Sequenced polymers for monitoring the filtrate

Abstract

The invention relates to a method for preparing a sequenced copolymer comprising a first block (A) connected to a second block (B), said method comprising the following steps of monitored radical polymerisation: (E1) bringing into contact, typically in an aqueous medium: unsaturated ethylene monomers m.sub.A, selected in order to constitute the block (A); a source of free radicals; and an agent for monitoring the radical polymerisation; and then (E2) bringing into contact: the polymer obtained from step (E1); unsaturated ethylene monomers m.sub.B; a source of free radicals; and a polymer P.sup.0 which is not ethylenically unsaturated and supports labile hydrogens.

Claims

1. A process for the preparation of a block copolymer P comprising a first block (A) bonded to a second block (B), the process comprising the following controlled radical polymerization stages: (E1) bringing the following into contact: ethylenically unsaturated monomers m.sub.A, which are identical or different, chosen for the construction of the block (A); a source of free radicals which is suitable for the polymerization of said monomers m.sub.A; and a control agent for the radical polymerization; then (E2) bringing the following into contact: the polymer obtained on conclusion of stage (E1), which acts as control agent for the radical polymerization; ethylenically unsaturated monomers m.sub.B, which are identical or different, chosen for the construction of the block (B); a source of free radicals which is suitable for the polymerization of said monomers m.sub.B; and a polymer P.sup.0 which is not ethylenically unsaturated and which carries labile hydrogens.

2. The process as claimed in claim 1, wherein the polymer P.sup.0 used in stage (E2) is a natural polymer which is not ethylenically unsaturated selected from the group consisting of: native or modified polysaccharides, lignites and lignosulfonates, alginates, gelatins, carrageenans, agars, humic acid, peptides, proteins, and the mixtures of these polymers.

3. The process as claimed in claim 1, wherein the polymer P.sup.0 used in stage (E2) is a natural polymer which is not ethylenically unsaturated selected from the group consisting of: PVAs, polyesters, poly(lactic acid)s, polyamides, polyacrylates, polyacrylamides, polyamines, poly(alkyl oxide)s, polyurethanes, styrene/butadiene copolymers, poly(N-vinylpyrrolidone)s, and the mixtures of two or more of these polymers.

4. A block polymer obtained according to the process of claim 1.

5. A fluid (F) for injecting under pressure into a subterranean formation, comprising a fluid loss control agent, wherein the fluid loss control agent is the block polymer (P) according to claim 4 comprising: the first block (A), a block known as short block, with a weight-average molecular weight of less than 30 000 g/mol; and the second block (B), also known as long block, with a composition distinct from that of said first block and with a weight-average molecular weight of greater than 10 000 g/mol and which incorporates at least a portion of the polymer P.sup.0 and which is soluble in the fluid (F).

6. The fluid claimed in claim 5, wherein the fluid (F) comprises particles (p) combined with the polymer (P), the polymer being advantageously employed as dispersing and stabilizing agent for the dispersion of the particles (p).

7. The fluid claimed in claim 5, wherein the fluid (F) does not comprise solid particles (p).

8. The process according to claim 1, wherein stage (E1) is in aqueous medium.

9. The process according to claim 1, wherein the control agent for the radical polymerization in (E1) comprises a thiocarbonylthio S(CS) group.

10. The process according to claim 2, wherein the native or modified polysaccharides are guars, celluloses, dextrans, chitosans, xanthans, rheozans or pectins.

11. The process according to claim 3, wherein the poly(alkyl oxide) is polyethylene glycol.

12. The fluid of claim 5, wherein the weight-average molecular weight of the second block (B) is greater than 100 000 g/mol.

