Shell Oil Co. has chosen a site near Pittsburgh for a major, multi-billion-dollar petrochemical refinery that could create thousands of construction jobs and provide a huge economic boost to the region. Dan Carlson, Shell's General Manager of New Business Development, said that the company signed a land option agreement with Horsehead Corp. to evaluate a site near Monaca, about 35 miles northwest of Pittsburgh. The so-called ethane cracking, or cracker, plant would convert ethane from bountiful Marcellus Shale natural gas liquids into more profitable chemicals such as ethylene. The next steps are environmental and design studies and further economic analysis, followed by requisite permits. Ohio, West Virginia and Pennsylvania had all sought the plant and offered Shell major tax incentives. Monaca is about 15 miles from both the Ohio and West Virginia borders, so workers in all three states are likely to benefit. The Marcellus Shale, which lies thousands of feet underground, has attracted a rush of major oil companies, who have drilled almost 5,000 new wells in the last five years. The Marcellus covers large parts of Pennsylvania, New York, Ohio and West Virginia, and drillers have also started to tap the adjacent, deeper Utica Shale formation.