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)

.... 

View the entire Presentation:

The Effect of Survey Station Frequency on Wellbore Position Accuracy

Jerry Codling

 

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