As a geologist, when chatting to people I am always surprised when they don't know what the term "black shale" means, considering all of the media coverage on fracking and shale gas. This post aims to explain what the term means, how they were formed in the past and how black shale formation in the present will reduce the amount of carbon dioxide in the atmosphere.
Black shales are fine-grained rocks, made up of mud-sized particles, with very high levels of TOC (Total Organic Carbon). TOC refers to the amount of carbon present in a rock sample which is bound in an organic compound. The organic carbon comes from dead animals, plants and faeces which were incorporated into the mud at the time it was laid down.
If the rock, and organic carbon, have been buried to sufficient depth to "cook" (temperature increases by approximately 1 degree C for every 100 m you go into the Earth ), then the organic carbon can start to form hydrocarbons: oil (less cooking) and gas (more cooking). If a rock has more than 2% TOC it is said to make a good source rock (4% TOC is a very good source rock). Black shales frequently have high TOC levels and it's the high TOC content which also gives the rock its black appearance.
Source rocks are rocks which, once cooked, produce hydrocarbons. Most oil and gas extracted around the world started out in a black shale, the source rock, but the hydrocarbons may have since moved into another rock (a reservoir rock), such as a sandstone. Where they have moved into a reservoir rock, this is known as a conventional play, and most oil and gas wells extract their hydrocarbons from sandstones. Where the hydrocarbons are still in the black shale, the technique of "fracking" needs to be employed to extract them because black shales are too fine-grained to allow the hydrocarbons to flow towards the well. Sandstones have more space between the grains, allowing the hydrocarbons to move.
So why do black shales have such high levels of TOC?
This can be summarised in three words: productivity, preservation and dilution.
To have high TOC levels preserved in a rock, you first need a large amount of organic matter to be produced; that means a lot of life to be living, pooing and dying. This is known as high productivity.
Once you have your high productivity, you still need that organic matter to be preserved. That means you need to limit its breakdown by bacteria (also known as rotting). The best way of doing this is restricting the amount of oxygen available: oxygen is required by bacteria to most efficiently break down organic matter. With limited oxygen, more organic matter is preserved.
Even if you have then produced a lot of organic matter, and preserved it, your rock will still not have a high TOC if there is a lot of sediment coming in because TOC is a measure of the total percentage of organic matter compared to the amount of other rock. With a high sedimentation rate, the organic matter will become diluted and the TOC percentage will drop; with a low sedimentation rate, the percentage of organic matter will be higher.
Where do black shales form?
Most black shales in the past formed in shallow seas that covered the continents millions of years ago when relative sea level was higher. They are found all over the globe and throughout geological time. They are often associated with limited circulation within the sea, which restricted the amount of oxygen reaching the sea floor.
In the modern they are forming beneath areas of high productivity where bacteria use up the limited oxygen supply whilst breaking down organic matter, before reaching the sea floor. Examples include areas of upwelling where blooms of plankton and marine organisms feast on the nutrients being brought up from the deep sea by ocean currents, or the out-wash of the Mississippi River which is full of fertilisers, resulting in algal blooms.
By having a bloom of productivity in the upper water column, the sea floor becomes "dead" with no metazoan life able to live there with no oxygen. However, these areas also become "carbon sinks", where the plankton in the upper water column take in carbon dioxide from the surface water and atmosphere during life, and then, when they die, that carbon is not re-realeased back to the atmosphere because their bodies are not fully broken down by bacteria, due to the limited oxygen. Instead that carbon is sequestered, or locked, into the sediments, raising the TOC, and possibly one day forming a black shale.
So whilst the burning of hydrocarbons from ancient black shales is increasing the amount of carbon dioxide in the atmosphere, the creation of new black shales in the modern is gradually decreasing the amount of carbon dioxide; it's just unfortunate that the rate of burning is higher than the rate of sequestration.
Friday 23 August 2013
Friday 9 August 2013
What's your level of social responsibility?
In a recent conversation I found myself discussing social and moral responsibility regarding climate change. The debate focused around the idea of "if we know that there is a problem, but that the solution to the problem is larger than one person, do we have a moral obligation to act?"
After years of educational campaigns, we all know that it is "good" to recycle, "good" to buy food from sustainable sources and "good" to try to reduce our climate emissions by walking, cycling or using public transport (the latter has also been promoted as increasing our daily exercise to remain healthy). However, many people now do these as a matter of routine, so when it comes to further helping the climate, they are unsure about what more they can do. People are already doing "the easy bits": they have already made the changes that will not have a large impact upon their lifestyles and, rightly so, they feel vaguely proud of the changes they have made.
In many ways climate change needs to be battled in a bottom-up approach because although each individual is one person, together in the UK we number over 63 million people, each one creating green house gases in our cars and our gas boilers (in the UK more gas is burned in domestic boilers than in the gas power plants). If each household insulates their home, turns down the heating and drives their car less, that adds up to a large reduction in climate emissions. However much of the UK's housing stock is older than 30 years old, making it harder to insulate efficiently, the young, elderly and infirm need to live in well-heated housing, and at times public transport just cannot replace a self-driven vehicle.
