Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to cementing in low temperature
envirOnments More partic~larly the inven-tion is concerned
with a dry cement compositi.on Eor use in prepari.ng a pumpable
slurry capable of setting and developing good compressive
strength at low temperatures. ~he invention is also concerned ~.
with such a pumpable slurry for cementing pipe, such as well
casing, in wells drilled through low temperature earth
formations, and with a process of cementing pipe in a ~ell that
penetxates a low temperature earth formation. Th~ invention
further relates to a process of preparing such slurries.
Description of the Prior Art
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U. S. Patent No. 3,891,454, issued June 24, 1975,
entitled "Composition and Method for Cementing Wells in Low
Temperature Formations", Cunningham et al, discloses a cement
composition for cementing p.ipe in wells drilled in formations
existing.at low temperatures, e.g. below 80 F. and as low as
15F.
The cement aomposition of the Cunningham et al
~atent contains Portland cement, sypsum, a monovalent chloride
salt, particularly sodium chloride, as a ~reezing point
depressant t and a setting ~ime retarding agent.
In one of its aspects, the present invention
` :provides a dry cement composition or use in preparing a
~ pumpable slurry capable of setting and developing good
compressive strength at lo~ temperatures consisting
~ essen-tially of:
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(a) Portland cement;
(b) about 100 ~o 400 parts by weight of gypsum cement per 100
parts by weight of Portland cement;
(c) about 5 to 20 parts by weight of calcium chlorlde per 100
parts by weigh~ of Portland cement; and
(d) about 0.1 to 1.0 parts by weight of a set~ing tiMe retarding
agent per 100 parts by weight of Portland cement;
(e) the cement composition being a palpabl.y dry~ powdery mixture.
In another of its aspects~ the invention provldes
a cement slurry composition for cementing pipe in wells drilled
through low temperature earth formations consisting essentially
: o (a~ Portland cement; (b? about 100 to 400 parts by weight of
gypsum cement per 100 parts by weight of said Portland cement; (c)
about 5 to 20 parts by weight of calcium chloride per 100 parts
by weight of said Portland cemen~; (d) about 0.1 to 1.0 parts by
weight of a setting time retarding agent per 100 parts by weight ~ -
`~ of said Portland cement; and (e) water in an amount to form a
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.~. pumpable slurry capable oE setting and developing good compressi~e
strength at low temperatures.
In still another of it5 aspects the present invention
:. provides a process for cementing pipe in a well which penetrates
.. a low temperature earth formation comprising depositing in the
space between sald pipe and ~aid formation a~ aqueous slurry of a
hydraulic cement composltlon and thereafter allowing said slurry to
set9 wherein said slurry consists essentially of ~a) Portland
cement; (b) about 100 to 400 parts by weight of gypsum cement per
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~-~ 100 parts by weight of said Portland cement, (e) about 5 to 20
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parts by weight of ealcium chloride per 100 parts by weight of
aid Portland cement; (d) about 0.1 to 1.0 parts by weigh~ of a
settin~ time retarding agent per 100 parts by weight of said
Por~land cement; and (e) water in an amount to form a pumpable
: slurry capable of setting and developing good compressive strength
at low temperatures.
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In yet another of its aspects, -the invention
provides a process of preparing a cement slurry composition
: for cementing pipe in wells drilled through low tempera-ture
ear-th formations which includes:
(a) providing a blend of a PortlancL cement
and a gypsum cement ranging from about
100 to 400 parts by weight of gypsum cement
to 100 parts by weight of Port:Land cement~
(b~ mixing said blend with water; and
~c~ prior to mixing said blend with water,
dissolving in at least a portion of said
water about 5 to 20 parts by weight of
calcium chloride per 100 parts by weight ., .
of Portland cement and about 0.1 to 1.0
parts by weight of a setting time re-
.~ tarding agent per 100 parts by weight of
Portland cement;
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~d) the water being in an amount to form a pumpable
~ slurry consisting essentially of the forego.ing
- . ~ substances and capable of setting and developing
good compressive strength at low temperatures.
,.,: ~ The practice of the last-mentioned process of pre-
~ paring a cement slurry composition allows the sacking and
¢.1~ storage of one or a few different standard dry blends of
i~ Por-tland cement and gypsum cement. Then, when the slurry
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composition is prepared at the well site, the required quantities
of calcium chloride and retarder can be added to the mix water
to achieve the desired free~ing poin-t and thickening time, as
required by conditions in the particular well being cemented.
