本文转自《Global CCS Institute (GCCSI)》发表的题为“From Kaya to EOR”的文章。

作者：Alex Zapantis

日期：2018.09.24

原文链接：https://www.globalccsinstitute.com/insights/authors/AlexZapantis/2018/09/24/kaya-eor?author=NDU3MTI4

If there is one thing to learn about preventing dangerous climate change from the past few decades, it is that emissions reduction is hard. Much has been done in the name of reducing global emissions but the simple reality is that despite trillions of dollars of investment, the vast majority on renewable technologies, global emissions continue their steady rise. Kaya, a Japanese economist, developed a simple equation to describe the relationship between CO2 emissions and a few macro-economic parameters that is very useful in understanding why emissions reduction is so difficult. The famous Kaya identity is below.

如果说要从过去几十年里预防危险的气候变化有什么值得学习的话，那就是减排很难。在减少全球排放的名义下，我们已经做了很多工作，但现实是，尽管在可再生能源技术上投入了数万亿美元，但全球排放量仍在稳步上升。日本经济学家卡亚(Kaya)提出了一个简单的方程式，用来描述二氧化碳排放与一些宏观经济参数之间的关系，这对于理解减排为何如此困难非常有用。下面是著名的Kaya身份。

        CO2 emissions = P x GDP/P x E/GDP x CO2/E

The Kaya identity says that anthropogenic CO2 emissions are proportional to:

• Population
• Gross Domestic Product per capita (ie, average personal wealth)
• Energy consumption per unit Gross Domestic Product (ie energy intensity of the economy), and
• CO2 emissions per unit energy consumption (ie emissions intensity of energy)

Now lets consider the Kaya identity in light of emission reduction targets. The International Energy Agency 2 degree scenario requires global emissions to reduce by around 75% by 2060.  The Kaya identity tells us that one way of achieving a 75% reduction in emissions is to:

• reduce global population by 30%, and
• reduce average personal wealth by 30%, and
• reduce energy intensity of the economy by 30%, and
• reduce the emissions intensity of the energy system by 30%.

This simple analysis immediately exposes a problem. Achieving a world with less people, who are on average poorer than we are today, is not a realistic proposition.  Rather, by 2060:

• global population is expected to increase by around 45% (assuming 0.9% annual growth), and
• Average personal wealth is expected to increase by around 245% (assuming 3% annual growth)

In summary, by 2060, there are likely to 45% more people on the planet and the average wealth of each individual will be more than triple what it is today. This large increase in personal wealth is actually a good news story as it will drastically improve the quality of human life, particularly in developing economies. However, with increased affluence comes increased demand for goods, products and services. The conclusion is that to deliver emission reductions, those goods, products and services must be delivered in a much more energy efficient manner and by using energy sources with a much lower emissions intensity. But how much lower? Cue the Kaya identity…

If population increases by 45% and GDP/capita increases by 245%, then reducing emissions by 75% requires energy consumption per unit Gross Domestic Product and the emissions intensity of the energy system to reduce by around 78% compared to today.  Is this achievable? Lets look at recent history.

Since 2010, the energy intensity of the global economy has reduced by an average of 2.1% per annum. To achieve a 78% reduction, energy intensity would need to fall by about 3.5% every year between 2018 and 2060. This is a significant increase in energy efficiency improvement but considering the low cost (or even negative cost) opportunities for energy efficiency that remain unexploited, such improvement definitely appears achievable. Also, there are many technologies available and ready for deployment now that deliver energy with 22% or less of the emissions of the current global energy system. They include renewables, nuclear and gas or coal with carbon capture and storage for electricity generation, biofuels, and hydrogen fuel cells for transport and hydrogen for heat.

OK.. so problem solved then! Energy efficiency and low emissions energy technologies can deliver the emission reductions we need.  Not quite… this is where we run into trouble due to economic and commercial headwinds. These low emission technologies are generally more expensive than conventional technologies. In some cases, they require massive capital investment and the retirement of existing and profitable large capital assets. In other cases, they are competing against technologies that are supported by over a century of investment in enabling infrastructure. An excellent example is oil’s role in transportation. Global infrastructure to support the production, processing, distribution and sale of oil-based products for use in transport provides oil with an enormous advantage over new entrants such as hydrogen, for which such infrastructure is still embryonic. It is clear that the free market will not deliver the transformation in the global energy system, at the rate necessary to stabilize the global climate. Strong and sustained policy is required, and every option must be employed.

