Analyses of the Accuracy and Reliability of Magnetic Directional Surveys

摘要

Multi-station processing techniques can be used to improvethe accuracy of wellbore directional surveys by removing theeffects of systematic errors. The main intention of this paper isto provide improved understanding and documentation of suchmethods when applied to magnetic surveys. Basic propertiesof the method are discussed in detail. The combined use ofstatistical tests and multi-station estimation techniques areevaluated, together with the ability to improve the accuracy ofwellbore positions. This is demonstrated for a wide range ofsurveying conditions.Due to a number of reasons; poor geometry, lowredundancy, high random noise levels, the presence of grosserrors, and errors in the Earth's gravity and magnetic fieldreferences, it is often possible that there will be amisinterpretation of the estimation results. This may lead toreduced accuracy and quality of the surveys. Even under thebest possible conditions it is demonstrated that the processingof multiple surveys does not necessarily improve accuracy,rather it impairs accuracy and produce unreliable results.The study also shows the importance of having a soundunderstanding of the simultaneous effects of potentialuncorrected systematic effects, in order to increase the chanceof making correct conclusions.