Use this geological calculation for a transparent first-pass interpretation of measured rock, soil, fluid, well, stratigraphic, isotopic, geophysical, or seismic data under an explicitly selected model.

GR log

Gamma ray reading in API units.

GR clean

Clean-sand gamma ray end member in API units.

GR shale

Shale gamma ray end member in API units.

Model

Transform model.

Convert a gamma ray reading in API units to shale volume using the linear or Larionov transforms. The tool evaluates the supplied inputs together and returns the named outputs below; it does not infer omitted operating conditions or change the units shown.^[1]

I_GR

Gamma ray index I_GR between zero and one.

V shale

Shale volume fraction from 0 to 1.

• Log-derived porosity, shale volume, permeability, and saturation depend on tool type, borehole conditions, invasion, lithology, matrix and fluid properties, environmental corrections, calibration, and depth matching. Core and pressure data should constrain interpretation.
• Use finite inputs in the displayed units and preserve more precision than the final presentation requires. Independently verify safety-critical, financial, compliance, or production decisions.

Compare independent measurements and models, retain units and analytical metadata, propagate uncertainty, and validate interpretations against logs, cores, maps, laboratory data, or field observations.

• Well Log Gamma Ray Index Calculator

  Linear gamma-ray index IGR = (GR - GR_clean) / (GR_shale - GR_clean) from log readings in API units; the standard first step toward Larionov-style Vshale estimates.

• Well Log Porosity Neutron Calculator

  Correct a neutron porosity log reading (limestone porosity units) for shale content using V_shale times the shale neutron reading.

• Magnetic Susceptibility Lookup

  Determine the dimensionless volume magnetic susceptibility chi = M / H (SI) from an induced magnetization in amperes per meter and a magnetizing field strength in amperes per meter, and convert it to CGS electromagnetic units (chi_cgs = chi_SI / 4 pi). A negative value indicates diamagnetic behavior.