WO2016108067A1 - Composite propping agent and method for using same - Google Patents

Abstract

The invention relates to the oil and gas industry, and to methods for optimizing the hydraulic permeability of a fracture. Proposed is a composite propping agent having a partially soluble coating. The composite propping agent consists of a material in the form of particles, where each particle contains: a propping agent particle base; an outer polymer coating which is soluble or partially soluble in wellbore fluid, and which is applied to the propping agent particle base; and also, located in or on the outer polymer coating, microparticles having encapsulated agents which activate the bonding of propping agent particles when same come into contact with each other or with a formation, and being located at least in a portion of the outer polymer coating; wherein, the non-activated portion of the outer polymer coating is dissolved in wellbore fluid. The invention additionally relates to a method for the treatment of a subterranean formation.

Description

 COMPOSITE SPLITTING AGENT AND

 METHOD OF ITS APPLICATION

FIELD OF TECHNOLOGY

The present invention relates to the oil and gas industry, to methods for optimizing the hydraulic permeability of a fracture, in particular to a composite proppant with a partially soluble coating, and also relates to a method for treating an underground formation.

BACKGROUND OF THE INVENTION

Hydraulic fracturing is the main tool for increasing the productivity of wells by placing or expanding highly conductive fractures leading from the wellbore to the producing formation. A proppant (or proppant) placed in the fractures created on the projected length of the fracture mechanically prevents the fracture from closing after pumping is stopped. After hydraulic fracturing and putting the well into oil / gas production mode, it enters the fracture and enters the wellbore through the packaging from the proppant.

The proppant return flow is one of the well-known problems encountered in the production phase. Currently, there are several methods to prevent proppant removal. Resin proppants and fibers are most popular. One of the disadvantages of the resin coated proppant is the reduction in hydraulic conductivity due to the resin layer on the proppant granules. The technology for the delivery of encapsulated reagents to the near-wellbore area is disclosed in patent application [US 201 10237465, publ. 09/29/2011 1]. Component A is placed in capsule B, and with the help of carrier fluid C it is delivered to the underground zone where, as a result of mechanical loading, the capsule is destroyed and chemical component A enters the treatment zone with a suspension of particles carrying a chemical agent. Suitable material for encapsulation is selected from the group of natural and synthetic polymers, for example, gelatin, guar, organo-polysiloxane.

A proppant with soluble composite coatings is described in patent RU2451710 (publ. 05.27.2012). The proppant in the form of a particle has a particle base, a water-soluble outer coating deposited on the base, and microparticles of a reinforcing and filling agent immersed in the water-soluble outer coating, so that the microparticles are released upon dissolution and destruction of the outer coating. The proppant package of such particles has increased strength (microparticles are not washed out of the contact area between the proppant particles) and increased conductivity.

There is a need to provide a proppant that will ensure proppant packaging stability at the production stage and at the same time ensure high proppant packaging permeability and prevent proppant removal.

ESSENCE

A new proppant structure with a polymer (resin) coating is proposed that does not reduce the hydraulic conductivity of the proppant barrier. According to this structure, the proppant particle (granule) is coated with a binder composition, activated under well conditions, determined, for example, by pressure and temperature. Coating dissolves in the fluid for hydraulic fracturing or in the reservoir fluid, while the activated part of the coating becomes insoluble. Part of the coating is activated at the points of contact of the proppant particles with each other or with the formation, i.e. under mechanical stress. Due to the dissolution of the non-activated part of the coating after binding (curing), an increase in permeability is observed.

 In accordance with the present invention, a composite proppant is provided. A composite proppant is a particulate material, where each particle contains a proppant particle base, an external polymer coating, soluble or partially soluble in the well fluid, and proppant particles deposited on the substrate, as well as microparticles placed on or on the outer polymer coating with encapsulated agents that activate the binding of proppant particles when the latter come into contact with each other or with the formation, at least in part externally th polymer coating. In this case, the non-activated part of the outer polymer coating dissolves in the well fluid.

