RO134502A2 - Additives for oil well cement slurries and aqueous based drilling fluids comprising microsilica and a method for production thereof - Google Patents

Abstract

The invention relates to an additive for oil well cement slurries and aqueous based drilling fluids and to a process for producing the same. According to the invention, the additive is a composite material consisting of 1...80% by weight in relation to the total weight of the dry matter, amorphous SiO2-type microsilica having the microparticle size within the range of 0.02...45 μ m, possibly one acrylamide derivative monomer and one acidic unsaturated monomer, respectively. The claimed process consists of the stages of microsilica surface modification with 0.1...20% polymerizable silane, and polymerization of modified microsilica with at least one acrylamide derivative monomer and copolymerization with 0.1...20% one acidic unsaturated monomer, the percentage being expressed by weight, to result in a composite material as concentrated dispersion of liquid to be used as additive of fluid loss control in drilling fluids or oil well cement.

Description

Additives for cement suspensions for oil wells and water-based drilling fluids comprising microsilicon and a method for their production

Technical field

The present invention relates to additives for cement suspensions for oil wells and water-based drilling fluids comprising microsilicas and a method for their production. Additives are composite materials based on modified microsilica and can be used as additives for fluid loss. The materials can also be used in other oilfield fluids, such as a viscosity enhancing agent in recovery fluids (EOR) and improved crude oil fracturing fluids. Moreover, the additives can be used in oil well cement to reduce the transition time from gel formation to hardening / hardening.

State of the art

Microsilica is a co-product of the production of silicon and ferrosilicon alloy. Microsilica is a spherical, sub-micron material, used in various applications, including cementing oil wells, as a gas migration control additive and as a filler to reduce the density of cement slurry. Microsilica helps to reduce fluid loss from a cement slurry for oil wells themselves, but the desired filtration values cannot be achieved without the addition of additional additives to microsilicas.

Additives, such as fluid loss control additives, are added to drilling fluids or oil well cement to reduce the amount of fluid lost in the formation during drilling and completion operations. Most of the fluid loss additives used for aqueous systems are water-soluble polymers, such as starch and starch derivatives, cellulose and cellulose derivatives, water-soluble synthetic polymers, such as acrylate and vinyl copolymers. Depth conditions, such as well temperature, specify the type of chemicals that will be suitable for this purpose.

US 2013/0203951 A1 discloses grafted copolymers in which silica reacts with silane and then the monomers are grafted onto silane. Copolymers are used as additives in various chemical applications.

DE 102006061327 A1 discloses grafted copolymers comprising silane-reacted silica and a sulfonic acid-containing polymer for use in chemical construction applications.

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CN 101818050 B discloses a nano-drilling fluid treatment agent comprising nano-silica, silane coupling agent and acrylamide.

Commonly used additives for cement wells for oil wells and water-based drilling fluids, in particular the class of additives used in high temperature high pressure (HPHT) conditions may have one or more of the following disadvantages:

1) They are expensive (expensive chemicals) due to complex production processes.

2) Generates a high viscosity at low temperature.

4) delays the process of hydration and stabilization of the cement.

5) It does not work well in cement containing salt.

6) Suffers from thermal degradation at extremely high temperatures.

Therefore, it is an object of the present invention to provide an additive for cement suspensions for oil wells and aqueous drilling fluids, which has eliminated the problems mentioned above.

Another object of the present invention is to provide a simplified method for producing such an additive.

Brief Description of the Invention In this invention, additives are provided for cement suspensions for oil wells and aqueous drilling fluids containing chemically modified microsilica and organic polymers.

In the present invention, it has surprisingly been found that by the addition of organic monomers to chemically modified microsilica, efficient additives for oil well cement suspensions and aqueous drilling fluids are obtained.

The present invention provides an additive for cement suspensions for oil wells and aqueous-based drilling fluids comprising microsilicas having a particle size in the range of 0.02 pm to 45 pm, the amount of microsilicas being in the range of 1- 80% by weight relative to the total weight of the dry matter, the surface of the microsilica comprising polymerizable silane, the polymerizable silane being in an amount in the range of 0.01 - 20% by weight relative to the total weight of the dry microsilica and the additive comprising in addition the at least one acrylamide-derived monomer.

In one aspect, the present invention provides a fluid loss additive for aqueous cement wells and drilling rigs on a water-based basis, in which 2020 00118

28/09/2018 the fluid loss additive comprises microsilica, in which the microsilica is in the form of amorphous SiO ₂ particles obtained from a process in which the silica is reduced to SiO-gaseous and the reduction product are oxidized in the vapor phase and condensed to form amorphous silica containing> 90% by weight of silica (SiO ₂ ) and having a specific density of 2,1 2,3 g / cm ³ , a surface area of 12-40 m ² / g and a particle size in the range of 0.02 pm to 45 pm, in an amount ranging from 1-80% by weight to the total weight of the dry matter, the surface of the microsilica comprising polymerizable silane in an amount ranging from 0.01 - 20% by weight of the total dry microsilica weight and fluid loss additive further comprising at least one acrylamide-derived monomer selected from the group consisting of acrylamide (AAm), 2-acrylamido-2-methylpropane sulfonic acid (AMPS), Ν, Ν-dimethylacrylamide (NN DMA), vinylformamide, N-tert-butylacrylamide (NTBAAm), N- (Hydroxymethyl) acrylamide (NHMAAm), Ν, Ν'-Methylenebisacrylamide (NNMBAAm), vinylbutyrolactam, acrylonitrile, and 2 (methylacrylate).

According to one embodiment of the invention, the additive further comprises at least one acid unsaturated monomer.

According to one embodiment of the invention, said at least one acrylamide-derived monomer is selected from the group consisting of acrylamide (AAm), 2-acrylamido-2-methylpropane sulfonic acid (AMPS), Ν, Ν-dimethylacrylamide (NNDMA), vinylformamide, N -tertbutylacrylamide (NTBAAm), N- (Hydroxymethyl) acrylamide (NHMAAm), N, N'Methylenebisacrylamide (NNMBAAm), vinylbutyrolactam, acrylonitrile, and 2 (dimethylamino) ethyl methacrylate.

In one embodiment of the invention, said slightly unsaturated acid monomer is selected from the group consisting of acrylic acid (AA), methacrylic acid, maleic anhydride (MA), itaconic acid, 4-vinylbenzenesulfonic acid, and vinylphosphonic acid.

In one embodiment of the invention, the additive comprises monomers derived from 2-acrylamido-2-methylpropane sulfonic acid acrylamide (AMPS) and Ν, Ν-dimethylacrylamide (NNDMA).

In one embodiment of the invention, the additive comprises monomers derived from 2-acrylamido-2-methylpropane sulfonic acid acrylamide (AMPS), Ν, Ν-dimethylacrylamide (NNDMA) and acrylamide (AAm).

a 2020 00118

28/09/2018 In one embodiment of the invention, the additive comprises monomers derived from 2-acrylamido-2-methylpropane sulfonic acid acrylamide (AMPS), N, N-dimethylacrylamide (NNDMA) and acrylamide (AAm) and the acid unsaturated monomer , acrylic acid (AA).

