FR2495630A1 - ADDITIVES FOR FRACTURING SOLUTIONS AND PROCESS FOR THEIR PREPARATION - Google Patents

Abstract

WATER-SOLUBLE POLYMERIC PRODUCTS USEFUL AS ADDITIVES FOR SOLUTIONS FOR USE IN RECOVERY FROM FRACTURING OIL WELLS, CONSTITUTED BY CYANOETHYL DERIVATIVES OF POLYGALACTOMANNANES, OF WHICH THE DEGREE OF SUBSTITUTION IS BETWEEN 0.3 AND 3.0 COMPLIANT.

Description

The invention relates to an improvement relating to the formulation and

  synthesis of modified polygalactomannans to be used in the recovery phase in oil wells by fracturing. The products according to the invention are essentially cyanoethylated derivatives of polygalactomamnane having a degree of substitution

  from 0.3 to 3.0. They are normally obtained by doing

  gir seeds of guar or carob, or better of the flo-

  cakes or corresponding flours, on acrylonitrile in

  presence of an alkaline catalyst. We know by the litera-

  technical and scientific erasure and by previous patents

  -the special characteristics of hydrosol polymers-

  wheat based on cellulose or polygalactomannans, more or less treated to improve their solubility in

  the water. We also know, for the same reasons, their de-

  chemical rivets obtained by formation, thanks to a

  tution on the hydroxyl group, of methyl ether groups

  that, ethyl ether, hydroxyalkyl ether, in particular

  link hydroxypropyl ether, of carboxymethyl groups

and / or their alkaline salts.

  We know the characteristics that can be

  obtained with products of this series, synthesized se-

  lon a formulation or techniques more or less ela-

  boreal. The property of paramount importance consists in improving the productivity of oil wells or

  of gas in the secondary recovery phase by frac-

  turation by means of aqueous solutions of these polymers.

  Indeed, they allow the realization of a work of

  greater fracturing with the use of a

  lower friction sion. The use of these solutions

  tions, as we know, takes place at the same time as that of solid bodies, called "proppants", whose

  dimensions are suitably chosen and which are normal-

  based on granulated quartz sands, glass pearls, etc. The most modern products in the categories

  above allow for performance improvements, no-

  especially thanks to the increase in permeability-lite

  basement subject to fracturing, this soils promotes fr-

mation of surface fluids.

  In order to better explain the advantages offered by the invention, below is a summary of the well known phases of recovery of oil or gas by fracturing. An aqueous sclution of viscous polymer is pumped at a sustained speed into a dezerminated zone of the underground iO. The fracturing process takes place as a result of the action of hydrosatic pressure. The aqueous solution in question has been added beforehand and correctly with support agents, frazter.ne enz agents or breaking agents based on specific enzymes and zr oxidizing products, usually persalts. Once the pumping of the solution is completed at the depth of the well5, the hydrolytic effect determined by the

  rupture and which takes place, depending on the dosage, at the end of each

  only hours or a few days. The total drop in viscosity in the aqueous phase determines a flow to the collecting base of the oil or gas well, which

  which is particularly favored by cue agents

  used. In this phase, which follows hydrolysis, a

  often required characteristic of thickener h - dro-

  soluble hydrolyzed is the suspending power of

  insoluble substances, if any, of pseudo- ^ i! o -

  dale or mineral micro-solids. This characteristic

  is all the more appreciated if one considers qo] e; a -

  cosiness, at this level, is really tiny.

  Following the enzymatic hydrolysis, the solution used for fracturing loses its viscosity, but insoluble products are formed there. These tend to settle on the support agent, in fractures, causing a decrease in porosity or permeability which

  is a very negative factor. The presence of consti-

  insoluble killers exhibiting said negative behavior can usually also be detected

  visual because they tend to form visible sediments

  wheat in the hydrolyzed solution. The presence of these sediments corresponds to a tendency to decrease the

  porosity of proppants. A solution does not give

  no visible sediment is certainly superior from this point of view because it infiltrates through

  proppants without imprisoning them.

