Note: Descriptions are shown in the official language in which they were submitted.
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Methods for preventing proppant carryover from fractures, and gravel-packed
filter
This invention relates to the oil and gas industry, in particular, to methods
affecting the formation productivity at the oil and gas production stage.
A carryover of proppant from a fracture to the well at the post-fracturing
period
either during the initial cleaning or sometimes even after completion of the
well
construction is a crucial issue for the oil production sector. As practice
experience shows,
up to 20% of proppant could be conveyed to the well, which, in its turn, could
lead to a
number of negative consequences; some of them are specified below. In marginal
wells,
proppant settles in a casing; thus, regular washings are required and the cost
of well repair
operations grows. A, premature wear and failure of electrical submersible
pumps is
another consequence of the carryover of unbound proppant or other solid
particles of
rocks. Also, oil or gas production decrease is observed due to a significant
loss of the near
wellbore conductivity caused as a result of a reduced fracture thickness or
overlapping of
a production zone.
At present, several methods allowing a significant decrease in the carryover
of
proppant or other propping agents from the fracture are known.
The most wide-spread approach is based on the application of proppant with a
hardening resin coating (US 5218038 ), which is injected into the fracture at
the end of
the treatment process. However, the application of this proppant has a number
of notable
restrictions which are caused by casual chemical reactions of the resin
coating with a
layer fracturing fluid. On one hand, this interaction causes partial
degradation and
disintegration of the coating, thus reducing the contact strength among
proppant particles
and, therefore, decreasing the. proppant pack strength. On the other hand, the
interaction
between the resin coating components . and fracturing fluid components causes
uncontrolled change in of rheological properties of the fluid, which also
diminishes the
fracturing process efficiency. The above-listed factors alongside with
periodic cyclic
loads emerged due to the well closure and construction as well as an extended
well
closure period could significantly reduce the proppant filler strength.
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In another method, a fibrous material mixed with a propping agent material is
added with the aim to limit the conveyance of a proppant placed in a formation
(US5330005); in this process, fibers interweave among proppant particles and
thus
increase the proppant strength and restricts the back-flow carryover of the
proppant.
Besides, the addition of fibers enables a more effective redistribution of
loads through
addition of bulkheads along a vast area of the proppant filler. A fibrous
structure is more
flexible as compared to cured resin proppant; it allows movements of proppant-
fibrous
filler without the strength property deterioration.
In another method (US 5908073), fiber bundles comprising about 5 to 200
separate fibers with a length of 0.8 to 2.5 mm and diameter of 10 to 1,000 m
are used
for preventing proppant carryover from the well. In this process, the fiber
bundle structure
is fixed from one side.
A method of mixing proppant with the deformable material in the bead-shaped
particles (US 6059034) is known. The said deformable particles are made of a
polymeric
material. Deformable polymeric particles could be differently shaped (oval,
wedge-like,
cubic, bar-like, cylindrical, conic, etc.); however, a maximum length-to-base
ratio of
equal to or less than 5 is preferable. In case of deformable materials with a
cone-shaped
diameter as well as for aluminum particles, the maximum length-to-base ratio
should be
equal to or less than 25. Deformable particles could be made as spherical
plastic balls or
composite particles containing a non-deformable core and a deformable coating.
Generally, the volume of the non-deformable core is about 50 to 95% (vol.) of
the total
volume of the particle and can be made of silica, cristobalite, graphite,
gypsum or talc. In
another embodiment (US 6330916), the core consists of deformable materials and
could
include milled or crushed materials, e.g., nutshell, seed shell, fruits
kernels and processed
wood.
For fixing a propping agent and restricting' its carryover, a mixture of the
proppant
with adhesive polymeric materials could be applied (US 5582249). Adhesive
compositions enter into a mechanical contact with the propping agent
particles, ensphere
and cover the particles with a thin sticky layer. As a result, particles glue
to each other as
well as with sand or crushed fragments of the propping agent, thus completely
preventing
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the carryover of solid particles from the fracture. The ability to maintain
adhesiveness
over a long period of time and at increased welibore temperatures without
stitching or
hardening is intrinsic feature of sticky compounds.
Sticky materials could combine with other chemical agents, which are used in
the
formation fracturing process, e.g., retarding agents, antimicrobial agents,
polymer gel
destructors, as well as antioxidant and wax-formation and corrosion retarding
agents (US
6209643).
There is another known method for fracture propping with the application of
sticky agents and resin proppants (US 7032667). The US patent No. 6742590
discloses a
method for protecting fractures from the carryover of the propping filler,
using a mixture
of sticky materials with deformable particles, which are on their own are
effective
additives to prevent the proppant carryover.
