Note: Descriptions are shown in the official language in which they were submitted.
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TITLE OF THE INVENTION
GLASS COMPOSITION AND PROCESS OF PROPPANTS MANUFACTURE
BASED THEREON
FIELD OF THE INVENTION
The present invention refers to propping agents for gas and oil wells and,
more particularly, to the glass composition and to the manufacture process of
glass spheres used as such propping agents.
BACKGROUND OF THE INVENTION
Glassceramics are known, having the composition containing Si02 - 67,1
weight %; A1203- 12,5%; MgO- 5,6; Li2O- 9,9; K20- 3,3; F- 2,7; B2O3 -1,0-(See
French Patent No. 1159785, 1958).
Also known is the glass for glassceramics containing: Si02- 25-60; B203-
3-15;, MgO -4-25; A1203-5-25; F- 4-20,R2O, where there is used at least one
oxide of the group K20-2-15; Na2O-2-15; Li20-2-7; Rb2O-2-20; Cs2 0-2-20 as
R2O (see Russian Patent No. SU-631065, 09.08.1971).
The known glass compositions for glassceramics cannot be used in the
manufacture of proppants because their main task is to improve dielectric
properties and mechanical workability. According to the international ISO
13053 standard, the main characteristics of proppants are crush resistance,
sphericity and roundness substantially determining the conductivity of
proppants
layers in a well. Proppants of natural gravel quartz sand prevail for economic
considerations. However, the sphericity and the roundness of gravel sand
generally do not exceed the value 0,7 as per ISO 13053, and its usage is
limited
to shallow wells because of low crush resistance. To improve its conductivity
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the natural sand may be covered by a film of phenol and formaldehyde, which
considerably increases its cost but insignificantly increases its
conductivity.
Also known are proppants corresponding to glass spheres that have high
sphericity and roundness, smooth surface but low crush resistance (see US
Patent
No. 3,497,008). In addition, glass proppants have low resistance to mud acid
(mixture of hydrochloric and hydrofluoric acids) thereby making unpractical
their use in wells subject to acid treatment.
Proppants of silica-alumina and silica-magnesia raw materials
manufactured in accordance with ceramic processing have been widely used
over the last years. Ceramic proppants have satisfactory acid-resistance and
high
mechanical strength, which allow their use in deep wells during hydraulic
fracturing (pressure at 1000 atm). At the same time, ceramic proppants,
because
of the singularity of their manufacturing process, have sphericity and
roundness
not exceeding 0,9 and there are always irregularities on their surface thereby
making oil laminar flow difficult. Ceramic proppants have microscopic open
pores that decrease their strength underwater in wells (temperature up to 130
C).
Another deficiency of ceramic proppants is the presence of pores in their
structure (15-25% of proppant volume). Fine pores appear as a result of vacuum
capture during ceramics sintering and large pores arise during granules layer
rolling-on of powder masses. The presence of structural defects results in a
partial failure of the granules during hydraulic fracturing. All of the above
mentioned defects of ceramic granules account for poor conductivity of ceramic
proppants layer injected in a well.
To remedy these shortcomings of silica-alumina proppants, US Patent
Publication No. 2007/0062699A1 suggests producing silica-alumina proppants
by the method of melt blowing during electrosmelting.
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Proppants manufactured by this method have smooth surfaces, high
sphericity and roundness (more than 0,97). High strength and permeability are
also declared in this Patent Publication, but data given in the description
indicate
that the characteristics of such proppants cede to those of ceramic proppants.
Comparative data regarding properties of known silica-alumina proppants
(fraction 20/40) are presented in the Table 1:
Table 1
Composition and information source
Ceramics Electrosmelting
Characteristics Glass silica-alumina
metrics US Patents CarboLight sphere
No. 3497008, US Patents US Patent
No. 3976138 No. 4427068, Publication No.
