Note: Descriptions are shown in the official language in which they were submitted.
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TITLE OF THE INVENTION
SILICEOUS PROPPANT PROCESS OF MANUFACTURE
FIELD OF THE INVENTION
The subject of the invention refers to the production of siliceous ceramic
proppants having a high percentage of SiO2 (preferably 71 mass.% and more) and
meant for oil industry as propping agents used during hydraulic fracturing
process.
BACKGROUND OF THE INVENTION
Proppants are solid spherical granules preventing cracks in oil wells from
closing
due to over high pressure and ensuring the necessary productivity of oil wells
by
creating a conductive channel in the layer.
Different organic and non-organic materials are used as proppants: walnut
shells,
sand, resin-coated sand, etc. However, due to the particularities of their
microstructure
ceramic proppants are of primary use because their main characteristics
determined by
ISO 13503-2:2006(E) requirements (granulometry, sphericity, roundness, crush
resistance, density, acid solubility, turbidity of fracturing fluid wetting
proppants) surpass
other products used in hydraulic fracturing processes.
Among ceramic proppants, silica-alumina and silica-magnesia proppants are the
most common. Siliceous proppants are less present on the market. The flow
sheets of
ceramic proppants production are similar in the majority of cases and include
charge
make-up (as a rule mixing of pre-grinded original components in specified
ratio), its
granulation and high-temperature burning to obtain the maximum density and
optimize
chemical and phase composition of ceramics.
Crush resistance and turbidity of fracturing fluid wetting proppants are very
important processing factors determining their consumer properties. Turbidity
index
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specifies the number of fine-dispersed particles suspended in the wetting
fluid. The
higher this index is, the higher the quantity of suspended particles in the
fluid is.
Fine-dispersed dust forms during proppants sieving, packing, transportation
and
feeding into the well due to some attrition of their granules during contact.
A high content of dust-like particles results in their accumulation in the
extraction
channel of proppants pack and reduces its permeability.
In recent years researchers have aimed their efforts at searching for natural
raw
materials ensuring admissible values of the above-mentioned characteristics.
In this
context siliceous proppants rich in silicon dioxide and having a fair quantity
of glass
phase in the volume of granules and on their surface are particularly
interesting.
A process is known for making ceramic proppants for oil wells manufacturing
from
magnesium silicate containing from 55 to 80% of forsterite. The material is
gradually
grinded, granulated and burned at 1150-1350 C. (Russian Federation Patent No.
2235703).
The disadvantage of this known process is that proppants manufactured in this
way have an increased index of turbidity of wetting fluid and insufficient
factor of
strength.
This is explained by the fact that the glass phase formed in these proppants
is of
low strength, non-uniformed by volume and has a coefficient of thermal linear
expansion
different from that of the master crystalline phase. Consequently,
microfractures that are
formed in volume and on proppant surfaces during its cooling reduce the
solidity of the
proppants and increase the turbidity of the wetting fluid.
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United States Patent No. 6.753.299 sets out the advanced composition of
lightweight proppants having less than 25% of alumina, 45% - 70% of silica and
less
than 10% of the binding agent wollastonite and talc (proportioning by weight).
This lightweight proppant is made by mixing grinded components of bauxite,
quartz,
shale and binding agents - talc and wollastonite. In addition starch and water
are added
to this mixture, which is subsequently granulated and burned. The burning is
made at a
temperature range of 1100- 12000 C.
A disadvantage of this known process is the increased index of turbidity of
the
wetting fluid and an insufficient strength. The reason is that wollastonite
and talc used
as binding agents form, together with other additives, fragile glass phase in
proppant
granules non-uniformed by volume and having a coefficient of thermal linear
expansion
different from that of the master crystalline phase.
SUMMARY OF THE INVENTION
Therefore, in accordance with the present invention, there is provided a
process
for the manufacture of siliceous proppants, comprising charge make-up by
mixing
reference grinded components, wherein a granulation and burning thereof
differing in
that at the stage of charge make-up, grinded inorganic fluoride is added in
the quantity
of 1-9 mass % and granule burning is made at a temperature range of between
950'C
and 1050'C.
The above process is also novel in that the fractional content of grinded
charge
and inorganic fluoride is of 40 microns and less.
