Sharpe: Don’t fear the frack!
“I’m not against oil and gas, I’m just against fracking!” That is a common thread I hear from many laypeople when I discuss the issue. With all the negative press from the anti-fracking movement, they understandably fear that their water is being contaminated. Perhaps if the public understands how and why we frack wells, and sees the evidence for fracture containment, it will ease their concern.
Fluid flows out of a reservoir because the reservoir pressure is greater than the wellbore pressure. The rate at which it flows out is equal to a whole bunch of Crap times that pressure difference. Two major components in the Crap term are the permeability of the formation and the thickness of the completed interval. Let’s talk about each.
Permeability and why we frack
Permeability is a measure of how easy (or difficult) it is for fluid to flow through the rock. If you fill a trash can with BBs and another trash can with basketballs, the percentage of space (porosity) between the spheres will mathematically be the same. However, while they both contain the same amount of fluid, the fluid will flow much easier between the basketballs than it will through the BBs.
Even the conventional sandstones in the San Juan Basin have grain sizes too small to see with the naked eye. Therefore, virtually every well in the basin has been fracked since the 1960’s. This process cracks the rock under very high pressure, and then before the pressure is released and the fracture closes, we fill the crack with the equivalent of playground sand to hold it open. The frack sand compared to the formation sand is like comparing basketballs to BBs. As a result, the permeability in the fracture is many thousands of times the formation permeability, so the frack becomes a super-highway by which fluids are able to get to the wellbore. In shales, the issue is exacerbated by grain sizes that are orders of magnitude yet smaller than the sandstones. Therefore, fracking is absolutely essential to be able to produce from a shale at ANY rate, much less a commercial rate.
Formation thickness and why we drill horizontal
All other variables being equal, a reservoir that is 200 feet thick will theoretically produce twice the rate as a reservoir that is 100 feet thick. In a vertical sense, the thickness of the reservoir is not something we control, as God made it whatever it may be. However, if we drill the well horizontally through the sand layer, we can increase the “thickness of the completed interval” to as much as 10,000 feet, potentially increasing the rate as much as 100 times.
However, if you were to frack a 10,000-foot horizontal well all together, the frack would seek out the weakest place in the rock and all the frack would go there, leaving most of the wellbore unstimulated. Therefore, most horizontal wells drilled prior to the year 2000 were in high permeability sandstones that didn’t need fracking. In the early 2000s, smart mechanical engineers figured out a way to isolate small segments of horizontal wells, allowing each segment to be fracked individually. So now, a 10,000-foot horizontal might have as many as 50 individual fracks over 200-foot intervals, basically replacing 50 vertical wells. Therefore this “new” process that has the public all up in arms is the optimization of a very old process that in fact reduces the impact on the land and the environment.
How we 'know' fracks don't get into the groundwater
It is hard to “prove” a negative, such as that fracking “never” gets into groundwater. But here’s the evidence, and it’s pretty solid.
1. We aren’t pumping enough water to make it to the surface or groundwater. While the total volumes are in the millions of gallons, the amount pumped on any individual stage won’t mathematically make it anywhere close to the surface, even if the frack went straight up.
2. Fracks don’t grow straight up. Like a crack in a single brick in a stack, the fracks don’t tend to cross the layer boundary, but propagate along the layer in which they are initiated.
3. Fracks only reach out from the wellbore 250 feet to 500 feet in both directions. Most shales are being developed with wells 500 feet to 1000 feet apart, the optimum distance before the frack from one well starts interfering with the frack from another.
4. A frack that cracks the rock is a minor, but measurable seismic event. In an effort to understand and optimize our fracks, we use seismometers to measure how far and where a frack grows. Measurements show the results of thousands of fracks in the Barnett shale, none of which came close to groundwater. (On a side note, the earthquakes in Oklahoma are NOT caused by fracking but by the long term disposal of water in a seismically active zone. The regulators are now limiting injection volumes in that region.)
5. There have been and will continue to be the occasional surface spills of frack fluids, but those are contained and cleaned up when they happen. But in over a million wells fracked over 65 years, there has NEVER been a documented case of frack fluid contaminating groundwater as a result of the fracking process itself.
So don’t fear the frack! If the anti-frackers successfully ban the process across the U.S. as they have in New York, you’ll still get your oil, it will just come from another country at a much higher cost.