DK172395B1 - Liquid loss reducing additives for borehole cementing materials - Google Patents

Description

DK 172395 B1

The present invention relates to cement slurry additives useful for preventing water loss from cement slurries. Another aspect of the invention relates to a method of preventing water loss from cement slurries. Another aspect of the invention relates to cement slurries having improved water loss properties. An external aspect of the invention relates to an improved method for cementing oil and gas wells.

Cement preparations are used in the oil and gas industry to cement the annular gap in the borehole between the surrounding formation and the pipe or casing. Typically, the cement slurry is pumped down the liner and back and upward outside the liner through the annular space. The amount of water used in the formation of the cement slurry will vary depending on the type of hydraulic cement selected and the working conditions available. The amount of water used can vary widely, depending on such factors as the required consistency of the slurry and the strength requirements of the present 20 cases.

In many cases, the hydraulic cement must be placed in or up to a porous medium, e.g. soil layer in the borehole. When this is the case, the water tends to filter out of the slurry and into the layers during the solidification of the cement. Many difficulties are associated with an uncontrolled fluid loss of this type, such as an uncontrolled curing rate, incorrect slurry placement, deteriorating strength properties and contamination of the surrounding layers. These conditions are all undesirable in oil and gas wellbore cementing processes.

Various materials have so far been used to reduce the loss of liquid from the aqueous cement slurry. Unfortunately, these materials often have adverse effects on the cement itself.

For example, U.S. Patent No. 4,015,991 discloses the use of a copolymer of acrylamide and 2-acrylamido-2-methylpropanesulfonic acid as a liquid loss additive for cement slurries. Although this copolymer will reduce the fluid loss from cement slurries, it also has the undesirable effect of decreasing the compressive strength of the cement and decreasing the rate at which the cement forms a solid body.

A further problem with the currently available liquid loss additives is their inefficiency at a temperature in the range of 149-232 ° C. Eg. For example, the copolymer described in U.S. Patent No. 4,015,991 is ineffective at a temperature above 121 ° C.

It would therefore be a valuable technical advance to develop additives that can reduce the water loss from cement slurries without having adverse effects on the compressive strength of the cement or on the rate at which the cement solidifies.

It would also be a valuable technical advance to develop additives that will reduce the water loss from cement slurries at elevated temperatures.

It is an object of the present invention to provide additives which will reduce the water loss from cement slurries without decreasing the compressive strength of the cement or decreasing the rate at which the cement solidifies.

It is a further object of the present invention to provide additives which will prevent the loss of water 25 from cement slurries at elevated temperatures. It is a further object of the present invention to provide a method of reducing the water loss from cement slurries without decreasing the compressive strength of the cement or reducing the rate at which the cement solidifies.

It is a further object of the invention to provide a method for reducing the water loss from cement slurries at elevated temperature. It is also an object of the present invention to provide cement materials having improved water loss properties at elevated temperatures. It is another object of the present invention to provide an improved method for cementing oil and gas boreholes.

It has been found in accordance with the present invention that an additive comprising (A) a tetrapolymer, (B) an electrolyte, (C) a base, (D) at least one surfactant 5, and (E) water will reduce the water loss from cement slurries without reducing the compressive strength of the cement or decreasing the rate at which the cement solidifies. It has also been found that this additive will control the water loss from cement slurries at elevated temperatures.

As used herein, the term "tetrapolymer" refers to a water-soluble polymer composed of a) 1-60% by weight N-vinyl-2-pyrrolidone, b) 1-60% by weight of at least one monomer selected from acrylic amide and methacrylamide, c) 10-90% by weight of at least one 15 monomer selected from 2-acrylamido-2-methylpropanesulfonic acid and sodium 2-acrylamido-2-methylpropanesulfonate and d) 1-60% by weight of at least one monomer selected from acrylic acid or sodium acrylate.

The tetrapolymers of the present invention 20 and their preparation are well known to those skilled in the art. Thus, they can be prepared by polymerization according to any of the well-known free radical methods in solution, suspension or emulsion, cf. U.S. Patent No. 3,547,899 or EP Patent Application No. 115,836. In addition, such other polymerization methods which will be apparent to one of ordinary skill in the art can be used, and the present invention is not limited to any particular process for preparing the subject tetrapolymers.

The molecular weight of the present tetrapolymers can be varied within a wide range. The molecular weight can be as low as 30,000 or as high as 1,000,000 or more, of course, provided that the properties of the aqueous slurry of hydraulic cement to which the tetrapolymer is added are not adversely affected thereby.

