CA1324127C - Welan gum in cement compositions - Google Patents

Abstract

TITLE OF THE INVENTION
WELAN GUM IN CEMENT COMPOSITIONS
ABSTRACT OF THE INVENTION
Cement compositions, i.e., mortar, structured concrete, pre-cast concrete, and oilfield cement, comprising 0.01-0.9% (wt/wt) welan gum are described.
The cement compositions exhibit improved workability, suspension of aggregates, air entrainment, sag resistance, flow characteristics and resistance to water loss. These improvements are maintained at elevated temperature.

Description

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X-2088~
(~ I . , TITLE O~ THE INVENTION
ELAN GUM IN CEMENT COMPOSITIONS
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., ~,0 ': ' BACKGROUND OF THE_INVENTION
Concretes and m~rtars are cement c~mpositions ad~i~ionally contain;ng aggregate (e.g., ( sand and rock) and water. When water is added to the :~
¦ : ~5 cement, this ~orms a paste which ~hen hardens to a solid structure. Various additives h~v8 been used in : ~hese cement compositions to modify their properties ~or specialized applications. Thus, long fibers such as asbes~os reduce the sagging of these pastes and ~hus is beneiclal w~i~n applying:tiles to a vertical : surace. Freezing point depressants are used when ; cements are to b~ poured in ~ubfreezing temperatures.
Cellulosic pol~mers have been used in cements to :~ control sedimentation o particles in the pastes.

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Bentonite clay has been used for this purpose. Other polymers, such as the polyvinyl alcohols ~nd methyl methacrylates, have been used ~o reduce friction when pumping ~hese pastes and to o~herwise modify ~heir workability. Fumed silica is used as an ~dditive to make stronger concrete with redu~ed permeabil;ty.
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. 10 SUMMARY OF THE INVENTIO~
It has now been found that cement ( comp~si~ions comprising 0.01 to 0.9% welan gum by weight of dry cement exhibit improved workability, suspension of aggregates, air entrai~ment, sag 15 resistance, flow characteristics, and resistance ~o water loss. Furthermore, these improvements are retained at slevated temperatu,res (i.e., greater than 93C). Preferably the range oE welan gum is 0.1 -0.5%.

: DETRILED DESCRIPTION
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By cement compositions is meant hydraulic f cements, i.e., finely ground and calcined calcium silicates and calcium aluminates which when mix~d 25 with water react ~o form a hard, rock-like mass. By ~ :
i cement, as used herein, therefore, is mean~ numerous ~,~ well known cement compositions, such as. portland : cement, portland pozzolan cement ~conta;ning about 15-40% poz201an) bl~s~ furnace slag cemen~, slag 3~ cemen~ ~containing blast furnace slag and hydrated ~`! lim0), masonry cement (e.g., adhesive mortar~
¦ construction co~crete (containing sand and aggregate , ¦ oil-w~ll cement ~i.e., cements with retarders to : prevent rap;d setting so that they may be used at ~ .

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high temperatures and pressure environments of deep wells~, aluminous cement (containing high amounts of calcium aluminates, expansive ~ements (containing high sulfate and alumina concentrations and whîch .~.
expand on hardening), air en~rained cement (cuntaining compound which re~ain air bubbles an~ ~hus yiQld frost- and chemical-resistant concrPtes~, ligh~weigh~
concrete (containi~g low density materials such ~s furnace clinker, pumice, foamed slag, fly ash, gas, wood, etc.) heavy concrete (containing d~nse~ materiaI
j such as barite, iron ore (i.e., illmenite or ~ hematit~), steel, etc.), and low heat concrete (with ! 15 modified compositions that minimize heat generation ¦ during the setting process).
i With respect to oilfileld cements, it is ~ desir2ble, while drilling a su'bterranean well, to ! line ~he ~urface of the hole wi~h hollow pipe known 29 as casing. The casing is held in place by attaching the casing to borehole wall with a cement ~lurry.
The cement slurry is put in place by pumpi~g the slurry down the inside of ~he casing to the bottom of the hole and up ~h~ annulus between ~he casing and ~orehole wall. The cement is ~hen allowed to set for : several hours to gain strength : :
bef ore any other operation are commenced.

