Patent Description:
Moreover, the invention concerns a plurality of hollow spherical glass particles.

Furthermore, the invention concerns a filler comprising a plurality of hollow spherical glass particles.

Furthermore, the invention concerns a use of the above-mentioned filler in metal matrix syntactic foams.

Moreover, the invention concerns a metal matrix syntactic foam comprising the above-mentioned filler.

Furthermore, the invention concerns a method for producing hollow spherical glass particles.

The invention also concerns a formulation comprising an inorganic binder and the above-mentioned filler.

Furthermore, the invention concerns a formulation comprising an organic binder and the above-mentioned filler.

Another aspect of the invention is a use of the above-mentioned filler in acoustic applications, heat insulation applications, self-levelling masses, repair mortars, lightweight concrete, freeze-thaw resistant concrete, insulating coatings and/or sound and vibration dampers.

Furthermore, the invention concerns a use of the above-mentioned filler in the development, exploitation and/or completion of underground mineral oil and natural gas deposits and in deep drillings.

Moreover the invention concerns a use of the above-mentioned formulation in the development, exploitation and/or completion of underground mineral oil and natural gas deposits and in deep drillings.

Hollow spherical glass particles, also known in the state of the art as "synthetic glass microspheres" or "glass microbubbles" or "glass microballoons", typically have low specific gravity, satisfactory heat resistance, heat insulating properties, pressure-resistance (e.g., crush strength) and impact resistance, and may achieve superior physical properties in comparison to conventional fillers. Each hollow spherical glass particle has an essentially spherical form and an essentially spherical inner void.

Due to their advantageous properties the hollow spherical glass microspheres are used in a variety of areas and applications. For example, the hollow spherical glass microspheres are used as light-weight fillers for composite polymeric materials of different kinds or in cryogenic technology, for fabrication of acoustic and thermal insulating materials or as targets for laser thermonuclear synthesis. An overview of the state of the art regarding the use, properties and technology of the hollow spherical glass particles can be found for example in "<NPL>.

Several methods for producing hollow spherical glass particles have also been developed and are described in the prior art. Early methods for manufacturing hollow glass microspheres involved for example combining sodium silicate and boric acid with a suitable foaming agent, drying (for example in a spray dryer) or crushing the mixture with addition ingredients (for example in a ball mill with a suspension of water, china clay, feldspars, metakaolin, sodium silicate and/or potassium silicate, zeolites, sodium carbonate and/or potassium carbonate and/or calcium carbonate and/or magnesium carbonate, aluminium hydroxide etc.), adjusting the size of the crushed particles and drying the mixture in a spray dryer in order to achieve granules. Subsequently the granules are fired. The firing temperature achieves values of between about <NUM> and <NUM>. However, these methods have a drawback that starting materials such as boric acid are required that can result in the formation of toxic compounds during production of and/or while using the hollow spherical glass particles.

<CIT> describes hollow spherical glass particles comprising aluminosilicate and methods of making same. The hollow spherical glass microspheres described therein comprise <NUM>,<NUM> wt. % to <NUM> wt. % calcium oxide and greater than <NUM> wt. % to less than about <NUM> wt. % sodium oxide, wherein the microspheres have a total alkali metal oxide content of less than about <NUM> wt. In addition, <CIT> describes that the presence of relatively high percentage of sodium oxide results in a poor chemical durability of the hollow spherical glass particles.

<CIT> (Pub. No: <CIT>) and <CIT> (Pub. No: <CIT>) describe hollow glass aluminosilicate microspheres and processes for their production. The mechanical durability of these microspheres is higher due to boron trioxide (B<NUM>O<NUM>). However, as described above, the presence of boron that may lead to toxic boron compounds is undesirable. Moreover, the presence of boron trioxide lowers the melting temperature of the microspheres.

The objective of the present invention is to provide a boron-free chemical composition for production of hollow spherical glass particles and materials comprising such particles with high mechanical durability and high melting temperature.

According to the invention, this objective is achieved by providing hollow spherical glass particles according to claim <NUM>.

