TIME-DEPENDENT HYDRAULIC FRACTURING IN POTASH MINES

This paper investigates by numerical methods the cause(s) of mine seismicity and mine flooding occurring at several potash mines in Saskatchewan, Canada. To assist in the investigation, a finite-element model based on viscoelastic/viscoplastic material behaviour has been utilized. From the analysis of various mining situations it is concluded that hydraulic fracturing of the brittle Dawson Bay formation occurs as a result of changes in the stress-strain regime due to mining and this might be a possible cause of induced seismicity. Hydraulic fracturing of the Dawson Bay and underlying evaporites also results in communication of the aquifer with the top of the mine development openings and rooms and hence a path for flow of pressurized water into the openings. Hydraulic fracturing of both the Dawson Bay and underlying evaporite layer are demonstrated to be dependent upon pore water pressure in the aquifer, the in situ state of stress prior to mining and the duration of mining.