The above process is further novel in that the grinded inorganic fluoride is
taken
as a mono-compound and/or as a mixture of several fluorine-containing
compounds.
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DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS OF THE INVENTION
In general terms, the present invention addresses the technical problem by
decreasing the wetting fluid turbidity during proppants use due to their
strength increase
by force of a general glass phase quantity growth and its more uniform
distribution
throughout the granule volume.
The mentioned result is obtained by adding grinded non-organic fluoride in the
quantity of 1-9 mass.% at the stage of the charge mixture of the conventional
process of
siliceous proppants manufacture which includes its granulation and the burning
of
granules at the temperature range of 950 -1050 C.
The fractional composition of grinded charge and non-organic fluoride is 40
microns
and less (during sieve analyses, not more than 1 % being retained on a screen
#004). In
addition, grinded fluoride is taken as a mono-compound as well as a mixture of
several
non-organic fluorine-containing compounds.
It is known that the majority of raw materials used in the manufacture of
siliceous
proppants contain low-melting oxides (K20, Na20, etc.), which form a liquid
phase while
burning and arbitrarily distribute between grains of master crystalline phases
in the form
of amorphous glass phase of variable chemical composition when cooling.
Additionally, supplementary internal stress is formed in the volume of
proppant
granule due to the difference in the coefficient of thermal linear expansion
between
glass phase and crystalline phase. On application of external stress, fracture
is
developed in areas having the smallest resistance to fracture initiation and
propagation. As amorphous glass phase has less strength properties in
comparison to
master crystalline phases, fracture of ceramic proppants is mainly of
intergranular
nature. Introduction of the abovementioned quantity of grinded non-organic
fluoride in
charge composition meant for siliceous proppants manufacture allows to reduce
the
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turbidity of wetting fluid and to increase proppants strength by means of
total glass
phase quantity increase and its more equal volume distribution in proppant
granule.
In the framework of the technical solution of the present invention, the
following
agents may be used as non-organic fluorides: fluorine-apatite, fluorite,
potassium
fluozirconate, sodium aluminum fluoride, etc.
Fluorine-containing non-organic compounds, being flux, reduce considerably
the sintering temperature of proppants and may be used as sintering additives
for
ceramic mixtures meant for siliceous proppants production. In the process of
glass
and glassceramics manufacture, fluorides are used as an accelerator and as a
catalyst
of crystallization.
Thus, burning of siliceous proppants granules results in the quick formation
of
glass phase and the presence of F-ions in material led to the fact that
amorphous glass
phase crystallizes with considerably increased strength properties.
A further advantage is that the introduction of non-organic fluoride in
specified
quantities into ceramic charge for proppants manufacture does not require a
supplementary crystallization as commonly used in glassceramics production
practice.
In addition, the presence of non-organic fluoride in material results in
additional
formation of increased quantity of glass phase in proppants volume and
especially on
their surface, which conduces in turn to the densification and abrasion
resistance
increase thereof.
The improvements in the operating characteristics of the proppants of the
present
invention, which are due to non-organic fluoride introduction into charge
composition, is
achieved only if the siliceous materials that are used have 71 mass % and more
of SiO2.
This is due to the fact that the abovementioned charge has a large quantity of
glass
phase which is strengthened under the F-ions influence.
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The choice of the type of fluoride is determined by the composition of its
primary
components and their balance.
The criteria of charge choice and burning temperature optimization are clear
for
specialists working in the industry of ceramic proppants production.
If the content of Si02 in the charge is less than 71 mass %, the total glass
phase
quantity in proppant volume is reduced thereby resulting in proppants density
and
strength decrease, and consequently in a turbidity rise of the wetting fluid.
Primary components and fluorine-containing additive grinding (40 microns and
less) is made to obtain a more equal distribution of glass phase in proppant
volume
during burning.
Experience has shown that when using specified materials with particle sizes
of
more than 40 microns, there is formed a lot of melting marks on the proppant
surfaces.
In addition, proppants have increased turbidity of wetting fluid and decreased
strength.
This is likely to be related to the coefficient difference of thermal linear
expansion
between non-uniform large areas of glass phase and particles of crystal phase.
