A New Apparatus to Measure the Coefficient of Friction and Changes in Fracture Permeability

The injection of large volumes of fluid into the subsurface can potentially result in seismic events or earthquakes. In this context, it is crucial to understand the conditions such as the frictional properties that control subsurface fault slip and cause the seismic events. A new triaxial apparatus has been developed that can characterize the frictional properties of rock samples. The new apparatus is different from the previous test system designs in its ability to measure additional parameters accurately such as fracture permeability in addition to frictional properties. The apparatus measures both the dynamic friction coefficient, the magnitude of stick–slip events, and changes in the fracture permeability during and after frictional slipping. It also enables us to estimate the effect of pore pressure and fluid/brine flow through the fracture. This ability to measure changes in fracture permeability after frictional slipping is unique and provides additional insight into changes that can occur in the subsurface due to fault slip. Another advantage is its ability to independently control shear stress on the rock sample, allowing for the direct measurement of shear stress rather than calculating it from total stress values. By independently controlling the confining stress, the axial shear stress, and the pore pressure using three hydraulically driven pumps, the entire range of frictional properties can be measured. Each load can be applied in different modes: constant strain rate loading or constant stress. The findings of frictional studies on Berea sandstone under various normal loads and stabilization times between slip occurrences are presented in this work. The results reveal important new information about how these parameters affect the frictional characteristics and stick–slip events in Berea sandstone.