Introduction – error propagation
- Observation error is unavoidable, regardless of survey activity, e.g. seismic positioning, well bore
- A position is worthless unless accompanied by some form of quality measure, e.g. precision
- Creation of a unified model with errors contributing from all data silos.
- Are the precision measures contained in the seismic trace data propagated correctly?
- Is precision of the tie-in point adequately described from errors from other silos?
What started this study?
- Creation of new replacement database comprising 12000+ wells within a controlled Data Quality Metrics (DQM) environment.
- Well headers: Assignment of coordinate tuples, CRS’, accuracy statement (with probability) and commentary.
- From where? Audit trail conducted on horizontal surface positions, from description of the seismic survey bin grids, processing grids and data loading to interpretation workstation. Conducted by Geomatics Dept., Seismic Acquisition and Seismic Processing
- Logic: If there are errors in the seismic trace data there will be errors of at least the same magnitude within surface activity performed afterwards, including well header positions.
Well header load sheets and captured metadata
- All metadata were captured within the new wells database, along with other notable parameters:
- Rig type
- Rig elevation
- Spud date
- Magnetic Dec. model
- Magnetic Dec. value
- Grid convergence model
- Grid convergence value
- Water depth
- Well environment …………
Are correct precision values passed on to drilling?
- Total precision associated with the coordinates of the tie-in point. Is it known and applied? Taken from positioning technologies of rig move only?
- Is its precision sufficiently described to achieve the precisions required for the drillers target at final bottom hole location?
- What size of uncertainties can be tolerated at tiepoint to achieve target objectives?
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View the entire Presentation:
Hollistic Approach to Survey Error Budgets
Martin Rayson, Geomatics