Silicate Chemistry: Speciation NSL Silicate Drilling Fluids Seminar

Acknowledgements u Dr. Jonathan Bass, PQ Corporation u Dr. Neil Miller, PQ Corporation u Rick Reifsnyder, PQ Corporation u Dr. Gary Turner, Spectral Data Services, Inc.

Outline u Technical Service Overview u Soluble Silicates u Manufacturing u Important Physical Properties u Basic Silicate Reactions u Silicate Speciation u Relevance to Silicate Product Selection and Drilling Mud Formulation

NSL / PQ Development Projects u High Temperature Formulations u Lubrication Technology u Alternative Viscosifiers u Mechanism(s) of Inhibition u Overcoming Mud Contamination

Other End-Use Applications u Adhesives u Binders u Cements u Detergency u Foundry u Feedstock u Grouting u Paints / Coatings u Pulp & Paper u Water Treatment u Waste Treatment u Miscellaneous

Health, Safety and Environment u All silicates are simple, three component products –silica -- alkali -- water u One of the safest industrial chemicals u No toxic or volatile material u Stable for extended periods of time u Mild reactivity u Non-flammable

Soluble Silicates u Soluble Silicates are the metal salts of Silicic Acid that exist in multiple polymeric forms in solution. Amorphous solids and powders are also manufactured. u All silicates contain three basic components: –Silica -- SiO 2 (Sand) –Alkali -- Na 2 O or K 2 O (Soda Ash or Pot Carb) –Water -- H 2 O

Silica Chemistry Solubility u Silicas are not dissolved by acids except HF u Apparent increase in solubility above pH 9: formation of monomer and silicate ion (SiO 2 ) x + 2H 2 O = Si(OH) 4 + (SiO 2 ) x-1 Si(OH) 4 + OH - = SiO(OH) H 2 O

Soluble Silicates Water Silica Alkali High Alkali Granular 2. Metasilicates 3. Glasses 4. Hydrous Powders 5. Commercial Liquids 50%

Soluble Silicates u Changing the proportions of silica, alkali and water will control chemistry and physical properties. u All combinations are possible but many yield unstable, insoluble and undesirable products. u Manufacturing experience and expertise can produce optimum silica species for each end use.

Manufacturing u Raw Materials: –Silica Sand -- Source determines purity –Sodium Carbonate or Potassium Carbonate –Softened Water u Na 2 CO 3 + xSiO 2 = Na 2 OxSiO 2 + CO 2 u K 2 CO 3 + xSiO 2 = K 2 OxSiO 2 + CO 2 u Combined in open hearth furnace

Silica Tree Raw Materials Heat Energy Add Water

Product Properties & General Chemistry

Important Product Properties u Alkali Content u Silica Content u Total Solids u Ratio u Density u pH u Viscosity u Clarity & Purity

Alkali Content u TTA (Total Titratable Alkali) %Na 2 O or %K 2 O u Simple acid /base titration using a colored mixed indicator. u Combination of active and inactive alkali

Silica Content u Multiple analytical methods u Gravimetric Silica Determination u Volumetric Silica Titration u Atomic Adsorption Spectroscopy u Colorimetric determination u Geriche Charts or the Silica Program. ( TTA and density in degrees Baume )

Total Solids u The combined total of the Silica & Alkali values. u Solubility and physical properties are affected by solids level. u As solids increase, there is a corresponding increase in viscosity for a particular ratio.

Ratio u Ratio is the most important physical property silicate variable. u Weight ratio is defined by the following: Weight % of silica divided by the Weight % of Alkali u Ratio determines: -- Solubility of solids & powders -- Reactivity of silicate -- Physical properties such as viscosity u Weight ratio and Molar ratio are nearly equivalent for sodium silicates but not for potassium silicates.

Density Of Silicates u Typically measured at 20 degrees C using a hydrometer. u The BAUME scale is ordinarily used. u Easily convertible to specific gravity. u 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 ) u The Baume scale is somewhat proportional to the solids content of the silicate being measured.

