Microseismic Data¶
Measurement Earthquakes¶
Seismologists currently prefer the moment magnitude scale \(M_w\) for measuring the size of earthquakes. The moment magnitude scale measures earthquake size in terms of energy release, which is based on the seismic moment of the earthquake. This works over a wider range of earthquake sizes than the traditional Richter scale. The seismic moment, denoted by \(M_0\), is defined, in a scalar form, by:
where:
- \(\mu\) is the shear modulus of the rocks involved in the earthquake, \(\mathrm{Pa}\)
- \(A\) is the area of the rupture along the geologic fault where the earthquake occurs, \(\mathrm{m}^2\)
- \(D\) is the average displacement on \(A\), \(\mathrm{m}\)
Both \(A\) and \(D\) can be calculated by using mathematical modeling of the seismograms. The seismic moment \(M_0\) has dimensions of energy (in SI units, the Joule).
Then the moment magnitude scale \(M_w\) is defined based on the seismic moment \(M_0\) as:
From Eq. (2), we can see that the energy released increases \(32\) times for each unit increase in the moment magnitude scale.
Microseismic Technology in Hydraulic Fracturing¶
During hydraulic fracture stimulation, the stress-induced deformation on pre-existing structures or the creation of new fractures releases energy by generating short duration acoustic wave emissions. Such emissions are referred as microseismicity or microseisms that may in some cases felt as small as the moment magnitude of an earthquake (\(-1\) to \(-3\)). The microseismic emissions then can be detected by microseismic detectors, known as geophones, and processed into images to enable live monitoring of hydraulic fracturing progress, including locating the hydraulic fracture(s), revealing the fracture geometry, determining the fracture propagation pattern etc. Currently, the microseismic imaging technology has proven a useful and practical approach for in-situ monitoring of fracture growth during hydraulic fracture stimulation.
Microseismic Table¶
In FrackOptima, the Microsiesmic Table is used to input microseismic data so the user can compare it with the simulation results. The East, North, Depth columns specify the location of the microseismic sources that have been detected, and the Moment Magnitude column specifies their magnitudes. The microseismic table is designed for simulation with practical input data that has already been treated, so it can be easily compared to the fracture geometry obtained by FrackOptima.