FR2516533A1 - AQUEOUS FLUIDS FOR DRILLING WELLS - Google Patents

Abstract

THE INVENTION RELATES TO A PROCESS FOR IMPROVING AQUEOUS FLUIDS USED IN THE DRILLING, STRENGTHENING AND MAINTENANCE OF BOREHOLE WELLS, CONSISTING OF ADDING TO SUCH A FLUID AND DISPERSING THERE AN EFFECTIVE QUANTITY OF A HYDROXYETHYL STARCH REQUIRED QUANTITY AND AN EFFECTIVE QUANTITY OF STARCH. FROM A MATERIAL CHOSEN FROM CARBOXYALKYL CELLULOSE ETHERS, XANTHAN GUM AND THEIR MIXTURES. IT ALSO CONCERNS IMPROVEMENT ADDITIVES FOR IMPLEMENTING THE PROCESS AS WELL AS AQUEOUS FLUIDS IMPROVED BY THESE ADDITIVES.

Description

16533

  The present invention relates to a method and a composition for increasing the viscosity and reducing the fluid loss of aqueous systems used as fluids for drilling, consolidating and maintaining wellbore, which fluids are referred to herein as "fluids for well "in

a goal of lightening the text.

  Aqueous media, especially those containing

  oilfield brines, are commonly used

  well fluids, such as drilling fluids, reconditioning fluids, finishing fluids, sealing fluids, well treatment fluids, subterranean treatment fluids, interval fluids,

  drilling fluids, etc. These well fluids must be

  to be efficient and economically attractive,

  proof of low fluid loss It is known to add

  well fluids certain hydrophilic polymeric substances

  philes to settle this loss For example, it is known to u-

  to use starch and cellulose products, in particular starch derivatives of maize and potato starch,

  as additives to the fluids in question, for example

  res, to limit fluid loss.

  An increase in the viscosity of aqueous well fluids, for example brines, is also necessary in many applications.

  derivatives of starch and cellulose to obtain such an increase

  mentation. Examples of the prior art describing various additives for well fluids, in order to increase their viscosity and / or limit fluid loss, are given in US Patent 3,625,889 which describes a fluid for

  well finishing, including calcium chloride a-

  carboxymethyl cellulose (CMC) and gum

  xanthan (XC polymer), and in US Pat. No. 3,953,336 which discloses

  of XC polymer blends with various derivatives, cellulosic

  such as hydroxyethyl cellulose, carboxymethyl cellulose, etc. The object of the invention is therefore to provide a new

  process as well as a new composition to increase

  nergically the viscosity and limit the fluid loss of 2. aqueous fluids for wells, including aqueous brine solutions. In one of its aspects, a subject of the invention is a method for decreasing the fluid loss of an aqueous well fluid, which comprises adding to said fluid and dispersing therein an effective amount of a hydroxyethyl crosslinked starch (HEA) and an effective amount of a material selected from

  carboxyalkyl cellulose ethers, the XC polymer and their

  diapers. According to another aspect, the subject of the invention is a composition that can be used to increase the viscosity and to reduce the fluid loss of an aqueous medium, in particular a fluid

  well, consisting of an effective amount of a hydroxyl

  crosslinked ethyl starch and an effective amount of a material

  chosen from carboxyalkyl cellulose ethers, the polymer

re XC and their mixtures.

  One of the polymeric constituents (polymer A) of the new

  compositions of the invention comprises a selected material

  among the hydroxyalkyl cellulose ethers in which the alkyl group comprises 1 to 3 carbon atoms, such as carboxymethyl cellulose (COC), carboxyethyl cellulose (CEC), etc., xanthan gum (polysaccharide biopolymer gum xanthomonas) commonly known as the XC polymer, and mixtures thereof The term "polymeric component" refers to one or more carboxyalkyl cellulose ethers, with or without

  Among the polymers mentioned above, the polymers

  Preferred are the XC polymer and carboxymethylcellulose.

  The XC polymers which can be used in the present invention

  Depending on the fluid preparation process for wells, they may be either in the form of a dry powder,

  essentially untreated, ie being an "activated" XC polymer.