  Better behavior of the above type can, in principle, be due to various causes such as less formation of insoluble products during hydrolysis or smaller dimensions of the insoluble particles, or,

  greater suspension power of the hydro-

  lysed. It is not easy to establish what is the cause

  specifies or to what extent the various possible causes

  contribute to better behavior of solutions

  in which no sediment is formed, or only

  to a lesser extent, but that doesn't matter

  tance since experience specifically indicates that reduction or elimination of sediment is related to

  better behavior and more useful solutions

  fracturing conditions obtained with thickened products

  improved health like those according to the invention.

  The tendency of thickened products to cause or not to cause, after hydrolysis, a reduction in the porosity or permeability of proppants can also be evaluated quantitatively by filtration tests through standardized filters. The solutions drawn from the improved products according to the invention have a filterability significantly greater than that of the solutions

  obtained with previously known products. Any-

  times, as we said, this advantageous property of

  products according to the invention can also be assessed visually-

  also, by checking the presence or absence of

  sediments, as indicated in particular in the example below.

  The products, made up of cyano- derivatives

  ethyl polygalactomannates and which are the subject of the

  vention, are obtained by reaction of acrylonitrile on

  polygalactomannan in the presence of an alkaline catalyst.

  The degree of substitution can be between 0.3 and

  3.0. A degree of substitution of 0.5 to 1.5 is preferred.

  This chemical reaction can be accompanied by other substitutions such as etherification with alkyl or hydroxyalkyl groups. During the reaction,

  also tolerates partial degradation of cyano-

  ethyl in carbamoyl groups, or saponification don-

  nant an alkaline ethylcarboxylate. These substitutions or modifications must not, however, exceed 70% of the

  basic reaction, i.e. cyano- substitution

  ethyl. The reaction can be carried out either in the dry phase or in suspension in a water-miscible polygalactomannan solvent, with acrylonitrile, in the presence of an alkaline catalyst. The preferred alkaline catalyst is

  sodium hydroxide, but you can also use hydro-

  potassium xyde, tertiary amines or qua- bases

  organic ternaries. The fundamental reaction can be represented as follows, the glucoside radical being indicated by R: R-OH + CH2 = CHCN AI-Ali b R-OCH2-CH2CN The physical conditions necessary for the reaction include temperatures between 20 and 800C and pressures from 0 to 8.1 bar depending on the formulation and the desired final product. Among the solvents used as

  suspending agents, it is preferred to use the solvents mis-

  targets with water but in any case not reactive towards the bodies set to react. Ethers derived from ethylene glycol, such as dimethyl, diethyl, dipropyl and dibutyl ethers are particularly suitable. After having

  conduct the reaction under the appropriate conditions until

  only to obtain the desired characteristics, it is necessary to

  read the final product with an organic or mineral acid

  so as to completely destroy the ether groups

  cells of the cellulosic molecule with the alkali (e.g.

  ple cellulose-sodium). By respecting these conditions, we obtain products with optimal solubility and

high viscosity.

  The water content of the reaction system can be

  from 3 to 20 56, but a content of 10 to 15% o is recommended.

  Since the reaction takes place in almost all phases

  heterogeneous days, it is necessary to scrupulously respect

  the conditions set for each formulation in order to

  to guarantee good consistency of reproduction. The mechanic

  nism of the installations must, purely and simply,

take this fact into account.

  Some examples are given below concerning the formulation and the process for preparing the polymers according to the invention; these examples illustrate the invention

  without limiting it. Examples of characteristics are also indicated.

  rization of the product, compared to other usual products,

  highlighting the special properties of the product se-

lon the invention.

Example 1

  We react guar flour on the acrylo

  nitrile in a proportion such that we have DS = 1 in

  presence of sodium hydroxide (10 5 of the poly-

  galactomannan). The water content is 13% of the total product reacted. The reaction is carried out in a closed circuit, in a first phase, at 400C, for 3 hours. The reaction is then completed at 650C for 3 hours, ensuring that the pressure in the reaction autoclave does not exceed 0.6 to 0.8 bar. We apply a vacuum of 940 mbar

  (700 mm Hg) and the reactor atmosphere is saturated with nitrogen.

