Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Agent and Method for Sealing or Consolidating Rock, Loose Rock or
Soils, Especially Boreholes
This invention relates to a composition and a process for sealing or
consolidating rock, mantle rock or soils and to the use for this purpose of
certain silica sols containing hardness stabilizers.
The consolidation or sealing of rock, mantle rock or soils is a
measure regularly necessary in construction engineering, for example for
underpinning buildings, for sealing building pits or tips, in tunnel and canal
construction and, above all, in geological exploration, such as the drilling
of
oil or natural gas pools. In the last of these applications, the sealing of
wells is particularly important. Wells are sunk into the ground until a
formation carrying oil, gas or - in well construction - water is reached. The
well is stabilized against the formation by a cement casing. This cement
casing is broken open at the bottom of the well so that the material to be
brought up is able to pass freely from the formation into the well. Besides
oil or gas, however, water also enters the well and has to be removed from
the oil/gas by elaborate processes. Accordingly, efforts are made to
minimize or avoid the penetration of water, so that the water-carrying parts
of the formation are sealed off by suitable binders. However, consolidation
or sealing is also a standard measure in the protection of agricultural land
against wind or water erosion.
In general, binders, such as cement, bitumen, calcium salts or
waterglass, are used in construction engineering. However, cement has
the disadvantage that the particles are often not small enough to be able to
penetrate into fine cracks or pores, resulting in an unsatisfactory sealing or
consolidating effect. Even the use of waterglasses (an aqueous solution of
sodium silicate) or microsilicas (an aqueous dispersion of amorphous
silicon dioxide) does not always produce the required sealing effect.
Accordingly, EP 530 600 proposes the use of silica sots for sealing or
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consolidation. Silica sots are colloidal solutions of amorphous silicon
dioxide which has a particle size of 7 to 50 nm. These silica sols gel in the
presence of certain electrolytes or in the event of changes in the pH of the
aqueous sols. By crosslinking of the Si02 units, the gel becomes more
viscous until consolidation is complete. Electrolytes which initiate gelation
are generally present in the material to be consolidated or sealed. They
are preferably salts of aluminium, iron, calcium or magnesium. However,
EP 0 530 600 A1 proposes using silica sots in combination with a calcium
donor in order to achieve rapid conversion of the sol into the gel.
Now, applicants have found that, surprisingly, the use of silica sots
does not always lead to the required sealing or consolidating effects. This
is particularly the case in the sealing of wells against penetrating formation
water. According to applicants' observations, a free water phase frequently
occurs which is a sign that no gelation and hence no sealing has taken
place. Accordingly, without being confined to one particular theory,
applicants assume that, in contrast to the teaching of EP 0 530 600 A1, the
formation of alkaline earth metal silicates and, above all, calcium silicate
can inhibit the gelation process. Accordingly, one of the problems
addressed by the present invention was to provide a sealing or
consolidating process which could even be carried out in the presence of
water containing alkaline earth metal ions.
In addition, it is often not desirable in the sealing of wells to achieve
rapid solidification of the binder. The binder is transported under pressure
to the bottom of the well through a suitable pipe and is forced into the
formation there. The effect of rapid solidification of the binder would be
that
the binder would also gel in the pipe itself which of course is not what is
wanted. On the contrary, the gelling effect should be delayed to the extent
that the entire binder is forced into the formation by flushing, for example
with water, so that gelation and consolidation only occur in the required
places. Accordingly, another problem addressed by the present invention
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was to provide a process for the delayed consolidation or sealing of rock,
mantle rock or soils.
It has now surprisingly been found that a mixture of aqueous silica
sol and certain inhibitors for Ca2+ ions solves the problems stated above.
In a first embodiment, the present invention relates to a water-based
composition for sealing or consolidating rock, mantle rock or soils in contact
with water containing Ca2+ ions, the composition containing 2 to 40% by
weight of Si02 (dry matter, based on the composition) in the form of an
aqueous silica sol and, in addition, hardness stabilizers from the class of
inorganic polyphosphates, phosphonic acids, aminoethylene phosphonic
acids, phosphoric acid esters, phosphonocarboxylic acids and
polycarboxylic acids or mixtures of these substances in concentrations of
0.01 to 400 ppm.
The compositions according to the invention are generally suitable
both for the consolidation and for the sealing of any type of rock, mantle
rock or soils in contact with water containing Ca2+ ions. Typical
applications include construction engineering, particularly tunnel and well
construction, and geological exploration, more particularly the sealing of
wells, more precisely their walls, against penetrating formation water.