  The term "activated" as used herein refers to an XC polymer

  who can hydrate or dissolve practically in a

  brine with a specific gravity greater than

  1 700 g / dm 3 without mixing, as by mixing

  rolling mill (hereinafter simply "mixing"), at temperatures

  Examples of these activated XC polymers may be

  can be found in U.S. Patent Application No. 146,286 of May 1980 as described in the prior patent application.

  activated XC polymers dissolve in aqueous solutions.

  brine without the need for mixing or any other

  in the form of mixing at elevated temperatures Generally speaking,

  any polymer XC that dissolves in a brine having a specific gravity greater than about 1700 g / dm 3 at the temperature of

  ambient temperature, can be considered as an XC polymer

  However, it is obvious that the present invention is not limited to the use of these activated XC polymers according to the mixing conditions and the composition of the aqueous fluid for

  well, inactivated or dry powdered XC polymers are

  The term "compatible" as used herein means that the XC polymer can be dissolved or solubilized in a given aqueous solution using mixing techniques such as mixing at temperatures. In contrast, an incompatible system is a system in which the XC polymer does not solubilize in the brine

  whatever the mixing conditions used.

  The other polymer component (polymer B) of the compounds

  The present invention is a crosslinked HEA. Such hydroxyethyl starches are produced by introducing non-ionic, hydroxyethyl groups onto the polymer chain.

  starch, followed by well-established cross-linking techniques.

  in the art, such as those described in US Pat. Nos. 2,500,950, 2,929,811, 2,989,521 and US Pat.

  In general, the hydroxyethyl starches crosslinked

  which can be used in the present invention are those

  in which the degree of substitution (DS) of the

  The hydroxyethyl tetramethyl ester is from about 0.15 to 0.8, preferably from about 0.25 to 0.6. A particularly preferred crosslinked hydroxyethyl starch is known by the trade mark Bohramyl CR, i.e. crosslinked potato starch, manufactured by Avebe (Veendam, The Netherlands) The Bohramyl CR derivative, which is a white, roughly flaky material, has a specific gravity (g / dm) of about 325 and a

DS about 0.4.

  The crosslinked HEA may be used in the form of a powder or dry flakes, essentially untreated, or it may be an "activated" starch in which the term "activated" has the same meaning as above. in the presentation on

  activated XC polymers.

  These are described in US Patent Application No. 119,805 of February 8, 1980. It is evident that the present invention is not limited to the use of activated HEA.

  characteristic of the invention that all the constitu-

  polymers can be used in dry form for

  to produce well fluids that demonstrate excellent

  rheological properties and low fluid loss

  during, in some brine solutions, an activation

  or a pre-dissolution of XC polymers and / or hydroxide

  thyl starch may be desirable to decrease the times of

  mixture and the severity of the conditions of the latter.

  The polymer composition of the present invention which can be used to decrease fluid loss and increase the viscosity of aqueous well fluids, comprises

  an effective amount of crosslinked HEA (polymer B) and a

  polymer XC, a polymer of carbonyl ether polymer

  Cellulose (CACE) or mixtures thereof (Polymer A) It has been found that when an XC polymer, a CACE polymer or a mixture of these polymers is added to the well aqueous fluids together with the HEA, According to the nature of the fluid, a synergistic increase in viscosity and / or a reduction in fluid loss is observed. The particular amount of each polymer component present in the additive varies according to the nature and composition of the aqueous fluid.

  well with which it must be mixed Generally speaking,

  the, the polymer composition according to the invention contains a

  weight ratio of HEA (polymer B) to polymer XC, polymer

  CACE and their mixtures (polymer A) of about 10/90 to 10, preferably about 33/67 to 75/25. The polymer composition according to the invention can be in the form of a dry mixture of HEA and XC polymer, CACE polymer or mixtures thereof, or, if preferred, in dissolved or activated forms of polymers Thus, for example, the HEA

  and the XC polymer can be activated and these solutions activate

  mixed together to provide the new composi-

  polymer compositions used according to the invention.

  The new well fluid according to the invention comprises

5.

  takes an aqueous medium and an effective amount of a hydroxy

  crosslinked ethyl starch and an effective amount of polymer

  XC, CACE polymers or mixtures thereof.

  of HEA and the other polymer component (polymer A) mixed with the aqueous medium are such as to give

  a synergistic decrease in fluid loss in the middle

  Here again, the precise quantity of each poly-

  mother used depends on the nature of the aqueous fluid.

