The quotes below come from the comments section on web site - http://tinyurl.com/owgbts
"First off, CO2 has what is known in the industry as a "triple point". A point on the temperature/pressure curve at which all three phases (liquid, solid, and gas) can co-exist. This is a dangerous situation because solids can plug up pipelines, liquids are incompressible, and gasses at that pressure are bombs waiting to blow. It is not at all uncommon for a pipeline to plug up due to a solid dry ice plug, burst due to the sudden spike in pressure from the incompressible liquids pumped in behind it, then flash to gas and cause an explosion. That is one reason it is not often used for oil well fracturing/stimulation, liquid nitrogen is far safer to handle/pump."
"The other issue is one of metallurgy. CO2, in the presence of water turns into carbolic acid. Carbon steel as well as most higher strength stainless steels are subject to severe pitting corrosion from carbolic acid. I have a piece of pipe that was in an oil well for two weeks in wet CO2 environment. It quite literally looks like a piece of wood that termites have been eating. Pitting corrosion is the most dangerous kind of corrosion because it is random and unpredictable in how deep it will go. Therefore you cannot build in a "corrosion allowance" into your designs to compensate for it the way you can with general corrosion. A corrosion allowance is when you specify a thicker wall for a pressure vessel than needed to account for the lost thickness due to corrosion over the vessel's life. But since pitting is localized and can go very deep very quickly, you cannot compensate for it in that manner."
"Carbolic acid also attacks the cement used to plug and case wells as well.
The way to compensate for it is to use group IV corrosion resistant materials. These materials are invariably very high Chrome, Nickel, Cobalt, and Molybdenum content materials. These are as you can imagine not cheap or plentiful, and were generally not used to drill or case the original oil wells that are to be used as CO2 injection wells. They also tend to present operational issues due to their propensity to gall. You cannot inject CO2 into a reservoir that has carbon steel cased wells that intersect it for there is a high likelihood that those capped wells may blow out later due to corrosion. Therefore using old oil wells is extremely problematic. Sure, it will work for a short time, but long term, those wells are ticking time bombs."
"Another issue is the energy required to capture, purify, liquefy, transport and pump the CO2. That energy has both a carbon and a financial cost associated with it. What good does it serve to sequester 1 MMCF of CO2 if you generate 1.25 MMCF in the process?
For example, carbonic acid in groundwater can dissolve limestone to form natural caves. We don't know what type of effect pumping such a volume of CO2 into the ground would have, so saying there could be an off-the-shelf system in the near-term is not reasonable."
Below are excerpts from the web site -http://tinyurl.com/ov9264
Beside the problem of carbon dioxide leaking out of old abandoned wells, there are other concerns.
Forcing carbon dioxide under pressure into rock formations could force natural gas and salt water out of those formations in unpredictable and undesirable ways – into shallow water wells, for example or to the surface, spilling natural gas (a potent greenhouse gas) into the atmosphere, or pushing brine into fresh water aquifers.
And in an ironic reversal, pumping gas under pressure into some rock formations could cause the surface of the ground to actually rise – as opposed to land subsidence caused by deep mining coal – damaging structures and affecting streams and drinking water aquifers.
Leaking carbon dioxide could find its way into drinking water aquifers, and while this sounds like it could produce club soda from the kitchen faucet, it would make the water more acidic, dissolving calcium and other minerals and creating a hard water problem, or in some cases dissolving toxic metals, raising trace elements to dangerous levels."