USE OF CSH SUSPENSIONS IN WELL CEMENTING

UTILISATION DE SUSPENSIONS DE CSH (SILICATE DE CALCIUM HYDRATE) DANS LE CIMENTAGE DE PUITS DE FORAGE

English Abstract

The use of a setting accelerator composition for inorganic binders which
comprises at
least one water-soluble comb polymer suitable as a superplasticizer for
hydraulic
binders and calcium silicate hydrate particles in the development,
exploitation and
completion of underground mineral oil and natural gas deposits and in deep
wells is
proposed.

The use according to the invention not only accelerates the setting and
hardening of
the cement slurries but also shortens the time in which the static gel
strength of the
hardening cement slurries increases from 100 lb/100 ft2 (4.88 kg/m2) to 500
lb/100 ft2
(24.4 kg/m2).

French Abstract

L'invention concerne l'utilisation d'une composition d'accélérateur de prise pour les liants inorganiques, laquelle comprend au moins un polymère à structure en peigne soluble dans l'eau convenant comme agent fluidifiant pour liants hydrauliques et des particules de silicate de calcium hydraté, pour la mise en valeur, l'exploitation et le conditionnement de gisements de pétrole et de gaz naturel ainsi que pour les forages profonds. L'utilisation selon l'invention n'accélère pas uniquement la prise et le durcissement des coulis de ciment mais raccourcit également le temps au cours duquel la résistance statique de gel des coulis de ciment durcissants augmente de 4,88 kg/m2 (100 lb/100 ft2)à 24,4 kg/m2 (500 lb/100 ft2).

Claims

6

CLAIMS:
1. A method for accelerating the setting of a cement slurry comprising
adding a
sufficient amount of an accelerator composition to a cement slurry;
wherein the cement slurry comprises water and an inorganic binder;
wherein the accelerator composition comprises a water-soluble comb polymer;
and
particles consisting of calcium silicate hydrate, wherein said particles are
smaller than 5 pm;
wherein the comb polymer has a main chain;
wherein the comb polymer has side chains comprising polyether functions and
acid
functions;
wherein the side chains are present on the main chain; and
wherein the inorganic binder comprises Portland cement.
2. The method of claim 1, wherein the time in which the static gel strength
of the
hardening cement slurry increases from 4.88 kg/m2to 24.4 kg/m2 is shortened
compared to
the time in which the static gel strength of an identical hardening cement
slurry that does not
comprise the accelerator composition increases from 4.88 kg/m2 to 24.4 kg/m2.
3. The method of claim 1, wherein the setting accelerator composition is a
suspension.
4. The method of claim 3, wherein the suspension is an aqueous suspension.
5. The method of claim 1, wherein the comb polymer is a copolymer which is
obtained
by free radical copolymerization of acid monomers and polyether macromonomers,
the
copolymer as a whole comprising at least 45 mol % of the acid monomer or the
polyether
macromonomer structural units.
6. The method of claim 1, wherein the comb polymer comprises at least one
member
selected from the group consisting of (meth)acrylic acid, maleic acid, a
polyalkylene glycol
vinyl ether, a polyalkylene glycol allyl ether and polyalkylene glycol
(meth)acylate structural
units.

7

7. The method of claim 1, wherein the comb polymer has an average molecular
weight
(Mw) of from 5,000 to 200,000 g/mol as measured by gel permeation
chromatography.
8. The method of claim 1, wherein the calcium silicate hydrate has a molar
ratio of
calcium to silicon of from 0.6 to 2Ø
9. The method of claim 1, wherein the molar ratio of calcium to water in
the calcium
silicate hydrate is from 0.6 to 6.
10. The method of claim 1, wherein said particles are obtained by reacting
a water-
soluble calcium compound with a water-soluble silicate compound, wherein the
reaction is
effected in the presence of an aqueous solution of the water-soluble comb
polymer.
11. The method of claim 1, wherein the inorganic binder further comprises
at least one
member selected from the group consisting of a calcium aluminate cement,
anhydrite, blast
furnace slag, slag sand, fly ash, silica dust, metakaolin, natural pozzolanas,
synthetic
pozzolanas and calcined oil shale.
12. The method of claim 1, wherein the inorganic binder further comprises
calcined oil
shale.
13. The method of claim 1, wherein said particles are smaller than 1 µm.
14. The method of claim 1, wherein the accelerating of the setting of the
cement slurry
occurs in an underground oil or natural gas well.
15. The method of claim 14, wherein the underground oil or natural gas well
is offshore.
16. The method of claim 14, wherein the underground oil or natural gas well
is in
permafrost region.
17. The method of claim 14, wherein the underground oil or natural gas well
is in a
permafrost region or is offshore.
18. The method of claim 1, wherein said particles are smaller than 500 nm.
19. The method of claim 1, wherein said particles are smaller than 200 nm.

