DETERMINING IN-SITU THE RELATION BETWEEN SEISMIC VELOCITY AND STATE OF STRESS IN AN UNDERGROUND FORMATION

摘要

A method of determining in-situ a relation between the seismic velocity and the state of stress in an underground formation located under a surface subjected to time-changing surface loading conditions, which method comprises selecting a relation between the seismic velocity and the state of stress containing at least one unknown parameter; placing a seismic source at surface or in a borehole penetrating the underground formation, and a seismic receiver at a distance from the seismic source at surface or in a second borehole; determining at two different times the seismic velocity of the formation along a path from the seismic source to the seismic receiver; converting the difference in surface loading conditions at the two times in a difference in states of stress in the underground formation; and calculating the unknown parameter(s) to obtain the relation between the seismic velocity and the state of stress in the underground formation.