Density vs. Solids

Viscosity vs. Ratio and Solids

pH u All silicate products are in the pH range from 11.0 to u pH is a function of: –Silicate composition (ratio) –Solids concentration u The pH of silicates does not reflect the true alkali content of solutions. u 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 u Four Basic Silicate Reactions –Hydration / Dehydration –Metal Ion Reactions –Surface Charge Modification –Polymerization / Gelation Reactions

Hydration/Dehydration u 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 u Soluble Silicates can react with all multivalent cationic metal ions to form the corresponding insoluble metal silicate, depending on reaction conditions. u Examples:Calcium Manganese Magnesium Cadmium Iron Aluminum u Silicates can precipitate these metals out of solution and render them insoluble and non-reactive. u In moderately alkaline silicate drilling fluids, precipitation of insoluble metal silicates can be easily controlled u Reaction of silicates at shale surfaces are predominantly polymerization / gelation reactions resulting in the formation of hydrous, sodium - rich metal silicate gels.

Shale Stabilization u Reaction with metal cations is basis of functionality. u Silica reacts with shale surfaces to form semi-permeable gel. u Also can gel in voids and small cracks. u Gels can be removed with water / alkali if desired ( e.g. payzone silicate breaker u Limits fluid penetration. u Stabilizes cuttings.

Hydrous Metal Silicate Gels

Effect of Contaminants u Metals and acidic materials will inactivate silica species. u Precipitation & Gelation. u May impact fluid rheology and ability to stabilize shale. u Maintain adequate silica and alkali reserves. u Maintain pH value

Silicate Speciation

u Definition and use of chemical features to provide performance benefits u Identify species control u Control and optimize species change

Silicates: Unit Chemical Structures Monomer, Q = 0 Trimer, Q = 1.3 Cyclic trimer, Q = 2.0 Cyclic tetramer, Q=2.0 Cubic octamer, Q=3.0

29 Si NMR of Silicates - Band Assignment Q0Q0 Q1Q1 Q 2 cyt Q2Q2 Q3Q3 Q4Q4 2 ratio, 3M

29 Si NMR of Silicates - Effect of Ratio 3.2 Ratio, 6M2.0 Ratio, 6M

29 Si NMR of Silicates - Effect of Concentration 3.2 Ratio, 6M3.2 Ratio, 1M

29 Si NMR of Silicates - Effect of Concentration 2.0 Ratio, 6M2.0 Ratio, 1M

Speciation: A Current View SiO 4 4- Dimer Planar Cubic Polymer Trimer Cyclics Octamer SiO 2 Charge Alkali Viscosity + +

Concentration Effects on Speciation u Decreasing concentration depolymerizes silicate anions and is more pronounced for lower ratio silicates u For 2.07 ratio, in the range 6M to 1M SiO 2, Q 2 4R and Q 3 3R decrease, bicyclic anions are relatively stable, Q 1 and Q 2 3R increase and Q 0 (monomer) increases  For 3.2 ratio, from 6M to 1M SiO 2, the larger cyclic anions are relative stable, while dimers and monomer increase.

Influence of Metals on Silicate Speciation u The common metal impurities sum to ~250 ppm on a liquid silicate basis u 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 u Calcium (and magnesium to a lesser degree) does not influence AMW vs. ratio, but does promote turbidity formation especially at higher ratio (Q 3 and Q 4 )

Influence of Temperature on Speciation u In general, temperature increases in the range RT to 200 o F promote depolymerization in silicates u 1.6 ratio silicate shows increases in monomer and Q 1 with decreases in large cyclics and smaller 3-D oligomers u 3.2 ratio silicate shows increases in monomer and Q 1 and decreases in large oligomers (Q 3 ) and polymer (Q 4 ) with temperature increase

Influence of Additives on Speciation u Additives influence speciation differently depending on additive type, concentration, and silicate ratio u As an example, 10% NaCl appears to stabilize Q 2 and Q 3 in lower ratios and Q 4 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 u RevDust added at 8, 17, 25 ppb to 2 ratio, 7% solids, 22% NaCl u Ratio increased 2 to 2.4 (alkali decrease) with RevDust loading u Large anions and polymer appear as RevDust loading increases, viscosity can increase, ultimate gel formation with addt’l ratio increase u Effects above increase with temperature u Effects follow from alkali depletion

Summary u 2.00 ratio provides the best overall balance between mud stability and inhibitive performance u Higher silicate concentration complements performance and provides resistance to contamination u Judicious selection of mud additives is crucial and will greatly affect performance