Hydrofracturing: An Overview
The national stage is brightly lit with heated conversation about the latest and greatest in petroleum recovery technologies: hydrofracturing. This buzzword is being discussed from California to New York. It is even a hot topic in North Carolina, where not one commercially viable cubic foot of natural gas has ever been produced! Grassroots community movements are springing up in any state where there has ever been a discussion about natural gas, mostly against the use of this technology.
But before the jury decides whether this technology is a boon or a menace, a few questions merit exploration.
First, what is it, anyway?
“Fracking” is a technology used to enhance the permeability of a gas reservoir. This allows the gas to flow out and be recovered. It requires injecting a variety of media into the subsurface under high pressures – high enough to create open pathways in the formation, allowing the gas to flow out. The injected media can include such things as water, acids, and solids like sand.
Is it new? No, this technology has been around since the mid-20th century, but the way it’s done now is different. For the first few decades of its use, fracking was used to stimulate tight sands and limestone reservoirs. In the last 15 years or so, it has been applied, increasingly, to tighter, less permeability formations like shales.
Shales are rocks made of small particles like silt and clay. They form in layers, and usually develop in quiet environments like swamps. These kinds of environments often contain a lot of organic material like worms, snails, fish and plant material. Because the environment may go undisturbed for long periods of time, a lot of this material may accumulate. As it gets buried it becomes consolidated, and the organic material, trapped between the layers of particles, eventually may, through the magic of time, pressure, and just the right amount of heat, decay and create natural gas. The problem with shales is that the gas, if present, is held within very small pore spaces that are often not connected. Fracking “cracks” the rock, making the flow of gas possible.
The concern over fracking centers not on whether it works; there is little debate about that, since it has been used successfully in gas plays like the Barnett Shale in Texas. As far back as 2002, the American Association of Petroleum Geologists (Shirley, Kathy, AAPG Explorer, July, 2002) reported that the gas field was estimated to contain about a trillion cubic feet of gas per square mile at a (relatively shallow) depth of about 7500 feet. This is an astonishing amount of gas from any kind of reservoir rock, let alone shale!
Then why the national hand-wringing? We need the gas, right?
Well, that depends on whom you talk to. Proponents are happy about the technology and the extra gas, but environmental groups question the real cost in potential damage to and depletion of drinking water supplies.
The heart of the problem is this: fracking is just the tip of the iceberg. It is estimated that a single treatment of a well may require up to a million gallons of water and 25 tons of solids. That water has to be acquired from somewhere, and the most likely source is groundwater.
Groundwater exists in many places as water stored in the pores between soil grains and fractures in bedrock. It is the most widely used source of drinking water in the world as well as in the U.S. In rural settings where drilling often takes place, there may be no other available source of drinking water. Extracting large amounts has the potential to reduce the availability of water for domestic consumption.
The deepest concern, however, is related to the problem of dealing with the water after it is recovered from the wellhead. By this point in the process, the water may be an unhealthy mix of water, acids, solids, and dissolved gases. The common practice is to inject this mix back into the deep subsurface, which, opponents say, creates a high potential for contaminating groundwater supplies. There is also concern that this injection process has been responsible for producing low magnitude earthquakes.
In a 2011 article entitled, “It’s the environment, Stupid!” (AAPG Explorer, November 2011), author Stephen M. Testa summarized the problem as one in which the search for energy has always carried significant environmental risk, and the more complex the exploration, the greater the risk. He cites the Deepwater Horizon as an example of the very high environmental cost associated with complex production scenarios. Testa points to a case in which a geologist was prosecuted after a number of earthquakes, allegedly from fracking operations, caused an estimated $9 million in damage to buildings. According to the author, the geologist was acquitted, but the fracking operations were cancelled as a result of the litigation.
This article encapsulates the underlying issue: Do we want to continue to have an uninterrupted supply of fossil fuels? If so, are we willing to bear the real cost?
Adding more fuel to the fire, the “real cost” is poorly understood. Arthur E. Berman, in a June 2011 Search and Discovery article, indicated that the economics of gas recovery are suspect. He claims that the fields are ultimately smaller in areal extent than has been advertised; that the reserve numbers have been drastically inflated, and that recovery costs will ultimately prove uneconomical.
What is the average citizen to make of this miasma of conflicting fact and myth?
The storm is likely just beginning. In an unexpected move in the summer of 2012, the State of North Carolina legislature overrode Governor Beverly Perdue’s ban on fracking, presumably opening the door for use of this technology here. In North Carolina, the discussion centers on the potential gas reserves in several Triassic basins. To date, little has been done to prove the reserves, and these basins have historically been considered to contain poorly developed groundwater systems. Still, the legislature saw fit to believe that the potential is great enough to merit not prohibiting the use of fracking should a gas play become a reality. In response, citizen groups, particularly in rural communities, are banding together to work against fracking, citing the potential harm to farming and domestic property.
It probably will be a long time before the exploration effort required to evaluate whether commercially viable natural gas exist in North Carolina takes place. And that is likely a good thing. As a state with no history of petroleum production, North Carolina lacks the regulatory framework and experience to adequately regulate these kinds of operations.
There is much to be done here, regardless of which side of the argument you take.