k – Haven’t been able to follow the entire conversation. But note on your map that the red dotes are wells that tested between 0 and 2 mmcf/d. In reality there are very few if any “dry holes” in the trend. But there may be a high percentage that test a non-commercial flow rate of NG and are thus never produced.
Not sure about the cap rock portion of the conversation. Typically there’s no cap rock or top seal with respect to the fractured shale plays. All the NG that is produced from such formations is that which has been taped in the naturally occurring fractures. Those fracture don’t extend infinitely upward. Where they stop vertically is where that production ceases. The effective trapping mechanism is that the formation immediately overlying the shale reservoir doesn’t develop fractures. In fact, it’s been proven that most of the production from the Eagle Ford has come from the lower portion of the formation which is more brittle (thus more fracture prone) due to higher calcite concentrations than the upper portion of the EFS. In effect the upper EFS is trapping the lower EFS. But that’s really an incorrect statement: the productive lower EFS just don’t extend to a significant degree up into the upper EFS.
As far as Cabot goes other than the state saying Cabot caused the contamination your link doesn’t provide any evidence the Cabot wells caused the problem. Saying there was methane contamination in the water after Cabot drilled doesn’t prove the water wasn’t contaminated before they drilled. There are also many references sighting natural methane contamination long before any wells were ever drilled. Likewise regarding the arsenic et al contamination. Those are also naturally occurring. I’ve read about a number of areas in PA were the local water supply was condemned long before any drilling was conducted. Specifics vary from area to area. Where I’m drilling Texas at the moment water wells above 160’s are not considered fit for human consumption…just ag uses. All the households get their drilling water below 160’
And from the right wing Opinion page of the New York Times:
http://dotearth.blogs.nytimes.com/2012/ ... risk/?_r=0“On the Green blog, Rachel Nuwer nicely summarizes the findings of a new Duke University study finding signs that natural geological pathways link deep briny fluids thousands of feet beneath the surface in Pennsylvania gas country with some shallow zones tapped for drinking water.
The study should ease concerns that reports of briny water mixing with drinking water have anything to do with gas drilling, including the process of hydraulic fracturing, or fracking, used to release gas from deep shale layers. The areas where water samples drawn from near-surface layers had traces of the natural contaminants from the deep shale layers showed no relationship to past or current gas drilling activity, the researchers reported.”
And another example which both sides of the debate can use to make their case. From Huffington:
PITTSBURGH — New research in Pennsylvania demonstrates that it's hard to nail down how often natural gas drilling is contaminating drinking water: One study found high levels of methane in some water wells within a half-mile of gas wells, while another found some serious methane pollution occurring naturally, far away from drilling. The findings represent a middle ground between critics of the drilling technique known as hydraulic fracturing who claim it causes widespread contamination, and an industry that suggests they are rare or nonexistent.
The contamination from drilling is "not an epidemic. It's a minority of cases," said Rob Jackson, a Duke University researcher and co-author of the study released Monday. But he added the team found that serious contamination from bubbly methane is "much more" prevalent in some water wells within 1 kilometer of gas drilling sites.
The Duke paper, published in the Proceedings of the National Academy of Sciences, is an expansion of a 2011 study that attracted widespread attention for its finding that drilling was polluting some water wells with methane. The new study includes results from 141 northeastern Pennsylvania water wells. It found methane levels were an average of six times higher in the water wells closer to drilling sites, compared with those farther away. Ethane, another component of natural gas, was 23 times higher in the homes closer to drilling.
Jackson said the researchers believe that faulty drilling can cause methane pollution, but that natural causes can, too. Eighty percent of all the water wells they tested contained some level of methane, including many with no nearby drilling.
There was some good news, Jackson said: The Duke researchers haven't found any evidence that chemicals from hydraulic fracturing, or fracking, have contaminated water wells.
"We're not seeing the things that people are most afraid of," Jackson said, referring to the chemicals used in fracking.
The situation is complicated because Pennsylvania has many layers of oil, gas, and coal-bearing rock as well as natural faults. All those can enable gas to seep naturally into water wells, even in areas without drilling.
Fred Baldassare, who worked for the Pennsylvania Department of Environmental Protection for 25 years, said the study doesn't present an accurate picture of the whole state because the Duke team went to areas where residents had complained about drilling contamination, rather than doing a random sample. Baldassare runs a research company called Eschelon Applied Geosciences.
The second water study was published online last week by the U.S. Geological Survey. It found that some Pennsylvania water wells in areas with no nearby drilling are naturally contaminated with high levels of methane. It also found that 85 percent of the samples had radon levels higher than federal safe limits. One well sample, taken at a hunting club, had such high natural methane levels, it could have been flammable, said hydrologist Ronald Sloto.
The USGS took samples from 20 wells in Sullivan County, in northeastern Pennsylvania, in order to establish a pre-drilling baseline for water quality. Sloto said his study and the Duke paper confirm that pre-drilling water testing is an absolute necessity for homeowners. "Once you have drilling you can't get a baseline, it's too late" to determine if drilling caused water problems or if they were already there naturally, Sloto said. Private water well quality and construction, as well as methane migration, is a longstanding public health issue in Pennsylvania, dating back decades.”
As I think I mentioned earlier getting a pre-drill analysis is the advice I gave every Yankee cousin that sought help from me. But we can go back and forth all day with he said…she said dueling articles. But at the end of the day I’m still looking for the details of the proof that an oil/NG well has caused problem with a water well. I’ve seen only one such case proven and it wasn’t due to a frac job. A company had their mud weight too high in the very shallow section of their well and damaged a nearby water well. No contamination per se but did damage the water well casing.
Again, I have no doubt there have been other instances of oil/NG drilling causing problems with local water supplies. As I keep saying despite best efforts sh*t happens. But I have yet to see anyone present any evidence of such problems on any significant scale. If this is as big a problem as many profess there should be hundreds of well documented examples. I’m still waiting to see even a handful.