Revision 03 January 1998 * Mark of Schlumberger SILICADRILL* - Silicate Water Based Drilling Fluid Applications Inhibitive Mechanism Concerns and Limitations

Revision 03January 1998

* Mark of Schlumberger

SILICADRILL* - Silicate Water Based Drilling Fluid

Applications

Inhibitive Mechanism

Concerns and Limitations

Engineering

Success Stories



SILICADRILL*Drilling fluids based on soluble sodium silicate first introducedin 1930’s.

Based on 20-50% soluble silicates Difficult to control because of high rheologies

Silicate water based fluids further explored by collaborationbetween Mobil, BP Exploration, Shell Research and BW Mud.

Recent silicate systems introduced based on lower concentrations of soluble silicates



SILICADRILL*

Ability of fluid to reduce shale hydration proportional to :

Increasing silicate concentration. Increasing salt concentration (KCl reducing shale hydration more than an equivalent level of NaCl).

Minimum 10,000 ppm SiO2 required (3% v/v silicate solution).

Optimum at higher pH (approaching pH 12) which additionally prevents fluid gelation. Evidence of synergy with polyalkylene glycols.

Factors Determining Shale Inhibition



0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

-10 0 10 20 30

Temperature (°C)

Vis

co

sit

y (

cP

)

2.5 : 1 (43%)2.0 :1 (42%)1.6 :1 (48%)2.0 : 1 (42%) + 10% ethylene glycol2.0 : 1 (42%) + 5% KCl

Physical CharacteristicsViscosity / Temperature Profiles for Sodium Silicate Liquors



SILICADRILL*

0

20

40

60

80

100

9 10 11 12

pH

Rec

over

y (%

)

15

20

25

30

35

40

45

9 10 11 12

pH

Moi

stur

e (%

)

Effect of Fluid pH on Shale Inhibition



SILICADRILL*Effect of Sodium Silicate Concentration on Shale Inhibition

0

20

40

60

80

100

0 4 8

%

Rec

over

y (%

)

20

24

28

32

36

40

0 4 8

%

Moi

stur

e (%

)



SILICADRILL*

20

25

30

35

40

45

50

3%6%

Effect of Salt Concentration on Shale Inhibition

Mo

istu

re (

%)

Sodium Chloride Potassium Chloride

Sodium Silicate

Blank 15ppb 30ppb 54ppb 109ppb 25ppb



SILICADRILL*Synergy with Polyalkylene Glycol

14

16

18

20

22

24

26

28

0 1 3

STAPLEX 500 (%)

Mo

istu

re (%

)



SILICADRILL*-Premix Formulation

Fresh Water 0.662 bbl

Sodium Silicate Liquor 0.255 bbl

KCl 60.0 lb/bbl

IDF-FLR XL 3.0 lb/bbl

IDFLO 9.0 lb/bblOCMA Clay

25% v/v sodium silicate liquor0

50

100

150

200

250

300

-5 0 5 10 15 20 25

Temperature (°C)

Vis

co

sit

y (

cP

)



SILICADRILL*-Fluid Formulations and Properties

Product ‘Clean’ Fluid ‘Dirty’ Fluid

Fresh Water 0.725 bbl 0.709 bbl

KCl 35.0 lb 35.0 lb

Sodium Silicate 0.110 bbl 0.110 bbl

IDVIS 1.0 lb 1.0 lb

IDF-FLR XL 1.5 lb 1.5 lb

IDFLO 4.5 lb 4.5 lb

PTS 200 2.0 lb 2.0 lb

Hymod Prima - 35.0 lb

BARITE 152.8 lb 125.5 lb

OCMA Clay

Fluid PV YPcP lbs/100 ft2

6 3 Gelslbs/ 100 ft2

pH APIcm3

Na2Omg/l

SiO2

mg/l

Clean 18 17 4 3 4/ - 12.5 11.6 27,900 52,125

Dirty 17 17 5 4 7/ 16 12.5 4.8 24,025 44,625



Mechanism

Invasion of filtrate (pH 12)

