Methane Hydrate Part I: The Science
In the coming months and years, you will be seeing more and more news stories about methane hydrate. Some will claim that it is the energy source of the future while others will warn that it will bring about the end of civilization as we know it. So what is methane hydrate and what drives both the excitement and the concern?
Let’s start with the basics. Methane (CH4) is the simplest of all hydrocarbons, consisting of a single carbon atom bonded to four hydrogen atoms. Methane is the primary component of natural gas and the two terms are often used interchangeably. To understand the different technologies which are used to extract and recover natural gas, you first need to understand how it was formed and why it came to be located in the various geologic structures it inhabits.
Natural gas and petroleum were both formed when ancient algae and bacteria died, fell to the bottom of the ocean, were covered in sediment, and then transported further below ground as a result of the movement of tectonic plates. Over time the organic matter from the decaying algae and bacteria were converted into a range of different hydrocarbon molecules. As you go deeper underground the temperature increases, which resulted in the formation of smaller and smaller hydrocarbons as depth increased. Therefore, the most shallowly buried organic material was converted into long-chain waxy material called kerogen, the material at medium depth was converted to shorter-chained liquid hydrocarbons (petroleum), and the most deeply buried portion was converted to the shortest-chained of all hydrocarbons, methane.
Since methane is a gas, if there was a viable pathway, it began to migrate upward towards the surface. Some methane found a open route all the way to the surface and escaped into the atmosphere where it was slowly converted to carbon dioxide. Some methane migrated part of the way to the surface until it collected under an impermeable layer of rock. These pockets of methane are what traditional natural gas wells tap into. A portion of the methane remained at its original depth, trapped in small isolated pockets. This is the methane that is currently being extracted via hydraulic fracturing (fracking).
Methane hydrates are formed when methane migrating up towards the surface encounters cold water in a high pressure environment. This occurs primarily on the ocean floor as well as under some areas of permafrost in Siberia and northern Canada. As shown in the graphic at the top of the page, methane hydrates consist of a lattice work of ice with methane molecules trapped inside the cages. Although estimates on the total amount of methane hydrate in the world vary significantly, it is clear that the amount of carbon contained in methane hydrates is on the same order of magnitude as the entire combined total of all of the other fossil fuels, including methane extracted by fracking, on Earth. It’s a truly staggering amount of natural gas.
The methane can be liberated from the hydrate either by heating it or by lowering the pressure on it. (There’s a rather fascinating, at least to me, potential discourse on thermodynamics and phase diagrams that I am glossing over here.). Heating is technically quite easy to do, but so much energy is lost during the process that this approach is not economically viable. Several experimental methods of lowering the pressure in the methane hydrate deposits have proven to be successful and, though challenges remain, it is clear that this approach will be both technically feasible and will become economically viable in several decades when the current glut of natural gas stemming from fracking operations tapers off. Experimental wells to tap into methane hydrate deposits are currently in operation in the U.S., Russia, Canada, and Japan.
Since the interest in the potential to extract methane from the methane hydrates is a relatively recent development, this reservoir has not typically been included in calculations for either global fossil fuel reserves or greenhouse gas emission projections. As I will address next week, adding methane hydrates into the mix of possible future fuels would have dramatic impact on the future of the planet.