CA1188878A - Aqueous well drilling fluids - Google Patents

Abstract

Abstract of the Disclosure A method and composition for decreasing the fluid loss of aqueous well servicing fluids in which an additive comprised of a cross-linked hydroxyethyl starch and a polymeric com-ponent such as a carboxyalkyl cellulose ethers or xanthan gum is added, in effective amounts, to the aqueous fluid, the aqueous fluid preferably being one which contains at least one water soluble salt of a multi-valent metal ion.

Description

71~

Background of the Invention The present invention relates to a method and comp~sition for increasing the viscosity and reducing the fluid loss of aqueous systems used as well servicing fluids.
Aqueous mediums9 particularly those containing oil field brines, are commonly used as well servicing fluids such as drilliny fluidsr workover fluids~ completion fluids, packer fluids, well treatin~ fluids, subterranean formation treating fluids, spacer fluids, hole abandonment fluids, etc. .5uch well servicing fluias, if they are to be effec~ive and economically attractive, must exhibit low fluid loss. It is known to add to the well servicing fluid certain hydrophilic polymeric materials for fluid loss control. For exa~ple, it is known to use starch and cellulose products, e.g.corn starch and potato starch derivatives, as additives to well servicing fluids, e.g. brines, for fluid loss control.
Viscosity enhancement of aqueous well servicing fluids, e~g. brines, is also necessary in many applications. Again, starch and cellulose derivatives have been used to achieve such viscosity enhancement.
Examples of prior art which discloses various additives to well servicing fluids for viscosity enhancement and/or fiuid loss control include U.~O Patent 3,S25,889 which teaches a ~ell completion fluid consisting of aqueous calcium chloride, carboxymethyl cellulose (CMC~ and xanthan gum ~XC
polymer~, and U.S. Patent 3,953,336 which discloses mixtures of XC polymer with various cellulose derivatives such as h~droxyethyl cellulose, carboxymethyl cellulose, etc.

-- - .

S~mmary of the Invention It is, therefore, an object of the present invention to provide a new composition for synergistically increasing the viscosity and controlling the fluid loss of aq~eous well servicing fluids.
A further object of the present invention is to provide a new composition useful for synergistically increasing the viscosity and lowering the fluid loss of aq~eous brine solu~ions used as well servicing fluids.
S~ill a f~rther object of the present invention is to provide an improved method for decreasing the fluid loss of an aqueous well servicing fluid.
The above and other objects o the presentinvention will become apparent from the description given herein and the appended claims.
In accordance with one embodiment of the present invention, there is provided a method for decreasing the fluid loss of an aqueous well servicing fluid comprising adding and dispersing in the well serviciny fluid an effective amount of 20 a cross-linked hydroxyethyl starch (HES) and an effective amount of a material selected from the class consisting of carboxymethyl cellulose ethers, XC polymer and mixtures thereof~
In another embodiment of the present invention, there is provided a compositionuseful for increasing the viscosity and lowering the fluid loss of an aqueous medium comprised of an effective amount of a cross-linked hydroxyethyl starch and an effective amount of a material selected from the class con-sisting of carboxyalkyl cellulose ~thers, XC polymer and mixtures thereof.
In yet another embodiment of the present invention, there is provided a well servicing fluid comprised of an aqueous medium, an effective amount of a cross linked hydroxyethyl starch and an effective amount of a material ~elected from the class consisting of carboxyal~yl cellulose ethers, XC poly-mers and mixtures thereof.

.
.

