The source rock for nearly a century of Upper Smackover production is a new target as a horizontal oil play.

A hot new horizontal “dirty shale” carbonate/shale play may surface from the Lower Smackover’s Brown Dense. Here are some facts about the formation. For a new report, see “At Closing” in the September issue of Oil and Gas Investor online Sept. 1. Available online now from March 2011: Let’s Talk Some Smack(Over).

--The Brown Dense play is also known as the Lower Smackover Brown Dense or LSBD. It is a Jurassic-age, kerogen-rich, carbonate/shale source rock. It is a “dirty shale” in that it is mixed with carbonate. It is also described as an organically laminated, carbonate mudstone. And, it is at times called a limestone.

--The formation is found from East Texas to Florida. In northern Louisiana, it and its Upper and Middle Smackover members are just below the Haynesville shale play. In the area, Lower Smackover is at 8,000 to 11,000 feet and is between 300 and 530 feet thick.

--Southwestern Energy Co.’s new 460,000-net-acre leasehold is in southern Arkansas and northern Louisiana. It is at an 82% average net revenue interest. The average primary lease term is four years with four-year extensions. It was leased at an average of $326 per acre.

--Two horizontal wells are under way now—one by Southwestern in southern Arkansas and one by Devon Energy Corp., which has some 40,000 net acres over Brown Dense. The Southwestern horizontal, in Columbia County, Arkansas, will have a vertical depth of some 8,900 feet and lateral length of 3,500 feet.

--Rehan Rashid, E&P analyst for FBR Capital Markets, says total organic content (TOC) is high and carbonate content appears to be 40% to 60%.

--The oil is light at 40 to 50 API gravity. There may be high sulfur content (H2S). Upper Smackover production, since the 1920s and which is sourced from Lower Smackover, is sour. Sour hydrocarbons will need processing.

--Porosity and permeability appear to be similar to that of the Eagle Ford shale play, which is also a carbonate/shale mix or “dirty shale.” Southwestern says a piece of a core sample it tested from Brown Dense was brittle.

--In southern Arkansas, laterals of some 4,500 feet are all that is allowed. In Louisiana, between 6,000 and 8,000 feet is allowed.

--Core Lab calls Lower Smackover Brown Dense “one of the most prolific source rocks in the Gulf Coast Basin area.”

–Nissa Darbonne, Editor-at-Large, Oil and Gas Investor,, Oil and Gas Investor This Week, A&D Watch,, Contact Nissa at