| Magnetic measurement errors significantly affect the wellbore positional accuracy in directional drilling operations taken by Measurement While Drilling (MWD) sensors. Therefore this research has provided a general overview of error compensation models for magnetic surveys and elaborated the most accurate calibration methods of hard- and soft-iron, as well as multiple-survey correction for compensating drilling assembly magnetic interference to solve the problem of wellbore positional uncertainty and provide accurate surveying solution downhole. The robustness of hard- and soft-iron calibration algorithm was validated through an iterative least-squares estimator initialized using a two-step linear solution. A case study of a well profile, a simulated well profile and a set of experimental data are utilized to perform a comparison study. The comparison analysis outcomes imply that position accuracy gained by multistation analysis surpasses hard- and soft-iron compensation results. Utilization of multiple-survey correction in conjunction with real-time geomagnetic referencing to monitor geomagnetic disturbances, such as diurnal effects, as well as changes in the local field by providing updated components of reference geomagnetic field, provide superior accuracy. |
