METHODES DE PREVENTION D'ENTRAINEMENT D'AGENT DE SOUTEMENT DE FRACTURES, ET FILTRE A GRAVIER

METHODS FOR PREVENTING PROPPANT CARRYOVER FROM FRACTURES, AND GRAVEL-PACKED FILTER

Abrégé français

Cette invention se rapporte à l'industrie pétrolière et gazière, en particulier aux méthodes influant sur la productivité des gisements, à la phase de production pétrolière et gazière. Cette invention propose une méthode de soutènement de fracture dans une couche souterraine, qui assure une protection fiable des puits contre l'entraînement de l'agent de soutènement de la fracture. Selon la méthode projetée, un fluide de fracturation est mélangé à un agent de soutènement et du matériau de liaison granulaire, avec un rapport longueur à largeur inférieur ou égal à 10. Par la suite, un processus de fracturation de gisement est mis en oeuvre. Ensuite, la matériau de liaison granulaire durcit et forme une masse homogène ferme avec l'agent de soutènement, ce qui entrave la fermeture de la fracture et empêche l'entraînement de l'agent de soutènement de la fracture. Une autre alternative consiste à utiliser une composition de fluide de fracturation obtenue en mélangeant un agent de soutènement avec un composé de liaison, sous forme de poudre dont la grosseur est comprise entre 1 et 500 mu.m. Un filtre à gravier est ensuite fabriqué. Le principe dudit filtre repose sur l'application du fluide de travail comprenant un produit d'apport de soutènement et un élément de liaison granulaire, avec un rapport longueur à largeur inférieur ou égal à 10, ou comprenant un produit d'apport de soutènement et un composé de liaison sous forme de poudre, avec une grosseur comprise environ entre 1 et 500 mu.

Abrégé anglais

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 method for fracture propping in a subsurface layer, which ensures a reliable
protection of wells from the proppant carryover from the fracture, has been
proposed.
According to the proposed method, a fracturing fluid is mixed with a propping
agent and
granulated binding material with a length-to-width ratio of less than or equal
to 10;
thereafter, a formation fracturing process is implemented. Then, the
granulated binding
material hardens and forms a homogenous firm mass with the propping agent,
which
impedes the closing of the fracture and precludes proppant carryover from the
fracture.
Or, a fracturing fluid composition obtained by mixing a propping agent with a
binding
compound in the form of a powder whose size varies from about 1 to about 500
µm. A
gravel-packed filter is then constructed; the said filter is based on the
application of the
working fluid comprising a propping filler and granulated binding component
with a
length-to-width ratio of less than or equal to 10, or comprising a propping
filler and a
binding compound in the form of a powder with a size varying from about 1 to
about 500
microns.

Revendications

9
CLAIMS:
1. A method for preventing proppant carryover from a fracture, according
to which a fluid used in the formation fracturing process is mixed with a
filler
component comprising at least one propping agent and at least one granulated
binding component having a length-to-width ratio of less than or equal to 10,
which
fluid solidifies under subsurface formation conditions.
2. The method of claim 1, wherein the granulated binder component is
present in the filler component in an amount of from 0.1% to 99.9%.
3. The method of claim 1 or 2, wherein the filler component comprises at
least one material selected from the group consisting of particulates having
been
hardened by a hydraulic hardening, air hardening or autoclave hardening, acid-
proof
binding materials and mixtures thereof.
4. The method of claim 1 or 2, in which the filler component comprises
gypsum binding materials.
5. The method of claim 4 wherein the filler component comprises CaSO4
crystalline hydrates and anhydrites.
6. The method of claim 1 or 2, wherein the filler component comprises
lime binding materials.
7. The method of claim 6, wherein the filler component comprises materials
selected from calcium oxides and CaO hydration and carbonization products.
8. The method of claim 1 or 2, wherein the filler component comprises
magnesium binding materials.
9. The method of claim 8, wherein the filler component comprises
magnesium oxide or a saline sealer.

10. The method of claim 1 or 2, wherein the filler component comprises a
lime-silica material comprising a mixture of CaO or Ca(OH)2 with fine-milled
silica
which hardens at subterranean formation temperatures.
11. The method of claim 1 or 2, wherein the filler component comprises
lime-pozzolanic and lime-slag materials.
12. The method of claim 1 or 2, wherein the filler component comprises
lime-containing components and reactive silicic acid in the form of amorphous
silica
or silicate glass, whose hardening is caused by the interaction of lime with
active
silica or glass with the formation of calcium hydrosilicates.
13. The method of claim 1 or 2, wherein the filler component comprises
slag-alkali binders comprising a constituent that includes a caustic alkali
and slag, in
a vitreous state, and whose hardening proceeds with the formation of alkaline
aluminum silicates.
14. The method of claim 1 or 2, wherein the filler component comprises
cement based on high-basic calcium silicates.
15. The method of claim 1 or 2, wherein the filler component comprises at
least cement based on calcium aluminate, calcium sulfoaluminates or calcium
fluoroaluminates.
16. The method of claim 15, wherein the calcium aluminate is CaAl, CaAl2
or C12AI7.
17. The method of claim 15, wherein the filler component comprises a
calcium aluminate cement, a high-alumina cement, or a sulfoaluminate cement.
18. The method of claim 1 or 2, wherein the filler component comprises an
iron or sulfur-iron cement.

11
19. The method of claim 1 or 2, wherein the filler component comprises
calcium ferrites or calcium sulfur ferrite cements, portland cement, roman
cement,
calcareous lime or mixtures thereof.
20. The method of claim 1 or 2, wherein the particulate binding component
comprises phosphates.
21. The method of claim 1 or 2, wherein the filler component comprises
watersoluble silicates.
22. The method of claim 1 or 2, wherein the filler component comprises
polymer-cement or polymer-silicate compositions comprising organic compounds
as
modifying agents and inorganic compounds as the base.
23. The method of claim 1, wherein the filler component comprises at least
one compound selected from the group consisting of hydroxy salts of alumina,
chrome, zirconium, colloidal silica solutions, partly dehydrated crystalline
hydrates of
aluminum sulfates and calcium aluminates.
24. The method of any one of claims 1 to 23, wherein at least one of the
fluid or the filler component further comprises at least one as additive
selected from
the group consisting of polymers, barite particles, red iron ore, glass beads,
porous
particles, sand with polymeric coating, ceramic particles, sand, cured or
curable
proppants and sands, swollen expanded clay, vermiculite, agloporite,
deformable
particles, adhesive materials and fibrous materials.
25. Method for preventing proppant carryover from fractures, in which a
formation fracturing liquid is mixed with a propping agent, granulated binding
component as well as with components precluding proppant carryover from
fractures,
including deformable particles, adhesive and fibrous materials.

Description

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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.