Successful policies to drive the deployment of new energy efficiency and low emissions technologies will need to overcome many economic and commercial headwinds to prevail. This is often referred to as finding the least-cost solution, usually predicated on the deployment of the optimum mix of new technologies which replace conventional technologies over time.

But what if there was a way to allow the continued use of some existing large capital assets and infrastructure whilst delivering emission reductions? This would certainly diminish some of the economic challenges previously mentioned. Well, there is. Retrofitting carbon capture and storage to existing gas and coal fired electricity generators and other industrial facilities is an obvious example. It allows the continued utilization of the existing assets as well as the fossil fuel supply chain that provides employment and supports so many communities around the globe. But there is another less obvious example that has not received the consideration it deserves. That opportunity is CO2 enhanced oil recovery – CO2EOR.

CO2EOR has been practiced for almost 50 years. It is a mature and well understood technology to extend the life and increase the production of oil fields that would otherwise be in terminal decline. CO2 is injected into the oil reservoir, increasing reservoir pressure and reducing the viscosity of the oil with the result being an increase in oil production. Some of the CO2 is produced with the oil, where it is separated and re-injected. Ultimately, all the CO2 injected remains permanently trapped in the pore space that originally held the oil. In many cases, CO2EOR makes commercial sense without any supporting policy as the revenue from the sale of the incremental oil production is sufficient to cover the additional cost of injection and provide a commercial return on investment.  In other cases, some policy support may be required to incentivize CO2EOR.

However there are a couple of complications. The utilization of the oil produced from CO2EOR produces CO2emissions and the monitoring required to verify that the injected CO2 remains permanently stored is generally not done.  There are solutions to both of these challenges.

• Well established sub-surface monitoring techniques, as currently used at CCS facilities, can be applied to CO2EOR operations to verify that the injected CO2 remains permanently stored.
• Life cycle analysis of oil produced using CO2EOR can be used to quantify emissions abatement.

MacDowell, Fennell, Shah and Maitland from Imperial College London published an analysis in Nature Climate Changein 2017 that included an analysis of the net CO2 emissions from CO2EOR. They found that in standard CO2EOR, approximately 3.33 barrels of oil are produced per tonne of CO2 injected resulting in net positive life cycle emissions of 0.43t of CO2. However, if CO2EOR is operated to optimize CO2 storage, 1.1 barrels of oil is produced per tonne of CO2 injected resulting in a net negative emission of 0.52 tonnes of CO2.

The significance of this result cannot be understated. Using CO2EOR that is optimised for storage, it is possible to produce negative emissions oil; for every barrel produced, emissions abatement of a bit under half a tonne of CO2would be delivered, including the emissions from the use of the oil. This abatement would be achieved whilst continuing to utilize existing oil production, processing, distribution and utilization infrastructure worth trillions of dollars, including the existing vehicle fleet. MacDowell et al estimate that CO2EOR could deliver 4-8% of the cumulative emission reduction challenge by 2050. Given the need to find ways to materially and rapidly reduce emissions whilst minimizing economic and social disruption, CO2EOR optimized for permanent storage ticks all the boxes and should certainly be part of the mix.

Despite the opportunity presented by CO2EOR, it is not yet accepted under international carbon accounting frameworks as a climate mitigation technology. The Kyoto Protocol recognised carbon capture and storage as “an environmentally sound technology” (Article 2.1.a.4), and CCS is permitted under the Clean Development Mechanism. However, CO2EOR was never formally discussed in those negotiations.

As Julio Friedman likes to say – “Do the math!”. Kaya’s simple identity is the math. It leads to an obvious conclusion. Achieving emission reduction targets requires a complete transformation in the way we produce and use energy. Every option will be necessary. Storage-optimized CO2EOR is an option that that can deliver material emission reductions whilst avoiding many of the commercial, economic and social disruptions associated with replacing global energy infrastructure. It is time to recognize it as part of the solution to climate change.