In accordance with the present invention also provides a method of processing an underground formation. A method of treating an underground formation comprises the following steps: pumping the composite proppant according to any one of claims 1 to 15 in the composition of the well fluid to form a proppant and / or gravel pack; keeping proppant and / or gravel packs in well conditions for at least partial destruction of microparticles with encapsulated agents placed in an outer polymer coating deposited on the basis of the proppant particle followed by activation of particle binding proppant when the latter come in contact with each other or with the formation, at least in part of the outer polymer coating with the formation of proppant pack of proppant particles; the interaction of the borehole fluid with the inactive part of the outer polymer coating of the composite proppant, and the borehole fluid dissolves the inactive part of the outer polymer coating.

The activation of the proppant particles binding occurs due to the curing of at least a part of the external polymer coating or binding agent when the proppant particles come into contact with each other or with the formation. Microparticles with encapsulated agents are at least partially destroyed under downhole conditions.

BRIEF DESCRIPTION OF THE DRAWINGS

 Figure 1 schematically shows the structure of a composite proppant.

 The Figure 2 shows the binding of proppant particles when the latter come into contact with each other or with the formation in borehole conditions.

DETAILED DESCRIPTION OF EMBODIMENTS

To reduce proppant removal without reducing the hydraulic conductivity of the proppant package, the present invention proposes a new polymer proppant proppant structure. Particles (granules) of the proppant are coated with a special composition that becomes insoluble by mechanical action. The polymer coating dissolves in the fracturing fluid or in the formation fluid. Mechanical impact (or activation) initiates the bonding or curing process in the coating, which occurs in the exposed areas of the polymer coating. The remainder of the polymer coating (non-activated portion) remains soluble in the fracturing fluid or in the formation fluid. Encapsulation and release of capsule contents are proposed as an activation mechanism.

After the local bonding or curing of the polymer coating is completed, zones are formed that provide a strong bond between the particles of the composite proppant with each other or with the rock, and the uncured part of the external polymer coating gradually dissolves in the oil-containing well fluid or in the flushing fluid or in the fracturing fluid in borehole conditions. Downhole conditions are characterized by a temperature in the range from 20 ° C to 200 ° C, mechanical loading of the crack closure in the range from 130 kPa to 100 MPa, and hydraulic pressure from 6.9 MPa to 100 MPa.

The mechanism for activating the local curing of the outer polymer coating consists in the destruction of microparticles containing a binding agent, a crosslinking agent and / or a catalyst, a crosslinking process, and the released chemical agents are mixed with the polymer coating and cause the polymer coating to cure.

The difference between the original polymer (resin) coating and the cured polymer (resin) coating is to increase the strength and decrease the solubility of the polymer, which is the result of crosslinking between the polymer molecules. In the literature, the corresponding categories of resins are known as “not cured” (pop cured) and “cured” (cured). The resin formulation and curing conditions are known in the art and are available in the description of the resin product. For curing the resin, the optimum proportions of the starting resin and hardener (accelerator), temperature and curing time are given. In this case, the task of curing the polymer (resin) coating is not set for the entire coating of the particle. The advantages of the present invention are associated with local curing of the coating in areas where sufficiently high concentrations of a binding agent, a crosslinking agent and / or a polymer crosslinking catalyst are created. Locally optimal high concentration zones arise due to local destruction of microparticles containing a binding agent, a crosslinking agent and / or a polymer crosslinking catalyst and their reaction with the polymer in the vicinity of the microparticles. Since in the proppant package (proppant package) in the crack there is an increase in mechanical load caused by the crack walls closing onto the proppant agent composite particles, the greatest destruction of microparticles with chemical agents occurs in the zones of contact between the composite particles between themselves or with the walls of the fracture. The release of various encapsulated chemical agents as a result of mechanical loading on the capsules (microparticles) is described in patent application US 201 1/0237465, which is incorporated by reference.

Thus, the coating-coating contact zone has a high ambient temperature and a high concentration of a bonding agent, a crosslinking agent and / or a crosslinking catalyst released from the microparticles. The curing reaction of the polymer (resin) under borehole conditions leads to strong adhesion of the particles of the composite proppant in the zones of contact (contact) between the particles (in the curing zones).

After closing the crack and lowering the pressure in the wellbore, the flow of well fluid begins. If the hydraulic fracturing operation is carried out for an oil-containing formation, this will be an inflow of oil-containing well fluid. In addition to oil, well fluid contains mineralized water and gas. Thus, well fluid penetrates through the pores in a hardened proppant pack. Since the polymer (resin) coating is selected so that the coating material dissolves in oil and hydrocarbon solvents or in water, the uncured part of the polymer (resin) coating is dissolved and washed out (outside the curing zone). This increases the pore size of the package and thereby increases the permeability of the proppant package over time.

