Influence of hydrological communication between basement-rooted faults and hydraulic fractures on induced seismicity: A case study

Abstract

The mechanical conditions that allow seismogenic faults to be activated in distinctive positions and moments remain uncertain. An integrated approach is proposed to quantify the hydrological connection between stimulated wells and associated seismogenic faults during fracturing stimulation. A case study in Fox Creek, Alberta, was conducted to demonstrate the applicability of this integrated approach. Ant tracking was used to identify the subvertical basement-rooted faults from a three-dimensional seismic reflection survey. A coupled flow–geomechanics simulation was conducted to quantify the well–fault hydraulic connection in terms of pore pressure diffusion and poroelastic stress perturbation during fracturing stimulation. Three identified basement-rooted faults were corroborated by the focal mechanisms and spatial distribution of induced siemsicity events. The negative shear stress gradient indicates the downward shear growth during hydraulic connections. The induced earthquakes were triggered by fluid diffusion through hydraulic fractures along high-permeability fault damage zones downwards into the basement. This basal fault slip was attributed primarily to the elevated pore pressure along the fault plane in response to fracturing fluid injection. The moderate distance (879 m for NS-oriented wells and 749 m for NW-SE-oriented wells) between the future horizontal wellbores and critically-stressed faults could mitigate the effects of well-fault hydraulic connection and reduce the seismicity risks.