GEOLOGICAL AND HYDROLOGICAL CONTROLS ON THE PRODUCIBILITY OF COALBED METHANE

Geological and hydrological comparison Of two United States coalbed me thane basins, the prolific San Juan Basin and the marginally producing Sand Wash Basin, indicates that coal distribution and rank, gas conte nt, permeability, ground-water flow, and depositional and structural s etting are critical controls on coalbed methane producibility. A compl ex interplay, and moreover, a synergy amongst these controls determine s high productivity. This paper proposes a basin-scale explanation for the prolific and marginal production in the two basins and that can b e applied to evaluation of coalbed methane potential in coal basins wo rldwide. High productivity is governed by (1) thick, laterally continu ous coals of high thermal maturity, (2) basinward flow of ground water through coals of high rank and gas content orthogonally toward no-flo w boundaries (regional hingelines, fault systems, facies changes, and/ or discharge areas), and (3) conventional trapping along those boundar ies to provide additional gas beyond that sorbed on the coal surface.