The menu on Sonic, Velocity & Density currently include ther following options.

  • Sonic to Velocity
  • Velocity to Sonic
  • Acoustic Impedance
  • Compute VPVS and PR
  • Estimate Vs from Vp
  • Esimate RHOB from Vp

  Each of these options is discussed in more detail in the sections below. 


9.6.1  Sonic to Velocity

Converts a slowness curve to a velocity curve. The input slowness can either be a compressional or shear slowness and will be automatically converted to the respective compressional or shear velocity. The input units of either us/ft or us/m will be automatically accounted for. The output units can be selected as either m/s of ft/s. 


9.6.2  Velocity to Sonic

Converts a velocity curve to a slowness curve. The input velocity can either be a compressional or shear velocity and will be automatically converted to the respective compressional or shear slowness. The input units of either m/s or ft/s will be automatically accounted for. The output units can be selected as either us/ft or us/m. 


9.6.3  Acoustic Impedance

Compute the Acoustic Impedance from the compressional sonic and bulk density curves. 


9.6.4  Compute VPVS and PR

Compute the VP/VS ratio and Poisson's Ratio from the compressional and shear sonic curves. 

$$\begin{align}  VPVS &= {\Delta T_{shear} \over \Delta T_{comp}} \\  \\ PR &= {{\left( 0.5 \cdot {VPVS}^2 - 1.0 \right)} \over  { \left( {VPVS}^2 - 1.0  \right) }}  \end{align}$$


9.6.5  Estimate Vs from Vp

Estimate the Shear Velocity ($V_S$) from the Compressional Velocity ($V_P$) using the Castagna relationship.

$$V_S = A \cdot V_P + B$$

where the $A$ and $B$ are determined by fitting a linear curve to a crossplot of $V_S$ against $V_P$. 

The water depth is a parameter if it is an offshore well. The water depth parameter can also be found in the Edit Wellsite data menu. If the log depth is less than the water depth, then $V_S$ will written as 0.0.

If the logs are two-way-time indexed, the water depth will converted to two-way-time using the current value of sea-water-velocity.

To estimate $\Delta T_{shear}$ from $\Delta T_{comp}$, first convert the compressional slowness to a velocity, then compute $V_S$ from $V_P$, then convert the shear velocity back to a slowness. This is functionally equivalent to $ {1 / \Delta T_{shear}} = {A / \Delta T_{comp}} + B$.  


9.6.6  Estimate RHOB from Vp

Estimate the Bulk Density ($\rho_b$) from the Compressional Velocity ($V_P$) using the Gardner relationship.

$$\rho_b = {A \cdot V_P}^ B$$

where the $A$ and $B$ are determined by fitting a power curve to a crossplot of $\rho_b$ against $V_P$.

The water depth is a parameter if it is an offshore well. The water depth parameter can also be found in the Edit Wellsite data menu. If the log depth is less than the water depth, then $\rho_b$ will written as 1.0.

If the logs are two-way-time indexed, the water depth will converted to two-way-time using the current value of sea-water-velocity.