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CO2 sequestration isn't practical

CO2 sequestration isn't practical


Let me save the state of Wyoming from wasting $45 million.

Gov. Dave Freudenthal’s budget recommendations to the Legislature include a $45 million allocation for the University of Wyoming’s "budget ... for continuation and acceleration of carbon sequestration research."

Tom Buchanan, UW president, put a self-reassuring exclamation mark on the plan: "The funds will support a carbon sequestration initiative" and "the purpose is to demonstrate the injection of carbon dioxide into underground rock formations. Injection will be followed by measuring, monitoring and verification to ensure that the carbon dioxide remains captured and behaves as expected."

Noble university goal on the surface and frankly others, including myself a year ago, would have applauded the effort. But after a recent definitive work, this project will be a major exercise in futility other than funding research programs of professors who, frankly, should have done their homework already. The indictment of the project is actually pretty simple.

Carbon capture and sequestration (CCS) has been the great hope of middle-of-the-road characters, people other than radical "greenies" or their "right-wing" adversaries. Coal and some oil companies and several world governments have jumped on this and it has figured prominently in many energy and climate scenarios by think-tanks and universities. In some ways it has acted as an "indulgence" certificate. The logic goes that no matter what one’s position is on anthropogenic global warming (whose science is suffering a slow and painful-to-watch death), we have a way to paper over the debate. Engineers, and in particular, petroleum engineers, the ones accused of destroying the planet by the products, have a solution. Let’s literally bury the problem by re-injecting the offending gas back into the ground. Targets can be old oil and gas reservoirs but, more mentioned, are deep saline aquifers of which there are plenty.

Several coal companies and even oil companies tout CCS and some petroleum engineers, who ought to know better had they done simple calculations, have jumped on the bandwagon. The stakes are high and the rewards for those that promote the idea are lucrative. As the Wyoming proposal shows there is plenty of government and even company money for this. As usual, some researchers, instead of studying the very feasibility of the process, already taken for granted in some circles, have started working on peripheral aspects, such as solubility of CO2 in water and even mineralization, things that take tens to hundreds of thousands of years to mature.

So, the capture and subsequent geologic sequestration of CO2 has been central to plans for managing CO2 produced by the combustion of fossil fuels. Most agree that the magnitude of the task is overwhelming in both physical needs and cost, and it entails several components including capture, gathering and injection. But in the current political environment how can anybody assess what an appropriate cost is if saving the planet is at stake?

The reality is a lot different. What have rarely been calculated are the rate of injection per well and the cumulative volume of injection in a particular geologic formation, which are clearly critical elements of the process.

In a peer-reviewed paper published recently with the smarter Economides, my wife, Texas A&M University Professor Christine Ehlig-Economides ("Sequestering Carbon Dioxide in a Closed Underground Volume") we addressed the feasibility of sequestering CO2 as a means of emissions management. The conclusions are quite negative and, in fact, sobering.

Earlier 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 percent of pore space. This will require from 5 to 20 times more underground reservoir volume than has been envisioned by many, including federal government laboratories, and it renders geologic sequestration of CO2 a profoundly non-feasible option for the management of CO2 emissions.

Injection rates, based on displacement mechanisms from enhanced oil recovery experiences, assuming open aquifer conditions, are totally erroneous because they fail to reconcile the fundamental difference between steady state, where the injection rate is constant, and pseudo-steady state, where the injection rate will undergo exponential decline if the injection pressure exceeds an allowable value.

The implications of our work are profound. They show that 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 percent 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 percent of the pore volume and likely as much as 100 times less.

We related the volume of the reservoir that would be adequate to store CO2 with the need to sustain injectivity. The two are intimately connected. The United States has installed over 800 gigawatts (GW) of CO2 emitting coal and natural gas power plants. In applying this to a commercial power plant of just 500 MW, which by the way produces about 3 million tons per year relentlessly, the findings suggest that for a small number of wells the areal extent of the reservoir would be enormous, the size of a small U.S. state. Conversely, for more moderate size reservoirs, still the size of the U.S.'s largest, Alaska’s Prudhoe Bay reservoir, and with moderate permeability there would be a need for hundreds of wells. Neither of these bode well for geological CO2 sequestration and the work clearly suggests that it is not a practical means to provide any substantive reduction in CO2 emissions.

There is no need to research this subject any longer. Let’s try something else.

Michael Economides is a professor at the Cullen College of Engineering at the University of Houston and editor-in-chief of the Energy Tribune.


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