This process is illustrated in FIG. 1, which shows a composite proppant particle that includes a solid base of proppant particle 1, a partially soluble polymer coating 2, and a plurality of microparticles 3 immersed in a partially soluble polymer coating 2. There is a pore between the plurality of proppant particles 1 the space filled with the borehole fluid (not shown in FIG. 1).

Figure 2 shows several proppant particles in a wellbore fluid. After hydraulic fracturing and closing of cracks, the proppant barrier is subjected to mechanical stress (step A). With this action, the microparticles 3 are destroyed at the points of contact, releasing the encapsulated agent (encapsulated substance), which activates the process of binding the proppant particles, while the zone of cured external polymer coating (shaded) firmly binds the base of the proppant particles 1. The next step (step B) is dissolution of non-activated parts of the outer polymer coating with water or oil at the production stage, which creates an expanded pore space (compared to pores m space between particles until dissolution / destruction of partially soluble outer polymer coating 2). After dissolving the outer polymer coating, the proppant barrier is highly permeable. The curing of polymers can occur through the mechanism of polycondensation (for example, curing of phenol-formaldehyde resins) or polymerization (for example, curing of polyester resins). In some cases, both mechanisms can be combined in one process (for example, curing epoxy resins with acid anhydrides in the presence of catalysts).

According to the present invention, the encapsulated agent (encapsulated substance) is added to the outer polymer coating in the form of microparticles (micro capsules). The microencapsulation technology of liquids is well known for chemical and pharmaceutical products. In the framework of the present invention, the microparticles have a size comparable (or smaller) with the thickness of the outer polymer coating. Thus, the microparticle size is from 1 to 500 microns. Too small microparticles carry an insufficient amount of chemical agent and it is difficult to break under mechanical stress. Therefore, it is proposed to add microparticles with a size of 10 to 500 microns to the shell. Microparticles (microcapsules) can be immersed in the outer polymer coating of the proppant particles, but also extend beyond the boundaries of the polymer coating. The wall thickness of the microparticles (not shown in FIG. 1) is sufficiently small so that under downhole conditions (temperature and load increase) the microparticle is destroyed. The process of curing the resin when combined with a curing agent, depending on the relative concentration of the hardener and the temperature of the reaction, is from several minutes to several days.

A fully cured polymer (resin) forms a strong and insoluble bond between the particles of the composite proppant or provides adhesion between the particles of the proppant and the surrounding rock.

Proppant Particle Base The basis of the proppant particle 1 is made of silicon oxide, sintered bauxite, sintered alumina, sintered zirconia, and other solid materials that withstand high mechanical stress arising in the packaging of the proppant (proppant). The particle size of the proppant agent base particles is from about 10 to about 100 mesh (2-0.15 mm).

Soluble external polymer coating

The outer polymer coating 2 is a curable polymerisation of a group of oil-soluble polymers: resoles, novolac resins, phenolic resins, phenol-aldehyde resins, malede-aldehyde resins, unsaturated polyester resins, epoxy resins, polyurethane resins, polyisoprene, polyester urethane, polyester urethane an agent and / or polymer curing accelerators. Or the outer polymer coating 2 is a polymer from the group of oil-soluble or water-soluble polymers: polyolefins, polyisobutylene, polystyrene, natural rubber and copolymers, polylactic acid, polyglycolic acid, polyvinyl alcohol, polyesters, polymethacrylates, cellulose ethers and their mixtures and copolymers using an encapsulated binding agent.

