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Description  |
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FIELD OF THE INVENTION
The present invention relates to a high density wellbore cement composition
that can form a pumpable slurry and, after curing, is capable of
withstanding elevated wellbore temperatures.
BACKGROUND TO THE INVENTION
Wellbores provided for the purpose of production of oil and gas are
typically cased with steel casings, and cement is placed around the
annulus of the steel casing. This cement is usually placed by pumping a
cement slurry down the casing and out the bottom of the casing into the
annulus between the wellbore and the outside of the casing. The slurry
must therefore remain pumpable for an extended time period, but it is also
desirable for the cement slurry to cure to a reasonable hardness within a
short time period after the cement slurry is placed within the wellbore so
that the well completion process may proceed.
Cements are available that are capable of withstanding elevated
temperatures. Temperatures as high as 1500.degree. F. to 2500.degree. F.
may be expected in production or injection wells when some thermal
recovery processes are utilized. Provision of wellbore cements that can
maintain sufficient strength at these temperatures and have acceptable
slurry properties remains a problem.
U.S. Pat. No. 3,734,188 discloses wellbore cement compositions comprising
alumina based cements and accelerators for setting those cement. These
cements can withstand temperatures of at least 1600.degree. F. according
to patent '188.
U.S. Pat. No. 5,226,961 discloses other high temperature cement
compositions that are also based on alumina cements. Patent '961 discloses
low density aggregates and conversion of drilling muds to alumina cement
slurries. In particular, graphite as a low density aggregate that imparts
excellent thermal conductivity to the cured cement is disclosed. Magnesium
chloride is utilized in these compositions as a set retarder.
U.S. Pat. Nos. 3,180,748 and 3,605,898 address the problem of retarding the
setting of cements. Patent '898 discloses heptalactone as a preferred
retarding agent for a wide variety of cement slurries that includes
alumina cement slurries. Patent '748 discloses boric acid, calcium lignin
sulfonate and alkali metal or alkaline earth metal phosphates as retarders
for alumina cement slurries. The phosphates are preferred as retarders
when the cement slurries include silica flour as an aggregate. Cements
disclosed in patent '748 are said to be capable of withstanding
temperatures of 1500.degree. F. to 2000.degree. F., and examples are said
to remain pumpable for up to three hours and twenty five minutes.
Retarders for alumina cement slurries that are more effective than those
available in the prior art would still be desirable.
It is therefore an object of the present invention to provide a cement
slurry composition that, after being cured, is capable of withstanding
service temperatures of 1500.degree. F. to 2500.degree. F. It is a further
object to provide such a composition wherein the slurry remains pumpable
for more than three hours after initially being blended.
SUMMARY OR THE INVENTION
These and other objects are accomplished by a high alumina wellbore
cementing composition comprising:
high alumina cement; and
an antigelant selected from the group consisting of phosphino organic
acids, phosphonic acids, organic polymers containing phosphinic acid
groups, salts thereof, and mixtures thereof in an amount effective to
prevent gelation of the cementing composition for a time period of at
least three hours.
This composition can be made to remain pumpable for a time period that is
long enough for the composition to be placed in a wellbore using
conventional wellbore cementing methods. After the composition is cured,
the composition is capable of withstanding elevated temperatures for
extended time periods.
The composition of the present invention may further comprise a thinner or
water reducing agents in an amount effective to render the composition
pumpable.
DESCRIPTION OF THE INVENTION
The alumina cements of the present invention are available and known in the
industry. Commercially available examples include: "FONDU," containing
about 39% by weight Al.sub.2 O.sub.3, "SECAR 41," containing about 41% by
weight Al.sub.2 O.sub.3, "SECAR 51," containing about 51% by weight
Al.sub.2 O.sub.3, "SECAR 71," containing about 71% by weight Al.sub.2
O.sub.3, and "SECAR 80," containing about 80% by weight Al.sub.2 O.sub.3,
all available from Lafarge Calcium Aluminates; "LUMNITE," containing about
47% by weight Al.sub.2 O.sub.3 and "REFCON," containing about 57% by
weight Al.sub.2 O.sub.3, available from Lehigh Portland Cement Co.; and
"CA-14," containing about 70% by weight Al.sub.2 O.sub.3 and "CA-25,"
containing about 80% by weight Al.sub.2 O.sub.3, available from Alcoa.
