Gibson Dunn, a global law firm that set up shop in Houston in February, will relocate to downtown's BG Group Place at 811 Main early next year. The firm, which specializes in the oil and gas industry in Houston, has subleased 55,000 square feet on floors 30 and 31 from Shell. Houston is now among 20 global offices for Gibson Dunn, which has 1,200 lawyers and traces its roots to 1890 in southern California. "Gibson Dunn had a geographic hole in their practice. That was Houston," said partner in charge of the Houston office Michael P. Darden. Shell, which has moved most of its downtown operations to west Houston, has found subtenants for the bulk of the approximately 300,000 square feet it put up for sublease at 811 Main.