# Tiab’s direct synthesis (TDS) technique

TDS technique for pressure transient analysis

01-23-2022

TDS technique was created by Tiab (1993) and provide a practical solutions using characteristic points reading from a log-log plot of pressure and pressure derivative. It may be use to estimate permeability, skin factor and WBS coefficient without the use of type curves.

Recommended procedure

1. Identify the horizontal part of the derivative corresponding ti IARF
2. Draw a horizontal line through the IARF data and read the value of the derivative during IARF, $$(t* \Delta P')_r$$
3. Pick a convenient time, $$t_r$$, during IARF and draw a vertical line to intersect the pressure-change curve.
4. Draw a horizontal line from the point of intersection of the vertical line to the y-axis, and read the pressure change, $$\Delta P_r$$
5. Calculate the permeability from $k = \frac{70.6q \mu B}{h(t* \Delta P')_r}$
6. Calculate the Skin factor from $s= \frac{1}{2}\left[\frac{\Delta P_r}{(t* \Delta P')_r} - ln \left(\frac{kt_r}{1688* \phi \mu c_tr_w^2} \right) \right]$
7. Draw a unit-slope line through data corresponding to WBS
8. Read the coordinates of any point on the unit-slope line $$(t,t* \Delta P')$$
9. Calculate the WBS coefficient from $C = \frac{qBt}{24(t* \Delta P')}$ Image 1

Example: TDS technique in Excel Data from [1]

From image 1, taking the characteristic points and estimate the parameters from the past equations

Excel File

References

1. Spivey, J. & Lee, J. (2013) Applied well test interpretation. Society of petroleum engineers
2. Escobar, F.H. (2019) Novel, integrated and revolutionary well test interpretation and analysis