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Ap1.5.3 Inputs Required Required input parameters for the weighting functions calculations:
Well site data: Total gravity value Total magnetic field value (MWD) Magnetic Dip (MWD) Horizontal magnetic field (function of total field and dip) (MWD) Latitude (Gyro)
Survey data at each station: Measured depth, Inclination, Azimuth, Toolface (early revisions)
Tool Model Terms: Error sources included Error magnitude for each source Error propagation mode Inclination bounds for change for mode or for each source (start , end) Misalignment calculation method (ALT=1,2,3) External reference method (gyro) Running Speed (gyro) Rotation of accelerometers between stations (R value, gyro)) Cant angle (gyro) Running mode (sliding or rotating must be defined, either via IPM or as a parameter to control propagation modes.)
Noise reduction factor at initialisations Minimum distance between initialisations
Ap1.5.4 Poorly Defined Functions The MWD model includes a set of equations for the cases where the weighting functions are mathematically ill-defined in vertical hole. The situation at 90 inclinations, 90 (or 270) azimuth is physically ill defined and a software implementation must handle these. The following weighting functions are ill-defined in vertical hole: ABX, ABIX, ABY,ABIY, MX,MY, XYM3, XYM4, ABXY-TI2 and ABIXY-TI2 References [1] and [5] include alternative calculation options that can be used to evaluate these functions.
Ap1.5.5 Test Cases The MWD paper [1] defines three standard test well profiles. These are for: a. an example North Sea extended reach well, b. a Gulf of Mexico fish-hook well, c. a Bass Strait designer well.
Fo ch s c s h w llp ofl ,loc on,m gn ud ndd c onof h E h’sm gn cf ld nd h un s(mo ft) are defined.
The MWD paper then defines seven test cases and error model results for each test case at Revision 0. The gyro paper defines six gyro models and applies each model to the same three test well profiles. The gyro paper also defines acceptance criteria as having numerical agreement to within ±1% of the results in the paper. Consistent Naming of Error Sources An attempt has been made to agree and utilise consistent naming conventions for error sources. Further details can be found in the Error Model Standardisation page of the ISCWSA website, www.iscwsa.org. Ap1.5.6
This naming convention has been used in this document, however it should be noted that same weighting functions should be preceded with the suffix, S, G, W or R depending on the associated propagation mode.
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