No. 4068718 2007/0062699A1
Conductivity
Darcy, at 5000 250 410 230
Psi (-j 350 atm)
Conductivity
md.f at 5000 Psi 5200 7450 4000
350 atm)
Sphericity and 0,97/0,97 0,9/0,9 0,95/0,95
roundness
Apparently, poor conductivity of electrosmelted spheres having low
strength results from defects generated by molten drops quenching. According
to
US Patent Publication No. 2007/0062699A1, the transition of silica-alumina
materials from liquid state to solid state occurs at the same temperature as
crack
formation results in the sphere's body during quenching because crystal oxide
materials are incapable of plastic deformation.
Another process of proppants manufacture is the proppants production of
glass spheres (see Russian Federation Patent No. 2336293, 24.09.2007),
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including oxide melt production, melt jet dispersion by water-cooled wheel to
form glass spheres, their crystallization burning and cooling.
Proppants produced by this manufacturing process have in whole high
operational properties for wells after hydraulic fracturing.
Amongst disadvantages of common glass ceramic proppants are their
insufficient strength and poor permeability at high pressures during hydraulic
fracturing in deep wells. This is due to the fact that the above-mentioned
Russian Federation Patent has only addressed the issue of proppants production
method, whereas the question of glass ceramic specific composition has not
been
examined.
SUMMARY OF THE INVENTION
Therefore, in accordance with the present invention, there is provided a
glass composition of proppants including Si02, MgO, A1203, Na2O, K20, F, and
further containing FeO, CaO, Cr203, Ti02, MnO, with the following rate of
mixture, mass%:
Si02 - 45 - 52
MgO-28-34
A1203 -7 - 10
FeO - 1,6 - 4,5
CaO-5-8
Na2O - 0,3 - 0,6
K20-0,3-1,5
P205-0,1-0,3
Cr203 - 0,1 - 0,8
Ti02 - 0,3 - 0,7
F- 1,0 - 3,2
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MnO - 0,1 - 3,6
The above process is characterized in that general number of oxides FeO +
Na2O + K20 + Cr203 + Ti02 + MnO is in the range of 2,6-11,4 mass %.
Also in accordance with the present invention, there is provided a glass
proppant manufacturing method including oxides melt production, melt jet
dispersion by water-cooled wheel to form glass spheres, their crystallization
burning and cooling; characterized in that glass fusion and its dispersion are
made at the temperature range of 1600-1700 C, and crystallization burning at
the
temperature range of 1100-1270 T.
The above manufacturing method is also characterized in that the oxides
melt production and melt jet dispersion are effected in EAF (electric arc
furnace).
The above manufacturing method is further characterized in that the melt
jet diameter for dispersion is chosen in the range of 5-30 mm.
The above manufacturing method is further characterized in that the rotary
speed of water-cooled wheel is chosen in the range of 1200 - 1800 rpm.
DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS OF THE
INVENTION
The glass composition properties of the proppants of the present invention
as well as the present operating practices result in an increase in the glass
ceramic proppants strength and durable conductivity at high pressure during
hydraulic fracturing process in deep wells.
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The above mentioned result is obtained by the fact that to the common
glass composition including SiO2, MgO, A1203, Na2O, K2O, F, there further
contains FeO, CaO, P2O5, Cr2O3, TiO2, MnO, along the following ratios of
components, mass %:
SiO2 - 45 - 52
MgO-28-34
A1203 -7 - 10
FeO - 1,6 - 4,5
CaO-5-8
Na2O - 0,3 - 0,6
K20-0,3-1,5
P2O5 - 0,1-0,3
Cr2O3 - 0,1 - 0,8
Ti02 - 0,3 - 0,7
F- 1,0 - 3,2
MnO - 0,1 - 3,6
In the above, the general number of oxides FeO + Na20+ K2O + Cr2O3 +
TiO2 + MnO is in the range of 2,6-11,4 mass %.
The present glass proppant manufacturing method includes oxides melt
production, melt jet dispersion by water-cooled wheel to form glass spheres,
their crystallization burning and cooling; glass fusion and its dispersion are
made
at the temperature range of 1600-1700 C, and crystallization burning at the
temperature range of 1100-1270 T.
