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Flammable ice: Understanding marine clathrates

Exploring marine clathrates, the co-existence of flammable gas trapped in a cage like structure made of ice.

To quote Captain Nemo, Jules Vernes’ hero from Twenty Thousand Leagues Under The Sea, “The sea is a vast reservoir of nature. It was through the sea that the earth, so to speak, began.”

Over the last few centuries, the human civilization has unearthed much wealth from the seas and oceans. Would you be surprised if we told you that you can find ice that can catch fire under the oceans? Well, be prepared to be intrigued as we take you on a journey of learning about marine clathrates found in and under the oceanic floor and how it can be of use to humankind.

Marine clathrates – an introduction

A chemistry textbook would define a clathrate as a molecule or molecules having a cage-like structure trapping another component within its crystal structure. It is derived from the Latin word clatratus which translates to bars or lattice structures. These clathrates that occur on the ocean floor and are often seen as deposited on the seabed are called marine clathrates. In an almost Stockholm syndrome-ish rationalization, the cage structure is called the host (even if it’s trapping its guest which is the molecule inside the lattice). It is rather intriguing that two components exactly opposite in nature and in properties co-exist in such harmony. Kidnapping? On second thoughts, a marriage more like.

When the cage-like structure is made of water molecules and it has methane gas trapped in it, it’s called a methane hydrate. In layman’s language, it is called as fire ice. This name comes from the fact that, on being subjected to higher temperatures, the ice melts, water drips and methane being highly flammable, catches fire.

It is to be noted that these clathrates hydrates trap not only methane gas but also, a few other gas molecules that are light in weight. Some commonly seen examples are hydrogen, nitrogen, oxygen, argon, xenon etc.
Important factors

Structure of a gas hydrate (methane clathrate) block embedded
in the sediment of hydrate ridge, off Oregon, USA.

So what controls the formation and sustenance of these captors and captives? Like most systems that exist on this planet, pressure, temperature and availability of a feasible environment are key factors in the formation of marine hydrates. Abundant water and methane are obviously needed. The main two factors are temperature and pressure. The right concoction of higher pressure and lower temperature has to be reached for methane that is primarily a gas under ambient conditions of pressure and temperature (atmospheric) to form a hydrate and maintain its equilibrium. The type of rock and the composition of this rock also affects their formation. Salt content or salinity along with the presence of gas other than methane affect gas hydrates. These gases, commonly, are carbon dioxide, hydrogen sulphide etc.

Where are these exquisite fuel “cubes” found on our planet? If you look at the world map and draw an outline along the continents (well most places, not all, but you get the gist), that’s where they occur deposited within certain types of rocks. These locations have the perfect recipe for their occurrence – abundant methane, water, high pressure from the water column being exerted on the raw material and low temperatures in the sea. Interestingly, they are also found on land. Polar Regions are the one place where you will see their existence. They are found below the permafrost.

Formation of marine clathrates in nature

The discovery of natural methane hydrates

In the quest to look for alternative fuel sources, the last ten to fifteen years has seen immense research into marine clathrates as a fuel source since its discovery in Russia back in the sixties.

It all started back in the nineteenth century when hydrates resided within four walls of a laboratory and at the mercy of their human creators. For the longest time, scientists had no reason to believe that hydrates can occur under natural circumstances. This was until the 1930s. The oil and gas industry was gaining speed. It was noticed that the flow of gas was being blocked by these mysterious structural formations. This led to investment in research work to impede the formation of gas hydrates in pipelines. These pipelines created a natural environment for the hydrates to form at low temperatures and high pressures.

 

Worldwide distribution of confirmed or inferred offshore gas hydrate-bearing sediments.
Worldwide distribution of confirmed or inferred offshore gas hydrate-bearing sediments.

