PORE STRUCTURE AND GAS RECOVERY IN BARNETT SHALE

The Barnett Shale in north Texas illustrates successful (and persistent!) commercialization of an unconventional reservoir. The extremely low permeability shale reservoir benefits from hydraulic fracturing treatments that establish long and wide fracture pathways, which results in connecting very large surface areas of the formation with an extremely complex fracture network. However, gas production in such tight shale has been technically challenging. The primary challenge facing gas producers is rapid initial depletion rate of new wells, with the average first year decline reported to be 64% for Barnett Shale. The gas recovery factor of Barnett Shale is only 8-15% even in stimulated fracture-shale systems, and there are very limited investigations on the low gas recovery factors in shale plays. From laboratory experiments and decline curve behavior analyses of producing wells, we report that low gas production is related to the coupled physical (migration in tortuous flow pathways) and chemical (desorption) processes in the low permeability shale matrix, which is characterized by nano-sized pore spaces.