Texas Farm to Market Road 669 drops off the rim of the Llano Estacado in southern Garza County unveiling the dramatic western scenery that characterizes the West Texas headwaters of the Double Mountain Fork of the Brazos River. It was here 200 years ago that the Comanche and Kiowa Indian tribes ended decades of hostility and forged an alliance that made the horse-mounted warriors Lords of the Plains. Richard Mason

Today the rim of the Llano Estacado is lined with hundreds of wind turbines, mute monuments to modern times. And it is here just south of the Borden/Garza county line that history may gain a new wrinkle as oil and gas operators prospect the northern Midland Basin for Mississippian carbonate targets.

Public datapoints are rare for Mississippian carbonates in West Texas. SM Energy Co. has drilled a handful of horizontal wells in Borden County targeting the Mississippi Lime, which is attracting greater industry attention 400 miles northeast along the Oklahoma/Kansas border. Callon Petroleum Co. joined SM Energy in the Midland Basin Mississippian effort in September with a Borden County horizontal test and was waiting on completion at press time.

Those nascent horizontal efforts in the northern Midland Basin merit attention. If successful, the tests will expand the scope of targets in the Midland Basin not only geographically, but geologically as well. With traditional vertical Wolfberry wells rising in cost, operators are redeploying capital to horizontal efforts prospecting the Wolfcamp and Cline shales along the southern edge of the Midland Basin.

In contrast, operators across the Central Basin Platform farther west have a variety of horizontal targets to choose from in the Delaware Basin of Texas and New Mexico, including the gassy Avalon shale, the oilier Bone Spring 1, 2 and 3 sands, and the underlying Wolfcamp shale.

Horizontal momentum switched to Wolf-camp and Cline shale targets in the southern Midland Basin over the past six months. Now operators have an opportunity to expand potential horizontal targets in the northern Midland Basin—if those Borden County Mississippian tests work.

SM Energy has been tight-lipped as the company adds Permian acreage, including 27,700 acres in first-half 2012. The Denver-based company employs a four-rig Permian program, including three rigs in the Midland Basin, one targeting Leonard shale objectives and two prospecting the Mississippi Lime. To date, SM Energy has released results from three horizontal tests on its Borden County Tredway Mississippian prospect, including the Roy 1301H, the Roy 2404H, and the Rebecca 807H. On average the wells produced at 30-day initial production (IP) rates of 540 barrels of oil equivalent per day from 4,000-foot laterals.

Callon Petroleum has taken notice. "We're very encouraged by what we're seeing over at SM Energy," chief executive officer Fred Callon told attendees at the San Francisco IPAA OGIS conference in September. Callon expects to finish fracture stimulation of its first Mississippian horizontal in November.

The Natchez, Mississippi-based company has reached critical mass at 30,000 net acres in the Midland Basin and is transitioning its Permian program from vertical Wolfberry wells to higher-return horizontal drilling. Callon cavorts with the big boys in the deepwater Gulf of Mexico as a nonoperated participant in projects with Murphy Oil and Royal Dutch Shell and is redeploying deepwater cash flow into expanding its Permian Basin beachhead.

That effort includes the Baird Ranch and Black Magic prospects just south of the Garza/Borden county line after Callon obtained whole cores in the Cline shale and Mississippian carbonate formations from its vertical Shirly Newton 4801 test.

At press time there were four rigs in Borden County prospecting targets such as the Mississippi Lime and the Cline shale with 30-day IPs of 500 to 600 barrels of oil equivalent, 85% liquids, and estimated ultimate recoveries of 500,000 barrels of oil equivalent.

Besides SM Energy and Callon, other operators in the area include privately held Common Resources II Inc., and Denver-based Berry Petroleum Co., which added 15,000 net acres in Borden County prospective for Mississippian and Cline shale targets during first-half 2012. Berry has drilled two vertical tests and is conducting appraisal work as it evaluates how to move forward on a 2013 development program.