8 gas migration cl 22 jun 00 a
DESCRIPTION
Gas migration for oil well cementsTRANSCRIPT
GAS MIGRATION
CAUSES AND CURES
Module CMT 102 June 2000
Gas migration: Causes and Cures
Consequences of gas migration
Gas migration paths
Root causes for gas migration
Schlumberger technology
Consequences of gas migration
Blow-out: surface or underground Danger to personnel
Lost rig
Less dramatic but important consequences Lost production
Treatment fluids injected in wrong zones
Annular pressure on surface
Damage to the environment
Repair required: prevention is better than cure
Gas Migration
FluidDensity ControlMud Removal
CementSlurry Design
Cement Hydration
Set Cement
Mechanical Properti
es
A complex problem involving a hierarchy of potential problems with a corresponding hierarchy of solutions
Gas migration paths
Mud channels
Mud cake
Channels due to free water development or sedimentation in the cement slurry
Cement matrix during liquid/solid transition
Cement matrix fissures/fractures, cement/casing or cement/formation interface once cement is set
Paths for gas migration
In the cement slurry before it sets
or during setting process
In a mud channel or mud cake
Paths for gas migration
GAS ZONECEMENT
In a channel due to free water or sedimentation of the cement slurry (highly
deviated wells)
FREE WATER CHANNEL
Paths for gas migration
In the cement after
it sets
At cement/casing or cement/formation
interface once cement is set
Paths in the drilling fluid
Mud removal is the KEY Remove the bulk of the mud:
Centralize the pipe
Pipe movement
Apply adequate displacement techniques: WELLCLEAN
Remove at least the soft part of the mud cake
Mud properties requirements Low rheology/gel strength
Low fluid loss and thin impermeable mud cakes
Paths in the cement before it sets
Hydrostatic pressure transmission is the key During the job
cement density is the key After placement cement loses its ability to fully
transmit hydrostatic pressure due to: Gel strength development Downhole volume variations: fluid loss, temperature and
hydration volume reduction
Consequence pore pressure within the gelling cement is decreasing and
may become smaller than formation pore pressure Gas can now possibly invade the annulus
Cement slurry requirements
Appropriate density
Appropriate rheology for good mud/spacer removal
Good stability at downhole conditions
Very low fluid loss to minimize volume variations downhole and hence slowdown hydrostatic pressure decline: API < 50 mL/30 min
Ideally right angle transition from liquid to solid
In practice during the transition period: Minimum gel strength development
Low permeability and low hydration volume reduction
Short transition time from 30 to 100 Bc
Paths in the cement after it sets Set cement has a very low permeability:
it acts as a seal
But set cement may fail at providing a seal: The cement itself may crack due to variations
downhole stresses: changes in temperature, pressure, far field stresses
The cement may debond from the casing and/or formation
These failure mechanisms provide paths for gas from the formation to possibly invade and migrate up the annulus
Example of cement sheath failure
t
rock
cement
casing
P,T
Radial crack: failure in tension (hoop stress) due to pressure and or temperature increase
Example of cement sheath failure
rr
rock
cement
casing
Cement debonding: failure in tension (radial stress) due to pressure and or temperature decrease
Set cement requirements Ductility is the key:
Requirement for a material that can better stand downhole stresses variations than most cement systems which are fairly brittle
Very important when large temperature or pressure variations are expected during the life of the well
Very important when large variations in far field stresses are expected during the life of the well e.g. formation subsidence
Good bonding to the casing and the formation
Low long term shrinkage
SLB technology
GASBLOK Service has been proved effective in a wide range of conditions:
Slurry density from 10 to 24 lb/gal (1.20 to 2.88 kg/L)
Temperatures up to 400°F (204°C)
Depths greater than 20,000 ft (6,000 m)
GASBLOK additives are used all over the world in particular in area where gas migration represents a significant hazard
Gas-migration-control slurries
GASBLOK (D600/D134) additives Suspension of submicron latex
particles
Temperature range from 150 to 400°F
(65 to 204°C)
Works in a wide density range 10 to 24 lb/gal (1.20 to 2.88 kg/L)
Easy to design and to mix
Synergetic effect with CemCRETE technology
Applications Gas migration in low (D500), medium
(D600) to high (D134) temperature wells
Gas-migration-control slurries
