Multistation analysis is a technique that provides drillstring magnetic interference compensation to magnetic surveys. This technique is now in common use in the industry, and this case study data verifies the capabilities of the multistation technique to improve measurement-while-drilling (MWD) azimuth measurement quality and accuracy. This study quantifies a significant improvement to standard MWD surveyed position uncertainty using actual survey data from drilling assemblies used in more than one hundred and twenty runs in over thirty-five different wells worldwide.
The use of multistation analysis, and the subsequent reduction in wellbore position uncertainty demonstrated can significantly reduce the overall surveying and drilling costs for the well, removing the need for correction runs and allowing for the penetration of smaller targets than previously possible with standard MWD surveying. This correction technique can be applied on a real-time basis at the point of surveying. Forecasting of the magnetization effects of the bottom hole assembly (BHA) using the same software, will also allow the driller to place the well more accurately. In some cases the use of multistation analysis with standard MWD surveys will enable the removal of one or more gyrocompass surveys from the survey program. This can reduce overall surveying time and cost, and the exposure of the BHA to additional stuck-in-hole risks that occur when running wireline surveying tools through drillpipe in extended-reach wells.
The main analysis method is based on a direct comparison of MWD survey data before and after multistation correction, against independent overlapping gyro survey data. The results achieved by this study are translated directly into improvements in current industry standard error models, and this paper proposes a standard error model for multistation analysis corrected MWD survey data.