News Release, Kansas Geological Survey, Dec. 5, 1997
The Cowley County well is a dramatic example of the way that horizontal drilling--a technique developed during the past decade that is becoming more common in Kansas--may change oil exploration and production in the state. That's the assessment of petroleum geologists at the Kansas Geological Survey, based at the University of Kansas.
According to Survey geologist Tim Carr, the Cowley County well is one of about 50 horizontal wells that have been drilled in Kansas. More are on the way, he says, and they could slow and maybe even reverse declines in the state's oil production.
"If they work in Kansas, lots and lots of these wells will be drilled," said Carr. "They could recover significant amounts of oil."
For more than a hundred years, traditional oil wells have been drilled vertically, straight down into the ground. When these wells reach an oil- bearing rock formation, oil drains into the well from the surrounding rock.
A horizontal well begins like a traditional vertical well, at least until it nears the oil-bearing rock bed. At that point, sophisticated technology is used to turn the drill bit and drive the well horizontally. The drill then chews its way laterally along the targeted rock layer. Traditional vertical wells drain oil from a single hole poked through a rock layer; horizontal wells encounter several hundred, or maybe several thousand, feet of a rock bed, allowing them to drain substantially more oil from the rock.
"This is technology that was originally applied primarily in Canada, in North Dakota, and in some fields in Texas," said Survey researcher Paul Gerlach, who has studied Kansas rock formations that might make particularly good targets for horizontal drilling. "Because many of those oil reservoirs are similar to the ones in Kansas, people are beginning to apply it here."
Most of the state's horizontal wells have been drilled in southwestern Kansas, where the target horizon is 4,000 to 5,000 feet deep. Recent wells have been drilled in Ness and Hodgeman counties, along either side of an underground geologic feature called the Central Kansas Uplift. A horizontal well in Ness County, for example, produced 250 barrels of oil per day upon completion.
Geologists say that the most common targets for horizontal drilling in Kansas are oil-bearing rocks deposited during the Mississippian Period of geologic history, about 350 million years ago. The technique works best in rock formations that are "heterogeneous," or vary greatly from place to place.
"In those settings, a horizontal well allows producers to recover oil that was by-passed by a vertical well," said Gerlach.
In addition, salt water blocks the oil's route to the drill hole in many traditional vertical wells. Horizontal drilling allows the well to come into contact with more oil-bearing rock.
"That means the well produces more oil, and much less water," said Carr. "It's an excellent method of producing marginal oil from fields that were producing relatively small amounts of oil and large amounts of salt water."
Horizontal drilling is challenging, however. Wells typically cost two or three times as much to drill as traditional vertical wells. And drilling a horizontal well requires detailed knowledge of the location and configuration of the drilling target, the underground rock.
"In Kansas, it will probably work well in some locations and not work in other locations," said Carr. "It is more expensive, so some people are a little wary of it. And many Kansas operations are small companies and their experience with horizontal drilling is limited. Now that a few people are having some success with it, operators are becoming more comfortable with trying it."
The potential is great. Kansas oil production peaked in 1956 at about 123 million barrels. Production declined until the early 1980s, when higher oil prices led to a brief jump in production, from about 58 million barrels in 1979 to 75 million barrels in 1984. Since that time, production has resumed its decline, dropping to 42 million barrels in 1996.
"Horizontal drilling could change the face of oil production in Kansas," said Carr. "It could bring on substantial reserves relatively quickly."
Story by Rex Buchanan, (785) 864-3965
Kansas Geological Survey, Publications and Public Affairs