Oxides melt production and melt jet dispersion are achieved in an
electrical arc furnace, with the melt jet diameter for dispersion being chosen
in
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the range of 5-30 mm and with the rotation rate of the water-cooled wheel
being
in the range of 1200 -1800 revolutions per minute.
The present glass composition does not correspond to glass ceramics of
pyroxenic and cordierite composition.
According to X-ray phase analysis, the main crystal phase is
klinoenstatite or its solid solution with malacolite. The second phase of
glass
ceramics is glass (up to 30% by volume) with a high content of A1203. The
third
phase is oxide (3-5% by volume) - MgO, FeO, Cr2O3, TiO2, MnO compounds.
The proposed composition allows to effect glass melting and
homogenization at a temperature less than 1700 C in a short period of time.
The melt has low viscosity and high surface stress that allows melt jet
dispersion and glass balls production at a temperature of more than 1300 C
virtually without fiber formation, but at lower dispersion temperatures the
fiber
glass portion sharply increases. The advantage of this composition is the
possibility to use such inexpensive raw materials as serpentinite, quartz and
arkose sand, dolomite, magnesite, clay, shale, apatite, fluorite and other
rocks,
the combination of which gives the present glass composition.
A preferred process of glass melt production according to the present
invention has the melting being carried out in an electric arc furnace under
charge bank at a temperature of 1600 - 1700 C, which allows to avoid
essential
losses of such elements as F, P205, Na2O, K20-
The melt jet dispersion step can be efficiently effected on a rotary wheel
with cross shoulders. Other dispersion methods (air or vapor blowing,
supersonic
stream of hot gas) result in jet partial bending toward blowing as well as the
formation of fiber, cotton and droplets with tails. Additionally, these
methods are
extremely power-consuming.
Recommended dispersion modes on the wheel:
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- melt jet diameter of not more than 30 mm;
- wheel rotary speed of 1200-2800 rpm; and
- melt jet temperature of 1600-1700 C.
If the melt jet diameter is less than 10 mm intense cooling of the exterior
part of the jet and non-spherical glass and fiber parts formation occur. If
the
diameter is more than 30 mm the jet is deformed in a tangential direction and
the
catching of the glass balls in the collection chamber is made difficult. The
optimal jet diameter is 15-20 mm. When the glass melt volume is large it is
necessary to split the jet into a few jets each having a diameter of not more
than
30 mm. Wheel rotary speed and the number of cross shoulders are determined by
specific proppants fractional composition: maximum values for 40/70, minimum
values for 20/40.
The melt jet temperature delivered on the wheel determines the quality of
the finished products: the hotter the melt, the larger it is, i.e. melt
delivery to the
dispersion wheel should be done through a heat-insulated spout having low heat
capacity and high resistance to melt, for instance through tubes of carbon and
oxide with outside heat insulation of mullite fiber. The diameter and width of
the
wheel are not a matter of principle and are rather determined by the cooling
system - overheating of wheel results in its deformation and short life.
Unlike
proppants manufactured by common methods (for example, see aforementioned
Russian Federation Patent No. 2336293), crystallization burning of the
proposed
glass composition should be done: first, at a higher temperature of 1100-1200
C, second optimal temperature of coarse balls crystallization should be higher
than the temperature of fine ones. Apparently, this is due to the fact that
glass
ceramics crystallization starts from the surface. Cocrystallization of several
fractions is possible but in this case proppants burned at optimum temperature
will have inferior properties. In this respect, an additional operation, such
as
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fractional sieving, is recommended before crystallization burning. In
connection
with some quantity of fiber and cotton presence in the glass spheres (up to
10%)
sizing on vibrosieves is not always efficient because of sieve blocking. Air
classification is more valid. Prior to burning it is also recommended to
remove
non-spheric particles by the instrumentality of a vibrodynamic classifier or a
spiral separator. Siftings and non-spherical particles are returned for
melting.
Example.
