CEMENT ALUMINATES OF CALCIUM LONG workability AND PROMOTES HARDENING BY ELEVATION OF TEMPERATURE AND

USE THEREOF TECHNICAL FIELD TO WHICH THE INVENTION The present invention relates generally to the field of cements whose hardening in the presence of water is favored by a temperature rise.

It particularly relates to a calcium aluminate cement comprising a calcium aluminate with a first crystallized mineralogical phase calcium dialuminate CA2 comprising a calcium oxide CaO for two aluminum oxide AI 2 O 3 and / or a second mineralogical phase crystallized alumina silicate dicalcium C2AS comprising two CaO calcium oxide to aluminum oxide AI 2 O 3 and a silicon dioxide SiO 2 .

It also relates to a cementitious composition comprising such calcium aluminate cement, mixed with water and optionally other compounds such as fly ash, granulated blast furnace slag, silica flour, silica fume, metakaolin, quartz, fine limestone, sand, and adjuvants.

The invention finds a particularly advantageous application in any application where a temperature increase is required or imposed, such as consolidating petroleum wellbore.

BACKGROUND

A cement is a mineral powder suitable to be mixed with water to form a cementitious composition in paste or liquid consistency which cures to form a final cured material.

There are many cement on the market that are characterized, first, by their reactive properties with water, and secondly, by the mechanical and chemical properties of the final cured materials they achieve.

For example, calcium aluminate cements provide the hardened final materials specific chemical properties of high resistance to acid corrosion and mechanical properties of high resistance to high temperatures and pressures.

The reactive properties of a cement when mixed with water determine the workability of the cementitious composition formed by mixing the cement with water, that is to say the length, also called " open time ", during which the cementitious composition has a viscosity suitable for use, namely, for example, a low viscosity to allow its injection in fissures, or moderate viscosity to allow its shaping in molds.

These reactive properties also determine the cure kinetics of the cement composition during subsequent reaction of cement with water phases. These include the characteristics of the hydraulic setting of the cementitious composition, the hydraulic setting being accelerated exothermic phase of the reaction of hydration of cement with water, and the speed at which final curing of the material occurs after the hydraulic setting, namely how long the final cured material reaches a desired mechanical strength.

On the other hand, it is known that a relatively high temperature, that is to say greater than about 50 ° C or above 30 ° C, can accelerate the curing kinetics of a cementitious composition, and reduce substantially workability in particular by promoting thickening of the cementitious composition and triggering the hydraulic setting faster.

To reduce the effect of temperature on the reactivity of the cement compositions, it is common to add adjuvants to cementitious compositions, such as retarders.

However, several retardants that can be used in the same cementitious composition, these retardants can affect each other and / or with other additives to the cementitious composition, and it becomes difficult to predict the cure kinetics of the cement composition.

In addition, the presence of retarder in the cement composition may lead to a lowering of the mechanical strength of the final hardened material.

In addition, it is also known that, because of these problems of workability and curing kinetics, cementitious compositions calcium aluminate base are generally manufactured on site, that is to say water is added to the cement directly on the place of use of cementitious compositions.

It happens so regularly that, on site, the cement compositions based on calcium aluminate cements are prepared in line

Production usually used to prepare the cementitious compositions based on Portland cement.

Production lines with dead zones difficult to purge and / or to clean, it can stay a little cement a production campaign to another. Thus, in the preparation of a cementitious composition based on a Portland cement, it happens that Portland cement was contaminated with calcium aluminate cement remnants, or vice versa.

However, it turns out that Portland cements and cements calcium aluminate interact, and that this interaction accelerates the cure kinetics of cementitious compositions obtained. Thus, the hydraulic setting of a cementitious composition based on a mixture of Portland cement and calcium aluminate cement is initiated earlier than what is expected for a cementitious composition for Portland cement or cement of calcium aluminate only. When this mixture is due to an unintentional pollution, taking acceleration may cause a blocking of facilities, which is very problematic.

An application in which high temperatures generally involved and for which it is essential to control the workability and the curing kinetics of the formed cementitious compositions is the consolidation of the wellbore.

Drilling wells, particularly oil wells, is a complex process that primarily involves drilling rock while introducing a tubular metal body.

It is known to cement the walls of the wellbore at the same time to strengthen the casing of the wells to protect from corrosion the tubular body inserted therein, and to seal said tubular body in the surrounding rock.

To do this, the industrial use of cementitious compositions in form of aqueous suspensions commonly referred to as slurry (or "slurry" in English), mainly comprising a cement, optionally aggregates or additions specific cementitious dispersed in a relatively large amount of water, they inject into the tubular body to the bottom thereof. The aqueous suspension then rises to the surface in the space between the rock wall and the tubular body.

It is then understood that the workability of the aqueous suspension should be

such that this aqueous suspension can be injected to the bottom of the tubular body, and that the hydraulic jack of the aqueous suspension should occur at a controlled time after the ascent to the surface of this aqueous suspension, and taking into account the conditions underground temperatures and high pressures.

Document US20130299170 discloses such complex cementitious compositions in the form of aqueous suspensions suitable for the consolidation of oil well which comprise calcium aluminate cements and retarders comprising an organic acid and a polymer blend .

