Tuesday, March 9, 2010

The Professors Economides and carbon sequestration

One of the problems in ensuring that there is sufficient energy available at some future date is that the supply, in virtually all cases, requires that a significant infrastructure is in place to deliver it. Thus, for those of us who have become used to having a light come on, when a switch is flicked, there needs to be some form of generator hidden at the other end of the wires to which the switch is connected. Stepping further back beyond the generator there must be some energy source, whether it be the sun’s rays; the wind blowing across the moors; or the fuel that fired the power station from which the electricity flowed.

Putting that infrastructure in place takes time. And the existing plant, over time, and even with good maintenance, will slowly decay and require replacement. At the same time just being able to generate power doesn’t necessarily allow me to flick the switch and see the computer screen as I type this. There has to be system, typically an electric grid of power cables, which carries the power to where it is needed. As Boone Pickens found out, putting wind turbines into West Texas was an exercise in futility, until such time as there is a network that will deliver the power to the folk that need it in East Texas, more than a few miles, and a few years of construction and permitting, away. As “just in time” manufacturing has grown as a cost control practice, so ordering large pieces of equipment carries with it longer delivery times, since the minerals must be mined, processed, produced, transported, made into parts and assembled, before the final product can be brought to a site and installed. The larger the facility, in many cases, the longer that process takes, and the more paperwork is likely going to be involved in the getting the installation into the ground. It is a lengthy process even when the need is generally recognized. If there is political opposition - regardless of merit – then you just added years to the delivery, construction and operational start times.

Power station construction is one of those things where the process is more likely to be beset with delays, than with dramatically earlier than scheduled delivery. And if the fuel comes out of the ground, whether coal, oil, natural gas or uranium, then delays can more critically compound, particularly at politically critical points, such as around election times.

I was thinking of this today, as I came across Chris Booker’s comments on the Conservative leadership views on electricity generation, at a time when the UK must, before long, have a General Election. Given that Britain must replace 14 of its current generating plants, under EU mandate, taking with them 40% of the current generating capacity of the country, he draws attention to the Conservative view that coal-fired power can only be allowed if there is full carbon capture and storage.

What makes it particularly interesting and relevant is that, after some 100 coal-fired power stations in the United States have been cancelled or postponed, we have folk such as the head of one of the largest generating companies in the Midwest virtually echoing the Conservative leader. And it is much the same position with the Department of Energy and the current Administration. Carbon sequestration is the also a current area for lots of research and planned development.
In October 2009, as part of President Obama’s stimulus package, the US invested $1.4 billion in 12 CCS demonstration projects. In December 2009, the US announced a further $979 million is to be invested in 3 further such projects. The same month the EU pledged over $1.4 billion towards building 12 CCS similar projects by 2015. The UK is also proposing to fund and bring online 4 CCS demonstration projects by 2020.

Now there has been the odd small problem with leakage at one of the few places that are actually carrying this out at present. Yet the current site at Sleipnir, has been injecting CO2 for years, though the gas it re-injects was initially a part of the natural gas mix that wells at the site produce.
Using a simple metallic tube measuring 50 centimetres (20 inches) in diameter, the platform operator, Norwegian oil and gas group StatoilHydro, has injected some 10 million tonnes of CO2 into a deep saline aquifer one kilometre (0.6 miles) under the sea.

"We bury every year the same amount of CO2 as emitted by 300,000 to 400,000 cars," said Helge Smaamo, the manager of the Sleipner rig, a structure so large that the 240 employees ride three-wheeled scooters to get around.
But that is not the concern that has been highlighted, nor is it the volumes of gas generated to run the compressors that drive the gas to liquid and up to the pressure at which it is injected. Rather it is the results of the pressure itself.

Last October Michael Economides and his wife presented a paper in Houston, that he has since abbreviated on his web site, and which Chris Booker has made reference to.

Simplistically he examines the relative volume, within an existing rock formation, that carbon dioxide can occupy, if it is injected into that rock and left there in storage. The number that he comes up with is 1% of the pore volume.