The currently preferred tetrapolymer contains 30-40% by weight of N-vinyl-2-pyrrolidone, 5-15% by weight of acrylamide, 50-60% by weight of sodium 2-acrylamido-2-methylpropanesulfonate and 1-10% by weight of acrylic acid. .

Suitable electrolytes (B) for use in the invention may be selected from sodium, potassium, lithium or ammonium chloride, bromide, iodide, nitrate or fluoride. Currently, the preferred electrolyte is potassium chloride.

Suitable bases (C) for use in the invention include those selected from potassium hydroxide, sodium hydroxide or ammonium hydroxide. The currently preferred base is 10 potassium hydroxide.

Suitable surfactants (D) for use in the invention may be selected from the following: 1) carboxylates of formula 15 RCOO + M + wherein R is selected from alkyl groups of 9-21 carbon atoms and M is selected from sodium, potassium and lithium, 2) polyalkoxy carboxylates of the formula

II

R- [OCH2CH2] nCH2C-O “M + 25 wherein R is selected from alkyl and alkylaryl groups of 10-21 carbon atoms, M is selected from sodium, lithium and potassium and n is an integer from 5 to 21, 3) sulfonates of formula 30 R SO3 "M + wherein R is selected from alkyl groups of 10-20 carbon atoms and M is selected from sodium, potassium and lithium; 4) alkylbenzenesulfonates of formula 35 RC6H4SO3" M + DK 172395 B1 wherein R is selected from alkyl groups having 5-20 lignin sulfonates, 6) Naphthalene sulfonates of formula 5 RC10H6SO3 "M + wherein R is selected from alkyl groups of 3-10 carbon atoms and M is selected from sodium, lithium, calcium and potassium; 7) naphthalene sulfonates condensed with aldehyde form; 8) α-olefin sulfonates of formula RC = CHSO 3 "M + 15 wherein R is selected from alkyl groups of 10-20 carbon atoms and M is selected from potassium, sodium and lithium, 9) polyethylene glycol monomethyl ethers of the formula 20 HO- (CH 2 CH 2 O) x ch ri x is can be from approx. 20 to approx. 225,000, 10) polyethylene glycols of the formula

H0 (CH2CH2O) x H

wherein x may be from ca. 20 to approx. 225,000, 11) alcohol ethoxylates of the formula

R [OCH 2 CH 2] n OH

wherein R is selected from alkyl groups of 6-20 carbon atoms and n is an integer from 2 to 100, 12) alkylphenyl ethoxylates of formula 35

RC6H4 (OC2H4) n OH

Wherein R is selected from alkyl groups of 8-15 carbon atoms and n is an integer from 2 to 70 and 13) petroleum sulfonates.

All of these surfactants and their preparation are well known to those skilled in the art. They are available from several commercial suppliers.

It is presently preferred that the water-loss-reducing cement slurry additive contains two surfactants.

One of the preferred surfactants is polyethylene glycol monomethyl ether. The surfactant will have a molecular weight in the range of approx. 200 to approx. 8000, preferably 200 to 1000. Currently, "Dow Froth 1012" having a molecular weight of approx. 385 the most preferred.

The other preferred surfactant is a naphthalenesulfonate-formaldehyde condensate. Such compounds are also known as sulfonated condensation products of formaldehyde and naphthalene or metal salts of condensation products of naphthalene sulfonic acid with formaldehyde.

Condensed naphthalene sulfonate formaldehyde condensates suitable for use in the present invention are negotiated by a number of companies under various names, and the preparation of some of these is e.g. disclosed in U.S. Patent No. 3,537,869 or 4,814,887.

Examples of commercially available naphthalenesulfonate formaldehyde condensates are "Lomar D", "CFR-2", "Tamol", "SM", "TIC", and "Doxad". Currently, "Lomar D" is the preferred naphthalene sulfonate-formaldehyde condensate.

Currently, it is also preferred that the water-loss-reducing additive (F) contains a preservative. The nature of the preservative is not critical to the practice of the invention, and any commercially available preservative is suitable for use in the invention. Currently, the preferred preservative is a para-formaldehyde.

