Southwestern Energy Co., Houston, said it has accumulated 460,000 net acres prospective for oil in Upper Jurassic Lower Smackover Brown Dense limestone along the Arkansas-Louisiana state line. The unconventional play is the first the company has revealed publicly of several new ventures it has been pursuing the last 1-2 years and in which it holds a combined 835,000 net acres. The formation’s commerciality is still to be determined, Southwestern said. Southwestern plans to spud its first horizontal well in the play, in Columbia County, Ark., just southwest of Atlanta and east of Dorcheat-Macedonia oil field, late in the third quarter...