There are also known US6143069 documents and US20040255822 cement compositions as an aqueous suspension of low density, adapted to the consolidation of oil well, including a commercial calcium aluminate, brand Secar-60 ™ or REFCON ™, ash fly, water, retarders such as citric, gluconic or tartaric and other additives such as foaming agents and agents to prevent fluid loss.

However, the cementitious compositions thus formulated to reduce the effect of temperature on their workability and hardening kinetics are particularly complex. They also generate by the use of many different chemical compounds, which can have a detrimental effect on the environment.

There is therefore a need to benefit from the properties provided by the hydration of calcium aluminate while easily controlling the period of workability especially when the temperature is high, and tolerating some pollution from Portland cement or cement Portland.

OBJECT OF THE INVENTION

To remedy the aforementioned drawbacks of the prior art, the present invention provides a new cement calcium aluminate, which has the advantageous properties of chemical resistance and mechanical strength of this type of cement, and a time naturally long open without adding retardant, and even if unintentional mixing with Portland cement.

More particularly, the invention provides a cement

calcium aluminate as described in the introduction, wherein the mass fraction of all of said first and second mineralogical phases in said calcium aluminate is greater than or equal to 80%.

Thus, through these crystallized mineralogical phases, calcium aluminate cement according to the invention a controlled hardening kinetics without requiring add-timer to it.

Specifically, the Applicant has found that calcium aluminate cements comprising these mineralogical phases exhibited at room temperature, an extremely long workability, and the reactivity of these phases with water was favored by a temperature rise. Thus, at room temperature, the reactivity of the calcium aluminate cement according to the invention with water is low and the kinetics of the hydration reaction is very slow. The workability of the cement composition based on this cement is thus controlled without addition of retarders in the form of additional chemical compounds.

In addition, the curing kinetics for controlled hydraulic setting can be initiated and / or accelerated by a temperature increase.

In addition, these mineralogical phases guarantee the calcium aluminate cement according to the invention reduced interactions with Portiand cements, reducing the problems associated with cross-contamination between Portiand cements and calcium aluminate cements.

Finally, the calcium aluminate cement according to the invention of the mechanical strength properties at high temperatures and high pressures, and chemical corrosion resistance to acids similar to those of calcium aluminate cements already known in 'state of the art.

Other non-limiting and advantageous characteristics calcium aluminate cement according to the invention, individually or in all technically possible combinations, are:

- said calcium aluminate also includes an amorphous portion, the mass fraction in said calcium aluminate is less than or equal to 20%;

- said calcium aluminate further includes a third crystallized mineralogical phase AC monocalcium aluminate having an oxide

CaO calcium (noted C according to the notation of the cement) to an aluminum oxide AI 2 O 3 (denoted A according to the rating of cement) and / or a fourth crystallized mineralogical phase hexa-aluminate of calcium oxide having a CA6 CaO calcium for six aluminum oxide AI 2 O 3 , the mass fraction of all of the third and fourth mineralogical phases in said calcium aluminate is less than or equal to 20%;

- said calcium aluminate further includes an additional license C4A3 $ phase calcium sulfoaluminate having four CaO calcium oxides to three aluminum oxide AI 2 O 3 and a sulfur oxide SO 3 ($ rated according to the notation of cement) ;

- it comprises, by weight based on the total weight of said calcium aluminate: 0% to 5% of an iron oxide Fe 2 O 3 , 0% to 5% of a titanium oxide TiO 2 , 0% to 5% of a sulfur oxide SO 3 , 0% to 5% of magnesium oxide MgO, 0% to 2% of alkaline compounds;

- it is in the form of a powder having a surface area

Blaine measured according to the NF-EN-196-6 standard between 2200 square centimeters per gram to 4500 square centimeters per gram, preferably between 2900 and 3900 square centimeters per gram;

- it comprises, by weight based on the total weight of said calcium aluminate: 50% to 60% of first crystallized mineralogical phase CA2, 26%

32% of second crystallized mineralogical phase C2AS (S designating the silica SiO 2 according to the notation of cement) 2.5% to 3.5% of third crystallized mineralogical phase CA, 0.5% to 1 5% of a fifth crystallized mineralogical phase ferro-aluminate tetracalcium C4AF (F designating the iron oxide Fe 2 O 3 according to the rating of cement), 10% to 15% more crystallized mineralogical phases;

- the calcium aluminate cement according to the invention comprises from 0.5% to 15% additional mineralogical phase sulphoaluminate C4A3 $ calcium, by weight based on the total weight of said calcium aluminate.

The invention also provides a cementitious composition comprising at least cement calcium aluminate according to the invention mixed with water and possibly cement additives such as fly ash and / or granulated blast-furnace and / or silica flour and / or silica fume and / or metakaolin, aggregates such as quartz and / or fine limestone and / or sand, and adjuvants.

The invention also provides a use of cement calcium aluminate as described above, that

a) a cementitious composition is produced by mixing at least said calcium aluminate cement with water,

b) establishes said cementitious composition,

c) said cementitious composition is heated to a temperature between 50 ° C and 300 ° C, preferably between 80 ° C and 28 ° C, so as to promote the taking of the cementitious composition.

The cementitious composition may further comprise aggregate (e.g. sand) and / or adjuvants (e.g., retarders, accelerator or the like) known to those skilled in the art.

Under the conditions of temperature of step c), the pressure is preferably chosen high, that is to say greater than or equal to the saturation vapor pressure, so that the water is present in liquid form or at least in the form of saturated vapor.