Advantageously, the hollow spherical glass particle comprises sodium oxide. It is generally understood from the state of the art that adding sodium oxide reduces the chemical stability of the hollow spherical glass particle. However, according to the present invention, the presence of sodium oxide and in generally alkali metal oxides, such as potassium oxide, in a right proportion can surprisingly increase the mechanical robustness (<NUM>% crush strength) of the hollow spherical glass particle. In the state of the art, the mechanical stability (<NUM>% crush strength) of the hollow spherical glass particle is usually provided by adding some boron compounds. According to the present invention, however, no addition of such, potentially toxic, compounds is needed.

In one preferred embodiment of the invention, the hollow spherical glass particle comprises between about <NUM> wt. % and about <NUM> wt. %, preferably about <NUM> wt. %, of Al<NUM>O<NUM>, between about <NUM> wt. % and about <NUM> wt. %, preferably about <NUM> wt. %, of SiO<NUM> and between about <NUM> wt. % and about <NUM> wt. %, preferably about <NUM> wt. %, of at least one alkali metal oxide.

In another preferred embodiment of the invention, the hollow spherical glass particle comprises between about preferably <NUM> wt. % and about <NUM> wt. %, preferably about <NUM> wt. %, of a mixture of K<NUM>O and Na<NUM>O. % ratio between the potassium and sodium oxides can be chosen arbitrary. Instead of or in addition to the potassium oxide a lithium oxide Li<NUM>O can be chosen as well. Without being wished to be bound to a certain theory, it is understood that due to mixing of at least two alkali metal oxides (for example of K<NUM>O and Na<NUM>O) a so-called mixed-alkali effect is achieved, which for example makes the hollow spherical glass particles chemically more stable.

Furthermore it can be provided that the hollow spherical glass particle has a particle diameter of between about <NUM> and about <NUM> microns.

As it will be demonstrated by the examples provided below, differently sized particles can have different <NUM>% crush strength. Generally and especially within the scope of the present invention it is understood that "<NUM>% crush strength" refers to a pressure at which essentially about <NUM>% of particles are destroyed, i.e. loose their essentially spherical form.

In one preferred embodiment it can be provided that the hollow spherical glass particle has an <NUM>% crush strength of at least <NUM> psi, more preferably at least <NUM> psi, especially at least <NUM> psi. The particles in this invention were subjected to an isostatic compressive strength test in a crush strength measuring apparatus (POREMASTER <NUM> GT by Quantachrome Istruments). It is important to note that no hardening (chemical hardening, temperature hardening or other type of hardening) of the hollow spherical glass particles according to the invention was performed prior to the above mentioned isostatic compressive test. Typically, a silane coating is added to the conventional hollow spherical glass particles prior to the isostatic compressive strength test, in order to increase their <NUM>% crush strength. No such hardening was performed with the hollow spherical glass particles according to the invention.

Moreover, in other embodiments, the hollow spherical glass particle has melting temperature of at least <NUM>.

According to the invention, the object is also achieved by means of a plurality of hollow spherical glass particles as described herein. In preferred embodiments, the plurality of the hollow spherical glass particles have a true density, i.e. the density of the particles that make up a powder or particulate solid, of between about <NUM>/cm<NUM> and about <NUM>/cm<NUM>, more preferably of between about <NUM>/cm<NUM> and about <NUM>/cm<NUM>, more preferably a true density of between about <NUM>/cm<NUM> and about <NUM>/cm<NUM>.

According to the invention the object is also achieved by means of a metal matrix syntactic foam comprising a filler, wherein the filler comprises a plurality of the hollow spherical glass particles according to the invention, wherein the metal in the metal matrix syntactic foam is aluminum alloy or aluminum.

Metal matrix syntactic foams, also known as "syntactic metal materials" (see e.g. U. Number <CIT>) or "metal syntactic foams" (see e.g. U. Number <CIT>), are known to the person skilled in the art mostly due to their exceptionally high strength.

There are different materials known in the art that can be used as fillers in such foams. Number <CIT> describes ceramic microballoons as a filler. Number <CIT> hollow metallic shells are used for filling purposes.

Thus, according to the present invention an aluminum metal matrix syntactic foam is provided by mixing melted aluminum or aluminium alloy having its melting temperature of between about <NUM> and about <NUM>, and a plurality of hollow spherical glass particles according to the invention and described herein. In contrast to the hollow spherical glass particles according to the invention, conventional hollow spherical glass particles have either a relatively high crush strength and a low melting temperature or relatively low crush strength and a high melting temperature.

