The Mississippi Lime has a rich past of oil production. For several decades. what is now Conoco Phillips drilled extensively into this formation on the Burbank field. Production resulted from. literally, thousands of vertical wells. The formation had all the hallmarks of a great field: porosity, permeability and lots of hydrocarbon deposits.

However, there was only so much traditional vertical drilling techniques could do, and these wells ran dry. The region saw activity slow to a crawl, and acreage could be had for dirt cheap.

Fast forward to today, and the Mississippi Lime is once again heating up. The same advanced horizontal and hydraulic drilling styles that are revolutionizing America’s shale formations are now being applied to limestone rock. The 350 million-year-old carbonate formation is pretty well suited for fracking. The technique allows firms to dig past the “chat” layer of rock (where vertical drilling stops) and into the tight lime below.

Horizontal wells in the US Midcontinent Mississippi lime oil play aren’t as productive as those in the Williston basin Bakken, but shallower depths and cheaper drilling costs are driving increased interest in the Mississippi lime, said IHS Inc.

The land play has expanded to more than 17 million acres in northern Oklahoma, western Kansas, and southern Nebraska, said Paul O’Donnell, author of the IHS Herold Mississippian Oil Play Regional Play Assessment.

“The Mississippian’s highly variable drilling results to-date, combined with increasing entry costs, might deter new entrants, but recent drilling reports suggest results could improve as knowledge of the play and technical adjustments increase.

“This is a shallow carbonate play, with depths ranging from 3,000 ft to 6,000 ft, and since it’s shallower than other US unconventional plays, operators can employ less expensive, lower horsepower rigs to drill it.”

The reservoir averages 300-500 ft thick with the Woodford shale as its source rock. Costs are estimated at $2.9-3.5 million/well, compared with $8-11 million in the Bakken.