In particular, the use of calcium aluminate cement has a particularly advantageous application in the consolidation of the wellbore, including oil well.

For this, in step a) the use according to the invention, the cementitious composition is in the form of an aqueous suspension, and in step b), the cement composition is placed in a wellbore oil.

DETAILED DESCRIPTION OF AN EMBODIMENT The following description in the accompanying drawings, given by way of non-limiting example, explains in what the invention is and how it can be achieved.

In the accompanying drawings:

- Figure 1 is a ternary diagram lime-silica-alumina, represented by mass fraction of lime, alumina and silica;

- Figure 2 is a zoom Figure 1 in the area of ​​interest [II-II] to describe the range of composition of calcium aluminate of the invention.

Within the meaning of the invention, and unless otherwise specified, the indication of a range of values ​​"X to Y" or "between X and Y" in the present invention, means as including the X and Y values

The present invention relates to a suitable calcium aluminate cement to be mixed with water to form a cementitious composition whose workability is naturally long, and whose reactivity is promoted by a rise in temperature.

In the following description, the term "cement" shall mean a powder suitable to be mixed with water to form a cementitious composition capable of curing to form a hard final material.

The term "cementitious composition" shall mean the mixing of cement with water and optionally other additional compounds.

Finally, as will be well explained below, the "reactivity" or

"Reactive properties" cement characterize the ability of the cement to react with water.

From a chemical point of view, the cement calcium aluminate according to the invention comprises at least one calcium aluminate, that is to say a compound comprising both calcium oxide and the aluminum oxide.

Specifically, here, the cement calcium aluminate according to the invention comprises calcium oxide commonly called lime CaO, aluminum oxide commonly known as alumina Al 2 O 3 , and commonly referred to as silicon dioxide silica SiO 2 .

In order to simplify the notation, as conventionally are the cement in their notation, we will shorten thereafter lime CaO with the letter C, alumina Al 2 O 3 by the letter A and the silica SiO 2 with S .

These three compounds, namely C lime, alumina and silica A S, are the major compounds present in the calcium aluminate according to the invention.

The calcium aluminate according to the invention may also comprise, by weight based on the total weight of said calcium aluminate:

- 0% to 5% of an iron oxide Fe 2 O 3 (abbreviated F according to the rating of cement)

- 0% to 5% of a titanium oxide TiO 2 (abbreviated T according to the rating of cement)

- 0% to 5% of a sulfur oxide SO 3 (abbreviated $ according to the notation of cement)

- 0% to 5% of a magnesium oxide MgO (abbreviated M according to the notation

of cement)

- 0% to 2% of alkaline compounds.

These other compounds are in the minority in the cement calcium aluminate according to the invention. They constitute impurities that usually come from the raw materials used to manufacture calcium aluminate.

On the mineralogical standpoint, the cement calcium aluminate according to the invention comprises a crystalline portion and an amorphous portion.

These amorphous and crystalline portions characteristic microscopic state of the calcium aluminate cement according to the invention: the crystalline part of the calcium aluminate cement contains atoms and / or molecules ordered according to a particular geometry, crystallized mineralogical phases while the amorphous part of the calcium aluminate cement contains atoms and / or molecules that are arranged in a disorderly manner to each other, that is to say, no particular order.

Here, the calcium aluminate cement according to the invention is mainly crystalline.

More precisely, advantageously, in the calcium aluminate cement according to the invention, the mass fraction of said crystalline portion in said calcium aluminate is greater than or equal to 80%.

In other words, the weight of the crystalline portion with respect to the total mass of the cement calcium aluminate according to the invention is greater than or equal to 80%.

Thus, in the calcium aluminate cement according to the invention, the mass fraction of the amorphous portion is less than or equal to 20%.

The crystalline portion has crystallized mineralogical phases that describe more specifically cement calcium aluminate according to the invention.

Indeed, the amount and nature of crystallized mineralogical phases present in the cement according to the invention reflect the chemical composition of said calcium aluminate.

In the following description, these "crystallized mineralogical phases" are sometimes called "mineralogical phases."

Here in particular, crystallized mineralogical phases describe both the structure at the atomic scale and the chemical composition of calcium aluminate, insofar as they involve several different compounds.

In particular, here, the mineralogical phases of the cement calcium aluminate according to the invention involve the C lime, alumina silica A and S.

Generally, the crystallized mineralogical phases of calcium aluminate are many. Among them include:

• phase having only lime and alumina C A, such as:

- the monocalcium aluminate phase CaAl 2 0 4 denoted by CA, whose crystal lattice has a lime molecule C for an alumina molecule A,

- the calcium dialuminate phase CaAl 4 0 7 denoted CA2, whose crystal lattice has a lime molecule C for two alumina molecules A,

- the phase of calcium hexa-aluminate denoted CA6, whose crystal lattice has a lime molecule C for six alumina molecules A,

- the tricalcium aluminate C3A phase designated, whose crystal lattice has three lime C molecules to an alumina molecule A,

- the dodecacalcium hepta-aluminate phase denoted C12A7, whose crystal lattice has two lime molecules C for seven alumina molecules A;

· Phases having only lime C and silica S , such that:

- the monocalcium silicate phase denoted CS, whose crystal lattice has a lime molecule C for a silica S molecule;

- the dicalcium silicate phase denoted C2S, whose crystal lattice has two lime molecules C for a silica molecule S,