Hydraulic components of these cements are compounds of calcium oxide and
alumina having principal mineralogical phases of monocalcium aluminate,
calcium bialuminate or similar compounds.
The amount of cement in the cementing composition of the present invention
is preferably between about 5% and 25% by weight of the total solids in
the finished slurry. The remaining 95% to 75% of solids are non-hydraulic,
and referred to as "aggregates."
The alumina cement reacts with water present in the slurry and forms
hydration products which bind the solids of the slurry together as a set
material. If the cement content is appreciably lower than about 5% by
weight of the total solids, then the set material does not have enough
strength to perform the normal functions of a wellbore cement. More than
about five percent by weight of the total solids of alumina cement is
therefore preferred.
The slurry of the present invention is intended for use where temperatures
of 1500.degree. F. to 2500.degree. F. will be encountered after the slurry
has set in the well. Water of the alumina cement's hydration products will
be driven off at the high temperatures, leaving a mass that has a
relatively high porosity. If a strong, highly heat conductive aggregate is
used in the slurry, the amount of cement incorporated into the slurry can
be reduced, resulting in a set cement composition that is strong, with a
lower porosity that is more conductive, and more heat resistant.
In addition, the alumina cement is quite expensive as compared to the
aggregate material. Use of a relatively low proportion of alumina cement
in the slurry is both economical and results in a set cement having
superior properties. Thus a concentration of the high alumina cement that
is less than 25 percent by weight based on the total solids is preferred.
The aggregates of the present invention may be any of the aggregates that
are known to be useful in high temperature wellbore cement compositions.
Alumina aggregates are preferred when the density resulting from the use
of alumina aggregates is acceptable. Graphite may also be a preferred
aggregate when the cement will be in a reducing environment in the
wellbore and a low density and high thermal conductivity aggregate is
desired.
Examples of acceptable high alumina aggregates are fused white alumina (99%
Al.sub.2 O.sub.3), ground calcinated bauxite (88% Al.sub.2 O.sub.3),
"MULCOA 90" (90% Al.sub.2 O.sub.3), "MULCOA 70"(70% Al.sub.2 O.sub.3)
"MULCOA 60" (60% Al.sub.2 O.sub.3), "MULCOA 47" (47% Al.sub.2 O.sub.3).
All of the "MULCOA" aggregates are available from C.E. Minerals. The
alumina aggregates are particularly preferred because they are very
strong, highly heat conductive, and produce a final set material that is
very strong and stable at high temperatures.
Fume silica is a preferably included as an aggregate when a dense, highly
heat conductive cement is desired. Fume silica is an extremely fine
particle material. These extremely fine silica particles fill the pore
space between the alumina cement and other aggregate particles, replacing
water in the slurry composition and resulting in a slurry composition that
has very little water. The resultant set cement therefore has lower
porosity and greater thermal conductivity.
The slurries of the present invention require an antigelant to delay the
setting reaction until the material can be mixed and placed in a wellbore.
Known cement retarders such as lignosulfonates provide a retardation of
the actual setting reaction (as evidenced by an exotherm). Alumina cement
slurries are subject to an additional gelation prior to this setting. This
gelation renders the slurry non-flowable. Thus alumina cements cannot be
placed in the wellbore without risking plugging of the tubulars with
gelated slurry unless this gelation can be delayed. The antigelants of the
present invention keep the slurry flowable until the setting reaction
occurs.
The antigelant of the present invention may serve both to prevent the
premature gelation and to retard the setting reactions. The antigelant may
be used either alone or in conjunction with other set-retarding or
accelerating materials.
The wellbore cementing compositions of the present invention include an
antigelant selected from the group consisting of phosphino organic acids,
phosphonic acids, organic polymers containing phosphinic acid groups,
salts thereof, and mixtures thereof in an amount effective to prevent
gelation of the cementing composition for a time period of at least three
hours. Acceptable antigelants include: polyacrylic acid phosphinate,
vinylphosphonic acid; diethylene triamine penta(methylene phosphonic
acid); hydroxy-ethylidene diphosphonic acid; aminotris(methylene
phosphonic acid) and salts thereof. Acid forms, or forms that are not
completely neutralized, are preferred because they are generally more
effective.
