Vorsana

By 2035 the EIA forecasts annual US CO2 emissions of 6.32 billion metric tons, 38% of which (2.40 billion) will be from coal plants alone. To put that in perspective, consider that in Texas the huge Permian Basin oil field’s current annual enhanced oil recovery (EOR) demand is only 7 million tons of CO2, about the output of a single 1 GW coal-fired power plant.  See this article from POWER magazine.  Clearly, EOR in depleted oil and gas reservoirs can't handle the expected volume of CO2 that must be stored each year just from power generation. 

The only other potentially available pore space, once we set aside the tiny capacity of depleted reservoirs, coal beds, and dry formations, is in deep saline formations.  Although deep saline formations have lots of pore space, i.e. spaces between grains in the rock, the pores in the rock are full of brine.  Deep saline formations are not empty tanks, but full tanks.  Moving the brine out and the CO2 in may well be impossible at the scale of billions of tons each year.  We hear a lot about the 25 years of successful experience with EOR, but it is the extrapolation of this EOR experience to permanent CO2 storage in deep saline formations that is at issue because there are not enough depleted reservoirs to accommodate the tremendous volumes of CO2 going to permanent storage.  So EOR in depleted reservoirs (empty tanks) is immaterial.    

Once injected into the formation, the CO2 would have to be securely contained there.  This fundamental point seems to have been overlooked. In 2010, a sobering article appeared in the refereed Journal of Petroleum Science and Engineering (70:123-130), authored by two distinguished full professors, Christine Ehlig-Economides and Michael J. Economides.  Here's a quote from the abstract:

“Published reports on the potential for sequestration fail to address the necessity of storing CO2 in a closed system. Our calculations suggest that the volume of liquid or supercritical CO2 to be disposed cannot exceed more than about 1% of pore space. This will require from 5 to 20 times more underground reservoir volume than has been envisioned by many, and it renders geologic sequestration of CO2 a profoundly non-feasible option for the management of CO2 emissions [my emphasis].” 

Profoundly non-feasible is a polite way of saying laughable.  Curiously, the Ehlig-Economides paper, a peer-reviewed article authored by two prominent experts in petroleum engineering, was not among the references cited in the recent interagency report on CCS.  So its optimism about sequestration may be based on ignorance.

A rebuttal was posted by Dooley et al.  The  Dooley, et al. paper does not dispute the merits of the Ehlig-Economides et al. paper.  Instead, Dooley et al. trump the merits by claiming the analysis is irrelevant because CO2 storage formations are not closed systems, but open systems which are expected to leak through permeable seals and therefore the 25 years of successful experience with EOR in open systems can be extrapolated. 

In the interest of fully informed debate on this important issue, here are links to other rebuttals to the Ehlig-Economides article: 

ZEP opinion piece

American Petroleum Institute rebuttal

Cavanagh, et al. rebuttal

Oldenburg, et al. rebuttal (Lawrence Berkeley National Laboratory)

Economides response

“Closure” is a term of art meaning that the volume is bounded vertically and horizontally by impermeable barriers, commonly called a seal.  See the testimony of USGS geologist Dr. Robert C. Burruss to Congress on July 24, 2008, p. 4.  Closure is of the essence in any storage plan, so the assumption of a closed underground volume by Ehlig-Economides et al. -- so vehemently rejected by Dooley et al. -- does not seem unreasonable, at least as to deep saline formations.

In EOR the flow is steady state and not intermittent because there is a production well that provides a path out of the formation and the flow is at constant pressure.  The CO2 dissolves in the oil and is recycled back into the reservoir after it is extracted.  The depleted reservoir is like an empty tank, with flow in and out, i.e. an open system.  All sequestration projects so far -- the “25 years of successful experience” -- are of this type, and they have been done because of the economic benefit to oil companies of capturing the CO2 and injecting it back into the formation to scavenge oil from depleted reservoirs.   