The purpose of primary cementing is~
: 30 1. To add suppor~ for the casing by physical bracing -~
~: or pre~ention of formation pressure being imposed on the casing. ~

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2. To allow segrega~ion of individual formations behind the pipe so that fluids from one formation .i 5 cannot flow into another. This allows production , from a speciic zone.

i 3. To retard corrosion by minimizing contact between the casing and corrosion formation waters.

Oilfield cements are basically the same ~s those us~d in constructions (i.e., portland cement~.
The ~nerican Pe~roleum Institu~e has set specifica-ions for oilfield cements. These as classified as i 15 "A" through "H", "J" and "N", all of which are useful ~ in ~he compositions o this inlrention.
j Cement additives in o:ilfield cements are materials mixed in the slurry ~Eor one or more of the following purposes:

1. Reducillg or increas}ng den~sity;
2. Increasing volume at reduced unit cost;
~, s 3. Accelerating or r~tarding ~slurry thicXening time;
4. ~ncreasing strength;
S. Pr~ventin~ loss of whole cernent slurry;
6. Increasing or improving the durability;
7. Decreasi~ wa~er los~ rom the slurry; :~
8~ Increasing or decreasing the viscosi~y of the cement slurry.
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The water loss of a "neat" cement slurry - .
(cement and water only~ is very high and rapid. When a slurLy contacts a porous ormation rock (such as an ~ oil ~earing sandst~ne) it may becom~ ~uickly -~:
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dehydrated by the water filtering in~o ~he formation.
This causes the cemen~ to "flash set." This may cause ~he casing to s~ick to the borehole before all the slurry is pumped in the annulus or before the casing is in the proper position.
Ben~onite in concentra~ions of 0-14%
(wt./wt. of dry cement) is used to control the wat~r loss from the slurry. Carboxymethylhydroxyethyl cellulose (CM HEC~ and hydroxyethyl cellulose (HEC), cellulosic polymers, are used at levels fro~ 0.2 to 9 .9%. - ' -It is an object of ~his invention to use 15 welan gum for controlling water loss frorn cemen~ :
slurries at gum concentrations of 0.01-0.9% (wt.~, :
preferably 0.1-0.5%. Welan gum Calso known as S~130) is a heteropolysaccharide described in U.S. Patent 4,342,~66. Thus, an embodiment; of this invention is 2~ a process f~r controlling water loss from cemen~ ~ .
slurries which comprises incorporating into said sluxries 0.01-0.9% (pref~rably, 0.1-O.S) welan yum, ba~ed on dry weight. In a preferred embodiment o f this invention, the slurry temperature is in the rang~ 93-127C, Welan gum does not have the effect of - lowering the slurry density and increasing ~he water ::-: required as does bentonite. The cellulosic polymers ~
~: ~ are ~trong retarders and require dispersants. The ~: 3Q cell~losics lose their effectiveness for controlling wa~er loss as the temperature increase~ and ar~ almos nonfunctional above 93~C. Welan gum does not require ::
: a dispersan~ and shows good funtionality up to 127C -.
~ at a lower concentration than cellulosic polymers.

