8 gas migration cl 22 jun 00 a

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


GAS ZONECEMENT

In a channel due to free water or sedimentation of the cement slurry (highly

deviated wells)

FREE WATER CHANNEL


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


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


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


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


Free water (mL) none


Rheology @ BHCT

Ty (lbf/100 ft2) 13

PV (cp) 28

10-min gel 25


Free water (mL) 0.4


Examples of D500 slurry designs

12.5 ppg: 80F 12.5 ppg: 120F 12.5 ppg: 160F

Slurry design:


D047 (gps) 0.03

D075 (gps) 0.50

S001 (%BWOC) 1

D500 (gps) 1.50

Slurry design:


D047 (gps) 0.03

D081 (gps) 0.10

D075 (gps) 0.50

S001 (%BWOC) 1

D500 (gps) 1.00

Slurry design:


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 free water (mL) 0.2


Rheology @ BHCT

Ty (lbf/100 ft2) 16

PV (cp) 13

10-min gel 19


API free water (mL) none


Rheology @ BHCT

Ty (lbf/100 ft2) 9

PV (cp) 11

10-min gel 194


API free water (mL) 1


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

8 gas migration cl 22 jun 00 a

Documents

gelling cement

setsset cement

cement slurrycement

job cement density

keyafter placement cement

field stressesthe cement

gas migrationin

gas migrationcauses