Another variety of materials used for proppant carryover fighting is
thermoplastic
materials (US 5501274, EP 0735235). Thermoplastic materials when mixed with a
propping agent are capable of softening being exposed to high temperatures of
rocks, and
thereafter they stick with the propping agent to form agglutinated aggregates
which
include a plural number of the proppant.
A method for using thermoplastic materials mixed with a resin proppant is
known
(US 5697440). In a number of methods, a thermoplastic material is mixed with
the
proppant in a liquid state or in the form of a solution in a suitable solvent
(US 6830105 ).
In this case, an elastomer-forming compound could solidify either itself, or
under the
influence of special additional chemical reagents, to form thermoplastic
materials.
Another known method describes the application of a fracturing fluid, which is
a
self-degrading cement (US patent application No. US 2006/0169448) comprising
acid
and main components, whose interaction causes formation of a cement material,
as well
as a degrading component, which could disintegrate under the fracture
conditions and
ensures the formation of cavities in the cement.
Another known method describes the formation fracturing process using a new
type of propping particles as well as the composition of a new material for
creating
gravel-packed filters with the application of hydrated cement particles with
an average
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size ranging from 5 m to 2.5 cm (US patent application No. 2006/0162926, US
2006/0166834 ).
This invention relates to the oils and gas industry, in particular, to the
development of a method for preventing carryover of proppant from fractures.
The
suggested method for fracture propping in an underground layer ensures as
reliable
protection of the well from the proppant conveyance from the fracture. In this
method, a
formation fracturing fluid is mixed with a propping filler and a granulated
binding
material with a length-to-width ratio of equal to or less than 10, and
thereafter, a
formation fracturing process is implemented. Then, the granulated binding
material is
solidified to form a homogeneous firm mass with the propping agent, which
obstructs the
closure of the fracture and precludes the proppant carryover.
Technical result of this invention is as follows.
1. Fracturing fluid composition obtained by mixing a propping filler and a
granulated binding component with a length-to-width ratio of equal to or less
than 10,
which could solidify under underground formation conditions.
2. Fracturing fluid composition obtained by mixing a propping filler and a
granulated binding composition in the form of a powder, whose size varies from
about I
m to about 500 m. In this case, powder-like particles of the binding
component get into
contact with the propping filler and are then solidified thus increasing the
propping filler
pack strength.
3. Fracturing fluid composition obtained by mixing a propping filler and a
granulated or powder binding material as well as other components obstructing
the
proppant conveyance from the fracture, including deformable particles and
adhesive and
fiber-like materials.
4. Development of gravel-packed filter which is based on the application of a
working fluid comprising a propping filler and a granulated binding component
with a
length-to-width ratio of equal to or less than 10, or comprising a propping
filler and a
granulated binding composition in the form of a powder, whose size varies from
about 1
m to about 500 m.
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At least one of the below-listed materials can be used as a propping filler:
ceramic
particles and sand of a different shape, plated solidified and curable
proppants and sands;
swollen expanded clay, vermiculite, and agloporite.
Proppant or polymer-coated sand can be used as a propping filler.
Granulated and powder-like binding components could be added in a fracturing
fluid either in a dry state, or in the form of suspension in water, working
fluid, gel or
other suitable solvent, including those modified with various surfactants.
At least one of binding components of the below-listed hardening classes could
be
used as a granulated binding component: hydraulic, air and autoclave hardening
as well as
acid-proof binding materials as well as their mixture, including:
1. Binding materials on the basis of crystalline hydrates CaSO4 and anhydrite
(gypsum binding materials);
2. Binding materials on the basis of CaO, CaO hydration and carbonization
products
(lime binding materials);
3. Binding materials on the basis of MgO and saline sealers (magnesian binding
materials);
4. Lime-silica binding materials comprising a mixture of CaO or Ca(OH)2 with
fine-
milled silica, which solidify at increased temperatures;
5. Lime-pozzolanic and lime-cindery binding materials comprising a lime-
containing
component and a reactive silicic acid in the form of amorphous silica or
silicate
glass, whose hardening occurs due to the interaction of a lime with an active
silicon oxide or glass with the formation of calcium hydrosilicates;
6. Slag-alkali binding materials, which include a component comprising caustic
alkali and slag, preferably, in a vitreous state, whose hardening is connected
with
the formation of alcaline aluminum silicate;
7. Cements (binding) on the basis of high-basic calcium silicates (portland
cement
clinker, natural cement, calcareous cement, hydraulic lime), whose binding
properties are essentially predefined by hydration of tricalcium (Ca3SiO5) and
dicalcium (Ca2SiO4) silicates, including slag-portland cement;
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8. Cements on the basis of low-basic calcium aluminates (CaA, CA2, C12A7) as
well
as on the basis of their derivatives, e.g. calcium sulfoaluminates, calcium
fluoroaluminates (aluminate cement, high-alumina cement, sulfoaluminate
cement); high iron oxide cements and sulfur high iron oxide cements;
9. Cements on the basis of calcium ferrites and their derivatives - calcium
sulfoferrites;
10. Phosphatic binding materials (cement and binding materials), which harden
due to
phosphate formation;
11. Watersoluble silicate - based binding materials including alkali metal
silicates
(soluble glasses) and organic base silicates;
12. Polymer-cement and polymer-silicate binding compositions which include
organic
compositions as modifying components and inorganic binding materials (cement,
soluble glass) as the base;
13. Hydroxy salts of aluminum, chrome, zirconium, colloidal solution of silica
and
aluminum oxide, partially dehydrated crystalline hydrates of aluminum sulfates
and calcium aluminates.