The problem that they identify (with computer models) is that as the carbon dioxide (which has been compressed under pressure so that it is delivered and stored as a liquid) is injected at a relatively steady rate, it flows into a formation where there is already some pre-existing fluid. Thus as the new fluid is pushed into the rock, in the reverse of the process that happens when oil flows out of the rock into the well, the driving pressure must increase to move the CO2 away from the well. This injection pressure must continue to build, over time, to keep the fluids moving, but it can only displace some of the existing fluid, and some it has to compress. Achieving the compression by increasing pressure has a couple of serious snags. The first is that fluid at low pressures is virtually incompressible, and the second is that to achieve it the pressures must therefore be increased significantly to, and above, the levels that the rock can easily stand.

What do I mean by that, well if you remember back to one of the tech talks, I mentioned that we can crack a rock by raising the pressure in the well above the strength of the surrounding rock. We do that to create paths that the oil can flow out through, into the well, driven by the pressure differential between the fluid in the rock, and the pressure in the well, that we lower after fracturing the well. We lower the pressures because we don’t want the crack to continue growing. If it did then it could easily grow through the reservoir rock, and then up through the cap rock that is holding the oil (or gas) confined within the reservoir rock. Once we crack through that cap rock, then the reservoir isn’t a reservoir any longer, since it has a leak path, through which the CO2 can escape.

As a result we can only inject CO2 into that reservoir until the pressure in the well starts to approach the fracture pressure of the rock. But we don’t start at zero pressure, we have to start at the existing pressure of the fluid in the rock, and it is only in the difference between these two pressures that we can drive the CO2 into the rock. And that range, the Economides have calculated, will only allow a 1% change in fluid volume before the pressure gets too excessive.

Now I have to add two caveats to this argument – the first is that it does not hold when the liquid is injected into a reservoir where the fluid is still oil, since CO2 will merge into the oil, lowering its viscocity, and this has been used previously to enhance oil recovery (EOR) and get perhaps another 10% production out of formations where it is feasible. And even when the oil can’t be recovered, it can accommodate larger levels of injection that that forecast.

The other point is that there is nothing that stops the site from extracting the contained fluid (generally water, though often brackish) to allow the CO2 to displace it, at a lower pressure (which could be considered as a reverse water flood). It may be a bit more expensive, but at least it would reduce the volume of space that would be needed from the huge areas that the Professors Economides currently anticipate would make carbon injection infeasible.

I suppose someone will realize that, after a bit, but in the meantime while the debate continues, and the example sites fail to yield reassuring results, the power stations are not being built, and the future needs of both the UK and the USA hang further in the balance.


  1. HO:

    I'm not following the argument here in the case of a reservoir that is connected to an aquifer below (which will be the most common case for an old oil/gas reservoir). One pushes down the CO2 and displaces the water back down into the aquifer. The strength of the rock places a limit on the rate of injection (just as it does with waterfloods), but I don't understand why it would limit the ultimate amount of storage (which seems like it would generally be set by the combination of the pore volume and the pressure of the aquifer, since we would be relying on the latter to keep the CO2 in place long term, but for deep reservoirs, that would seem like it would usually be pretty high).

  2. Do you have citations for Sleipnir leakage?

  3. Stuart:
    I think it is not an absolute limitation on storage capacity, but as I interpret Professor Economides work, a combination of the amount that has to be injected from a given generator as a steady injection stream flow rate, thus giving a rate of injection contribution to the equations. It is the condition of the cap rock, and the potential for failures in the cement around the injection point that are more of a concern, I gather at this point.

  4. Gail:
    I have now sat through two presentations that have shown the leakage on the seabed at Sleipnir, but so far I haven't been able to find a reference that I can quote from the web, but I continue to look.

  5. The Economides couple got this one wrong. Their assumptions have been rebutted by a wide array of scientific and research bodies as well as stakeholders from across the board. For more details read my blog here: http://switchboard.nrdc.org/blogs/gperidas/economides_x2_try_their_hand_a.html

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