Natural-gas wells on public land in the Jonah Field of western Wyoming. Fracking is routine for most gas wells drilled now in the U.S. Photo courtesy EcoFlight.
Recent highly publicized drinking water contamination incidents linked to gas drilling, and the popularity of the documentary film Gasland (can you light your tap water on fire?), have raised the public profile of this game-changing drilling process. The U.S. Environmental Protection Agency is studying the safety of fracking. Congress is holding two hearings this week, in the House and in the Senate, to try to get some answers. No doubt many of the problems stem from the mundane details of drilling that can plague any complex construction job: bad well design and construction, ill-advised shortcuts, and - the leader of the pack - poor cementing.
Industry wants us to believe that if we just fix those problems then fracking can be done safely. Disclosing the chemicals used in fracking at each drilling site, so homeowners know what to test their water for, would be a good start.
Tanks for handling fracking fluids at a new Marcellus Shale natural-gas well site in northeast Pennsylvania. Photo courtesy J. Henry Fair.
But we wonder if hydraulic fracturing is intrinsically unsafe, even if the well design and construction is totally by-the-book. Here's why: fracking works by levering open fractures in the rock, and propping those fractures open with sand (or synthetic microbeads). Tectonically "open" fractures, that are aligned parallel to the regional stress field, are most susceptible to being pried open. If a frack job intersects pre-existing open faults or other natural fractures in the bedrock -- especially vertical fractures that can span multiple geologic formations above and below the target zone -- how do we ensure that fracking fluids don't migrate in unpredictable ways via these natural flowpaths?
Smart drillers don't want to lose all their fracking fluid into a single fracture or fault: it's expensive, a waste of time, and doesn't accomplish what they want. But avoiding those features requires doing borehole imaging studies on the well to identify and map them, which also costs time and money. It's not hard to imagine a driller weighing the expense of borehole imaging surveys vs. the risk of performing an ineffective frack job.
We know just enough about this to raise a few questions, and would appreciate some real experts weighing in by commenting on this post:
- What do companies do to avoid the undesired result of fluids migrating out of the fracking target zone?
- What actions to avoid this result are required, and how are they verified by regulators?
- What actions are voluntary, and how commonly are they used?