  But, in general, the weight ratio of

  the HEA to the other polymer in the fluid is between

  Viron 10/90 and 90/10, preferably between about 33/67 and / 25. In general, well fluids contain the

  polymers in amounts of from about 1.50 to 30 g / l of hydroxy-

  starch (polymer B) and from about 0.70 to 14 g / l of

  polymer component (polymer A).

  The aqueous medium used in well fluids

  according to the invention can range from pure water to brine den-

  with a density greater than 2 260 g / dms.

  well fluids, such as those used for

  in finishing and reconditioning operations, are prepared from aqueous media containing salts

  such as, for example, a soluble salt of an alkali metal

  alkaline earth metal, a Group Ib or Ib metal, as well as water-soluble ammonium salts and other

  cations Polymeric compositions are particularly

  suitable for the preparation of dense brines with low fluid loss, ie aqueous solutions of salts

  soluble multivalent ions, for example Zn and Ca.

  The preferred dense brines, usable for

  The well fluids according to the invention are those whose specific gravity is greater than about 1 310 g / dm, in particular greater than about 1 735 g / dm 3. These dense brines consist of aqueous solutions of selected salts.

  calcium chloride, calcium bromide, chlorine

  zinc chloride, zinc bromide and mixtures thereof.

  Carrier agents can optionally be added to fluids for well maintenance to aid in the fight against fluid loss. In fact, their use will result in slightly lower filtrates. However, it is a distinct and unexpected feature. of the invention that a support agent is not required to obtain

  low fluid loss values in aqueous brines.

  Thus, using the product of the invention, it is

  possible to obtain clear brines with

  ticks of low fluid loss and characteristics

Theological little accentuated.

  The following non-limiting examples are given in

  Illustrative of the invention * Unless otherwise indicated

  re, all measurements of physical properties are made

  according to the test methods described in "Standard Pro-

  for testing Drilling Mud "A Pl RP 13 B, 7th edition, A-

  April 1978 Unless otherwise indicated, the cross-linked REA used

  is the product Bohramyl CR marketed by Avebe (Veen-

dam, Netherlands).

Example 1

  To show the synergistic effect on viscosity and fluid loss, obtained by mixing HEA and XC polymer, was added to a 10% by weight aqueous solution of NaCl 0 or 17 g / l of Bohramyl. CR and was mixed for 25 minutes on a Kultimixer Then the samples were passed to the mill mixer at 660 C, cooled to 230 ° C. and stirred for minutes before determining the rheology and loss of API fluid. The data obtained and reported in FIG. Board

  I below (see end of description) show that Bohra-

  myl CR, when mixed with the XC polymer, decreases

  nergically the loss of fluid in the aqueous solution of

  sodium chloride and increases its viscosity.

Example 2

  The procedure of Example 1 was repeated with the difference that carboxymethyl cellulose (CMC) was used.

  rather than polymer XC The results reported in Table

  II clearly show that the combination of hydroxyethyl

  crosslinked starch and CMC polymer gives synergetic results.

  both in terms of fluid loss and viscosity. It should be noted from the data shown in Tables I and II that cross-linked HEA gives results.

  much better than the non-crosslinked product.

Example 3

  To evaluate the effectiveness of the polymeric compositions

  In accordance with the invention of dense charged drilling fluids, various amounts of Bohramyl CR and XC polymer were added to a 1,430 g / dm 3 solution of sodium chloride.

  loaded with Baroid (registered trademark of a

  baryte-based marketed by the firm NL Baroid,

  Houston, Texas) Bohramyl CR was first added to the

  sodium chloride solution and mixed on a Multimedia

  After 10 minutes the polymer XC was added and mixing was continued for 10 minutes before the Baroid was added, after which the mixture was mixed on the Multimixer for 10 minutes. The rheology and of fluid loss A P1 on the drilling fluid

  Thus prepared the fluid was passed to the rolling mill-mill

  16 hours at 660 ° C. and the rheological properties were evaluated.

  and fluid loss After this, the

  samples and stirred for 5 minutes, then again

  The properties obtained and reported in Table III below show that the XC polymer,

  when combined with Bohramyl CR, decreases synergi-

  loss of fluid and increases the viscosity of fluids.

  dense drilling It was also noted that there was no

  there is no sedimentation of the filler.