~oreover, if -the slurry is mixed in a continuous manner as it
is pumped into -the casing, substan-tially uniform distribution
of the additives is achieved throughout all port:ions of the
slurry Such uniformity of distribution of the additives
is more di~icult to obtain when the additives are dry-
blended with the Portland cement and gyp5um cement before the
dry blend is mixed with the water.
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It is advantageous to use calcium chloride in
place of sodium chloride as the freezing point depressant.
The compressive strength of the set cement using calcium
chloride is oftentimes greater than the compressive strength
o a s.et cement using sodium chloride in the slurry, where
: the amounts of the respective freezing point depressants are
present in proportions that are effective to lower the freezing
point of the water to the same temp.erature, and the slurry
compositions are otherwise the same.
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;~ The compositions of the present invention include .
~ Portland cement, gypsum cement, calcium chloride, a set-ting
:~ time retarder, and water.
.~ The Portland cement employed in the p~actice o
: this invention may be one of the Portland cements commonly
used in cementing pipe or casing in oil or gas wells. Use-
ful, commercially available Portland cements include Class
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A, B, C, G or H, as designated in accordance with the classi-
. ication o~ the American Petroleum Institute. See "API
: Specification for Oil-Well Cements and Cement Additives",
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issued by American Petrolcum Ins-titute, Division of Procluction,
300 Corrigan Tower suilding~ Dallas, Texas 75201, API Spec
lOA, 18th ED. January 1974. Other usable Portland cements
are Type I, II, III, IV or V of the classification established
by The American Society Eor Testing Ma-terials~
The gypsum cement used is the finely ground
calcined material, also known as Plaster of Paris or calcined
gypsum It approxima-tes in composition the hemihydrate oE
calcium sulphate, CaSO4 . 1/2 ~I2O.
Any good grade of calcium chloride may be employed
as the freezing poin-t depressant. Finely ground anhydrous
calcium chloride is preferably used in -the dry blended com-
positions of the invention. Where the calcium chloride is
dissolved in the rnix water prior to mixing the water wi-th
the dr~ substances, the equivalent in crys~als of calciu~
chloride may be used.
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A variety of setting time retarders ar~ available
for use in carrying out the invention. Sodium citrate is the
preferred setting time retarder. Either the anhydrous sal-t
or t~e dihydrate, Na3C~H5O7 . 2H2O, is satisfactory, with t~e
former being especially suitable in the dry powder compositions.
The dihydrate, because of its lower cost, is advantageously
used in solution in the mix water. Citric acid is also effective
as a setting -time retarder, as are also certain sulfonates,
such as those referred to in the fore~oing United States patent
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Water suitable for use :in the invention may be fresh
water, such as occurs in rivers, lakes ana ponds. Preferably,
the wa-ter should be as pure as possible, and substantially :Eree
from suspended or entrained materials
The relative quantities oE inyredients that are
incorporated in the dry composltions of the inven-tion are based,
for convenience of description on lO0 lbs. of Portland cementO
It will be understood that, in practice, these ~uantities will
be scaled up or down in accordance with the weight of Portland
cement actually employed. From lO0 lbs. to 400 lbs of calcined
gypsum are used with each lO0 lbs~ of Portland Cement Calcium
chloride in amounts rom about 5 to 20 lbs. is used with each
lO0 lbs. of Portland cement About O.l to l.0 lbs~ o~ the set-
ting time retarding ayent are employed per lO0 lbs. o Por-tland
cement.
In preparing the dry composition, the powdered ingre-
dient~ are thoroughly mixed together in a dry materials blender
or other suitable dry mixing equipment The resulting mixture
may be sacked for delivery to the well site, or may be delivered
to the well site in bwlk quantities.
~ t the well site, the cement slurry i5 made up in
a conventional cement mixerr either batch or continuous, by
mixing the required amount of water with the dry cem~nt
composition. The amount of water needed will depend, to a
large extent r upon the combined quantities o Portland cement
and calcined gypsum in the dry mix. For each lO0 lbs~ combined
weight o Portland cement and calcin-ed gypsum, about 5.5 gals
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of water are employcd. Over the useful range of Portland
cement and calcined gypsum (1:1 to 1:4), the amount of water
reguired will vary from about 11 gals. for the 1:1 ra-tio to
28 gals. for the 1:4 ratio Eor each 100 lbs of Por-tl~nd cement
in the dry mix-ture.