In another embodiment of the invention, the amount of microsilicon comprising polymerizable silane on its surface is in the range of 20-70% by weight relative to the total weight of the dry matter, 20-60% by weight relative to the total weight of the dry matter, 25 - 55% by weight of the total weight of the dry matter, 25 50% by weight of the total weight of the dry matter, 30 - 50% by weight of the total weight of the dry matter, 30 - 40% by weight compared to the total weight of the dry matter.

In another embodiment of the invention, said at least one acrylamide-derived monomer is present in an amount in the range of 20-90% by weight relative to the total weight of the dry matter, 50-90% by weight relative to total dry weight, 60-80% by weight of the total dry weight.

In another embodiment of the invention, said at least one said unsaturated acid monomer is present in an amount in the range of 0.1 -20% by weight relative to the total weight of the dry matter, 1-15% by weight relative to the total weight of the dry matter, 2-10% by weight relative to the total weight of the dry matter.

In another embodiment of the invention, the dimensional distribution of the additive particles measured by the light scattering method is in the range of 0.05 pm to 500 μτη with an average size (D50) in the range of 5 μτη to 20 μm. μιη.

In one embodiment of the invention, the polymerizable silane is selected from the group consisting of vinyltrimethoxysilane, triethoxyvinylsilane, vinyltris (2-methoxyethoxy) silane, dimethoxymethylvinylsilane, diethoxy (methyl) vinylsilane, trichlorovinylsilane, triethyl ether (3) propyl (trimethoxysilyl) propyl acrylate, propyl 3- (trimethoxysilyl) methacrylate, propyl 3- [tris (trimethylsilyloxy) silyl] methacrylate and propyl 3- (triethoxysilyl) methacrylate.

In one embodiment of the invention, the polymerizable silane is vinyl trimethoxysilane or propyl 3- (trimethoxysilyl) methacrylate.

The present invention further relates to a method of producing an additive for cement suspensions for oil wells and aqueous drilling fluids comprising the steps of:

a) modification of the microsilica surface! with polymerizable silane by contacting microsilicas! in an amount ranging from 80 to 99.9% by weight compared to the weight of 2020 00118

28/09/2018 total dry matter, with silane polymerizable in an amount in the range of 0, ΙΣΟ% by weight compared to the total weight of the dry microsilica;

b) polymerization of modified microsilica with polymerizable silane in an amount of 1 - 80% by weight relative to the total weight of the dry matter, with at least one monomer derived from acrylamide in an amount in the range of 50 - 90% by weight compared to the total weight of the dry matter.

In another aspect, the present invention provides a method of producing a fluid loss additive for cement wells for oil wells and aqueous drilling fluids according to the invention, comprising the steps of:

a) modification of the surface of the microsilica with polymerizable silane by bringing the microsilica in an amount in the range of 80 - 99.9% by weight compared to the total weight of the dry matter in contact with a polymerizable silane in an amount in the range of 0 , 1 - 20% by weight of the total weight of the dried microsilica;

b) polymerization of modified microsilica with polymerizable silane in an amount of 1 - 80% by weight relative to the total weight of the dry matter with at least one acrylamide-derived monomer selected from the group consisting of acrylamide (AAm), 2-acrylamido- 2-methylpropane sulfonic acid (AMPS), Ν, Ν-dimethylacrylamide (NNDMA), vinylformamide, N (hydroxymethyl) acrylamide (NHMAAm), Ν, Ν'-methylenebisacrylamide (NNMBAAm), vinylbutyrylamethyl, and methylbutyrolactamate, of ethyl, in an amount ranging from 50 to 90% by weight relative to the total weight of the dry matter.

In one embodiment of the invention, the polymerized silane-modified microsilica is further polymerized with at least one acid unsaturated monomer in an amount in the range of 0.1 - 20% by weight relative to the total weight of the dry matter.

In one embodiment of the invention, the surface of the microsilica is modified with polymerizable silane using a dry method.

In one embodiment of the invention, the surface of the microsilica is modified with polymerizable silane using a wet method.

In one embodiment of the invention, the polymerizable silane-modified microsilica is polymerized using a free radical polymerization technique.

In one embodiment of the invention, said at least one acrylamide-derived monomer is selected from the group consisting of acrylamide (AAm), 2-acrylamido-2-methylpropane sulfonic acid (AMPS), Ν, Ν-dimethylacrylamide (NNDMA), a 2020 00118

28/09/2018 vinylformamide, N- (Hydroxymethyl) acrylamide (NHMAAm), N, N'-Methylenebisacrylamide (NNMBAAm), vinylbutyrolactam, acrylonitrile, and ethyl 2- (dimethylamino) methacrylate.

In one embodiment of the invention, said at least one said unsaturated acid monomer is selected from the group consisting of acrylic acid (AA), methacrylic acid, maleic anhydride (MA), itaconic acid, 4-vinylbenzenesulfonic acid, and vinylphosphonic acid. .

In one embodiment of the invention, the polymerizable silane is selected from the group consisting of vinyltrimethoxysilane, triethoxyvinylsilane, vinyltris (2-methoxyethoxy) silane, dimethoxymethylvinylsilane, diethoxy (methyl) vinylsilane, trichlorvinylsilane, trisyl ethyl, 3- (tris) propyl (trimethoxysilyl) propyl acrylate, propyl 3- (trimethoxysilyl) methacrylate, propyl 3 [tris (trimethylyloxy) silyl] methyl acrylate and propyl 3- (triethoxysilyl) methacrylate.

In one embodiment of the invention, the polymerizable silane is vinyl trimethoxysilane or propyl 3- (trimethoxysilyl) methacrylate.

These and other features, advantages and benefits and objects will become apparent to one skilled in the art by carefully considering the detailed description and representative embodiments of the invention below and the accompanying drawings.

Short description of the drawings

The embodiments of the invention will now be described with reference to the following drawings.

Fig. 1 shows an electronic scanning micrograph of an additive according to the invention prepared according to Example 4.

Fig. 2 shows an electronic scanning micrograph of an additive according to the invention prepared according to Example 4.

Fig. 3 shows an electronic scanning micrograph of an additive according to the invention prepared according to Example 4.

Fig. 4 shows the dimensional distribution of the particles of an additive according to the invention prepared according to Example 4 measured by the light diffusion method.

Fig. 5 shows the development of static gel strength (straight line) and compressive strength (dotted line) as a function of time, for a conventional cement slurry for oil wells.

Fig. 6 shows the development of the static resistance of the gel (straight line) and of the compressive strength (dotted line) as a function of time, for a cement suspension for oil wells, which comprises an additive according to the invention.

