silicate chemistry: speciation nsl silicate drilling fluids seminar
TRANSCRIPT
Silicate Chemistry: Speciation
NSL Silicate Drilling Fluids Seminar
National Silicates Ltd.an affiliate of The PQ CorporationNational Silicates Ltd.an affiliate of The PQ Corporation
Acknowledgements
Dr. Jonathan Bass, PQ Corporation Dr. Neil Miller, PQ Corporation Rick Reifsnyder, PQ Corporation Dr. Gary Turner, Spectral Data Services, Inc.
Outline Technical Service Overview Soluble Silicates Manufacturing Important Physical Properties Basic Silicate Reactions Silicate Speciation Relevance to Silicate Product Selection and
Drilling Mud Formulation
NSL / PQ Development Projects
High Temperature Formulations Lubrication Technology Alternative Viscosifiers Mechanism(s) of Inhibition Overcoming Mud Contamination
National Silicates Ltd.an affiliate of The PQ CorporationNational Silicates Ltd.an affiliate of The PQ Corporation
Other End-Use Applications
Adhesives Binders Cements Detergency Foundry Feedstock
Grouting Paints / Coatings Pulp & Paper Water Treatment Waste Treatment Miscellaneous
Health, Safety and Environment
All silicates are simple, three component products– silica -- alkali -- water
One of the safest industrial chemicals No toxic or volatile material Stable for extended periods of time Mild reactivity Non-flammable
Soluble Silicates Soluble Silicates are the metal salts of
Silicic Acid that exist in multiple polymeric forms in solution. Amorphous solids and powders are also manufactured.
All silicates contain three basic components:– Silica -- SiO2 (Sand)
– Alkali -- Na2O or K2O (Soda Ash or Pot Carb)
– Water -- H2O
Silica ChemistrySolubility
Silicas are not dissolved by acids except
HF
Apparent increase in solubility above pH
9: formation of monomer and silicate ion
(SiO2)x + 2H2O = Si(OH) 4 + (SiO2)x-1
Si(OH)4 + OH- = SiO(OH)3- + H2O
Soluble Silicates
Water
SilicaAlkali1
4
2
5
3
1. High Alkali Granular2. Metasilicates3. Glasses4. Hydrous Powders5. Commercial Liquids
50%
Soluble Silicates Changing the proportions of silica, alkali
and water will control chemistry and physical properties.
All combinations are possible but many yield unstable, insoluble and undesirable products.
Manufacturing experience and expertise can produce optimum silica species for each end use.
Manufacturing Raw Materials:
– Silica Sand -- Source determines purity
– Sodium Carbonate or Potassium Carbonate
– Softened Water
Na2CO3 + xSiO2 = Na2O•xSiO2 + CO2
K2CO3 + xSiO2 = K2O•xSiO2 + CO2
Combined in open hearth furnace
Silica Tree
S an d
B rites ilG & G D
H yd ra tedS ilica tes
N yaco lP rod u c ts
E K A N ob e l
C o llo id a l S ilica(S ilica S o ls )
IM P A QB TR S ep ara tion s
D u p on t
B ritesorb
S ilica G e ls
Q u soG & W R S eries
D eg u ssa
P rec ip ita tedS ilicas
M etsoP rod u c ts
M etas ilica tes
V a lfo rP rod u c ts
Z eo litesS od iu m A lu m in o
S ilica tes
L iq u id S ilica tes
S ilica te G lass
F u rn ace1 1 0 0 to 1 2 0 0
d eg rees C
S od a A sh
Raw Materials Raw Materials
Heat Energy
Add Water
Important Product Properties
Alkali Content Silica Content Total Solids Ratio
Density pH Viscosity Clarity & Purity
Alkali Content
TTA (Total Titratable Alkali)%Na2O or %K2O
Simple acid /base titration using a colored mixed indicator.
Combination of active and inactive alkali
Silica Content
Multiple analytical methods Gravimetric Silica Determination Volumetric Silica Titration Atomic Adsorption Spectroscopy Colorimetric determination Geriche Charts or the Silica Program.
( TTA and density in degrees Baume )
Total Solids
The combined total of the Silica & Alkali values.
Solubility and physical properties are affected by solids level.
As solids increase, there is a corresponding increase in viscosity for a particular ratio.
Ratio Ratio is the most important physical property
silicate variable. Weight ratio is defined by the following:
Weight % of silica divided by the Weight % of Alkali
Ratio determines:-- Solubility of solids & powders-- Reactivity of silicate-- Physical properties such as viscosity
Weight ratio and Molar ratio are nearly equivalent for sodium silicates but not for potassium silicates.
Density Of Silicates Typically measured at 20 degrees C using a hydrometer. The BAUME scale is ordinarily used. Easily convertible to specific gravity. Other density measuring methods
– Pycnometer ( Accurate but difficult )– Graduated Cylinder ( Easy but precision is limited )– Digital Density Meter ( Very accurate and easy to use, however
the equipment is expensive and must be thoroughly maintained )
The Baume scale is somewhat proportional to the solids content of the silicate being measured.
pH All silicate products are in the pH range from 11.0 to 13.5. pH is a function of:
– Silicate composition (ratio)– Solids concentration
The pH of silicates does not reflect the true alkali content of solutions.