Furthermore, the invention concerns a method for producing hollow spherical glass particles according to claim <NUM>.

A uniform feeding of the dried mixture can be achieved by feeding the particles (of the dried mixture) into the heating device at some constant rate. It is to be understood that this rate can vary depending for example on the geometry and size of the heating device. Various heating devices can be used for this purpose. For example the heating device can be designed as a conventional tube furnace and a graphite tube as a heating element, wherein argon can be used as a protective gas for providing a protected atmosphere in the furnace. One can also use other heating devices that for example comprise a heating element made of molybdenum alloy or silicon molybdenum alloy or heating devices with induction heating.

The term "enough flowability" as used herein means that the flowability of the mixture is adjusted in order to allow spray drying of the mixture. The skilled person is able to choose an suitable flowability of the mixture based on her/his common knowledge and/or through routine experimentation.

In one preferred embodiment of the method the hollow spherical glass particles can be collected at about <NUM> below the furnace.

In a preferred embodiment of the method according to the present invention comprises a step of milling the mixture, for example in a ball mill, in order to achieve a milled powder, such that an average size of particles in the milled powder is of at most about <NUM> microns, wherein the milling of the mixture is performed after Step <NUM> and before Step <NUM>.

Another aspect of the invention is a formulation comprising an inorganic binder and a light aggregate in form of a filler, which filler comprises a plurality of hollow spherical glass particles according to the present invention. Such formulations can be used for instance in the development, exploitation and/or completion of underground mineral oil and natural gas deposits and in deep drillings. Preferably such formulations can be used in borehole cementing and/or drilling muds. For example cementing of oil and gas wells can serve the following purposes:.

Some of the known cementing techniques are:.

Among the above listed methods the methods that are most frequently used are the single-stage and the multi-stage cementing. Comparing to the multi-stage cementing the single-stage cementing is easier to perform: it requires less equipment, materials and labor. The advantages of the single-stage cementing include for example a shorter cementing time due to a lack of the second stage and less waiting-on-cement time. The simplicity of the technique leads to lower risks of equipment failure and mistakes by personnel. This makes single-stage cementing a more attractive alternative.

However, the strength of the state-of-the-art formulations represents a problem. Wells are usually cemented with the use cement slurry. Portland cement containing various types of microspheres including artificial glass, ceramic or polymer, fly ash products, so called ash aluminosilicate microspheres (cenospheres) as light aggregate is widely used as the basic plugging material to prepare lightweight cement slurry. The main disadvantage of lightweight systems based on Portland cement containing microspheres for single-stage casing cementing is a limited depth at which this type of the cement slurry can be used. This is primarily linked to insufficient shell strength of ash aluminosilicate microspheres - the most frequently used main lightweight component of cement slurries. According to experiments performed at TyumenNIIgiprogas LLC (see reference below) and the plugging department of the Tyumenburgaz branch an excess water suspension pressure from <NUM> to <NUM> MPa (the pressure at the depth of <NUM>,<NUM> to <NUM>,<NUM> where the vast majority of oil and gas deposits are located) leads to destruction and sedimentation of <NUM> to <NUM>% of the industry standard spheres (e.g. cenospheres). Some microspheres collapse with breakdown of the particles into separate fragments while a majority of the microspheres develop microcracks on the surface. This means that at high pressures these microspheres are not destroyed but their cavities are filled with grouting fluid through microcracks leading to particle sedimentation. The slurry increases its density and creates a risk of premature thickening of cement slurry, loss of circulation and nonlifting of the lightweight slurry to the well mouth (see e.g. <NPL>). A formulation comprising hollow spherical glass particles according to the present invention is stronger than the known state-of-the-art formulations and can be used in the lower depths.

In one preferred embodiment of the formulation according to the present invention comprises from <NUM> to <NUM> wt. -%, preferably <NUM> to <NUM> wt. %, of the filler according to the present invention, based on the dry weight of the inorganic binder.

Advantageously the inorganic binder is selected from cement, gypsum and/or a geopolymer binder.

In a preferred embodiment the formulation is in the form of an aqueous dispersion or a water-based or dry foam.

