Chapter VII Squeeze Cementing Remedial procedure repair casing
- Slides: 23
Chapter VII Squeeze Cementing
Remedial procedure • repair casing leak • excessive gas or water production - coning • abandon a producing interval • repair of primary cementing failures
Pump cement under pressure into: • formation voids • porous zones • other issues listed earlier P > formation pressure = high < formation pressure = low
High Pressure Squeeze ~ 50 % successful (at best) Fractures are vertical NOT horizontal.
1950's - Low Pressure Squeeze Displacing water out (squeezing) of the cement. Too fast = flash set
Bull heading required if packer is closed coning But open the packer allows circulation Once cement is “spotted” set the packer $ apply pressure 200 -500 psi @ surface
9. 5 lb/gal SW x 0. 052 = 0. 465 psi/ft 465 psi normally pressurized 465 psi 200 - 500 psi overbalanced
Once cement has been placed: 2 options 1. ) Let it set then drill it out 2. ) Release the packer and "reverse" cement out.
"Reverse" out means Pump down the annulus and return excess cement up the tubing. Cement stays in perfs because 1. Cement in perfs has set 2. Flow direction
Doing this right requires water loss control ! Ordinary cement loses water too quickly
LWL - Low water loss cement. Measure water loss cc/30 min 1000 cc/30 min 300 cc/30 min 150 cc/30 min 25 cc/30 min
Placement Techniques Bradenhead Technique: (no packer or release packer) • Tubing below perfs. • Hole full of water • Casing value open • • Spot cement Close casing valve Raise tubing above cement Reverse out excess cement
Casing bears the full pressure - Eliminates this method for high pressure squeeze - hole has to be full of water to start
Packer Method • Set packer after cement is spotted • Squeeze • Release packer • Reverse out cement
Designing a squeeze job. - Design slurry. - pumping time - avoid flash setting (low end of water loss) (high end of water loss) class G: depth > 6000 ft add retarder
Avoid Formation Fracture gradient of the formation Defines - the maximum surface pressure you can use
Fracture gradient = 0. 6 psi/ft @ 10, 000 ft what pressure fractures the formation = 6000 psi Fill hole with 10 lb/gal saltwater 10 lb/gal x 0. 052 x 10, 000 ft = 5, 200 psi 800 psi at surface 800 psi + 5, 200 psi downhole
1800 psi Pfrac 6000' hole Psurface 4339 psi = 0. 72 psi/ft 6000 ft q stepwise test Pbh = 1800 psi + (6000 x 0. 052 x 8. 33) – 60 = 4339 psi
Fracture Gradient
Maximum Surface Pressure 2 fluids saltwater cement Safety Margin = 300 psi fracture gradient = 0. 75 psi/ft
Maximum PBH Pfrac = 6975 ft × 0. 75 psi/ft = 5231 psi - 300 psi = 4930 psi DO NOT EXCEED
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