The Cline Shale:

A Brief Overview


Excerpt from the May 2012 issue of AAPG Explorer Magazine

The Cline Shale (also known as the Lower Wolfcamp) lies over a very large area on the eastern shelf of the Permian Basin. The “Cline” is a localized name for the Pennsylvanian aged shale that some recognize as the D bench of the Permian aged Wolfcamp.  Starting at the Wolfcamp A bench down to the bottom, Wolfcamp C bench, the rock has less carbonates.  However, the underlying shale is interbedded with sand and silt, indicative of its depositional environment.   The Cline source rock lies on a broad flat shelf, with very little relief.  Total Organic Content (TOC), porosity, permeability, and OOIP are all fairly comparable in both the Wolfcamp and the Cline.  Even though the Wolfcamp is thicker, which can be a driver for production in shale plays, it is the pressure and thermal maturity of the Cline that set it apart.  The pressure gradient is around 0.55-0.65 psi/ft with an Ro value of 0.85-1.1%.  Along with NGLs, this allows for a nice, light crude with an API gravity of 38-42 degrees, which some say is comparable to the Eagle Ford.  The industry type curve for the Cline Shale is quoted at 420 Mboe EUR/well with 60% oil and a 30 day IP of 575 Boe/d with 75% oil.

In short, the Cline is an organic rich shale, with Total Organic Content (TOC) of 1-8%, with silt and sand beds mixed in. It lies in a broad shelf, with minimal relief and has nice light oil of 38-42 gravity with excellent porosity of 6-12% in thickness varying 200 to 550 feet thick. 

Active players in the shale include Devon Energy, Chesapeake, Firewheel Energy, Apache Energy, Laredo Petroleum, Exco, Callon Petroleum, Pioneer Resources and others.

Counties included in the shale are Fisher, Nolan, Sterling, Coke, Glasscock, Tom Green, Howard, Mitchell, Borden and Scurry.

The formerly low profile Cline shale, equivalent to the Cisco, has captured the attention of Tulsa-based Laredo Petroleum and, more recently, other operators. Laredo’s Permian activity is centered on the basin’s eastern side about 35 miles east of Midland, Texas, which has long been dubbed capital of the Permian Basin. The company’s production/exploration fairway is about 20 miles wide and 80 miles long. In 2011, it drilled 262 wells (234 operated) on its Permian Basin assets with a 100 percent success rate on the 239 wells that were completed during 2011. “The overall Wolfberry interval, which is the principal focus of our vertical drilling activities, is an oil play that also includes a liquids rich natural gas component,” said Laredo founder, chairman and CEO Randy

Foutch, an AAPG member. “Prior to our purchase of Broad Oak, the exploration and drilling efforts in the southern half of our acreage block were centered on the shallower part of the Wolfberry,” he said. “But the emphasis in the northern half has always been on the deeper intervals, including the Wolfcamp, Cline shale, Strawn and Atoka formations. “We have identified significant potential throughout our total acreage block for the entire Wolfberry interval from the shallow zones to the deepest,” he noted. Consequently, the company expanded

its drilling program to include a horizontal component targeting the Cline and Wolfcamp shales. “Our Cline shale drilling began after we conducted an extensive technical review, including whole core analysis and single zone testing in vertical wells,” Foutch said. “We believe the Cline shale exhibits similar petrophysical attributes and favorable economics compared to other liquids-rich shale plays, such as in the Eagle Ford and Bakken shale formations. “We have acquired 3-D seismic data to assist in fracture analysis and the definition of the structural component within the Cline shale,” he added. Eighteen wells were drilled as part of the company’s Cline drilling program in 2011, and Laredo had two horizontal rigs drilling in the program at year-end. Efforts are under way to optimize well performance according to lateral length, fracture density, proppant amounts and pumping rates. Laredo also has completed six horizontal wells in the Wolfcamp shale. “This is all very fast moving,” Foutch commented. “No one was talking about horizontal Wolfcamp even 18 months ago. We think there will always be vertical drilling in the Wolfberry, but the results in the horizontals are such that you’ll see expanding horizontal drilling activity. We were the only ones doing much Cline work until maybe six months ago, and now the industry has picked up on it,” Foutch continued. “We anticipate it will turn out to be a pretty spectacular world class horizontal oil shale target.”

There’s another key factor at work in this big play – the money. “At the start of 2000, oil was about $20 a barrel,” another industry player noted. “Because it went up, we could afford to implement these huge fracturing techniques where we’re fracturing these 10,000-feet-deep vertical wells with a million gallons of water. “When this began, the cost to drill and complete a well was $700,000, and now it’s $1,700,000,” he said. “This is mainly due to increased costs, such as more fracturing stages and adding more Wolfcamp and other formations. Plays such as this are a big deal for the players and for anyone who uses anything even remotely related to oil, i.e. everyone. “There will be a million acres or more involved in this play,” he predicted. “If it’s all drilled out at 40-acre spacing, it should recover about three billion barrels of oil. “The U.S. Geological Survey said it’s the largest discovery in the last 50 years in the Permian Basin.”

In Pursuit of a Liquids-Rich Play in the Cline Shale