Frackability

A semi-quantitative measure of how well a rock will take hydraulic fracture stimulation. Perhaps some combination of:
 * Brittleness, itself a slippery subject
 * Energy required to fracture
 * Tendency for long, connected fracture swarms to form
 * Tendency for fractures to stay open

Lev Vernik, Marathon: For isotropic linear elastic fracture behaviour, the breakdown pressure of a formation is a function of the maximum horizontal stress, the vertical stress, the pore pressure, and the fracture toughness. Unfortunately, rocks we'd like to frack are not isotropic, and need to be understood in terms of anisotropy and inelastic strains.