Effect of Overburden Pressure on Anisotropic Parameters in a Layered Orthorhombic Medium

A physical modeling study of the effect of overburden pressure on anisotropic parameters was conducted using intrinsically orthorhombic phenolic boards as the model. These boards were coupled together with the help of a pressure device and uniaxial stress was gradually increased while time arrival and velocity measurements were repeated. Results show maximum increase in compressional and shear wave velocities ranging from 4% to 10% in different directions as a function of increasing uniaxial stress. Anisotropic parameter gamma generally diminished with increasing pressure and ranged from 0% to 33%. We observed anisotropic behavior attributable to both orthorhombic and VTI symmetries. Polar anisotropy behavior is due primarily to layering or bedding and tends to increase with pressure. Certain anisotropic parameters however unveil inherent orthotropic symmetry of phenolic.