Determining stimulated reservoir volume from passive seismic monitoring

A method for determining a stimulated rock volume from microseismic signals, comprising:

• determining a position of each of a plurality of seismic events from seismic signals recorded in response to pumping fracturing fluid into a formation penetrated by a wellbore, the signals generated by recording output of a plurality of seismic receivers disposed proximate a volume of the Earth's subsurface to be evaluated, the signals being electrical or optical and representing seismic amplitude;
• determining a source mechanism of each of the plurality of seismic events;
• determining a fracture volume and orientation of a fracture associated with each of the plurality of seismic events from each source mechanism;
• successively subtracting a volume of each fracture, beginning with fractures closest to a wellbore in which the fracturing fluid was pumped from a total volume of a proppant pumped with the fracture fluid and continuing such subtraction for successively radially more distant fractures until the total volume of the proppant is associated with fractures;
• and
• determining a stimulated rock volume from the total volume of fractures associated with the volume of proppant pumped.