Certain wells in the Peace River region of Alberta, Canada, produce heavy crude oil along with H2S and CO2. The heavy crude oil is normally recovered with enhanced production methods involving thermal wells whereby the crude is heated to very high temperatures to facilitate production. One such well became plugged by scale deposits and efforts were made to clean out the obstruction using coiled tubing (CT) intervention techniques. However attempts to do so with jetting tools and acidisation proved to be ineffective and the only alternative left was to run a mill with a downhole motor. A major problem was posed by the bottomhole temperature of 300° C (572°F) which precluded the use of standard motors. The operator was thus faced with the probability of having to make an extended shut down to allow the well temperature to decline to an operable temperature level where standard equipment could be used, or look to alternatives.

In an attempt to avoid this extended downtime it was decided to run a non elastomeric high temperature downhole motor, which uses a positive displacement principle with a stainless steel stator and rotor system with no elastomers, which as a result is rated to 260°C (500°F). The 2-7/8″ OD motor was run with a 3-9/16″ OD mill on 2″ OD CT to try to mill out the obstruction in the 4-1/2″ slotted liner while circulating KCl fluid at the rate of 50 litres/min (13gallons/min) and Nitrogen at 30 standard cubic meters/min (1100 standard cubic feet/min). The obstruction was encountered at 820.6 meters (2,692ft) and successfully milled to 929m (3048ft) where the mill broke through and was run to bottom at 945m (3100ft) to circulate clean before pulling out. The whole operation took a total of 9 hours.

In this paper the authors will review the well conditions and the motor design and explain the decision to run it at downhole temperatures in excess of its rating. They will go on to detail the milling operation which was successful in returning the well to production at a considerable saving in production downtime when compared to the available alternatives.

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