Natural gas production has a long and rich history, but until recently, unconventional reservoirs have been a rounding error in terms of supporting global demand. Now these “tight” gas wells are an essential part of U.S. energy policy. And yet, many fundamental questions about the physics of production remain unanswered.
Assessing the production potential of shale gas plays can be assisted by simple mechanistic models of productivity of individual wells. I consider two simple flow geometries: gas pressure diffusion into planar fractures and radial diffusion into a line pressure sink. I compare these two models with data from 16,533 wells in the Barnett shale. It turns out that gas flow is linear for up to 12 years (and possibly longer) in vertical and horizontal wells with or without refracturing.
However, my constrained inversion of the field data suggests a gas hydraulic diffusivity which is one to two orders of magnitude larger than that measured in shale matrix in laboratory. Numerical simulations were run with these larger diffusivities giving credence to the idea that interference between fracture planes in hydrofractured wells could adversely affect well production and impact the well economics.