Lithology, Porosity, and TOC

Integrated evaluation of petrophysical properties

To determine if a formation has commercial hydrocarbon potential, we must first understand the rock type (lithology) and its storage capacity (porosity). In unconventional and many deepwater plays, defining kerogen, bitumen, or tar volume is also critical to production success. Schlumberger petrotechnical experts have the domain expertise and practical experience it takes to obtain and evaluate comprehensive lithology, porosity, and total organic carbon (TOC) data from your reservoir, helping you make the most of your petrophysical information to maximize production.

Lithologic description

Petrophysical evaluation of porosity and saturation first requires an accurate evaluation of matrix density (grain density), which is a function of formation mineralogy. Mineralogy, matrix density, and clay volume can be measured continuously with a neutron-induced gamma ray spectroscopy logging tool. Schlumberger has a variety of spectroscopy tools that provide several options for capturing important lithology data.


Our petrophysical experts can help you determine the volume of solid hydrocarbon material in your formations, whether in the form of kerogen, bitumen, pyrobitumen, or tar. We can estimate TOC via standard industry practices or by using the Litho Scanner high-definition spectroscopy service, which isolates the inorganic carbon from the total carbon, resulting in an accurate TOC measurement.

Porosity determination

Once mineralogy is identified, accurate porosity is determined using the matrix-corrected bulk density measurement and the matrix-corrected neutron porosity.

Magnetic resonance provides a lithology-independent porosity measurement and is affected by the hydrogen density of the formation fluids. Light hydrocarbons are indicated when magnetic resonance porosity reads lower than the density porosity. Solid hydrocarbons are completely transparent to magnetic resonance, so a porosity deficit is also seen in the presence of solids, including bitumen, tar, and kerogen.

With an accurate determination of the mineral content, clay volume, and TOC content, the porosity can also be determined via sonic transit time. The transit time recorded represents the quickest path the sonic wave can travel, bypassing any isolated porosity. Thus the sonic porosity, when compared to the total porosity from another source, can quantify isolated porosity.

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Accurate, TOC-Corrected Matrix Density and Porosity

Mineralogy determined from Litho Scanner elemental weight fractions is confirmed by core mineralogy.The Litho Scanner element logs.Litho Scanner Minerals Plot
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