Comment

K.M. Brown et al. have committed an error in using effective stress in analyzing hydraulic fracturing. The analysis of hydrofracture dilatancy of existing cracks using an effective stress criterion can be successful only if the minimum principal total stress in the tectonic stress state is vertical. It would be more accurate to use total stress criterion in the analysis. Moreover, the workers have also used a wrong equation in relating horizontal effective stress to change in pore pressure.