Understanding Depth And Uncertainty
- Depth as an issue
- Assumptions and expectations
- Drilling depth measurement
- Calibration and correction
- Way-point method and uncertainty
- First field test results
- The value model
Early Observations - 1938
Later Observations – 2013 – 75 Years Later
- Unsure accuracies
- Inconsistent correlations
- Geological inconsistencies
- Reservoir description issues
- Diminished certainty
- Cost
- Asset valuation compromise
Driller’s Depth 101
- Pipe depth = pipe tally and surface travelling block movement.
- Surface travelling block movement is used to control WoB and RoP, so block position is not necessarily related to changes in bit position.
- LWD is based on bit position, recorded while drilling down, inferred from pipe tally and surface travelling block movement.
Calibration ??
- What is the accuracy associated with the calibration process for measurement of driller’s depth ?
- Calibration conditions
- Process consistency
- Results recording
Corrections while drilling vs POOH
- LENGTHENING EFFECT
- Tension profile (incl. sliding friction) Temperature profile
- SHORTENING EFFECT - NO
- Sliding frictional forces Differential pressure Compressional torqueing Tensional torqueing Mud density Mud velocity Weight On Bit Bit hydraulic pressure Rotational frictional forces Mud pressure
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What Depth ? More Accurate Driller’s Depth DwpD Field Results
Harald Bolt