These compounds are generally available and used commercially, among other
things, as scale inhibitors or dispersants. An example of a preferred
compound is BELLASOL S-29 (also known as BELSPERSE 161). This is an
acrylic acid polymer with sodium phosphinate available from FMC Corp.
Another preferred component is BELLASOL S-30 also from FMC Corp. This is
also an acrylic acid polymer with sodium phosphinate. Monsanto Corp.
markets a DEQUEST series of chemicals that are also preferred. This series
includes DEQUEST 2000, amino tri(methylene phosphonic acid); DEQUEST 2010,
1 hydroxyethylidene-1,1 diphosphonic acid; DEQUEST 2060,
diethylenetriamine penta(methylene phosphonic acid); DEQUEST 2006, the
penta sodium salt of DEQUEST 2000; DEQUEST 2016, the tetra sodium salt of
DEQUEST 2010; and DEQUEST 2066, a multi-sodium salt of DEQUEST 2060.
Generally, about two weight percent of the antigelant, based on the weight
of the alumina cement of the present invention, is sufficient to prevent
gelation of the cementing composition prior to the desired set time.
Cementing compositions of the present invention preferably contain a
considerable amount of very fine particles of aggregate, and these very
fine particles absorb part of the antigelant because of the surface-active
nature of the antigelant. Between about three and about six weight percent
of the antigelant (based on the weight of the cement) is therefore
preferred when the composition includes very fine particles of aggregate
such as fume silica.
The different antigelants of the present invention act as set-retarding
agents with differing levels of effectiveness. Thus it may be desirable to
use other set-retarding or set-accelerating materials in conjunction with
the antigelants to obtain the desired control of both the pumping and
setting times. Other components that may be incorporated into the
cementing composition include fluid loss additives, suspending agents and
dispersants. Salts present in the mixing fluids may also affect the
setting time. Thus the antigelant and set control agents must be
controlled considering the cementing composition as a whole.
Set-retarding materials that may be used in conjunction with the antigelant
materials of the present invention include materials such as
lignosulfonates, dicarboxylates, gluconates and mixtures thereof,
lignosulfonates, reducing sugars and acids of reducing sugars such as
gluconic acid, tartaric acid, glucaric acid, itaconic acid and salts
thereof, blends of lignosulfonates with acids or salts of acids of
reducing sugars, phosphinic acids and salts thereof, phosphonic acids and
salts thereof, aluminum chloride hydrate, calcium sulfate, barium
chloride, barium hydroxide, boric acid, cellulose products, glycerine,
glycols, hydroxycarboxylic acid and salts thereof, isopropyl alcohol,
magnesium chloride, magnesium hydroxide, phosphate, seawater, sodium
chloride, sodium sulfate, sugars, starch, and compounds containing these
materials and mixtures thereof.
A preferred lignosulfonate is SPERSENE, available from MI Drilling Fluids.
Preferred dicarboxylates include oxalic, maleic, succinic, glutaric,
adipic, phthalic, fumaric acids and salts thereof.
It can be beneficial to utilize both the antigelant/retarder of the present
invention, to prevent premature gelation, and an accelerator to result in
the composition curing within a desired time. Known accelerators for
alumina cements may be used. Examples include, for example, alkalis and
alkaline compounds, anhydrite, calcium hydroxide (hydrated lime), calcium
sulfate, calcium sulfate hemihydrate (plaster of Paris), calcium sulfate
dihydrate (gypsum), lithium salts including lithium carbonate, Portland
cement, potassium carbonate, potassium hydroxide, potassium silicate,
sodium carbonate, sodium hydroxide, sodium silicate, sodium sulfate,
sulfuric acid, triethanol amine, sodium aluminate, and lithium hydroxide.
Thinners that may be incorporated in the compositions of the present
invention include, but are not limited to: polymaleic acid (AQUATREAT
AR980); partially neutralized sodium polyacrylate (ALCOSPERSE 602ND);
sodium polyacrylate (ALCOSPERSE 149D); polyacrylic acid (DAXAD37); sodium
polyacrylate copolymer (DARVAN 811D); and sodium polymethyacrylate (DARVAN
7-S). ALCOSPERSE and AQUATREAT compounds are available from National
Starch, DAXAD37 is available from W. R. Grace and DARVAN compounds are
available from R. T. Vanderbilt. Other thinners useful in the present
invention include, without limitation: polynaphthalene sulfonates
(condensation polymers of formaldehyde with naphthalene sulfonic acid);
polycarboxylic acids such as polyacrylic acid and polymethacrylic acid,
polymaleic acid, and salts thereof; quaternary ammonium compounds such as
dialkyldimethyl ammonium chlorides (examples include ARQUAD 2C-75 and
ARQUAD HTL8 both available from AKZO Co.) and polyoxyethylated quaternary
ammonium salts (an example is ETHOQUAD C/12-75 available from AKZO Co.).