Example 4

  To evaluate the effectiveness of the polymeric compositions

  of the invention with regard to the increase of the

  viscosity and the limitation of fluid loss in

  dense soils, eg brines containing chloride

  of calcium, various amounts of HEA and poly-

  mother XC to a 5% aqueous solution of calcium chloride

  and mixed on a Multimixer for 20 minutes and determined

  undermined the theological properties A P1 (initial properties).

  The samples were then passed to the kneader-mill for 16 hours at 360 ° C., subjected to the hot state tests and

  Unstirred The samples were cooled, stirred for 5 minutes,

  nutes on a Multimixer and determined rheology and loss

  in fluid API The data obtained and reported in Table

  Figure 8 below shows that when Bohramyl CR HEA and XC polymer are combined, they synergistically decrease the fluid loss in the aqueous solution of chlorine chloride.

  calcium and increase the viscosity.

Example 5

  The procedure of Example 4 was repeated, except that after adding the polymer to the calcium chloride solution, the equivalent of 70 g / l of Glen Rose shale was added and blends were mixed. After 5 minutes, the equivalent of 570 g / l of Baroid was added to the compositions and the mixing was continued on the Multimixer for another 5 minutes.

  initial properties of the samples.

  mills for 16 hours at 660 C and proceeded to

  Hot tests without agitation Then the samples were cooled

  samples, mixed for 5 minutes on a Multimixer and deter-

  undermined theological and loss properties in API fluid.

  The data reported in Table V below shows that, even in the presence of a filler and a shale such as can be encountered in a borehole, there is a synergistic increase in the viscosity and a limitation of loss of fluid using a mixture of Bohramyl CR and polymer

  In addition, the sedimentation of solids is much lower than

  re in the case where a mixture of the polymers is used.

Example 6

  In this example, the effectiveness of

  polymer positions of the invention on charged drilling fluids using dense brines, by adding different amounts of Bohramyl CR and XC polymer to a 5% calcium chloride solution charged with the equivalent of 570 g / i of Baroid On first added Bohramyl CR to the solution

  of calcium chloride and mixed on a Multimixer pen-

  After 10 minutes, the polymer XC was added and the mixture was continued for 10 minutes before adding the Baroid and continuing mixing on the Multimixer for 5 minutes. The rheology measurements A P1 (initial properties) on

  the drilling fluid thus prepared has passed the fluid to the

  laxeur-rolling mill for 16 hours at 660 C and obtained the

  rheological properties of the hot, unstirred drilling fluid.

  9. After that, the samples were cooled and stirred for 5 minutes.

  minutes before determining the rheological properties again

  and loss of fluid The data obtained and

  Table VI below shows that the XC polymer, when combined with HEA Bohramyl CR, synergistically decreases the fluid loss while at the same time increasing the viscosity in the dense drilling fluids. that when HEA Bohramyl CR and polymer XC are combined, there is virtually no sedimentation of the

Baroid charge material.

Example 7

  The procedure of Example 4 was repeated using different amounts of Bohramyl CR and XC polymer.

  The data reported in Table VII below show clearly

  the synergistic effect on viscosity and the limitation of fluid loss resulting from the use of a mixture of

Bohramyl CR and XC polymer.

Example 8.

  The procedure of Example 6 was repeated, with the difference that various amounts of XC polymer were used.

  and that the equivalent of 570 g / I of Baroid was added to the samples

  After the addition of the polymers, the samples were mixed for 5 minutes on the Multimixer. The samples were passed to the kneader-mill for 16 hours at 66 ° C. and the rheology A P1 (initial properties) was determined.

  cooled the samples, mixed for 5 minutes on Mul-

  timixer and determined the rheological and loss properties

  in API fluid The data, reported in Table VIII below

  after, demonstrate again the amazing synergistic effect ob-

  held on the viscosity and the limitation of fluid loss using a mixture of polymers As can be seen

  also from the data in Table VIII, it does not occur

  no sedimentation of the Baroid charge when

read a mixture of polymers.