The components of the water loss reducing additive are present in the following quantities:

Wide range Preferred range (% by weight) (% by weight) 5 A Tetrapolymer 0.1-70 1.5-10 B Electrolyte 0.1-37.2 2-10 10 C Base 0.1-3 0.2-2 D Surfactant 0.1-40 5-15 15 E Water 29 - 95 70 - 80 F Preservative 0.001 - 5 0.008 - 0.05 20 (optional) The liquid additive of the present invention is suitable for use with any hydraulic cement. The term "hydraulic cement" shall include any organic cement which cures under water. Hydraulic cement types include e.g. portland cement, aluminum and puzzolan cement and the like. The term hydraulic cement shall also include cement types containing minor amounts of extender agents such as bentonite and gilsonite, and shall also include cement varieties used either without a substantial amount of sand or aggregate material, or such cement mixtures mixed with granular filler material. such as sand, ground limestone and the like, e.g. any of the Class A-J cement types listed in API Spec. 10, section 35 2, 1st ed., January, 1982, suitable for this purpose. Strength enhancing agents such as silica powder can also be used.

The dry hydraulic cement component and the fluid loss additive of the present invention are mixed with 40 water to form a pumpable, solidified cement slurry. The cement solidifies to a monolithic solid. The water used to form the cement slurry may be any naturally occurring form of water suitable for the preparation of cement slurries. Seawater can be used, which is convenient for offshore operations. It is a particular advantage of the liquid loss additive according to the invention that it is effective in reducing the liquid loss from cement slurries, even when using salt water to prepare the slurry. This is another significant advantage of the invention over many other known cement additives.

The amount of water used to prepare the hydraulic cement slurry is not critical, and generally the amount of water needed to form a hardenable cement mix having the desired properties will be an amount of from 25 to approx. 150% by weight, calculated on the weight of the dry hydraulic cement. As mentioned above, the amount of water should only be one sufficient to provide a pumpable slurry. The use of the water loss additive according to the invention makes it unnecessary to add an excess of water in anticipation of significant water losses.

In general, the amount of liquid loss additive used will range from 0.76 to 9.5 liters of additive per liter. 42.6 kg of cement used to prepare the cement slurry.

The liquid loss additive of the invention is suitable for use in cement slurries subjected to temperatures in the range of 27-232 ° C.

In the method of cementing a borehole with the present additive, a hydraulic cement, water and the fluid loss additive of the invention are mixed together to form a pumpable slurry. The cement slurry thus prepared is then pumped to the desired location in the borehole and allowed to harden to a solid mass.

The invention is illustrated by the following examples which are not to be construed as limiting.

35 DK 172395 B1 9

Example 1

The purpose of this example is to demonstrate the composition and method of preparing the preferred liquid loss additive of the invention.

The composition of the preferred fluid loss additive system of the invention is set out below.

Table I

10 Material Quantity (aram)

Water 78

Potassium chloride 2

Potassium hydroxide 1

Paraformaldehyde 0.02 Sodium Naphthalene Formaldehyde Condensate 9.8

Polyethylene glycol monomethyl ether 2) 4

Tetrapolymer3) 5 1) "Lomar D", Diamond Shamrock 20 2) "Dow Froth 1012", Dow 3) a copolymer of sodium 2-acrylamido-2-methylpropanesulfonate, N-vinyl-2-pyrrolidone, acrylamide and acrylic acid containing 55% by weight sodium 2-acrylamido-2-methylpropanesulfonate, 35% by weight N-vinyl-2-pyrrolidone, 10% by weight acrylamide and 5% by weight acrylic acid commercially available as "HE" polymer from Phillips Petroleum Company.

A preferred method of preparing this liquid loss additive is to mix the ingredients in the order listed with stirring.

Example 2

A variety of cement slurry materials of the invention having the compositions listed in Table II below are prepared by mixing the additive system of Example 1 with water and a Class H cement.

DK 172395 B1

Table II

10

Water loss i

Material Menade liter / bag of cement

Cement A

Class H cement 829.85 g 1.14 liter

Water 313.5 ml

Water loss additive 22.2 ml

Cement B

Class H cement 829.85 g 1.55 liters

Water 305.5 ml

Water Loss Additive 30.3 ml

Cement C

Class H cement 829.85 g 2.27 liters

Water 285.5 ml

Water Loss Additive 50.2 ml

Cement D

Class H cement 829.85 g 2.57 liters

Water 285.5 ml

Water Loss Additive 50.1 ml

Cement E

Class H cement 829.85 g 2.84 liters

Water 280.42 ml

Water Loss Additive 55.2 ml 30 Cement F (control)