Introduction of fluorine-containing non-organic compounds in the charge in a
quantity of less than 1 mass % does not have notable effect on proppants
properties,
and if their quantity is more than 9 mass % there results in the formation of
a large
number of cakes due to the abrupt increase of glass phase quantity.
Proppants burning at a temperature of less than 950 C does not result in a
sufficient densification of proppants granule when sintering. Consequently,
the material
has weak strength properties and increased turbidity of wetting fluid. At a
burning
temperature of more than 1050 C, granules are alloyed.
A natural raw material that is particularly well suited for use in the
realization of the
technical solution of the present invention is feldspar quartz sand that has
more than 71
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mass % of SiO2. Russian sands from Pyshminskoe, Malyshevskoe and Nikolskoe
deposits of the Sverdlovsk region were used to run experiments.
Examples of implementation of the present invention.
Example 1.
Proppants of silica-magnesia material (fraction 20/40 mesh) were manufactured
in compliance with the present invention as follows: 1 kg of previously
grinded material
(fraction 40 microns and less) with forsterite content 55-80% (48-50 mass % of
SiO2)
and 12 grams (1,2 mass %) of fluorine-apatite (fraction less than 40 microns)
were
placed in a dry-grinding mill. The components were mixed during 30 minutes,
granulated
and burned at different temperatures. Proppants trials with different
percentages of
fluorine-apatite were prepared similarly and burned at different temperatures
sufficient
for complete sintering of the proppants.
Example 2.
Proppants 20/40 mesh were manufactured in compliance with the present
invention as follows: 1 kg of material having 21 mass % of A1203, 64 mass % of
SiO2,
mixture of FeO, CaO, MgO, K2O, TiO2 material, ( the rest is analogous to U
patent N2
6,753,299) were placed in dry-grinding mill; thereto were added 90 grams (9
mass %) of
fluozirconate of sodium (fraction less than 40 microns). The components were
mixed
during 30 minutes, then granulated and burned at temperatures sufficient for
complete
proppants sintering.
Example 3.
20/40 mesh proppants of Pyshminsky deposit sand (86 mass.% - SiO2, 8
mass.% - A1203, 3,2 mass.% - K20+N20, additives - the rest) and feldspar (67.5
mass.% - SiO2, 17.3 mass.% - AI2O3, 12.2 mass.% - K20+N20, additives - the
rest)
were manufactured in compliance with the present invention as follows: 1 kg of
previously grinded sand and feldspar (to have 40 microns fraction) in balance
9:1, 50
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grams (5 mass%) of CaF2 (fraction less than 40 microns) were placed in dry-
grinding
mill, mixed during 30 minutes, then granulated and burned at different
temperatures.
Proppants trials with different percentages of CaF2 were prepared similarly
and burned
at different temperatures sufficient for complete sintering of the proppants.
Example 4.
20/40 mesh proppants of Malyshevsky deposit sand (79 mass.% - SiO2, 11 mass.% -
A1203, 8 mass.% - K2O+N2O, additives - the rest) and clay (67.5 mass.% - S102,
17.3
mass.% - A1203, 12.2 mass.% - K20+N20, additives - the rest) were manufactured
in
compliance with the present invention as follows: 1 kg of preliminary grinded
sand and
clay (40 microns) in ratio: 9.5: 0.5, 15 grams (1.5 mass %) of fluozirconate
of
potassium, and 15 grams (1.5 mass %) of aluminum fluoride of sodium (fraction
less
than 40 microns) were placed in dry-grinding mill, then mixed during 30
minutes,
granulated and burned at different temperatures.
Proppants trials of Ilynsky sand (93 mass.% - SiO2, 3 mass.% - A12O3, 2 mass.%
- K20+N20, additives - the rest) and of Nikolsky sand (70 mass.% - SiO2, 12
mass.% -
AI203, 5 mass.% - K20+N20, additives - the rest) of Sverdlovsky region
deposits were
prepared similarly.
The following tests of prepared trials were done:
1) crush test at 7500 psi
2) turbidity test of wetting fluid in accordance with standard method of ISO
13503 -
2:2006(E).
The tests results are presented in the Table 1 here below.