Gellation of invading silicate species in lower pH environment Precipitation of insoluble Ca2+, Mg2+ silicates Chemical dissolution of Al / cementation of clays

Ca2+Mg2+

Mg2+Ca2+

pH 7

Barrier formation at near well bore



a b c

Transmission Electron Micrographs of Kaolin clay treated with various fluids: a) raw untreated clayb) aged for 3 days at 300 F in distilled waterc) aged for 3 days at 300 F in a 3% aqueous sodium silicate solution at pH 12

Mechanism-Clay Alteration



Concerns Sensitive to solids contamination

Sensitive to CO2 and H2S contamination Can cause severe gellation and elevated fluid loss if pH is not maintained.

Low shear viscosity is borderline, limiting applications for deviated wells.

Lubricity is poor compared to other water-based muds. Foaming problems identified with IDLUBE XL. Alternative lubricants under review.

Temperature stability limited to wells where BHST is below 230°F. Concern over formation damage in some reservoirs. Depth of invasion of damage not determined.

Elastomer Compatibility Progressive gellation of silicate fluids over long time periods. Not recommended as packer fluids.

Logistics. The volume of sodium silicate stabiliser (C307) recommended for optimum shale control is 8-12 % by volume of the brine phase.



Temperature Stability

0

5

10

15

20

25

30

35

140 160 180 200 220 240 260

Temperature (°F)

YP API Fluid Loss

Fluid FormulationFresh waterSodium silicate Liq. 10%KCl 40.0 ppbIDVIS 1.3 ppbIDF-FLR XL 1.5 ppbIDFLO 4.5 ppbPTS 200 2.0 ppbHMP 35.0 ppb Barite 97.1 ppb

Mud Weight 11.5 ppg

Effect of Temperature on Fluid Properties

TFL



-20

20

60

100

140

180

f(

F/d

) H

ard

ne

ss (

%)

QUADRILLSilicateKCl / polymer

Polypak Polypak Polypak PolypakNW6 NW6 MZ3 MZ3 Seal Boot Seal Boot (o-ring) (o-ring)

Elastomer Compatibility

CARBOXYLATED VITON NITRILE HSNNITROXILE

Change in Elastomer Surface Hardness



-40

-30

-20

-10

0

10

D

ep

th (

%)





Change in Elastomer Dimensions



-4

-2

0

2

4

6

8

10

W

eig

ht

(%)





Change in Elastomer Weight (Swelling / Erosion)



Lubricity

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 100 200 300 400 500 600 700 800 900

Load (daN)

Fri

cti

on

Co

eff

icie

nt

Blank

3% DP97/016

Frictional Wear Almen-Wieland Lubricity Results



Contamination PV

(cp)

YP

(lb/100ft2)

pH 6

(cp)

3

(cp)

Gels

(lb/100ft2)

API

(ml)

Na2O

(ppm)

SiO2

(ppm)

None

CO2

5% Carnalite Brine(1)

10% Carnalite Brine(2)

20

24

23

28

19

24

24

36

12.5

11.0

11.9

12.4

5

6

7

19

4

5

5

15

5/8

8/13

6/8

20/30

7.1

38.0

4.6

8.0

25,575

18,600

13,950

6,200

53,000

3,000

18,000

3,750

CO2 and Carnalite Brine

5% Carnalite Brine(1) 1.8 lb/bbl NaOH used to buffer pH to 1210% Carnalite Brine(2) 4.0 lb/bbl NaOH used to buffer pH to 12

Effect of CO2 and Carnalite Brine on Fluid Properties

Properties after heat ageing at 160 °F.