TABLE I.

  N of the sample Polymer XC, g / l Bohramyl CR, g / 1 D.S. Cross-linking

1 2 3

2.85 O 2.85

0 17.1 17.1

0.30 0.30

yes yes After mixing 25

4 5 6 7

0 2.85 O 2.85

17.1 l 7.1 17.1 17.1

0.40 0.40 0.22 0.22

yes yes no no mn on Multimixer

8 9

0 2.85

17.1 17.1

0.62 0.62

  no no Apparent viscosity, Pa / s x 10-3 Plastic viscosity, Pa / s x 10-3 Pour point, Pa p H Filtrate API, + ml Filtrate API ,, m

2.5 9.5 30

2 8 20

0.48 1.44 9.36

7.6 8.6 7.9

26 to 7.5

After rolling to

6.5 23

S 0.48 8.5 17.3

66 C,

8 21

16 7 14

6.72 0.96 6.96

8.8 8.2

6.0 NC 219

cooling to

13.5 3 13.5

* 0.96 8.8 NC 23 C

8.5 2 7,

4.8 0.96 5,

8.0 8.3 7,

NC NC N

and mix for 5 minutes.

  Visible viscosity, Pa / s x 10-3 Plastic viscosity, Pa / s x 10-3 Pour point, Pa p H Filtrate API +, ml

8 11 28 6.5 22.5

4 10

3.84 0.96

7.1 8.4

240 33

6.72 7.7 0.48 8.3 19.5

8.5 19

12 8 13.5

0.48 5.04

7.5 8.6 7.7

6.6 71.5 250

NC = not verified.

  1 l O 17.1 0.80 no 2.85 17.1 0.80 no C O 4.5 11 l

3.5 13

  0.48 8.2 NC 7.68 7.6 NC 0.48 7.8 NC 7.5, 52 7.2 NC Re Vin os Ln LY

TABLE II.

  N of the CMC sample, g / l Bohramyl CR, g / 1 D.S.

1 2 3

2.85 O 2.85

0 17.1 17.1

0.30 0.30

yes yes After mixing 25 1 i or

4 5 6 7 8 9

2.85 O 2.85 O 2.85

7.1 17.1 17.1 17.1 17.1 17.1

), 40 0.40 0.22 0.22 0.62 0.62

  Li yes no no no no mn on Multimixer Apparent viscosity, Pa / s x 10-3 Plastic viscosity, Pa / s x 10-3 Pour point 6, Pa p H Filtrate A Pl +, ml

9 9.5 41.3 6.5 31

7 8 25.5

1.92 1.44 15.12

6.9 8.6 8.5

68 30 17

After rolling to 0.48 8.5 17.3

66 C.

8 24 5 13 3 12

7 18

, 5 G 0.96 5.52

8.8 8.7

7.0 NC 80

cooling to

4 11 2 10

0.96 2.1 S 0.96 2.16

8.8 8.4 8.3 7.3

NC 100 NC 100

23 C and mix 5 min.

  Visible viscosity, Pa / s x 10-3 Plastic viscosity, Pa / s x 10-3 Pour point, Pa p H Filtrate A Pl +, ml

8 11 35 6.5 28.5

  0.48 7.2 0.96 8.4 8.64 8.2 0.48 8.3 19.5 8.16 8.3 8.0

8.5 19

3 15

0.48 3.84

8.6 8.4

71.5142

4,5 11

4 10

0.48 0.96

8.2 8.0

NC 151

3.5 11

3 9

0.48 1.68

7.8 7.7

NC 150

NC = not verified.

  o 17.1 0.80 no 2.85 17.1 0.80 no. An A 12.

TABLE III

  Number of samples 1 2 3 Material, g / l Bohramyl CR 17.1 17.1 Polymer XC 0.71 0.71 Baroid 570 570 570 After mixing for 10 minutes on Multimixer Bohramyl CR, addition

  XC, 10 min mixing, addition of Baroid, 10 min mixture.

