A new methodology for estimating field horizontal stress from microseismic focal mechanisms

摘要

The full stress state in a formation is characterized by the directions and magnitudes of the three principal stresses. It is common practice to take the vertical stress, σ_v, and the minimum and maximum horizontal stresses, σ_(hmin) and σ_(Hmax), as the principal stresses in unconventional reservoirs. Considering the relatively high depth of most unconventional reservoirs, which results in a very high vertical stress magnitude, this assumption holds true in most cases unless a geological feature such as a fault or fold changes the stresses locally. The magnitude of vertical stress can easily be determined by integrating the density of overburden rocks from density logs. A good estimate of σ_(hmin) magnitude can be obtained from well test results such as a mini-frac test or a diagnostic fracture injection test. The magnitude of σ_(Hmax), however, remains the most challenging stress component to determine.