Class H cement 829.85 g 0

Water 335.7 ml

Cement G (control) Class H cement 850.96 g 0

Water 328.9 ml

Cement H

Class H cement 645.92 g 1.55 liter 40 Sand 226.1 g

Water 284.35 ml

Water Loss Additive 23.51 ml

Cement I

45 Class H cement 645.92 g 2.27 liters

Sand 226.1 g

Water 273.46 ml

Water Loss Additive 34.4 ml

50 Cement J

Class H cement 645.92 g 2.84 liters

Sand 226.1 g

Water 264.86 ml

Water Loss Additive 43.0 ml DK 172395 B1 11

Cement K

Class H cement 829.05 g 3.01 liter

Water 275.8 ml

Water Loss Additive 58.9 ml 5

Cement L

Class H cement 829.85 g 3.79 liters

Water 261.1 ml

Water Loss Additive 73.7 ml 10

A Class H cement is defined in API Spec. 10, Section 2.2, 1st Edition, January 1982. The cement used is commercially available from General Portland under the name "TRINITY LAFARGE H".

15

Example 3

To demonstrate that the water loss additive of the present invention will reduce the water loss from cement slurries over a wide range of temperatures, the water loss properties of cement slurry materials prepared in Example 2 according to API Spec are determined. 10, Appendix F, 1st ed., January 1982.

The following results are obtained.

25 30 35

Table III

DK 172395 B1 12

Concentration of Additive Temp. Liquid loss 5 Cement (liter / 42.6 kg cement) ° C cm3 / 30 min.

B 1.55 27 66 B 1.55 38 76 10 D 2.57 38 40 F (control) 0 38 +1298 B 1.55 52 74 D 2.57 52 46 F (control) 0 52 +1298 15 B 1 , 55 77 80 D 2.57 77 46 F (control) 0 77 +1500 H 1.55 77 78 I 2.27 77 48 20 H 1.55 93 118 I 2.27 93 131 I 2.27 110 138 I 2.27 121 40 J 2.84 149 54 25

The water loss properties of cement slurries prepared without the additive of the invention (cement F) are determined at temperatures of 38 to 77 ° C. These cement slurries lose between 1298 and 1500 cm3 of liquid during the 30-minute test period.

The water loss properties of cement slurries made with the additive of the invention are determined at temperatures of 27 to 149 ° C. These cement slurries lose only 40 to 138 cc of liquid during the 30-minute test period.

Thus, these results show that the additive of the invention provides cement with superior water loss properties over a wide range of therapeutic range.

Example 4 40 To demonstrate that the liquid loss additive of the invention does not decrease the compressive strength of the resulting cement material, a series of cement materials made in Example 2 according to API Spec. 10, Section 7, Compressive Strength Tests, 1st ed., January 1982.

DK 172395 B1 13

The following results are obtained.

Table IV

5 Concentration 24-hour compressive strength (kg / cm2) of additive at atmospheric pressure at 210.9 kq / cm2

Cement (liter / 42.6 kg of cement) 27 ° C 52 ° C 66 ° C 77 ° C

10 - ---- - F (control) 0 104.3 247.3 326.6 337.4 A 1.14 104.3 261.9 330.2 331.4 B 1.55 106.0 256.1 329.7 352.4 C 2.57 109.0 265.4 411.1 435.3 15

Cement F is manufactured without liquid loss additive according to the invention. It exhibits a compressive strength of 104.3 kg / cm 2 at 27 ° C during a 24 hour compressive strength test.

Cements A, B and C are made with the liquid additive of the invention. They exhibit compressive strengths of 104.3 to 109.0 kg / cm 2. Thus, additivity according to the present invention does not reduce the compressive strength of the cements.

A similar trend is observed in the tests conducted at 52, 66 and 77 ° C.

25

Example 5

To demonstrate that the additive of the present invention will reduce the loss of liquid from cement slurries prepared with saline, 30 cement slurries B ', D', L 'and M' are prepared, as are the cement B, D, L and M of Example 2. except that different concentrations of saline are used to prepare the cement slurry. In comparison, a cement slurry F is prepared as in Example 2.

The liquid loss properties of these cement slurries are determined according to API Spec. 10, Appendix F, 1st ed., January 1982.

The following results are obtained.