- tricalcium silicate C3S phase designated, whose crystal lattice has three lime C molecules to a silica S molecule;

- tricalcium disilicate phase denoted C3S2, whose crystal lattice has three lime C molecules to two molecules of S silica;

• phase consisting only of alumina and silica S, such that:

- tri-aluminate disilicate phase denoted A3S2, whose crystal lattice has three alumina molecules A two S silica molecules;

• phase comprising both lime C, alumina and silica A S, such that:

- the dicalcium silicate phase alumina denoted C2AS, whose crystal lattice has two lime molecules C for an alumina silica molecule A and a molecule of S,

- the monocalcium alumina disilicate phase denoted CAS2, whose crystal lattice has a lime molecule C for an alumina molecule A and two S silica molecules;

this list is not exhaustive.

These mineralogical phases are generally chosen based on the properties they provide calcium aluminate cement, especially in terms of reactivity and mechanical properties of the final hardened material.

It is common to represent graphically in a ternary diagram different mineralogical phases that can adopt a calcium aluminate based on the relative proportion of each of three compounds C lime, alumina and silica A S in said calcium aluminate.

There is shown such a ternary diagram in Figure 1 showing some of the different mineralogical phases can coexist in a calcium aluminate, based on the proportion by mass of C lime, alumina and silica A S contained in said calcium aluminate.

On this diagram, we can read the mass fraction of lime C contained in calcium aluminate on the side of the triangle between the vertices A and C, the mass fraction indicating lime mass C contained in calcium aluminate by based on the total mass C of lime, alumina and silica A S contained in said calcium aluminate.

The mass fraction of lime C is found within the ternary diagram along a line parallel to the opposite side of the triangle at the top C.

Similarly, one can read the alumina mass fraction A contained in the calcium aluminate on the side of the triangle between vertices S and A, and this mass of alumina fraction A is found inside the ternary diagram all along the parallel line to the side of the triangle opposite the apex A.

Similarly, the silica mass fraction of S contained in the calcium aluminate on the side of the triangle between vertices C and S, and the mass fraction of silica S is found within the ternary diagram throughout the straight line parallel to the side of the triangle opposite the apex S.

In addition, this ternary diagram, appear particular points that represent pure mineralogical phases. In other words, if the composition of the crystalline part of the calcium aluminate exactly corresponds to the molar fraction of C lime, alumina and silica A S of this particular point, then said crystalline portion of the calcium aluminate comprises 100% of this particular crystallized mineralogical phase. This is the case for example at the point C2AS, or CA Point or the CA2 and CA6 points.

In practice, it is rare that calcium aluminate include a single phase pure, it includes more usually several phases coexist.

Here in calcium aluminate according to the invention, the majority crystallized mineralogical phases are:

- CA2 phase, called the first crystallized mineralogical phase,

- the C2AS phase, called second crystallized mineralogical phase. More particularly, remarkably, the mass fraction of all of said first and second mineralogical phases CA2, C2AS in said calcium aluminate is greater than or equal to 80%.

In other words, the aggregated mass of the first and second mineralogical phases CA2, C2AS represents at least 80% of the total weight of the calcium aluminate of calcium aluminate cement according to the invention.

Thus, unlike calcium aluminate described in the prior art, the majority mineralogical phase AC phase here, the majority or mineralogical phases are the first and second phases of mineralogical CA2, C2AS.

The remaining 20% ​​of the cement calcium aluminate of the invention, in weight based on the total weight of said calcium aluminate, may include minority mineralogical phases such that:

- the CA phase, called third crystallized mineralogical phase, and

- the CA6 phase, called fourth crystallized mineralogical phase. Indeed, as shown in the ternary diagram of Figures 1 and 2, these third and fourth AC mineralogical phases, CA6 lie in direct proximity of the first and second mineralogical phases CA2, C2AS, so that, during manufacture of cement calcium aluminate according to the invention, it is very likely to form the third and fourth AC mineralogical phases, CA6.

Preferably, the mass fraction of all of the third and fourth crystallized mineralogical phases CA, CA6 in said calcium aluminate of calcium aluminate cement according to the invention is less than or equal to 20%.

The remaining 20% of the calcium aluminate cement according to the invention may also include minor compounds constituting the calcium aluminate impurities according to the invention referred to above: iron oxide Fe 2 0 3 (F), titanium oxide Ti0 2 (T), sulfur oxide S0 3 ($), magnesium oxide MgO, or alkali compounds.

In particular, minority compounds may form mineralogical phases with at least one of the major constituents of the calcium aluminate such as alumina A, C and S. lime silica

In particular, the remaining 20% of calcium aluminate of calcium aluminate cement of the invention may comprise an additional mineralogical phase calcium sulphoaluminate C4A3 $ comprising four CaO calcium oxides to three aluminum oxide Al 2 0 3 and an oxide of sulfur S0 3 .

This additional mineralogical phase C4A3 $ having a crystal lattice comprising four lime molecules C for three alumina molecules A and a sulfur oxide molecule is also called $ Ye'elimite.

Calcium aluminate cement of the invention may thus comprise 0.5% to 15%, preferably from 0.5% to 12% of this additional mineralogical phase sulphoaluminate C4A3 $ calcium, by weight with respect to the total weight of said calcium aluminate.

