The just recently fracked a well in Maverick County in the Eagle Ford Shale:
http://www.eaglefordshale.com/2011/08/propane-frack-test-in-maverick-county-jadela-gasfrac-packers-plus/
My question is why is CO2 not being used more? With water short and coming at a high cost. Co2 was used less then two years ago, looks to me like a no brainer.
Pure CO2 isn't easy to come across. Denbury is close to, if not already, finishing a pipeline to bring CO2 to southeast Texas and that is after a $1 billion investment. Also, if the formation produces any water you get carbonic acid which means you're replacing pipe more often than you'd like.
It can be done, but CO2 is more scarce than water as crazy as that sounds. If you can invent a cheap technology to pull it out of the air, I'll invest!
There are reclamation plants in West Texas, but as Reagan points out, there’s no viable infrastructure in South Texas for the service. Thanks for the above link RT. Good information there for those interested.
CO2 fracs are still done in some parts of the country, the problem is price of CO2. A frac may require anywhere from 200 to 500 tons of liquid CO2, which runs about $100/ton. It starts adding up pretty quickly.
Chemistry is another issue with the CO2. Borates are the cheapest (and probably the most commonnly used) chemical used to create a higher viscosity gel for fracturing. The technical term would be “cross-linking” the molucules making up the gel. In many cases it is vital to be able to crosslink the gel so that proppant can be carried more effectively, but CO2 changes the pH of the fluid and destroys the crosslink. There are other methods of crosslinking gel (titanates, zirconates), but they can get very expensive and have their own disadvantages. So, in very specialized applications, CO2 can be very effective, but as a general rule, cost and chemistry rule it out.
Terra slicing is the best alternative.