Mechanical, Acoustic, And Failure Properties of Shales

Shales carry significant economic importance. Success in dealing with shales requires good un· derstanding of their deformation and failure properties as well as their wave propagation charactedstics. Solution to diverse, specific problems such as the description of hydrocarbon-bearing reservoirs, slope stability, and detection of gas pockets and other zones with different consolidation properties widens the applicability of such understanding. Applicability ranges from petroleum engineering and geophysics into marine science and hydrogeology as well as civil and environmental engineering. Investigation of propelties of shales requires study of wave propagation as well as deformational behavior and failure properties under in situ stress and temperature. An understanding of wave propagation is especially important because shales are quite often identified only by the signature of waves transmitted through them and reflected from their interfaces with other types of rocks. For the past forty years, various groups of scientists have studied wave propagation in shales for different purposes within the more general category of wave propagation in porous media. In some cases, interest has focused on low frequency waves as in seismic prospecting and earthquake seismology studies. Other times, high frequency waves for fine structural details have been of interest such as in marine science and offshore engineedng research. A wide range of frequencies has been studied for geological matedais ranging from gumbo shales to hard shale formations. However, the strain amplitudes in these studies are small; and only dynamic properties have been studied in detail. There is, furthermore, very limited literature on the static stress-strain behavior and failure properties of shales. Well-established theories for wave propagation and failure mechanisms under dynamic conditions are not directly applicable to the behavior of shales under static conditions..