Initial charges were made-up of Bajenovsky and Anatolievsky serpentinite
formation (Ural), asbestos tailing from Thetford Mines (Canada), Pyshminsky
quartz-feldspar sand (Ural), chamotte from Troitsko-Baynovsky and Nizhny-
Uvelsky deposits (Ural), shale (Quebec, Canada), apatite concentrate
(Karelia),
fluorite concentrate (Mongolia, Mexico), dolomite (Bilimbay) and magnesite
(Satka).
Charges melting were made at the temperature 1600 C and 1700 C in a
three-phase EAF under initial charge bank. Furnace lining is made of
chromomagnesite bricks and periclase ramming mass. Glass melt discharge was
made through heat-insulated chute of corundum and graphite to insulated
crucible of corundum and graphite with two (2) openings of 17 mm diameter,
through which melt was delivered to a water-cooled wheel having a 700 mm
diameter with shoulders. After cooling in settling chamber, sieving at air
classifier and spiral separator, three (3) main fractions of glass balls
40/70, 30/50
and 20/40 were produced. Yield was 40-75% of initial working mass. Chemical
composition of produced glass balls is presented in the Table 2. Compositions
with high contents of silicon and aluminum oxides (total of SiO2 + A12O3 >
62%)
produced a large amount of fibers interrupting spheric granules separation at
all
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examined melting practices, even with large quantities of additives being used
to
reduce viscosity, and consequently were judged unpromising.
Chemical analysis were carried out with an X-ray fluorescent energy-
dispersing spectrometer Quant x. It should be noted that the compositions in
Table 2 are brought to 100% as per 12 components, though in some cases the
device registered insignificant quantities of sulfur, nickel, cobalt and
zirconium.
Fluorine test was carried out in analytic laboratories of Uralmechanobr
Institute
(Yekaterinbourg), Polevsky cryolite factory and in Quebec's laboratory
(Canada).
Table 2
Chemical composition of glass balls
Charge Oxides content, mass %
SiO 2 MgO A1203 FeO CaO Na2O K2O P2O5 Cr2O3 TiO2 F MnO
1 50,3 27,4 6,3 5,4 4,5 1,7 2,0 0,8 0,5 0,3 0,7 0,1
2 43,6 24,3 9,2 4,8 8,9 0,5 1,1 0,2 0,2 0,4 3,0 3,8
3 41,5 35,1 6,9 6,2 5,1 0,8 1,7 0,4 1,0 0,8 0,4 0,1
4 56,2 20,8 12,6 1,4 3,1 2,4 1,6 0,4 0,2 1,3 0,0 0,0
47,1 30,8 8,1 2,8 6,7 0,4 0,9 0,2 0,4 0,5 1,8 0,3
6 52,2 27,8 10,1 2,1 5,2 0,3 0,2 0,0 0,2 0,4 4,3 0,2
7 45,3 29,4 8,1 4,3 7,9 0,6 0,3 0,1 0,6 0,5 2,7 0,2
8 45,9 28,0 9,8 4,3 7,0 0,6 0,5 0,2 0,8 0,7 1,9 0,3
9 45,2 33,8 7,2 4,5 5,0 0,3 0,2 0,0 0,2 0,6 2,8 0,2
45,4 28,1 7,1 2,2 7,2 0,5 1,5 0,1 0,7 0,4 3,2 3,6
11 48,2 29,4 8,0 2,9 5,3 0,4 1,2 0,3 0,4 0,5 2,2 1,2
12 51,4 28,5 10,0 1,7 5,1 0,9 0,3 0,0 0,2 0,6 1,0 0,3
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The produced glass spheres were burned at the temperature range of 900-
1200 C. Proppants strength resistance in accordance with ISO 13053 is
indicated
in Table 3.
