SILDRILSilicate/Polymer Mud System

North Sea

Development & Application

Presentation by Chris Atkinson

KCl/PHPA Salt sat/silicate Base OilKCl/Glycol Synthetic Oil mud

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KCl/PHPA Salt sat/silicate Base Oil

London Clay Dispersion Tests

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Silicate Performance

Comparative Shale Inhibition

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SiO2:M2O Ratio

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Recovery of Foss Eikeland Recovery of Foss Eikeland Clay with 3% SilicateClay with 3% Silicate

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Recovery of Foss Eikeland Clay with 3% SilicateRecovery of Foss Eikeland Clay with 3% Silicate - Effect of Molar ratio - Sodium Silicate- Effect of Molar ratio - Sodium Silicate

Silicate Performance

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Silicate Concentration (% volume)

Effect of Silicate concentration on recovery of Effect of Silicate concentration on recovery of Foss Eikeland ClayFoss Eikeland Clay

Silicate Performance

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PV - Foss Eik

YP - Foss Eik

PV - Wyoming

YP - Wyoming

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Solids added (kg/m3)

Solids Tolerance of NaSilicate (2.6:1)

3% Silicate / 3% KCl System 3% Silicate / 3% KCl System at 11.7 ppgat 11.7 ppg- Solids Tolerance- Solids Tolerance

3% Silicate / 3% KCl system 3% Silicate / 3% KCl system at 11.7 ppgat 11.7 ppg- Solids Tolerance- Solids Tolerance

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YP - Wyoming

PV - Foss Eik

YP - Foss Eik

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Solids tolerance of NaSilicate (2.0:1)

Silicate Based FluidsField Use

Choice of Sodium and Potassium Silicates - Economics / Practicalities

Standard Polymer type WBM Formulations

Application as Superior Shale Inhibitor / Wellbore Stabiliser

Silicates are “Low Cost” Additives

- Barrel cost not very low !!

- Cost per Foot generally good

• Silicate Gels formed on contact with low pH (Formation

Water / Acid Gas)

• Silicate precipitation with divalent cations (Ca/Mg)

• Precipitated / gelled Silicates bridge across Clays/Sands

• Better stability with added Salts (KCl / NaCl)

• Inhibition optimised using ±5% Silicate alone

• Inhibition optimised using ±4% Silicate with Salt(s)

SILDRILSystem Performance

SILDRILDescription / Formulation

Drill Water (S/W) - Base Fluid Silicate (Na) - Primary Inhibitor(provide water barrier) KCl / NaCl - Secondary Inhibitor (reduce

swelling) PAC UL / Starch - Fluid Loss Control PAC Reg - Rheology (Fluid Loss) XCD Polymer - Rheology / LSRV Caustic Soda (KOH) - Hardness Control (pH) Soda Ash - Hardness Control Bentonite (optional) - Fluid Loss / Filter Cake Barite / Marble - Density

SILDRILEngineering Guidelines

Rheology Xanthan for 6/3 RPM readings -

Variation with Silicate conc.

Fluid Loss ±3.0 ppb PAC U/L & Reg (9 - 6cc)

Silicate 5 - 7% by vol.

KCl 25 - 35 ppb

MBT Generally low (highly inhibitive)

pH 11 - 12 (natural level) Hardness Zero (positive Silicate)

Corrosion Inhibitors not necessary

SILDRILEngineering Guidelines (Cont’d)

• Hole Cleaning Integrity of cuttings requires

optimising LSRV’s & Flow Rates

• Wiper Trips Recommended regularly to

ensure no packing-off

(especially in deviated hole)

• Trips Overpulls on first trip through

new hole due to ± gauge.

Minimise backreaming to avoid

stripping Silicate “membrane”

SILDRILEngineering Guidelines (Cont’d)

Normally 5 - 7% by vol. of Na Silicate (Less in Chalks / low reactive Clays)

Normally 25 - 35 ppb KCl (Less in Chalk)

pH run high - 11.0 to 12.0 - Must be kept well above 10.5 (Na Silicate base @ ±12.2)

Ca++ / Mg++ contamination - May affect rheology but definitely depletes Silicate

API Fluid Loss test not directly related to wellbore filtration levels (sealing mechanism)

SILDRIL - UK FIELD EXPERIENCEGeneral Properties (20 Hole Sections)

HoleSize

MudWt

(ppg)

PV YP FluidLoss(cc)

pH Silicate(%)

KCL(ppb)