Advantageously, the minority phase Ye'elimite has an effect on the reactivity of the cement composition. In particular, the proportion of minority phase Ye'elimite C4A3 $ increases in the cementitious composition, the higher the viscosity at room temperature, this cementitious composition increases. This effect is even more pronounced when the temperature surrounding the cement composition increases.

The minority phase Ye'elimite also has an effect on the reactivity of the cement composition at high temperature. Notably higher the proportion of minority phase C4A3 $ Ye'elimite increases in the cementitious composition,

over the setting time is lengthened at elevated temperature.

In the context of the manufacture of a cement suitable for application in drilling oil wells, the choice of a calcium aluminate composition comprising a non-zero proportion of minority phase Ye'elimite seems particularly advantageous. In particular, a proportion of between 3 and 5%, for example equal to 3%, 4% or 5% of the phase $ Ye'elimite C4A3 is appropriate.

These remaining 20% ​​also include the amorphous part of the calcium aluminate cement according to the invention, if one exists.

On the ternary diagram of Figures 1 and 2, there is a particular straight line D connecting the individual points representing the first and second mineralogical phases CA2, C2AS.

If the calcium aluminate cement according to the invention belongs to this particular line D, whereas it comprises from 100% of first mineralogical phase CA2 and 100% of second mineralogical phase C2AS.

In other words, if the calcium aluminate cement according to the invention belongs to this particular line D, the calcium aluminate is crystalline, and the mass fraction of all of said first and second mineralogical phases CA2, C2AS in aluminate calcium cement according to the invention is 100%.

Thus, to the mass fraction of all of said first and second mineralogical phases CA2, C2AS in said calcium aluminate is greater than or equal to 80%, the calcium aluminate to be located in an area Z near this particular line D .

This zone Z is represented graphically in Figures 1 and 2. The points V, w, x and y of the figures correspond to the following mineralogical composition:

- the point v includes 80% of first CA2 mineralogical phase and 20% of fourth mineralogical phase CA6,

- the point w comprises 80% of first mineralogical phase CA2 and

20% of third mineralogical phase CA,

- the point x comprises 80% of second C2AS mineralogical phase and 20% of CA third mineralogical phase, and

- the point y comprises 80% of first mineralogical phase C2AS and

20% of fourth mineralogical phase CA6.

Thus, the surface of the ternary diagram bounded by the contour line linking points [v - CA2 - w - x - C2AS - y - v] corresponds to the zone Z in which the sum of the first and second phases CA2, C2AS is greater than or equal to 80%.

In addition, it is possible to find the chemical composition of calcium aluminate knowing its position in the ternary diagram.

For example, the composition of the point Y on the ternary diagram of Figures 1 and 2 was 34.4% by lime C, 48.1% alumina A, and 17.5% in S. silica

Thus, according to the same principle, the chemical composition ranges in C lime, alumina and silica A S of any calcium aluminate belonging to the zone Z can also be determined graphically on the ternary diagram using Figure 2.

Of course, when minority compounds are present in the calcium aluminate, it is still possible to position this calcium aluminate in the ternary diagram by determining the relative proportions C lime, alumina and silica A S with respect to the total mass C lime, alumina and silica A S included in the calcium aluminate.

Moreover, surprisingly, the first and second phases of mineralogical CA2, C2AS of particular responsiveness when in the presence of water.

Indeed, these first and second mineralogical phases CA2, C2AS are very reactive with water at room temperature. In other words, they are adapted to react very slowly with water at room temperature.

here means a mineralogical phase reacts with water when hydrated by water, and it is possible to characterize this reactivity by a quantity called "degree of hydration" of the mineralogical phase.

The degree of hydration reflects the ability of a mineralogical phase to be hydrated by water, that is to say that the molecules constituting the crystal lattice of said mineralogical phase pass into solution in the water as ion, in other words it is to evaluate the ability of existing bonds between the molecules constituting the mineralogical phase to be broken by interaction with water.

However, as will be demonstrated in the examples, the first and

second mineralogical phases CA2, C2AS are adapted to react effectively with the water under the effect of a temperature rise.

In other words, the degree of hydration of these first and second mineralogical phases increases with temperature.

In particular, these first and second mineralogical phases CA2,

C2AS are adapted to react with the water much faster than at room temperature when the curing temperature is between 50 degrees Celsius (° C) and 300 ° C, preferably ente 80 ° C and 280 ° C.

Advantageously, it is further possible to adjust the relative amount of each of the first and second mineralogical phases CA2, C2AS included in the calcium aluminate cement according to the invention to adjust the reactivity of the calcium aluminate cement according to the invention at this temperature according to the degree of hydration of the first and second crystallized mineralogical phases CA2, C2AS at a given temperature.

Unlike the first and second mineralogical phases CA2,

C2AS, third CA mineralogical phase is known to be very reactive at ambient temperature when in the presence of water, so its mass fraction in the cement calcium aluminate according to the invention is maintained less than or equal 20% to maintain the characteristics of long workability of the cement of the invention.

The fourth mineralogical phase CA6 is, for its part, completely inert regardless of the temperature at which it is subject, ambient or elevated. Thus, it does not hydrate even during a rise in temperature.

However, when present in the calcium aluminate, it significantly contributes to the high cost for producing the calcium aluminate since it contains a lot of alumina which is the most expensive part of said calcium aluminate. Therefore its mass fraction in the cement calcium aluminate according to the invention is kept below or equal to 20%.