Table 3
Proppants strength resistance of examined compositions
Charge Broken granules percentage at different pressures, %
number Fraction 20/40 Fraction 30/50 Fraction 40/70
as per 7500 10000 12500 15000 7500 10000 12500 15000 7500 10000 12500 15000
Table 2 Psi Psi Psi Psi Psi Psi Psi Psi Psi Psi Psi Psi
1 7,4 12,9 18,8 23,7 1,9 2,7 6,5 13,8 0,4 1,6 5,4 13,2
2 10,3 13,4 19,7 26,9 2,1 3,8 9,0 16,5 0,5 2,0 4,3 11,4
3 11,8 20,1 27,5 33,1 4,0 10,2 15,6 21,8 0,9 2,8 8,6 10,0
4 6,9 14,4 17,9 24,8 2,0 3,2 7,5 13,6 0,6 2,4 4,1 8,8
8,1 15,0 20,7 25,5 2,2 3,0 8,4 14,9 0,7 2,9 6,6 10,4
6 9,6 17,3 24,9 30,8 2,7 5,3 16,1 19,7 0,8 3,0 7,0 9,2
7 3,2 5,7 9,0 13,6 1,0 1,9 6,5 10,9 0,3 1,0 2,8 6,1
8 3,0 4,9 8,4 12,9 0,8 2,1 6,0 9,6 0,3 0,8 2,4 5,1
9 2,1 3,1 5,9 10,7 0,4 1,8 5,0 8,3 0,2 0,7 2,7 3,4
1,9 2,4 5,0 9,3 0,5 1,9 4,8 7,0 0,2 0,6 2,5 3,8
11 1,3 1,7 6,4 10,9 0,5 0,9 3,0 4,8 0,2 0,9 2,2 4,0
12 1,6 1,9 5,3 8,1 0,6 2,0 4,3 6,2 0,3 0,9 3,1 5,2
Data analysis of Tables 2 and 3 allows to split conditionally the examined
compositions into two (2) groups: stronger (7-12) and less strong (1-6).
Proppants manufactured with glass compositions 7 to 12 are limited by the
following ratio of components:
SiO2 -45-52mass%
MgO - 28 - 34 mass %
A12O3-7-10mass %
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FeO - 1,6 - 4,2 mass %
CaO - 5 - 8 mass %
Na20- 0,3 - 0,6 mass %
K2O - 0,3 - 1,5 mass %
P2O5 -0,1- 0,3 mass %
Cr2O3 - 0,1 - 0,8 mass %
Ti02 - 0,3 - 0,7 mass %
F- 1,0 - 3,2 mass %
MnO - 0,1 - 3,6 mass %
The major specially introduced charge elements are SiO2, MgO, A12O3, CaO,
P2O5 and F. Other components are always associated additives of used material
and
furnace lining; their quantity however is also very important for the
proppants
manufacturing process (FeO, P2O5, Cr2O3 and TiO2 are glass crystallization
initiators; and K2O, Na2O, FeO, MnO reduce viscosity and increase melt
superficial
tension). The total quantity of FeO, Na2O, K2O, Cr2O3, TiO2 and MnO should be
in
the range of 2,6 - 11,4 mass %.
Some of the examined proppants were sent to FracTech and Stim-Lab
laboratories for long-term conductivity determination. The results are
presented in
Table 4.
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Table 4
Proppants long-term conductivity in accordance with ISO 13203-2/APJRP
Charge N as per Table 2, Conductivity, and-ft, at pressure, Psi
Proppant fraction 2000 4000 6000 8000 10000 12000
1, fraction 20/40 7478 6000 2988 1101 388 -
11, fraction 20/40 7560 6295 4436 2673 1338 627
2, fraction 30/50 2863 1496 1186 448 - -
3, fraction 30/50 2693 1303 1009 459 - -
6, fraction 30/50 3267 1960 1453 725 70,3 -
7, fraction 30/50 2699 2413 1984 1374 777 506
10, fraction 30/50 3259 2833 2324 1689 967 513
12, fraction 30/50 2908 2570 2209 1573 964 -
4, fraction 40/70 1693 1303 1009 459 - -
8, fraction 40/70 1554 1351 1171 888 619 -
9, fraction 30/50 3259 2833 2324 1689 967 513
Thus, glass ceramic proppants of offered compositions have high long-term
conductivity.
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