A 4.6 magnitude earthquake emanating from the gas fields in northeast British Columbia during the summer was caused by hydraulic fracturing and is the largest induced seismic event ever recorded in the province, the BC Oil and Gas Commission has confirmed.
It surpasses two 4.4 magnitude induced earthquakes in Alberta and one of similar magnitude in B.C. last year that have been attributed to gas drilling activities, adding to growing concerns about a relatively new and controversial extraction process commonly known as fracking.
The commission, which regulates the industry, confirmed in August that fracking caused last year’s 4.4 event. It said in a statement this week that it has now determined the 4.6 earthquake “was caused by fluid injection during hyrdraulic fracturing from an operator in the area.”
“More and bigger,” is how John Cassidy, a seismologist with the Geological Survey of Canada, describes the pattern of earthquakes triggered by gas extraction. “The overall pattern is that there’s an increase in the number of induced earthquakes – and there is an overall or average increase in the magnitude as well.”
The 4.6 earthquake was big enough that workers at the drill site reported their pick-up trucks shook and power poles swayed.
Dr. Cassidy said the growing number of earthquakes is not a public-safety concern because most are so small. But there is no doubt that fracking in the area has led to the increase.
A study by Dr. Cassidy and colleagues last year reported that in 2002-03, before fracking started in northeast B.C., 24 earthquakes were recorded. But in 2010-11, during the peak of fracking activity in the Horn River Basin, there were 189 earthquakes. That mirrors a pattern in the United States, where a dramatic increase in earthquakes has occurred in parallel with the spread of fracking since 2009. In Oklahoma, the number of earthquakes has increased to two a day from two or three a year since drilling increased there.
“What we’re finding is with the hydraulic fracturing, we are seeing an increase in the number of induced earthquakes. These are almost all tiny, tiny earthquakes, however. They are not associated with all wells, in fact, it’s a very small fraction of the wells that show induced earthquakes,” he said.
Ken Paulson, chief operating officer of the commission, said the company operating the drill rig that triggered the 4.6 earthquake, Progress Energy Canada Ltd., followed regulations and stopped operations as soon as the magnitude was known.
In B.C. and Alberta, any seismic event of magnitude 4.0 or higher results in a suspension of operation until a mitigation plan is developed.
“We allowed them to continue operations with a reduced pump rate, but if another event were to occur of 3.5 or greater, you have to shut in again and we’ll try something different,” Mr. Paulson said.
The pump rate is the amount of fluid injected underground to fracture rock. He said no other significant earthquakes occurred at the drill site once the pump rate was reduced.
“We take this incident very seriously, Stacie Dley, a spokesperson for Progress Energy, said in an e-mail. “We will continue to be diligent and monitor our activities and adjust our operations as needed, such as decreasing fluid volume and pressure.”
Markus Ermisch, a spokesman for the Canadian Association of Petroleum Producers, said that while research has established a link between fracking and earthquakes, it has also shown that gas extraction can be done safely within the regulatory framework.Report Typo/Error