Certain approaches to hydraulic fracturing — the more of it, the better — and directional drilling appear the secret to successfully tapping a previously unprofitable oil deposit, according to a Wyoming State Geological Survey report released Monday.
For decades, geologists thought the Codell Sandstone of southeast Wyoming was too dense to make drilling worthwhile.
Then came the two techniques that have opened access to such deposits nationwide: Fracking, or pumping pressurized water mixed with fine sand and chemicals into wells to break open deposits, and directional drilling.
The Codell Sandstone has received far less attention than the overlying Niobrara Shale in Colorado, Wyoming and Nebraska but the same techniques have revolutionized drilling in both.
Six companies have produced oil from 119 wells targeting the Codell Sandstone east of Cheyenne over the past five years. The Wyoming State Geological Survey looked at what the most productive Codell wells have in common.
Some of the wells, besides tapping the almost 9,000-foot-deep layer of oil-bearing sandstone, were drilled up to two miles to the side of the well pad. Wells drilled into the Codell toward the north or south tended to produce more than those drilled toward the east or west, geologists Rachel Toner and Erin Campbell wrote.
Such wells might intersect with more oil-bearing fractures in the formation, they speculated.
The top-producing Codell wells also have undergone the most fracking. Each had at least 40 frack stages, or individual fracking zones, along their course.
They also used at least 200,000 barrels of water-chemical mix and between 10 million and 12.5 million pounds of proppant, or the fine sand used to prevent the cracks that are opened by fracking from closing back up again.
Eventually the expense of fracking a well outweighs the benefits. But in general, how where a well is drilled in the Codell Sandstone appears less important than how it's drilled, the geologists wrote.
