Methane: The Arctic's Buried Treasure
By Kira Coley
In pursuit for the Arctic’s buried treasure: methane
Trapped beneath permafrost and ocean sediments, the release of the world’s largest natural gas resource, methane, has become a hot topic for international research. As rising temperatures continue to warm the Arctic region, the vast frozen fields of gas, known as gas hydrates, grow unstable beneath the retreating ice. The Centre for Arctic Gas Hydrate, Environment, and Climate (CAGE) strives to address one of the greatest scientific uncertainties: how much greenhouse gas threatens to escape the sub-seabed sediments and what will this mean for (1) the global climate gas budget, and (2) the Arctic marine ecosystem?
Located at the gateway to the Arctic, the Arctic University of Norway in Tromsø (UiT) is the northernmost university in the world. With an innovative research group and a suite of advanced technology, CAGE scientists study methane release from gas hydrates beneath the Arctic Ocean to unveil potential impacts on marine environments and global climate systems.
CAGE director, Jürgen Mienert, explains, “We have several connected themes so that we can understand the complete carbon recycling system related to gas hydrates from the sub-seabed to the atmosphere. First, we accomplish 4D time-lapse seismic studies to visualize potential sub-seabed gas hydrate accumulation and gas migration pathway areas. Second, we work in the water column taking both ocean spatial and methane gas concentration measurements using different types of laser spectrometers but also test new technologies in collaboration with the Laboratoire de Glaciologie et Géophysique de l’Environnement (LGGE) in Grenoble, France. Oxygen isotope measurements identify where the methane sources are coming from, and whether they are shallow biogenic or deep thermogenic sources.”
“When the methane reaches the upper water column where you have light, an interesting scenario develops, particularly for the Arctic, you have a higher biological productivity. In the future, if increases of methane release in a more ice-free Arctic Ocean occur, one could hypothesize that there will be an increase in biological productivity and thus, ocean life. Once methane reaches the air, we use airplanes in cooperation with National Centre for Atmospheric Science, Department of Chemistry; the University of Cambridge and the Facility for Airborne Atmospheric Measurements (FAAM); Cranfield University; and Norwegian Institute for Air Research (NILU). Together we investigate the gas compositions and the concentration of methane above those gas hydrate fields – this is a typical cross-disciplinary research scenario for us.”
CAGE uses and develops long-term multi-sensor ocean observatories, cabled and non-cabled, together with Kongsberg Maritime and Norway’s Institute of Marine Research (IMR). The cabled observatories allow scientists to utilize these stations for a decade on the seabed. The non-cabled observatories remain in key locations for one year and provide the site flexibility required by researchers working in demanding and complex environments.
Developing new high-resolution geophysical technology within acquisition, processing and interpretation, CAGE wants to directly detect and image marine methane hydrate reservoir dynamics in the Arctic, based on acoustic and electromagnetic data and inverse modeling. To date, calculations of the methane and its ice form, gas hydrate, differ substantially across studies. While the most cited global estimate is 10,000 gigatonnes (or one billion tons), a recent calculation suggests this was hugely misjudged and global estimates of 74,000 Gt of methane stored as hydrates is more likely.
How much is beneath the seabed is dependent on the supply of biogenic and/or thermogenic methane, and the sedimentology – how much pore space is available to build up the gas hydrate. In addition to these, the pressure and sub-seabed temperature determine the zone where hydrates can exist. The gas hydrate stability zone – the area in which the hydrates are still stable – sometimes several hundred meters deep in the Arctic, together with the type of sediment, methane supply and heat flow rates, provides a basic quantification of how much methane hydrate may be available.
The other parameter that may be substantial is the variability of the geothermal gradient or the heat flow within the sediment. The heat flow determines how stable the fields are over an extended period as well as the ocean warming from above the sea floor, contributing to the melting of hydrates.
