Recent interest in fracking (fracturing) shale layers to release methane (CH4) and oil is stirring quite a controversy. I want to make some comments that may shed some light and reduce the smoke a little<G>. There are a number of anecdotal stories about burning ice, water wells that gush bubbling water and well water that fizzes.
Methane gas, CH4, (or carbon dioxide, CO2) rather easily bound to clusters of water molecules in a few different ways. In the middle US states, frequently by sufficient relatively low pressure, gaseous CH4 or CO2 are readily absorbed in to cool water such as one could pump from say a 120 foot deep well for drinking water. When this water is brought to the surface the CH4 or CO2 will bubble off and go into the atmosphere and is perfectly drinkable. As a fact well pumps have been designed to separate the CH4 or CO2 at the well bottom and let the CH4 rise (lighter than air) and vent harmlessly. They are careful NOT to make the well top airtight. The CO2 being heavier than air will sink to the bottom of the well shaft. This is NOT from hydration.
AN ASIDE: If it is necessary to send a service person down to the pump unit, CARE has to be taken to vent and remove CO2 trapped at the well bottom or the person has to wear a breathing mask.
Next, hydrates and clathrates----what are they? Really they are the same thing, one being when the water is liquid and the other when the water is just freezing or below freezing. In both these cases it evolves that 23 water molecules will "host" 4 CH4 molecules. BTW this "hosting" takes place equally as well with 4 CO2 molecules. The range of pressure is from about 10 atm upward and the temperature range of interest is from -5C to about +(10C-15C). Relatively a small temperature range and a much larger pressure range. SO within the bounds of pressure of 10 atm upwards is the region where clathrating and/or hydrating can and do take place depending upon the temperature being above or below freezing.
ANOTHER ASIDE: The 23 molecules of water are grouped in 3 groups of 6 and 1 group of 5. This is the 4 groups and each will "host" one CH4 or one CO2 molecule but not both.
Now how does this relate to "fracking"? If you drill and cement a well to say 10000 feet and fill from the bottom up say 300 meters, then the hydrostatic pressure will be 30 atm or about 30 x 14.7= 441 psi. If you fill to 3000 meters, then the hydrostatic pressure will be 4410 psi.!! So in the simplest cases after drilling the well to the shale layer of interest they then load in fine sand and fill with the water height to produce the pressure desired. The idea is to wedge open the shale layers and push the sand in to keep the facture open. This now lets the methane gas escape into the water in the well shaft and thence to the surface and recovery (hopefully). During this operation they continue to monitor to see they secure the fracturing desired.
Fracking for oil is slightly different because the oil is liquid and more viscous. Frequently to increase the flow rate a dispersant is added to the sand and forced into the fracture. One "good news" feature about the BP spill in the GOM is that intensive studies of more han 8 dispersants have been undertaken. Main interest was upon small fish---little thought was put into toxicity to humans. Belief was the residual levels made swimming by humans perfectly safe. Intentional drinking was another matter and not considered.
So that is where it stands. The Internet message traffic is rife with pro and con about fracking for NG and oil. The writer's opinion is that methane or NG fracking is completely safe. The toxicity of dispersants used in fracking for oil may (?) have some long-term effect on humans BUT intensive study should answer that question to such a point that the government could certify as to its level of safety.
Interesting.
The secrecy that is kept as to what the dispersants are is very worrisome. I further worry about the reported changes in water quality in communities that are near to where fracking operations are already taking place. In my view, contaminated water tables are disasters in the making and all we have by way of safety assurances comes from those who are driven by monetary issues.
Posted by: John Dunn | February 11, 2012 at 09:52 AM
Cabot Oil and Gas is drilling in Dimock, Pa. Since 2008 the well water of several residents has been contaminated with toxic chemicals, flammable gas, heavy metals, and radioactive material. The Pennsylvania Department of Environmental Protection (DEP) determined that Cabot was at fault, but DEP allowed Cabot to cease delivery of clean water to affected residents (who had leases with Cabot) on 11/30/2011. The Sierra Club paid for the delivery of replacement water from the New York City watershed by means of a 5700 gallon truck.
Posted by: Dick LaRosa | February 11, 2012 at 05:13 PM