Shale shakers Suction line

21.DRILLINGPROBLEMS

1. 
   BIT BALLING
   

Water sensitive, young shales can form soft sticky clay when exposed to water. This sticky clay can adhere to water wet metal. If the problem becomes severe the clay may block the annulus, or cover the bit completely.
PREVENTION

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  Ensure good bit and hole cleaning.
  
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  Specify an inhibitive fluid to limit the water imbibition. Ca++, Cl- and PO₄--- ions are generally very effective.
  
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  CURE
  
• 
  Apply a concentrated slug of phosphate surfactant to ensure oil wetting of the metal surfaces.
  
• 
  Apply an inhibitor to limit the water imbibition.
  

2. 
   TORQUE AND DRAG
   

Torque is rotational resistance arising from contact with the wellbore. Drag is the linear resistance. Excessive wall contact and sticky clays / thick filter cake can increase the torque and drag; reducing drilling efficiency
VERTICAL HOLES
In vertical holes torque and drag are usually well within tolerable levels. High values are an indicator of a more specific problem and should be investigated to determine the actual cause. Curing without such an investigation may mask a more serious problem.
DEVIATED HOLES
In deviated holes the drill string is in more intimate contact with the wall. Over long sections the contact may eventually require a lubricant to optimise the delivery of power.
Again, excessive build up of torque and drag is generally an indicator of a different problem and all possible causes should be thoroughly investigated before applying treatments with lubricants.
DIFFERENTIALLY STUCK PIPE
The inability to move the drill string can result from a number of circumstances; many of which have already been covered. The remaining, drilling fluid related, cause is differential sticking.Cause:
Differential pressure, towards the formation, also acts on any pipe in contact with the filter cake. A soft, thick, cake can act like a ‘suction’ cup and hold the pipe in place.
PREVENTION

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  Ensure that the minimum drilling fluid density, to safely drill the well, is maintained.
  
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  Use additives that will give a thin, tough, slick, impermeable cake under downhole conditions.
  
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  Use fluted or spiral drill collars.
  
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  Do not let pipe remain stationary longer than absolutely necessary and never when pumping.
  

CURE

• 
  Carefully(!) reduce the mud gradient (well control!)
  
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  Immediately reduce the pump rate and commence jarring. Do not stop pumps entirely as the cuttings must be circulated out to avoid complicating the problem.
  
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  Spot one of the proprietary blended spotting fluids (packaged oil based fluids).
  
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  Use sufficient to cover the zone plus 10% above. A further volume is required, as the pill should be moved 5 m up the hole every 10 minutes to ensure good contact. Normally soaking time should be approximately 1 hour. Therefore an extra 30 m of annular volume is needed.
  
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  The spotting fluid should be weighted to prevent an ingress of formation fluid.
  
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  Failing this an overshot with a drilling face is needed. During fishing the drilling fluid must be highly treated to minimise new filter cake build up. High levels of lubricant should be used to minimise friction on both overshot and drill string. The fluid density must be kept to a minimum to ensure that the overshot is not stuck as well.
  

3.