Oscillatory methane release from shale source rock

Abstract

Temporal oscillations in methane release rate from a kerogen-rich shale may result from a nonlinearity in transport. The nonlinearity arises from a coupling of the permeability and the fluid pressure through the genesis of fractures via an overpressuring developed through the additive effects of methanogenesis, compaction and thermal expansion of the fluid. Healing of the fractures plays a role in providing a hysteresis central to the oscillation. Oscillatory release is modeled via reaction-transport equations accounting for kerogen breakdown to release methane, the effect of fluid pressure-induced fracturing on permeability, and the transport of methane in aqueous solution via flow and diffusion.