8~dl~

Descri tion of the Preferred Embodiments P _ _ One of the polymeric components (Polymer ~) of the novel compositions of the present invention include a material selected from the class consisting of carboxyalkyl cellulose ethers wherein the alkyl group has from 1-3 carbon atoms such as carboxyme~hyl cellulose (CMC), carboxyethyl cellulose (CEC), etc.; xanthan gum (xanthomonas polysaccharide gum bio-polymer) known commonly as XC polymer; and mixtures thereof.
The term polymeric component is intended to include one or more of the carboxyalkyl cellulose ethers with or without XC
polymer. Of the above named polymers, the preferred polymers are XC polymer and carboxymethyl cellulose.
The XC polymers which are useful in the presen~ inven-tion, depending upon the method of preparation o the well servicing fluids, can either be in the form of a dry powder, essentially untreated, or can be an "activated" XC polymer.
The term "activated" as used herein refers to an XC polymer which will substantially hydrate or solubilize in a brine solution having a density greater than about 14.2 pounds per gallon (ppg~ without the necessity for mixing, as by rolling, at elevated temperatures. Examples of such activated XC
polymers are to be found in co-pending Canadian ~atent Application No. 374,309, filed March 31, 1981. As disclosed in the aforementioned patent application, XC polymers which have been activated will solubilize in brine solutions with-out the necessity for rolling or other forms of mixing at elevated temperatures. In general~ any XC polymer which will solubilize in a brine having a density in excess of about 14 2 ppg at room temperature can be considered an "activated"
XC polymer. It is to be understood, however, that the present invention is not limited to the use of such activated XC polymers. Depending upon the condition of mixing, and the composition of the aqueous well servicing fluid, unactivated or dry powder XC polymers are compatible with the aqueous well servicing fluids used in the present inventionO The term 'Icompatible" as used herein, means that the XC polymer can be solvated or solubilized in a given aqueous solution 7~

with the use of mixing techni.ques such as rolling ~t elevated temperatures. Thus, an incompatible system i5 one in which the XC polymer will not solubilize in the brine regardless of the mixing conditions usedO
The other polymeric component (Polymer B) of the composi-tions of the present invention is a cross-linked HES. Such hydroxethyl starches are produced by introduction of non-ionic hydroxyethyl side groups onto the polymer chain of the starch followed by cross linking techniques well known in the art such as, for example, those disclosed in U.S. Patents Nos.

2,500,950; 2~929,811; 2,989,521 and 3,014,901. Generally speaking, the cross-linked hydroxyethyl starches which are useful in the present invention are those in which the hydroxethyl side chain degree of substitution (DS) is from about 0.15 to about 0.8, preferably from about 0.25 to about 0.6. A particularly useful cross-linked hydroxethyl starch is known as BOHRAM~L C ~, a cross-linked potato starch derivative manuactued by Avebe (Veendam, Holland~. BOHRAMYL
CR, which is a coarse white flaky material, has a bulk density ~kg/m3) of approximately 325 and a DS of about 0O4~
The cross-linked H~S may be utilized either in the form of a dry powder or flake, essentially untreated, or can be an "activated" starch, wherein the term "activated" has the same meaning as used above wi~h respect to the discussion of activ-ated XC polymers~ Methods of activating the cross~linked ~ES are disclo~ed in Canadian Patent Application Serial No~
359,357, filed February 27, 1981. It i5 to be understood that the present invention is not limited to the use of activated HES. Indeed, it is a feature of the present invention that all of the polymer components can be used in dry form to pro-duce well servicing fluids which exhibit excellent rheological properties and low fluid loss. However, in certain brine solutions, activation or pre-solvation of the XC polymers and/or the hydroxyethyl starch may be desirable to reduce mixing times and severity of conditions of mixing.

