C0001D sonic processing note

For anybody who uses hole C0001D sonic log cure from SonicVision:

* The compressional slowness curve was labeled based on a basic idea, which is to make a continuous curve. Therefore, for interval where both MPS-Wide and Leaky-P have low coherence and hard to pick, I labeled it along the basic trend of coherence.
* Above 2400m, itfs hard to say labeled slowness is formation compressional or mud arrival. I tend to say it is mud arrival as slowness value is more or less constant @ 200us/ft.
* Meanwhile, considering very slow formation with its slowness close to mud, mud arrival could have some interference on formation signal.
* Interval 2750m ~ 3100m is less accurate. Slowness was labeled based on not only MPS Wide but also Leaky-P mode. However as we know, Leaky-P mode is dispersive, whatfs more the data are very noisy, low signal noise ratio  at this interval, please check STC projection coherence before use.
* Note leaky-P only is applicable to very slow or extremely slow formation, do not use Leaky-P mode processing for fast or intermediate formation.


Liu Wei
Data & Consulting Services
Beijing CHG, Schlumberger


Note
The depth in this document is the meter from KB (Drill floor on Chikyu), therefor you should subtract 2228.0m to convert mbsf (meter below sea floor).
MPS_Wide: wide frequency band processing
LeakyP:   frequency dispersion processing