Contamination PV

(cp)

YP

(lb/100ft2)

pH 6

(cp)

3

(cp)

Gels

(lb/100ft2)

API

(ml)

Na2O

(ppm)

SiO2

(ppm)

None

10 lb/bbl Bentonite

20 lb/bbl Bentonite

30 lb/bbl Bentonite

40 lb/bbl Bentonite

50 lb/bbl Bentonite

60 lb/bbl Bentonite

20

22

24

26

27

31

33

19

17

19

21

26

28

30

12.5

12.4

12.3

12.3

12.1

12.1

11.9

5

5

5

6

6

7

8

4

4

4

4

5

5

6

5/8

5/-

5/6

5/-

6/7

6/-

7/9

7.1

7.4

4.9

5.8

3.9

5.1

3.3

25,575

25,575

24,025

-

23,250

23,250

20,150

53,000

47,250

44,625

-

42,750

41,625

39,000

Drilled SolidsEffect of Bentonite Contamination on Fluid Properties




Contamination PV

(cp)

YP

(lb/100ft2)

pH 6

(cp)

3

(cp)

Gels

(lb/100ft2)

API

(ml)

Na2O

(ppm)

SiO2

(ppm)

None

35 lb/bbl Chalk (Fine)

2.5% Cement Slurry(4)

5% Cement Slurry(4)

20

30

28

32

19

24

30

21

12.5

12.4

13.0

13.0

5

7

13

8

4

5

11

6

5/8

8/10

9/15

6/6

7.1

18.2

4.8

6.1

25,575

23,250

20,150

18,600

53,000

41,250

31,500

23,625

Cement Slurry(4) 50% w/w slurry in fresh water

Cement and ChalkEffect of Cement and Chalk Contamination on Fluid Properties




Contamination PV

(cp)

YP

(lb/100ft2)

pH 6

(cp)

3

(cp)

Gels

(lb/100ft2)

API

(ml)

Na2O

(ppm)

SiO2

(ppm)

None

5% ULTIDRILL

10% ULTIDRILL

20

29

41

19

30

38

12.5

12.4

12.5

5

9

14

4

7

12

5/8

9/15

12/19

7.1

4.3

4.2

25,575

17,050

-

53,000

38,250

-

ULTIDRILL ContaminationEffect of Contamination of an ULTIDRILL Invert Synthetic Fluid




0

20

40

60

80

100

0 5 10 15 20 25 30

NaCl Brine

Mixed Brine (Ca, Mg, Fe)

Reservoir Damage Characteristics

Time (min)

% R

etu

rn P

erm

eab

ility

Return Permeability Studies on Berea Sandstone Cores



Concentration MonitoringTitration Procedure (NaF - HCl)

0

10,000

20,000

30,000

40,000

50,000

60,000

0 3 6 9 12 15

% Silicate Liq. (v /v)

mg

/dm

3

Si02

Na2O



SiO2 Adsorption Isotherms

30,000

35,000

40,000

45,000

50,000

55,000

0 10 20 30 40 50 60

Drilled solids (lbs /bbl)

SiO

2 (m

g /d

m3)

Hymod Prima

Bentonite

Silicate Depletion on LGS



Effective Engineering

Maintain pH with Routine Additions of Caustic Soda. Control LGS with pre-defined Dump & Dilute Programme Maintain SiO2 with Additions of Sodium Silicate Liquor

Pf / Mf Ratio



SILICADRILL* - Special Considerations

Be aware of the dilution rates. They are very high for SILICADRILL and willrequire some heavy logistics.

System Dilution Coefficient (bbl/ft)

Glycol Mud 0.5 to 1OBM 0.3 to 0.4Silicate Mud 1.5 to 1.7

Elastomer compatibility might be an issue. Please get in contact with our sistercompanies (W&T, Sedco and Anadrill) and make sure that they know we aregoing to use a silicate mud.

SILICADRILL is not tolerant to high LGS concentration. The level should alwaysbe maintained below 5%. So make sure that the adequate solid controlequipment is in place otherwise a heavy dump & dilute approach will have totake place.



Environmental Impact

Not classified as toxic or dangerous (main hazard attributable to high alkalinity)

Silicates known to form an important resource in the marine food chain.