DK 172395 B1 14

Table V

Concentration of Additive NaCl Temp. Liquid loss 5 Cement (liter / 42.6 kg cement) wt% ° C cm3 / 30 min.

F (control) 0 0.0 38 +1298 B * 1.55 3.0 27 123 10 B '1.55 10.0 27 134 B' 1.55 18.0 27 180 B '1.55 37.2 27 68 D '2.57 3 38 50 D' 2.57 3 52 48 15 D '2.57 3 66 50 D' 2.57 3 79 53 D '2.57 10 38 49 D' 2.57 10 52 46 D 2.57 10 66 63 20 D 2.57 10 79 66 L 3.03 3 38 43 L · 3.03 3 52 45 L * 3.03 3 66 48 L · 3.03 3 79 42 25 L '3.03 10 38 49 L · · 3.03 10 52 52 L ·' 3.03 10 66 54 L '3.03 10 79 56 M' 3.79 18 93 94 30 M '3.79 37.2 28 104 M '3.79 37.2 52 110 M * 3.79 37.2 66 122 M' 3.79 37.2 79 130 M '3.79 37.2 93 146 35

Cement F prepared without the additive of the invention exhibits a fluid loss of over 1298 cm 3 over the 30 minute test period. The cement slurries made with the liquid loss additive according to the invention lose only 40 from 43 to 180 cm 3 during the 30 minute test period. Thus, the liquid loss additive of the invention will reduce the water loss from cement slurries prepared with saline.

45 DK 172395 B1 15

Example 6

To demonstrate that the liquid loss additive of the invention does not decrease the rate at which the cement solidifies, cement materials are prepared as in Example 2, and the rate at which the cement thickens is determined according to API Spec. 10, Section 8, 1st ed., January 1982.

The following results are obtained.

Table VI

10

Concentration Thickening time1) of additive Temp. API (hours)

Cement (liter / 42.6 kg cement) (° C) scheme 70 Bc 100 Bc 15 F 0 27 lg3 4:45 4:57 B 1.55 27 lg3 4:11 4:25 C 2.57 27 lg3 5 : 08 5:19 20 F 0 38 3g4 2:49 3:14 B 1.55 38 3g4 2:54 3:28 C 2.57 38 3g4 3:02 3:30 F 0 52 5g3 1:36 1:46 25 B 1.55 52 5g3 1:43 1:47 C 2.57 52 5g3 1:52 2:00 1) Variations of 30 minutes or less of thickening time are considered to be within the normal 30 experimental uncertainty.

Cement F, which does not contain the liquid loss additive of the invention, is thickened at 4 hours and 45 minutes by testing at 27 ° C.

Cements B and C containing the additive according to the invention are thickened at 4 hours and 11 minutes at 5 hours and 8 minutes respectively.

Although it appears immediately that the additive of the invention decreases the rate at which cement 40C solidifies, this is not the case.

Due to the large test uncertainty inherent in the test procedures, cements thickened before 30 minutes relative to each other are considered to have the same thickening rates. Therefore, the additive of the invention does not slow down the rate at which cement slurries solidify.

Claims (10)