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1 32~ 1 27 It is a further object of this invention to use welan gum as a suspending agent for cement slurries. Although welan gum has been described in U.S. Patent ~,342,866 to be an excellent viscosifier and suspending agen~ in ayueous brines, i~ was unexpected that the polym~r would be compatible with and incrQase the suspension properties of cement lU slurries. Many other commercially available polymer~ :-are not compatible orlfunctional in cement slurrie The compatibility andlsuspe~sion properties o~ welan gum are advantageous in several oilfield and industrial applications. For example, welan gum increases the workability of c~ment compositions, i.e., it improves the ability of cement slurri~s to be easily placed in crowded areas such as around re-inforcing bars without ag~regate settling. Under such conditions a stiff or "dry~" concrete slurry would be extremely difficult to position but a more mobile .
"wet" slurry would produce a weak concrete and would allow settling of aggregate. :~
f Thus, ~nother ernbodiment of this invention is a process for improving the suspension of cement 25 slurri~s which comprises incorporating ther~in 0.01-0.9% ~preferably, 0.1 0.5) welan gum, based on dry weight of cemen~. In ia preferred embodiment of this invention the slurry temperature is 93-127~C.
In these applications the use of an addi~ive or admixture d;spersing (or plasticizing~ the cement slurry is corunonly used. Th~ dispersant lowers the viscosi~y of the slurry so that handling, purnping, or :
other posltiorling of the slurry i8 made possible.
OncQ th~ slurry is dispersed and the viscosity 1 32~ 1 27 ~ 6266P/5372P - 7 - X-2088IA
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lowered, settling of the cement particles begins and ~, separation of ~he water from the slurry toward the 1 5 surface is greatly accel~ra~ed. The use of welan gum '., controls separation in these dispersed cement composi~ions. The concen~ration of dispers~n~ ~or plasticizer~ may vary greatly depending on the slurry formulation, additive used, and p~rcent water needed 3 lo in the application. In general, the dispersant -~l concentration is between 0.1 and 1.5% based on the weight of dry cement in the slurry.
Another embodimen~ of this inven~ion is ~ ~:
cement slurry comprising 0.1 to 1.5% dispersant and ~ 15 0,01 0.9% (preferably, 0.1-O.S~ welan gum, both based J on dry weight of cement.
.,~ Cement slurries contai.ning welan gum show more uniform density as the cur-inq process proceeds.
The suspension properties of welan gum keeps the 20 slurry more uniform, yielding ~.ess aggragate settlinq .
and less free water o~ the sur~ace of the slurry.
Since welan gum is an excel~ent cement :.
. suspension aid, it can be used to suspend liquid 1 mix~ures ~hat are subseguently added to cement slurries. For example, fumed silica, a white 1uffy powder containing almost 100% amorphous silicon dioxid~ is a concrete additive used to produce high strength, low permeability concre~e. ~ecause of its extremely low bulk densi~y, in the powder form it is 30 ~ very dificult to handle. Therefore, aqueous formul-ations of fumed silica are desirable and convenient.
However, such formulations tend to se~tle out on standing ~or a day or more. The suspending ~:: properties of welan gum ma~e its use in fumed silica ~-J ;

~ 32~ 1 27 aqueous compositions highly adva~tag~ous ~nd such ~ompositions are a convenient way to add welan 5 gum to cement compositions. Similar aqueous composi~ions are within the 5cope of ~his invention utilizing welan gum's ability to suspend particulat~
materials in cement additives.
In 60me applications, th~ cement slurry is viscous enough that additional viscosity imparted by an additive such as welan gum would be undesirable in term~ of handling or positioning the slurry. This is , ( particularly true for cements where it is desirable i to achieve the lowes~ viscosity possible without any settling of the cement slurry and still obtain water loss control.
For these applications, a lower viscosity welan gum can be prepared which re~ains fluid loss ¦ control. Lower viscosity welan gnun can be prepared 2~ by several methods. On~ process involves the use of hydrogen peroxide in a formulation similar to 1 Fenton's Reagent. The formulatiGn c~ntains .~ .
i ,. 0.1~-0.25% H202, 0.05% FeS04 and 0.10% EDTA `~
ethylenedinitrilo tetraacetic acid tetrasodiuun s~lt.
Using this formula~ion a 5% welan gusn solution can be degrad2d from greater than 10,000 cP to as low as 100 cP, as mea~ur~d on a ~rookfield LVT viscometer a~ 60 RPM. Both the degradation and thP degradation rate : are proportional to peroxide concentration and 30 temperature. Therefore, one can make welan gum having a range of viscosities and yet exhibit good f luid loss control .
This low viscosi~y welan gum can be prepared from ermentation broth or from dry powder. To ~ -~.:
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6266P~5372P - 9 - K-2088IA
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minimize peroxide use, the gum may firs~ be purified as by the use of a proteolytic enzyme prior to further treatmen~.
The ermentation broth is then heated to 140F (60C~ and ferrous sulfa~e plus tetrasodium EDTA added as a solution. ~ydrogen peroxide is then ~ added over a period of 1-3 hours. The viscosity drop '' 10 is moni~ored ~o only 8C cP, spindle 2, 60 rpm, at which point the fermentation broth is cooled to 80F
' (26.6C~ and neutralized using dilute potassium :~, ( hydroxidle. The low Yiscosity welan gum is then ¦ precipitated wi~h isopropanol, dried, and milled. ~:-~, lS If dry powder is used ferrous sulfate plus ~-Na4EDTA is dissolved in water ollowed by ~he welan 3 gum and hydrogen peroxide. The solution is heated ~:.
for 1-2 hours a~ 75C, and ~he viscosity monitored.
The solution is cooled, precipita~ed with isopropanol, dried, and milled.
Following degradation, the low viscosity polysaccharide is recovered from solution by precipitation with 2-4 volu~e of isopropanol, ( followed by drying and milling.
f 25 Low viscosity welan gum of this invention is . useful in a varie~y of indus~rial and agricultural ~,~ applications. Such uses include tex~ile printing and I dy~ing, especially in foamed dye or ink formula~ions;
3 paper prin~lng, esp~cially foamed ink formulations;
f 30 petroleum operations, including oil well fluids for drilling and workover operations; lithography, as in lithographic ountain solutions; detergents;
microencapsulation; coati~gs; inks; seramics;
1,; bind~rs; protective colloids; agricultural foam -:

