Directional survey in the drilling process is widely used, and it is an essential part of the operational drilling along the predetermined path. Another type of measurement while-drilling, namely, measurement of the natural radioactivity of the rocks is currently becoming relevant. Information on the values of natural gamma radiation of rocks provides control of the drilling tool orientation in horizontal drilling. Measuring natural radioactivity of the rock can be used instead of wire line logging or used in combination with gamma-ray well logging to provide correlation and improve assessment of rocks as well.

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Theoretical aspects of gamma-ray distribution in rock are described in the article. Information concerning the values of natural gamma radiation of rocks provides for the control of the drilling tool's orientation during horizontal drilling. A simulation of gamma-ray distribution in rock, based upon the example of western Siberian fields, has been made in a COMSOL Multiphysics interactive environment. Test results for a prototype, two-probe device for horizontal borehole positional control are contained in this document. The maximum distance for the registration of changes in the natural gamma radiation of rocks was determined. The attenuation coefficient for the natural gamma radiation of rocks introduced by the influence of a nonmagnetic drill collar was calculated. Practical advice for improvements in the registration characteristics of the prototype device is provided.