Thus, very advantageously, the cement according to the invention comprising few of these third and fourth phases CA, CA6 react slowly when mixed with water at room temperature, without the need to add retardant, and it is advantageous from an economic point of view.

For example, a calcium aluminate cement according to the invention of particular interest includes, by weight based on the total weight of said calcium aluminate:

- 50% to 60% of first crystallized mineralogical phase CA2;

- 26% to 32% of second crystallized mineralogical phase C2AS;

- 2.5% to 3.5% of third crystallized mineralogical phase AC; - 0.5% to 1 5% of a crystallized mineralogical phase fifth ferro-aluminate tetracalcium C4AF;

- 10% to 15% more crystallized mineralogical phases. Thus, this composition according to the invention has both a majority of the first and second crystallized mineralogical phases CA2, C2AS and a minority of crystallized mineralogical phases CA, CA6.

More specifically, an example of calcium aluminate cement according to the invention comprises exactly conceivable, by weight based on the total weight of said calcium aluminate:

- 55% of first crystallized mineralogical phase CA2;

- 29% of second crystallized mineralogical phase C2AS;

- 3% of third crystallized mineralogical phase AC;

- 1% of a crystallized mineralogical phase fifth ferro-aluminate tetracalcium C4AF;

- 12% more crystallized mineralogical phases. Additional crystallized mineralogical phases include eg phase Ye'elimite $ C4A3. This example calcium aluminate cement according to the invention comprises, for example, by weight based on the total weight of said calcium aluminate between 0.5 and 12% of this phase Ye'elimite C4A3 $.

More specifically, in the example given above, the calcium aluminate cement includes, for example 4% of this phase Ye'elimite, including within 12% more crystallized mineralogical phases.

In the diagram in Figure 2, we find this particular composition in I. It is very close to the particular line D and even seems to belong to that particular line D in Figure 2.

Moreover, to make cement calcium aluminate according to the invention, a co-ground operator, that is to say mixed and ground in a single operation, bauxite and limestone to obtain a powder comprising particles whose maximum diameter is less than or equal to 100 micrometers (μιτι).

The co-grinding operation can be carried out using a ball mill or other mill known to the skilled person.

The powder obtained at the end of this co-grinding operation is then granulated with water, that is to say, the fine powder particles are agglomerated with water to form granules of diameter greater than that of the powder.

These granules are then introduced into an alumina crucible which is itself introduced into an electric furnace. The electric furnace containing the crucible is heated to a temperature of 1400 ° C at a temperature ranpe 600 ° C per hour. When the oven reaches 1400 ° C, a 6 hour baking step is applied.

At the output of the electric furnace, the calcium aluminate granules are ground finely so as to form the powder forming calcium aluminate cement according to the invention.

Advantageously, the calcium aluminate cement powder according to the invention has a Blaine specific surface area measured according to the NF-EN-196-6 standard, between 2200 square centimeters per gram to 4500 square centimeters per gram.

Preferably, the Blaine specific surface of the calcium aluminate cement according to the invention is between 2900 and 3900 square centimeters per gram.

More Blaine specific surface area, the greater the powder constituent grains are fine.

In addition, preferably, the cement according to the invention having such a Blaine specific surface is adapted when mixed with water, to have an optimal contact surface with the water.

In addition, the cement according to the invention having the Blaine specific surface area is adapted to be mixed homogeneously with a large amount of water, that is to say, the cement is adapted to be dispersed in a large amount water equivalently at any point of the mixture.

In other words, even in the presence of a significant amount of water, the cement according to the invention does not bleeds.

Calcium aluminate cement of the invention may be mixed with water to form a cementitious composition.

More specifically, the cementitious composition of the invention may

comprise other compounds as calcium aluminate cement according to the invention, such as:

- SCMs selected from fly ash and / or granulated blast-furnace and / or silica flour and / or silica fume and / or metakaolin,

- the aggregates of more or less large diameters selected from quartz and / or fine limestone and / or sand, and

- additives of any kind known in the art, for example thinners or retarders.

These compounds possibly other lists included in the cementitious composition are not limiting.

Fly ash match the ash produced during combustion at high pressures and temperatures of pulverized coal.

One can add particular very fine pulverized fly ash called fly ash (called "pulverized Fuel Ash" in English) or fly ash larger dimensions (called "Furnace Bottom Ash" in English). The EN4750 commercial products "N" fly ash® Scotash of society, or class F ash® bottom of FlyAshDirect society are examples.

Table 1 below gives the main physical and chemical characteristics of the fly ash.

Table 1

The line LAW ie "Loss Ignition is" in English, or Fire loss in French, here includes volatile items.

The granulated blast furnace slag derived from the surface layer which is formed during melting of iron in blast furnaces, said surface layer being separated from the iron melt and then cooled in the form of granules to form said slag.

The Slag® commercial product from Ecocem company is one example. Table 2 below gives the main physicochemical characteristics of this slag.

Table 2

The fumed silica is a pozzolanic material comprising amorphous silica. It is typically a byproduct of the production of silicon alloys and / or ferrosilicon in electric arc furnaces. It can take different aspects: one can find notably in the form of very fine powder, granules or hard a few millimeters in diameter.

Commercial products U® 971 of the Elkem company and Dray Powder S® Norchem of society are examples.

Table 3 below provides the key physicochemical characteristics of the silica fume.