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20. The method of claim 1, wherein said particles are smaller than 100 nm.
21. The method of claim 1, wherein the setting accelerator composition is a
powder.
22. The method of claim 1, wherein the comb polymer comprises at least one
member
selected from the group consisting of a polyalkylene glycol vinyl ether and
polyalkylene glycol
(meth)acrylate structural units.
23. The method of claim 1, wherein the accelerating of the setting of the
cement slurry
occurs in an underground mineral oil, natural gas, or water deposit, wherein
the deposit is
under high pressure and varying temperature conditions.

Description

1
Use of CSH suspensions in well cementing
The present invention relates to the use of CSH suspensions in the
development,
exploitation and completion of underground mineral oil and natural gas
deposits and in
deep wells.
Underground mineral oil, natural gas and water deposits are often under high
pressure.
Drilling in such formations requires that the pressure of the circulating well
fluid be
sufficiently high to counteract effectively the pressure of the underground
formations
and thus prevent the uncontrolled emergence of the formation fluids into the
well.
As a rule, wells are lined section by section with steel pipes. The annular
gap between
the well casings and the underground formations is then filled with cement.
This can be
effected by forcing a cement slurry directly into the annular gap or through
the well
casing into the well in order then to flow backwards into this annular gap as
a result of
the pressure applied. The hardened cement firstly prevents formation fluids
from
emerging in an uncontrolled manner into the well and secondly prevents
formation
fluids from penetrating unhindered into other formations.
The temperature conditions of the deposits vary considerably. The temperatures
in
surface-near areas of permafrost regions, such as, for example, Alaska, Canada
and
Siberia, and in offshore wells at high latitudes may be below freezing point
and may be
up to 400 C in the case of geothermal wells. For this reason, the setting
behavior of the
cement slurries used must always be adapted to the prevailing conditions.
While
retardants are generally required at elevated temperatures, setting
accelerators often
have to be used at low temperatures. Moreover, the use of superplasticizers
and/or
fluid loss additives known per se in the prior art in the cement slurries used
can lead to
a prolongation of the setting times, which likewise necessitates the use of
accelerators.
According to Erik B. Nelson, Well Cementing, Schlumberger Educational
Services,
Sugar Land, Texas, 1990, chapter 3-3, calcium chloride is without a doubt the
most
frequently used, most effective and most economical setting accelerator for
Portland
cements. The CaCl2 is as a rule used in concentrations of 2-4% bwoc (% by
weight,
based on the cement fraction). Unfortunately, the results are unforeseeable at

concentrations above 6% bwoc, and premature setting reactions may occur. In
addition, there is a risk of corrosion of the casing string by the chloride
ions.
The object of the present invention was therefore substantially to avoid the
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disadvantages associated with the prior art. In particular, there was a need
for
alternative accelerators which do not have the above disadvantages.
This object was achieved by the features of claim 1. The dependent claims
relate to
preferred embodiments.
WO 2010/026155 Al describes curing accelerator compositions which, in addition
to a
water-soluble comb polymer suitable as a superplasticizer for hydraulic
binders, also
comprise calcium silicate hydrate particles of suitable size (see for example
claims 40
to 52 of the WO specification).
It has now surprisingly been found that such compositions can also be used as
setting
accelerator compositions for inorganic binders in the development,
exploitation and
completion of underground mineral oil and natural gas deposits and in deep
wells.
The present invention accordingly relates to the use of a setting accelerator
composition for inorganic binders which comprises at least one water-soluble
comb
polymer suitable as a superplasticizer for hydraulic binders and calcium
silicate hydrate
particles in the development, exploitation and completion of underground
mineral oil
and natural gas deposits and in deep wells.
The setting accelerator composition is used here either as a suspension,
preferably as
an aqueous suspension, or in powder form.
The comb polymer is preferably a copolymer which has side chains comprising
polyether functions as well as acid functions, which are present on a main
chain. It is
obtainable, for example, by free radical copolymerization of acid monomers and

polyether macromonomers, the copolymer as a whole comprising at least 45 mol%,

preferably at least 80 mol%, of structural units derived from the acid
monomers and/or
the polyether macromonomers.
The comb polymer preferably comprises structural units derived from
(meth)acrylic
acid, maleic acid, polyalkylene glycol vinyl ethers, polyalkylene glycol allyl
ethers
and/or polyalkylene glycol (meth)acrylates. For a detailed discussion of
suitable
structural units, reference is made to claims 47 to 49 of WO 2010/026155 Al.
Suitable
comb polymers expediently have average molecular weights (Mw) of from 5000 to
200 000 g/mol, preferably from 10 000 to 80 000 g/mol and in particular from
20 000 to
70 000 g/mol, measured by means of gel permeation chromatography.
In addition to said comb polymer, polycondensates, in particular of the type
disclosed in
claims 28 to 33 and 50 of WO 2010/026155 Al, may also be present.

