The Ministry of Foreign Affairs revealed on January 5, 2022 that Bangladesh 'has found the presence of 17-103 trillion cubic feet (Tcf) of ice like hydrate (gas hydrate) deposits containing huge amounts of methane'. The report has been interpreted as a 'blessing' and 'a ray of hope' for the country with the expectations that Bangladesh has all the opportunities to tap into the 'potential goldmine'.
Available reports suggest that the Oceanography Centre at Southampton UK, Petrobangla, BAPEX and local experts have made some study using the 3,500 km long 2D seismic survey data acquired by a French Company in 2007-08 and 3,000 km long 2D seismic survey data acquired by a Dutch company. Based on the available seismic survey data presence of gas hydrate was identified at water depths from about 1,300-2,850 meters below the seabed at a depth ranging from 220 to 440 meters in the Bay of Bengal. Limited seismic data was responsible for a speculative prediction for the 'potential' natural gas volume in the gas hydrates in the Bay of Bengal.
The USGS ( Fact Sheet, January 2017) informs that gas hydrate (crystal like solid formed of water and gas) represents a highly concentrated form of methane (1 cubic inches of gas hydrate may leave 0.8 cubic inches of water and 180 cubic inches of methane once the hydrate breaks down at room temperature and pressure). Gas hydrates are generally formed below the sediments of continental margins of the seabed typically at depths of approximately 500 meters (may also form at the deeper zones). Presence of gas hydrates have been identified in the sediments of the northern Gulf of Mexico, in the US Atlantic and Pacific Ocean margins, offshore of Oregon, Vancouver (Canada) Japan, India, South Korea and China and many other parts of the world. A part of gas hydrate presence is identified in the polar permafrost areas. Gas hydrates are identified in the regional scale using electromagnetic and seismic surveys. In the local scale drilled boreholes with the support of specialised tools help to identify gas hydrates (in the permafrost and sea floors) and their environment and characteristics. Published sources suggest that the gas hydrates (so far identified) may hold 106,000-876,000 trillion cubic feet (Tcf) of methane on the earth.
As the gas hydrates trap huge amount of methane gas in a compact form, it invites interests as potential energy sources. So far, some research studies enable short term gas productions from gas hydrate in the permafrost areas of Canada and in the United states and in the marine environment of Japanese and Korean offshore. The available information suggests that the depressurisation technique is used within the sediments to enable the gas from the hydrate (breaking into gas and water). Japan was successful in extracting some volume of natural gas from methane gas hydrate deposits under its sea (80 km off the coast of central Japan in the Pacific ocean). Despite the breakthrough, the Guardian reported (March 12, 2013) that the cost of extracting gas from the seabed was much higher than other form of gas extraction. The report further informed that the Japan Oil, Gas and Metals National Corporation and the National Institute of Advanced Industrial Science and Technology, a research institute of the government used their unique technology to reduce pressure in the methane hydrate concentration areas at a depth of 1,330 meters to extract gas through a well.
Chinese Global Television Network (CGTN) reported (March 26, 2020) that the country had extracted 861,400 cubic meters of natural gas (methane) from gas hydrate 'deposit' in the South China Sea during one month of trial production. It was a follow up trial production for extracting methane gas from subsea gas hydrate deposit in 2017. During a seven day experimental operation from 10 May 2017 Chinese scientists successfully extracted for the first time methane gas from Shenhu area of the South China Sea. China Geological Survey reported that the natural gas extraction from gas hydrate in the Shenhu area was accomplished by drilling 203-277 meters below the water depths of 1,266 meters. China Geological Survey further reported an accumulated 120,000 cubic meters of gas output in 2017 from gas hydrate.
Environmental activists are critical about the endeavours for methane gas extraction from gas hydrates. Methane is 25 times more active Green House Gas than carbon dioxide and extraction of methane gas from deep seabed gas hydrates may accelerate huge amount of methane gas release in the atmosphere if something goes wrong with the operation. There is a fear that the research endeavours for working out commercially viable technology for extraction of methane gas from gas hydrates may jeopardise the efforts to reduce Green House Gas emission to fight climate change. Climate scientists observe large volumes of methane gas release from the permafrost regions because of global warming. Scientists observed in 2008 in the East Siberian Arctic Ocean that the methane gas concentration level was up to 100 times above normal. It was the prediction then that extreme high methane concentration was possible from the area as the methane was released from 'pockets' of methane hydrate embedded in ice on the sea floor which had been destabilised by the warmer weather.
Gas hydrate formation is observed in the gas pipelines during natural gas production process when liquid water becomes condensed in the presence of methane at high pressure. If gas hydrates form, they may block the pipeline and gas processing plant equipment. They are generally removed by reducing the pipeline pressure and applying heat or by using chemical substances. However, the cleaning process demands careful control to avoid sudden release of huge amount of water and gas due to phase transition of the solid gas hydrate.
Researchers have been trying to work out economically feasible and commercially manageable technology for extracting natural gas from gas hydrate deposits. So far, extraction of methane from gas hydrate is in a nascent state. Therefore, it is pre-mature to anticipate any timeline when the commercially feasible technology and interested investment initiatives will come to explore the potential for gas hydrate exploration in the maritime boundary of the Bay of Bengal.
Mushfiqur Rahman is a mining engineer and writes on energy and environment issues.