Dynamic Field Acceptance Criteria
MWD STD system uses the dynamic field acceptance criteria similar to the approach described in [1]:
- The covariance matrix Cem compiled on the basis of the MWD error model [2] is converted to the GBD space using the Jacobian J, a function of the survey inclination and azimuth, which recalculates the error terms to the total G, total B, and dip angle errors:
- The dynamic field acceptance criteria are derived from the GBD covariance matrix as twice the square root of the main diagonal of the matrix:
Thus, for each survey, its own quality criteria are calculated depending on the inclination, azimuth and MWD error model. Further, MWD STD system builds confidence intervals from the reference corrected by MSA, which makes it possible to more realistically evaluate the quality of measurements; while the geomagnetic reference is evaluated separately.
Reference Field Acceptance Criteria
As the MSA correction calculates the geomagnetic reference offset, the computed total B and dip angle values are compared to the 2 sigma error of the geomagnetic model being used. The error models of the main geomagnetic models were found in [3]. This test allows you to validate the used magnetic declination error model: if the total B or dip angle are out of the geomagnetic error budget, then it is most likely that the magnetic declination also does not match the selected error model.
In addition, this test allows you to identify such problems as poor MSA performance, bad calibration of the D&I module, considerable drift or offset of the total B and dip angle, etc.
MSA Control
Minimal Requirements
The input data for the MSA correction is checked against the minimum requirements for drillstring interference correction set out in [4]:
Convergence
Since the MSA algorithm is non-linear, MWD STD system checks during the solving process that the algorithm converges.
Accuracy
MWD STD system controls the accuracy of the MSA solution: a posteriori covariance matrix is calculated for the MSA corrected measurements, then the square root of the diagonal elements of the matrix is compared with the corresponding error budgets of MWD error model [5]:
Expectation
MWD STD system also controls the MSA results: the calculated MSA error term value is compared with the 2 sigma of MWD error model for the corresponding error term, except for MBZ, the MBZ correction result is compared with the error budget obtained in [6].
BHA Sag Control
For BHA sag correction MWD STD system controls the algorithm convergence and BHA sag correction result vs 2 sigma of MWD error model for SAG error term.
External Control
MWD STD system monitors the actual inclination and azimuth in relation to the planned inclination and azimuth. A significant deviation could mean a potential problem.
1. Ekseth, R., et al., 2006, The Reliability Problem Related to Directional Survey Data, IADC/SPE 103734
2. Williamson H.S. 2000. Accuracy Prediction for Directional Measurement While Drilling, SPE 67616, SPE Drilling and Completion, 15(4)
3. Maus, S., et al., 2014, Systematic and Random Contributions to the Disturbance Field (IFR 2), ISCWSA meeting
4. Nyrnes E., Torkildsen T., and Wilson H., 2009. Minimum requirements for multi-station analysis of MWD magnetic directional surveys. SPE/IDAC 125677
5. ISCWSA MWD Error Model Revision 4, 2015
6. Shuba Love, 2019, An Empirical Analysis of Survey Errors in North American Land Operations, ISCWSA meeting