OSPAR green list - Category ‘A’

UK CNS (Chemical Notification Scheme) category ‘E’ rating

The proposed Preliminary Assessment Information Rule under TOSCA included soluble silicates : The environmental regulatory profile of soluble silicates provides incentive for their preference over more hazardous and more highly regulated alternate materials



HSE Issues Main hazard of sodium silicate liquor attributable to high alkalinity.

Rabbit dermal irritancy study on silicate drilling fluid indicated no reaction (up to 4 hours exposure).

No field problems reported with respect to skin irritancy of silicate drilling fluid on any well intervals drilled using SILICADRILL*.

PVC slicker suits recommended if heavy contamination expected.

PVC or rubber gloves are recommended

Eye contact must be avoided. Glasses or goggles should always be worn, and preferably face visors while working on the drill floor or in the mud processing area.

Vapours from the drilling fluid will not be a problem, but mists possibly generated from the shale shakers could be irritating to the respiratory tract. Adequate ventilation will keep mist to a minimum, but if mists are generated respiratory protection in the form of a dust respirator type P1 is recommended.



Shale Hydration

0

5

10

15

20

25

30

35

40

Mo

istu

re (

%)

ULTIDRILL

Silicate-glycol

Silicate

QUADRILL

KCl/IDBOND

VISPLEX

Seawater/PHG

H20 Adsorption from Drilling Fluid



Shale IntegrityPenetrometer Hardness Profiles

0

300

600

900

1200

1500

1800

2100

2400

2700

0 1 2 3 4 5

ULTIDRILLSilicate-glycolSilicateQUADRILLKCl-IDBONDVISPLEXSeawater/PHG

Fo

rce

(g)

Penetration (mm)



Current Status

First Dowell Silicate well spudded July 1997 (Canada).

Dowell Canada have used and seen benefits from the lubricant (XE859) First Dowell Silicate Well in the North Sea -a full success Sept 1997.

Engineers’ Training of this new mud system is ongoing at UTC and KTC.

Resources are now in place to extend applications wrt Improved Thermal Stability Improved lubricity and ROP Improved hole cleaning capabilities



Future Work

Further evaluation of XE859 (SHELL, Houston). Initial indications that it aided clean up on MI-BP Tester metal surfaces.

Further evaluation of highly modified cross-linked starches. For higher temperature applications or where restrictions on use of PTS 200.

Accretion concerns in silicate fluids formulated with NaCl (GOM). “Anti-accretion” organics to be further investigted, possibly in conjunction with XE859 Lubricant. Dispersants No significant thinning action in solids laiden muds, but still to evaluate in Ca2+/Mg2+ - silicate gelled system. (IDSPERSE XT, DRILLTHIN, D145, TKPP).



SILICADRILL* Field Experience

Ten hole intervals (July 1997-Jan 1998)

4 X 16” and 4 X12 1/4” intervals offshore Canada

1 X16” and 1 X 171/2” intervals in the Central North Sea

All intervals drilled with SILICADRILL* after extensive laboratory

evaluation of offset well cuttings

- XRD Mineralogical analyses

- Shale inhibition studies cf. ULTIDRILL & QUADRILL

- Evaluation of Accretion tendency



Drilling with SILICADRILL* in the North Sea

Case History #1: Appraisal Well

* Objective to Drill 12 1/4” section through reactive shales in the central North Sea

* Formation was soft plastic shale stones from 3037 to 7920 ft

* Previous attempts to drill with water based muds in this area were unsuccessful

* S-shaped well trajectory reaching a maximum inclination of 46 °

* SILICADRILL* was chosen ahead of SBMs on environmental grounds

* BHST @ 168 °F, max mud weight 13.1 ppg




Case History #1 (Cont’d): Appraisal Well

* Rig-site evaluation of inhibitive performance using BP cuttings hardness tester

* Excellent wellbore stability: hole in gauge despite 29 days open hole time Mud related NPT= 3.7%

* All Logging and coring completed successfully

* Logging fluid designed using Fann 70 which determined clean mud was required to avoid gelation

