Numerical analysis of rock fracturing by gas pressure using the extended finite element method

High energy gas fracturing is a simple approachof applying high pressure gas to stimulate wells by generatingseveral radial cracks without creating any otherdamages to the wells. In this paper, a numerical algorithmis proposed to quantitatively simulate propagation of thesefractures around a pressurized hole as a quasi-static phenomenon.The gas flow through the cracks is assumed as aone-dimensional transient flow, governed by equations ofconservation of mass and momentum. The fracturedmedium is modeled with the extended finite elementmethod, and the stress intensity factor is calculated by thesimple, though sufficiently accurate, displacement extrapolationmethod. To evaluate the proposed algorithm,two field tests are simulated and the unknown parametersare determined through calibration. Sensitivity analyses areperformed on the main effective parameters. Consideringthat the level of uncertainty is very high in these types ofengineering problems, the results show a good agreementwith the experimental data. They are also consistent withthe theory that the final crack length is mainly determinedby the gas pressure rather than the initial crack lengthproduced by the stress waves.