Although the variables used to calculate the fracture pressure commonly are generalized as a smooth curve, there are local variations and departures from this generalized curve. The principal horizontal stress, ε<sub>3</sub>* and [http://en.wikipedia.org/wiki/Poisson%27s_ratio%20Poisson's%20ratio Poisson's ratio] depend on lithology and bed geometry as well as depth and compaction.<ref name=ch10r52 /> | Although the variables used to calculate the fracture pressure commonly are generalized as a smooth curve, there are local variations and departures from this generalized curve. The principal horizontal stress, ε<sub>3</sub>* and [http://en.wikipedia.org/wiki/Poisson%27s_ratio%20Poisson's%20ratio Poisson's ratio] depend on lithology and bed geometry as well as depth and compaction.<ref name=ch10r52 /> |