Table 3

Metakaolin is an anhydrous aluminum silicate and poorly crystalline produced by dehydroxylation of the kaolin at high temperatures.

The commercial product Metasial V800® of Soka (Société

Kaolinière Armoricaine) is an example.

Table 4 below provides the key physicochemical characteristics of this metakaolin.

Table 4

In practice, the cement composition may for example include:

- from 0% to 50% of SCMs, by weight based on the dry weight of the cementitious composition, and / or

- from 50% to 100% of calcium aluminate cement according to the invention, by weight based on the dry weight of the cementitious composition;

the dry weight of the cementitious composition corresponding to the total mass of all the compounds comprised in said composition except cementitious water.

Thus, the cementitious composition may for example comprise 0%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45% or 50% of SCMs, by weight relative to the dry weight of the cementitious composition, and / or 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 100% of cement of calcium aluminates according to the invention, by weight based on the dry weight of the cementitious composition.

Whatever the compounds included in the cementitious composition, calcium aluminate cement present reacts with water, that is to say, it occurs a chemical reaction, commonly called "hydration" between cement calcium aluminates and water, in which the molecules constituting the crystalline portions and / or amorphous cement according to the invention are hydrated by water, namely that they go into solution in the water under form ion.

Conventionally, due to this chemical reaction, the consistency of the cementitious composition formed by the mixture between water and cement according to the invention is likely to change over time.

Specifically, we can identify three phases of evolution of said cementitious composition, these three phases constituting the "global hardening" of the cementitious composition:

- a first phase, called thickening phase, during which the viscosity of the cementitious composition increases slowly, without preventing its implementation;

- a second phase, called phase plug or phase hydraulic jack, in which the cementitious composition hardens rapidly; and,

- a third phase, said final curing phase, during which the cement composition continues to harden more slowly.

The duration of the thickening phase can vary from cement to another since it depends a lot on the reactivity of the cement used.

The open time generally corresponds to the duration of the thickening phase. It is of the order of hours in general.

In practice, the duration of the thickening phase can vary several minutes to several hours depending on the envisaged application, cement and optionally added adjuvants.

In the case of an application in oil drilling wells, the thickening phase generally lasts a few hours.

The duration of the thickening stage also depends on external parameters such as pressure, temperature, and the relative proportion between water and cement.

During hydraulic setting phase, the cementitious composition rapidly changes from a liquid state to a solid state, these states are defined in the mechanical sense of the term, that the liquid state is a state in which the cementitious composition deforms irreversibly when subjected to deformation, while the solid state is a state in which the cementitious composition can deform elastically when subjected to deformation.

In practice, it is considered that the cement composition has reached its solid state when being tested Vicat ASTM C91 described later in the example section, the Vicat needle is unable to cross

fully the cementitious composition. On the contrary, it is considered that the cementitious composition is in its liquid state when subjected to the same test Vicat, the Vicat needle passes completely through the cementitious composition.

Thus, at the end of the hydraulic-setting phase, the cementitious composition a cured appearance is already present, so that it can be regarded as a final cured material. However, it continues to harden during the final curing stage.

In practice, here, the invention provides a use of calcium aluminate cement according to the invention, in which

a) a cementitious composition is produced by mixing said calcium aluminate cement with water,

b) establishes said cementitious composition,

c) said cementitious composition is heated to a temperature between 50 ° C and 300 ° C, preferably between 80 ° C and 28 ° C, so as to promote the taking of the cementitious composition.

In step a), a user form the cementitious composition by mixing the cement calcium aluminate with said other compounds optionally included in the cementitious composition, and with water.

Initially, that is to say when the water, cement, and optionally said other components are mixed, the consistency of the cementitious composition formed is more or less fluid as a function of the mass of water contained therein relative to the total weight of said cementitious composition.

The amount of water added to cement according to the invention and said optional other compounds depends primarily on the application for which it is intended cementitious composition.

For example, a user may choose to form a cementitious composition as a fairly fluid paste.

According to a particular use of calcium aluminate cement according to the invention, in step a), the user can form an aqueous suspension of cement.

Specifically, in the case where the cementitious composition is an aqueous suspension exclusively formed by water and the cement according to the invention, the mass fraction of water in said aqueous slurry is between 15% and 45%.

The mass fraction of water in this aqueous suspension, between 15% and 45%, equivalent to a water / cement ratio of between 20% and 70%, said ratio being the ratio of the water mass and the mass dry cement forming the aqueous suspension.

In the case where the cementitious composition is an aqueous suspension and comprises water, cement, calcium aluminate according to the invention and SCMs, the mass fraction of water in said aqueous slurry is between 20% and 60%, for example equal to 29%, 31%, 33%, 37%, 52%, or 55%.

The mass fraction of water in this aqueous suspension, between 20% and 60%, equivalent to a ratio water / dry compounds between 25% and 150%, said ratio being the ratio of the water mass and the mass dry cementitious composition comprising cement and SCMs. For example, the ratio water / dry compounds of the aqueous suspension is 41%, 48%, 60%, 80%, 1 10%, or 120%.

These general considerations are known to the skilled person and the amount of water to be added to cement and possible other compounds to obtain a cementitious composition having a consistency suitable for each type of application will not be detailed further below after.

In step b), as the cement composition is in the thickening stage, the user can set up the cementitious composition.