Alternatively, the cement slurry may be made up by
mixing the Portland cement and the gypsum cement, preferably
in the form of a dry blend of the two cements, with the re-
quired amount of water tha-t contains, in solution, the necessaxy
quantities of calcium chloride and setting time retarding agent.
In this way, the dry blend of ingredients may be prepared in
advance at a blending plant and transported to the well site.
There, depending upon the temperature and other conditions in
the ~ell, the needed amounts of calcium chloride and setting
time retarding agent are added to the water for the slurry,
and the solution is then mixed with the dry blend to foxm the
slurry, In accordance with this method of making the slurry,
one or a small number of dry blends containing predetermined
propoxtions of cement and calcined gypsum can ~e premixed
and held in readiness for use. Then, at the well location,
a water solution containing the calculated guantities of water~
calcium chloride and setting time retarding agent is mixed
with the required ~uantity of a selected dry blend of Portland
and gypsum cements to foxm the cement slurry, which is then
pumped into the annulus between the casing and the well bore
and allo~ed to set.
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Other additives may be incorporated in the cement
slurries oE this inven-tion, such, for example, as thickening
agents, lost circulation materials, densi:Eiers and -the like,
without substantially afEecting the low temperature handling
and setting qualities of the slurries.
The .invention finds particular application in
cementing casing in permafrost, where the temperatures in the
permafros-t may fall as low as about 15F. The slurries of
the invention are also employable at higher -temperatures on
up to about 60 to 80F. Above these latter temperatures,
conventional oil well cements will perform satisfactorily.
The following examples illustrate some of the
desirable properties of the cement slurries oE the inven-tion
and of the set cemen-t produced therefrom,
The basic slurry mixture used in all of the herein~
after-reported runs contains the ingredien-ts in the propor-tions
indicated in Table 1.
TABLE 1
Ingredient Weight (lbs.) %
Class G Cement 100 38.0
Plaster of Paris 162.9 62.0
Mixing Water: 14.4 gal. (120% by weigh-t of
Class G Cemen-tl
The densities and yields of the foregoing basic
slurry mixture, as affected by variations in the content of
calcium chloride, are shown in Table 2.
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TABI,F. 2
Anhydrous Calcium Chloride Slurry Yield
Tes-t% by weight % by weigh-t of Density Cu Ft, per
Noof wa-ter Clo G Cemen-t pcf ppg 100 lb. cement
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1 0,0 0,0 - 112.6 15~1 3.~0
~ ~,0 9,6 11~,2 15~3 3.4~
: 3 12,0 14,~ 115,0 15.4 3,~6
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~rom Table 2 it is seen that both the slurry density
.:and the yield increase as the percentage of calcium chloride is
increased.
The manner in which the consistency of the basic
slurry mixture changes with changes in percent of calcium
chloride and percent of retarder ~sodium citrate dihydrate)
is shown in Table 3.
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TABL~ 3 ~.
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Anhydrous Calcium Chloride Retarder*
% by % by 50 hy wt. Consistency, Uc,
TestWeight of Weiyht of Cl. of Cl, G~
NoO Wa-ter G. Cement Ce~ent 0 min. 5 min, 10 mir
4 0 0 0,3 8 9 10
0 0 0.8 7 7 8
6 8,0 9,6 0.15 8 8 11
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``~ i 8 0 0 g,6 0.45 ~ 8 9
. 8 12,0 14.4 0015 9 11 12
~-` 9 12.0 1~.4 0045 9 9 10
* Sodium citrate dihydrate
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The consistency, Uc, report~cl in Table 3, is de-termined
in an atmospheric pressure consis-tometer as described in ~ppendix
A, API Recommended Practice lOB, 'Nineteen-th Edition.
From Table 3, .it is concluded -that, within the per-
centage ranges of anhydrous calcium chloride ancl retarder used,
-the consistency of the basic slurry mixture :remains within
acceptable limits.
Variations in thickening time of the basic slurry
mixture with changes in the percentages of anhydrous calcium
'chloride and retarder are presented in Table 4.