Liquid loss additive for cement slurries, characterized in that it comprises: a) 29-95.0% by weight of water, 5 b) 0.1-70% by weight of a tetrapolymer, wherein the tetrapolymer is composed of i) 1-60% by weight of N-vinyl 2-pyrrolidone, ii) 1-60% by weight of at least one monomer selected from acrylic amide and methacrylamide, iii) 10-90% by weight of at least one monomer selected from sodium 2-acrylamido-2-methylpropanesulfonate and 2-acrylamido. 2) methylpropane sulfonic acid and iv) 1-60% by weight of at least one monomer selected from acrylic acid and sodium acrylate, c) 0.1-37.2% by weight of an electrolyte, d) 0.1-3% by weight of a base, and e) 0.1-40% by weight of at least one surfactant. Liquid loss additive according to claim 1, characterized in that the a) electrolyte is selected from sodium, potassium or ammonium chloride, bromide, iodide, fluoride or nitrate, b) the base is selected from potassium hydroxide, sodium hydroxide or ammonium hydroxide; c) the surfactant is selected from 25 i) carboxylates of formula RCOO "M + wherein R is selected from alkyl groups of 9-21 carbon atoms 30 and M is selected from sodium, potassium and lithium, ii) polyalkoxy carboxylates of formula O II R- [ Wherein CH is selected from alkyl and alkylaryl groups of 10-21 carbon atoms, M is selected from sodium, lithium and potassium, and n is integers from 5 to 21, sulfonates of the formula RS03 "M + 5 wherein R is selected from alkyl groups of 10-20 carbon atoms and M is selected from sodium, potassium and lithium; d) alkylbenzenesulfonates of formula RC6H4SO3" M + 10 wherein R is selected from alkyl groups of 10-20 carbon atoms and M is selected from sodium, l f) naphthalenesulfonates of formula 15 RC10H6SO3 M + wherein R is selected from alkyl groups of 3-10 carbon atoms and M is selected from sodium, lithium, calcium or potassium, 20 g) naphthalenesulfonates condensed with formaldehyde, h) α-olefin sulfonates of formula RC = CHSO 3 "M + 25 wherein R is selected from alkyl groups of 10-20 carbon atoms and M is selected from potassium, sodium or lithium, i) polyethylene glycol monomethyl ethers of formula HO- (CH 2 CH 2 0) xCH3 30 wherein x may be from ca. 20 to approx. 225,000, j) polyethylene glycols of the formula H0 (CH2CH2-0) xH wherein x may be from ca. 20 to approx. 225,000, 35 k) alcohol ethoxylates of formula R [OCH 2 CH 2] n-OH 5 wherein R is selected from alkyl groups of 6-20 carbon atoms and n is an integer from 2 to 100, l) alkylphenylethoxylates of formula RC6H4 (OC2H2 ) n -OH 10 wherein R is selected from alkyl groups of 8-15 carbon atoms and n is an integer from 2 to 70 and m) petroleum sulfonates. Liquid loss additive according to claim 1, wherein the g-15 further comprises from 0.001 to 5% by weight of a preservative. Liquid loss additive according to claim 3, characterized in that the preservative is paraformaldehyde. Liquid loss additive according to claim 3, wherein the a) tetrapolymer is present in an amount of 1.5-10% by weight and contains 30-40% by weight N-vinyl-2-pyrrolidone, 50-60% by weight sodium 2-acrylamido-2-methylpropane sulfonate, 1-10% by weight acrylic acid and 5-15% by weight acrylamide, b) the electrolyte is present in an amount of 2-10% by weight, c) the base is present in a d) the surfactant is present in an amount of 5 to 15 wt%, e) the preservative is present in an amount of 0.008-0.05 wt%, and f) the water is present in an amount of 70-80% by weight. Liquid loss additive according to claim 3, wherein the a) tetrapolymer contains 35% by weight of N-vinyl-2-pyrrolidone, 55% by weight of sodium 2-acrylamido-2-methylpropane sulfonate, 5 (b) the electrolyte is potassium chloride; (c) the base is potassium hydroxide; (d) the surfactants are sodium naphthalene-formaldehyde condensate and polyethylene glycol monomethyl ethers; and (e) the preservative is paraformaldehyde. Liquid loss additive according to claim 6, characterized in that the a) the copolymer of sodium 2-acrylamido-2-methylpropanesulfonate, N-vinyl-2-pyrrolidone, acrylamide and acrylic acid is present in an amount of approx. . B) the potassium chloride is present in an amount of about 5% by weight; C) the potassium hydroxide is present in an amount of about 2% by weight; D) The sodium naphthalene formaldehyde condensate is present in an amount of about 1% by weight. 9.8% by weight and the polyethylene glycol monomethyl ether is present in an amount of approx. E) pairs of the worm aldehyde are present in an amount of approx. And (f) the water is present in an amount of approx. 78.5% by weight. Cement slurry, characterized in that it comprises: a) water, b) hydraulic cement and c) the liquid loss additive according to any of claims 1-7, wherein the liquid loss additive is present in an amount of 0.7-9.5 liters per . 42.6 kg of cement present in the slurry. A process for producing a cement exhibiting low fluid loss, characterized in that it comprises mixing a) water, b) a hydraulic cement and DK), the fluid loss additive according to any one of claims 1-7 in an amount of 0.7-9.5 liters per 42.6 kg of cement present therein. A method of cementing oil and gas wells, wherein a slurry of hydraulic cement is pumped into the wellbore and allowed to solidify, characterized in that it comprises admixing 0.7 to 9.5 liters of the liquid loss additive according to one of the claims 1-7 per 42.6 kg of cement used to form the cement slurry, whereby the hydraulic cement slurry is particularly exposed to temperatures from 27 to 232 ° C.