  The installation is arranged under distillation conditions.

  tion and, by applying a moderate stream of nitrogen,

  holds at 700C for 3 hours. We check the characteristics

  ticks of the product by successive withdrawals to the desired point. We neutralize the product with formic acid

  up to pH 6.5. Cool to 500C. We discharge in re-

  linking the device to the desiccation and grinding installation. The ground product is sieved so as to obtain particles not exceeding 200 μm. A powder is obtained which, in aqueous solution at 2 ç of solids, has a viscosity of 18 Pa.s (18,000 cps), measured at 250C at

Brookfield RVT viscometer.

Example 2

  Guar flour is reacted on the acrylonitrile so as to obtain DS = 0.5, methyl chloride at the rate of DS = 0.7 in the presence of sodium hydroxide representing 12% of the polygalactomannan. The operation is carried out with a water content of 16 ° C. of the total product reacted. The reaction is carried out in a closed circuit in a first

  phase at 400C for 3 hours. We then complete the reaction

  tion at 650C for 2 hours then at 800C for 2 to 4 hours

  res by maintaining at 80 ° C. until the pressure in the reactor drops to 0.5 bar. During the reaction, the pressure must never exceed 4 bar. A vacuum of 940 mbar (700 mm Hg) is then applied. We saturate with nitrogen

  the atmosphere of the reactor and one maintains between 70 and 750C.

  The characteristics of the product are checked by means of

  successive steps until reaching the desired values,

  We neutralize and finish as in Example 1. The pro-

  duit obtained has good solubility in water ez gives a 2% solution of solids having a viscosity of 14 Pa.s (14,000 cps), measured at 25 C with a viscometer

Brookfield RVT.

Example 3

  We react guar flour on acryloni-

  trile at the rate of DS = 0.3 and on propylene oxide at the rate of DS = 0.6. The reaction is carried out in the presence of 1,2-dimethoxyethane at the rate of 50% of the guar, using

  as catalyst triethylamine in an amount of 2 tsp of guar.

  The operation is carried out with a water content of 7% c of the total product reacted. The reaction is carried out in a closed circuit in a first phase at 60 ° C. for 3 to 4 hours. Sodium hydroxide is added in an amount of 5 'of the guar, operating with an aqueous solution so as to bring the total water content to 20% of the product reacted. The temperature is raised to 800C and maintained for about 2 to 4 hours until the pressure drops to 0.8

  bar. During the reaction, the pressure must never exceed

  be 3 bar. A vacuum of 940 mbar (700 mm Hg) is applied by distilling the recovered solvent (1,2-dimethoxyethane) through a condenser. We finish the recovery of the soil-

  Before vacuum between 70 and 75 C. The nitrogen is saturated

  reactor mosphere. The characteristics of the product are checked by successive withdrawals until the desired values are reached. Neutralized and completed as in Example 1. The product obtained, which has good solubility in water, gives a 2% solution of solids which has a viscosity of 16.5 Pa.s (16,500 cps) ,

  measured at 25oC with the Brookfield RVT viscometer.

Example 4

  We react guar flour on acryloni-

  trile at the rate of DS = 0.7 in the presence of 1,2-diethoxy-

  ethane (20% guar) using potassium hydroxide-

  sium at 8% of the guar. The operation is carried out with a water content of 16% on the total product reacted. We continue

  the reaction until the end following the suc-

  stops indicated in Example 3. A product is obtained

  having good solubility in water and giving, in solu-

  2% aqueous tion, a viscosity of 24 Pa.s (24,000 cps),

  measured at 250C with the Brookfield RVT viscometer.

  Example 5 The product of Example 1 is prepared with DS = 1.5 by bringing the sodium hydroxide to 12% of the guar. Once

  the addition of acrylonitrile completed, a saponi-

  forced fication of the cyanoethyl group by maintaining the product under a moderate current of nitrogen and a controlled current of vapor at the temperature of 800C while operating so that

  the water content of the reaction product is from 16 to 18%.

  Maintained at 800C under these conditions until a 1% solution of the product in water gives a pH of 7.8 to

  8.2. Neutralize and complete as in Example 1.

  The product obtained has good solubility in water.

  At 2% in water, it has a viscosity of 12 Pa.s (12,000 cps)

  at 25 C, measured with the Brookfield RVT viscometer.