One preferred embodiment of the present invention concerns the use of the formulation according to the present invention and/or the filler according to the present invention in borehole cementing and/or drilling muds.

The invention is further explained by the following non-limiting examples describing a method for producing hollow spherical glass particles according to the invention and a formulation comprising an inorganic binder and the filler according to the present invention that can be used in the development, exploitation and/or completion of underground mineral oil and natural gas deposits and in deep drillings and preferably in borehole cementing and/or drilling muds.

Three samples were prepared by mixing ingredients containing aluminium oxide Al<NUM>O<NUM>, sodium oxide Na<NUM>O, silicon dioxide SiO<NUM> and potassium oxide K<NUM>O (for example the resulting mixture can comprise china clay, feldspar, potassium carbonate, zeolites, aluminium hydroxide, potassium or sodium silicate, porcelain) in order to achieve an atomic ratio of aluminum, silicon and either sodium or potassium or both sodium and potassium atoms of about <NUM>:<NUM>:<NUM>, i.e. AAl:Si:(Na + K)=<NUM>:<NUM>:<NUM>. This means that for each Al atom there is essentially one Si atom and essentially one Na or K atom in the mixture. For two Al atoms there are essentially two Si atoms and either essentially one Na atom and essentially one K atom or essentially two Na atoms or essentially two K atoms. In particular, in this example the mixture comprised about <NUM> wt. % of Al<NUM>O<NUM>, about <NUM> wt. % of SiO<NUM>, about <NUM> wt. % of Na<NUM>O and about <NUM>% of K<NUM>O. Depending on the purity of these ingredients there might be may be impurities, i.e. other chemical compounds, present. However, the total amount of impurities (other chemical compounds) should not exceed <NUM>-<NUM> wt.

After mixing the ingredients above, the mixture can be milled in a ball mill, in order to achieve an average size of particles of at most about <NUM> microns. The milling can be dry or wet and can be omitted if the particle size does not have to be adjusted. Thereafter the mixture was further mixed with water and blended, in order to achieve enough flowability for subsequent spray drying. After drying in a spray dryer at the temperature of about <NUM>-<NUM>, a powder with granules (particles) having an with average size of about <NUM>-<NUM> microns was achieved. The granules was then separated according to their size into three fractions: Fraction <NUM>: about <NUM>-<NUM> microns; Fraction <NUM>: about <NUM>-<NUM> microns; and Fraction <NUM>: about <NUM>-<NUM> microns; all fractions having a moisture content of at least about <NUM>% and at most <NUM>%. After the separation step, each fraction was fed into a tube furnace with induction heating at a rate of about <NUM> grams/min. A graphite tube was used as a heating element and argon was used as a protective gas for providing a protected atmosphere in the furnace. The temperature in the furnace was between about <NUM>° and about <NUM>° C. Residence time of the particles in the furnace was at least <NUM> sec. After processing the respective granules fractions <NUM>, <NUM> and <NUM> in the tube furnace, the resulting hollow spherical glass particles were collected <NUM> below the furnace.

As a result, three types of the hollow spherical glass particles were obtained. Their properties are summarized below.

Type <NUM> (resulting from Fraction <NUM>): The hollow spherical glass particles of the first type have an essentially white color and exhibit a bulk density of about <NUM>/cm<NUM>, a true density of about <NUM>/cm<NUM>, a particle diameter of between about <NUM> micron and about <NUM> micron, a melting temperature of about <NUM> and an <NUM>% crush strength of about <NUM> psi (100Mpa).

Type <NUM> (resulting from Fraction <NUM>): The hollow spherical glass particles of the second type have an essentially white color and exhibit a bulk density of about <NUM>/cm<NUM>, a true density of about <NUM>/cm<NUM>, a particle diameter of between about <NUM> micron and about <NUM> micron, a melting temperature of about <NUM> and an <NUM>% crush strength of about <NUM> psi (85Mpa).

Type <NUM> (resulting from Fraction <NUM>): The hollow spherical glass particles of the third type have an essentially white color and exhibit a bulk density of about <NUM>/cm<NUM>, a true density of about <NUM>/cm<NUM>, a particle diameter of between about <NUM> micron and about <NUM> micron, a melting temperature of about <NUM> and an <NUM>% crush strength of about <NUM> psi (70Mpa).

