Reverse Circulation of Foamed Cement in Geothermal Wells

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Reverse Circulation of Foamed Cement in
Geothermal Wells
Rafael Hernández
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Overview

• What is Reverse Circulation Cementing
• Why Reverse Circulation Cementing
• Benefits of Reverse Circulation Cementing
• Challenges of Reverse Circulation Cementing
• Placement Techniques
• What is Foamed Cement
• Benefits of Foamed Cement
• Case History
• Summary

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What is Reverse Circulation Cementing?

• In conventional cementing processes the spacer
  and cement materials are pumped down the casing
  or tubing and the drilling fluid is returned
  upwards through the annulus
• In the reverse circulation method the spacers and
  cement are pumped down the annulus directly and
  the drilling fluid is returned upwards through
  the casing or tubing internal flow path

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Why Reverse Circulation Cementing?

• A potential solution for difficult conventional
  cementing challenges such as
• Large volumes with long displacement times
• Temperature restrictions
• Deep high temperature zone(s)
• Shallow low temperature zone(s)
• Low equivalent circulating density margins
• Lost circulation
• Seepage loss

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Benefits of Reverse Circulation Cementing?

• Reduced equivalent circulating densities ECDs
• Gravity forces and density differences aid the
  fluid flow process
• Reduced placement time of cement
• Reduced thickening times allow cements to set
  more rapidly
• Ability to customize the thickening time of
  cement slurries
• Minimizes the concentrations of retarders
• Less potential for production zone invasion by
  cement slurry
• Reduced pumping pressure requirements for cement
  placement

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Reverse vs. Conventional ECDs
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Challenges of Reverse Circulation Cementing?

• Software packages are generally not designed to
  simulate RCC
• Standard float equipment is not adequate
• May require backpressure to control cement slurry
  free fall
• Additional tools or methods are required to
  estimate the top of cement
• May require additional well conditioning
• Requires different iron configuration on surface
• May require larger spacer volumes and shoe track
  volume

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Placement Techniques

• Volumetric
• Using a logging tool and radioactive tracers
• Using a stab-in Drill pipe (Case history)

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Stab-in

• Method
• Stab drill pipe into float shoe or collar of
  casing
• Circulate cement until marker reaches surface
• Un-stab and reverse out
• Advantages
• No drill-out of cement after job
• No pressure left in Casing
• Certainty when cement is inside casing
• Disadvantages
• Higher ECDs
• Additional time and expense to run DP

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What is Foamed Cement?

• A fine dispersion of N2 gas in a cement slurry
  creating a low-density cement matrix with low
  permeability and relatively high strength.

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Benefits of Foamed Cement

• Improved properties
• Ductility, youngs modulus
• Anti-gas migration
• Loss circulation control
• High apparent viscosity
• Wet ability

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Case History

• Wellbore parameters
• 11-3/4-in. casing
• 14-3/4-in. hole with 50 excess
• Vertical well 5,064 ft

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Case History

• Job Procedure
• Pressure test surface lines to 3,000 psi.
• Pump 90 bbl of SAPP water at 4 bbl/min.
• Pump 20 bbl of foamed SAPP water.
• Pump 498 bbl of foamed cement.
• Once good cement is at surface, shutdown. Shut-in
  annulus.
• Pump 32 bbl of 15.6 lb/gal unfoamed cement down
  drill pipe.
• Drop dart. Displace drill pipe clean of cement
  with 10 bbl of fresh water and 81 bbl of
  water-based mud.
• Land dart with 500 psi over landing pressure.
• Squeeze 17 bbl of cap cement and 3 calcium
  chloride down annulus.
• Shutdown.

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Reverse vs. Conventional ECDs
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Summary

• Reverse cementing is a viable alternative
• Foamed cement properties enhance the life of the
  well
• Reduced potential for production zone invasion
• Elimination of remedial cementing requirements
• Reduced environmental impact