Table 1 - properties of siliceous proppant
Ns Proppant composition Temperatu Crush Turbidity,
re of resistance, FTU
sintering, mass.% at
C 7500 psi
1 Prop ants of magnesia-silica 1180 5.0 63
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F 2analo )
Proppant of composite 1150 4.3 60
siliceous material (prototype)
3 Proppant of composite 950 4.1 58
siliceous material with 9% of
fluozirconate of potassium
(fraction less than 40
microns)
4 Proppant of magnesia-silica 1050 4.7 60
material with 1.2 mass.% of
fluorine-apatite (fraction less
than 40 microns).
Proppant of magnesia-silica 950 -1050 Multiple cakes -
material with 10 mass.% of are formed
fluorine-apatite (fraction less
than 40 microns).
6 Proppant of magnesia-silica 1040 4.9 61
material with 4 mass.% of
fluorine-apatite (fraction less
than 40 microns).
7 Proppant of Pyshminsky 1000 3.8 38
sand and feldspar (9:1) with
5 mass.% of CaF2
8 Proppant of Pyshminsky 1060 4.3 -
sand and feldspar (9:1) with Proppants
1 mass.% CaF2 cakes are
(fraction less than 40 formed
microns).
9 Proppant of Pyshminsky 950 - 1050 Proppants -
sand and feldspar (9:1) with cakes are
mass.% of CaF2 (fraction formed
less than 40 microns).
10 Proppant of Pyshminsky 1050 Large quantity -
sand and feldspar (9:1) with of cakes are
10 mass.% of CaF2 (fraction formed
more than 40 microns).
11 Proppant of Malyshevsky 980 4.0 32
sand and clay (9.5 : 0.5) with
1.5 mass.% of fluozirconate
of potassium and 1.5 mass.%
aluminum fluoride of sodium
(fraction more than 40
microns).
12 Proppant of Malyshevsky 1000 3.3 34
sand and clay (9.5 : 0.5) with
1.5 mass.% of fluozirconate
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of potassium t4 1.5 mass.% of
aluminum fluoride of sodium
(fraction less than 40
microns)
13 Proppant of Malyshevsky 1020 3.5 30
sand and clay (9.5 : 0.5) with
1.5 mass.% of fluozirconate
of potassium Vl 1.5 mass.% of
aluminum fluoride of sodium
(fraction less than 40
microns)
14 Proppant of Malyshevsky 1060 Proppants -
sand and clay (9.5 : 0.5) with cakes are
1.5 mass.% of fluozirconate formed
of potassium t4 1.5 mass.% of
aluminum fluoride of sodium
(fraction less than 40
microns)
15 Proppant of Malyshevsky 1040 5.4 56
sand and clay (9.5 : 0.5) with Proppants
1.5 mass.% of fluozirconate cakes are
of potassium 11 1.5 mass.% of formed
aluminum fluoride of sodium
(fraction more than 40
microns)
16 Proppants of Malyshevsky 1050 6.0 58
sand and clay (9.5 : 0.5) with
0.4 mass.% of fluozirconate
of potassium and 0.4 mass.%
of aluminum fluoride of
sodium (fraction more than
40 microns)
17 Proppants of Nikolsky sand 950 - 1050 4.3-8.0 57 - 60
and clay (9.5: 0.5) with 1.5
mass.% of fluozirconate of
potassium and 1.5 mass.%
aluminum fluoride of sodium
(fraction less than 40
microns)
18 Proppants of Ilynsky sand 950 - 1050 3.3-3.7 30 - 34
and clay (9.5: 0.5) with 1.5
mass.% of fluozirconate of
potassium and 1.5 mass.%
aluminum fluoride of sodium
(fraction less than 40
microns)
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The analysis of the table data demonstrates that process of the present
invention of siliceous proppants manufacture allows to get proppants (samples
## 7, 11-13, 18) having decreased turbidity of wetting fluid and raised
mechanical
strength obtained by the increase of general quantity of glass phase and its
more
equal distribution in the volume of proppant granule compared to common
analogs.
Proppants manufactured from raw materials containing less than 71 mass
% of Si02 and without non-organic fluoride (samples ## 1,2,3,17), have
decreased mechanical strength and raised turbidity of wetting fluid.
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