“Heat flow measurements in the Arctic are very rare, and that means you have a high uncertainty in your calculations. The other uncertainty relates to permafrost. We are still in what I would call the ‘post-glacial’ time, meaning we still see the effects of the ice ages today. Particularly in the Arctic, areas as far as the Barents Sea and north of Norway were covered by massive ice sheets several kilometers in thickness, which caused high pressure and low temperature on the sub-seabed. So, the methane hydrates stability zone was much more extensive than it is today. They covered an enormous area of the Arctic – another reason why we have such a high uncertainty in our calculation of a very dynamic system on geological time scales. To be more robust, we use observations together with modeling exercises using ice sheet conditions, pressure, low temperature, and retreat of the ice sheet to see where we may still have both permafrost and hydrates in those Arctic gas hydrate fields.”
In July, CAGE undertook an expedition to the sedimented and gas-hydrate charged Vestnesa Ridge, offshore Svalbard. Vestnesa lies on the active ridge system of the oceans, which are undersea mountain chains formed by tectonic movement and stretching around the globe. Utilizing advanced technology, an expert team of engineers, operators and researchers battled the elements, drilling at 1,200 meters of water depths down into the gas-hydrated sediments in an attempt to determine how much methane is captured beneath the Arctic sub-seabed and, when released, how it will impact the regional Arctic marine ecosystems. The expedition was in collaboration with MARUM in Germany and their mobile drilling rig, MeBo, which was used to acquire gas-hydrate core samples from the sediments.
Mienert describes, “During this summer we had the drilling operation based on our 3D and 4D images. But CAGE undertook several expeditions this year that also focused on retrieving data regarding the development of marine ecosystems in the dark ocean floor areas of the Arctic. We also investigated the impact of methane release on benthic fauna as we expect an expansion in those benthic fauna regions based on the increase methane release from the seabed. The third operation was in deep water, where we operated a deep-sea ROV at 2,000m. This activity was also related to investigating biofauna in the dark, chemosynthetic communities, the conditions they live in and the search for new species – these highly specialized species may produce chemical compounds that can be of interest for pharmacy and medical purposes in the future.”
CAGE’s goal is to provide new information and improve our understanding of the variability of methane release, which can be related to retreating glaciers from the last glacial until today. Using a suite of specialized technology and modeling data, the scientists will reconstruct changes in the Arctic region over million, millennial and decadal time scales.
“In the Arctic, we wish to drill deeper reaching beyond the base of the gas hydrate stability zone. So, the next phase for us is to work with industry to get a commercial vessel to one of the gas hydrate fields, which will allow us to recover more of the gas hydrated sediment formations. We can then understand the geological system that is giving you the boundaries, so that we can calculate total amount of methane hydrate that may be stored in the Arctic marine sub-seabed environment. That, of course, may relate to unconventional energy resources, an interest for industry. So we are looking at where the gas hydrate fields are; how much methane is stored there, what type of sediment exists; how it will impact the environment and global climate; whether the technology is ready to drill the gas hydrate fields, and if not ready, what is needed to extract the gas hydrates in the future.”
Currently, the Arctic region produces about one-tenth of the world’s oil and a quarter of its natural gas. New estimates suggest that a significant fraction of the world’s petroleum reserves still lie undiscovered within the Arctic.
“The most exciting places for those in the industry are conventional hydrocarbon fields, where you have oil and gas directly beneath a gas hydrate field as it will allow you to extract gas from two reservoirs. But there are some challenges both in terms of technology and environmental impact, that need to be better understood. In the long term, we hope to get a team of international geoscientific experts with an Integrated Ocean Discovery Program (IODP) to the Arctic. The hope is to use the Japanese ship Chikyu, which recently drilled gas hydrates offshore Japan and India. They carried out the largest expedition for drilling and mapping of gas hydrates ever, with great success.”
“In the future we will use more observational data and modeling scenarios to identify target areas and increase success. We have more observations now in the Arctic than ever before, so the integration of observations and modeling is the key to identifying the areas in the Arctic that are of highest interest for environmental and climate research,” concludes Mienert.
(As published in the November/December edition of Marine Technology Reporter)
Other stories from November 2016 issue
- BG Group & the FlatFish AUV page: 8
- AUV Mission in the Great Lakes page: 18
- Uncontended Voice and Data Through TDMA Networks page: 20
- Brexit: What’s in Store for the Subsea Sector? page: 28
- Methane: The Arctic's Buried Treasure page: 34
- Tech File: Blue Robotics BlueROV2 page: 40
- Preview: OI North America 2017 San Diego page: 50