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Detailed description of the invention

The term "microsilica", used in the description and claims of this application, refers to amorphous SiO ₂ particles obtained from a process in which silica (quartz) is reduced to SiO-gas and the reduction product is oxidized in the vapor phase and condensed to form amorphous silica. The microsilica may contain at least 70% by weight of silica (SiO ₂ ) and preferably> 90% by weight and has a specific density of 2.1 - 2.3 g / cm ³ and an area of 12 - 40 m ² / g, typically 20 m ² / g. The microsilica particle size is in the range of 0.02 μm to 45 μm and is preferably in the range of 0.05 μm to 0.5 μm. The primary particles are substantially spherical and have an average particle size (D50) below 1 pm, the average particle size (D50) can be between 0.12 pm and 0.25 pm, the average particle size (D50) can be in around 0.15 pm. Microsilica is preferably obtained as a co-product in the production of silicon alloys in electric reduction furnaces.

More specifically, the novel additives are composite materials comprising microsilicas, which are chemically modified with polymer (s). The bulk size of the silica particles in the polymer matrix improves the sealing properties of the additive. The use of inorganic functional fillers, such as modified microsilica, significantly reduces the total cost of production. It can provide other benefits for cementing oil wells, such as improving the connection between cement and formation. In addition, the composite dispersion has a better viscosity profile compared to aqueous solutions of pure synthetic polymers. Modified microsilica additives are suitable for applications at high temperatures as well as in salt-containing cement. The presence of the inorganic part in the composite extends the thermal stability of the polymer matrix. The composite can be used in most aqueous drilling fluids. In addition, the composite comprising microsilicons and hydrophobic copolymers such as styrene-butadiene, maleic anhydride or methyl methacrylate can be used for non-aqueous drilling fluids. The composite can be produced with a high solids content, without the need for dilution during polymerization, which is common for conventional polymerization methods. Concentrated liquid dispersion can be used directly, thus reducing the cost of the drying process.

Chemically modified microsilica is produced by gluing / grafting the water-soluble polymer on the surface of microsilica spheres through a chemical bond. There are various ways of bringing the microsilica into contact with said polymer in order to make such a change. One way is by adding grouped polymers of 2020 00118

28/09/2018 functional, which reacts with the surface of silica to form covalent or ionic bonds. Another way is to modify the silica with a coupling agent, such as silane, and then graft the polymer to the surface by means of the coupling agent. Grafting / coupling of silica with polymers can take place in a gaseous, liquid or solid state.

Microsilica itself cannot satisfactorily reduce filtration loss. With the present invention, the filtration was controlled to the desired value by the use of modified silica. The surface of the microsilica is modified with polymerizable silane by bringing the microsilica into contact with said polymerizable silane. The surface of the microsilica is modified with polymerizable silane by forming covalent bonds by the reaction of silanol groups on the surface of the microsilica with the alkoxysilane. The final products are modified polymerizable microsilica and alcohols.

Both dry and wet methods can be used to bring microsilica into contact with polymerizable silanes. In a dry method, the polymerizable silane as such is either dissolved in an alcohol, such as methanol, ethanol, can be sprayed onto microsilicas. Then, the polymerizable microsilica / silane mixture is mixed or rotated for a period of time and then dried to obtain the modified microsilica. The dry modification can also be carried out by a vapor deposition process, where the polymerizable silane is gasified at high temperature and deposited on silica particles, in a wet method, the polymerizable silane can be added to a dispersion which comprises microsilica and water or non-aqueous solvent, such as toluene or benzene.

Examples of suitable polymerizable silanes are vinyltrimethoxysilane, triethoxyvinylsilane, vinyltris (2-methoxyethoxy) silane, dimethoxymethylvinylsilane, diethoxy (methyl) vinylsilane, trichlorovinylsilane, tris (trimethylsilyl) trimyl ethyl vinyl ethyl, 3- (3-) propyl methacrylate, propyl 3- [tris (trimethylsiloxy) silyl] propyl methacrylate, or propyl 3- (triethoxysilyl) methacrylate.

Without modification with polymerizable silane, the microsilica adheres poorly to the polymer matrix. The silica content can be up to 80% by weight of the composite material. The lower limit is 0.1% by weight but then there will be a loss of almost pure polymeric fluid, which is expensive. The amount of microsilica in the additive can be in the range of 1 - 80% by weight relative to the total weight of the dry matter, 20 - 70% by weight relative to the total weight of the dry matter, 20 - 60% by weight relative to the total weight of the dry matter, 25 - 55% by weight of the total dry weight, 25 - 50% by weight of the total dry weight, 30 - 50% by weight of the total dry matter, 30 8 of 2020 00118

28/09/2018% by weight compared to the total weight of the dry matter. The amount of polymerizable silane is in the range of 0.01 - 20% by weight relative to the total weight of the dried microsilica, in the range of 0.01 - 10% by weight relative to the total weight of the dried microsilica, in the range of 0.5 - 5% by weight relative to the total weight of the dried microsilica, or in the range 1 - 2% by weight relative to the total weight of the dried microsilica.

The additive according to the invention does not cause gelling at low temperatures and is usable for most cementing applications, such as high temperature high pressure (HPHT) cement, light cement, high density cementation, salt-containing cement, etc. Modified microsilica with polymerizable silane can be used in other applications, such as drilling fluid filtration control and fluid fracturing. Furthermore, it can be used as a viscosity enhancing agent for an improved crude oil recovery fluid (EOR).

To produce the composite additive, the microsilica modified with polymerizable silane is copolymerized with one or more of the monomers mentioned below. The polymer chain can be copolymer, terpolymer, tetrapolymer or pentapolymer, etc. For simplicity, it is mentioned in the application as a copolymer, but other types of polymers are also part of the subject of the present invention.

Suitable acrylamide-derived monomers are selected from the group consisting of acrylamide (AAm), 2-acrylamido-2-methylpropane sulfonic acid (AMPS), N, N-dimethylacrylamide (NNDMA), vinylformamide, N-tert-butylacrylamide, N N- (Hydroxymethyl) acrylamide (NHMAAm), Ν, Ν'-Methylenebisacrylamide (NNMBAAm), vinylbutyrylactam, acrylonitrile, and 2 (dimethylamino) ethyl methacrylate.

Suitable acid unsaturated monomers are selected from the group consisting of acrylic acid (AA), methacrylic acid, maleic anhydride (MA), itaconic acid, 4-vinylbenzenesulfonic acid and vinylphosphonic acid.

Additives comprising microsilica modified with polymerizable silane and comprising two monomers may be used, such as, for example, mixtures of two monomers derived from acrylamide or mixtures of a monomer derived from acrylamide and an acid unsaturated monomer or mixtures of two monomers unsaturated acids. Such mixtures can be used in the temperature range of 50-150 Ό.

For applications of aqueous drilling fluids, especially freshwater systems, a composition comprising two acrylamide-derived monomers of 2020 00118 has been shown to be sufficient.

28/09/2018 together with microsilica modified with polymerizable silane. This is probably due to the low salinity of freshwater liquids. For use as an aqueous drilling fluid, a suitable additive according to the invention comprises microsilica modified with polymerizable silane and monomers derived from 2-acrylamido-2-methylpropane sulfonic acid acrylamide (AMPS) and Ν, Ν-dimethylacrylamide (NNDMA).