TABLE 4
CaC12 Anhydrate Retarder* ~hickening Time
Test % by Weigh-t of ~ by''Weight ' (hr:min to 100 Uc~
No. ClG.Cement of Cl, G Cement -20F. 40F. 60 F. 80F.
0 0,3 1:07 0:44
11 0 0.45 1:54 1~12 ~ :
12 0 0.6 3:23 1~41
13 0 : 0.8 3-45 3:03
14 9.6 0.15 1:12 0:~9 0:33
9.6 0.30 2:14 2:30 1:51
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' ~ i6 9.6 0.45 3~26 4:47 3:40
~' 17 14.4 0.15 1:20 1:17 1:11 0:47
~" ~ 18 14.4 0,30' 3:00 2:~7 1:4~ :
~ . 19 14,~ ~ 0,45 5:50 ~:~0 5:10 6:17
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The thickening times set Eorth in Table 4 were
determined accorcling to the l'Arctic Cement.irlCJ Tes-ting Procedure
: (~entative)l- as given in Section 11, paye 47, API Recon~ended
Practice lOB, Nineteenth Edition. This procedure mentions
: th.ickening time tests only at 40F. However, tests can be made
at the other temperatures reported in Table 4 (20F, 60F, and
80F~ by maintaining these temperatures in the consistometer
in which the tests are made.
From Table 4 it appears that slurry mixtures can be
selected that have adequate thickening time for cementing wells
: having temperatures from 20F to 800F.
.~ Variations in compressive strength o~ set cements
~, yielded by the basic slurry mixture when cured for 8, 16
~` and 24 hours at different temperatures, and with variations
in the percentages of anhydrous calcium chloride and sodium
. citrate dihydrate, are tabulated in Table 5.
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T~BLE 5
CaC12 ~nhyd. Retarder* Cure Compressive Strength
Test % by Weight % by Wëight Time PSi
No. of Cl. G Cement of Cl. G Cement Hrs, 20F 30~F 40F 80F
0 0.30 8 940 87~
21 0 0.30 16 968 12~3
22 0 0.30 24 793 1435
23 0 0.45 8 906 695
24 0 0,45 16 ~90 955
Q 0.45 24 97~ 1235
26 0 0,60 8 823 6~0
27 0 0.60 16 975 935
28 0 0.60 24 1001 1184
29 9.6 0.15 8 843 835
9.6 0.15 16 779 856
31 9.6 0~15 24 933 984
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32 ~.6 0.30 8 590 505
33 9.6 0.30 16 566 588
34 9.6 0.30 24 860 619
9.6 0.45 8 ~ 553 ~38
36 9.6 0~45 16 54~ ~50
37 9~6 0.45 2~ 680 ~ 525
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~ 38 14.4 0~15 8 681 863 860
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39 14~4 0.15 161010 12151338
; 40 14.4 0.15 2~1328 13501428
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14.40.30 8 496 6Q5 483
4274.4 - 0.30 16 680 805 763
4314.4 0~3Q 24 934 990 1041
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44 14.4 0.45 8 4~1 345 363
~5 1~.4 0.45 16 638 500 478
46 1~4 0.45 24 70~ 635 78Q
* Sodium citrate dihydrate -12-
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The compressive strength values given in Table 5
were determined according to the "~rctic Cementing Testing
Procedure (Tentative~" previously mentioned, except that the
compositions were not s-tirred ("pumped") for 1 1/2 hou:rs be~ore
they were pou,red into molds for curing. This procedure mentions
curing temperatures o:E 20F and ~0F only but a similar procedure
can be used for the other temperatures reported in Table 5.
Compressive strengths oE about 500 psi or higher are
acceptable. These strengths are reached after eiyht hours of
curing in all tests but No. 49. The latter is up -to minimu:m
desired strength af-ter 16 hours curing time.
From Table 5, it appears that increasing the calcium
chloride content of the slurry either increases compressive
strength or does not substantially change it when the same
percentage of retarder is used. It also appears that increasing
the retarder content tends to decrease compressive strength.
In general r the lower the curing temperature the lower is the
compressive strength of the cured cement. Compressive strength
is also seen to increase with increased curing times up to
t~enty-four hours.
From the :Eoregoing description it is seen that the
invention provides cement compositions and slurries suitable
for use in low temperature environments, such as in permafrost,
as well as an improved me-thod oE preparing the cement slurries.
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