UPDATE 1-SM Energy to raise $300-$500 mln via divestitures

* Says to look at sale or joint venture partner

* Says marketing Marcellus, non-core assets

Aug 23 (Reuters) - Oil and gas company SM Energy Co (SM.N) plans to raise at least $300-$500 million over the next 12 months via joint venture agreements and sale of assets, including its Marcellus shale positions.

The company, formerly St. Mary Land & Exploration Co, said it will look at divestitures of its 43,000-net acre Marcellus shale in McKean and Potter counties of Pennsylvania.

SM Energy, which operates in the Mid-Continent, Rocky Mountains, ArkLaTex, Permian Basin and the U.S. Gulf Coast, said Bank of America Merrill Lynch will market the Marcellus assets.

The Denver, Colorado-based company has engaged Albrecht & Associates to market some other non-core assets, with current capacity of 13 million cubic feet equivalent per day. The company did not give further details on the non-core assets.

The Marcellus shale -- spanning Pennsylvania, New York, Ohio and West Virginia -- is one of the top gas-producing zones in continental United States, and oil majors have jockeyed to take positions in the zone, fetching holders of assets huge premiums.

Shares of SM Energy, which have lost about one-fifth of their value in the last month, fell marginally in extended trade after closing at $35.57 Monday on the New York Stock Exchange. (Reporting by Krishna N. Das in Bangalore; Editing by Unnikrishnan Nair)