Schlumberger

Litho Scanner High-Definition Spectroscopy Service

The science of spectroscopy

Litho Scanner high-definition spectroscopy service provides the key quantitative measurements of elements and mineralogy, delivered with previously unavailable accuracy and speed.

Download: Litho Scanner spectroscopy workflow (497 KB PDF)

Spectral acquisition

Spectral acquisition



1. The spectroscopy workflow begins with the emission of neutrons by the pulsed neutron generator (PNG) of the Litho Scanner tool to induce the emission of gamma rays from the formation via two primary interactions: inelastic scattering and thermal neutron capture. Each of these interactions produces gamma rays with a specific set of characteristic energies.

The gamma rays are detected by the LaBr3:Ce scintillator coupled to a high-temperature spectroscopy photomultiplier, producing signals that are integrated, digitized, and processed by a high-performance pulse-height analyzer. The analyzer determines the pulse height (proportional to energy) of each detected gamma ray and accumulates pulse-height histograms (spectra) that tally counts versus pulse height. Spectra are acquired during and after each neutron burst, which enables clear separation of the inelastic and capture gamma rays.

Spectral stripping

Spectral stripping

2. Each spectrum is decomposed into a linear combination of standard spectra from individual elements. This step involves correction for some environmental and electronic factors.

Elemental weight fractions

Elemental weight fractions

3. The coefficients of the linear combination of the standard spectra are converted to elemental weight fractions via a modified geochemical oxides closure model or by using an inversion approach.

Interpretation

Interpretation

4.Two approaches are available to generate mineralogy and lithologic fractions from the elemental concentration logs. One is sequential SpectroLith processing, which is based on the derivation of empirical relationships between elemental concentrations and mineral concentrations. The other is by using an iterative inversion technique, such as the Techlog Quanti multicomponent inversion ELAN module.

See How It Works

Litho Scanner
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Determine Mineralogic Complexity with High-Definition Spectroscopy

Litho Scanner service offers the ability to compute total organic carbon and to quantify the mineralogic components of complex lithologies.
Read article (1.48 MB PDF)