General Trends:– pH of silicate solutions is maintained until almost complete
neutralization.– The buffering capacity of silicate solutions increases with
increasing proportions of soluble silica.
Basic Chemical Reactions
Four Basic Silicate Reactions
– Hydration / Dehydration
– Metal Ion Reactions
– Surface Charge Modification
– Polymerization / Gelation Reactions
Hydration/Dehydration The addition or removal of water from silicates:
– Soluble Silicates are unique in the way that the solid materials dissolve and the liquids dry.
– Rate of Solution as well as Rate of Drying depend greatly on product Ratio.
– The Glassy Nature of Silicates imparts strong and rigid physical properties to a dried film or coating.
– This property impacts handling procedures.
Metal Ion Reactions Soluble Silicates can react with all multivalent cationic metal ions to form
the corresponding insoluble metal silicate, depending on reaction conditions.
Examples: Calcium Manganese MagnesiumCadmium Iron Aluminum
Silicates can precipitate these metals out of solution and render them insoluble and non-reactive.
In moderately alkaline silicate drilling fluids, precipitation of insoluble metal silicates can be easily controlled
Reaction of silicates at shale surfaces are predominantly polymerization / gelation reactions resulting in the formation of hydrous, sodium - rich metal silicate gels.
Shale Stabilization Reaction with metal cations is basis of
functionality. Silica reacts with shale surfaces to form
semi-permeable gel. Also can gel in voids and small cracks. Gels can be removed with water / alkali if
desired ( e.g. payzone silicate breaker Limits fluid penetration. Stabilizes cuttings.
Effect of Contaminants
Metals and acidic materials will inactivate silica species.
Precipitation & Gelation. May impact fluid rheology and ability to
stabilize shale. Maintain adequate silica and alkali
reserves. Maintain pH value
Silicate Speciation
Definition and use of chemical features to provide performance benefits
Identify species control Control and optimize species change
Silicates: Unit Chemical Structures
O
O
SiO
O
OSi
OSi
OSi
O
O
O
O
O
O
O
Monomer, Q = 0 Trimer, Q = 1.3
Cyclic trimer, Q = 2.0
Cyclictetramer, Q=2.0
Cubic octamer, Q=3.0
29Si NMR of Silicates - Band Assignment
-60 -70 -80 -90 -100 -110
ppm
Q0
O
O
SiO
O
Q1
OSi
OSi
OSi
O
O
O
O
O
O
O
Q2cyt
Q2
Q3
Q4
2 ratio, 3M
29Si NMR of Silicates - Effect of Ratio
-70 -80 -90 -100 -110 ppm -60 -70 -80 -90 -100 -110 ppm
3.2 Ratio, 6M 2.0 Ratio, 6M
0
10
20
30
40
50
60
70
80
0 0.5 1.0 1.5 2.0 2.5 3.0 3.5
Ratio
Apparent
Relative
Concentratio
n
Monosilicate Chains & Cyc Trimers Larger Rings Complex Structures
Figure 2
Qualitative Interpretation ofSilicate Anion Structure Equilibria - 1 Molar Solution
Spec PQ CORPORATION
Speciation: A Current View
SiO44- Dimer Planar Cubic Polymer
Trimer Cyclics Octamer
SiO2
Charge
Alkali+ -- ++ -
Viscosity+ +
Concentration Effects on Speciation
Decreasing concentration depolymerizes silicate anions and is more pronounced for lower ratio silicates
For 2.07 ratio, in the range 6M to 1M SiO2, Q2
4R and Q33R decrease, bicyclic
anions are relatively stable, Q1 and Q23R
increase and Q0 (monomer) increases For 3.2 ratio, from 6M to 1M SiO2, the
larger cyclic anions are relative stable, while dimers and monomer increase.
Influence of Metals on Silicate Speciation
The common metal impurities sum to ~250 ppm on a liquid silicate basis
Metal ions such as Al, Fe, Ti are network formers but at ppm levels do not affect overall distributions as visible by NMR; these metals are incorporated into the larger anions
Calcium (and magnesium to a lesser degree) does not influence AMW vs. ratio, but does promote turbidity formation especially at higher ratio (Q3 and Q4)
Influence of Temperature on Speciation
In general, temperature increases in the range RT to 200 oF promote depolymerization in silicates
1.6 ratio silicate shows increases in monomer and Q1 with decreases in large cyclics and smaller 3-D oligomers
3.2 ratio silicate shows increases in monomer and Q1 and decreases in large oligomers (Q3) and polymer (Q4) with temperature increase
Influence of Additives on Speciation
Additives influence speciation differently depending on additive type, concentration, and silicate ratio
As an example, 10% NaCl appears to stabilize Q2 and Q3 in lower ratios and Q4 in higher ratios when temperature is increased
Excessive additive concentration can interact with large oligomers and polymer in silicates to yield precipitates and gelation, e.g., 3.2 ratio, high salt, high calcium.
Effect of RevDust on Speciation
RevDust added at 8, 17, 25 ppb to 2 ratio, 7% solids, 22% NaCl
Ratio increased 2 to 2.4 (alkali decrease) with RevDust loading
Large anions and polymer appear as RevDust loading increases, viscosity can increase, ultimate gel formation with addt’l ratio increase
Effects above increase with temperature Effects follow from alkali depletion