Generally and especially within the scope of the present invention it is understood that the bulk density is not an intrinsic property of the hollow spherical glass particles and can essentially slightly change depending on how the particles are handled. Within the scope of this invention the hollow spherical glass particles have a bulk density of between about <NUM>/cm<NUM> and about <NUM>/cm<NUM>.

<FIG> shows a microscopic image of the hollow spherical glass particles of the above example, in which the granules were not separated according to their size. Therefore, all three types (Type <NUM>, Type <NUM> and Type <NUM>) of the hollow spherical glass particles are depicted in <FIG>. The minimal size (diameter) of the hollow spherical glass particles in <FIG> is about <NUM> microns, the maximal size (diameter) is about <NUM> microns.

<FIG> shows a mercury porosity test performed on Type <NUM> hollow spherical glass particles with an average diameter of about <NUM> microns (solid line) and on cenospheres produced by ENVIROSPHERES PTY LTD (E-Spheres) with about the same average diameter (dashed line). The test was performed using Quantachrome isostatic press described above at the Quantachrome laboratory, Munich, Germany. <FIG> shows that a pressure of <NUM>-<NUM> bar (<NUM>-<NUM> MPa) causes virtually no destruction of Type <NUM> hollow spherical glass particles, but leads to destruction of <NUM>% of the cenosphere volume, which makes Type <NUM> hollow spherical glass particles a better material for example for use as a light aggregate in a binding agent in the single-stage well cementing.

In order to formulate a cement slurry with a density of less than <NUM> pound per gallon (ppg) a filler, for example in form of hollow spheres, can be used to reduce slurry weight. In this example two different types of the hollow spheres were used as a filler: Type <NUM> hollow spherical glass particles according to the present invention and industry standard spheres (S <NUM>, borosilicate glass, <NUM>). The dosage of the Type <NUM> hollow spherical glass particles according to the present invention with a specific gravity of <NUM>,<NUM>/mL can range from <NUM>% by weight of the cement (bwoc) up to <NUM>% by weight of cement. A typical dosage of the hollow spheres (e.g. industry standard spheres or (any type of the) hollow spherical glass particles according to the present invention) would be in the range of <NUM> - <NUM>% by weight of cement.

In order to create a cement slurry with <NUM> ppg density <NUM> of API Class G cement is mixed with <NUM> of water and <NUM> (= <NUM>% bwoc) of bentonite with a Warring Blender Type according to API Recommended Practice 10B at high speed. The bentonite increases the viscosity of the cement slurry and thus, prevents separation of the cement slurry. After mixing <NUM> of hollow spheres (= <NUM>%bwoc) - in this example industry standard spheres or Type <NUM> hollow spherical glass particles according to the present invention - are added to the mixed cement slurry and gently homogenized with a spatula.

The density of the cement slurry containing (any type of) the hollow spheres is usually measured with a pressurized mud balance. Then the slurry is put into an autoclave and nitrogen pressure is applied for <NUM>. After decompression of the autoclave the density of the cement slurry is measured again. The density stays unchanged in case the hollow spheres withstand the pressure. The density increases in case the hollow spheres are crushed by the pressure.

In this example several pressures have been applied on samples of the cement slurry comprising either the industry standard spheres or the Type <NUM> hollow spherical glass particles according to the present invention and prepared as described above. The tests with each pressure were performed individually. Applied pressures were <NUM> psi, <NUM> psi, <NUM><NUM> psi, <NUM><NUM> psi and <NUM><NUM> psi.

<FIG> shows the results of these tests. The cement slurry containing the Type <NUM> hollow spherical glass particles according to the present invention withstand a pressure of <NUM><NUM> psi without density increase (ADF S-Spheres S-<NUM>, dashed line in <FIG>). Industry standard spheres (S <NUM>, borosilicate glass, <NUM>) were tested in comparison. The density of the cement slurry containing the industry standard spheres continuously increased with every tested pressure. At <NUM><NUM> psi the density of the cement slurry containing the industry standard spheres increased for about <NUM>% (<NUM> Glass Bubbles S60, dotted line in <FIG>). The density of the neat cement slurry without any hollow spheres does not change with the pressure and is shown in <FIG> as a comparison (solid line in <FIG>).