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marker~, fire fighting foams, including fluoro- and non-fluoro-based proteins and non-protein agents, and ; ~ hydraulic cement compssitions.
Those skilled in the art recognize that other chemical treatmen~s, for example acid or caustic degradation, exis~ that would alss yield lower viscosity welan g~m. ~-1~ There are also appli~ations in which welan gum exhibitiny hiyh viscosities (i.e., welan gum having a 0.25% viscosity in the range of 1500-4500 cP
(- as measured on a Brookfield LVT viscometer, spindle .
#2, at 3 rpm) is desirable. Such a gum can ~e 1~ prepared ~y treating a welan gl~m solution with enzyme.
~enerally, after the welan gum ferment~tion is complete, the pH is adjusted to 9,0 using KOH. The beer is t~en heated to 4~-52C, an alcalase enzyme is ¦ added at a concentration of 500-1500 ppm, and the ~eer mixed and aerated for 6 hours. The resulting product is then cooled to 29-3:2C and precipitated with isopropyl alcohol.
. Welan gum has di~tinct advantages in cement ( compositions.
i 25 reduces th~ fluid loss of cement csmpositions, , even ~t high temperatures.
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2. The fluid loss control o welan gum is directly proportional to polymer concen~ration, unlike the ::
cellulosics which increase logari~mically.

3. It gr~atly increases the suspension proper~ies of cement ompositions.

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4. Welan ~um increases the workabili~y of cement and conrre~e compositions, i.e., it improves the ability of cement slurries ~o be easily placed in crowded areas such as around re-inorcing bars - without ~ggregate settling.
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S. The suspension properties of welan gum can also :-:.
~A 10 help entrain air into cem~nt compositions such as mortar and gunite.

( 6. I~ c10es not ret~rd the set of cement composi~ions, compared to cellulosic addi~ives.
"f 7. Much lower concentrations of welan gum can be used ~o achieve effects comparable to other addi~ives.

8. Welan gum does not require the use of a ;~ dispersant, as do other additives, when used as a water loss co~trol agent.

( Table I is a list of representative cemen~
additives which are useable in compositions of this inY~ntion~ As the specific formulation of thes~
~: additives are proprietary, they are shown in the :-~
ble by the trademarXs of five diferent vendors ¦ ~hereof. This Iistiny is not a suggestion that the ~: 30 products included can be directly substituted one for he other.

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, .~ , TABLE I
OIL ~IELD CEMENT ADDITIVES
. 5 , Accelerators " Calcium chloride, sodium silica~e (Diacel A), sodium chloride ~sal~), ammonium chloride (NH4Cl~, or combina~ions or solutions of these sal~s are used 10 by cemen~ing companies. Some trade names of these i products are:
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Western Co. Dresser Titan Halliburton Dowell-SchlwmberRer ~ 3 :'~ 15 WA-4 MCA-L ~A-5 S-l A-7 MA-2 D-77L h-7L
Diacel A S-57 A-5 .