A suitable additive according to the invention comprises microsilica modified with polymerizable silane and monomers derived from acrylamide, 2-acrylamido-2-methylpropane sulfonic acid (AMPS) and acrylamide (AAm).

Additives may be used comprising microsilica modified with polymerizable silane and comprising three monomers such as, for example, mixtures of three acrylamide-derived mononers or mixtures of two acrylamide-derived monomers with an acid unsaturated monomer or mixtures of a derived monomer of acrylamide with two acidic unsaturated monomers.

A suitable additive according to the invention comprises microsilica modified with polymerizable silane and monomers derived from acrylamide, 2-acrylamido-2-methylpropane sulfonic acid (AMPS), Ν, Ν-dimethylacrylamide (NNDMA) and acrylamide (AAm).

A suitable additive according to the invention comprises microsilica modified with polymerizable silane and monomers derived from acrylamide, 2-acrylamido-2-methylpropane sulfonic acid (AMPS) and Ν, Ν-dimethylacrylamide (NNDMA) and the unsaturated acrylic acid monomer (AA).

A suitable additive according to the invention comprises microsilica modified with polymerizable silane and monomers derived from acrylamide, 2-acrylamido-2-methylpropane sulfonic acid (AMPS) and Ν, Ν-dimethylacrylamide (NNDMA) and the unsaturated acid monomer, maleic anhydride (MA).

Additives comprising microsilica modified with polymerizable silane and comprising four monomers may be used such as, for example, mixtures of four monomers derived from acrylamide or mixtures of three monomers derived from acrylamide with an acid unsaturated monomer or mixtures of two monomers derived from acrylamide with two acidic unsaturated monomers or mixtures of a monomer derived from three acidic unsaturated monomers.

For the cementation of an oil well, additives are needed comprising mixtures of acrylamide-derived monomers and acidic unsaturated monomers containing a carboxylate group (s) to achieve better adsorption on the positively charged phases of the cement granules. For cementing applications, an additive suitable according to the invention of 2020 00118

28/09/2018 comprises modified silica with polymerizable silane and monomers derived from acrylamide, 2-acrylamido-2-methylpropane sulfonic acid (AMPS), acrylamide (AAm) and N, N-dimethylacrylamide (NNDMA) and acid unsaturated monomer, acrylic acid (AA).

Additives comprising microsilica modified with polymerizable silane and comprising five or more monomers in which the monomers are combined in any way possible, as described above, may also be used.

The monomer (s) derived from acrylamide is (are) present in the additive in an amount in the range of 20-90% by weight relative to the total weight of the dry matter, 50-90% by weight relative to total dry weight, 60-80% by weight of the total dry weight.

The acid (day) unsaturated monomer (s) is (are) present in the additive in an amount in the range of 0,1 - 20% by weight relative to the total weight of the dry matter, 1 - 15% by weight relative to the total weight of the dry matter, 2-10% by weight relative to the total weight of the dry matter.

The particle size distribution for the fluid loss particles is in the range of 0.05 μm to 500 μm and preferably in the range of 0.1 μm to 15 μm. The average particle size (D50) is in the range of 5 μm to 20 μm, preferably about 10 μm.

The method for producing an additive for cement suspensions for oil wells and water-based drilling fluids comprises a first step of modifying the surface of the microsilica with polymerizable silane, using a dry or wet method, in which the microsilica is brought into contact with the polymerizable silane . Microsilica is chemically modified to allow better integration into the polymer network. Microsilica is added in an amount ranging from 80 to 99.9% by weight relative to the total weight of the dry matter and the polymerizable silane is added in an amount ranging from 0.1-20% by weight to the weight total dry microsilica. The polymerizable silane is selected from the group specified above.

Silane-modified microsilica is subsequently polymerized using a free radical polymerization technique. Free radical polymerization is a widely used method for the polymerization of unsaturated monomers, in which free radicals initiate polymerization. The additives according to the invention can be produced by any free radical polymerization method such as solid state polymerization, solution, suspension or emulsion.

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28/09/2018 in the polymerization step, the microsilica modified with silane in an amount of 1 - 80% by weight compared to the total weight of the dry matter is polymerized with at least one monomer derived from acrylamide; said at least one said acrylamide-derived monomer being added in an amount in the range of 50-90% by weight to the total weight of the dry matter and optionally at least one acid unsaturated monomer. If present, said at least one said unsaturated acid monomer is added in an amount in the range of 0,5 to 20% by weight relative to the total weight of the dry matter. Acrylamide-derived monomers and acidic unsaturated monomers »1>» are selected from the groups specified above.

Preparation of chemically modified silica fluid loss additives

Unless otherwise specified, the microsilica suspension used in the examples was the Microblock® suspension, which is a suspension of about 50% by weight (% gr) water and about 50% gr (amorphous silica powder with other additives, produced by Elkem AS.

The process for producing microsilica-containing additives consists of two steps:

1) Silica modification

To incorporate silica into a polymeric matrix, the surface of silica is modified with chemicals, such as polymerizable silane. Common wet or dry modification methods apply.

Example 1: Modification of microsilica with polymerizable silane using a dry method

1000 g of microsilicas were collected from an ARC silicon production furnace. The sample was dried at 105 ° C overnight. After drying overnight, the sample was charged to a Hubert mixer and 20 g of 3 (trimethoxysilyl) propyl methacrylate was sprayed onto microsilica. The mixture was stirred for 30 min and then dried overnight at 40 ° C in vacuo.

Example 2: Modification of microsilica with polymerizable silane using a wet method

Microsilica was dried overnight at 105 ° C. Then, 300 g of dried microsilica was dispersed in 1000 mL of toluene and washed quickly with nitrogen. The temperature was raised to 50 ° C. After raising the temperature, 15 g of propyl 3- (trimethoxysilyl) methacrylate were added in portions. The mixture was stirred overnight under reflux for 2020 00118

28/09/2018 at 50 ° C. The modified silica was filtered and washed with 200 ml of ethanol twice. Finally, the mixture was dried overnight at 40 ° C under vacuum.

The dry modification method is faster and more cost-effective compared to the wet modification method.

2) Polymerization

The polymerized silane modified microsilica is polymerized with one or more monomers derived from acrylamide and optionally one or more acid unsaturated monomers using a free radical polymerization technique, which can be carried out by solid state, solution, emulsion, emulsion polymerization methods. inverted, mini-emulsion or suspension. Examples of monomers that can be polymerized with microsilica modified with polymerizable silane are acrylamide-derived monomers selected from the group consisting of acrylamide (AAm), 2-acrylamido-2-methylpropane sulfonic acid (AMPS), Ν, Ν-dimethylacrylamide (N) , vinylformamide, N-tert-butylacrylamide (NTBAAm), N- (hydroxymethyl) acrylamide (NHMAAm), Ν, Ν'-methylenebisacrylamide (NNMBAAm), vinylbutyrolactam, acrylonitrile and 2 (dimethylamino ethyl) and dimethylamethyl ether consists of acrylic acid (AA), methacrylic acid, maleic anhydride (MA), itaconic acid, 4vinylbenzenesulfonic acid, and vinylphosphonic acid.

