Methods and systems for seismic monitoring

A system for determining a depth z at which to install a borehole receiver in a monitoring borehole, comprising:

• at least one seismic source configured to generate, within a geologic reservoir, a set of surface waves having a plurality of frequencies in a frequency band of interest;
• at least one seismic receiver placed at a distance d from the seismic source, wherein the seismic receiver is configured to receive the set of surface waves;
• an antenna;
• a computing device operatively connected by the antenna to each seismic receiver, wherein the computing device includes an electrical circuitry, a memory storing program instructions and at least one processor configured to execute the program instructions to:
• determine a smallest frequency f1 of the plurality of frequencies;
• determine a surface wave velocity v for the smallest frequency f1;
• calculate a longest wavelength WL of the surface wave in the frequency band of interest based on
• WL
• =
• v
• f
• ⁢
• 1
• ;
• and
• a drilling system configured to install at least one borehole receiver in the monitoring borehole at the depth z equal to the longest wavelength WL.

A method of monitoring microseismic events in a geologic reservoir undergoing multi-stage fracturing, comprising:

• installing a near surface array including at least one seismic receiver at a surface of the geologic reservoir;
• installing a seismic source at a distance d from the at least one seismic receiver;
• generating, with the seismic source, a set of surface waves having a plurality of frequencies in a frequency band of interest, wherein the frequency band of interest is in a range of about 10 Hz to about 30 Hz;
• operatively connecting a computing device to receive measurements from each seismic receiver, wherein the computing device includes an electrical circuitry, a memory storing program instructions and at least one processor configured to execute the program instructions for:
• determining a surface wave velocity v for a smallest frequency f1 received by the at least one seismic receiver;
• calculating a longest wavelength WL of the surface wave in the frequency band of interest based on
• WL
• =
• v
• f
• ⁢
• 1
• ;
• installing, by a drilling system, at least one borehole receiver in a monitoring borehole at a depth z equal to the longest wavelength WL in the monitoring borehole;
• receiving by the computing device, from the at least one borehole receiver, seismic signals;
• and
• identifying, by the computing device, the microseismic events caused by the multi-stage fracturing.