Slowness of the Formation Formula
Slowness of the Formation calculates formation slowness observed by sonic log for rock properties workflows in petrophysics.
How engineers use this formula
Use this formula when the listed inputs (t_l, L_s, Delta_t_m, d_h, d_t, l_c) 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, Delta_t equals 50 us/ft.
188.72983346207417
3
200
0.7
0.3
0.1
Inputs
t_l
usFirst-Arrival Acoustic Travel Time
L_s
ftTransmitter-Receiver Spacing
Delta_t_m
us/ftMud Acoustic Slowness
d_h
ftBorehole Diameter
d_t
ftTool Diameter
l_c
ftTool Eccentricity or Mudcake Offset
Outputs
Delta_t
Formation Slowness Observed by Sonic Log
t_m
Mud Path Correction Time
D_b
Borehole Mud Path Length
t_l
First-Arrival Acoustic Travel Time
L_s
Transmitter-Receiver Spacing
Source and review
reviewedTheory, Measurement, and Interpretation of Well Logs, Bassiouni, Z. (1994)
Bassiouni, Z. 1994. Theory, Measurement, and Interpretation of Well Logs. SPE Textbook Series Vol. 4, Chapter 10, Page 189.