AN EXPERIMENTAL INVESTIGATION OF DYNAMIC AND STATIC ELASTIC PARAMETERS OF COMPACTED CLASTICS, THE NORTHEAST SICHUAN BASIN, CHINA

The ultrasonic wave velocities and mechanical parameters of compacted clastics of Upper Triassic and Middle Jurassic in the northeast Sichuan Basin,with current burial depths ranging from 320 0 m to 420 0 m,aremeasured simultaneously under simulated formation conditions(including temperature,pore pressure,confining pressure,air-dried or saturated by water,and different directions of samples).The composition and structure of rock are the inherent factors determining the velocities and mechanical parameters,with the velocities and Young's modulus decreasing along with the increases in clay content and porosity.Generally,the velocities and dynamic elastic moduli of samples parallel to bedding are greater than those perpendicular to bedding,while the Poisson's ratio is an exception.The velocities,dynamic Young's modulus and bulk modulus increase along with the decrease in temperature and increase in effective confining pressure,while the Poisson's ratio shows no evident rule to the changing of temperature,and increase for air-dried samples and decrease for samples saturated with brine as the effective confining pressure increases.Both P-wave and S-wave velocities increase firstly and then decrease along with the increase in additional axial stress,with the maximum velocities corresponding respectively to 80% and 50% ultimate compressive strength of sandstones.The P-wave velocity and dynamic elastic moduli of samples saturated by brine are greater than those of air-dried samples,with the exception of(S-wave).The dynamic Young's moduli of all samples are greater than the static Young's moduli,but the dynamic and static Poisson's ratios show no such rule.