17~

The polymer composition of the present invention which can be used to decrease fluid loss and increase the viscosity of aqueous well servicing fluids is comprised of an effective amount of cross-linked HES (Polymer B) and an effective amount S of XC polymex, a carboxyalkyl cellulose ether (CACE) polymer or mixtures ~ereof (Polymer A). It has been found that when either XC polymer~ a CACE polymer or a mixture thereof are added to aqueous well servicing fluids together with HES, depending upon the nature of the fluid, synergistic enhance-ment of viscosi~y and/or fluid loss control is achieved. Thepartioular amount of each of the polymeric oomponents present in the additive composition will vary depending upon the nature and composition of the aqueous well servicing fluid wi~h which the additive is to be admixed. In general, the polymer composition of the present invention will contain a weight ratio of E1ES ~Polymer ~) to XC polymer, CACE polymer or mixtures thereof (Polymer A) o~ from about 10 to 90 to about 90 to 10, preferably from about 33 to 67 to about 75 to 25. The polymeric composition of the present invention can be either in the form of a dry mixture of the HES and either the XC
polymer, CACE polymer or mixtures thereof or~ if preferred, it can be in the form of solvated or activated forms of the polymers. Thus, for example, the HES and the XC poly~er can be activated and those activated solutions mixed together to provide the novel polymeric compositions used herein.
The novel well servicin~ fluid of the present invention comprises an aqueous medium and an effective amountof a cross-linked hydroxyethyl starch and an effective amount of XC
polymer, CACE polymers or mixtures thereof. The relative amount~ of ~he HES and the other polymeric component (Polymer A) admixed with the aqueous medium is such as to provide a synergistic decrease in the fluid loss of the aqueous medium.
Again, the precise amount of each of the polymeric components used will depend upon the nature of the aqueous well servicing fluid.
In general, however, the weight ratio of the HES to the other polymer component in the well servicing 1uid will be from about 10 to 90 to about 90 to 10, more preferably from about 33 to 67 to about 75 to 25.
In yeneral, the well servicing fluids will contain the polymer components in amounts of from about 0.5 to aboutlDppb hy~roxyethyl starch (Polymer B) and from ab~ut 0.25 to about 5- 5 ppb of the other polymeric component (Polymer A).
The aqueous medium used in the well servicing fluids of the presen~ invention can range from fresh water to heavy brines havin~ a density in excess of 19 ppg. Generally speaking, well servicing fluids as, for example, those used in completion and workover operationsl are made from aqueous mediums containing soluble salts such as, for example, a soluble salt of an alkali metal,an ~kaline earth metal, a Group Ib metal, a Group IIb metal, as well as water soluble salts of ammonia and other cations. The polymeric zompositions are particularly useful in the preparation of low fluid loss, heavy brines, i.e. aqueous solutions of soluble salts of multi-valent ions, e.g. Zn and Ca.
The preferred heavy brines useful in forming the well servicing fluids of the present invention are those having a density greater than about 11 ppg, especially those having a density greater than 15 ppg. Such heavy brines are comprised of water solutions of salts selected from the group consisting of calcium chloride, calcium bromide, zinc chloride, inc bromide, and mixtures thereo.
If desired, bridging agents may be added to the well servicing fluids ~o aid in fluid loss control. Indeed, somewhat lower filtrates are obtained with their use. ~ow-ever, it is a distinct and unexpected feature of the invention that a bridging agent is not necessary to achieve low fluid loss values in aqueous brines. Thus, using the present invention, it i~ possible to obtain clear bxines having low fluid loss characteristics and low rheological character-istics.
~o more fully illustrate the present invention, the following non-limiting examples are presented. Unless other--~ise indicated, all physical property measurements were made in accordance with testing procedures set forth in STANDARD
PROCEDURE FOR TESTING DRILLING MUD API RP 1 3B, Seventh .

Edition, April, 1978. The cross-linked hydroxyethyl starch employed, unless o~herwise indicated, was BOHRAMYL CR
marketed by Avebe (Veendam, Holland)~

. Example 1 ~ To show the synergistic effect on viscosity and fluid loss achieved by mixing HES and XC polymer, one lb. per barrel (ppb) of XC polymer at either 0 or 6 ppb levels of BOHRAMYL CR
were added to an aqueous 10~ by weight Na Cl solution and mixed for 25 minutes on a Multimixer. Thereafter~ the samples were rolled at 150Ft cooled to 74F and stirred for 5 minutes and the API rheology and fluid loss determined. The data obtained and given in Table I below show that the BOHRAMYL CR when admixed with the XC polymer synergistically decreased the fluid loss in the aqueous sodium chloride solution and increased the viscosit~.

~ 9~ 7~ :

_~ ~o o , ,, -o ~ ..
O

O ~ z Lll U~ O O
o ~

~:
r~ ~1 ~ ~ O ~~ ~ ~ O~ 0 ~ Z~ ~ ~ u~
o ~ ,, ~ ,,~
~o c~ a7 ~ ,,, u~
:~
~ ~1 ~D O Ul ~ ~ ~i O ~ Ul C~ ~ I
~ a3 ~ ~ ~1 _4 . ~
~O ~ O 9 ~ ~
~:1~ o ~o o u~ ~ u~ u~ ~O ~ ~ ~
~ep ~ u~ ~

~1 ~D O U~ ~ O O In a~ ~ a~
~ ~ c ~
o ~ -~
c~ ~o o u~ In ~
O. ~ ~ ~ u~ _~ ~ 0 ~
~ ~ O I I ~ LO ~ ~ C~l er ~ ~ O
-~ o ~ ~O ~ ~ ~ ~
~, o ~ 8 o ~ ~
L~ ~ U a) ~
YC C ~ -c o ~
~1 0 ~ 4 ~ ~ 1 O ~ n5 al H ~ J H
- u~ x m a c~

Example 2 The procedure of Example 1 was followed with the exception that carboxymethyl cellulose (CMC) was employed rather than XC polymer. The results, given in Table II, clearly show that the combination of cross-linked hydroxy-- ethyl starch and the CMC polymer gives synergistic results both as to fluid loss and viscosity.

