A team of experts formed by the Ministry of Energy and Mineral Resources has visited Sylhet to find out the cause of the recent tremors that shook the city within the span of nine days.
On Sunday, they visited several wells of Sylhet Gas Fields Limited in Haripur and Golapganj areas of the district.
Quoting the team members, Senior Meteorologist in Sylhet Saeed Chowdhury said that drilling at the ninth well of Haripur field had remained stopped for the last few months.
The committee was formed with Petrobangla Director (Product Sharing Contract) Engineer Md Shahinur Islam as the convener and a general manager (GM) level officer of Bangladesh Petroleum Exploration and Production Company Limited (Bapex), a GM of Petrobangla and two professors of Dhaka University as members.
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Md Shahinur Islam told Dhaka Tribune that they had collected information in Sylhet from Friday to Sunday, and would submit a report to Petrobangla soon. “The results will be shared with other organisations through a proper channel.”
The five-member team on Sunday also went to Raja GC High School, where one of the buildings developed cracks due to the latest earthquake that hit on June 7. Earlier, the city corporation authorities shut down 25 risky buildings.
The experts had a meeting with Sylhet Divisional Commissioner Md Khalilur Rahman on Saturday, while the Petrobangla director visited the Haripur gas field.
Bangladesh has long been extracting gas and oil from some major wells in Sylhet, which is located near the Dawki Fault, responsible for a number of devastating quakes for over a century, and most of the epicentres were near the city, according to the United States Geological Survey (USGS).
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Drilling at the ninth well in Haripur field commenced on October 1 last year to unearth natural gas, mineral gas or crude oil. Officials said in January that the new gas reserve had been found at a depth of 1,998 meters underground and that it would produce 188 barrels or 7 million cubic feet of natural gas per day.
In quest of natural gas, the then Pakistan Petroleum Limited (PPL) in 1955 commenced drilling activities at Haripur, a small village under Jaintapur police station in Sylhet district near the border.
There were two moderate earthquakes in Sylhet on May 29 and May 30 accompanied by three aftershocks. Another tremor was felt on the evening of June 7.
Last year, two strong earthquakes hit Sylhet city – a magnitude 4.2 tremor on June 3 and a 4.5 one on January 27.
Concerned by the series of tremors, the Sylhet City Corporation (SCC) authorities began working with Shahjalal University of Science and Technology (Sust) to identify the risky buildings in the city. On Sunday, the experts’ team also sat with Sust Dean of the Faculty of Applied Science Dr Mushtaq Ahmed.
In 2009, the government announced that 24,000 out of the 52,000 buildings surveyed in Sylhet town were at risk from earthquakes.
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This result emerged from a survey conducted in Dhaka, Chittagong and Sylhet cities in 2008-09 under the Comprehensive Disaster Management Program (CDMP) project under the Ministry of Disaster Management and Relief.
At the time, experts suggested demolition or retrofitting of risky buildings to avoid loss of lives and a massive economic loss.
What the scientists say
Scientists have long been talking about a possible link between earthquakes and gas and oil drillings.
A study by the Oklahoma Geological Survey conducted in 2015 linked earthquakes in Oklahoma, Texas and other parts of the US to the practice of injecting wastewater from oil and gas operations deep underground, according to a report of the Wall Street Journal.
They considered it “very likely” that most of the hundreds of earthquakes in the state’s center in recent years were “triggered by the injection of produced water in disposal wells.” Produced water is salty fluid that naturally flows up wells along with oil and gas, the WSJ report adds.
In Texas, a team of college and federal researchers headed by scientists at Southern Methodist University also concluded that a string of earthquakes that began in 2013 northwest of Fort Worth was also likely caused by wastewater injection.
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To produce oil and gas from shale formations, it is necessary to increase the interconnectedness of the pore space (permeability) of the shale so that the gas can flow through the rock mass and be extracted through production wells. This is usually done by hydraulic fracturing or "fracking".
Fracking intentionally causes small earthquakes (magnitudes smaller than 1) to enhance permeability, but it has also been linked to larger earthquakes. The largest earthquake known to be induced by hydraulic fracturing in the United States was a magnitude 4 earthquake in Texas, said United States Geological Survey (USGS).
In addition to natural gas, fracking fluids and saltwater trapped in the same formation as the gas are returned to the surface. These wastewaters are frequently disposed of by injection into deep wells. The injection of wastewater and saltwater into the subsurface can also cause earthquakes that are large enough to be damaging.
The USGS also says that wastewater disposal is a separate process in which fluid waste from oil and gas production is injected deep underground far below ground water or drinking water aquifers. The largest earthquake known to be induced by wastewater disposal was a magnitude 5.8 earthquake that occurred near Pawnee, Oklahoma in 2016.
