DCAL
Schlumbergeryd[US]Differential Caliper
The difference between measured borehole diameter and bit size — a direct washout and mudcake indicator. Positive where the hole is enlarged, negative across mudcake on permeable beds, near zero in gauge hole.
- Property
- Differential Caliper
- Diameter
- Quantity
- length
- yd[US] · link[Cla] · µm · m[Ger] · nm · Mm · yd[Ind37] · link[BnB] · ft[BnB] · 100 ft · yd[Cla] · yd[SeT] · 0.1 ft · ft · link[BnA] · ft[BnA] · ft[GC] · 0.1 ft[US] · 1/64 in · ft[Ind62] · km · 100 km · yd[Ind] · fur[US] · 0.1 yd · chain[SeT] · in · mil · chain[BnB] · mm · yd[Se] · mi · mi[naut] · 1/² ft · ft[Br65] · Gm · Em · rod[US] · fathom · ångström · ft[Cla] · dm · ft[Ind37] · chain · chain[Cla] · link[SeT] · link[US] · ft[US] · chain[Ind37] · link[Se] · yd[Ind75] · hm · m · ft[Ind75] · in[US] · chain[Se] · dam · 1/32 in · ft[Se] · 30 ft · yd[BnA] · fm · chain[BnA] · mi[US] · Tm · link · 10 km · ft[Ind] · ft[SeT] · 10 ft · 0.1 in · yd · 1000 ft · 10 in · pm · chain[US] · cm · 30 m · 1/16 in · yd[BnB] · ft[Br36] · mi[nautUK] · yd[Ind62]
- Typical range
- ~-2–10.4 gAPI
- inches, deviation from bit size
Logging tool
No logging tool is associated with this curve.
Service company
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View Schlumberger mnemonics →What is the DCAL curve?
How it's measured
Computed as caliper minus bit size, isolating hole-condition deviation without needing to eyeball CALI against BS.
How it's used
A one-curve hole-quality flag and a quick screen for where pad logs (density, PEF) are unreliable. Negative excursions mark permeable, mudcaked, potentially reservoir beds.
Common gotchas
It is a derived difference — its usefulness depends on an accurate bit-size entry. Interpret sign conventions carefully (some vendors flip it), and remember it inherits any caliper-arm limitations.
In LAS files
Recorded as DCAL in inches. Zero is gauge; watch for sustained positive (washout) intervals.
Also seen with DCAL in real logs
Curves that appear alongside DCAL in the same wells across the public corpus.