Properties of fractures explained
The FracFocus website has added information about the propogation of fractures in the subsurface.
Certain predictable characteristics or physical properties regarding the path of least resistance have been recognized since hydraulic fracturing was first conducted in the oilfield in 1947. To see more about the properties of hydraulic fractures go to Hydraulic Fracturing: The Process page.
Hydraulic fractures are formed in the direction perpendicular to the least stress. Based on experience, horizontal fractures will occur at depths less than approximately 2000 ft. because the Earth’s overburden at these depths provides the least principal stress.