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Fracking – the pressure is on

EU-funded researchers have developed new efficient mathematical models to simulate hydraulic fracturing and advance the understanding, control and safety of the process.
Fracking – the pressure is on
Contrary to widely held belief, hydraulic fracturing is not a drilling process. Performed after drilling of the wellbore has been completed, this technique involves the injection of large amounts of fluids under high pressure. By creating fractures in reservoir rocks, it establishes additional paths that allow the extraction of hydrocarbons to increase.

Although this technology can be backdated to the 1930s, it has been in the last twenty years that hydrofracturing has become commonplace. Fracking is highly controversial with opponents arguing that it puts the environment at risk, while its supporters emphasise the economic benefits. Not surprisingly, this technique has stimulated a lot of research, in which the mathematical modelling of the underlying physical process plays a prominent role. The findings showed that there is a need for more accurate simulations of the coupling between fracture propagation and fluid flow.

Moreover, the fundamental impact of that research goes far beyond the fracking process. The phenomenon has also been used in other technological processes (like C02 sequestration) and observed in nature (magmatic intrusions in the earth crust, subglacial drainage of water).

The HYDROFRAC (Enhancing hydraulic fracturing on the basis of numerical simulation of coupled geomechanical, hydrodynamic and microseismic processes) study responded to this need. Over the course of this four-year-long project, researchers developed mathematical models of geomechanical, hydrodynamic and microseismic processes to help improve the design of hydrofracture operations.

New fundamental results were obtained during the project concerning basic properties of the respective mathematical models, which enabled to develop highly efficient, flexible and accurate computational algorithms. Performance of the respective 1D and 2D simulators was verified on the basis of dedicated benchmarks and compared with the data available in literature.

In general setting, fracture propagation was traced using 3D boundary element models of poroelastic media combined with finite difference models for non-Newtonian liquid flows. HYDROFRAC researchers implemented new methods for solving the boundary integral equations. Among others, a fast multipole method helped speed up calculations with better accuracy.

In addition, researchers developed a dedicated computer code to simulate microseismic events induced by changes in local stresses. Microseismicity was simulated by seeding initial flaws with parameters of predefined statistical distribution. Data collected from simulated events were carefully analysed to estimate strength and stability of flaws over time.

All codes were adjusted to meet practical needs in close collaboration with the project’s industrial partner. Specifically, synthetic microseismicity was compared with that observed during hydraulic fracturing to calibrate the input parameters and improve the modelling results. Model parameters were also finely tuned based on the predicted oil or gas output as compared with that observed in the field.

Knowledge gained within HYDROFRAC was shared with the scientific community through publications in peer-reviewed and open access journals as well as presentations at international conferences.

Related information


Mathematical models, hydraulic fracturing, hydrocarbons, HYDROFRAC, non-Newtonian liquid, microseismicity
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