Description

EXAMPLES

Example 1

(1) Polymer Known as NaAMPS/.sub.N, N-DMA/AS/AM/Caustized Lignite/PAA-Xa Hybrid

(2) 1.1: Synthesis of a Poly(Acrylic Acid) Block Having a Xanthate Ending

(3) (PAA-Xa)

(4) 30 g of acrylic acid in an aqueous solvent; a mixture of 35 g of distilled water and 28 g of ethanol, 6.24 g of 0-ethyl S-(1-(methoxycarbonyl)ethyl) xanthate of formula (CH.sub.3CH(CO.sub.2CH.sub.3))S(CS)OEt and 312 mg of 2,2-azobis(2-methylpropionamidine) dihydrochloride were introduced into a 250 ml round-bottomed flask at ambient temperature. The mixture was degassed by bubbling with nitrogen for 20 minutes.

(5) The round-bottomed flask was subsequently placed in an oil bath thermostatically controlled at 60 C. and the reaction medium was left stirring at 60 C. for 4 hours.

(6) On conclusion of these four hours, the conversion was determined by .sup.1H NMR.

(7) An analysis by size exclusion chromatography in a mixture of water and acetonitrile (80/20) additivated with NaNO.sub.3 (0.1N) with an 18-angle MALS detector provides the weight-average molar mass (M.sub.w) and polydispersity index (M.sub.w/M.sub.n) values given in table 1 below.

(8) TABLE-US-00001 Block Xanthate Conversion M.sub.w synthesized M.sub.n, th (g) (.sup.1H NMR) (g/mol) M.sub.w/M.sub.n A1 1000 6.24 >99.9% 2100 1.8
1.2: Synthesis of the Polymer

(9) 384.6 g of demineralized water and 3.81 g of SYN-320E (silicone antifoaming agent) were introduced into a 1 l jacketed reactor. The mixture was stirred using a magnetic bar, then 33.9 g of Super Treat lignite treated with sodium hydroxide were added and stirring was allowed to continue for 15 min.

(10) While maintaining stirring, the following compounds were introduced: acrylamide (68.2 g of a 50% solution in water), NaAMPS (sodium salt of 2-acrylamido-2-methylpropanesulfonic acid) (156.2 g of a 50% solution in water), N,N-dimethylacrylamide (32.28 g), sodium allylsulfonate (7.34 g of a 35% solution in water), Versene 100 (0.194 g), demineralized water (6.78 g), PAA-Xa prepared in stage 1.1 (7.50 g of a 47.9% solution in water).

(11) The pH of the solution was adjusted to between 8.7 and 9.5 with a 25% NaOH solution (3.53 g).

(12) The reaction mixture was heated to 50 C. and degassed by bubbling with nitrogen for 30 min while stirring; at the end of these 30 min, a nitrogen headspace was maintained in the reactor with a reduced flow rate of 1 scfh.

(13) A sodium persulfate solution (2.65 g of sodium persulfate in 7.92 g of demineralized water) was subsequently injected using a syringe and stirring was allowed to take place for 1 min before introducing a sodium metabisulfite solution (0.95 g of sodium metabisulfite in 3.74 g of demineralized water). The reaction medium was stirred for 10 min, after observation of the end of the polymerization exothermicity.

(14) A second injection of initiators (sodium persulfate and sodium metabisulfite) was then carried out using the same addition protocol as for the first injection (0.839 g of sodium persulfate in 2.5 g of demineralized water/0.95 g of sodium metabisulfite in 3.74 g of demineralized water). The reaction medium was stirred for 10 min.

(15) After observation of the end of the polymerization exothermicity, a third injection of initiators was carried out using the same protocol as above (0.56 g of sodium persulfate in 1.66 g of demineralized water/0.69 g of sodium metabisulfite in 2.71 g of demineralized water). Stirring was continued for 30 min after observation of the end of polymerization exothermicity and the nitrogen flow was cut off.

(16) 1.3. Performances

(17) The performances in terms of fluid loss control were evaluated using class H cement with a density of 3.18 g/cm.sup.3. The formulation and the filtration test were carried out according to the standard of the American Petroleum Institute (API recommended practice for testing well cements 10B, 2nd edition, April 2013).

(18) The polymer to be tested (36.0 g) and demineralized water (256.1 g) were introduced into a mixer and were mixed at low speed, until a homogeneous mixture was obtained.