Dispersants may also be utilized in the compositions of the present
invention to suspend solids. Some useful antigelation agents, such as
BELLASOL compounds, are also useful as dispersants. Other components that
are typically incorporated in wellbore cementing compositions may also be
utilized in amounts typically used and for the purposes they are typically
used in the compositions of the present invention.
The cement composition of the present invention is placed in wellbores by
methods well known in the art. When the density of the cement slurry
exceeds the fracture gradient of the formation in which the wellbore is to
be cemented, the cement may be placed using a coiled tubing unit in stages
so that the hydraulic head of unset cement never exceeds the fracture
gradient of the formation.
EXAMPLES
For the purposes of the following examples, the following test methods have
been employed:
1) "Thickening Time." A stationary paddle is immersed in a cementing
composition contained in a heated, rotating cylindrical cup. The torque on
the paddle, reflecting the cement's resistance to flow, is measured. The
time from the start of the test until it is estimated that the cement can
no longer be pumped into a well is termed the thickening time.
2) "Exotherm Time." A sample of the cementing composition, in a sealed,
plastic hypodermic syringe with a thermocouple attached, is heated to a
test temperature and is placed in a closed Dewar flask that is maintained
at the test temperature in an oven. The cement setting reaction is
exothermic and a recording of the thermocouple output versus time
indicates when the exotherm starts and when it reaches its peak.
The distribution of particle sizes of the solids in the cementing slurry is
controlled to be about that which, according to the Furnas particle
packing principle, would minimize the volume between solid particles.
Table 1 shows the distribution of the solids in the systems used.
Distribution 2, having the ten percent Secar 71, has a higher strength at
moderate temperatures than does Distribution 1 (five percent Secar 71).
TABLE 1
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DISTRIBUTION
DISTRIBUTION
1 2
MATERIAL MESH LB/BBL WT % LB/BBL WT %
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MULCOA 60 14-28 67 10 67 10
MULCOA 60 -14 167 25 167 25
MULCOA 60 -20 134 20 134 20
MULCOA 60 -325 201 30 167 25
FUME SILICA
-- 67 10 67 10
SECAR 71 -- 34 5 67 10
670 100 669 100
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Water content for slurries of both Distribution 1 and Distribution 2 are 16
percent by weight of the solids (107 lb/bbl). This amount of water results
in a non-settling slurry when combined with an appropriate amount of
dispersant, retarder, antigelant and suspending agents.
To prepare the cement slurries, a suspending agent (XCD, an xanthan gum
from Kelco) was first stirred into the fresh water and allowed to fully
hydrate (at least 15 minutes). Then when a dispersant/retarder (SPERSENE,
a chrome lignosulfonate from MI Drilling Fluids) was included, it was
added with continued stirring (about 5 minutes). The antigelant (BELLASOL
S-29) was then added and stirred for about three minutes.
The aggregate solids, beginning with the smallest particles, were then
added with continued stirring for about five minutes. This resulted in
uniform slurries. Finally, the alumina cement (SECAR 71) was added and
stirred for about three minutes to produce the final slurry.
Cement slurries having densities of 18.5 pounds per gallon were mixed with
each of solids distributions 1 and 2. Both slurries contained 0.5 lb/bbl
XCD xanthan gum suspending agent, 1.35 lb/bbl BELLASOL S-29
retarder/antigelant, and 16 percent water by weight of the solids. The
slurries were cured for seven days at 120.degree. F., and then fired for
twenty hours at 1600.degree. F. Crush tests were made before and after
firing to determine compressive strengths. Distribution 1 had strengths of
90 psi and 1025 psi before and after firing respectively. Distribution 2
had strengths of 828 psi and 2435 psi before and after firing
respectively.
