The inset to figure 7 shows that this ratio is zero at an initial
confining pressure of 50 kPa, indicating complete static liquefaction.
Strength and acoustic velocities increase with increasing
confining pressure. With increasing temperature, kerogen becomes much softer than the matrix minerals.
After the fracture was filled with distilled water,
confining pressure was applied to the vessel by injecting water using a hand pump.
The influence factors of dynamic strength mainly include relative density,
confining pressure, initial shear stress, test method, sampling pattern and lithology etc.
Figure 2 shows that the changes of sandstone permeability with
confining pressure at different heating temperatures.
It can be seen from Figure 5 that, due to the effect of
confining pressure [[sigma].sub.3], the ordinate intercept of reference systems II and III is not 0.
The
confining pressure [[sigma].sub.3] was set as 5 MPa, 10 MPa, 20 MPa and 30 MPa, respectively.
Three samples of standard sizes from each tube were tested under the increasing
confining pressures and strains rates.
The elastic modulus of oil shale will greatly influence the permeability under the
confining pressure, especially in in-situ pyrolysis conditions.
Usually, the stress sensitivity experiments of clean sandstone and shale were conducted by increasing
confining pressure at first and decreasing later [6-9].