FR2732009A1 - CEMENT COMPOSITION CONTAINING A DISPERSING AGENT AND ITS APPLICATION TO THE CEMENTATION OF OIL WELLS - Google Patents

Abstract

The invention relates to a cementing composition for oil, gas, water, geothermal or similar wells comprising as dispersing agent a salt of polyvinylsulfonic acid, from 0 to 20% of the monomer groups being replaced by acrylic monomers. or methacrylics. The invention is applied in particular to the cementing of wells the temperature of which does not exceed 85 ° C.

Description

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  The present invention relates to the technical field of cementing oil, gas, water, geothermal or similar wells. More specifically, the invention relates to

  cementing compositions for such wells.

  After drilling a well, casing is lowered into the hole and, in most cases, cement grout is injected into the annulus between the casing and the well's underground wall, both to consolidate the wells and isolate different areas in order to master

  the flow of fluids present at different levels of training.

  The cement grout is injected into the casing and pumped by the annular to make it go up

  In this one. Once the placement is complete, let the cement be taken.

  A cement slurry is a highly concentrated solution of solid particles. The aqueous base is generally constituted by sea water or brine and comprises in fact a whole series of ionic species to which are added various organic or mineral additives intended to modify properties such as setting time, losses. fluids due to filtration by certain types of formations crossed, the density of cement etc. These multiple species, to which we must of course add the cement itself, are subject to very many interactions of the electrostatic or Van der Waals type. As a result, the rheological behavior of the cement slurry is far removed from that of a Newtonian fluid. In particular, a flow threshold is frequently observed which

  displacement at low speed and creates sharp irregularities of flow.

  To overcome these difficulties, the composition of the cement slurry generally comprises a dispersing agent whose function is to modify the distribution of electrical charges on the surface of the cement particles and more generally the surface interactions between the particles. The most dispersants Commonly used in this industry are polyelectrolytes, i.e. water-soluble filled polymers, and especially polyanions having sulfonate groups attached to a backbone consisting of a polymer with a high degree of branching. These include polymelamine sulphonate (PMS), polynaphthalene sulphonate (SNP), melamine / formaldehyde condensation product with sulphonate group, polystyrene sulphonate or lignosulphonates. Another large class of ionic dispersants is polyacrylic acids of low molecular weight dispersants widely used in the building, but not used in cements

  oil tankers because of their very large retarding effect.

  Other non-ionic dispersants, such as low molecular weight polysaccharides, cellulose derivatives, polyvinyl alcohol and the like. are also known. Finally, there are also non-polymeric dispersing agents, such as citric acid. In general, the nonionic or non-polymeric dispersants are little used, at least as a dispersing agent, because of their very great retarding effect on the setting of the cement.

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  Polynaphthalene sulfonate (PNS) -based polymers have the main disadvantage of having a certain toxicity, which is particularly troublesome in the case of

  offshore drilling where it is more difficult to recover the waste from an operation.

  The present invention aims at a new cementing composition suitable for cementing oil, gas, water, geothermal or similar wells essentially consisting of an aqueous base and a Portland-type cement, comprising a new type of dispersing agent. not having the disadvantages of the products according to the art, particularly in

  toxicity, in particular likely to be discharged at sea.

  The cement compositions according to the invention comprise, as dispersing agent, a polyvinylsulphonic acid salt, from 0 to 20% of the monomer groups that can be replaced by acrylic or methacrylic monomers. This salt is usually supplied in solution

aqueous.

  The polymers according to the invention - whether unsubstituted homopolymer or copolymers with acrylic or methacrylic units - do not pose specific problems of toxicity and satisfy, in environmental matters, the most important criteria.

  currently in force in some countries.

  The cation is advantageously chosen from alkali metals, in particular sodium.

  The chains are preferably relatively short, with a molecular weight not exceeding

  preferably not 4000 and more preferably between 1500 and 3000.

  The dispersants according to the invention are advantageously soluble in water and can thus be used as a liquid additive, which simplifies their implementation, in particular from the point of view of dosages. Good results are obtained with aqueous solutions comprising% dry matter, for volume concentrations of between 9 and 13% of the volume of cement. On the other hand, they are compatible with most of the additives commonly used in the preparation of petroleum cements, such as cement accelerators or retarders, weighting agents,

  filtrate, anti-foam agents or other additives well known in the art.

  It has been verified that the polyvinylsulphonic acid salts have a retarding effect at temperatures of

  less than or equal to 185 F (85 C). Measurements were not made for

higher temperatures.