~ It ~ 7~

~ _~ ~o o ~ ~ o u~ ~ o ' ,~
0 ~ ~ . . o ~ . . U~
O C~ ~ ~ ~ ~ ~ ~1 ,~ o ~o o o ~ ~ ~
co Z co Z ~ r Z
o a~w ~ O
~r ~ _t co ,4 o ~ O~

~o ~ O ~ a3 u~ ~ o ~ a~
Z ~ ~ ,~ ~ _t ~ .~
1 L~
Cl ~ ~ r-~ ~ o u~ ~ ~ O u~ ,~ O ~ I O u~ O r~
~ o ~ C ~
~ ~-~ ~r ~D ~r ~ u~ u~

~' E~ ~ ~ ~ Lf) .
O ~ N r~ '' O
C~l O ~O O U~ Lr~ U~ ~1 0 ~ ~r ~ -CO ~ ~ O ~ ~
. ~ ~ . ~ ~ C~
O
,~ o I I a~ o~
~ ~ t--J-~1 .

~.) r--l O O O
1 3 ~i O
8o -' " o u~ ,, U~ o tr; ~ ~ut ~ ~ ~ Ul V J Z
Ll c,~ C 0 ~
JJ ~ O ~ J- ~ O
C U P~ ~I C U ~ r~
Q` ~ l 1'1 F52 ~ ~ 0 ~ ~ ~ a ~

It should be noted with regard to the data shown in Tables I and II that the crosslinked H~S gives signifi-cantly better results than non-crosslinked material.

Example 3 To test the effectiveness of the polymeric composi-tions of the present invention on weighted drilling fluids, various amounts of BOHRAMYL CR and XC polymer were added to a 12 lb./gal.sodium chloride solution weighted with BAROI ~ (Trade mark of a bartyte weighting material marketed by NL Baroid, Houston, Texas). The BOHRAMYL C~
was first added to the sodium chloride solution and mixed with a Multimixer for 10 minutes. This was followed by the addition of the XC polymer and the mixing continued for 10 minutes after which the B~ROID was added and further mixing continued on the Multimixer for an additional 10 minutes. API rheology and fluid loss measurements were obtained on ~he thus prepared drilling fluid. The fluid was rolled for 16 hours at 150F and the rheological and fluid 105s properties tested. Thereafter, ~he samples were cooled and stirred for 5 minutes and the properties again determined. The data obtained and given in Table III below show that the XC polymer, when combined with the BOHRAMYL CR, synergistically decreases the fluid loss and increases the viscosity in weighted drilling fluids. It was also noted that there was essentially no settling out of weighting material.

~' 7~

T A ~ L E I I I
-Sample I'lark _ 2 MATERIA~, lb/bbl BOHRAMYL CR, 6 6 XC Polymer, O . 25 , 25 B~ID 200 200 200 PR~PER~ S AE~ MULTIMIXI:N(; BOHRAMYL CR 10 MIN, ~DDING
POI.YMER, MIXING 10 MIN., P,DDING BAROID, MIXING 10 MIN.
AE~parent Viscosity, cp. 16.0 23.0 7.0 Plastic Viscosity, cp. 15.û 19.0 7.0 Yield Point, lb/100 sq.ft. 2.0 B.0 0.0 10 Sec. (~el. lb/100 sq.ft. 5.0 5.0 0.0 10 Min~ Gel. lb/100 s~.ft. 14.0 7.0 6.0 p~ 8.2 8.1 8.1 Filtrate Loss, API, ml 11.5 8.8 57.4 PRf)PEE~ T~ POLIING 16 HR AT 150C~F., I~STED H~r A~parent Vis~sity, ~p. 13.S 17.0 5.5 Plastic Viscosi~, cp. 13.0 14.0 5.0 Yield Point, lb/100 sq.ft. 1.0 6.0 1.0 10 Sec. Gel. lb/100 sq.ft. 8.0 3.0 1.0 10 Min. Gel. lb/100 sq.ft.:L4.0 11.0 15.0 PR~:)~ES ~< CO~LING P~D STIRR~dG 5 MIN. MULTIMIXER
~parent Viscosity, cp. 17.5 24.5 ~.5 Plastic Viscosity, cp. 17~.0 21.0 6.0 Yield Point, lb/100 sq.ft. 1.0 7.0 1.0 10 Sec. Gel. lb/lû0 ~. ft. 3.û 2.0 3~0 10 Min. Gel. lb/100 s~.ft. 5.0 6.0 0.0 p~ 7~ 7.~ 7.6 Filtra~e Loss, API, ml 6.6 5.8 266 Settling of BAP~ID med.light hvy ,:, - . -,.- : ~