Free radical initiators such as potassium persulfate, ammonium persulfate, benzoyl peroxide, 2,2'-azobisisobutyronitrile (AIBN), tert-butyl peroxide were used. in addition, redox initiators can be used.

Example 3: Polymerization in solution

1) 15 g of microsilica modified with propyl 3- (trimethoxysilyl) methacrylate, prepared using the dry method using 1.5% g of propyl 3- (trimethoxysilyl) methacrylate by weight over the dried microsilica, mixed dry with 25 g of 2-acrylamido-2-methylpropane sulfonic acid (AMPS) and 7 g of Ν, Ν-dimethylacrylamide (NNDMA) monomers and mixed in 200 mL of deionized water.

2) The pH of the mixture was adjusted to 7 using 50% g of NaOH solution.

3) The mixture was then transferred to a 500 liter flask equipped with a reflux condenser, magnetic stirrer and thermometer.

4) The reaction vessel was heated to 60 ° C.

5) 0.33 g of ammonium persulfate dissolved in 10 ml of water as a free radical initiator were added to initiate the reaction.

6) The reaction was carried out for 2 hours, finally obtaining a viscous suspension.

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Example 4: Solution polymerization

1) 15 g of microsilica modified with propyl 3- (trimethoxysilyl) methacrylate, prepared using the dry method using 1.5% g 3- (trimethoxysilyl) propyl methacrylate by weight compared to the dried microsilica were mixed in the dry state with 2.5 g acrylic acid (AA), 2 g acrylamide (AAm), 3 g Ν, Ν-dimethylacrylamide (NNDMA) and 25 g 2-acrylamido2-methylpropane sulfonic acid (AMPS) as monomers and mixed in 200 mL of deionized water.

2) The pH of the mixture was adjusted to 7 using 50% g of NaOH solution.

3) The mixture was then transferred to a 500 liter flask equipped with reflux condenser, magnetic stirrer, nitrogen gas and thermometer.

4) The reaction vessel was heated to 60 ° C.

5) 0.33 g of ammonium persulfate dissolved in 10 ml of water were added as a free radical initiator to initiate the reaction.

6) The reaction was carried out for 2 hours, at the end a viscous suspension was obtained.

Example 5: Semi-continuous polymerization process in solution

1) Solution A consisting of 15 g of microsilica modified with propyl 3- (trimethoxysilyl) methacrylate mixed dry with 25 g of 2-acrylamido-2-methylpropane sulfonic acid (AMPS), 3 g of acrylamide (AAm), and 7 g N N-dimethylacrylamide (NNDMA) as monomers was mixed in 200 mL of deionized water.

2) The pH of the mixture was adjusted to 7 using 50% gr NaOH solution.

3) Solution B consisting of 0.33 g of ammonium persulphate was dissolved in 10 ml of water as a free radical initiator.

4) 10% of the total solutions A and B, in this case 25,5 g of solution A and 1,03 g of solution

B, were transferred to a 500 liter flask equipped with reflux condenser, magnetic stirrer, nitrogen gas, and thermometer.

5) The reaction vessel was heated to 60 ° C.

6) The remaining solutions A and B were fed into the reaction vessel using 2 metric pumps within 75 min.

7) The reaction was performed for 1 hour after the addition of the solutions.

8) The reaction was terminated by cooling to room temperature and finally a viscous suspension was obtained.

Morphology of modified microsilica with additive of 2020 00118

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Figures 1, 2 and 3 show electron scanning micrographs of an additive according to the invention produced by the procedure described in Example 4. The composite material is a large agglomerate filled with microsilica, which is surrounded by polymeric materials. At high shear, such particles deform and fill the gaps between the cement particles and reduce fluid loss. The size of the composite material according to said invention was also measured by the light scattering method, as shown in Figure 4.

Cementing of oil wells

To illustrate the application of the new invention, oil well cementation tests using chemically modified microsilica with polymers according to the invention were performed according to API 10 standard. The Microblock® suspension produced by Elkem AS was used as a raw material to prepare the modified microsilica. Other chemicals, such as conventional fluid loss additive, dispersant, retarder and de-foamer are common chemicals to formulate an oil well cement. Silica flour, Milisil M10 (23 pm & 2.65 sg (specific gravity)) supplied by Sibelco was used to prevent the retrogression of the resistance to temperatures above 110 ° C. Cement G was supplied by Dyckerhoff (fineness (Blaine) was 326 m ² / kg).

The following equipment was used for the preparation and characterization of the cement slurry: Fann 35 thermometer with thermo-cup, atmospheric and HPHT (high temperature high pressure), consistometers, equipment for measuring fluid loss (HPHT), ultrasonic compression strength analyzer ( UCA), constant speed countermeasure mixer, measuring cylinder of 200 - 250 ml and precision balance.

Use of chemically modified microsilica in a standard 1.9 sg (specific gravity) suspension for oil wells

Example 6

The cement formulation shown in Table 1 was used to prepare a cement slurry with a density of 1.9 g / cm ³ . In this example, the performance of the developed chemical was tested in a typical oil well cement model with a density (specific gravity) of 1.9 g / cm ³ . Suspensions 1 and 2 were prepared without additives for fluid loss. In suspensions 1 and 2, the Microblock® suspension was added with an amount of 25% and 33% by weight of cement, respectively. Suspension 3 was prepared using a conventional polymeric fluid loss additive containing 2-acrylamido-2-methylpropane sulfonic acid, acrylamide and N-vinyl-N-alkylalkanamide in an amount of 1% by weight of cement (BWOC). Suspension 4 was prepared with an additive of 2020 00118

28/09/2018 fluid loss according to the invention, prepared according to Example 4, with an amount of 1% by weight dry equivalent to the weight of the cement.

Plastic viscosity was measured in centipoise (cP), which is equal to one millipascal second (mPa · s) in SI units (1 cP = 10 ^-3 Pa-s = 1 mPa-s).

The yield strength was measured in pounds / 100 square feet (lbs / 1 OOft ² ), which is equal to 0.049 kg / m ² in SI units.

The specific density or weight (sg) of the suspensions is measured in grams per cubic centimeter (g / cm ³ ).

Table 1: Cement formulations for HPHT oil wells with and without fluid loss additives.