  It should be noted that the dispersants according to the invention differ from the dispersants commonly used in petroleum cement compositions, in particular by a linear, unbranched structure. The electostatic interactions between the sulfonate groups - and possibly the acid groups - of the polymer chains tend to stiffen the chains. Under these conditions, the adsorption, on the surface of the cement grains, of the polyanionic chains according to the invention is a priori not favored. The effectiveness of the polyvinylsulphonic acid salts as a dispersing agent in petroleum cement compositions is therefore most surprising. Advantageously, the dispersants according to the invention make it possible to reduce the amount of free water. This is all the more surprising since the dispersants according to the art are known to the contrary, to promote the phenomenon of formation of free water, so that additives of

  Suspended suspension is most often associated with dispersants.

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  Other details and advantageous features of the invention are apparent from the description

  Reference is made hereinafter with reference to the appended figures which represent: FIG. 1: curves representative of the rheology of cementation composition without

  or with a dispersant according to the invention.

  * Figure 2: representative curves of the rheology of cementing composition for

  different concentrations of the dispersant according to the invention.

  FIG. 3: a curve showing the evolution of the plastic viscosity as a function of the

dispersant concentration.

  FIG. 4: a curve showing the evolution of the shear threshold as a function of the

dispersant concentration.

  FIG. 5: a curve illustrating the influence of the dispersant concentration on the volume

of free water in the composition.

  * Figure 6: curves illustrating the influence of temperature on the rheology of

  cementing composition for different dispersant concentrations.

  * Figure 7: representative curves of the rheology of cementing composition with

  different dispersants according to the invention.

  For all tests, a cement base was prepared by mixing with water a Cemoil Class G Portland cement. A density of 1.89 g / cm 3 (15.8 PPg) was obtained. The rheological measurements were carried out, after 20 minutes of conditioning at the measuring temperature, with a rotary viscometer comprising a rotating outer cylinder, of Chan model conforming to the API standards, Section 10, Appendix H. The units and symbols used are the following: following (the units in square brackets correspond to the

  units recommended by the API (American Petroleum Institute).

  Concentration volume [gps = US gallons per sack] PV: plastic viscosity (mPa.s) [cP] Ty: shear threshold (Pa) [lb / 100sqft] Frost resistance (kg / 100 m2) [lb / 100sqft]

Example 1

  A polyvinylsulphonic acid sodium salt of the formula - (CH 2 -H) n SO 3 was added to the base.

  in aqueous solution, with a solids concentration of about 35%.

  This salt is marketed by the company Rhone Poulenc, France, under the name

  Bevaloid XB16 / 20. The manufacturer indicates a molecular weight between 3500 and 4000.

  The rheological tests were performed at 100 F (37.78 C). The results are as follows:

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  Test n% by volume Viscosity Resistance Threshold of plastic dispersant gel shear after 10 seconds

1 0 39.5 2384 [49.8] 87.8 [18]

  2 5.57 [0.2] 24.3 531 [11.1] 63.4 [13]

  3 13.93 [0.5] 18.5 101 [2.1] 63.4 [13]

  The percentages of dispersant correspond to the solution concentrated to 35%. A concentration of 5.57% therefore corresponds in fact to a volume of "active ingredient" of about 1.95%. The corresponding rheological curves are shown in FIG. 1, where the torque to be exerted (as a function of the deflection of the apparatus) is represented according to the speed

  communicated to the bowl (in turns per minute).

Example 2

  Example 1 was repeated for different dispersant concentrations (in 35% solution).

  Figure 2 shows the rheological curves then obtained. There is a marked improvement in the rheology when the concentration goes from 0.2 gps (5.57% by volume, a concentration of 0.27% based on the weight of cement) to 0.25 gps (6.96% in volume) then 0.35 gps (9.75% by volume). On the other hand, the rheology of the grout is not appreciably

  improved when the concentration is as large as 0.5 gps (13.93% by volume).

  For the 85 C tests, a lignosulphate-refined cement setting retarder was

  added at a rate of 0.3% based on the weight of the cement.

  FIG. 3 shows the curves giving the evolution of the plastic viscosity (in centipoises) according to the concentration of dispersant (in solution), and for temperatures equal to 100 F (37, 78 C) triangles or 185 F (85 C). Figure 4 gives the thresholds of

  shear for these same compositions.

  The dispersant according to the invention is perfectly compatible with usual additives and does not entail restrictions as to the choice of the other additives included in the formulation of the

cement grout.

  There is a slight decrease in the plastic viscosity, however, the shear threshold decreases very significantly - and in a virtually linear manner - for concentrations between 0 and about 0.35 gps. For even higher concentrations, the shear threshold is little modified, and for the test at 85 C, even tends to

  rise slightly for concentrations of 0.5 gps.

  These different curves indicate that a concentration of a dispersant solution of about 0.35 gps (9.75% by volume or about 0.5% by weight of cement3.41%) constitutes the

  better compromise and is therefore preferred according to the invention.

