Diagraphics

A diagraphics (" well log" of English) consists in measuring, after having carried out a drilling, the characteristics of the crossed Roche S, using various probes. Generally, one calls diagraphics any recording of a characteristic of a geological formation crossed by a survey according to the depth. There exist instantaneous diagraphics: the characteristics of the formation are then recorded during drilling (" LWD: logging while drilling"). There exist also differed diagraphics, the characteristics of the formation being recorded after drilling, the trimming of drilling having been withdrawn of the well. The measuring instruments are then connected to an electric cable (" Wireline Logging").

The differed diagraphics can record, when they cross a material:

its resistivity and spontaneous potential
its natural radioactivity (contents out of Potassium, Thorium and Uranium);
speed of sound in this material;
density of the formation, its porosity, its permeability.
the temperature of the " boue" of drilling
of the geometrical parameters, like the diameter of the survey.

The instantaneous diagraphics can record, when they cross a material:

its content hydrocarbons and/or water
rate of advance of the trepan which drills;
its porosity;
its permeability;

Diagraphic measurements make it possible to estimate the contents (the " saturations") out of water and hydrocarbons of the crossed tanks. They also make it possible to determine the dip of the layers, the determination of the characteristics of the well of drilling, the comparison of the various wells between them, and to locate the producing layers of the insulating layers (not-producing).

These measurements are determining for the effectiveness of oil exploration. They make it possible to confirm or not the indices detected during the preliminary phases of seismic of surface and drilling. If the indications are favorable, they will be followed phases of tests of well (in order to test production capacities of the studied well) and of equipment (" completion")if the well is considered commercially profitable.

They are the brothers Conrad and Marcel Schlumberger which invented the diagraphics (initially called " coring électrique"). The first measurement of this type dated September 5th, 1927. It was carried out on the well Pechelbronn # 7 in Alsace.

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