In order to accurately calculate drilled trajectories, the method of quantitatively recognizing borehole trajectory models was provided, and a case analysis was conducted. Because the measurement-while-drilling data provide with measured values of tool-face angle besides inclination angle and azimuth angle, this paper presents the technological approach of recognizing borehole trajectory models based on tool-face angle. A universal tool-face angle equation was established based on the directional deflection mechanism of steerable drilling tools, and it can calculate the tool-face angles with characteristic parameters of various borehole trajectory models. Then, by evaluating the error between the theoretical values and the measured values of tool-face angle, the trajectory model most consistent with the actual well trajectory can be selected. The model recognition of borehole trajectory provides with the quantitative evaluation index and selection basis of survey calculation methods, which can avoid subjectively and randomly selecting the survey calculation method, and consequently improve the monitoring accuracy and reliability of borehole trajectory.
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