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Retarders, i Calcium or sodium lignosulfonates or other i : liqnin deriva~ives, borax compounds, CM ~EC*, sodium .~
or calcium gluconates, and sug2rs are used in ~:
: combînations or solutions by cementing companies and 2 are marketed as:

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, ' Dress Titan ~alliburton D-S B J Titan We~tern Co.
MLR-l HR-7 D-13 Kembrank WB-l MLR-3 ~R-4 D-28 R-5 WR-2 MHR-8 HR-12 D-93 R-ll WR-6 MH~-9 HR-15 D-8 M-5R.9 ~R-7 ~ MFLR-7 Diacel LWL D-99 R-6 Diacel LWL
"~ 10 ~R-600 HR-20 D-81 R-17 MHR-600 ~R-6L D-109 R-l 2L WR-Ll , ~ MLR-L HR-13L ~-D-120 R-14L~
,~ MHR-L ~R-5 17-133 '~ HR-8 D-800 ~ * Carboxymethylhydroxyethylcellulose ., ,.
Fluid Loss Reciuc~rs :20 Bentonite, hig-h, medium and low viscosi~y HEC, polye~hylene imines and annines, long chain :~
alcohols, ~ HEC, polyvinyl pyrrolidones, and fine ~.
inorganic solids (such as talc~ are used in fluid loss reduc~rs. Cementing companies market these :25 chemicals or cornbinat;ons of these chemical~ ~n dry mixes or solution~; a5:
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Dress Titan Halliburton D-S B J Titan Western Co.
MFL-4 ~alad 9 D-60 D-l9 CF-l MRL-5 Halad 14 D-59 D-22 CF-2 :J:: ~ MFLR-7 Diacel LWL D-73L R-6 Diacel LWL
MRL-L CRF-~ D-108 FL-10 MXP-56 LA~2 D-108L FL-19 .:.
Ralad 4 D-127 ~alad 22AD-503 ;

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~, Dis~ersants Sodiums citrates, sodium napht~alene sulfonates, sodium melamine sulfonates, lignin and lignin derivatives are used by cementing companies to reduce v;~cosities of cemen~ ~lurries and to aid in - fluid loss control by dispersing the particles in the slurry. They are used alone or in combina~ions and 1~ are marke~ed a~:
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Dress T tan ~alliburton Dowell-Sch umber~er B J Titan West~r~ Co.
( MCD-3 CFR-2 D-45 CD-31 T~-4 MCD-4 CFR-l D-65 CD-31L TF-5 :; D~
" D-604 Extenders and Loss Circulation Materials 2~ Pozzalc,ns, asphalts, qilsonites, bentonite, dia~omaecous ear~h, and variouis; materials ar~ used ~o ~1 plug passages where loss of whol~ cement occurs.

An~ifoam Aqents ~S Long chain alcohols such as octanols, ~:
~i steara~es and their salts are often marke~ed as:
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J Titan ~alliburton D~Schlumber~er B J Titan Western CoO - .-: ~ MFR-5 NR-P ~-46 FP-6 AF~8 -:
30 MRP-L D-~IR 2 D-47 L FP-216 AF-L -: .
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Weiqh~inq Materials Bari~e, hematite, and illmenite are the . 5 primary agent~ use to increase the dens~y of ~ement :. slurri~s.
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The cement compositions of ~his invention can be prepared by adding welan gum to the rest of the compositions as a dry powder, or, preferably, as :.~ an aqueous suspension at the time of adding any other liquid additives or the w~ter for pasting if no other additives are used.
The invention is further defined by .i 15 reference to the following preparations and examples, ~-which are intended to be illus~rative and not ';j limiting. -;

ComPatibility o Welan Gum With Cement The compatibility of welan gum with cement :
was compar~d to that o xanthan gum. Using two different methods of adding the gums and also using a retarding a~en~ all cases xanthan gum gelled the cement slurry whereas welan gum did no~.
For the following da~a, API type G cement was tested a~ 100 lb cement~5 gallon o slurry. The xa~th~ ~um used was KELZAN*XCD (trademark of : 30 Merck ~ Co., Inc.~.

