29.7 Recommended Use of QC Methods

This section provides an overview of the error terms that can be controlled using the various QC test described here and makes recommendations for an optimal sequence of tests to be performed at different stages of the drilling process3.

Table 1 indicates those error terms that can be quality controlled during or after each survey station/section using georeference comparison and multi-station tests, and those terms that can be controlled using repeated measurements and independent surveys tests. The table shows that a few highly significant error terms (continuous gyro drift, sag, and declination) can rarely or never be controlled or are very difficult to control, with georeference comparisons and multi-station tests. However, these error terms can be controlled using repeated measurements based on in-run/out-run survey comparisons and independent verification surveys. It is concluded that it is usually necessary to use one or more of the independent surveys tests to QC a survey fully with respect to its entire error model.