The Marcellus shale natural gas play is expected to draw in more than $100 billion in investments from operators, Wood Mackenzie says.

Energy consultant group Wood Mackenzie describes Marcellus as the largest natural gas basin of its kind in the world when based on production. The group said there may be more than $90 billion left in value in the play based on projected output from new wells.

Jonathan Garret, a researcher in the exploration and production market in the United States, said the top 20 operators in Marcellus are expected to generate $86 billion in shale value.

"These operators are forecast to spend nearly $110 billion in the play and to drill over 25,000 Marcellus wells through 2035," he said in a statement Wednesday.

By 2020, Wood Mackenzie estimates Marcellus, centered largely in Pennsylvania, should produce an average of 20 billion cubic feet of equivalent per day, which it said would represent 25 percent of the total U.S. natural gas supply.

Wood Mackenzie says the number of active rigs in the Marcellus play have fallen since the beginning of 2012. Energy companies are getting better at pulling gas from the reserve area, however, which the group said is contributing to expected growth.