The same samples as in the Example <NUM> were prepared for compressive strength tests. Then the rheology is measured according to API RP 13B.

<FIG> shows that Type <NUM> hollow spherical glass particles according to the present invention only moderately increase the viscosity of the neat cement slurry without any hollow spheres (ADF hollow spheres S-<NUM>, dashed line in <FIG>), whereas the industry standard spheres (<NUM> hollow spheres S60, dotted line in <FIG>) strongly increase the cement slurry viscosity. High viscous cement slurries require additional additives like dispersants to adjust their pumping properties.

Comparison of the Type <NUM> hollow spherical glass particles according to the present invention with industry standard spheres (S <NUM>, borosilicate glass, <NUM>).

The Type <NUM> hollow spherical glass particles according to the present invention and industry standard spheres have approximately the same specific density of about <NUM>/cm<NUM>. This is why for a defined density reduction of a cement slurry approximately the same amount of hollow spheres is required.

However, bulk density strongly differs. The Type <NUM> hollow spherical glass particles according to the present invention have bulk density is <NUM>,<NUM>/cm<NUM> while the industry standard spheres (S <NUM>, borosilicate glass, <NUM>) have bulk density is <NUM>,<NUM>/cm<NUM>. Low bulk density is a disadvantage due to the large space needed for storage e.g. on an oil platform offshore.

The Type <NUM> hollow spherical glass particles according to the present invention also show excellent flow properties as a powder without any dust formation. The industry standard spheres (S <NUM>, borosilicate glass, <NUM>) form aggregates which makes the powder dump like flour and creates heavy dust.

The Type <NUM> hollow spherical glass particles according to the present invention exhibit a compressive strength of more than <NUM><NUM> psi in a cement slurry with only a shell thickness of about <NUM> micron and a particle diameter of <NUM> micron. The industry standard spheres (S <NUM>, borosilicate glass, <NUM>) with a compressive strength of about <NUM><NUM> psi have a shell thickness of about <NUM> micron and a diameter of about <NUM> micron.

Cement and slurry properties were tested on samples of a standard cement slurry (API Class G Cement) and different slurry mixtures including light-weight additives. The cement slurries including additives were mixed to have a common density. All samples were prepared in the laboratory of the chair of Drilling & Completion Engineering at the Montan Universität in Leoben, Austria and tested for their rheology according to industry standards.

Four different cement slurries were mixed according to the compositions listed in Table <NUM> by following API RP 10B-<NUM>.

Six different batches of each sample type (A, B, C, D) were prepared and tested further. A1 - A6 correspond to batches of type A, B1 - B6 correspond to batches of type B, C1 - C6 correspond to batches of type C and D1 - D6 correspond to batches of type D (cf. Table <NUM>).

Two batches of each cement slurry type were prepared and measured with a pressurized ("Tru-Wate") mud balance according to API RP 10B-<NUM>. Moreover, Table <NUM> also lists the temperatures of the cement slurries during the density measurements.

Cement slurry rheologies were measured using a multi-speed Chandler viscometer Model <NUM> following API RP 10B-<NUM>. Table <NUM> lists dial readings for each rotational speed setting, sample type, and batch. The apparent Newtonian viscosity, µa, can be calculated in centipoise from the readings and rotor speeds by <MAT> where θN is the dial reading in degrees and N is the rotor speed in revolutions per minute.

Claim 1:
A hollow spherical glass particle, comprising:
aluminum oxide Al<NUM>O<NUM>, silicon dioxide SiO<NUM> and at least one metal oxide, wherein the metal oxide is selected from the group consisting of alkali metal oxides;
wherein the hollow spherical glass particle comprises between <NUM> wt. % and <NUM> wt. % of Al<NUM>O<NUM>, between <NUM> wt. % and <NUM> wt. % of SiO<NUM>, and between <NUM> wt. % and <NUM> wt. % of at least one alkali metal oxide selected from sodium oxide and/or potassium oxide;
wherein the hollow spherical glass particle has a particle diameter of between <NUM> and <NUM> microns;
with the proviso that the hollow spherical glass particle is free of boron.