Introduction:
- There is concern that ISCWSA MWD error model is not sensitive to station length
- SPE67616 MWD Paper states “survey interval no greater than 100’”
- Establish the effect of survey interval length on wellbore position accuracy
- Provide systematic error terms to add to MWD error model based on station length and angle change
- Old survey data, with long intervals
- Big rigs with 120-140’ stands
- Misruns or some stations missing validation
- Pressure to survey less often – save rig time
Method Steps - Empirical:
- Look at continuous Gyro surveys with stations reported at 10-30’ (5-10m) regular intervals
- Remove alternate stations, calculate the survey and note the difference in bottom location
- Divide by run length and present as Error / 1000 – Graph the results
- Compute trend line, repeat for other lengths
- Correlate to angle change (dogleg) and length
Continuous Gyro Surveys 10-20’
- 51 FINDS Inertial tool run till 1985 (1700m)
- 90 RIGS Ring Laser Gyro 1985-2000 (2200m)
- 106 Continuous Gyros: Gyrodata, SDI Finder/Keeper, GCT, UK North Sea (2900m)
- 57 SDI Continuous Gyros: Norway (2800m)
- 80 Drill Pipe Gyros Horizontal pump down (2800m)
- 24 SDI Drill Pipe Gyros run in 3 ½” drill pipe (1350)
- 53 Gyrodata 3m, some 1m surveys (2000m)
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View the entire Presentation:
The Effect of Survey Station Frequency on Wellbore Position Accuracy
Jerry Codling