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Compass IPM Issues
A guide to some issues associated with ipm files taken from Compass.
The Well Seeker Install includes a range of Instrument Performance Models (IPM) which have been created in line with the most up to date ISCWSA guidelines. In addition to these IPM files, Well Seeker is also able to utilize IPM files taken from Compass. These IPM files can be added manually, or they can be pulled in automatically as part of the Compass import process.
Care should be taken when assigning imported Compass IPM files. If assigned IPM files are giving unexpected results, then the user should check the below points.
In the IPM Co-efficients, there is a Vector and Tie-On entry for each row. An entry of “n” means that the associated error term is used as an intermediate calculation step in the error model calculation.
One of the issues seen with imported IPM files is that the tie-on column is marked as “n”, but the vector column is not. This can be seen in the below left screen shot, which is incorrect and incompatible with the ISCWSA standards.
If experiencing issues, check that any terms marked as “n” in the tie-on column are also marked as “n” in the vector column. The below right screen shot is correct.
The first column of the IPM file contains the name of the error term and the second contains the vector. Well Seeker (and the ISCWSA) requires the error term name to be unique for a given vector. If there are duplicate names with the same vector, the IPM can give unexpected results.
As an example, in the below left, the cgsys terms are duplicated as they all have the same name and vector. To address this issue, these terms must be renamed so they are unique (below right) and any other terms which use them must also be renamed. Note, in the below right that the vector was also changed from “a” to “n”, in line with the Vector Tie-On issue detailed above.
For some error terms, the weighting function may reference another error term in the formula. In the below, the term cgransq3 uses the term stiltavg.
In a situation like the above, any term which is referenced in the weighting function of another term, must come above it in the error file. The above example is correct, but if the stiltavg term was below the cgransq3 term, you would get unexpected results.
Some MWD IPM files have two values entered for the term drfr. These two entries have different numbers (usually 2.2 and 0.35) in the “Value” column. The term with the magnitude 0.35 is correct and the other term must be deleted.