Page 111 - The Geological Interpretation of Well Logs

- SONIC OR ACOUSTIC LOGS -

GAMMA RAY API INTEAVAL TRANSIT TIME
50 156 140 At pitt 40

GAMMA RAY LITH INTERVAL TRANSIT TIME
<=
API
At ptt
90
140
100

22300m 2? =
2725
2926m A y —s
oS 2750

Le
metres
depth,
KE — finely laminated shale NN
L_] sit H shale
Figure 8.14 Sonic response to shale structure ia a shallow Figure 8,15 Subtle textural and structural variations in deep
marine, coarsening-up sequence. The finely laminated shales sea, turbidite sands, shown on the sonic log. The log changes
at the base of the sequence show a high interval transit time indicate variations in grain-size, texture and structure but
(low velocity), while in the more massive, bioturbated, silty which dominates in this example is not known.
upper parts of the sequence, interval transit mes are lower
(velocity higher),

90 RS

90 us

—
—
b
f
90 ps
90 xs bye"
<] Yn
90 & ps = v
a = Wi v a™,
a ad
MARKER =
a
= ~

wry

st

7
q
DATUM
e

é $ é
Figure 8.16 The ‘character’ of the sonic log used for correlation. The tog is sensitive to lithological changes (texture and
composition) as indicated by the logs in this shale sequence. The outside wells are 40kim apart, the zone between 40m and
75 thick.
101