Ehlig-Economides et al. challenge the steady state assumption underlying capacity calculations for deep saline formations: “models that assume a constant pressure outer boundary for reservoirs intended for CO2 sequestration are missing the critical point that the reservoir pressure will build up under injection at constant rate.  Instead of the 1–4% of bulk volume storability factor indicated prominently in the literature, which is based on erroneous steady state modeling, our finding is that CO2 can occupy no more than 1% of the pore volume and likely as much as 100 times less.”  I'm inclined to trust their sincere expert guidance when lives may be at stake.  See here the textbooks that these authors have written. 

The steady state assumption is clearly not appropriate with respect to deep saline aquifers, where there exist no means for flow out of the formation, and injection would have to be against high pressure into a full tank, raising the pressure.  Pumps to hammer in the supercritical CO2 and displace the brine would produce pulsed, not steady, flow.  As the more CO2 goes in, the pumps will have to work even harder against higher pressure. 

The density of the injected supercritical CO2 is only 50-70% of the density of the saline water, (Burruss, p. 4) so sequestered CO2 would be buoyant and would have to be physically trapped by caprock and lateral containment.  Hydraulic fracturing of the sealing formation by high pressure (the fracture pressure of the sealing formation is >4200 psi), pulses during supercritical CO2 injection might have disastrous consequences.  Lateral leakage of buoyant supercritical CO2 out of the sealing formation would also be a disaster because this high pressure bubble could find its way around the caprock and erupt at the surface, or into groundwater supplies.  The CO2 cannot dissolve in the brine or become carbonate quicky enough to mitigate the danger from leakage.  When sequestration proponents expect the storage formations to leak enough to be classified as open systems, then there seems to be no point (other than EOR for the oil companies) of injecting CO2 underground and it probably is safer to dump it in the atmosphere.  

The lifetime emissions from just one large coal-fired power plant would displace water equal to the size of a giant oil field (4.1 billion oil barrels), as USGS research geologist Robert Burruss pointed out in his testimony to Congress in 2008.  Work would be required to lift all of that brine to the surface to make way for the tremendous volume of CO2.  That work would presumably come from combustion of fossil fuels, adding to the CO2 emissions.  Will the energy for CCS create more CO2 than it stores? 

What will be done with all of that brine once it is extracted?  Reverse osmosis reject brine (brine concentrate) is classified as “industrial waste” by the EPA, and the extracted deep saline brine will be even saltier (up to 463,000 ppm).  Disposal of reverse osmosis reject brine is already a limiting factor in desalination deployment, and this will be a much bigger and saltier waste stream. 

You can't just dump it, so where will that deep saline brine go to make way for the tremendous volumes of CO2 that will replace it deep underground?  If the plan is to hammer the supercritical, buoyant CO2 into the saline formation in order to force the water to flow elsewhere underground, will that even be possible against the tremendous pressure at the depth required to maintain supercriticality?  Will the displaced brine flow up to pollute fresh water supplies or increase soil salinity, leading to famine?  Will the hydraulic hammering of pumping CO2 fracture the sealing formation, leading eventually to a disaster like Lake Nyos in 1986, where 1,700 people died from asphyxiation when CO2 erupted from underground? If a CO2 plume does escape from the sealing formation, what can be done about it?

Repeating the “25 years of successful experience” line is not an answer to these questions.  Especially not after the BP blowout. 

The Government Accountability Office (GAO) report of September 30, 2008, noted that sequestration  also faces huge political obstacles, such as: (1) the vast infrastructure that would have to be built to transport and inject the CO2 emissions, (2) public resistance to a lethal gas dump under their neighborhood, and (3) the liability issues associated with ownership of a CO2 dump.  Public resistance (e.g. Mattoon, Illinois) is already hardening. 

It's time to punt sequestration.  Let's not blow what remains of the scarce Recovery Act CCS research money on a “profoundly non-feasible option” which might result in an even worse environmental disaster -- migration of brine into groundwater supplies and CO2 eruptions that kill people.

 -  Wilmot H. McCutchen