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`' S ' i~ VISOCOSITY* OF BIOPOLYMERS IN C~MENT SLUR~Y
~ WELAN XCD CONTROL
,~' 0.5 lh~bbl 1 lb/bbl 0.5 lb~bbl I lb/bbl (No Gum) Gum wlo Cement 120 370 120 360 Gum w/ Cement 1700 4000 Gelled Gell~d llOO :-,, . . :.
:~ ~ *Fann 35, 3 rpm Viscosi~y (~P) : -¦ lb/bbl = pounds per 42 gallon barrel of slu~ry I The da~a of Table 1-1 were obtained by .j adding dry cement ts gum solutions. The resul~s show :-:1 that welan thickened the slurry whereas xanthan gum ::
produced a lumpy gelled mixture.

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- ~ ", I ~ VISOCOSI~Y* nF CEMENT SLURRIES FOLLOWING GUM
2$ - - POWDER ADDITION
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~EL~N XCD CONTROL :--O.S lb/bbl l lb/bbl O.5 lb/bbl l lb/bbl (No Gum~ -Gum w~ Cemeat 3100 6200 Gelled Gelled 2100 : :: :~ '.,',-*Fann 35~ 3 rpm ~iscosity ~cP) . . . ~::,: -i' ~ ~ ~ ""''.,'' . -~:

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~ 'or Table 1-2~ the gums were added as powders to the cement slurries. Visco~ y increased wi~h increasing welan ~um concentration. The produc~ was : a homogenous, smooth,and soft for about 20 minutes, : after which it felt sol id to ~he ~ouch. The xanthan gum slurry set to a solid in about 1 minute and had a lumpy, gelled appearance.

VISCOSITY* OF CEMENT SLURRIES WITH CEMENT RETARDER
- _ FOLLOWING GUM POWDER ADDITION
WELAN %CD CONTROL
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1 lb/bbl1 1b/bbl _No Gum) Gl~ ~//Cement 1400 Gelled 200 * Fann 35, 3 rpm Viscosity The slurries of Table 1-3 were re~arded with ( calcium lignosulfate, followed by gum addition. The --welan slurry remained smooth and set in about ~.5 hour~. The xan'~han slurry had a lumpy appearance.

EX~MPLE 2 ,~ , Control of Fluid Los~

The control of fluid loss with increasing welan gum concentration was determined as follows. :

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Portland cement type A, 46% water, 0.S ~o 0.~%
dispersant ~Lomar P~, and 0 ~o 0.3% welan gum ~all based o~ dry weight of cement) were mixed in an Os~erizer blender. F1uid loss was measured at 26 ~ 6~C, 1~00 pSî N~ with no back pr~ssure. Thz later Tab1e 3-1 shows ~hat 1uid loss decreases with i~creased we1an gum concentration and that the use of dispersing agent is beneicial.

FLUID LOSS DETERMINATION OF WELAN GUM
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~ DISPERS~NT WELAN FLUID LOSS
I CONCENTRATION CONCENTRATION(~LJ30 MIN.) ~%~
1 0.5 0 1~5 20 0.5 0.05 137 0.5 ~.1 12~ -0.5 0.2 118 ~
0.5 0.3 74 :

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The control of f1uid loss a~ elevated `:-temperatures was det~rmin~d according to API -Speci~ication 10 "Oil Well Cemen~ Tes~ing". Table 2-2 shows that welan sum re~ains better 1uid loss .`
control at 127C than does HEC.

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Table 2-2 HIGH TEMPERATURE FLVID LOSS DETERMINATION
5F1uid Loss at 127~C
i (m1.~30 minute) Base cement* >1000 Base Cement ~ 0.~% ~ow 1~ Viscosity HEC 70 .
Base Cement ~ 0.3%
(. we1an gum 220 * Base Cement = Portl2nd cement type A, Q.3% high tempera~ur~ retard~r, 38% water.