A granulated binding component could comprise either one component, or have a
multi-component composition. In addition to binding components, the A
granulated
binding component could include components which ensure required strength
properties
(e.g., polymers) and density (e.g., particles of barite, red iron ore, glass
beads, porous
particles).
A granulated binding component could be differently shaped: spherical,
cylindrical,
sparry, cubic, oval, flaked, scaly, irregular shape, or a mixture of the above-
mentioned
shapes, but with a length-to-width ratio to be equal to or less than 10.
The content of granulated binding filler in the total volume of propping and
granulated fillers varies in the range from 0.1 to 99.9% by weight.
Actual density of granulated binding agent could vary in the range from 0.3 to
5
3
g/cm.
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At least one of binding components of the below-listed hardening classes could
be
used as a powder binding component: hydraulic, air and autoclave hardening as
well as
acid-proof binding materials as well as their mixture, including:
1. Binding materials on the basis of crystalline hydrates CaSO4 and anhydrite
(gypsum binding materials);
2. Binding materials on the basis of CaO, CaO hydration and carbonization
products
(lime binding materials);
3. Binding materials on the basis of MgO and saline sealers (magnesian binding
materials);
4. Lime-silica binding materials comprising a mixture of CaO or Ca(OH)2 with
fine-
milled silica, which solidify at increased temperatures;
5. Lime-pozzolanic and lime-cindery binding materials comprising a lime-
containing
component and a reactive silicic acid in the form of amorphous silica or
silicate
glass, whose hardening occurs due to the interaction of a lime with an active
silicon oxide or glass with the formation of calcium hydrosilicates;
6. Slag-alkali binding materials, which include a component comprising caustic
alkali and slag, preferably, in a vitreous state, whose hardening is connected
with
the formation of alcaline aluminum silicate;
7. Cements (binding) on the basis of high-basic calcium silicates (portland
cement
clinker, natural cement, calcareous cement, hydraulic lime), whose binding
properties are essentially predefined by hydration of tricalcium (Ca3SiO5) and
dicalcium (Ca2SiO4) silicates, including slag-portland cement;
8. Cements on the basis of low-basic calcium aluminates (CaA, CA2, C12A7) as
well
as on the basis of their derivatives, e.g. calcium sulfoaluminates, calcium
fluoroaluminates (aluminate cement, high-alumina cement, sulfoaluminate
cement); high iron oxide cements and sulfur high iron oxide cements;
9. Cements on the basis of calcium ferrites and their derivatives - calcium
sulfoferrites;
10. Phosphatic binding materials (cement and binding materials), which harden
due to
phosphate formation;
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11. Watersoluble silicate - based binding materials including alkali metal
silicates
(soluble glasses) and organic base silicates;
12. Polymer-cement and polymer-silicate binding compositions which include
organic
compositions as modifying components and inorganic binding materials (cement,
soluble glass) as the base;
13. Hydroxy salts of aluminum, chrome, zirconium, colloidal solution of silica
and
aluminum oxide, partially dehydrated crystalline hydrates of aluminum sulfates
and calcium aluminates.
The size of the powder-like binding materials varies from about 0.5 to 500 m.
The content of powder-like binding materials in the propping filler varies
from 0.1
to 99.9% by weight.
The density of the powder-like binding materials could vary from about 0.5 to
about 5
g/cm3.
Granulated or powder-like binding materials will be used in the mixture with a
propping agent whose concentration in the mixture could vary in the range of
0.1 to
99.9%.
Granulated or powder-like binding materials could be added to the propping
fluid
either in a dry state or in the form of suspension in water, working fluid,
gel or other
suitable solution including those modified by various surfactants.
