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

2. Silicate Performance

3. 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

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

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

6. 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)

7. 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)

8. 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

9. 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)

10. 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

11. 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 % by vol.
KCl ppb
MBT Generally low (highly inhibitive)
pH (natural level)
Hardness Zero (positive Silicate)
Corrosion Inhibitors not necessary

12. 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”

13. SILDRIL Engineering Guidelines (Cont’d)
Normally 5 - 7% by vol. of Na Silicate (Less in Chalks / low reactive Clays)
Normally ppb KCl (Less in Chalk)
pH run high to Must be kept well above (Na Silicate ±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)

14. SILDRIL - UK FIELD EXPERIENCE General Properties (20 Hole Sections)

15. 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)

16. SILDRIL - UK Field Experience

17. 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)

18. 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 )

19. 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)

20. 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 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)

21. 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)