Besides water, the compositions according to the invention contain
silica sols containing amorphous Si02 in quantities of 2 to 60% by weight,
expressed as dry matter and based on the sol, as carrier liquid. However,
silica sols containing 25 to 50% by weight amorphous Si02 are preferred
for the compositions according to the invention. The amorphous Si02 is
present in the form of non-interlinked spherical individual particles surface-
stabilized by hydroxyl groups. The average particle diameter is in the
range from 1 to 150 nm, preferably in the range from 5 to 70 nm and more
particularly in the range from 5 to 40 nm. The specific surface of the silica
sols is in the range from 50 to 700 m2lg, as measured by the BET method.
By virtue of the colloidal distribution of the particles, no sedimentation of
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particles is observed with silica sols. Accordingly, the sots may be stored
for years. Aqueous silica sols are generally used. However, amorphous
Si02 may also be converted into sols in other solvents, for example
acetone or short-chain organic alcohols, such as methanol, ethanol or
propanol (cf. Ullmanns Encyklopadie der Technischen Chemie, 4th
Edition, Vol. 21, pages 456 to 463, Weinheim 1982). However, the
compositions according to the invention contain only aqueous silica sols.
The compositions according to the invention contain in all, i.e.
including the water content of the silica sots, between 60 and 98% by
weight and more particularly between 60 and 80% by weight of water which
preferably contains only small amounts of electrolytes, for example
between 0.001 and 0.1 % by weight. The water is preferably free from
electrolytes. Electrolytes in the present context are understood in particular
to be cations of mono- and divalent alkali metal and alkaline earth metal
ions, i.e. Na+, K+, Ca+ and Mg2+ ions. Aqueous silica sols of the type
described above are present in the compositions in quantities of 20 to 60%
by weight. According to the invention, so-called hardness stabilizers are
added to the mixture of silica sol and water in concentrations of 0.01 to 400
ppm. Hardness stabilizers are compounds which, in less than
stoichiometric quantities known for the purpose, are capable of completely
and permanently preventing the precipitation of hardness ions from
supersaturated aqueous solutions. To this extent, it was surprising that the
addition of these compounds only leads to delayed gelation of the silica
sols but does not permanently suppress their gelation. Hardness ions are
mainly alkaline earth metal ions, more particularly calcium and magnesium
ions (threshold effect). Particulars can be found in Rompps Chemie
Lexikon, 9th Edition, Vol. 6, 1994, pages 5000 to 5002.
The compositions according to the invention contain compounds
from the class of inorganic polyphosphates, phosphoric acid,
aminoethylene phosphoric acids, phosphoric acid esters,
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phosphonocarboxylic acids and polycarboxylic acids or mixtures thereof as
hardness stabilizers. Salts of these compounds are also suitable.
Compositions containing hardness stabilizers from the group consisting of
aminotris(methylenephosphonic acid), 1-hydroxyethane-1,1-diphosphonic
acid, phosphonobutane tricarboxylic acid, polyacrylic acid, polyaspartic
acid, polymaleic acid or derivatives thereof or mixtures of these compounds
are particularly preferred. Compositions containing tetrakis-[(phosphono-
methyl)-imino]-bis-[2,1-ethanediylnitrido-bis-methylene]-phosphonic acid
andlor salts thereof as hardness stabilizers are most particularly preferred.
Preferred mixtures of these stabilizers contain, for example, 1-
hydroxyethane-1,1-diphosphonic acid sodium salt and polyacrylic acid or 1-
hydroxyethane-1,1-diphosphonic acid sodium salt, aminotris-
(methylenephosphonic acid) and polyacrylic acid. The concentration in
which the hardness stabilizers are used is between 0.01 and 400 ppm,
more particularly in the range from 0.1 to 200 ppm and preferably in the
range from 1 to 100 ppm, based on hardness stabilizer active substance.
In another embodiment, the present invention relates to a process
for sealing or consolidating rock, mantle rock or soils in contact with water
containing Ca2+ ions, in which the material to be consolidated or sealed is
contacted with a solution containing aqueous silica sol and hardness
stabilizers from the class of inorganic polyphosphates, phosphonic acids,
aminoethylene phosphonic acids, phosphoric acid esters, phosphono-
carboxylic acids and polycarboxylic acids or mixtures of these substances.
Aqueous silica sols containing 20 to 60% by weight Si02 (dry matter,
based on the aqueous sol) are preferably used for this purpose. In
general, the composition is forced under pressure into the material to be
sealed or consolidated. The hardness stabilizers are then added during or
after the treatment with the silica sol. They are preferably used in such
quantities that the stabilizer concentration, based on the aqueous silica sol
solution, is in the range from 0.01 to 400 ppm, preferably in the range from
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0.1 to 200 ppm and more particularly in the range from 1 to 100 ppm.