When applying the outer polymer coating 2 with microparticles 3 to the proppant particle 1, the polymer coating 2 is selected so that the outer polymer coating 2 is slightly soluble in aqueous fluid (fracturing fluid for transferring solid particles) under surface conditions. In this case, the outer polymer coating 2 is strong enough to hold the microparticles 3 during the injection of a suspension of particles using pumps deep into the well. To achieve the result, the outer polymer coating 2 may be partially cured. The difference between the stages of "partially cured" and "fully cured" polymer (resin) coating is clear to a person skilled in the chemistry of polymers and resins. Examples of the use of such terminology are given in patent US 7153575 B2 "Particulate material having multiple curable co-^ s", publ. 12/26/2006, revealing the technology for the preparation of a partially cured resin coating. In conditions where 25-50% of the optimum amount of hardener is used for coating, a proppant with a partially cured coating (curable coating) is obtained. Such a coating has lower strength compared to a fully cured coating, but has a marked solubility in some organic solvents. In US Pat. No. 7,153,575 B2, the criterion for incompletely curing the polymer shell is a test for the yield of polymer components that are soluble in acetone (> 5 wt.% “Acetone-soluble fractions”). Coatings based on molten novolak were selected as examples of the implementation of the complete and partial curing of the coating; moreover, the hardener for novolak was selected from the list: hexaethylenetriamine, formalin, paraformaldehyde, oxazolidines, phenol-aldehyde resole polymers. Aqueous solutions of ammonium chloride or ammonium sulfate were selected as the curing catalyst. The temperature for partial curing of the resin coating is selected in the range from 120 ° C to 165 ° C. In the present invention, the percentage yield of acetone-soluble fractions may be a criterion for achieving partial curing of the partially soluble outer polymer coating 2 based on the proppant particle 1.

Another example of the use of the terminology of "cured" and "uncured" polymer coating (in the form of a two-layer resin coating on the proppant) is described in patent US 5837656 B2, publ. 10/17/1998, in which an outer coating of a thermosetting resin is described, the inner layer of the shell being selected from the group consisting of phenol-aldehyde resin, melamine-aldehyde resin, epoxy resin, furfural-alcohol resin and their copolymers, and the outer (solid) layer of resin from the same group, but the processing temperature of the particles causes curing of only the outer layer, while leaving the inner layer of the shell uncured. In embodiments of the present invention, it is essential that the partially cured outer polymer coating 2 is soluble in oil and hydrocarbon (or organic) solvents, and the fully cured polymer coating (shaded area in FIG. 2) is slightly soluble in such solvents (“weak” criterion solubility: yield of acetone-soluble components <5%). This fully cured polymer coating provides a strong bond between the particles of the composite proppant 1, even under prolonged exposure to an oil-containing well fluid. In addition, the fully cured polymer coating remains neutral to the various flushing fluids that are used in well maintenance.

Embodiments of the present invention are a water-soluble or oil-soluble coating containing an encapsulated binding agent. An example of such a bonding agent is a resol polymer, which at high temperature (60–9 ° C) begins to solidify and forms a three-dimensional network. The binding agent may also be polyurethane resins which, upon release, are activated by water. In addition, polyurethane is a self-healing polymer. Water-soluble polymers suitable for the present invention are listed in US Pat. No. 7,380,601 B2 (Schlumberger). Suitable oil-soluble polymers for the present invention are polyisoprene, polyether urethane, polyester urethane, polyolefins (e.g., polyethylene, polypropylene, polyisobutylene and polystyrene), natural rubber and copolymers, as well as mixtures thereof. Other embodiments of the present invention are a water-soluble or oil-soluble coating containing an encapsulated crosslinking agent. An example of such a coating is a partially oil-soluble novolak polymer with encapsulated urotropine (hexamethylenetetramine), etc., which is a crosslinking agent for novolak. Under mechanical action, urotropin is released from the capsule and cross-links novolak. A soluble linear epoxy resin with encapsulated aliphatic polyamines, or oligoaminoamides, or polybasic carboxylic acids and amines, dicarboxylic acid anhydrides, which serve as crosslinking agents for the epoxy resin, can also be used. Under mechanical loads, poly- or oligoaminoamides are released from the capsule and crosslinked linear epoxy resin.

Further embodiments of the present invention are a water-soluble or oil-insoluble coating comprising an encapsulated crosslinking catalyst. An example of a resin is a melamine-aldehyde resin or a urea-aldehyde resin with encapsulated acids or an acid precursor that acts as a catalyst for the curing process (phosphoric acid, phosphoric esters, ammonium chloride, salts of halogen carboxylic acids, etc.). In addition, a linear polyurethane with an encapsulated catalyst may be used. Soluble epoxy resin with encapsulated tertiary amines, acids or Friedel-Crafts catalysts, which are catalysts of the curing process, can also be used.

