New gas material balance to quantify biogenic gas generation rates from shallow organic-matter-rich shales

► New theory to describe production from shallow biogenic shale gas reservoirs applied to two fields in Western Canada. ► Significant fraction of stabilized rate due to currently generated biogenic gas. ► Biogenic shale gas productivity potentially enhanced if microbes are stimulated. ► Two new Langmuir isotherms obtained from preserved core samples presented in paper.