A natural gas fracking well near Shreveport, Louisiana.
Fracking has been studied mainly because of what it can potentially do to the surface environment. The chemicals used in fracking fluid, as well as the gas and brines that can come back into the wells, all pose environmental risks that must be managed. What is often not considered is that the well is a bit of a two-way street. The fracking fluid, which is anything but sterile when injected, also contaminates the environment deep beneath the Earth’s crust.
A new study, released this week by Nature microbiology reveals that fracking creates an entire ecosystem 2.5 km below the Earth’s surface, an ecosystem that can survive for at least a year after the fracking. And the microbes that thrive there may even have implications for the production and sustainability of the fracking wells.
The people behind the work (14 of them at three different institutions) took a relatively simple approach: sample the fracking fluid at a few wells before sending it underground, then sample the fluid coming out of the wells at various times, including more than 300 days after fracking. The sampling included a look at the organic chemicals in the fluids and DNA sequencing sufficient to reconstruct entire genomes of whatever is present.
The chemical analysis revealed that the fracking fluid being injected actually contains chemicals that can act as energy sources for microbes, including sucrose and ethylene glycol. After the fracking process is complete, some of this fluid returns to the wells, but is usually quickly displaced by the salty brine that exists deep below the surface. But those brines were accompanied by molecules typically produced by salt-tolerant bacteria and archaea (more on that below).
That’s where the DNA analysis came into play. After fracking, the authors were able to detect the presence of at least 29 different types of microbes in the fluid coming out of the wells. Over time, populations changed; At 80 days after fracking, the population was largely composed of only six salt-tolerant bacterial and archaeal species. At least one of these is genetically distinct from its previously characterized relatives; the authors suggest the name “Frackibacter” for its genus.
At least one of these species was clearly present in the feed fluid, despite the addition of a biocide. Two other species the researchers looked for were not present in the input fluid, although the authors suggest this is because they were rare enough to be below the detection limit. Only after reaching the deep brine could they thrive.
The species that did well are all salt tolerant. Some of the biological signature chemicals found in the fluid that came out of these wells are even used by microbes to adapt to high salt environments. Meanwhile, the nutrients in the fracking fluid seemed to be rapidly metabolized and were gone after 80 days. The authors surmise that the community was surviving at the time by feeding on the chemicals used for salt tolerance.
There was only one problem: those chemicals are normally produced and stored in cells. How did they enter the environment to provide food? The answer, it seems, is viruses. There was evidence of over 300 different viruses in the genomic sequence, with the prevalence of different species changing over time. And there was evidence in the genomes of the microbes that they were exposed to viruses as the ecosystem evolved. The viruses spread by causing cells to burst open, which the authors say could ensure that enough nutrients are released back into the ecosystem for the surviving microbes to feed on.
Overall, not much chemical is likely going on in these brines, so the resulting ecosystem may not survive in the long run. But that doesn’t mean there can’t be short-term consequences. The bacteria could produce organic acids and sulfides that could react with the steel in the well hardware. And the species present had the potential to form biofilms, which could potentially disrupt the movement of materials in the wells or in their environment. Any of these can pose problems for the production of these wells.
Still, the whole thing is an impressive testament to the resilience of life. The fracking fluid contained chemicals that should kill all microbes, and it was injected into an area of crushing pressure and salt concentrations that would kill most species on our planet’s surface. But somehow, species so rare as to be undetectable end up forming an ecosystem that lasts for at least a year.
Nature microbiology2016. DOI: 10.1038/NMICROBIOL.2016.146 (About DOIs).