Example ~
To test the effectiveness of the polymeric compositions of the present invention of viscosity enhancement and fl~id loss control in heavy brines, e.g. brines containing calci~m chloride~ various amounts of HES and XC polymer were added to an aqueous, 5~ calcium chloride solution and mi~ed for 20 ~ minutes on a Multimixer and the API rheological properties determined (Initial Properties). Thereafter, the samples were rolled for 16 hours at 150F, tested hot and unstirred.
The samples were cooled, stirred 5 minutes on a Multimixer and the API rheology and fluid loss determined~ The data obtained and given in Table IV below show that, when the BOHRAMYL CR and X~ polymers are combined, they synergistically decrease the fluid loss in the aqueous calcium chloride solution and increase the viscosity.

. . . .

T A B L E I V

Sample Mark 1 2 3 4 5 6 BOHRh~iYL CR, ppb 9 6 5.4 5 0 0 P~lymer, ppb 0 0 D.6 1 1 1.5 INITIAL PROPERTIES
-Appar~nt Viscosity, cp. 25.5 1025.5 27.5 13 14.5 Plastic Viscosity, cp. 19 8 21 15 12 10 Yield Point, lb/100 sq. ft. 13 4 9 25 2 9 10 Sec. Gel. lb/100 sq. ft. 1 2 5 7 2 4 10 Min. Gel. lb/100 sq. ft. 1 2 5 9 4 6 p~ 7_3 7.4 7.5 7O4 7.~ 7.4 AFTER ROLLING 16 HR AT 150F TESTED HOT, UNSTIRRED
~ : .
Apparent Viscosity, ep. 11 4.5 13 16.5 4.5 9 Plastic Viscosity, cp. 8 4 ~ 7 3 4 Yield Point, lb/100 sq. ft. 6 1 10 19 3 10 10 Sec. G~l. lb/100 sq. ft. 0 1 2 4 0 s 10 Min. Gel. lb/100 sq. ft. 0 1 3 5 0 2 Apparent Viscosity~ cp. 29 1121.5 26 7 12 Plastic Viscosity, cp~ 20 9 12 12 4 6 Yield Point, lb/100 s~. f~. 18 4 13 28 6 12 10 Sec. Gel. lb/100 sq. ft. ~ 1 5 7 0 10 Min. Gel. lb/100 sq. ft. 2 1 5 8 0 5 pH 7.~ 7~4 6.8 6.7 5.6 5.6 ~PI Filtrate, ml 6.7 9.0 7.3 7.1 226 194 7~3 .

Example 5 The procedure o~ Example 4 was followed except that following addition of the polymeric material to the calci~m chloride solution, the equivalent of 25 ppb of Glen Rose shale was added and the compositions mixed for five minutes. Fol-lowing this, the eq~ivalent of 200 ppb of BAROID was added to ~ the compositions and mixing on the Multimixer continued for an additional five minutes. The initial properties of th~
samples were then determined~ The samples were rolled for 16 hours at 150F and tested hot and unstirred. The samples were then cooled, mixed an addi~ional five minutes on a Multimixer, and the API rheological and fluid loss properties determined.
The data, given in Table V below, show that even in the presence of a weighting agent and a shale such as would be encountered in borehole drilling, there is synergistic en-hancement of viscosity and control of fluid loss using a mixture of the BOHRAMYL CR and XC polymer. Additionally, solids settling is much lower in the case where a mixture of the polymers i5 utilized~