  Viscosity apparent, Pa / s x 10-3 16.0 23.0 7.0 Plastic viscosity, Pa / s x 10-3 15.0 19.0 7.0

Pour point, Pa 0.96 3.84 -

Gel at 10 s, Pa 2,4 2,4 -

  Gel at 10 min, Pa 6.72 3.36 2.88 p H 8.2 8.1 8.1 Loss in filtrate, API, ml 11.5 8.8 57.4

  After rolling 16 hours at 66 ° C, hot test.

  Viscosity apparent, Pa / sx 10 13.5 17.0 5.5 Plastic viscosity, Pa / sx 1073 13.0 14.0 5.0 Pour point, Pa 0.48 2.88 0.48 Gel at 10 s, Pa 3, 84 1.44 0.48 Gel at 10 min, p 6.72 5.28 7.2

  After cooling and stirring for 5 minutes on Multimixer.

  Viscosity apparent, Pa / sx 1073 17.5 24.5 6.5 Plastic viscosity, Pa / sx 1073 17.0 21.0 6.0 Pour point, Pa 0.48 3.36 0.48 Gel at 10 s, Pa 1.44 0.96 1.44

Gel at 10 mn, pa 2,4 2,88 -

  p H 7.8 7.8 7.6 API filtrate, ml 6.6 5.8 266 Barid sedimentation medium light dense N samples Bohramyl CR, g / l Polymer XC, g / l Apparent viscosity, Pa / sx 1073 Viscosity plastic, Pa / sx 10-3 Pour point, Pa Gel at 10 s, Pa Gel at 10 min, Pa p H 13.

TABLE IV.

1 2 3 4 5 6

, 6 o

17.1 15.4

0 1.7

  Pro Dries, 5 10 6.24 0.48 0.48 7.3 Ants 1.92 0.96 0.9, 7.4

14.2 O

2.85 2.85

initials.

, 5 27.5 13

  4.32 2.4 2.4 7.5 3.36 4.32 7.4 mill pass 0.96 0.96 1.92 7.4.4 4. 3 14.5 4.32 1.92 2 , 88 7.4 during 16

  hours at 66 C, test at, warm, without

  tation. Visible viscosity, Pa / sx 10 3 Plastic viscosity, Pa / sx 1073 Pour point, Pa Gel i 10 s, Pa Gel at 10 min, Pa Viscosity apparent, Pa / sx 10-3 Plastic viscosity, Pa / sx 10- 3 Pour point, Pa Gel at 10 s, Pa Gel at 10 min, Pa p H Filtrat API, ml

11 4.5 13 16.5 4.5 9

8 4 8 7 3 4

2.88 0.48 4.8 9.12 1.44 4.8

  o 0.48 0.95 1.92 O s o 0.48 1.44 2.4 O 0.96

  After cooling and mixing

5 minutes on M Iultimixer.

  he 21.5 26 8.64 0.96 0.96 7.4 6.7 1.92 0.48 0.48 7.4 9.0 9.2 2.4 2.4 6.8 7.3 13.4 3.36 3.84 6.7 7.1

7 12

  2.88 o, 6, 76 1.92 2.4, 6 N samples Bohramyl CR, g / l Polymer XC, g / il Glen Rose Schist, g / li Baroid, g / 1

TABLE V.

1 2

, 6 17.1

O O

71.2, 4 1.7 14.25 2.85

71.2 71.2 71.2 71.2

570 570 570 570

  Initial Properties Visible Viscosity, Pa / s x 10-3 Plastic Viscosity, Pa / s x 10-3 Pour Point, Pa Gel at 10 s, Pa Gel at 10 min, Pa

51 24 46.5 49.5

* 31 20 33 18

19.2 3.84 12.96 25.4

9.6 3.36 4.8 7.2

12.96 5.76 7.2 9.12

After rolling 16 hours

hot, without agitation.

16 24

12 15

3.84 8.64

1.44 2.88

2.4 3.36

  at 66 ° C, test Visible viscosity, Pa / sx 1073 Plastic viscosity, Pa / sx 10-3 Pour point, Pa Gel at 10 s, Pa Gel at 10 min, Pa Viscosity apparent, Pa / sx 10-3 Viscosity plastic , Pa / sx 10-3 Pour point, Pa Gel at 10 s, Pa Gel at 10 min, Pa p H Filtrate API, ml Sedimentation Baroid, 5 15

38 35 13.5 21

27 14 30 21

8.16 0.96 5.76 13.4

4.32 1.92 3.36 2.88

, 76 2.4 3.84 4.32

After cooling and

on Multimixer.

