New study published in the journal Science has something for everybody as to how shale gas industrialization impacts water quality. The report summarizes findings of some previous work and offers a fair explanation of the various ways that shale gas wells can contaminate groundwater. In basically confirms what we (Ingraffea, Allstadt, Bishop, Myers, Rubin, et al) have been saying for years – albeit in guarded, industry-laced jargon. They also cite industry studies in the same context as peer reviewed scientific articles, often to contradict the scientific articles. A close reading of those industry sponsored studies typically reveals cherry-picked data.
How Gas Wells Can Contaminate Aquifers – Quickly or Slowly
Despite pro forma industry denials to the contrary, the authors describe how fracks can indeed hit an aquifer. As previously noted, this is simply a matter of how much separation there is between the target formation and the aquifer. Which, in some cases, is not enough. (It is also a function of time – since, given enough time, the frack water can mix with subsurface water, as the Myers study pointed out.) This is their take on how the Pavilion, Wyoming water could have been contaminated, the gas wells were 1,200 feet deep, and the water wells were 800 feet deep, leaving a separation of only 400 feet.
The Pavillion gas field consists of 169 production wells into a sandstone (not shale) formation and is unusual in that fracturing was completed as shallow as 372 m below ground. In addition, surface casings of gas wells are as shallow as 110 m below ground, whereas the domestic and stock wells in the area are as deep as 244 m below ground. The risk for direct contaminant transport from gas wells to drinking-water wells increases dramatically with a decrease in vertical distance between the gas well and the aquifer.
If there is any localized faulting, it is hard to imagine how fracks could not contaminate those deep aquifers – which we have been saying for a few years now, and a DOE test well just re-confirmed.
They also discuss the movement of frack fluids over time – and go out of their way to try to contradict the Myers paper – which described how frack water might not migrate as rapidly as Myer suggested:
The (Myers) study concluded that changes induced by hydraulic fracturing could allow advective transport of fracturing fluid to groundwater aquifers in <10 years. The model includes numerous simplifications that compromise its conclusions. For example, the model is based on the assumption of hydraulic conductivity that reflects water-filled voids in the geological formations, and yet many of the shale and overburden formations are not water-saturated. (But many are saturated, and the wellbore and naturally occurring faults are as well. JLN)
Furthermore, although deep joint sets or fractures exist, the assumption of preexisting1500-m long vertical fractures is hypothetical and not based on geologic exploration. (Myers used this fault length as hypothetical in his paper. JLN)
Hence, there is a need to establish realistic flow models that take into account heterogeneity in formations above the Marcellus Shale and realistic hydraulic conductivities and fracturing conditions.
The authors conclusion is substantially the same as Myers’s conclusion:
The rapid expansion of hydraulic fracturing requires that monitoring systems be employed to track the movement of contaminants and that gas wells have a reasonable offset from faults.
Since Myers wrote his paper, the DOE has demonstrated that an errant frack can travel up 1,800 feet – far enough to hit a water saturated fault that can serve as a transport mechanism into an aquifer.
How Gas Wells Leak
The authors address the issue of stray gas coming up the well bore, how it is likely to happen, and where it is likely to happen – in areas where there are shallow gas bearing formations (like the Marcellus) that are likely to be vented by well bores. This is, of course, Ingraffea 101, or my version, Ingraffea Lite: http://www.scribd.com/doc/65577477/How-Gas-Wells-Leak
Gas migration out of a well refers to movement of annular gas either through or around the cement sheath. Stray gas, on the other hand, commonly refers to gas outside of the wellbore. One of the primary causes of gas migration or stray gas is related to the upper portion of the wellbore when it is drilled into a rock formation that contains preexisting high-pressure gas. This high-pressure gas can have deleterious effects on the integrity of the outer cement annulus, such as the creation of microchannels (36).
They show a cross section of a well bore to illustrate the various ways this can happen. Note that the more casing and cement layers there are (and the deeper they are), the greater the overall circumference on the well – and the more apt the well is to leak on the outside of the outermost layer – between the cement and the well wall – when it encounters a shallow gas bearing formation, which has been conspicuously omitted from their illustration:
The authors show where such leaks have occurred and are likely to occur – in areas that already exhibit gas venting from shallow deposits. Meaning, if there is evidence of methane in groundwater, that is the most problematic place to drill a large diameter shale gas well – that is apt to simply vent more gas into groundwater.
If the local water “has been on fire since 1692” don’t drill a big gas well bore there.
The methane found in groundwater is 20X higher near gas wells:
They cite an industry /Penn State Study that purported to contradict the Duke methane study, but that was so grossly flawed that had to be withdrawn as soon as it was published by PSU:
They also cite the USGS/ Duke study which found no clear evidence of methane contamination from shale gas drilling in the Arkansas area of the Haynesville Shale field. This study was the exception that proves the rule – most shale gas wells will ventilate shallow gas deposits (not necessarily the target shale formation) under the right circumstances:
1. A horizontal shale well (a large well bore) that is heavily fracked
2. The presence of shallow gas intervals to be vented by the well bore
3. Lack of natural sealants (such as layers of clay between the shallow gas deposit and aquifers)
4. Shallow water wells – to accumulate the vented gas – and evidence its accumulation to the public
Then all that is necessary is a microscopic separation between the outermost layer of cement and the well wall – and up comes the methane.
The authors also go on to discuss the rather thorny question of how to make several billion gallons of toxic radioactive flowback disappear (for the next 1,000 years or so) when there are Class II disposal wells handy (to induce earthquakes with). And other issues for which there is, thankfully, one rather simple and elegant solution . . .