T A B L E V

Sample Mark I 2 3 4 5 6 BOHRAMYL CR, ppb 9 6 5 . 4 5 0 O
XC Polymer, ppb 0 0 û . 6 1 . 1 1. 5 Glen Rose shale, ppb 25 25 25 25 25 25 BAROID, ppb 200 200 200 200 200200 INITIAL PROPERTIES
Apparent ~Tiscosity, cp. 51 24 46.5 49.5 lG 24 Plastic Viscosity, cpO 31 2û 33 18 12 15 ~ield Point, lb/100 sq. ft. 40 8 27 53 8 18 10 Sec. Gel. lb/100 sq. ft. 20 7 10 15 3 6 10 Min. ;Gel. lb/100 sq. ft. 27 12 15 19 5 7 A~TEP~ ROLLING 16 BR AT 150F TESTED HOT, UNSTIRRED
Appar~nt Viscosity, cp. 35 . 5 15 36 3513 . 5 21 Plastic Viscosity, cp. 27 14 30 21 14 lÇ
Yield Point, lb/100 sq. ft. 17 2 12 28 0 11 10 SecO Gel. lbJ100 sq. ft. g 4 7 6 10 Min. Gel. lb/10û sq. f~. 12 5 8 9 1 5 Apparent Viscosity, c:p. 50.5 23.5 45.5 46 16 24 Plastic Viscosity, cp. 34 18 33 26 14 16 Yield Point, lb/100 sq. ft. 33 11 25 40 4 6 lû Sec. Gel. lb/100 sq. ft. 10 6 10 12 0 4 10 Min. Gel. lb/100 sq. ft. 21 12 14 16 0 S
pH 7.17.2 7.. 0 7.0 7q0 7.0 API ~iltrate, ml 3.6B.2 7.9 7.6 ~2.120.8 Settling c~f BAROID ~ea~fT~ }Iea E~ I,igh~ None Ligh~ Lighl:

ltrace to light; 21ight to moderate ... . . ..
, . . .. . . . . .. . . . . - . . .

Example 6 In this Example the effectiveness of the polymeric com-positions of the present invention on weighted drilling fi~ids employing heavy brines, various amounts of BOHRAMYL CR and XC
polymer were added to a 5% calci~m chloride solution weighted with the eq~ivalent of 200 pounds per barrel of BAROID was tested. The BOHRAMYL CR was first added to the calci~m chloride solution and mixed with a M~ltimixer for 10 minutes.
This was followed by the addition of the XC polymer and continued mixing for 10 minutes after which the BAROID was added and further mixing on the Multimixer continued for an additional 5 minutes. API rheology measurements (Initial Properties) were obtained on the thus prepared drilling fluid.
The fluid was then rolled for 16 hours at 150F and the rheological properties of the hot, unstirred drilling fluid obtained. Thereafter, the samples were cooled and stirred for five minutes and the rheological and fluid loss properties again determined. The data obtained and given in Table VI
below shows the XC polymer, when combined with the BOHRAMYL CR, synergistically decrease the fluid loss and while increasing the viscosity in weighted drilling fluids. It should also be noted that when BOHRAM~L CR and XC polymer are combined, there is essentially no settling out of the BAROID weighting mate-rial.

.. .. .
..

T A B L E V I

Sarnple Mark 1 2 3 Bo~ rL CR, ppb 6 6 XC Po.lymer, ppb Glen Rose Shale, pp~ 25 25 25 BAROID, ppb 200 2D0 200 Apparent Viscosity, cp.24 56 16 Plastic Viscosity, cp. 20 23 12 Yield Point, lb/100sq. ft. 8 59 8 10 Sec. (;el. 13:~/100 sq. ft. 7 18 3 10 Nin. Gel. lb/100sq. ft. 12 - 25 5 pH 7.1 7.2 7.1 AFT R ROLLING 16 HR A 150F TE~TED HOT, UNSTIRRED
Apparent Viscosity, cp. 15 46 13 O 5 Plastic Viscosity, cp.14 22 14 Yield Point, lb/100 sq.ft. 2 47 0 10 Sec. Gel. lb/100 sq.ft. 4 12 10 Min. Gel. lb/100 sq.:Et. 5 14 AFTER COOLIN(; AND MIXING 5 MIN ON A MULTIMIXER
Apparent Viscosity, cp. 23.5 60 . 16 Plastic Viscosity, cp.18 32 14 Yield Point, lb/100 sq~:Et. 11 56 4 10 Sec. Gel. lb/100 sq.ft. 6 18 10 Min. Gel. lb/100 sq.ft. 12 24 0 pH 7.2 7.0 7.0 API Filtrate, ml 8 . 2 5 . 0 32 .1 Setting of Solids Heavy None Light to Moderate So~t Scf t . ...
.. , .. . . ~ . . .