, 5 23.5 45.5 46

  , 8 4.8 7.1 3.6 dense soft, 28 2.88, 76 7.2 8.2 dense soft 4.8 6.7 7.0 7, 9 19.2, 76 7.68 7, 0 7.6 Leg 11 Nil

14 16

28

0.48 1.92

0.48 2.4

mix 5 mn

16 24

  1.92 7.0 32.1 light (2) 2.88 1.92 2.4 7.0, 8 slight (l) traces to light (2) light to moderate 14. o 2.85 o 4.3 71.2 15.

TABLE VI.

  N samples Bohramyl CR, g / l Polymer XC, g / l Schist Glen Rose, g / l Baroid, g / il Apparent viscosity, Pa / sx 10-3 Plastic viscosity, pa / sx 10-3 Pour point, Pa Gel at 10 s, Pa Gel at 10 min, Pa p H After rolling 16 hours

agitation Viscosity apparent, Pa / s x 10-3 Viscosity plastic, Pa / s x 10-3 Item

  of flow, Pa Gel at 10 s, Pa Gel at 10 min, Pa After cooling and timixer. Visible viscosity, Pa / s x 10-3 Plastic viscosity, Pa / s x 103 Pour point, Pa Gel at 10 s, Pa Gel at 10 min, Pa p H Filtrate API, ml Sedimentation solids

1 2 3

17.1 17.1

2.85 2.85

71.2 71.2 71.2

570 570 570

Initial properties

24 56 16

23 12

3.84 28.3 3.84

3.36 8.64 1.44

, 76 12 2.4

7.1 7.2 7.1

at 66 C, hot test, san E

46 13.5

14 22 14

0.96 22.6 -

1.92 5.76 0.48

2.4 6.72 0.48

mix 5 minutes on Mul-

  23.5, 3.88, 76 7.2 8.2 dense 26.9 8.64 11.5 7.0, 0 none soft 1.92 7.0 32.1 mild to moderate soft S 16.

TABLE VII.

  Number of samples Bohramyl CR, g / il Polymer XC, g / il Apparent viscosity, Pa / sx 10-3 Plastic viscosity, Pa / sx 10-3 Pour point, Pa Gel at 10 s, Pa Gel at 10 min, Pa p H After rolling 16 hours

without agitation.

  Visible viscosity, Pa / s x 10-3 Plastic viscosity, Pa / s x 1073 Pour point, Pa Gel at 10 s, Pa Gel at 10 min, Pa After cooling and Multimix. Viscosity apparent, Pa / s x 10-3

Plastic viscosity, pa / s x 10-

  Pour point, 10 s Gel, 10 d Gel, Pa p H Filtrat API, ml

1 2 3

17.1 17.1

2.85 2.85

Initial properties

30.5 13

8 16 12

1.92 13.9 0.96

0.96 3.84 0.96

0.96 4.32 1.92

7.4 8.0 7.4

  at 66 C, hot test, 4.5 0.48 0.48 0.48 blend 1.92 0.48 0.48 7.4 9.0

19 4

3

8.64 O

  0.96 1.44 minutes on, 5 14.9 3.36 3.84 7.0 6.5 2.88, 6-17.

TABLE VIII.

  Number of samples Bohramyl CR, g / l Polymer XC, g / 1 Apparent viscosity, Pa / sx 1073 Plastic viscosity, Pa / sx 10-3 Pour point, Pa Gel at 10 s, Pa Gel at 10 min, Pa p H After rolling during

hot test, without shaking.

  Viscosity apparent, Pa / s x 103 13 Plastic viscosity, Pa / s x 10-3 14

Pour point, Pa -

  Gel at 10 s, Pa 0.96 Gel at 10 min, Pa 1.92 After cooling and mixing

on a Multimixer.