HPHT 1.9 sg suspension 1 (without fluid loss additive) suspension 2 (without fluid loss additive) suspension 3 (with conventional fluid loss additive) suspension 4 (with additive of loss of fluid according to the invention) Water, g 233.3 174.1 275.0 247.0 dispersant HT (high temperature), g 4.1 4.1 4.2 4.2 FLAC (fluid loss additive for cement), g 0.0 0.0 5.7 33.5 HT delay (high temperature), g 1.9 1.9 2.0 2.0 Suspension Microblock®, g 162.7 272.6 84.9 84.9 Silcolapse 140, g 1.9 1.9 2.0 2.0 Silica flour, g 189.8 174.1 198.1 198.1 Cement G, g 542.3 545.2 565.9 565.9 FLAC (fluid loss additive for cement) % BWOC (in weight relative to cement) 0.0 0.0 1.0 1.0 Viscosity readings at rpm 20 ’C 85 'C 20 ’C 85 'C 20 ’C 85 'C 20 ’C 85 'C 300 40 29 76 45 180 155 134 136 two hundred 32 22 65 39 130 114 96 97 100 21 13 52 32 75 69 54 54 60 17 10 46 29 51 48 36 35 30 13 7 42 28 31 30 21 19 6 11 5 39 25 14 9 7 5 3 10 4 39 25 10 5 6 3 Plastic viscosity cP (mPa-s) 28.5 24 36 19.5 157.5 129 120 123

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Elasticity limit lbs / 100ft ² (kg / m ² ) 11.5 (0.56) 5 (0.25) 40 (1.96) 25.5 (1.25) 22.5 (1.10) 26 (1.27) 14 (0.69) 13 (0.64) Density (sg) at 20 ° C, g / cm ³ 1.9 1.9 1.9 1.9 Fluid loss, ml, at 150 ° C 666 267 59 48 Filter cake, mm dry dry 28 25

The results shown in Table 1 indicate that microsilica cannot control filtration alone. Suspensions 1 and 2 show large fluid losses. Increasing the amount of microsilica reduces the fluid flow, but the value of 267 ml after 30 minutes is still quite high and it is not possible to use such a cement effectively. In addition, increasing the microsilica content increases the viscosity to an undesirable value. The cement slurry prepared with a conventional polymeric HPHT fluid loss additive containing 2-acrylamido-2-methylpropane sulfonic acid, acrylamide and N-vinyl-Nalkylalkanamide (suspension 3) ensures a fluid loss of 59 ml. The slurry 4 prepared with a fluid loss additive according to the invention, prepared according to Example 4, by 1% by weight dry equivalent to the weight of the cement, provides a fluid loss of only 48 ml and a thinner filter cake. The viscosity of suspension 4 was stable and quite similar at temperatures of 20'O and 85O.

Table 2 shows the formulation of HPHT oil well cement without the use of Microblock® slurry or other pozzolanic materials. Only silica flour was added to prevent the resistance from regressing. A conventional HPHT fluid loss additive containing 2-acrylamido-2-methylpropane sulfonic acid, acrylamide and N-vinyl-N-alkylalkanamide was used in suspension 5. Suspension 6 was prepared using a fluid loss additive according to the invention, prepared according to Example 4 Again, the HPHT oil well cement comprising an additive according to the invention shows good results at 150'O.

Table 2: Formulations and performances of cement for HPHT oil wells.

HPHT cement suspensions 1.9 sg suspension 5 (with conventional fluid loss additive) suspension 6 (with fluid loss additive according to the invention) Water, g 324.5 302.0 HT dispersant, g 4.4 4.4 FLAC, g 5.9 29.6

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HT retarder, g 1.8 1.8 Silicone defoaming agent, g 2.1 2.1 Silica flour, g 206.7 206.7 Cement G, g 590.6 590.6 FLAC% BWOC 1.0 1.0 Viscosity readings at rpm 20 ’C 85 'C 20 ’C 85 'C 300 209 132 193 122 two hundred 146 89 135 84 100 79 46 71 45 60 49 28 44 28 30 26 13 2. 3 15 6 7 2 6 4 3 4 1 4 2 Plastic viscosity, cP (mPa-s) 195.0 129.0 183.0 115.5 Elasticity limit, lbs / 100 ft * (kg / m ² ) 14.0 (0.69) 3.0 (0.15) 10.0 (0.49) 6.5 (0.32) Density (sg) at 20 ° C, g / cm ³ 1.9 1.9 Fluid loss, ml, at 150 ° C 47 36 Filter cake, mm 40 15

Suspensions 7 and 8 were prepared by adding 18% sodium chloride salt by volume to the volume of fresh water. Salt cement is commonly used to cement salt-containing formations to avoid hydration of ordinary cement salt with oil well. Filtration control for this type of cement requires a liquid loss additive that is compatible with the NaCL salt. Suspension 7 was prepared with a conventional HPHT fluid loss polymer additive containing 2-acrylamido-2-methylpropane sulfonic acid, acrylamide and N-vinyl-N-alkylalkanamide, while suspension 8 was prepared with a fluid loss additive according to the invention, prepared according to Example 4.

The additive according to the invention ensures an efficient control of the salt cement filtration.

Table 3: Salt cement formulations for HPHT oil wells and performance.

1.9 sg HPHT salt cement suspension 7 (with conventional fluid loss additive) slurry 8 (with conventional fluid loss additive according to the invention) Water, g 304.8 282.0 Dispersam, g 4.2 4.2 Fluid loss additives, g 5.6 28.0 retardant, g 2.2 2.2

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Silicone foaming agent, g 2.0 2.0 NaCl, g 56.1 56.1 Silica flour, g 195.6 195.6 Cement-G, g 558.8 558.8 FLAC% BWOC 1.0 1.0 Viscosity readings at rpm 20 ’C 85 C 20 ’C 85 ° C 300 173 62 181 59 two hundred 121 41 129 40 100 65 21 73 20 60 41 12 47 12 30 21 7 27 5 6 5 1 10 2 3 3 <1 7 0 Plastic viscosity, cP (mPa-s) 162 61.5 162 58.5 Elasticity limit, lbs / 100ft ² (kg / m ² ) 11 (0.54) 0.5 (0.03) 19 (0.93) 0.5 (0.03) Free water, ml 4 2 Density (sg) at 20 ° C, g / cm ³ 1.9 1.9 Fluid loss temp, ° C 150 150 Fluid loss, ml 22 22 Filter cake, mm 3 2

Table 4 shows the model and performance of a fluid loss additive according to the invention (suspension 10), which was produced according to Example 4, compared to a conventional polymeric fluid loss additive HPHT containing 2-acrylamido2-methylpropane sulfonic acid, acrylamide and N-vinyl-N-alkylalkanamide (suspension 9) in a light formulation with a density of 1.35 sg. At an amount of 1.5% BWOC, the additive according to the invention provides a good model of cement suspension.

Table 4: Formulations and performance of light HPHT cement, density 1.35 sg.

