A recent British Columbia Oil and Gas Commission study has concluded that fluid injection during hydraulic fracturing allegedly caused 38 seismic events between 2.2 and 3.8 on the Richter scale. BC Oil and Gas Commission, Investigation of Observed Seismicity in the Horn River Basin, August 2012. Focused on seismic activity in the northeastern Horn River Basin shale gas region between 2009 and 2011, the study purportedly found that human activity can alter previously stable subsurface conditions, leading to fault movement. It suggested that injected fluid flows into the pore system of the rock and preexisting fractures and faults, increasing pore pressure and opening an existing fault plane, thereby causing fault slippage. Potential causes identified in the report included “fluid injection for secondary recovery in hydrocarbon reservoirs, injection of waste fluids into deep rock formations, withdrawal of hydrocarbons from reservoirs and geothermal energy operations involving deep fluid injection.”
At the same time, however, the study ruled out wastewater injection wells as a source of the seismic activity. The Canadian report thus recommends submitting microseismic reports to monitor hydraulic fracturing for containment of micro fracturing, notification and consultation, and further study of the relationship between fluid injection rates and seismicity.