Geosteering is usually responsible for addressing geological uncertainties, such as the uncertainty in the position of the horizon structure or the structural dip angle. During drilling, the directional survey measurements are taken as true, whilst the uncertainties related to the instruments are not considered. Measurement errors cannot be completely excluded, but they can be reduced to a minimum (reducing the "ellipse of uncertainty" of measurements) by considering the variability of the Earth's magnetic field and the influence of the external factors on the tool (by employing quality control and correction of directional measurements), as a result, reducing the risks of crossing the fluid contacts by the wellbore.

This work is devoted to the methods of detecting and minimizing the inclinometer measurement error while drilling, as well as the application of the results for geological support of drilling. The article describes the principle of the methodology for correcting the inclinometer measurements while drilling and indicates the cases in which the correction method is applicable. The paper considers the prerequisites for using the measurement quality control method and tools to reduce the measurement error in these cases. The possibility of using the method of geomagnetic referencing IFR, as well as methods for correcting measurements of the telemetry system BHA Sag and MSA, to fulfill geological tasks is considered.

This paper provides an example of quality control of directional measurements after drilling a well with an extended horizontal section. In the course of the work, the values of measurement errors along the vertical and lateral were established at a large deviation from the wellhead of the considered well. Attention is focused on the analysis of the identified inclinometry errors, their consequences and impact on the geological drilling of the wellbore and considered an example of improving the quality of geological support using the method of correcting directional measurements while drilling.

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