Cement Additives

Dowell

Cement Additives

Additives 1

Dowell

Well Conditions ADDITIVE CATEGORY

PROBLEM Well control over pressure and weak formations

SLURRY PARAMETER Density

SOLUTIONS Extenders Weighting agents

Temperature

Thickening time

Accelerators Retarders

Permeable formations

Fluid Stability Fluid loss control

FLAC

Mud removal Friction pressure Mixability/Pumpability

Rheology

Dispersants Gelling Agents

Lost circulation

Plugging/Bridging properties Density

Abnormal and specialized conditions: Hydration product Strength retrogression Foamers Stabilized foam capability Foam

Foaming tendency

{

LCM Extenders Silica Foaming agent & stabilizers Anti foamers Additives 2

Dowell

Cement Additives l Accelerators and Retarders n Change thickening time n Alter rate of compressive strength development

l Extenders n Reduce slurry density n Increase slurry yield

l Weighting Agents n Increase density

l Dispersants n Improve mixability n Reduce friction pressure

Additives 3

Dowell

Cement Additives l Fluid Loss Control l Lost Circulation Material l Specialty: n Antifoam/defoamer additives n Bonding agents n Expansive additives n Gas migration control additives n Gelling and suspending additives n Foaming additives

Additives 4

Dowell

Conductors l Prevents washing out under rig l Short rig downtime l Quick setting cement - rapid development of compressive strength l Accelerated slurries, e.g..: n Neat cement + NaCl (D44) 3-5% n Neat Cement + CaCl2 (S1) 2-4% n Neat cement + seawater

l Lightweight slurries Additives 5

Dowell

Surface Casings l Unconsolidated zones l BOP support l Protect surface waters l Prevent fluid flow l Very large volumes of slurry l Light weight slurries l Strong slurry at shoe (accelerated) l Extended lead with neat tail, e.g..: n

Prehydrated bentonite 2-3% 12.8 ppg

n

Neat cement + 0.5-1% S1 15.8ppg

Additives 6

Dowell

Thickening & Setting Time l Control to n Reduce WOC (reduce rig-time) n Reduce chance for fluid/gas flow n Allow time to complete job

l Affected by n Temperature n Pressure n Cement type (class and grind) n Mixing and placement methods n Accelerators and Retarders n Other additives (salt, dispersant, fluid loss additives)

Additives 7

Dowell

Accelerators l Applications n Shallow casings (conductor, surface) n Low temperature conditions n Offset retarding effects of other additives

l Additives n Calcium Chloride (CaCl2) - 1-4% n Sodium Chloride (NaCl) - 6% D20) l Slurry stabilizer (free water and sedimentation) l High concentrations (>12%) provide fluid loss control ( dispersion Additives 46

Dowell

Use of TIC D80 in ETD 20

30

30

Underdispersed

Yield Value ( /100ft2)

25

Overdispersed

Yield value

Acceptable Range

25

15 20

20

Free water 10

15

Free Water 15 (%)

10

10

5

Viscosity

Plastic Viscosity 5 (Cp)

0.00

0.05

5

0.10

0.15

0.20

0.25

D80 (gal/sk)

Note: ETD Cement at 185°F Additives 47

Dowell

Use of TIC D604M in ETD 20

30

30

Underdispersed

Yield Value (lb/100ft2)

25

Yield value

25

Acceptable Range

15

20

20

Viscosity 10

15

Free Water 15 (%)

10

10

5

Plastic Viscosity 5 (Cp)

0.00

0.05

Free water

0.10

0.15

0.20

5

0.25

D604M (gal/sk)

Note: ETD Cement at 185°F Additives 48

Dowell

Fluid Loss in Cement Slurries l Definition: n Filtrate lost to the formation n Filter cake deposited at formation face n Cement particles left in annulus

l Why cement loses water: n Differential pressure n Permeable medium (formation)

l Fluid loss stages: n Dynamic n Static

Additives 49

Dowell

Dynamic vs. Static Fluid Loss l Dynamic n Placement n Loss is proportional to time n Filter cake reaches pseudo-stable thickness n Density increases n Slurry properties change

l Static n After placement n Loss is proportional to square root of time n Cake grows n May result in annular restrictions u

Causes loss of hydrostatic pressure Additives 50

Dowell

Effect of Fluid Loss l Damage to some formations by filtrate l Gas migration through thick filter cake and through poor quality cement l Other properties: REDUCED n n Slurry yield n n Free water n n Thickening time n n Settling n n Bulk Shrinkage n n Mud removal efficiency (?)