HPHT cement 1.35 sg suspension 9 (with conventional fluid loss additive) suspension 10 (with fluid loss additive according to the invention) Water, g 280.5 263.1 Dispersant, g 0.9 0.9 Fluid loss additive, g 4.4 21.8 retardant, g 1.7 1.7 Microblock® slurri, g 144.8 144.8 Silicone foam, g 1.5 1.5

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Cenosphere, g 87.4 87.4 Cement G, g 291.3 291.3 FLAC% BWOC 1.5 1.5 Viscosity readings at rpm 20 C 85 'C 20 ’C 85 'C 300 79 79 93 65 two hundred 61 60 72 50 100 42 38 47 30 60 32 27 35 20 30 24 18 25 14 6 20 6 10 5 3 17 5 9 4 Plastic viscosity, cP (mPa-s) 55.5 61.5 69 52.5 Elasticity limit, lbs / 100 ft ² (kg / m ² ) 23.5 (1.15) 17.5 (0.86) 24 (1.18) 12.5 (0.61) Free water, ml 0 0 Density (sg) at 20 ° C, g / cm ³ 1.35 1.35 Fluid loss temp, ° C 85 85 Fluid loss, ml 32 24 Filter cake, mm 8 7

Similar to oil well cement, synthetic polymeric materials are used to control fluid losses for an aqueous HPHT (high pressure, high temperature) drilling fluid, which is used for drilling wells with bottom temperatures> 1500. Such materials must withstand at a high temperature, which can be in the range of 150-2500. The modified microsilica composite has large deformable particles that can form an elastic filter cake on the surface of the formation and can reduce fluid loss.

Tables 5 and 6 show the formulation and performance of an HPHT aqueous drilling fluid with a specific gravity (sg) of 2.1 containing the additive according to the invention, as a fluid loss additive. The fluid loss additives in Tables 5 and 6 are produced according to the procedure described in Example 3.

The results show that the developed material is stable at a temperature of 2000. The fluid loss was in the range of 20-22 ml after thermal aging in 1750 and 2000, respectively. The viscosity was stable after thermal aging.

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Table 5: Formulation of an aqueous HPHT drilling fluid with sg 2,1 comprising a fluid loss additive according to the invention, prepared according to the procedure described in example 3.

Material Quantity (g) Quantity (ml) For mixing (min) The water 465.0 465.0 Modified montmorillonite 12.0 4.6 5 NaOH 1.0 0.5 10 Chemtrol ™ X lignite fluid loss additive from Baker Hughes 9.8 9.8 5 Fluid loss additive according to the invention prepared according to Example 3 50.0 45.5 5 Manganese tetroxide (Mn ₃ O ₄ ) 974.0 202.9 10 HPHT dispersant 10.0 10.0 2 Total 1521.8 738.3 37

Table 6: Performance of a 2.1 sg aqueous HPHT drilling fluid comprising fluid loss additive according to the invention prepared according to the procedure described in Example 3.

Flow of 2.1H sgHT remote watering cans thermal aging 16 h BSHA (before static thermal aging) ASHA (after static thermal aging) ASHA (after static thermal aging) 175 ° C 200 ° C Rheology at 50 ° C 600 rpm 151 152 126 300 rpm 90 92 76 200 rpm 67 71 59 100 rpm 42 47 40 6 rpm 10 14 12 3 rpm 8 12 11 Gels 10, lb / 100 ft ² (kg / m ² ) 9 (0.44) 12 (0.59) 10 (0.49) 10 ', lb / 100 ft ² (kg / m ² ) gels 16 (0.78) 14 (0.69) 12 (0.59) Plastic viscosity, cP (mPa-s) 61 60 50 Elasticity limit, lb / 100 ft ² (kg / m ² ) 29 (1.42) 32 (1.57) 26 (1.27) Static Sag Sag Static Factor 0,500 0.506 Density at 20 ° C, g / cm ³ 2.09 2.1 2.1 Filtration Fluid loss at 175 ° C, ml 12 20 22 Filter cake, mm 8 7 9

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Modified microsilica composites and acrylamide derivatives have a high water retention capacity and can control the filtration of aqueous fluids in the oil field and are thus suitable as additives for fluid loss in aqueous drilling fluids, as shown in Table 6 above. up.

Table 7 shows examples of additive formulations according to the present invention. The amount of water in the formulations was 200 ml. All quantities expressed by weight in Table 7 are in grams. In addition to the amount of monomer, 0.2 g of potassium persulphate and 5 g of sodium hydroxide were added.

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Table 7-Formulations of additives of the invention

formulation microsilica modified with 3-trimethoxysilyl) propyl methacrylate (G) Acrylamide (AAm) (g) 2-acrylamido-2-methylpropane sulfonic acid (AMPS) (g) acrylic acid (AA) (g) N, N-dimethylacrylamide (NNDMA) (g) Maleic anhydride (MA) (g) 1 15 3 25 0 0 0 2 15 3 22 0 3 0 3 15 0 20 2 6 0 4 15 0 20 0 6 2 5 15 3 20 2 3 0 6 10 3 22 0 3 0 7 20 3 22 0 3 0 8 15 0 20 0 10 0

Example 7

The additive according to the invention was tested in cement suspension. During the curing process, the cement slurry is first converted to a gel state and finally to a solid state. In order to mitigate the risk of gas migration through the cement column during the hardening / hardening process, the transition time should be as short as possible and the development of compressive strength should be as fast as possible. The transition time is the time required to increase the static resistance of the gel from 50 to 500 psi (3.45 - 34.5 bar). The transition time should be less than 40 minutes and preferably less than 30 minutes to mitigate gas migration.

The static gel strength analyzers (SGSA) provided by Ametek Oii & Gas use acoustic / ultrasonic attenuation to monitor the cement hardening process of an oil well under conditions of temperature and deep pressure. The equipment measures the development of the static resistance of the gel and the development of the compressive strength of a cement suspension as a function of time.

A shortening of the transition time for the cement slurry containing the additive according to the invention was observed. Figures 5 and 6 show the process of hardening the suspensions 5 and 6 prepared for cementing an oil well, as shown in Table 2. Suspension 6 comprises an additive according to the invention, prepared according to Example 4. Suspension 5 comprises a polymeric additive for loss of conventional HPHT fluid containing 2-acrylamido-2-methylpropane sulfonic acid, acrylamide and N-vinyl-N-alkylalkanamide. The tests were performed at a temperature of 150 ° C and a pressure of 3000 psi (206.8 bar). The transition time was 36 min for suspension 5 and 9 min for suspension 6. in 2020 00118

28/09/2018 plus, the compressive strength was developed much faster for the suspension 6 formulated with the additive according to the present invention, compared to the suspension 5 formulated with a conventional polymeric HPHT fluid loss additive. Within 12 hours of hardening, the suspension 5 achieved a compressive strength of 1802 psi (124.24 bar) while the suspension 6 reached a compressive strength of 2427 psi (167.33 bar).

This indicates that the cement prepared with an additive according to the present invention offers additional benefits in terms of the properties of a cement slurry, namely the prevention of gas migration by shortening the transition time and increasing the compressive strength to a large extent.

The additives according to the invention can be used in formulations for cementing oil wells or for water-based drilling fluids. The additives according to the invention are used, for example, as additives for fluid loss and also as viscosity modifiers (viscosity enhancers) for crude oil fracturing or recovery (EOR) applications.

After the preferred embodiments of the invention have been described, it will be apparent to those skilled in the art that other embodiments incorporating such concepts may be used. These and other examples of the invention, illustrated above, are for exemplary purposes only and the actual scope of the invention is determined by the following claims.