(19) While using a moderate rotational speed, an intimate mixture of the following solid additives (intimately mixed beforehand in a flask) was introduced into the mixer: class H cement (600 g), silica fume (210 g), setting retarder of lignosulfonate type (9.0 g).

(20) 2 ml of Syn-320E were subsequently added to the mixer and then vigorous stirring was applied until an unchanging vortex was obtained, i.e. up to approximately 60 seconds after the end of the introduction of the solids and Syn-320E.

(21) The appliance used to measure the fluid loss is the model 7120 from Chandler Engineering. The cement grout prepared in the mixer was poured into the cell of the Chandler appliance. The cell was closed and pressurized at 500 psi (35 bar) in order to condition the cement at a temperature of 176 C. Stirring was maintained in the cell throughout the duration of the conditioning. When the temperature of the product reached 176 C., the stirrer motor was switched off, the cell was inverted and the pressure of the main cylinder was increased to 1125 psi. The back pressure of the fluid loss collector was adjusted to 125 psi, so as to ensure filtration with a pressure difference of 1000 psi. The valve at the bottom of the appliance was subsequently opened. The fluid loss volume recovered was measured every 2 min for 30 min.

(22) After filtration for 30 min, the total volume collected was measured. This volume, multiplied by two, corresponds to the fluid loss according to the standard API 10B: the FLV (fluid loss volume) for the polymer tested is 20 ml at 176 C.

Example 2

(23) Poly(Acrylic Acid)-b-Poly(N,N-Dimethylacrylamide-Co-AMPS) Diblock Copolymers Grafted with PVA (Polyvinyl Alcohol)

(24) 1.1: Synthesis of a Poly(Acrylic Acid) Block Having a Xanthate Ending

(25) The synthesis was carried out at the laboratory scale in a glass reactor equipped with a mechanical stirrer, a system for heating/cooling and for efficient temperature regulation and with a system for reflux/condensation of the vapors.

(26) The composition of initial charges of the reactants and solvents (acrylic acid AA, xanthate, water, ethanol and V50) placed in the reactor is given in table 1.

(27) O-ethyl S-(1-{methoxycarbonyl}ethyl) xanthate (Rhodixan A1) of formula (CH.sub.3CH(CO.sub.2CH.sub.3))S(CS)OEt was used as MADIX transfer agent. The amount shown in table 1 corresponds to the value of the theoretical number-average molecular weight expected (Mn, th=1 kg/mol), calculated by the ratio of the amount of monomer to the amount of xanthate.

(28) Sparging of the reaction mixture with nitrogen was used throughout the synthesis.

(29) The solution of the monomer in water and the solution of the initiator V-50 (2,2-azobis(2-methylpropionamidine)dihydrochloride) in water were introduced into the reactor separately, in a semicontinuous manner, over predetermined periods and while retaining an unchanging temperature of 60 C.+/2 (see table 1 with charges and reaction conditions).

(30) The general synthesis procedure is as follows: Solutions of initiator and of the monomer in water are prepared and are placed in feed vessels; subsequently, feed lines of the reactor are filled with these solutions. Sparging of the reactor with nitrogen is begun. Sparging is maintained throughout the reaction. The demineralized water, the ethanol, the acrylic acid (first part), the Rhodixan A1 and the initiator V50 (first part) are charged to the reactor. Stirring is begun at 150 rpm. The reactor is heated to 60 C. At a temperature of 60 C. (+/2), cofeeding of the initiator solution semicontinuously with separate feeding of the monomer solution are begun. Appropriate amounts of the initiator solution (2) are provided with the passing of the appropriate time (see table of reaction conditions for a specific example). Starting from the same time, appropriate amounts of the monomer solution are provided in the appropriate time (see table 1 below of the reaction conditions). After the end of two semicontinuous feeding operations, heating is maintained at 60 C. for 3 hours. The product is cooled to a temperature <40 C. and the product is discharged for analyses.

(31) According to this procedure, polyacrylic acid functionalized by the xanthate group was synthesized with a number-average molecular weight targeted at 1000 g/mol.

