ABSTRACT
A comprehensive description is provided of the most common technique of quantitatively estimating the in situ state of stress at depth in the Earth’s crust. Basic concepts central to crustal stress measurement are first provided as motivation. The equations of stress concentration around the borehole resulting from far-field in situ stresses and borehole fluid pressure provide the basis of the theory of hydraulic fracturing. The advantages and disadvantages of the various borehole testing setups are discussed with particular emphasis on straddle-packer assemblies that allow for the most reliable stress measurements. The recommended protocols for a multi-cycle pressurization stress measurement test are described and justified in light of expected behavior of fracture initiation and propagation. This is assisted by illustrative idealized pressurization curves that highlight the critical pressures that are interpreted in terms of the prevailing in situ principal stresses. The effect of the differing assumptions with regards to breakdown, fracture closure, and fracture re-opening on the determined principal in situ stresses is reviewed. This highlights the complexity associated with computing the magnitude of the greatest horizontal compression. Finally, the various directions of future research on hydraulic fracturing stress measurements are described.
