| Popis: |
Multi-Station Analysis (MSA) is a technique widely used in MWD directional surveying to provide additional quality control and to correct for systematic errors. Although the method's potential to enhance survey quality has been demonstrated through several publications, experience has shown that MSA can produce unstable solutions and poorly interpretable results. In such cases, it is likely that the uncertainty estimate assigned to the data is invalid. Unfortunately, there is no standard in the oil industry defining the correct use of MSA. Different companies have developed different requirements and acceptance criteria, making it difficult to judge and compare survey quality between companies. The industry should therefore seek to establish a common standard for the application of MSA. This paper presents a set of fundamental requirements that have to be fulfilled in order to ensure the correct application of MSA in drilling operations. The requirements consist of a set of mathematical rules and corresponding acceptance limits. Survey quality can be verified against any MWD error model by using the same mathematical framework, but changing the acceptance limits. Requirements and acceptance criteria are presented for two specific error models: Basic MWD without axial interference correction (Williamson 2000) and the same model assuming enhanced geomagnetic referencing. The results presented in this paper show which systematic errors can be estimated for any given data set. A mechanism for determining tolerable survey noise is also included. This prevents misapplication of MSA under poor surveying conditions such as magnetic storms and drill-string vibration. The objective has been to develop requirements that are easy to apply in operations and which can form the basis for standardization across the industry. |
