In-situ stress dependence of wave velocities in reservoir and overburden rocks

Abstract

Seismic waves propagate through a stressed earth. Sonic waves recorded by a borehole sonic logging tool propagate in the near-well environment—which is also stressed, albeit under different stress conditions than the untouched formation far away. Cores excavated from within the earth undergo stress release, and are then reloaded in the laboratory—but hardly ever to the complete, fully anisotropic in-situ state of stress and pore pressure. Based on this, we easily recognize that stress sensitivity affects our ability to compare and correlate geophysical and petrophysical measurements of wave velocities. On the other hand, it also provides an avenue to extract information about rock stresses. As an example, the presence of abnormally low velocities in seismic or log data is evidence of high pore pressure.