24”/26” 9.5 - 10.5 15 - 25 25 - 48 6 - 10 11.0 - 12.0 3 - 7 30 - 35

17½”/16” 9.5 - 11.8 15 - 32 25 - 50 6 - 9 11.3 - 12.0 4 - 8 22 - 35

12 ¼” 9.5 - 12.8 20 - 45 25 - 35 5 - 10 11.0 - 12.0 4 - 8 25 - 35

8 ½” 10.5 - 11.0 20 - 30 25 - 28 5 - 6 11.3 - 11.8 4.5 - 6 30 - 35

Field Mud Properties - Sildril (2.6:1)

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YP

26” Section 17 1/2” Section

Rheology vs Solids - Field ResultsRheology vs Solids - Field Results - Na Silicate (2.6:1)- Na Silicate (2.6:1)

SILDRIL - UK Field Experience

Well No Hole Size Formations Consumption(bbl/ft)

Cost per Foot(£/ft)

43/19-4 24” Tertiary Clay / Cret Chalk/Marl 2.62 (Inc Dump) 38.72

22/23-CX 17 ½” Tertiary Clay 0.72 17.65

22/23-CZ 17 ½” Tertiary Clay 1.06 16.26

22/23-CY 17 ½” Tertiary Clay 2.0 (Dump) 27.08

22/18-6 17 ½” Tertiary Clay 1.44 (Dump) 26.96

29/14c-5 17 ½” Tertiary Clay 0.82(No cleaning @TD)

14.38

17 ½” S/Trk* Tertiary Clay 2.76 (Dump) 46.34 *

22/13b-6 26” Tertiary Clay 2.48 (Dump) 45.00

50/21-2 16” Tertiary Clay / Cret Chalk 2.20 (Losses) 48.10 (Inc LCM)

12 ¼” Jurassic Clay/Sand / Top Zechstein Salt 1.30 10.90

49/9b-W2 16” Tertiary Clay / Cret Chalk 0.54 17.71

12 ¼” Cret Chalk / Trias Clay/Sand / Top Zechstein Salt 0.91 18.40

49/8b-3 26” Quat.Silt / Tertiary Clay / Cret Chalk 1.10 (Losses) 17.85

16” Cret Chalk / Trias Clay/Sand 0.44 17.68

14/28b-E 12 ¼” Cret Chalk / Jurassic Marl/Clay 0.58 8.53

8 ½” Jurassic Clay/Sand 1.20 (Dump) 16.30

14/29a-G 12 ¼” Tertiary Sand/Clay / Cret Chalk 0.47 6.17

8½” Cret Chalk/Marl / Jurassic Sand/Clay 1.14 (Dump) 14.28

47/10-6 16” Cret Chalk 0.39 10.14

12 ¼” Jurassic Chalk/Clay / Trias SaltAnhydrite/Carnalite / Top Zechstein Salt

1.45(Largedepletions)

24.28

Silicate Based Fluids

Pro’s

Environmentally acceptable (Category E - full discharge)

Safe Handling for Rig Crews (pH from Silicate) Good Shale inhibition + wellbore stability

(extended OH periods) Good gauge hole through reactive Clays or

Chalks Corrosion Inhibitor (sealant effect) Lower Cost per Ft (cf: PHPA;KCl/Poly;Glydril)

Silicate Based Fluids

Con’s Debatable use for reservoir drilling (Unless

perforate Liner) Needs close monitoring (pH / Silicate) Sensitive to Hardness (divalent ions) Anhydrite formations / Acid Gases Temperature stability only to ±260 º F “Green” Cement (Depletion of SiO2) Lower Lubricity (M-M Coeff of Friction - 0.34)

Effect of New Lubricant vs Concentration

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Effect of Sil-Lube in 11.7 ppg Effect of Sil-Lube in 11.7 ppg Sildril (2.6:1)Sildril (2.6:1)with 5% Drill Solidswith 5% Drill Solids

SILDRILField Experiences

KNOW THE FORMATIONS TO BE DRILLED !!

- Require Good Planning & Expert Engineering

MUD WEIGHTS - Slightly higher than OBM’s (less pressure transmission due to barrier)

FLUID LOSS - Generally 6 - 10 cc (Can be higher in younger formations with high water content)

LOGISTICS - Check on bulk Silicate requirements

LSRV - Variable Silicate conc will inc/dec 6/3 RPM

BREAKOVER - Generally no problems from KCl to Sat Salt

DEPLETION - Encounter Ca/Mg or low pH (Formations / Acid Gas)

SILDRIL SYSTEMSPotential Developments

• Use of novel Lubricants for deviated hole sections >40º

• Use of Stabilisers / Extenders for temperatures >260ºF

(e.g. TKPP / DP-3 to retard gellation prior to cement jobs)

• Solid Silicate (To reduce logistics problems with bulk liquids)