Invasion Percolation Application to Fracking
Fracking is a method for increasing the permeability of a reservoir by creating fractures in the reservoir rock. Water is injected from a well perforation using pressures sufficient to fracture the surrounding rock. The preexisting anisotropic stress field concentrates the fractures in a horizontal plane. The spatial distribution of these fractures are typically recorded using microseismic data. Microseismic data for a four stage frack in the Barnett Shale is shown [1].
We associte the microseismicity observed in fracking with the bursts of invasion percolation. To simulate the concentrating effects of an anisotropic stress field, we modify our original invasion percolation model as follows
- • Bonds that are oriented vertically are assigned radom numbers in the range 0 to 1.
- • Bonds that are oriented horizontally are assigned radom numbers in the range 0 to 0.1
This modification gives a strong preference to fractures growing in the horizonal direction. By plotting the burst epicenters for an invasion simulations, we obtain a spatial distribution of bursts that is very similar to observed fracking microseismicity.
[1] Maxwell, S. (2011). The Leading Edge, 30(3), 340–346.