  Visible viscosity, Pa / sx 10-3 19.5 Plastic viscosity, Pa / sx 10-3 16 Pour point, Pa 3.36 Gel at 10 s, Pa 1.92 Gel at 10 min, Pa 2.88 p H 7.1 Filtrat API, ml 10.4 dense, soft Baroid sedimentation

1 _ 2 3

17.1 17.1

1.4 1.4

Initial properties

17.5 11.5 36

17 11 27

0.48 0.48 8.64

1.44 2.4

3.36 4.3

16 hours at 66 C 6O C

8 25

11 19

  6.72 0.96 2.4 for 5 minutes dc di

) 38

3 26

11.5 2.4 3.36

7.1 7.1

1.8 6.7

Teaching, None 1 (13:18.

Claims (13)

  A method for decreasing fluid loss of aqueous wellbore fluids, characterized in that   disperses in such a fluid an effective amount of a hydro-   crosslinked xylethyl starch and an effective amount of a   a polymer selected from carboxyalkyl cellulose ethers;   in which the alkyl group has from 1 to 3 carbon atoms   xanthan gum and mixtures thereof, the relative amounts of the hydroxyethyl starch and the polymer component being such as to provide a synergistic reduction of   the fluid loss of the aqueous fluid.   2 Process according to Claim 1, characterized in that the aqueous fluid comprises an aqueous solution of at least one water-soluble salt of a multivalent metal ion, in particular calcium chloride, calcium bromide, zinc chloride and bromide. zinc or a mixture of these salts.   3. Process according to claim 1 or 2, characterized   in that the aqueous medium has a higher specific gravity   at about 1,400 g / dm, preferably about 1,425 to 2,285 g / dm   Process according to any one of the claims   1 to 3, characterized in that the weight ratio of   the hydroxyethyl starch to the polymer component is included in   be about 10/90 and 90/10, preferably between about 33/67 and 75/25.   Process according to any one of Claims 1 to 4, characterized in that the hydroxyethyl starch is   activated before being dispersed in the aqueous fluid.   Process according to any one of the claims   1 to 5, characterized in that the polymer component comprises carboxymethyl cellulose which is activated prior to   to be dispersed in the aqueous fluid.   7 Composition for increasing the viscosity and reducing   the fluid loss of aqueous fluids for wells   characterized in that it comprises a mixture of an effective amount of a crosslinked hydroxyethyl starch and an effective amount of a polymeric component selected from the group consisting of   carboxyalkyl cellulose ethers in which the group   19. kyle has 1 to 3 carbon atoms, xanthan gum and   their mixtures, the relative amounts of hydroxyethyl a-   midon and the polymer constituent being such as to   a synergistic decrease in the fluid loss of said aqueous fluid.   8 Composition according to claim 7, characterized   in that the weight ratio of hydroxyethyl starch to polymer component is between about 10/90 and 90/10,   preferably between about 33/67 and 75/25.   9 Composition according to claim 7 or 8,   characterized in that the hydroxyethyl starch is activated.   Composition according to any one of the   7 to 9, characterized in that the polymer component comprises activated carboxymethyl cellulose before being   dispersed in said aqueous fluid.   A wellbore fluid, characterized in that it contains an aqueous medium, an effective amount of a crosslinked hydroxyethyl starch and an effective amount of a polymeric component selected from carboxyalkyl cellulose ethers wherein the alkyl group has 1 to 3 atoms   of carbon, xanthan gum and their mixtures, the amounts   relative quantities of hydroxyethyl starch and the constituent   polymer being such that they provide a   of the fluid loss of said aqueous medium.   12 Fluid according to claim 11, characterized in that said aqueous medium comprises a solution of at least one water-soluble salt of a multivalent metal ion, in particular calcium chloride, calcium bromide, zinc chloride, bromide and the like. zinc or a mixture of these salts.   13 Fluid according to claim 11 or 12, characterized   in that the aqueous medium has a specific gravity   less than about 1,400 g / dm 3, preferably about 1,425 g / dm 3 at 2,285 g / dm 3.   Fluid according to any one of the claims   11 to 13, characterized in that hydroxyethyl starch is activated.   Fluid according to any one of the claims   11 to 14, characterized in that said poly- 20.   mother comprises activated carboxymethyl cellulose.   16 Fluid according to any one of the claims   11 to 15, characterized in that the weight ratio of   the hydroxyethyl starch to the polymer component is included in   be about 10/90 and 90/10, preferably between about 33/67 and 75/25.