* The biggest problems were logistical. The mud was run at higher solids levelsthan programmed (7.3 cf 4%) due to low stocks of silicate liquor

* DUALFLO successfully used to boost low end rheology



SILICADRILL* - Offshore North Sea

10

12

14

16

18

20

22

24

3000 3500 4000 4500 5000 5500 6000 6500 7000 7500

MD (ft)

Bit Size (inch)

Hole Caliper (inch)

Case History #1: Hole Caliper Logs Operational SummaryWell Well AInterval 12¼”Field CNS OffshoreDepth 3,040 - 7,320 ftMax. Angle 46°Max. Mud Weight 13.1 ppg

Time Breakdown HoursDrillingCoringLoggingP&ANon Productive

33096

2224856

Drilling Days 18Total Days 29

Cost Efficiency Relative toSBMs

ratio

Cost/ftCost/bblbbl/ft

1.20.781.66

Volume Analysis bblSurface Cuttings/SCE

Dumped11406097

Wellbore FormationLeft in well

153740

Initial hole enlargement associated with physical wellbore instability due to insufficient mud weight (cavings).




Case History #2:

* Objective to Drill 17 1/2” section through 6547ft of reactive shale in CNS

* Decision to drill made by operator following success of #1

* Vertical to 7500 ft building to 22.8° by 8450 ft, TD at 9535 ft

* Open Hole time of 47 days with no wellbore stability

* 17 days drilling time; delays due to non mud related equipment failures, WOW and

wellhead problems

* Largest Volume of hole drilled by Operator in the North Sea to date

* FMP successfully used with this mud system for the first time



Case History #3: Developmental Wells

* Objective to drill two 16” sections through 7000 ft reactive and dispersive shales

* Formation was mainly siltstone and mudstone

* Maximum hole inclination of 40 °

* SILICADRILL* was chosen on environmental grounds

* STAPLEX 500 was included to maximise inhibitive performance (lab tests)

* BHST 180 °F, max mud weight of 10.1 ppg

Drilling with SILICADRILL* offshore CANADA



Case History #3: Developmental Wells (Cont’d)

* No wellbore stability issues despite 20+ days open hole

* Observed 30% depletion of K+ and SiO2 whilst drilling initial formation

* Fluids also used to drill 12 1/4” sections successfully

* Silicate depleted and mud converted to salt/ polymer/ carbonate

* Well logged, cored and tested without problem-now producing at a satisfactory rate

* Costs reduced by > two thirds over course of next 4 sections via optimising

fluid (lower silicate, removal of STAPLEX 500 and replacement of IDVIS with prehydrated bentonite gel)




15

16

17

18

19

20

21

1600 2600 3600 4600 5600 6600 7600

MD (ft)

Ho

le S

ize

Bit Size (inch)

Well East

Case History #3: Hole Caliper Logs Operational SummaryWell Well EASTInterval 16”Field Canadian off shoreDepth 1,690 - 7,707 ftMax. Angle 40°Max. Mud Weight 10.1 ppgMax. BHST 53°C

Time Breakdown HoursDrillingLoggingCasingNon Productive

3721176

123Drilling Days 16Total Days 24

Cost Efficiency Relative to SBMs ratioCost/ftCost/bblbbl/ft (cf 0.2 forSBM)

2.131.531.49

Volume Analysis bblSurface Cuttings/SCE

DumpedC/F to next Interval

4487.11610.82904.0

Wellbore FormationLeft in well

00




50

55

60

65

70

75

30,00031,000

32,00033,000

34,00035,000

36,000

37,000

22

23

24

25

26

27

28

29

30

31

22

23

24

25

26

27

28

29

30

31

SiO 2 (mg/L)

KCl (Kg/m 3)

% H2O


Extent of Claystone Hydration with K+, SiO2 Concentration (16” Interval, Well-East)

Documents

Revision 03 January 1998 * Mark of Schlumberger SILICADRILL* - Silicate Water Based Drilling Fluid Applications Inhibitive Mechanism Concerns and Limitations