In one particularly preferred embodiment, the process according to
the invention is used for sealing underground formations, more particularly
wells. To this end, the silica sollwaterlstabilizer mixture is pumped through
the feed pipe by suitable pumps to the bottom of the well, such a pressure
being applied that the mixture penetrates deeply into the formation. This is
followed by flushing with water until the mixture has been completely
removed from the pipe. In this connection, the process according to the
invention enjoys another advantage because the composition used only
gels with a certain delay. Under the temperature, pH and pressure
conditions at the bottom of the well, the composition preferably solidifies
some 30 to 60 minutes after contacting with the material to be consolidated
or sealed and hence with the water containing Ca2+ ions. The
temperatures at the bottom of the well are normally in the range from 30 to
200°C, depending on the depth. The pressure is typically between 10 and
500 bar, again dependent on depth.
The most suitable stabilizer concentration can be selected in
dependence upon the concentration of Ca2+ ions in the water with which
the material to be consolidated or sealed is in contact. It has been found
that the hardness stabilizers should preferably be present in the
compositions according to the invention in such quantities that, based on a
predetermined volume, the ratio by weight of Ca2+ ions to the hardness
stabilizers is in the range from 0.5 to 5.0:1. The quantity of Ca2+ ions may
readily be calculated through the determination of the water hardness.
The water in contact with the material to be consolidated or sealed
generally has a content of Ca2+ ions of greater than 2 mmolll and preferably
greater than 4 mmolll. Typical Ca2+ concentrations are in the range from 3
to 8 mmol/l. The pH of the formation water is generally in the acidic to
mildly alkaline range, i.e. between 6 and 9. It has been found that a
reduction in pH to values of 2 to 5 can generally prevent gelation.
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Accordingly, the process according to the invention is preferably carried out
at pH values of 6 to 9 or the composition according to the invention is
preferably formulated by addition of acids or bases in such a way that its
pH value is in the range mentioned.
The present invention also relates to the use of the compositions
described in the foregoing for consolidating or sealing rock, mantle rock or
soils in contact with water containing Ca2+ ions.
Examples
The effectiveness of the process according to the invention was
determined as follows: 11 g of a silica sol (Kostrosol~ 0830 of
Chemiewerk Bad Kostritz) were mixed with 40 g of deionized water and
hardness stabilizers were subsequently added to the sol in various
quantities. Between 0.7 and 1.0 ml of a calcium chloride solution
(concentration of Ca2+ ions: 28,200 ppm) was then added dropwise to the
resulting mixture, followed by heating for 15 minutes to 100°C. The
vessel
was left standing without stirring to cool. After 30 minutes, the degree of
gelation was visually determined.
The following evaluation was made:
100% solid ++
80 to almost 100% solid +
less than 80% solid -
The following hardness stabilizers were tested:
A: 1-hydroxyethane-1,1-diphosphonic acid
B: amino-tris-(methylene phosphonic acid)
C: 1-hydroxyethane-1,1-diphosphonic acid disodium salt
D: mixture of B and C and polyacrylic acid
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The stabilizers were used in the form of commercially available
aqueous solutions (all products of Henkel KGaA):
A: 60% by weight active substance (Turpinal~ SL)
B: 50% by weight active substance (Turpinal~ D2)
C: 10% by weight active substance (Turpinal~ -2-NZ)
D: 30% by weight active substance (Fostex~ 617 B)
The quantities in Table 1 are based on active substance.
The results of the tests are set out in Table 1.
Table 1
No. StabilizerStabilizerCaCl2 Ca2+ contentRatio by Gelation
concentrationsolutionin the weight after
ppm] ml solution Caz+atabilizer30
% b wei mins.
ht
1 A 0.1 0.8 0.04 0.7 ++
2 A 0.2 0.8 0.04 1.0 ++
3 B 0.3 0.8 0.04 1.4 +
4 B 0.3 0.7 0.04 2.0 ++
C 0.7 1.0 0.06 1.3 ++
6 C 0.7 1.0 0.06 1.5 +
7 D 0.7 1.0 0.06 4.0 ++
Tests were also carried out at elevated temperature and pressure in
order to simulate the conditions prevailing at the bottom of the well.
Quantities of 5 g of a 50% by weight aqueous silica sol were diluted with 45
g of water and a certain ratio by weight of Ca2+ to Si02 was then adjusted
by addition of a CaCl2 solution (0.04% by weight Ca2+). The system was
then heated for 30 minutes to 150°C in an autoclave under 10 bar
pressure
(nitrogen atmosphere) and left under those conditions for two hours. The
results of the visual evaluation of the solutions are set out in Table 2.
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Table 2
Solution Ca:Si02 Effect
b wei ht]
8 0.005 Thinly liquid
9 0.010 Slight gelation
0.020 Gelation
11 0.030 Gelation
Various quantities of stabilizer D were then added to solution 10
under the described conditions. It was found that the addition of 100 and
200 ppm of stabilizer resulted in delayed gelation after three hours. At
higher concentrations, there was no sign of gelation. Accordingly, the
process according to the invention leads to a desired delay in the gelation
of the silica sol solutions, even at elevated temperature and pressure.
