Comparing Energy Calculations - Hydraulic Fracturing and Microseismic Monitoring

In this paper we compare the input and output energy during a hydraulic fracture treatment to evaluate microseismic efficiency – the fraction of total input energy that is radiated as high-frequency seismic waves. We use three approaches to compute energy. “Injection energy” is the total energy input into the system. “Fracture energy” is an estimate of the work done during the deformation process to open a fracture. Finally, “radiated seismic energy” is the sum of all the energies for each high-frequency microseism, after converting the reported moment magnitudes into an energy based scale. We attempted to correct the seismic energy for missing data by estimating the Gutenberg-Richter b value and determine the contribution each event makes from a magnitude of -3 up to the maximum recorded magnitude. To our knowledge, such a correction has not been previously attempted, but it is very significant for determining the seismic energy. Injection, fracture and radiated seismic energy were calculated for 10 stimulated stages. Fracture energy was found to be 12-41% of the total injected energy, whereas the ratio of radiated energy to fracture energy ratio was consistently less than 1% for all stages.