The analysis of human-caused low-intensity micro-earthquakes, including their magnitude and frequency, has become an important factor in mining. This is a consideration not only for the safety of mine personnel, but also for mining rates and mine stability which can have major impacts on business performance.
More and more, the practice of hydraulic fracturing is being used to precondition mines and lessen the magnitude of induced tremors as well as to reduce the number of rock fragments extracts.
A new report published in EPJ B assesses the impact of hydraulic fracturing on seismic risks such as micro-earthquakes, an important issue for worker safety and the continuation of mining operations. The article is written by Erick de la Barra, Pedro Vega-Jorquera and Héctor Torres from the University of La Serena, Chile, alongside Sérgio Luiz EF da Silva from the Politecnico di Torino, Department of Applied Science and Technology, Turin, Italy.
Hydraulic fracturing is the pumping of large amounts of fluids into a wellbore at high pressures. This has the effect of widening the fractures in the target rock formation. Does this translate into an increase in oil or gas yield from the rocks? —? Particularly from low permeability rocks like sandstone, shale, and sometimes coal beds.
The authors attempt to quantify the benefits of preconditioning with hydraulic fracturing by integrating previous investigation models to create a more realistic approximation of seismic failures.
This model was applied to a mine in the O’Higgins area of Chile to assess the induced seismic activity due to the effect of hydraulic fracturing. The team also took into account both the magnitude of the micro-earthquakes and the time elapsed between events.
This was done by considering 15 436 micro-earthquakes recorded between 2003 and 2008 in three sections of the mine. These were then compared according to whether the area had been preconditioned by hydraulic fracturing or not.
The results seemed to imply that hydraulic fracturing decreases the magnitude and micro-earthquakes.
The model the team worked on could also be used to predict seismic activity and to understand so-called earthquakes occurring on the red planet.
“In reference to the next stage of this investigation, our interest is to work with the problem when self-similarity is broken,” Vega-Jorquera said. “Thus, by considering the problem of multisources and relating them to multimodal distributions, it would imply to evaluate possible modifications of the seismic hazard by way of hydraulic fracturing.”