HYDRAULIC FRACTURING FOR IN SITU STRESS MEASUREMENT AND RESOURCE EXPLOITATION: THE LEGACY OF M.K. HUBBERT

In his classic paper, “Mechanics of Hydraulic Fracturing”, published with David Willis in 1957, M.K. Hubbert established two basic principles about hydraulic fracture initiation and propagation that have led to its becoming the foundation for in situ stress measurements at depth and an extraordinarily effective technique for improved recovery from oil and gas (and geothermal) reservoirs around the world. Hubbert and Willis established the principle that hydraulic fracture propagation would always be in a plane normal to least principal stress because such an orientation minimizes the energy necessary to propagate the fracture. They further demonstrated the principle that the initiation of hydraulic fractures at the wall of a pressurized wellbore is governed by the concentration of stress around the wellbore. The magnitude and orientation of far field stress controls the location and pressure at which hydraulic fractures initiate at a wellbore wall.

In this talk I will demonstrate how the principles established by Hubbert and Willis have led to a suite of techniques that makes measurement of the complete stress tensor at great depth possible. Such stress measurements have proven important in establishing the frictional strength of the brittle crust and the fact that it is in a state of frictional failure equilibrium. This, in turn, enables us to address a wide range of problems of interest to Hubbert in other contexts, such as crustal pore pressure and permeability. I will also review how stress measurements made with the hydraulic fracturing technique allow us to examine some unusual aspects of the relationship between pore pressure and faulting proposed by Hubbert in terms of the effective stress principle.

Finally, while the manner in which hydraulic fracturing is used for resource exploitation is generally well-known, I will review a number of novel aspects of this, such as the role hydraulic fracturing may play in timely issues such as CO2 sequestration.