I don't know anything specific about that field but many other dry gas fields are related to high thermal maturity of the source rocks. The Barnett Shale is a good example. It was an oil-prone source rock but was heated in certain areas to the level where all the liquid hydrocarbon was cracked to gas. Other dry gas fields are sourced by rocks that only have gas-prone organic matter. Some coal-bed methane fields would be examples. Other dry-gas fields are the result of bacterial conversion of organic matter to methane ("biogenic methane") at low thermal maturity. The Antrim Shale is the Michigan Basin is an example.