NONLINEAR VISCOELASTIC BEHAVIOR OF SEDIMENTARY-ROCKS, PART II - HYSTERESIS EFFECTS AND INFLUENCE OF TYPE OF FLUID ON ELASTIC-MODULI

Uniaxial stress cycling experiments were conducted on dry, brine satur ated and hexadecane saturated Berea sandstone samples to observe in de tail the hysteresis in stress-strain diagrams and to understand the in fluence of different fluids on the strain amplitude dependence of elas tic moduli and attenuation, Cycling experiments were also conducted wi th sandstone samples saturated with CTAB, a cationic surfactant that r enders the mineral surfaces hydrophobic. Hexadecane and CTAB were sele cted so as to investigate the relative contributions of adhesion hyste resis and stick-slip sliding on attenuation in sedimentary granular ro cks. Young's moduli and Poisson's ratios obtained from the cycling tes ts show a significant dependence on strain amplitude on dry as well as water and hexadecane saturated samples. Bow-tie-shaped diagrams are o btained when loading and unloading tangent moduli are plotted against strain, The type of fluid in the pore space and at the grain contacts has a large influence on the hysteresis observed in the stress-strain diagrams.