For example, if the cement composition is in the form of an aqueous suspension, the user can run the cementitious composition in a slot.

In particular, according to the particular use of calcium aluminate cement according to the invention as an aqueous suspension in step b) said aqueous slurry is injected into an oil well.

This injection is done by means of one or more pumps that drive the aqueous suspension in a tubular body to the wellbore bottom. Once reaching the bottom of the wellbore, this suspension may rise naturally to the surface, between the rock wall and the tubular body.

When the cementitious composition in the form of a paste, the user can put it into shape so as to prefabricate beam or slab-like objects.

In step c), the activating hydraulic setting phase of the cement composition is favored by a heating of the cementitious composition at a temperature between 50 ° C and 300 ° C, depréférence between 80 ° C and 280 ° C .

Specifically, this heating the cement composition may be voluntary or suffered.

Thus, in practice, depending on the particular use of the cementitious composition as an aqueous suspension for the oil well, the aqueous cement slurry is naturally heated between 50 ° C and 300 ° C by the surrounding rock, after remontéevers the surface.

For example, at a depth between 3000m and 5000m below the surface, the temperature is generally between 120 ° C and 180 ° C, and heating of the cementitious composition is then sustained.

Thus, advantageously, depending on the particular use of calcium aluminate cement according to the invention, the aqueous suspension has a satisfactory workability at room temperature, that is to say that its viscosity at room temperature is sufficiently low to permit its injection by means of pumps, and curing said aqueous suspension occurs after its injection into the well, when the surrounding temperature rises.

Advantageously, there is no need to add retarder to the aqueous suspension formed.

CLAIMS

1. Calcium aluminate cement comprising a calcium aluminate with a first crystallized mineralogical phase CA2 calcium dialuminate comprising a calcium oxide CaO for two aluminum oxide AI 2 O 3 and / or a second crystallized mineralogical phase silicate alumina dicalcium C2AS comprising two CaO calcium oxide to aluminum oxide AI 2 O 3 and a silicon dioxide SiO 2 ,

characterized in that the mass fraction of all of said first and second mineralogical phases in said calcium aluminate is greater than or equal to 80%.

2. Cement calcium aluminate according to claim 1, wherein said calcium aluminate also includes an amorphous portion, the mass fraction in said calcium aluminate is less than or equal to 20%.

3. Cement calcium aluminate according to one of claims 1 and 2, wherein said calcium aluminate further includes a third crystallized mineralogical phase AC monocalcium aluminate having a calcium oxide CaO for an aluminum oxide AI 2 O 3 and / or a fourth crystallized mineralogical phase hexa-aluminate of calcium CA6 comprising a calcium oxide CaO for six aluminum oxide AI 2 O 3 , the mass fraction of all of the third and fourth mineralogical phases in said calcium aluminate is less than or equal to 20%.

4. Cement calcium aluminate according to one of claims 1 to 3, wherein said calcium aluminate further includes an additional mineralogical phase calcium sulphoaluminate C4A3 $ comprising four calcium oxide CaO for three aluminum oxide AI 2 O 3 and a sulfur oxide SO 3 .

5. Cement calcium aluminate, according to one of claims 1 to 4 comprising, by weight based on the total weight of said calcium aluminate:

- 0% to 5% of an iron oxide Fe 2 O 3 ,

- 0% to 5% of a titanium oxide TiO 2 ,

- 0% to 5% of a sulfur oxide SO 3 ,

- 0% to 5% of magnesium oxide MgO,

- 0% to 2% of alkaline compounds.

6. Cement calcium aluminate according to one of claims 1 to 5, which is in the form of a powder having a Blaine specific surface area measured according to the NF-EN-196-6 standard between 2200 square centimeters per gram and 4500 square centimeters per gram, preferably between 2900 and 3900 square centimeters per gram.

7. Cement calcium aluminate according to one of claims 1 to 6, comprising, by weight based on the total weight of said calcium aluminate:

- 50% to 60% of first crystallized mineralogical phase CA2,

- 26% to 32% of second crystallized mineralogical phase C2AS,

- 2.5% to 3.5% of third crystallized mineralogical phase CA, - 0.5% to 1 5% of a crystallized mineralogical phase fifth ferro-aluminate tetracalcium C4AF,

- 10% to 15% more crystallized mineralogical phases.

8. Cement calcium aluminate according to one of claims 1 to 7, comprising 0.5% to 15% additional mineralogical phase calcium sulphoaluminate C4A3 $ weight relative to the total weight of said calcium aluminate.

9. A composition comprising at least cement cement calcium aluminate according to one of Claims 1 to 8 mixed with water and possibly cement additives such as fly ash and / or granulated blast-furnace and / or silica flour and / or silica fume and / or metakaolin, aggregates such as quartz and / or fine limestone and / or sand, and adjuvants.

10. Use of calcium aluminate cement according to one of claims 1 to 8, wherein:

a) a cementitious composition is produced by mixing at least said calcium aluminate cement with water,

b) establishes said cementitious composition,

c) said cementitious composition is heated to a temperature between 50 ° C and 300 ° C, preferably between 80 ° C and 28 ° C, so as to promote the taking of the cementitious composition.

January 1. Use of calcium aluminate cement as claimed in claim 10, wherein, in step a), the cementitious composition is in the form of an aqueous suspension, and that in step b), the cementitious composition is placed in an oil well.