Silicate/Polymer Mud System SILDRIL Silicate/Polymer Mud System North Sea Development & Application Presentation by Chris Atkinson

Silicate Performance

Recovery of Foss Eikeland Clay with 3% Silicate Comparative Shale Inhibition 100 90 NaSil Na/K Sil 80 Ksil 70 60 50 Shale Recovery (%) 40 30 20 10 3 2 3.6 3.4 3.3 2.9 2.8 2.6 2.5 2.2 2.1 1.8 1.65 SiO2:M2O Ratio

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

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

3% Silicate / 3% KCl System at 11.7 ppg - Solids Tolerance Solids Tolerance of NaSilicate (2.6:1) 50 40 30 20 YP - Wyoming 10 PV - Wyoming YP - Foss Eik PV - Foss Eik 100 150 200 250 300 Solids added (kg/m3)

3% Silicate / 3% KCl system at 11.7 ppg - Solids Tolerance Solids tolerance of NaSilicate (2.0:1) 45 40 35 30 25 20 15 YP - Foss Eik 10 PV - Foss Eik 5 YP - Wyoming PV - Wyoming 100 150 200 250 300 Solids added (kg/m3)

Silicate Based Fluids Field 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

SILDRIL System Performance 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)

SILDRIL Description / 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

SILDRIL Engineering 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

SILDRIL Engineering 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”

SILDRIL Engineering 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 EXPERIENCE General Properties (20 Hole Sections)

Rheology vs Solids - Field Results - Na Silicate (2.6:1) Field Mud Properties - Sildril (2.6:1) 55 26” Section 17 1/2” Section 50 45 40 35 LGS (%) 30 10sec 10 min 25 30 min 20 PV 15 YP 10 5 84 188 303 622 627 941 1168 1256 1341 1439 1543 1546 Drilled Length (m)

SILDRIL - UK Field Experience

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 Sil-Lube in 11.7 ppg Sildril (2.6:1) with 5% Drill Solids Effect of New Lubricant vs Concentration 0.35 0.3 0.25 0.2 Friction Coefficient 0.15 0.1 0.05 1 2 3 4 5 Lubricant Concentration (% vol)

SILDRIL Field 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 SYSTEMS Potential 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)