Well Trajectory Measurement Error Based on Gyro Survey

Abstract

Gyroscopic survey technology is one of the key technologies to promote the progress of directional drilling technology. It is of great practical significance to study the error of well trajectory measurement based on gyro surveys and identify the main error sources. This paper introduces the error sources which lead to the uncertainty of borehole position in gyroscopic survey, six gyroscopic survey error models, and the calculation model of the contribution rate of the error sources to the error ellipse. The differences between gyro and MWD survey errors and the main error sources of gyro surveys are investigated with an example. The results show that gyroscopic surveys cannot reduce the uncertainty of borehole position compared to MWD surveys in the environment without magnetic interference. The static measurement by a three-axis gyro inclinometer is more beneficial for the improvement of the measurement accuracy of the borehole position. The error sources that contribute to the measurement error of the well trajectory are also different in the vertical section, build-up section, and horizontal section. Unlike the main error source of the MWD survey, the g-dependent error sources of the gyro sensor significantly contribute to the measurement error of the borehole trajectory. Therefore, the measurement error of the well trajectory can be significantly reduced by improving the gyroscope survey tool and reducing the influence of spin mass unbalance.

Keywords

• directional drilling
• gyro
• measurement error
• contribution rate