EXAMPLES

Example 1 The procedure for preparing a composite proppant with a partially soluble polymer coating with the inclusion of microparticles with encapsulated agents. In the examples, the terms “proppant” and “proppant particles” are used interchangeably. A solution of polylactic acid in acetone was mixed with a microencapsulated powder (microparticles) of the dye fluorescein in a ratio of 5: 1. The sizes of microcapsules insoluble in water at room temperature ranged from 15 to 30 microns. Then, 100 g of rounded CarboProp 1620® ceramic particles (sieve size 160/20) from CARBO Ceramics Inc., (Houston, Texas, United States of America) were mixed with 10 g of the mixture (polylactic kilosta + dye fluorescein) and coated with constant stirring. dry while maintaining bulk material flow. Received particles of ceramic proppant with a polymer coating, in which embedded microparticles indicators.

Example 2. CarboProp 1620® ceramic proppant particles with the h polymer coating of Example 1 were placed in a standard proppant conductivity cell (API conductivity cell) described in [Oilfield Review, Autumn 201 1, vol. 23, n. 3, P 4-18]. The composite proppant layer of Example 1 with a layer thickness of 10 mm was placed in a cell (for testing the proppant conductivity depending on the fracture closure stress) and the core cores were applied in the range from 1000 to 6000 psi (6.9 - 41 MPa) and a temperature of 121 ° C . In this case, a weakly saline aqueous solution was periodically pumped through the cell. At a pressure on the proppant pack above 2000 psi (14 MPa), the microparticles of the fluorescent indicator in the proppant shell gradually degraded, which manifested itself as an increase in the intensity of the dye fluorescence spectrum in the liquid after the test cell.

Example 3 The base of the composite proppant was BadgerSand 2040® sand (sieve size 20/40) from BADGER®Sa i i /, Badger Mining Corporation (Berlin, Wisconsin, United States of America), which was coated with a hardener epoxy resin (diethylene triamine ( DETA) or triethylenetetramine (TETA)) in a 10: 1 ratio.

The composite proppant was weighed and washed with acetone in a funnel filter to determine the proportion of the acetone-soluble resin coating fraction. Depending on the type of resin and the aging time, the proportion of the acetone-soluble fraction was from 100 to 20%. Such a test showed that an uncured or partially cured resin coating is washed out with an oil-containing fluid.

Example 4

The ceramic proppant BadgerSand 2040® (sieve size 20/40) from BADGER®Sa “i /, Badger Mining Corporation (Berlin, Wisconsin, United States of America), which was coated with epoxy resin and hardener ( diethylenetriamine (DETA) or triethylenetetramine (THETA)) in a 5: 1 ratio. A composite proppant was placed under a load, creating a pressure of 2000-4000 psi.

When the proppant bed was heated to 120 ° C, the composite proppant was completely polymerized into the hardened mass. When washing the sample with acetone (soaking in acetone for 24 hours in a flask), the proportion of the acetone-soluble fraction did not exceed 10%. The test showed the properties of a fully hardened polymer coating under downhole conditions.

Example 5

CarboProp 3060® ceramic proppant (sieve size 30/60) from CARBO Ceramics Inc., (Houston, Texas, United States of America), which was coated with an epoxy coating, was chosen as the basis of the composite proppant. epoxy resin hardener resins and microcapsules (diethylenetriamine (DETA) or triethylenetetramine (THETA)) in a 5: 1 ratio.

A bulk sample up to 10 mm thick was placed in a proppant conductivity test cell and heated at a pressure of 14 MPa to a temperature of 120 ° C for 8 hours. In this case, the hardener microcapsules were destroyed, which came into contact with the resin coating of neighboring proppanate particles and caused the resin curing reaction (polymerization). After exposure to propate filling under these conditions for 8 hours, the sample was removed from the cell and washed with acetone. The proportion of the acetone-soluble fraction was more than 90%, while the proppant pack retained its shape, which indicates the activation of the polymer at the points of contact and the leaching of the inactive polymer.

The present description has been made in the form of various specific embodiments of the present invention, which have several advantages over the prior art. However, it should be noted that the present invention is not limited to the above-described specific embodiments of the present invention, and various modifications and changes can be made to them without deviating from the essence of the present invention, which is expressed in the attached claims.