GASBLOK D600 Temperature range from 150 to 250°F (65 to 121°C)
Above typically 200°F (93°C) with D135 stabilizer
Density range 13 to 24 lb/gal (1.56 to 2.88 kg/L)
Can be mixed with fresh or sea water
Salt tolerance: Up to 6% NaCl or KCl BWOV without D135
Up to 18% NaCl BWOV with D135
Concentration depends on BHST and slurry porosity
Stabilizer and dispersant: D65/D80/D604/D135
Gas-migration-control slurries
GASBLOK HT D134 Temperature range from 200 to 400°F (93 to 204°C)
Density range 15.6 to 24 lb/gal (1.87 to 2.88 kg/L)
Can be mixed with freshwater only
Stabilizer D135
Dispersants: D121, D65, D080
Concentration depends on BHST and slurry porosity
Use D066 above 230°F (110 °C) BHST
D600/D134 GASBLOK slurries
Excellent slurry rheological properties Very good stability Very low API fluid loss (lower than 50 mL/30 min)
Extremely low fluid loss rate Thin and impermeable filter cakes
Low permeability during liquid/solid transition Low hydration volume reduction in particular in
CemCRETE slurries Short transition time from liquid to solid
D600/D134 GASBLOK cements
Improved bonding and mechanical properties (SPE 13176)
Improved set cement resistance to chemical attack
Conventional cement GASBLOK cement
Example of D600 slurry design
Density : 20.1 lb/galAPI Class G cement30% BWOC Silica flour85% BWOC Hematite0.8% BWOC D1213.10 gal/sk D6000.06 gal/sk D0800.05 gal/sk D0472.38 gal/sk Fresh water
Yield 1.76 ft 3̂/skThickening time 5 hr 20 minFluid loss 34 mL/30 minFree water NilPV at 80 deg.F 260 cpTY at 80 deg.F 15.7 lbf/100ft 2̂PV at 185 deg.F 211 cpTY at 185 deg.F 34.8 lbf/100ft 2̂24 hours CS > 6000 psi
Gas-migration-control slurries
GASBLOK LT (D500) additive A liquid microgel (submicron particles) with a density
of 1.0 kg/L Environmentally friendly Temperature from 80 to 165°F (27 to 74°C) Slurry density from10 to 16.5 lb/gal (1.20 to 1.98 kg/L) Easy to design and to mix Compatible with all Dowell accelerators and retarders Non-retarding Synergetic effect with CemCRETE technology Non-damaging to formations
D500 GASBLOK LT slurries Applications of D500 slurries
Shallow annular gas migration Gas migration in cold wells
Properties of slurries and set cements using D500 Excellent slurry rheological properties Excellent stability Extremely low API fluid loss (lower than 40 mL/30 min)
Extremely low fluid loss rate Thin and impermeable filter cakes
Low permeability during liquid/solid transition Low hydration volume reduction in CemCRETE slurries Shorter transition times at low temperatures
Summary Slide
D500 Fluid-Loss Control Behavior
Examples of D500 slurry designs
15.8 ppg: 80F 16.4 ppg: 120F 15.8 ppg: 160F
Slurry design:
Dyckerhoff Class G +
D047 (gps) 0.03
D080 (gps) 0.04
S001 (%BWOC) 1
D500 (gps) 0.80
Slurry design:
Lonestar Class H +
D047 (gps) 0.03
D080 (gps) 0.06
D500 (gps) 1.00
Slurry design:
Indocement Class G +
D047 (gps) 0.03
D145A (gps) 0.14
D500 (gps) 1.20
Rheology @ BHCT
Ty (lbf/100 ft2) 10
PV (cp) 49
10-min gel 24
API fluid loss (mL) 20
API free water (mL) 0.5
Thickening time@ BHCT (hr:min) 3:50
Rheology @ BHCT
Ty (lbf/100 ft2) 3
PV (cp) 58
10-min gel 24
API fluid loss (mL) 26
Free water (mL) none
Thickening time@ BHCT (hr:min) 3:30
Rheology @ BHCT
Ty (lbf/100 ft2) 13
PV (cp) 28
10-min gel 25
API fluid loss (mL) 18
Free water (mL) 0.4
Thickening time@ BHCT (hr:min) 5:38
Examples of D500 slurry designs
12.5 ppg: 80F 12.5 ppg: 120F 12.5 ppg: 160F
Slurry design:
Dyckerhoff Class G +
D047 (gps) 0.03
D075 (gps) 0.50
S001 (%BWOC) 1
D500 (gps) 1.50
Slurry design:
Dyckerhoff Class G +
D047 (gps) 0.03
D081 (gps) 0.10
D075 (gps) 0.50
S001 (%BWOC) 1
D500 (gps) 1.00
Slurry design:
Dyckerhoff Class G +
D047 (gps) 0.03
D081 (gps) 0.10
D075 (gps) 0.50
D500 (gps) 1.50
Rheology @ BHCT
Ty (lbf/100 ft2) 29
PV (cp) 17
10-min gel 31
API fluid loss (mL) 28
API free water (mL) 0.2
Thickening time@ BHCT (hr:min) 12:00
Rheology @ BHCT
Ty (lbf/100 ft2) 16
PV (cp) 13
10-min gel 19
API fluid loss (mL) 30
API free water (mL) none
Thickening time@ BHCT (hr:min) 4:22
Rheology @ BHCT
Ty (lbf/100 ft2) 9
PV (cp) 11
10-min gel 194
API fluid loss (mL) 34
API free water (mL) 1
Thickening time@ BHCT (hr:min) 6:17
GASBLOK technology
Encompasses WELLCLEAN mud removal as the first key element
Superior slurries with GASBLOK additives
Thin, but stable (no free water, no sedimentation),
Non gelling Excellent fluid loss
control Short transition times Impermeable to gas
A complete technique covering all aspects of the gas migration problem
FluidDensity Control
Mud Removal
CementSlurry Design
Cement Hydration
Set CementMechanical Properties
Superior set cement characteristics for long term