Will Water Wells and Fracking Cracks Intersect? –
Because the fracked cracks can extend some 2,000 feet above the well bore hole, wells that lie less than a mile (5,280 feet) below the surface pose a higher risk for water contamination. According to Stanford University scientist Robert Jackson:
“Not all shallow wells pose the same threat to groundwater. The “riskiest” fracked wells are both shallow and use high levels of water—1 million gallons or more, said Jackson. Studies have shown that when these high-pressure wells fracture the bedrock, the cracks can extend as much as 2,000 feet upward. This provides an opportunity for the chemical-laced water used in fracking to migrate to the shallower depths of the water table. And the smaller the gap between drilling and surface water, the greater the chance of interaction.”
Water in eastern Bucks is supposed to be perched atop bedrock that lies between 100 and 250 feet below the surface. Sampling a few records in the domestic well database I found wells drilled to depths of 500 feet below the ground level in Wrightstown, and 300 feet in Newtown Township, but the ups and downs of local terrain influence the depth relative to the geological data. Some of the drillers reported drilling through bedrock at less than 10 feet. Some wells are for withdrawal of potable water, others are used for geothermal heat.
Most of the aquifer is recharged by infiltration from the surface and nearby streams and the Delaware River. The shale gas layers that have fair to good gas potential begin at 3,000 feet. Simple math says that hydraulic fracturing could reach to within 500 feet of layers reached by domestic water wells. One can’t know, of course, what natural fissure and cracks may exist in the bedrock that might provide pathways for fracking chemicals pumped into the ground at 9,000 psi to find there way upward. But the notion that “miles of bedrock” lie between the fracked layer and the water layer simply is not true in the Newark Basin.
Given the poor record of the gas and oil drilling industry for predicting or preventing leaks, it would seem very risky to do shallow fracking. If it were to be allowed, there should be mandatory independent monitoring of groundwater quality utilizing test wells near the drill pad. Equally important there must be substantial financial bonding and insurance requirements to fund remediation should methane or fracking chemical contamination be found.
Time is the missing dimension in the scientific work that seeks to estimate how far fracking cracks extend from the bore hole. Here is what science is sure of:
– The shallower the formation, the longer the vertical crack.
– The crack length is influenced by amount of pressure and duration of pressure.
– Natural cracks (called chimneys) form due to natural hydraulic fracturing and they can be many times longer than the ones we “stimulate” with fracking.
– Earthquakes have been caused by waste disposal into injection wells.
Injection of waste water is often accomplished by gravity. The waste water is poured into the well. But when the well is full of water, say two miles deep, the pressure at the bottom is just shy of 6,000 psi and it is unrelenting. Hold that in mind and consider fracking for a moment.
Fracking involves large pumps driven by locomotive-like V12 diesel engines … maybe 12 of these working together. They pump an average of 4 million gallons of water at 9,000 psi. Each fracturing event lasts from a couple of hours of pumping to maybe 4 or 6 hours — so the pressure is higher, but the duration is short relatively speaking. This makes cracks averaging 1000 feet long, with some longer. Maybe half of one percent go 2000 feet. It costs money to run those big diesels, and 1,000 feet is satisfactory, so on to the next frack.
Back to natural fracturing. If the chimney is pressurized by a gravity fed source the pressure is unremitting, other natural processes have time to work eating away at the rock, propping open the crack. Nature has time that the driller does not. That is why chimneys can be so much longer that fracked cracks.
So how long does this take? Well, the same study cited in the article above reports on studies of natural chimneys forming. The time is more than hours and less than years — many days.
The very big question the article does not speculate about is what may happen in a spent gas well that allows water to leak in and continue the process begun by artificial stimulation. Will derelict wells develop natural chimneys extending thousands of feet upward? No on knows. But the bore hole is forever, and future generations will surely find out.