Abstract

Geological interpretation starts from a description of a rock in terms of mineralogy and texture. The compositional description of the rocks derived from conventional wireline logs is restricted by the complexity of the mineralogical model, and the limited sensitivity of conventional logs (except for the photoelectric factor) to mineralogical changes.

Recent advances in geochemical logging and interpretation give a direct, in situ access to the chemical composition of the rock, thus opening the way to quantitative and complex mineralogical analysis.

Furthermore, a large number of key formation characteristics can be better evaluated through the detailed knowledge of the mineralogical assembly: for example, porosity, permeability, grain size, cation exchange capacity. Conventional log analyses can be improved by the additional information brought by the geochemical log.

Finally, a better characterization of the rock facies, in terms of sand classification and clay typing is obtained.

It is hoped that these results will ultimately contribute to better prospect definition, reservoir evaluations, and completion strategies.

Much of the material presented in this paper is derived from an earlier paper published in French by Colombani et al (1988).