:~&~

.

Example 7 The procedure of Example 4 was followed using differing amo~nts of BOHRAMYL CR and XC polymer. The data, given in Table VII below, clearly show the synergistic effect on viscosity and fluid loss control using a mixture of BOHRA~'YL
CR and XC polymers.

T A B :L E_ V I I

Sample Mark _ 2 3 BOHRAMYL CR, ppb 6 6 XC Polymer, ppb INITIAL PROPERTIES
Apparent Viscosity, cp. 10 30.5 13 Plastic Viscosity, cp. 8 16 12 Yield Point, lb/100 sq. ft. 4 29 2 10 Sec~ Gel. lb/100 sq. ft. 2 8 2 10 ~in. Gel. lb/100 sq. ft. 2 9 4 pH 7.4 8.0 7.4 AFTER ROLLING 16 HR AT 150F TESTED HOT,_ UNSTIRRED
Apparent Viscosi~, cp. 4.5 19 4.5 Plastic Viscosity, cp. 4 10 3 Yield Point, lb/100 sq. ft. 1 18 2 10 Sec. Gel. lb/100 sq. ft. 1 2 0 10 Min. Gel. lb/100 sq. ft. 1 3 0 AFTER COOLING ~ND MIXING 5 MIN ON A MULTIMIXER
~pparent Viscosity, cp. 11 30.5 7 Plastic Viscosity, cp. 9 15 Yield Point, lb/100 sq. ft. 4 31 6 10 ~ec. Gel. lb/100 sq. ft. 1 7 0 10 Min. Gel. lbjlO0 sq. ft. 1 8 0 pH 7.4 7.0 5.6 API Filtrate, ml 9.0 6.5 226 Example 8 The procedure of Example 6 was followed except differing amounts of XC polymer were employed and the eq~ivalent of 200 ppb of BAROID was added to the samples after addition of the polymers, the samples being mixed for five minutes on a Multimixer. The samples were then rolled for 16 hours at 150F
and the API rheology determined (Initial Properties). The samples were then cooled, mixed five minutes on a Multimixer and the API rheological and fluid loss properties determined.
~he data, given in Table VIII belowl again demonstrate the dramatic, synergistic effect achieved on viscosity and fluid loss control using a mixture of the polymers. As can also be seen from the data in Table VIII, no settling out of the weighting agent, BAROID, occurs using a mixture of the poly-mers.

- - . , , ~ . ., T A B L E V I I I

SamE~le Mark 1 2 3 BO~ARAMYL CR, pp~ 6 0 6 XC Polymer, ppb O O. 5 O. 5 INITIAL PROPERTIES
Appa~ent Viscosity, cp.17.5 11.5 36 Plastic Viscosity, cp17 11 27 Yield Point, lb/100 sq. ft. 1 1 18 10 Sec. Gel. lb/100 sq. ft. 3 0 5 10 Min. GelO lb/100 sq. ft. 7 0 9 pH
AFTER ROLLING 16 HR AT 150F TESTED HOT, UNSTIRRED
_ _ Apparent Viscosity, cp.13 8 25 Plastic Viscosity, cp.14 11 19 Yield Point, lb/100 5q. ft. 0 0 12 10 Sec. Gel. lb/100 sq. ft. 2 0 2 10 Min. Gel. lb/100 sq. ft. ~ 0 5 Apparent Viscssity, cp.19.5 10 38 Plastic Viscosity, cp.16 13 26 Yield Point, lb/100 sq. ft. 7 0 24 10 Sec. Gel. lb/100 sq. ft. 4 0 5 10 Min~ Gel. lb/100 sq. ft. Ç 0 7 pH 7.1 7.0 7.1 API Filtrate, ml10.461.8 6.7 Settling of BAROIDHeavy~eavy None SoftHard -2~-It should be noted with regard to the data shown in Tables I and II that the crosslinked HES gives significantly better res~lts than non-crosslinked material.
The invention may be embodied in other specific forms without departing from the spirit or essential character-istics thereof. ~he present embodiments are therefore to be considered in all respects as illustrative and not restric-tive, ~he scope ~f the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalence of the claims are therefore intended to be embraced therein.

j, . . .

