ABSTRACT:

To probe mechanisms of the controls of mineral composition on fault friction, stability and dilation properties during reservoir stimulation, simulated fault gouges comprising powdered samples of major reservoir rocks in China were sheared in double direct shear configuration under water-saturated conditions at room temperature. The samples span a range of phyllosilicate contents from 0 to 30 wt.% and with grain sizes <150 µm. Velocity-stepping tests were performed to assess the key friction parameters at three different normal stresses. Experimental results show that the phyllosilicate minerals have a strong influence on gouge friction, stability and dilation properties. The friction coefficient decreases monotonically with increasing phyllosilicate contents and the frictional stability parameter (a – b) increases with an increase in phyllosilicate content with a transition from velocity weakening to velocity strengthening behavior at 15 wt.% phyllosilicate content. Gouge dilation is observed upon a change in shearing velocity and may be used as a proxy for permeability evolution in gouge-filled faults. The dilation scales positively with friction coefficient and negatively with frictional stability parameter (a – b). The above results provide insight in understanding the potential for induced seismicity and permeability evolution during reservoir stimulation.

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