In the 1960s, during the ongoing exploration and production of gas wells in the Messoyahka gas field of the Western Siberian basin, methane hydrates were first encountered occurring in a natural state followed by several other global sightings. Obtaining core samples is a regular feature of any drilling program in oil and gas explorations. These samples are usually rocks dug out of the earth in tubes. During a deep sea drilling program off the coast of Guatemala, the core samples recovered showed a presence of hydrate-bearing rocks. This discovery was the dawn of viewing them as a natural methane source and the possibility that these are a widespread occurrence in nature

Methane hydrates as an energy source

Methane is a widely used source of fuel and is relatively clean. It is also a large component of natural gas. But why pick methane hydrates as an energy source? They have great potential to be optimised and monetised. At normal surface temperature and pressure, one cubic foot of solid methane hydrate will release about 164 cubic feet of methane gas. It has been estimated that globally, reserves in place would be about 700,000 trillion cubic feet (Tcf) of methane within hydrates.

Having said that, mind you, not all of it is economically feasible for recovery. Picture it as a pyramid. The recoverable varieties are found at the top of the pyramid structure. Hundreds of Tcf has been estimated to be found in the arctic sandstones. While the marine sands seem to hold 10,000s of Tcf of methane.

‘Burning ice’

The lower you travel down the pyramid the harder it is to make an economically feasible recovery. 100,000s of Tcf are located in this part of the pyramid. Each of these deposits is in a different geological setting and have their own recovery challenges. Several oil and gas majors have taken a keen interest in bringing methane to surface level. From an international standpoint, countries like the USA, China and Japan are voraciously looking into methane hydrates as a fuel source. Japan is one of those countries that are ecstatic to invest in this. As a country with high fuel import costs, they’ve invested excellent research and were the first ones to successfully produce methane from hydrates.

In our own backyard, India is showing a keen interest in the commercial production of hydrates. India has set aside about $56 million for research alone. This has been an ongoing area of interest, in fact, since 1996. Several leading organizations are working towards defining the zones of interest in the continental shelf regions of both, the Bay of Bengal and the Arabian Sea. Research is also indicative of gas hydrate deposit off the coasts of the Krishna-Godavari river deltas and the Andaman & Nicobar Islands.

Understanding its effects on the climate

As a civilization going through a major cycle of climate change, we are asked to assess environmental impact. This topic will surely perk the interests of our climate change enthusiasts and so it should. Methane is widely known as a greenhouse gas and is perfectly capable of affecting Earth’s carbon cycle. Much research needs to be completed before we go “El Dorado” on hydrates. 

Do we know when to stop? We can’t be greedy and turn an exploration mission into an exploitation mission. That won’t turn out well. Are we well equipped to deal with introducing additional methane into our environmental system? Minimal environmental impact and maximum economic recovery is an equilibrium that should be reached after careful research and considerations before we move ahead.

What do we think so far?

Yes, it is fascinating and sounds like the answer to several problems that comes with the paucity of non-renewable fuels. Hell, if someone told us there exists ice that we can set on fire and they exist in rock under the sea, it would seem like a fairy tale. As we venture into newer possibilities of fuel sources, it is key to have a thorough understanding of its repercussions, its pros and its cons. If used correctly, they are the answer to our energy problems as they are plentiful, abundant and easy to mine. There possibly is more methane present in hydrates than in all petroleum reserves globally. It’s no secret that the oil industry has been on the decline for the last three years due to several (geopolitical) reasons. Gas hydrate production is a realm of unconventional energy potential which has brought together several big powers to collectively invest in research into exploring, developing and producing hydrate fields. Once a nuisance in the oil industry, hydrates might now actually be the prophet that leads an exodus of transferable skills (geologists, petroleum engineers, etc.) into the happily ever after.

Written with inputs from Andrea Dsilva, Geoscientist and oil industry specialist

This article was first published as a part of the May 2018 issue of Digit magazine. To read Digit’s articles first, subscribe here. You could also buy Digit’s previous issues here.

Sanket Nikte