Claims (20)

1. Fluid loss additive for cement suspensions for oil wells and water-based drilling fluids, characterized in that the fluid loss additive comprises microsilicas, in which the microsilica is amorphous SiO ₂ in particulate form, obtained from a process in which the silica is reduced to SiO-gas and the reduction product is oxidized in the vapor phase and condensed to form amorphous silica containing> 90% by weight of silica (SiO ₂ ) and having a specific density of 2.1 - 2,3 g / cm ³ , a surface area of 12-40 m ² / g and a particle size in the range of 0,02 pm to 45 pm, in an amount in the range of 1-80% by weight relative to the total weight of the dry matter, the microsilica surface! comprises polymerizable silane in an amount in the range of 0.01 - 20% by weight relative to the total weight of the microsilica! and the fluid loss additive further comprises at least one acrylamide-derived monomer selected from the group consisting of acrylamide (AAm), 2-acrylamido-2-methylpropane sulfonic acid (AMPS), Ν, Ν-dimethylacrylamide (NNDMA), vinylformamide , N-tert-butyl acrylamide (NTBAAm), N- (hydroxymethyl) acrylamide (NHMAAm), N, N-methylenebisacrylamide (NNMBAAm), vinylbutyrolactam, acrylonitrile, and 2 (dimethylamino) ethyl methacrylate. The fluid loss additive of claim 1, further comprising at least one acid unsaturated monomer. A fluid loss additive according to claim 2, wherein said at least one said unsaturated acid monomer is selected from the group consisting of acrylic acid (AA), methacrylic acid, maleic anhydride (MA), itaconic acid, 4-vinylbenzenesulfonic acid , and vinylphosphonic acid. The fluid loss additive of claim 1, wherein the acrylamide-derived monomers are 2-acrylamido-2-methylpropane sulfonic acid (AMPS) and Ν, Ν-dimethylacrylamide (NNDMA). a 2020 00118 28/09/2018 The fluid loss additive of claim 1, wherein the acrylamide-derived monomers are 2-acrylamido-2-methylpropane sulfonic acid (AMPS), Ν, Ν-dimethylacrylamide (NNDMA) and acrylamide (AAm). The fluid loss additive of claim 3, wherein the acrylamide-derived monomers are 2-acrylamido-2-methylpropane sulfonic acid (AMPS), Ν, Ν-dimethylacrylamide (NNDMA) and acrylamide (AAm), and the acid unsaturated monomer is acrylic acid (AA). Fluid loss additive according to any one of the preceding claims, wherein the amount of microsilica comprising on its surface a polymerizable silane is in the range of 20 - 70% by weight relative to the total weight of the dry matter, 20 - 60% by weight in relation to the total weight of the dry matter, 25 - 55% by weight in relation to the total weight of the dry matter, 25 - 50% by weight in relation to the total weight of the dry matter, 30 - 50% by weight in relation to the total weight of the dry matter, 30 - 40% by weight of the total weight of the dry matter. A fluid loss additive according to any one of the preceding claims, wherein said at least one acrylamide-derived monomer is present in an amount in the range of 20-90% by weight relative to the total weight of the dry matter, % by weight relative to the total weight of the dry matter, 60-80% by weight relative to the total weight of the dry matter. A fluid loss additive according to any one of claims 2 to 8, wherein said at least one acid unsaturated monomer is present in an amount in the range of 0.1 to 20% by weight relative to the total weight of the dry matter, 1 - 15% by weight of the total weight of the dry matter, 2 - 10% by weight of the total weight of the dry matter. A fluid loss additive according to any one of the preceding claims, wherein the dimensional distribution of the particles of said fluid loss additive, measured by the light scattering method is in the range of 0.05 μm to 500 μm with an average size ( D50) in the range of 5 pm to 20 pm. a 2020 00118 28/09/2018 A fluid loss additive according to any one of the preceding claims, wherein the polymerizable silane is selected from the group consisting of vinyltrimethoxysilane, triethoxyvinylsilane, vinyltris (2-methoxyethoxy) silane, dimethoxymethylvinylsilane, diethoxy (methyl) vinylsilyl, trichlorethylsilyl ) vinyl silyl, propyl 3- (trimethoxysilyl) acrylate, propyl 3 (trimethoxysilyl) methacrylate, propyl 3- [tris (trimethylyloxy) silyl] methacrylate and 3 (propyl triethoxysilyl) methacrylate. The fluid loss additive of claim 11, wherein the polymerizable silane is vinyl trimethoxysilane or propyl 3- (trimethoxysilyl) methacrylate. A method of producing a fluid loss additive for cement wells for oil wells and aqueous drilling fluids according to claim 1, characterized in that it comprises the steps of: a) modification of the surface of the microsilica with polymerizable silane by bringing the microsilica in an amount in the range of 80 - 99.9% by weight compared to the total weight of the dry matter in contact with a polymerizable silane in an amount in the range of 0 , 1 - 20% by weight of the total weight of the dried microsilica; b) polymerization of modified microsilica with polymerizable silane in an amount of 1 80% by weight relative to the total weight of the dry matter with at least one acrylamide-derived monomer selected from the group consisting of acrylamide (AAm), 2acrylamido-2- acid methylpropane sulfonic acid (AMPS), Ν, Ν-dimethylacrylamide (NNDMA), vinylformamide, N- (hydroxymethyl) acrylamide (NHMAAm), N, N'-methylenebisacrylamide (NNMBAAm), vinylbutyrylactamate, ethylamethyl (acrylethyl) , in an amount ranging from 50 to 90% by weight relative to the total weight of the dry matter. The method of claim 13, wherein the microsilica modified with polymerizable silane is further polymerized with at least one acidic unsaturated monomer in an amount in the range of 0.1 - 20% by weight relative to the total weight of the dry matter. A method according to claim 13 or 14, wherein the surface of the microsilica is modified with polymerizable silane using a dry method. a 2020 00118 28/09/2018 A method according to claim 13 or 14, wherein the surface of the microsilica is modified with polymerizable silane using a wet method. A method according to any one of claims 13 to 16, wherein the polymerized silane-modified microsilica is polymerized using a free radical polymerization technique. A method according to any one of claims 14 to 17, wherein said at least one acid unsaturated monomer is selected from the group consisting of acrylic acid (AA), methacrylic acid, maleic anhydride (MA), itaconic acid, 4-vinylbenzenesulfonic acid, and vinylphosphonic acid. A method according to any one of claims 13 to 18, wherein the polymerizable silane is selected from the group consisting of vinyltrimethoxysilane, triethoxyvinylsilane, vinyltris (2-methoxyethoxy) silane, dimethoxymethylvinylsilane, diethoxy (methyl) vinylsilane, trichlorovinylsilyl, trichlorovinylsilyl, Propyl 3- (trimethoxysilyl) acrylate, propyl 3- (trimethoxysilyl) methacrylate, propyl 3- [tris (trimethylsilyloxy) silyl] methacrylate and propyl 3- (triethoxysilyl) methacrylate. The method of claim 19, wherein the polymerizable silane is vinyl trimethoxysilane or propyl 3- (trimethoxysilyl) methacrylate.