The authors are concerned that the claim of increased accuracy for MWD directional surveys processed using multistation analysis (MSA) may not always be valid, resulting in incorrect assumptions regarding the probability of well collision and target intersection. Very little information is available about the MSA methods currently in use. The only relevant published work identified by the authors is an SPE paper defining the minimum survey log conditions required to validate surveys against the ISCWSA MWD error model, but the requirements do not support assumptions of increased accuracy, post correction.
It was therefore decided to determine if MSA can be used to reliably increase survey accuracy. The study also evaluated the validity of using the published minimum requirements to validate data against a typical MSA enhanced error model. The mathematical technique of consider covariance analysis was used to quantify post correction position uncertainty, and compare it to typical MSA error model assumptions. The results were validated using monte carlo simulation.
The study showed that use of the published minimum data condition requirements to validate surveys against the increased accuracy claim typical of MSA error models is invalid. For the minimum requirements method to provide validation of such arbitrarily enhanced error models, new requirements must be defined specific to the MSA model. However, typical MSA error model assumptions are likely to result in requirements that can very rarely be met. Consider covariance analysis offers a reliable method of evaluating actual survey data against an arbitrarily enhanced error model on a case-by-case basis, which would allow more frequent use of the MSA error model.