We1an gum con~rols f1uid loss to such an extent tha~ the dispersant conc:entration can be 1Owered or e1iminated, as showTI in the following table~
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Tab1 2-3 EFFECT OF WEL~N GUM WITHOUT DISPERSAN?
2S F1uid Loss at 26C --~ml.~30 minute) :-Neat ~emen~ ~1000 Neat Cement ~ 0.3% welan gum 132 Neat Cement + 0.5~ dispersant ~8 eat Cemen~ + 0.3% we1an gum ~ ;
0.5~ ~isp~rsant 74 .~
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xample 3 usPension Pro~erties ::
A slurry containing Type H cement, 0.7%
dispersant, and 46% water with and without 0.3% welan gum was poured into a two foot long by one inch I.D.
PVC pipe and allowed to cure at room temperature ::
(22DC) overnight. The tubes were maintained in a vertical position for the duration of the curing time. The ~ubes were_then cut in~o two parts twelve ~ -inches from the ends of the tubes. The csment was then removed from the pipes, vol~mes were determined, 15 the samples weighed, and their densities calculated. ::
The results in the following table show ~hat the ~uspension prop~rties of welan gum yields a more ~:.
uni~orm slurry as the slurry cur~s.

TABLE 3~1 Dens i t~lb . /~a l . ) _ Slurrv _ Top Section Bottom Section Base Slurry ~1.4(1) 18.8 Bas~ Slurry + 0.3~ welan gum 14.1(2) 14.8 1) Two inches of free wa~er on top 30 : (2) No~f~ree wa~er on top :
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o EXAMPL~ 4 . 5 Preparation of Low Viscosity Welan ~um ! The following reagents were used to prepare low viscosi~y welan gum:
.~, Weiqht (q) ~i 10 Distilled Water 750.0 -~-Welan g~n 40.0 ~eSO~ 0 5 ~DTA~4Na 1.2 i, The water was heated t:o 60C then placed in a Waring blender. The other reagents were added in ;I the order shown ancl the mixtures sheared for 30 ¦ minu~es at 60C. The mixture wa then allowed ~
cool to ~mbient tempera~ure ancl ~he gum precipi~ated ., ~ with f our volumes of isopropanol ( IPA) . The precipitate was dried overnight at ~0C, then milled - through a 40 mesh screen.
~: The visco~i~ies o 5% ~olutions of the gums on a Brookield LVT YiSCometer were:
~1 (cp~ :
Welan gum >lo,00~1 Low viscosity welan gum 110~ -3~ .
~ pindle #4, ~0 rpm.
:~ : :2. Spindle ~2, 60 rpm.

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132~127 ~

Example 5 Viscosity and Fluid Loss Control :;
_ of Low Viscosity Welan Gum Por~land cemen~ Type A slurries cc~n~aining 0 . 75% dispersan~, 46% water, and ei~her welan gum or the low ~riSCosity welan ~um described in F:xample 4 : -~; were prepared and ~cested for viscosity and f luid loss lû at 22C. Note in the ~ollowing tal~le how the low YisCoSity welan gum controlled fluid loss without seriously increasing the slurry viscosity.

.::
lS Table 5-1 iscosity and F1uid Loss Control ., Polymer Concentration Viscosity* Fluid Loss - :
Polymer Z _ (cP) (ml./30 min.) Low vis. welan gum 0~2 900 16.5 f ~ 0.3 1050 1~.5 1, -( ~ .i ..... .. ~ ,. 0.4 1350 6.5 2~
We1aD gum 0 . 2 5350 31**

0.3 8150 33 30"~ " 0.4 10~00 28.5 * ~ Fann 35 Viscometer, 3 RPM
** 31 ml . /lS m;n. ..
: .
¢
4 ~
;, ; ' .' i~ ~ ,.. ' ' i. . ' :' 6266P/5372P _~ ~32 4 1 2 7 K-2088IA

Example 6 Viscosity iand Fluid Loss Control of Hiqh Viscosity Welan Gum Cemen~ composi~ions containing 0.~% polymer, optionally 0.5% dispersant (Lomar ~, sodium melamine sulfonate), and 38% water were tested at 80F
19 (26.6JC~ ~or viscosity and fluid loss. . .
Table 6-1 shows that a high viscosity welan gum ~0.256 viscosity in excPss of 1500 cP, Brookfi21d LVT viscorneter spindle #2, 3 rpm~ exhibi~s lower fluid loss values and higher viscosities than welan ~um.
Slurry viscosi~ies are shown in Bearden I Units, which are measured in acc:ordiance wi~h the I Americian Petroleum Insti~ute, S~ecification 10, 1987.

