Reduced Density Keys Success in Cementing Geothermal Well

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Reduced Density Keys Success in Cementing
Geothermal Well
S. Matlick - Ormat Nevada Inc., R. Hernández,
and H. Nguyen, Halliburton
2
Overview

• Background
• Location
• Geology
• Challenges
• Technology and Operations
• Conclusions

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Background

• ORMAT generates more than 700 MW of power in 22
  countries
• Including 237 MW in the USA
• - Heber wells
• Beginning 2005 for 10 MW expansion
• 3 new production wells
• 4 new injections wells
• 20 in surface casing form 240 ft to 420 ft
• First 2 wells required 222 excess cement
• First well (well P-12) required 4 top jobs
• Inital volume pumped 328 cuft (50 excess)
• After top jobs 1514 cuft total

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Location
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Geology

• Heber Reservoir
• Capping clays above 1,800 ft
• Sedimentary matrix permeability 1,800-5,500 ft
• Fracture permeability below 5,500 ft Seepage loss

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Challenges

• Providing good cement around surface casing
• Reduce or eliminate cement top jobs
• Factors contributing to challenges
• Rapid penetration rates and pumping rates
  (inducing fractures and washouts)
• Weak formations could not withstand hydrostatics
  pressures of regular cements
• Cement set times not adequate

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Technology and Operations

• Rate of penetration (ROP) and pump rates
• ROP Limited to 60ft/hr
• Pump Rate reduced form 500 gal/min to 350 gal/min
• Density reduction material
• Use of lightweight cement additive (Microspheres)
• Provide early compressive strength
• Have good thermal insulation properties
• Accelerated slurry set
• Use of calcium sulfate
• Aid in lost circulation control
• Impart thixotropic properties

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Technology and Operations (Contd)

• Flushes/Spacers
• Reactive spacers
• Improve mud displacement and cement bonding
• Control fluid loss

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Conclusions

• Reducing cement-slurry density
• , decreasing drilling rates and drilling-fluid
  pump rates,
• accelerating cement-set times, and
• applying reactive flushes ahead of the slurry
• have reduced surface-casing cement costs by about
  37.