The surge in oil development in western North Dakota is boosting the state's collection of rock samples that provide information about the region's geologic history.

Oil companies that drill wells are required to send core samples and drill cuttings to the Wilson M. Laird Core and Sample Library on the University of North Dakota campus in Grand Forks. The library belongs to the North Dakota Geological Survey.

Library director Julie LeFever reports a large increase in drill cuttings, which are small bits of rock chipped by a drill bit at the bottom of a well and brought to the surface in drilling fluid. They can help oil company geologists determine the odds of finding oil.

State and oil industry officials say about 335 oil wells were drilled in North Dakota last year. So far this year, about 300 oil wells already have been drilled in the state, and every well has drill cutting samples, LeFever said.

Not every well has a core sample, a continuous cylinder of rock that averages about 30 feet in length. Core samples can provide more geologic information than drill cuttings, but they also are more expensive and less practical in the oil patch these days.

Ed Murphy, the state geologist, said energy companies viewed 45,000 feet of core samples in the Grand Forks library last year - the highest amount since the record of 105,000 feet in 1992. The library holds some 350,000 feet of core.

In the second quarter of this year alone, 20,000 feet of core were viewed. "We're on pace to maybe set a new record since '92," Murphy said.

The Bakken shale formation encompasses some 25,000 square miles in North Dakota, Montana, Saskatchewan and Manitoba. About two-thirds of the acreage is in western North Dakota.

Most wells being drilled in the Bakken are using horizontal drilling, which produces fewer core samples, Murphy said. The technique involves drilling vertically to about 10,000 feet, then drilling horizontally while fracturing the rock to release the oil trapped in microscopic pores in the area known as the "middle" Bakken, where oil-producing rock is sandwiched between layers of shale.

Core samples also can produce fossils, though the fossils typically are not separated from the rock in an effort to keep the sample intact. The state fossil collection is housed at the North Dakota Heritage Center on the state Capitol grounds.

State paleontologist John Hoganson said core sample fossils are some of the oldest ever found in North Dakota, because they come from thousands of feet below the earth's surface.

"Most of these fossils are remains of animals that would have been living in shallow-water oceans, such as corals, clams," he said.

A new Heritage Center exhibit planned late this year will feature some of those fossils, from old core samples.

"The oldest fossil that will be on exhibit is 450 million years old. We have a core sample that has on the surface of the core shells of animals called brachiopods, clamlike animals," Hoganson said. "We would never know about these fossils if it wasn't for oil exploration."