The set of tests shown as Table 2 illustrate the actions the dispersant,
antigelant, and suspending agents. These tests were run using the solids
Distribution 1. The suspending agent XCD was used in all of the mixes.
TABLE 2
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Test
XCD SPERSENE
BELLASOL S-29
Exotherm Time
Temp.
No.
LB/BBL
LB/BBL % bwow
% bwos
hr:min .degree.F.
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1 0.5 2.0 0.5 0.08 1:40 100
2 0.5 2.0 1.0 0.16 4:20 100
3 0.5 0 1.5 0.24 3:43 120
4 0.5 0 1.75 0.28 8:44 120
5 0.5 0 2.0 0.32 24:26 120
6 0.75 0 3.0 0.48 60:35 120
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Tests 1 and 2 indicate that the antigelant BELLASOL S-29 functions also as
a set retardant.
Tests 2 and 3 show that the dispersant SPERSENE functions also as a set
retardant because even with an increased amount of BELLASOL S-29, the set
time decreased with the SPERSENE removed. Tests 3 through 6 show the
increasing set retardation with increasing amounts of BELLASOL S-29. Tests
3 through 6 also show, because a non-setting slurry was provided, that the
BELLASOL S-29 also is an effective dispersant, making the SPERSENE
unnecessary in the systems of this example.
Tests summarized in Table 3 show that both a dispersant and an antigelant
are useful under some conditions. The aggregates and water alone cannot be
mixed in a slurry. Also the aggregates, water, and SPERSENE mix to form a
fluid slurry but when the SECAR is added the slurry becomes unmixable
within three minutes even though the exothermic setting reaction occurs
considerably later.
Different antigelants, even various members of the same chemical family,
behave quite differently in the cement slurries. As examples, Table 3
lists the gelling and setting properties noted for several members of the
BELLASOL family (poly acrylic acid with sodium phosphinate), including
BELLASOL S-29. The tests were made at 120.degree. F. with solids
Distribution 2 at an antigelant concentration of 3.35 lb/bbl of slurry and
0.5 lb/bbl XCD as a suspending agent. The table also shows the effects of
an additional retarder (SPERSENE) on the setting properties. Setting times
and gelation times are relatively short for tests of Table 3 compared to
those of Table 2 because the solids Distribution 2 includes 10% of cement
as opposed to 5% in solids Distribution 1.
TABLE 3
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EXOTHERM TIMES
GELATION TIME
TEST
ADDITIVE SPERSENE
START PEAK More Than
Less Than
NO. NAME MOL. WT.
LB/BBL HOUR:MINUTE
HOUR:MINUTE
HOUR:MINUTE
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7 DP3152 900 0 1:42 3:04 -- --
8 BELLASOL S-30
2000 0 1:13 2:53 -- --
9 " " 0.8 3:01 5:29 00:30 1:00
10 " " 1.0 3:37 6:27 00:30 1:00
11 BELLASOL S-29
3800 0 1:53 9:22 -- --
12 " " 1.0 12:19 30:35
24:18 89:09
13 " " 2.0 103:35
123:05
89:00 128:00
14 DP3326 8000 0 0:24 1:24 -- --
15 " " 1.0 2:43 5:10 -- 0:37
16 " " 2.0 7:05 11:05
-- 0:37
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At the additive concentration of Test Nos. 7 through 16 (3.35 lb/bbl), each
of these four materials gave satisfactory initial antigelant and
dispersant actions but none, acting alone, had a sufficient set-retarding
ability. When an effective retarder (SPERSENE) was added, only BELLASOL
S-29 retained its antigelant properties long enough to make the system
useful for wellbore cementing.
Stirability imparted to the alumina cement slurries by the antigelant
materials is further demonstrated by the thickening time tests shown as
Table 4. These tests were at 120.degree. F. using solids Distribution 2,
0.5 lb/bbl XCD, amounts of BELLASOL S-29 listed in Table 4, and no
additional dispersants or retarders.
TABLE 4
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TIME TO
TEST BELLASOL EXOTHERM PEAK THICKENING
NO. S-29 LB/BBL
HOUR:MINUTE TIME
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17 2.95 6:34 2:20
18 3.48 154:57 17:52
19 3.82 92:47 11:15
20 4.06 139:31 19:30
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These data show that the antigelants can extend the gelation times of the
alumina cement slurries sufficiently to allow safe placement in wells.
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Description |
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