RHOB
Schlumbergerlbm/gal[US]Bulk Density
Formation bulk density from gamma-gamma scattering — the primary porosity log. Combined with a matrix and fluid density it yields density porosity, and paired with neutron it is the workhorse lithology and gas crossplot of formation evaluation.
- Property
- Bulk Density
- Density
- Quantity
- mass per volume
- lbm/gal[US] · 0.01 grain/ft³ · µg/cm³ · grain/gal[US] · lbm/gal[UK] · 0.001 lbm/gal[UK] · 0.001 lbm/bbl · kg/dm³ · g/gal[UK] · g/m³ · mg/dm³ · t/m³ · mg/gal[US] · g/L · lbm/in³ · mg/m³ · 10 Mg/m³ · mg/L · lbm/ft³ · kg/L · lbm/bbl · 0.001 lbm/gal[US] · Mg/m³ · 0.1 lbm/bbl · g/cm³ · g/gal[US] · grain/ft³ · g/dm³ · kg/m³
- Typical range
- ~1.4–2.7 g/cm³
- g/cm³ across typical clastics and carbonates
Logging tool
No logging tool is associated with this curve.
Service company
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View Schlumberger mnemonics →What is the RHOB curve?
How it's measured
A pad-mounted gamma source (Cs-137) irradiates the formation; two detectors count Compton-scattered gammas, whose attenuation scales with electron (≈ bulk) density. A spine-and-ribs correction removes mudcake effects.
How it's used
Porosity from ρb = ρma(1−φ) + ρf·φ, gas detection via neutron-density crossover, and lithology identification with PEF. One of the two logs in nearly every porosity evaluation.
Common gotchas
It is a shallow, pad-contact measurement — washouts and thick mudcake drive it too low (reads too porous). Always screen RHOB with its DRHO correction and the caliper; a large DRHO means the density is suspect.
In LAS files
Recorded as RHOB (or DEN, ZDEN) in g/cm³. Its partner correction DRHO and the caliper should travel with it.
Also known as
Variants of RHOB seen in real LAS files — PetroCurve maps each of these on import.
Based on 35,011,462 samples in the public corpus.
Also seen with RHOB in real logs
Curves that appear alongside RHOB in the same wells across the public corpus.