Whipstock Milling Operation - Best Practices



  • Ensure that a drill pipe strainer is ALWAYS in the pipe when pumping fluids into the well
  • Ensure 4 x ditch magnets are in place for extracting milled cuttings.
  • Prepare sweeps prior to milling operations to aid clean up.
  • Theoretical swarf weight estimation has been noted from whipstock supplier.
  • Consider inclusion of circulation sub in the string for increased hole cleaning capability (especially if milling 7” liner – position circulation at top of liner activate and sweep at high flow rate).
  • Include a non ported float in the BHA to prevent plugging the mill with swarf.
  • Include string magnets in any contingency clean up BHA (note: do not remove transit tape as it makes it easier to clean).
  • Ensure there is sufficient spaceout to allow milling operation to be performed without connection breaks.
  • Confirm maximum allowable torque according to drill pipe connections.
  • Highlight the safety practice of using correct PPE when handling metal cuttings and ensure all personnel are wearing suitable gloves when handling metal swarf.
  • Particular attention should be paid to ensuring that good hole cleaning practices are observed during the milling phase. These practices include regular sweeps and use of ditch magnets.
  • Maintaining effectiveness of ditch magnets is extremely important. Prior to removing a magnet from the ditch for swarf removal and weighing, first insert a clean magnet.
  • Clean magnets and collect swarf for weight measurement.
  • Record total weight of swarf retrieved (ditch magnets, junk basket & string magnets) since start of milling and compare with theoretical milled steel weight.
  • Sweeps should follow the Baroid Fluids recommendations for consistency, volume, and frequency. Record swarf weight for each sweep.
  • The Barolift pills should be caught at surface and disposed of to avoid mixing with new mud.
  • Barolift is mixed through the hopper into a separate volume of circulating fluid. After mixing, circulate (15-30 min) through the hopper’s venturi to disperse the product into the fluid and prevent clusters of product in the fluid.
  • Do not work mills in area of whipstock tip for any prolonged period (max 30 mins).
  • Do not sit in the same place on the whipstock face for prolonged period – mill may eat into whip face.
  • Estimate and record percentage of cement against formation from shakers.
  • Inspect and record mill wear.
  • When running follow up drilling assembly – orient to window exit and slide through without circulation

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