Cracks from the Computer

The “FracRisk” research project team has spent three years researching the risks associated with fracking. Computer models are now available, which provide more insights into the risks involved in the process.

In many places throughout the world, natural gas reserves are found in so-called unconventional reservoirs, which means that the natural gas is locked away in shale and coal seams in deep rock strata and is, therefore, not amenable to conventional extraction methods, i.e., via boreholes. Instead, a technical process referred to as hydraulic fracturing or, as it has come to be known around the globe, “fracking” is used, which has polarized opinion in terms of its cost-benefit profile. There have also been anti-fracking protests in Germany, the participants in which fear irreversible environmental damage. On the other hand, organizations, such as the German Federal Association of Oil, Gas and Geothermal Energy, assure the public that fracking could “make a decisive contribution to meeting Germany's natural gas requirements” for decades to come. On its website, by contrast, the German Federal Environmental Agency states that fracking is “controversial”, primarily because of the risk it poses to groundwater reserves.

However, Professor Holger Class will not be pronouncing judgement on fracking per se: “that's not our role as researchers”, says the Deputy Director of the Department of Hydromechanics and Hydro-System Modelling at the University of Stuttgart's Institute for Modelling Hydraulic and Environmental Systems (IWS). according to the scientific consensus, he goes on, fracking is associated with risk, inevitably so given the nature of underground conditions. The task now is to specify these risks: “We're working on computer models that could serve as tools in the decision-making process”, says Class. The “we” to whom he refers are the researchers working as a consortium in the FracRisk project, which is funded by the EU. The project is coordinated by the University of Edinburgh and the Stuttgart group is responsible for the “Modelling” work package. The project title “FracRisk” is a more manageable abbreviation of “Furthering the Knowledge for Reducing the Environmental Footprint of Shale Gas Development”. Thus, it is about furthering and expanding our knowledge about the risks involved in extracting natural gas trapped in shale seams deep underground, so-called shale gas.

To date, there is not much reliable data available, at least for Central Europe, about the effective forces and processes that take place underground during the technical procedure. “The Americans have a lot of experience with fracking”, Class confirms, “whereas we have very little valid data”. However, data from America cannot simply be transferred, as different geological formations have developed on the European continent. Moreover, the shale seams containing the trapped methane are much deeper underground. Nevertheless, researchers from the USA are contributing to the FracRisk project with their experiences of the extraction method. The lack of European data is due to the difficulty in obtaining any sort of reliable data from several thousand meters underground.

In principle and in practice, fracking involves a drilling team drilling down to the stratum in which the gas is trapped, which is far below the groundwater level and overburden. Once there, the borehole pans to the horizontal and progresses more or less parallel with the surface. Next, the fracking specialists pump the fracking fluid, a mixture of water, quartz sand or ceramic spheres and highly diluted, sometimes poisonous, chemicals into this layer under high pressures of up to 1000 bar for up to two hours. This mixture, which ExxonMobil describes as a “slightly water-polluting mix, breaks up the rock and causes it to fracture - hence the name “frack”. In this way, the methane can be released and extracted. At the end of the process, the fluid is pumped back out and disposed of.

For example, gas or water can theoretically enter the groundwater if the cracks opened up in the process extend through to the porous overburden or if there are any fault zones, i.e., natural flow paths, in the rock, for example, along upthrows or fissures. Then it would be possible, in the worst-case scenario, for the gas and fracking fluid to penetrate through to the higher groundwater layers. Whilst Christopher McDermott, Project Coordinator at the University of Edinburgh, considers this risk to be vanishingly small, particularly as specialist fracking firms put a great deal of effort into monitoring their boreholes, the potential impact on fresh drinking water reserves is too important an issue to be left unaddressed. That is why Project FracRisk has been studying the risks in precise detail for the past three years.

So far, predictions about the actual geological conditions in gas fields have barely been possible. Fracking companies had to sink a series of test boreholes and analyze the drill cores in addition to reconnoitring the environment using seismic measurements. One result of the FracRisk project is that, in future, simulation models can contribute towards calculating the specific risks in potential gas fields with a high degree of probability. This is essentially based on models developed by Professor Class and his team at the IWS during the project period. It all sounds much simpler than it really is, because countless calculations on high-performance computers are required to verify such models.

Jens Eber