The US Geological Survey (USGS) cited estimates of the methane (CH4) trapped in global methane hydrate (aka methane clathrate, Fire Ice, etc.) deposits are 3600 times more than the 2016 US consumption of natural gas. The 2016 US consumption of natural gas (natural gas is mostly methane), according to Donn Dears, was 27.5×10^12 cubic feet.
The estimate of trapped gas in the deposits ranges from 10^17 to 5×10^18 cubic feet*. Those are estimates and further those estimates probably include some amount of methane hydrate that will never be economical to produce. Even so, oil reserves that were supposed to have peaked many years ago, keep growing because of new technology. eg. Fracking. So, who knows?
*(For the non-engineer or scientist that might not know how much that is, it can be restated as 1 followed by 17 zeros to 5 followed by 18 zeros cubic feet of natural gas.)
Where are the hydrate deposits found?
Methane hydrate deposits are found (or predicted) to be associated with continental margins and onshore permafrost areas. The chart below global areas where deposits are to be found.
First, let’s discuss where the methane originates. Methane is largely produced by micro-organisms that act on the plankton that has accumulated deep in the ocean floor sediments. In the upper layers of the sediment where the temperature and pressure are suitable, the rising CH4 bubbles are captured in very cold water and the hydrate is formed. While methane produced biogenically is considered the most widespread source, there is another source. Thermogenic methane is produced where high pressures and high temperatures cook organic matter.
Methane hydrates are ice-like combinations of gas and water that form naturally and in great quantities. Water molecules, which make up approximately 85% of a gas hydrate, form a crystalline lattice. The lattice is stabilized by the methane molecules that are enclosed in the lattice cavities.
On the left: Methane hydrates occur worldwide. This ice-like block with a honeycomb structure was obtained from the sea floor during a research expedition off the coast of Oregon.
On the right: In methane hydrates, the methane gas molecules are tightly enclosed in cages composed of water molecules. Increasing temperatures render the cages unstable, the gas escapes.
The formation of the hydrate only occurs under certain combinations of pressure and temperature. The pressure has to be in excess of 35 bar (about 515 psi) and with temperature from 0 to 4 C (32 to 39F).
The phase diagram chart, below, shows the relationship of pressure and temperature within the stability zone:
Summary Graphic 2: Phase diagrams illustrating where methane hydrate is stable in marine (A) and permafrost settings (B). Hydrate can exist at depths where the temperature (blue curve) is less than the maximum stability temperature for gas hydrate (given by the hydrate stability curve in orange). Pressure and temperature both increase with depth in the Earth, and though hydrates can exist at warmer temperatures when the pressure is high (orange curve), the temperature in the Earth (blue curve) gets too hot for hydrate to be stable, limiting hydrate stability to the upper ~1km or less of sediment.
In methane hydrates, the methane gas molecules are tightly enclosed in cages composed of water molecules. Increasing temperatures render the cages unstable, the gas escapes.
Diagram and summary are from “A GLOBAL OUTLOOK ON METHANE GAS STABILITY”
A graphic display of the locations of the methane hydrate are illustrated. Note that only about 1% of the methane hydrate is on shore.
Mining The Deposits
The technique is to drill down through the ocean sediment to the deposit.
The technique on shore is similar with a drilling through, typically, sandstone into the deposit. But from there, it is tricky.
“Economic deposits of hydrate are termed Natural Gas Hydrate (NGH) and are unique in that they store 164 m3 of methane, 0.8 m3 water in 1 m3 hydrate. “ .
From the arsTechnia posting titled” Japan, China have extracted methane hydrate from the seafloor” we learn this:
“This month, teams from Japan and China have successfully extracted methane hydrate, a hydrocarbon gas trapped in a structure of water molecules, off the seafloor.”
“Such vast reserves of fossil fuels are untapped because of how difficult it is to extract them. As a 2012 post from the Energy Information Agency (EIA) stated, until recently, methane hydrates “provided more problems than solutions.” Preventing their formation around deep-water oil and gas drilling operations has been a crucial part of planning ocean wells. The “ice” substance that contains the gas generally can’t just be picked up off the seafloor because it disintegrates outside of its high-pressure environment. The South China Morning Post wrote that current extraction efforts involve machinery “to depressurize or melt [the methane hydrate] on the sea bed and channel the gas to the surface.”
“The researchers used a platform oil rig in the South China Sea and were able to extract about 113,200 cubic meters of methane hydrate, with an estimated 99.5 percent methane content. The Straits Times says China is planning two or three more tests to study extraction methods.”
“The Japanese effort tapped methane hydrate off of Japan’s central coast in early May. That study is ongoing. Japan has been pursuing methane hydrate extraction for some time, too. A study in 2013, “ended abruptly after less than a week due to problems with sand flowing into the well,” according to Reuters.”
An illustration of the mining of these deposits is below:
The US and other nations are working on these problems. One technique that is said to have worked was injecting CO2 into the deposit where the CO2 exchanges places with the CH4. The CH4 is then collected as a gas with no extra water to separate and dispose. Using this as a means of disposing the CO2 would seem to be a good method, but most of the CO2 sources would probably be remote from the recovery operations.
The environmental groups have a list of things that could go wrong with mining methane hydrate. Blowouts where huge quantities of CH4 would be released to the atmosphere; CH4 being a more potent greenhouse gas than CO2 might be a problem; Causing landslides of sediment; and Just another source of fossil fuels that would delay the advent of renewables. Look up most any environmental group website and search for methane hydrate.
For the moment, my guess is that the economics are the biggest hurdle. Japan is the world’s largest importer of LNG and the cost of energy has not been lessened by the shutting down their Nukes. They have a lot more incentive than most countries and they are clever people, so maybe they will make a technological breakthrough. The locations are likely to be remote and that will mean costly new systems to get the natural gas to market.