Claims

CLAIM 1. A composite proppant, which is a particulate material, where each particle contains a proppant particle base, an external polymer coating soluble or partially soluble in the wellbore fluid, and proppant particles deposited on the substrate, as well as those placed in the external polymer coating or microparticles on it with encapsulated agents that activate the binding of proppant particles when the latter come into contact with each other or with the formation, at least in part an existing polymer coating, the non-activated portion of the external polymer coating dissolving in the well fluid. 2. The composite proppant according to claim 1, in which the activation of the binding of the proppant particles occurs by curing at least a portion of the outer polymer coating when the proppant particles come into contact with each other or with the formation. 3. A composite proppant according to claims 1 or 2, in which the microparticles with encapsulated agents are at least partially destroyed under downhole conditions. 4. The composite proppant according to claim 1, wherein the outer polymer coating is a curable polymer that is soluble in a well fluid in an uncured form and insoluble in a well fluid in a cured form. 5. A composite proppant according to claims 1 or 4, in which the outer polymer coating is selected from the group of water-soluble or oil-soluble polymers consisting of resoles, novolac resins, phenolic resins, phenol-aldehyde resins, malede-aldehyde resins, unsaturated polyester resins, epoxy resins, polyurethane polymers, polyisoprene, polyether urethane, polyesterurethane, polyolefins, polyisobutylene, polystyrene, natural rubber and copolymers, polylactic acid, polyglycolic acid, polyvinyl alcohol, polyesters, polymethacrylates, cellulose ethers and their mixtures and copolymers. 6. The composite proppant according to claim 1, wherein the microparticle is a microcapsule with an encapsulated binding agent. 7. The composite proppant according to claims 1 or 6, wherein the bonding agent is selected from the group of polymers consisting of resole polymers, polyurethane resins. 8. The composite proppant according to claim 1, wherein the microparticle is a microcapsule with an encapsulated crosslinking agent. 9. The composite proppant according to claims 1 or 8, wherein the crosslinking agent is selected from the group of substances consisting of hexamethylenetetramine, aliphatic polyamines, oligoaminoamides, polybasic carboxylic acids and amines, dicarboxylic acid anhydrides, styrene, radical polymerization initiators, tertiary amine diols. 10. The composite proppant of claim 1, wherein the microparticle is a microcapsule with an encapsulated catalyst for a crosslinking process. 1 1. The composite proppant of claims 1 or 10, wherein the crosslinking catalyst is selected from the group of polymers consisting of acids or acid precursors, for example, phosphoric acid, esters of phosphoric acid, ammonium chloride, salts of halogenated carboxylic acids, from tertiary amines, Lewis acids, Friedel-Crafts catalysts. 12. The composite proppant of claim 1, wherein the microparticle size is close to or less than the thickness of the outer polymer coating. 13. The composite proppant of claim 1, wherein the particle size of the proppant particle is from about 10 to about 100 mesh. 14. The composite proppant according to claim 1, wherein the proppant particle base is selected from the group consisting of silica, sintered bauxite, sintered alumina, sintered zirconia, synthetic resin, or a combination thereof. 15. The composite proppant according to claim 1, in which the borehole fluid that dissolves or partially dissolves the outer polymer coating is oil, saline water, gas, or a mixture thereof. 16. A method of processing an underground formation, comprising the following stages: pumping the composite proppant according to any one of claims 1 to 15 in the composition of the well fluid to form a proppant and / or gravel pack; keeping proppant and / or gravel packing in well conditions for at least partial destruction of microparticles with encapsulated agents placed in an outer polymer coating deposited on the basis of the proppant particle with subsequent activation of the proppant particles binding when the latter come into contact with each other or with the formation at least in part of the outer polymer coating to form a proppant pack of proppant particles; the interaction of the borehole fluid with the inactive part of the outer polymer coating of the composite proppant, and the borehole fluid dissolves the inactive part of the outer polymer coating. 17. The method of processing an underground formation according to clause 16, in which the activation of the binding of particles of the proppant occurs due to the curing of at least part of the outer polymer coating when the particles of the proppant come into contact with each other or with the formation. 18. The method of processing the underground reservoir according to clause 16, in which the microparticles with encapsulated agents, at least partially destroyed in borehole conditions. 19. The method of treating an underground formation according to clause 16, wherein the composite proppant is a plugging agent, fracturing packing, or gravel packing particles.