EFFECT OF POROUS FLUID ON NONLINEAR ELASTIC BEHAVIOR OF ROCKS

摘要

Rocks display hysteretic nonlinear elastic behavior, i.e. nonlinear, hysteresis, discrete memory and energy dissipation, which is strongly influenced by the porous fluids. Uniaxial cyclic tests performed on Hefei sandstones and Dali marbles with various type of saturated fluid demonstrate influence of porous fluid of water, oil, pump-oil, pump-oil+asphalt on attenuation, hysteresis and elastic properties (Young's modulus and Poisson's ratio). The applied forces were harmonic loading, with static loading a little larger than dynamic loading and frequencies of 0.05Hz, 0.1 Hz, 0.5Hz, 1 Hz, 5Hz and 10Hz, respectively. Results show that attenuation as well as modulus and Poisson's ratio of porous saturated rock increases with increase of fluid viscosity coefficient. Rocks display asymmetrical "X" shape of tangent modulus and Poisson's ratio subjected to cyclic loading, which reflects hysteresis characteristic of rock. Inclination of "X" shape of tangent modulus is related to porous fluids of rock. Our calculation demonstrates that with increase of viscosity coefficient of porous fluid, inclination of "X" shape of tangent modulus increases, i.e., hysteresis of rock is more distinct. Investigation of influence of porous fluid on nonlinear elastic behavior in rock is significant for seismic wave attenuation mechanism of saturated rock, and exploration of relationship between lithological properties of attenuation, Young's modulus, Poisson's ratio and seismic velocity, and existing environment of oil and water.