Wyllie Time-Average Sonic Porosity - Uncompacted Formations Formula
Wyllie Time-Average Sonic Porosity - Uncompacted Formations calculates compaction-corrected sonic porosity for rock properties workflows in petrophysics.
How engineers use this formula
Use this formula when the listed inputs (Delta_t, Delta_t_f, Delta_t_ma, Delta_t_sh) are known and the assumptions behind the cited rock properties relationship match the engineering case being checked.
Assumptions
- Input values are representative for the well, reservoir, fluid, or equipment case being evaluated.
- The declared units match the field-unit constants used in the formula.
- The cited formula applies to the selected petroleum engineering workflow.
Limitations
- The calculation does not replace a full engineering model or operating procedure.
- Accuracy depends on the source correlation, assumptions, input quality, and unit consistency.
Common mistakes
- Mixing unit systems without converting the inputs.
- Using default example values as field recommendations.
- Applying the formula outside the source assumptions.
Default example
Using the default inputs, Phi_s equals 0.246567 fraction.
95
189
55.5
120
Inputs
Delta_t
us/ftObserved Formation Transit Time
Delta_t_f
us/ftFluid Transit Time
Delta_t_ma
us/ftMatrix Transit Time
Delta_t_sh
us/ftAdjacent Shale Transit Time
Outputs
Phi_s
Compaction-Corrected Sonic Porosity
B_cp
Compaction Correction Factor
Delta_t
Observed Formation Transit Time
Delta_t_sh
Adjacent Shale Transit Time
Source and review
reviewedBassiouni, Z. 1994. Theory, Measurement, and Interpretation of Well Logs, SPE Textbook Series Vol. 4, Chapter 3, Page 54.
Source