths seldom reached in Kansas.
The KGS preserves cores, cuttings, and oil, gas, and water drillers’ logs. Drillers’ logs are archived electronically in the Data Resources Library at the KGS office in Lawrence. Cuttings are archived at the KGS’s Wichita Well Sample Library. The KGS Drill Core Library holds more than 67,000 boxes of core and rock samples, representing more than 5,000 drill holes, primarily from Kansas. Most core is stored in Lawrence, but some materials are held at the Wichita location. Once records, cores, and cuttings are submitted to the state or donated to the KGS, they are accessible to the public.