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In the calcium silicate hydrate used, the molar ratio of calcium to silicon is
preferably
from 0.6 to 2.0, in particular from 1.1 to 1.8. The molar ratio of calcium to
water in the
calcium silicate hydrate is preferably from 0.6 to 6, particularly preferably
from 0.6 to
2.0 and in particular from 0.8 to 2Ø
The calcium silicate hydrate particles used are expediently obtainable by
reacting a
water-soluble calcium compound with a water-soluble silicate compound, the
reaction
preferably taking place in the presence of an aqueous solution of the water-
soluble
comb polymer suitable as a superplasticizer for hydraulic binders. Regarding
further
details of a suitable preparation process, reference is made to claims 1 to 38
of
WO 2010/026155 Al.
Suitable calcium silicate hydrate particles are expediently smaller than 5 pm,
preferably
smaller than 1 pm, more preferably smaller than 500 nm, particularly
preferably smaller
than 200 nm and in particular smaller than 100 nm.
Preferably, Portland cements, calcium aluminate cements, gypsum, anhydrite,
blast
furnace slag, slag sands, fly ashes, silica dust, metakaolin, natural and
synthetic
pozzolanas and/or calcined oil shale, preferably Portland cements, are
suitable as
inorganic binders whose setting is accelerated according to the invention.
These binders are expediently used in the form of a cement slurry, the
water/cement
value preferably being in the range from 0.2 to 1.0, in particular in the
range from 0.3 to
0.6.
One field of use which is considered in particular according to the invention
is well
cementing of mineral oil and natural gas wells, in particular in permafrost
regions and in
the offshore sector.
Here, the use according to the invention accelerates the setting of the cement
slurry. At
the same time, the hardening rate of the cement slurry is advantageously
increased.
Moreover, the time in which the static gel strength of the hardening cement
slurry
increases from 100 lb/100 ft2 (4.88 kg/m2) to 500 lb/100 ft2 (24.4 kg/m2) is
advantageously shortened. This is advantageous particularly in well cementing
since
the hardening cement slurry tends to crack in the middle range of gel strength
owing to
ascending gas bubbles. This range is passed through quickly according to the
invention.
The setting accelerator composition is used according to the invention
advantageously
together with other additives customary in well cementing, in particular
superplasticizers, water retention agents and/or rheology-modifying additives.

4
The present invention will now be explained in more detail an the basis of the
following
working example with reference to fig. 1. Here:
Fig. 1 shows the increase in the compressive strengths of different
cement
slurries as a function of time.
Use example 1
The preparation of the cement slurries was effected according to API
specification 10,
section 5 and appendix A. For this purpose:
700 g of cement (Lafarge, class H)
266g of tap water
3.5 g of Liquiment K3F (superplasticizer, product of BASF Construction
Polymers
GmbH)
3.5 g of Polytrol FL 34 (fluid loss additive, product of BASF Construction
Polymers
GmbH)
1.0 g of tributyl phosphate (antifoam)
were homogeneously mixed. Either no additives (blank value), 0.80% bwoc of
CaCl2 or
different amounts of X-Seed 100 (product of BASF Construction Polymers GmbH;
aqueous calcium silicate hydrate suspension, particle size < 100 nm, solids
content
about 21% by weight, active proportion of calcium silicate hydrate about 7% by
weight,
comb polymers used: MVA2500 and EPPR312, both according to the present
invention, likewise commercial products of BASF) were added to the samples.
The X-Seed 100 was added in an amount of 0.07% bwoc, 0.15% bwoc,
0.30% bwoc and 1.50% bwoc, based in each case on the active proportion of
calcium silicate hydrate.
The samples were measured in a static gel strength analyzer (Chandler
Engineering)
at a temperature of 23 C and a pressure of 1000 psi (about 69 bar). The time
in which
the static gel strength of the samples increased from 100 lb/100 ft2 (4.88
kg/m2) to
500 lb/100 ft2 (24.4 kg/m2) is stated in table 1
Table 1
Sample Time [min]
Blank value 76.5
0.80% bwoc of CaCl2 44.0
0.07% bwoc of X-Seed 100 52.5
0.15% bwoc of X-Seed 100 38.0
0.30% bwoc of X-Seed 100 13.5
1.50% bwoc of X-Seed 100 15.5
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In addition, the variation of the compressive strength with time was measured.
The
results are shown in graphical form in fig. 1.
It is evident that the calcium silicate hydrate suspension accelerates the
increase in the
compressive strength to a greater extent at lower dose than CaCl2, at the same
time
the time in which the static gel strength of the samples passes through the
critical
range being substantially shortened.

Representative Drawing