I 2~
¦ Ti~ble 6-1 Viscosity and Fluid Loss Control Slurry Vi~c. .
(Bearden Units) Fluid Los~
_o~ Dlspersant Initial Final (ml./30 min.) ~2 5 ~igh ~isO welan gum No 34 26 307 Ri8h vis. welarl gu~ Ye~ 18 23 93 Wela~ gu~n Yes 13 16 181 3iD
Il Exam~le 7 i ~ Following a procedure similar ~o that of Example 3, cement slurries (~4% water) were prepared :
with and withou~ welan gum and dispersant and placed in 30" columns. Aft,er curing, density measuremen~s ~ , were taken every 2". The data are presented in the following tables . Densities ar~ +0 . S lbtgal and no 5 densities are provided for air or wat~r at the top of some columni5.
! :
j .
Ta~le 7-1 ~, 10 Welan Gum and Sodium Melamine Formaldeh~de Sulfonate Density (lb/gal~ :
Cement ~ 1% Cement + 1 Cement ~ 1~ Sikament ~ Sikament +
15 Inch Cement_ Sikament 86* 0.05~ Welan 0.1% Welan 2~ 14.5 11 16.~ 16.5 26 lfi.5 12.5 16.~ 16.5 24 16.5 13 16.5 16.5 ~0 22 16.5 14 16.5 16.5 j 20 16.5 16.5 16.5 16.5 18 1~.5 17.5 16.5 16.5 16 16.5 17.5 16.5 16.5 , ; 14 16.5 18.5 16.5 16.~ .
12 16.5 l9 16~5 16.5 ~ :
1~.5 19 l~.S 16.5 - :
8 16.S 19 1605 16.5 6 16.5 19.5 16.5 16.~ `~
` ` ~ 16.S 19.5 16.5 16.5 :-', 30 2 16.5 19.5 16.5 16.5 * Sodium melamine formaldehyde sulfonate ~`~

:.
.

6266P/5372P - 25 ~ 2088IA

Table 7~2 Welan GU~f And Sodium Naphthlaene Formaldehyde Sulfonate Density (lb/gal) Cement Cement + 1.0~ Cement + 1.0~
Inch ~ 1.0~ Lomar D* Lomar + .05% Welan omar ~ .12 Welan l~ 3~ - 14.5 15 , 28 - ~6 15.5 ', 26 11.5 16 . 15.5 24 14 l~ 16 ~ lS 20 18 16 16 f 18 1~.5 16 1~
~ 16 18.5 16 16 ql 14 18.5 16.5 16 12 18.5 16.5 16 2~ ~ 1~.5 16 16 :-8 18.5 16.5 16 6 18.5 16 16 ::
~ l9 16 16 ~:
f 2 19 16.5 16 :

~; ~ * Sodium naphthalene formaldehyde sulfonate These data show that in each case, the :: 30 substan~ially homogenous density profile of neat ~:
'f ~~ cement is substantially degraded by the addition of a dispersan~, leading to significant density varia~ions ~:
f~: :
~ ' '~ ' ' ':

~.

over the length of the columns. The addition of welan gum ~estores the densi~y profile to approxima~ely that of neat cemen~.

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Claims

WHAT IS CLAIMED IS:

1. A low viscosity welan gum having a 5% (wt.) aqueous solution viscosity of 100 cP as measured on a Brookfield LVT viscometer, at 25°C, spindle 2, 60 rpm.

2. A process for preparing a heteropolysaccharide of Claim 1 which comprises degrading a welan gum solution by heating at 48° to 83°C for a sufficient amount of time in the presence of 0.05 to 0.25% EDTA 0.01 to 0.1% ferrous sulfate, and 2-6% hydrogen peroxide, based on the weight of heteropolysaccharide.