Some people have taken up the government's financial incentive and installed solar panels and/or wind turbines onto their properties, thus becoming part of an ever-growing self-generation collective. This "green energy" is then used on the property, reducing the amount of electricity that property requires from the Grid. In some cases, any excess energy is sold to the Grid thereby increasing the proportion of "green produced" energy compared to fossil fuel-based energy. Some people argue that the installation of solar panels for self-generation is a really good idea, and great for the environment, whilst others argue that Britain's climate is unsuitable for such a scheme to be worthwhile. Not all properties in the UK are suited to have self-generation equipment installed, and it is also a costly process, although in theory over many years you will save money due to increasing Grid energy prices.
So if you already recycle, you already walk or take public transport, you are already thinking about the sources of the products that you buy in shops, you already have your heating on for the minimum amount of time and your home is well-insulated, and you have already installed self-generation equipment, is that it? Have you already done all that you can for climate change? Aren't you already doing enough? Is it now up to someone else to "fix" it?
For some the answer is yes; it is now up to scientists to come up with new technologies, and new methods which will reduce emissions and possibly remove emissions that have already been created. Others say that it is now up to businesses and large corporations to make a difference. After all, a corporation creates many more emissions than a single household and they have some control over how things are made and transported. Others say it is now up to governments and world leaders to create international policies to change the way that other countries operate so that they cut their emissions, and to change the way that businesses and public services run so that waste is reduced and energy saved.
For others the answer is no, the individuals have not done enough. For them climate change is an individual's problem as well as a global problem. After all, government's should listen to their people and enact the policies that are important to them, scientists can only do research if there is money and if there are people researching those areas, and businesses need to make a profit and therefore need people's custom. Some people devote a lot of time and effort into joining lobbyist groups, whilst others try to have direct influence by becoming a member of government, becoming a scientist, joining a company or creating their own "green" company, or by using their money to sponsor research.
Whether "yes" or "no" is the correct answer is very difficult to say. Each person has their own priorities in life, and each also has their own level of moral and social responsibility regarding climate change. The more direct routes are not for everyone, and for some people climate change is not high on their agenda: it's not directly affecting them and they have other more pressing issues in their own lives. For others, they feel it is important to try and preserve the planet for future generations Each person needs to decide upon their own level of social and moral responsibility. What's yours?
After years of educational campaigns, we all know that it is "good" to recycle, "good" to buy food from sustainable sources and "good" to try to reduce our climate emissions by walking, cycling or using public transport (the latter has also been promoted as increasing our daily exercise to remain healthy). However, many people now do these as a matter of routine, so when it comes to further helping the climate, they are unsure about what more they can do. People are already doing "the easy bits": they have already made the changes that will not have a large impact upon their lifestyles and, rightly so, they feel vaguely proud of the changes they have made.
In many ways climate change needs to be battled in a bottom-up approach because although each individual is one person, together in the UK we number over 63 million people, each one creating green house gases in our cars and our gas boilers (in the UK more gas is burned in domestic boilers than in the gas power plants). If each household insulates their home, turns down the heating and drives their car less, that adds up to a large reduction in climate emissions. However much of the UK's housing stock is older than 30 years old, making it harder to insulate efficiently, the young, elderly and infirm need to live in well-heated housing, and at times public transport just cannot replace a self-driven vehicle.
Some people have taken up the government's financial incentive and installed solar panels and/or wind turbines onto their properties, thus becoming part of an ever-growing self-generation collective. This "green energy" is then used on the property, reducing the amount of electricity that property requires from the Grid. In some cases, any excess energy is sold to the Grid thereby increasing the proportion of "green produced" energy compared to fossil fuel-based energy. Some people argue that the installation of solar panels for self-generation is a really good idea, and great for the environment, whilst others argue that Britain's climate is unsuitable for such a scheme to be worthwhile. Not all properties in the UK are suited to have self-generation equipment installed, and it is also a costly process, although in theory over many years you will save money due to increasing Grid energy prices.
So if you already recycle, you already walk or take public transport, you are already thinking about the sources of the products that you buy in shops, you already have your heating on for the minimum amount of time and your home is well-insulated, and you have already installed self-generation equipment, is that it? Have you already done all that you can for climate change? Aren't you already doing enough? Is it now up to someone else to "fix" it?
For some the answer is yes; it is now up to scientists to come up with new technologies, and new methods which will reduce emissions and possibly remove emissions that have already been created. Others say that it is now up to businesses and large corporations to make a difference. After all, a corporation creates many more emissions than a single household and they have some control over how things are made and transported. Others say it is now up to governments and world leaders to create international policies to change the way that other countries operate so that they cut their emissions, and to change the way that businesses and public services run so that waste is reduced and energy saved.
For others the answer is no, the individuals have not done enough. For them climate change is an individual's problem as well as a global problem. After all, government's should listen to their people and enact the policies that are important to them, scientists can only do research if there is money and if there are people researching those areas, and businesses need to make a profit and therefore need people's custom. Some people devote a lot of time and effort into joining lobbyist groups, whilst others try to have direct influence by becoming a member of government, becoming a scientist, joining a company or creating their own "green" company, or by using their money to sponsor research.
Whether "yes" or "no" is the correct answer is very difficult to say. Each person has their own priorities in life, and each also has their own level of moral and social responsibility regarding climate change. The more direct routes are not for everyone, and for some people climate change is not high on their agenda: it's not directly affecting them and they have other more pressing issues in their own lives. For others, they feel it is important to try and preserve the planet for future generations Each person needs to decide upon their own level of social and moral responsibility. What's yours?
Subscribe to:
Posts (Atom)