Abstrakt
This article compares static moduli determined using uniaxial tests and dynamic moduli calculated from elastic wave propagation velocities. On the example of limestones, we present the fact that for isotropic and intact rock, static and dynamic moduli correspond to each other over a broad range of frequencies.
In damaged rock (cracks, weathering), a difference occurs and static moduli decrease. To include the effect of damage, T-matrix model has been selected.
Dynamic moduli, porosity, density changes and information about properties of macroscopic cracks are necessary data for model calculation. These data are provided by other well logging methods such as an acoustic log with full waveform registration, density log, neutron log and acoustic scanner.
Using all these data, a T-matrix model can predict static moduli from dynamic moduli. As we are dealing with well log data, we calculated vertical component of the elastic tensor only.
This component is represented by Young's modulus E and Poisson's ratio ν. The functionality of the model has been verified on real well logging data and corresponding limestone specimens acquired from borehole core.
The differences between values of E modulus, originally up to 20 %, decreased to values similar to differences in intact rock, i.e. the order of the first units of percent. In the case of ν values, demonstrable reduction of dynamic values, approaching static values was achieved, the resulting difference being less than 15 %.