Overcoming Fundamental Restrictions: Novel Multistation Measurement While Drilling Survey Correction

Abstract

Summary The traditional multistation analysis (MSA) method for drilling string magnetization compensation considers significantly limited information, only consisting of a single measurement while drilling (MWD) six-axis survey run. The limitations of this approach are an excessive scatter in the corrected azimuth values, poor accuracy in attitudes near the horizontal east/west directions, and low robustness of the algorithm, which make it nearly impossible to automate the survey processing. A novel MSA correction, involving further elaboration of the conventional MSA method, is proposed in this study. The proposed algorithm utilizes all available drilling information, including data from geomagnetic reference, error models, multiple six-axis runs, bottomhole assembly (BHA) designs, and slide sheets. This improvement moves the optimization task to find the survey correction vector from multiple independent spaces of total gravity field, total magnetic field, and dip angle (GBD) for each MWD run into a single GBD + north/east/vertical space of the entire well. Unlike the conventional MSA, which processes only a small portion of the available information, each MWD runs independently, the proposed algorithm finds the survey correction vector for all MWD runs simultaneously with additional constraints of trajectory steering and drillstring interference (DSI) modeling. Consequently, the proposed MSA method provides the best borehole positional accuracy for MWD surveys. Depending on the input conditions, the accuracy of the proposed MSA can be improved by an order of magnitude relative to the accuracy performance of the conventional MSA correction. In addition, this approach demonstrates better stability and robustness than the conventional MSA. The proposed method provides high startup performance, especially during the drilling of the tangent section. This is critically important for building automatic drilling systems and avoiding nonproductive time. Under normal conditions, the proposed MSA algorithm does not have a no-go zone and allows the correction of MWD surveys at the horizontal east/west tangent sections.