A recent UK report declared the use of fracking to release oil shale gas safe for the UK.
Fracking, the practice of increasing the permeability of otherwise “tight” rocks by forcing fluids into them, has become a worldwide energy-and-the-environment issue.
Formally known as hydraulic fracture stimulation (hydrofracking), fracking increases permeability by orders of magnitude by small percentage increases in fracture porosity. In the case of gas-rich, permeability-poor shales, fracking has dramatically increased both current and potential production of more climate-friendly natural gas. In waste disposal applications, it has a potential role in carbon capture sequestration.
But the technique has also been featured as the waterpolluting antagonist in the documentary film Gasland, raising public calls for its banning and consequent oil and gas industry ire. Further, national-academy level reports in several countries demonstrate its link to induced seismicity. As a result of all these problems, fracking moratoriums have in fact been instituted in North America and Europe, and are now being considered in Africa, Asia, and Oceana.
“Fracking is controlled primarily by natural fractures and these do not lend themselves to any type of average description”
So can its impacts be acceptably controlled? It would seem to come down to the predictability of an individual fracking activity.
The problem is that fracking is controlled primarily by natural fractures and these do not lend themselves to any type of average description. As aconsequence, local physical property measurements at a given site do not predict anything about a nearby one, even though the two sites might be geologically and mechanically connected.
Even taking into account obvious factors such as subsurface depth and rock-type, the erratic nature of fracture flow paths renders frack-driven flow improvement and leak avoidance unpredictable. As currently implemented, a frack can “short circuit” the desired distributed fracture network by opening up a chance straight flow channel.
Better remote sensing methods need to be used to characterise frack sites. These include more penetrating seismic and electrical profiling techniques. In the case of induced earthquakes, high sensitivity background seismicity monitoring at magnitudes far below current surface network capabilities need to be acquired.
Even when these steps have been taken, the frack itself needs to be closely watched and implemented in an incremental manner. In geotechnical terms an observational method is required. The fracking process must be carried out as a staged event. It is not helpful to have the major microearthquake activity occurring after the fracking pressure is reduced.
Surely, no one can afford current fracking potentials for the short circuits that limit gas extraction, connect deep and surface groundwaters, and lubricate potentially active faults? The geotechnical community has the tools to look ahead and monitor this activity. My hope is that considered and informed discussions will be held to improve fracking and monitoring processes and commensurate public policies will be put in place.