(32) TABLE-US-00002 TABLE 1 Conditions of the synthesis of living poly(acrylic acid) block having a xanthate ending AA solution to be V50 solution (2) to be introduced semicontinuously introduced semicontinuously Theoretical Initial charges of the reactants in the reactor 38.7% AA Duration of 10% V50 Duration of Mn targeted Water Ethanol AA Xanthate V50 (1) in water introduction in water introduction Reference g/mol (grams) (grams) (grams) (grams) (grams) (grams) (minutes) (grams) (minutes) A1 1000 14.5 21.7 5.0 10.4 0.11 116.3 180 6.80 240

(33) The conversions of monomer and of Rhodixan A1 were determined by .sup.1H NMR.

(34) An analysis by size exclusion chromatography in a mixture of water and of acetonitrile (80/20) additivated with NaNO.sub.3 (0.1N) with an eighteen-angle MALS detector provided the values of weight-average molar mass (M.sub.w) and of polydispersity index (M.sub.w/M.sub.n) given in table 2 below.

(35) TABLE-US-00003 TABLE 2 Xanthate AA Block conversion conversion M.sub.w synthesized M.sub.n, th (g) (.sup.1H NMR) (g/mol) M.sub.w/M.sub.n A1 1000 >99.5% >99.5% 1800 1.4
2.2: Synthesis of Diblock Copolymers Grated with PVA Starting from the Block A1
Polymers P1 to P3

(36) The block A1 prepared as indicated in section 1.1 was employed in its reaction medium obtained, without purification, with a weight of polymer block A1 as given in table 3 below.

(37) The synthesis was carried out at the laboratory scale in a glass reactor equipped with a mechanical stirrer, with a system for heating/cooling and for efficient regulation of temperature and with a system for reflux/condensation of the vapors.

(38) The composition of initial charges of the reactants and the solvents (first block A1, 2-acrylamido-2-methylpropanesulfonic acid sodium saltAMPS(Na), dimethylacrylamideDMAM, water, ammonium persulfateAPS, hydroxymethanesulfinic acid monosodium salt dihydrateNaFS) placed in the reactor is given in table 3. The pH of the reaction mixture placed in the reactor as initial charge was adjusted to pH=2.2+/0.2 with 10% HCl in water.

(39) The block A1 was used as MADIX transfer agent. The amount shown in table 3 corresponds to the value of the theoretical number-average molecular weight expected for the second block (Mn, th=200 kg/mol), calculated by the ratio of the amount of monomers to the amount of blocks A1.

(40) Sparging the reaction mixture with nitrogen was used throughout the synthesis.

(41) The solution of the mixture of the monomers (AMPS(Na) and DMAM) in water, the solution of the reducing agent (NaFS) and the solution of the polyvinyl alcohol (PVA) in water were introduced into the reactor separately, in a semicontinuous manner, over predetermined periods and while retaining an unchanging temperature of 40 C.+/2 (see table 3 with reaction conditions and charges).

(42) The general synthesis procedure is as follows: Solutions of reducing agent, of the monomers and of the polyvinyl alcohol PVA in water are prepared and are placed in feed vessels; subsequently, feed lines for the reactor are filled with these solutions. Sparging of the reactor with nitrogen is begun. Sparging is maintained throughout the reaction. The demineralized water, block A1, AMPS(Na) (first part), DMAM (first part), the initiator APS and reducing agent NaFS (first part) are charged to the reactor. Stirring is begun at 150 rpm. The reactor is heated to 40 C. At a temperature of 40 C. (+/2), the time is marked as T0 and cofeeding of the solution of reducing agent (2) semicontinuously with separate feeding of the solution of the monomers are begun. Appropriate amounts of the solution of reducing agent (2) are provided with the passing of the appropriate time (see table of the reaction conditions for a specific example). Starting from the same time, appropriate amounts of the solution of the monomers are provided in the appropriate time (see table 1 of the reaction conditions). At time T0+15 minutes or T0+60 minutes (see table 3 for each specific diblock), semicontinuous feeding of the PVA solution is begun for 60 minutes. After the end of all the semicontinuous feeding operations, heating is maintained at 40 C. for 3 hours. The product is cooled to <30 C. and the product is discharged for analyses.