INCREASED n n Hydrostatic n n Slurry density n n Plastic viscosity n n Yield point n n Compressive strength n n Bonding

Additives 51

Dowell

Thickening Time (min)

160

Thickening Time versus Density

Yield Value

TH ICK EN ING TIM E

40

E YIELD VALU

15.6

Slurry Density (ppg)

16.4 Additives 52

Dowell

Mechanisms of Fluid Loss Control l Reduce cement filter cake permeability n Particulate materials to fill voids n Polymer particles to plug pores n Change cement particle distribution with dispersants

l Increase viscosity of aqueous phase n Water soluble polymers n Small effect compared to permeability reduction

Additives 53

Dowell

Mechanisms

Particle Plugging

Polymer Plugging Additives 54

Dowell

FLAC* Additives l Particulate n Gel - D20 n Latex - D600 (MT,M-HD,L) D134(HT,HD,L) n Microgels - D300, D500(AD,LT,L) l Water Soluble Polymers n Cellulose Derivative u D60, D59(MT,ND,S) D112(MT,LD,S) n Non-Ionic Polymer u D127(LT,S) B30(LT,S) D159(L-MT,AD,L) D160(L-MT,AD,S) n Anionic Polymer u D603(MT,ND,L) D143, D158(M-HT,HD,L), D156(LT,AD,S) n Cationic Polymer - D73.1(M-HT,ND,L) n FLAC Enhancer - D136 (below 200oF) * Mark of Schlumberger Additives 55

Dowell

Dispersant Effect on Fluid Loss Mechanism of action •• ••

Disperse cement grains and improve packing --> reduced permeability Flocculate w/salt ---> plugging action

FILTER CAKE WITHOUT DISPERSANT

WITH DISPERSANT

RANDOM PACKING

ORDERED PACKING

HIGH PERMEABILITY

LOW PERMEABILITY Additives 56

Dowell

Acceptable Fluid Loss Limits l Gas zones

30 - 50 mL/30 min

l Liner

< 50 mL/30 min

l Casing

200 - 300 mL/30 min

l Horizontal well

alpha dicalcium silicate amorphous strong, impermeable C/S = 1.5

crystalline weak, permeable C/S = 2.0

l Prevented by addition of 30 - 40% BWOC silica (reduces C/S ratio of C-S-H gel) CSH gel + silica ---------> Tobermorite C/S = 0.8

Tobermorite

---------> Xonotlite + Gyrolite C/S + 1.0

C/S + 0.8

Care should be given to production temperatures Additives 60

Dowell

D30 Silica Sand & D66 Silica Flour Particle size US Mesh

D30 SILICA SAND 70 - 200

Additional Water

±10% 1.12 gal/sk

Specific gravity

2.63

NAME

D66 SILICA FLOUR > 200 + 12% 1.34 gal/sk 2.63

Applications: High density

Preferred

Alternative

Low density

Alternative

Preferred

Settling Problems

Alternative

Preferred

Mixing Problems (Rheology)

Preferred

Alternative

Use above 300°F

Alternative

Preferred Additives 61

Dowell

Antisettling Agent D153 l Controls free water and/or sedimentation l Compatible with all Dowell products and cements l No significant effects on slurry properties, except rheology l Dry-blend or prehydrated (preferred), fresh or sea water l Temperature range: less than 302oF (150oC) l Concentration: 0.1 to 1.5%BWOC (depending on density) Additives 62

Dowell

Slurry Stability

Additives 63

Dowell

Antifoam Agents l Purpose n Prevent slurry gelation n Allow true slurry density to be mixed and pumped n Prevent pump cavitation (due to aeration)

l Mechanism of action: n Lower surface tension n Reduces film and causes rupture

l Types of antifoam agents n Polyglycol ethers

Solid : D46 (0.2 lb/sk) Liquid : D47 (0.05 gal/sk) n Silicones

Liquid : D144 (0.01 - 0.02gal/sk) Liquid : M45 (0.05 gal/sk) Additives 64

Dowell