The Challenge of Lithology Characterization

Lithology interpretation is a widespread need in almost every subsurface-related industry. Our process is based on a well log combination of measurements including Density, Neutron, Sonic, Spectral Gamma Ray, Borehole Magnetic Resonance and Acoustic/Optical borehole images, combined to provide answers in varying degrees of detail. Formation bulk density, neutron porosity and spectral gamma ray logs (total natural radioactivity and the contributions of three main radioactive series: K40, Th232, U238) drives compositional interpretation. Density and neutron can reflect specific minerals/groups of minerals if they are dominant in the formation (particularly in monomineralic rocks such as anhydrite, halite, etc). The natural radioactivity of some minerals or compounds (i.e organic matter) is above the average for one of the three main radioactive series as seen on the spectral gamma ray log. Borehole magnetic resonance provides textural information, allowing the identification of the main grain size fractions (clay, silt, sand). Oriented borehole images complete the picture by giving us the ability to see surfaces and geometric patterns. Surface interpretation allows us to identify sedimentary beds and their thicknesses, natural fractures, faults and even in some cases sedimentary structures (cross bedding, lamination, etc). Patterns can highlight biological/diagenetic sedimentary structures (massive, nodular, bioturbation) and coarse grained fabrics beyond the capabilities of other tools (such as conglomerates, breccias, clast/mud-support fabrics). Three strategically-packaged well log combinations are provided to achieve your specific objectives.

LithoSight™ – Base

This base level option is composed of Spectral Gamma Ray and Borehole Magnetic Resonance data. This combination is expected to identify levels of sand, shale and evaporites generically speaking. It is possible to spot K-Evaporites from non K-Evaporites. Every interpreted lithology is described in terms of the characteristic log responses, allowing its definition and further correlation.

LithoSight™ – Plateau

An intermediate level well log combo. LithoSight™ – Plateau adds neutron and density to the LithoSight™ – Base combination to offer the general log response spectrum of many of the expected sedimentary lithologies. Sonic data can be integrated in cased holes replacing the density log. The final result is a lithology model combining compositional and textural data. Dominant minerals/groups of minerals can be spotted.

LithoSight™ – Summit

A full well log combination for advanced lithology interpretation, LithoSight™ – Summit builds on the LithoSight™ – Plateau with the addition of acoustic/optical borehole images. The final result is a lithology model combining compositional, textural and fabric/sedimentary structures data. Dominant minerals/groups of minerals can be spotted. Fabrics and sedimentary structures data allows a new level of discrimination (e.g. massive and laminated evaporites).
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