  A side effect often observed with dispersants according to art is a tendency to

  promote the formation of density gradients from the top to the base of a column of cement.

  Depending on the case, these gradients result in sedimentation phenomena more or less pronounced, with the extreme true segregation according to the density of the particles of the composition or by the formation of a so-called layer of free water that floats on Mountain peak

of the column.

  In a manner very surpémrnante and unique to the knowledge of the inventors, and as shown in Figure 5, far from promoting this phenomenon, the dispersant according to the invention actually contributes to reducing the amount of free water. The curve shown in Figure 5 indicates the volume of water

  (in milliliters) observed on a column of cement of 250 ml depending on the concentration

  dispersing. The test is carried out according to the API Spec 10 procedure (Section 6,

  dice M), at a temperature of 85 C. The dispersant according to the invention can advantageously be used alone, without the need to add an agent a suspending agent such as bentonite, polysaccharides compatible with the cement as the wallanes or

  metal salts including magnesium salts.

  On the other hand, it can be noted that the retarding effect on the setting of cement, observed with all the dispersants, is of the same order of magnitude as that obtained with the polymers of the type

PNS or PMS commonly used.

Example 3

  The formulation of Example 1 was repeated, again adding a retarding

  lignosulphate-type cement, at a concentration of 0.3%, based on the weight of

  is lying. The rheology curves in Figure 6 illustrate the influence of temperature and dispersant concentration (in solution). It is noted that the curves at 100 F (37.781 C) and F (62.78 C) are practically merged, which is an important advantage in that the temperature at the bottom of the well is not always known very accurately and o, moreover, even when the well is not considered particularly deep, and therefore particularly hot, there is always a fairly large temperature difference between the surface and the bottom of the well and it is always easier to proceed with the cementing operation of the well with a grout whose rheological properties remain

  constant throughout the cement movement cycle.

  At 185 ° F (85 ° C.), the dispersant according to the invention no longer makes it possible to preserve this same rheology, but it remains very effective when compared with the reference composition without dispersant. For this test, the dispersant concentration was varied between 0.35 gps (0.47% based on cement weight) and 0.8 gps (1.06% based on cement weight). It is noted once again that the gain obtained by increasing the concentration of dispersant is, for this concentration range, relatively low, with even a reversal of the results for the high stresses. In fact, at this temperature, the best results are obtained for a concentration of dispersant solution equal to 0.45 gps (0.60% relative to the weight of cement).

Example 4

  As indicated above, from 0 to 20% of the vinylsulfonic monomers may be substituted

  killed by acrylic or methacrylic monomers.

  The test was thus resumed by comparing the rheologies obtained with the unsubstituted polymer A used for the preceding examples and copolymers B and C respectively comprising or 20% of acrylic monomers. These products are marketed by the company Rhone Poulenc, France, under the name Bevaloid XB16 / 31D and Bevaloid XB1631C. Their

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  molecular weight is between 1500 and 2000. As before, they present themselves

  in the form of an aqueous solution concentrated to 35%; all the concentrations listed below

  after corresponding to the concentration in solution and not in active material.

  The corresponding curves correspond to FIG. 7. The dispersing effect of these copolymers

  is verified even if, at identical concentration, the homopolymer has substantially better performances.

  It has thus been verified that the dispersant according to the invention can be substituted for the dispersants known in the art, because of both a good effectiveness as dispersing agent, a retarding effect comparable to that of the products of art and a reducing effect on the formation of free water. On the other hand, it should be emphasized that the product according to the invention does not exhibit any particular toxicity and satisfies the most stringent environmental standards.

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Claims (8)

claims   1. Cementation composition of oil, gas, water, geothermal or similar wells   comprising an aqueous base, a Portland cement, a dispersant and optionally   other additives, characterized in that the dispersant is a polyvinyl   sulphonic acid, from 0 to 20% of the monomer groups being replaced by monomers ac- rylic or methacrylic.   2. Composition according to claim 1, characterized in that the salt is a sodium salt.   3. Composition according to one of the preceding claims, characterized in that the   The polymer has a molecular weight of 1500 to 4000.   4. Composition according to one of the preceding claims, characterized in that it comprises   additionally carries at least one additive of accelerator or set retarder type of cement, weighting agent, filtrate control agent, antifoam agent, etc.   5. Composition according to one of the preceding claims, characterized in that the   polymer is used in aqueous solution, concentrated to 35% dry matter.   6. Composition according to claim 5, characterized in that the dispersant solution is   added to a volume concentration of between 9 and 13% of the volume of cement.   7. Application of the composition according to one of the preceding claims to the   cementing in wells whose temperature does not exceed 85 C.   8. Application according to claim 6 to the control of free water during cementation in oil wells.