Example 6

  We examine here various samples of derivatives

  hydrosul modified lulosics and polygalactomannans

  wheat compared to polygalactomannan derivatives

  according to the invention. We analyze the behavior of solu-

  aqueous ions at 0.48% solids after degradation with a breaking agent, after different periods of time, and it is shown in the table below. The times are

  noted from the time of preparation of the solution.

  Visco- Visco- Presence Visco- Presence Insoluble sity sity of sedi- sedity from tip to tip to tip to tip butt 40 h from h 100 h Product A 30 38 30 2 32 12%

B 24 25 0 12 0 00

C 26 30 18.8% 5 19.2 0.63%

D 28 30 15.3% 4.5 16 0.55%

E 32 34 00 8 00 00

F 24 26 00 10 00 00

G 27 31 00 5 00 00

H 36 40 2 6 3 0.7%

  In this table, the products are as follows: A is the surface treated guar; B is a methyl hydroxypropyl cellulose in which DSmethyl = 0.5 and DL hydroxypropyl = 1, and which has a viscosity of 10 Pa.s (10,000 cps) at 2% in water;

  C a hydroxypropylguar having DS = 1.2 and a viscous

  sity of 12 Pa.s (12,000 cps) at 2% in water; D a methylhydroxyethylguar in which DSmethyl = 0.4 and DShydroxyethyl = 0.8 and which has a viscosity of 14 Pa.s (14,000 cps) at 2% in water; E is the product according to Example 1; F is the product according to Example 2; G is the product according to Example 3;

H is the product according to Example 4.

  The table highlights the fact that the cyanoethylated guar products according to the invention allow

  to prepare fracturing solutions which, after hy-

  drolysis, contain insoluble sedimentable products in much smaller quantities than those prepared

  with previously known products. These characteristics

  ticks respond to the ideal behavior required in the phase

  which follows the biochemical degradation of poly-

  water-soluble mothers so as to promote better listening

  lement of the extracted oil fluid (oil or gas) at the pumping base of the wells and therefore a better yield

  in fracturing recovery.

Claims (10)

  1 - Useful water-soluble polymer products co.Tme additives for solutions to be used in recovery from oil wells by fracturing, characterized in that they consist of cyanoethylated derivatives of polygalactomannans.   2 - Additives according to claim 1, characterized   in that the degree of substitution is 0.3 C 3.0.   3 - Additives according to claim 1, characterized in that the cyanoethyl group is substituted, to an extent not exceeding 70%, by other groups, for example alkyl, hydroxyalkyl, carbamyl, carboxyethyl and alkali carboxyethyl salt.   4 - Additives according to claim 1, characterized in that the polygalactomannans are derived from seeds of guar or carob.   - Recovery process in oil wells by fracturing, characterized in that a solution containing a polymer additive is used and which gives rise, after enzymatic hydrolysis carried out according to the   known technique, to a solution free of insoluble products iubles sedimentables.   6 - Process for the preparation of cyanoethylated derivatives   polygalactomannans, useful as additives for solu-   fracking, characterized in that the polygalactomannans or seed flours which contain them are treated with acrylonitrile in the presence of water and a alkaline catalyst.   7 - Method according to claim 6, characterized   in that the alkaline catalyst comprises at least one component   titrant selected from alkali hydroxides, amines   tertiary and organic quaternary ammonium bases.   8 - Method according to claim 6, characterized   in that water is present at a rate of 3 to 20% of the pro- had to react.   9 - Process according to claim 6, characterized in that the polygalactomannans which are reacted on acrylonitrile contain substituents other than it cyanoethyl group.   - Method according to claim 6, characterized   in that we react the polygalactomannans not only   Lely on acrylonitrile but on reagents capable of introducing, into the molecules of polygalactomannans,   substituents other than the cyanoethyl group.   11 - Method according to one of claims 9 and 10,   characterized in that the substituents other than cyano-   thyle are chosen from alkyl, carbamyl, hy-   droxyalkyl, carboxyethyl and alkali salt of carboxyethyl.   12 - Fracturing solutions characterized in that they contain a water-soluble polymer thickener   according to one of claims 1 to 4.