Reduction of Wellbore Positional Uncertainty During Directional Drilling.

摘要

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.