Figure 4
Comparison of the strain rates. The strain rate of tight sandstone49,50,51,52,53,54 obtained from the fractional Maxwell model is plotted against time for each sample. It is represented by a straight line on a log-log scale as a result of its power-law dependence on time. Also plotted are various experimental data (filled squares) and estimations (squares) for general sandstone (not necessarily tight sandstone). The factional Maxwell prediction is consistent with these results up to several years; the observation that it seems to reach some lower bound of sandstone strain rate is also in accord with the fact that tight sandstone is typically “harder” than many other kinds of ordinary sandstone.