(43) According to this procedure, poly(acrylic acid)-b-poly(N,N-dimethylacrylamide-co-AMPSNa) diblock copolymers grafted with PVA (polyvinyl alcohol) were synthesized with a number-average molecular weight targeted at 200 000 g/mol.

(44) The specific charges of the reactants and the reaction conditions are given in tables 3a and 3b below.

(45) TABLE-US-00004 TABLE 3 a Solution of the monomers to be Initial charges of the reactants in the reactor introduced semicontinuously Theoretical 50% AMPS(Na) AMPS(Na) (50% Duration of Mn targeted Water in water DMAM Block A1 APS NaFS (1) DMAM in water) Water introduction Reference g/mol (grams) (grams) (grams) (grams) (grams) (grams) (grams) (grams) (grams) (minutes) P1 200 000 80.6 3.65 3.15 0.47 0.025 0.0002 17.87 20.66 20.15 120 P2 200 000 61.7 3.65 3.15 0.47 0.025 0.0002 17.87 20.66 15.42 120 P3 200 000 61.7 3.65 3.15 0.47 0.025 0.0002 17.87 20.66 15.42 120

(46) TABLE-US-00005 TABLE 3b Solution of NaFS (2) to be introduced semicontinuously Theoretical PVA solution to be introduced semicontinuously 0.25% NaFS Duration of Mn targeted PVA PVA Water Start of in water introduction Reference g/mol grade (grams) (grams) introduction at (grams) (minutes) P1 200 000 Celvol PVA 502 8.30 50.9 T0 + 15 minutes 1.90 300 P2 200 000 Celvol PVA 523 8.30 74.6 T0 + 15 minutes 1.90 300 P3 200 000 Celvol PVA 523 8.30 74.6 T0 + 60 minutes 1.90 300 Tables 3a and 3b: Conditions of the synthesis of diblocks grafted with PVA

(47) The conversion of the monomers was calculated by .sup.1H NMR analysis (results in table 4 below).

(48) The viscosity of the solution of the polymer was measured at 25 C. (Brookfield, speed 20 rpm, RV element #3). Analytical results are given in table 4 below.

(49) TABLE-US-00006 TABLE 4 Polymers P1 to P3 Solids Conversion Viscosity content Polymer Short block DMA AMPS (cP) (%) P1 A1 >99.5 >99.5 1280 20.0 P2 A1 >99.5 >99.5 1220 19.5 P3 A1 >99.5 >99.5 1410 20.5
2.2: Evaluation of the Diblock Polymers in Cement Grouts

(50) The diblock polymers P1 to P3 prepared in the examples were used to prepare oil cement grouts having the following formulation: Municipal water: 334.4 g Diblock polymer (at 20% in aqueous solution): 19.5 g Organic antifoaming agent: 2.1 g Dykheroff black label cement (API Class G): 781.5 g

(51) The fluid loss control agent is mixed with the liquid additives and with the municipal water before incorporation of the cement.

(52) The formulation and the filtration test were carried out according to the standard of the American Petroleum Institute (API recommended practice for testing well cements, 10B, 2nd edition, April 2013).

(53) After mixing and dispersing all the constituents of the formulation, the grout obtained was conditioned at 88 C. for 20 minutes in an atmospheric consistometer (model 1250 supplied by Chandler Engineering Inc.), prestabilized at this temperature, which makes it possible to simulate the conditions experienced by the cement grout during descent in a well.

(54) The fluid loss control performance was determined by a static filtration at 88 C. in a double-ended cell with a capacity of 175 ml equipped with a 325 mesh60 mesh metal screen (supplied by Ofite Inc., reference 170-45). The performance levels of the polymers in the cement formulations are given in table 5 below:

(55) TABLE-US-00007 TABLE 5 performance levels Polymer tested API vol (ml) P1 42 P2 42 P3 38