Claims (26)

I claim:

1. A method of decreasing the fluid loss of aqueous well servicing fluids comprising dispersing in said fluid an effective amount of a cross-linked hydroxyethyl starch and an effective amount of a polymeric component selected from the class consisting of carboxyalkyl cellulose ethers wherein the alkyl group has from 1 to 3 carbon atoms, xanthan gum and mixtures thereof, the relative amounts of said hydroxyethyl starch and said polymeric component being such as to syner-gistically decrease the fluid loss of said aqueous fluid.

2. The method of Claim 1 wherein said aqueous fluid comprises an aqueous solution of at least one water soluble salt of a multi-valent metal ion.

3. The method of Claim 1 wherein said aqueous medium has a density greater than about 11.7 pounds per gallon.

4. The method of Claim 2 wherein said water soluble salt is selected from the group consisting of calcium chloride, calcium bromide, zinc chloride, zinc bromide, and mixtures thereof.

5. The method of Claim 2 wherein the density of said aqueous brine is from about 12.0 pounds per gallon to about 19.2 pounds per gallon.

6. The method of Claim 1 wherein the weight ratio of said hydroxyethyl starch to said polymeric component is from about 10 to 90 to about 90 to 10.

7. The method of Claim 6 wherein said weight ratio is from about 33 to 67 to about 75 to 25.

8. The method of Claim 1 wherein said hydroxyethyl starch is activated prior to being dispersed in said aqueous fluid.

9. The method of Claim B wherein said polymeric component comprises carboxymethyl cellulose which is activated prior to being dispersed in said aqueous fluid.

10. The method of Claim 8 wherein said polymeric com-ponent comprises xanthan gum.

11. A composition for increasing the viscosity and decreasing the fluid loss of aqueous well servicing fluids comprising a mixture of an effective cross-linked hydroxy-ethyl starch and an effective amount of a polymeric component selected from the class consisting of carboxyalkly cellulose ethers wherein the alkyl group has from 1 to 3 carbon atoms, xanthan gum and mixtures thereof, the relative amounts of said hydroxyethyl starch and said polymeric components being such as to synergistically decrease the fluid loss from said aqueous fluid.

12. The composition of Claim 11 wherein the weight ratio of said hydroxyethyl starch to said polymeric component is from about 10 to 90 to about 90 to 10.

13. The composition of Claim 12 wherein said ratio is from about 33 to 67 to about 75 to 25.

14. The composition of Claim 11 wherein said hydroxy-ethyl starch is activated.

15. The composition of Claim 14 wherein said polymeric component comprises carboxymethyl cellulose which is activated prior to being dispersed in said aqueous fluid.

16. The composition of Claim 14 wherein said polymeric component comprises xanthan gum.

17. A well servicing fluid comprising:
an aqueous medium; and an effective amount of a cross-linked hydroxyethyl starch and an effective amount of a polymeric component selected from the class consisting of carboxyalkyl cellulose ethers wherein the alkly group has from 1 to 3 carbon atoms, xanthan gum and mixtures thereof, the relative amounts of said hydroxyethyl starch and said polymeric component being such as to synergistically decrease the fluid loss of said aqueous medium.

18. The composition of Claim 17 wherein said aqueous medium comprises a solution of at least one water soluble salt of a multi-valent metal ion.

19. The composition of Claim 17 wherein said aqueous medium has a density greater than about 11.7 pounds per gallon.

20. The composition of Claim 18 wherein said water soluble salt is selected from the group consisting of calcium chloride, calcium bromide, zinc chloride, zinc bromide, and mixtures thereof.

21. The composition of Claim 18 wherein the density of said aqueous medium is from about 12.0 pounds per gallon to about 19.2 pounds per gallon.

22. The composition of Claim 17 wherein said hydroxy-ethyl starch is activated.

23. The composition of Claim 22 wherein said polymeric component is activated carboxymethyl cellulose.

24. The composition of Claim 22 wherein said polymeric component comprises xanthan gum.

25. The composition of Claim 17 wherein the weight ratio of said hydroxyethyl starch to said polymeric component is from about 10 to 90 to about 90 to 10.

26. The composition of Claim 25 wherein said ratio is from about 33 to 67 to about 75 to 25.