RU2375563C1 - Propping agent with resinous surface and method of its backflow prevention - Google Patents

Abstract

FIELD: oil-and-gas production.

SUBSTANCE: propping agent granule, based on a substratum and resinous coating - resinous layer, its external surface covered with at least one more extra coating - extra layer, consisting of mixture of low density polyethylene and paraffin with 7:3 ration, which has secure function against at least resinous layer parasitic reactions with chemicals from hydraulic fracturing fluid, and polymer destroyers, thickness of the extra layer is from 10 up to 30 mcm. Method of hydraulic fracturing execution includes pumping propping agent - mentioned above propping granules, into hydraulic fracturing slot.

EFFECT: keeping of polymer fluid required viscosity along the hydraulic fracturing procedure, prevention of propping agent early settlement into the slot, increase of consolidated propping pack strength, better slot cleaning out of polymer gel remains.

10 cl, 1 dwg

Description

The invention relates to the oil and gas industry and can be used to increase production well productivity by preventing fracture closure using proppant proppant beads during hydraulic fracturing of productive oil formations.

A serious problem of oil production is the removal of proppant from the fracture into the well after hydraulic fracturing during the initial cleanup, and in some cases even after the complete development of the well. Practice shows that up to 20% of proppant can be delivered to the well, which leads to a number of negative consequences, among which the following can be distinguished. In low-flow rate wells, proppant settles in the casing, which requires periodic flushing and leads to more expensive repair operations. Another consequence of the removal of loose proppant or solid rock particles is premature wear and failure of electric centrifugal submersible pumps. Also, a decrease in hydrocarbon production due to a significant loss of near-barrel conductivity due to a decrease in crack thickness or overlapping of the productive zone was noted.

Currently, a number of methods are known that can significantly reduce the removal of proppant or other proppants from the fracture.

The most common approach is based on the use of a hardening resin coated proppant (US patent 3492147, US patent 3929191, US patent 5218038, US patent 5639806), which is pumped into the crack at the end of processing. However, the use of this proppant has a number of significant limitations caused by adverse chemical reactions of the resin coating with the fracturing fluid. On the one hand, this interaction leads to partial degradation and violation of the integrity of the coating, reducing the strength of the contacts between the proppant particles and, accordingly, reducing the strength of the proppant packing. On the other hand, the interaction between the components of the resin coating and the components of the fracturing fluid leads to an uncontrolled change in the rheological characteristics of the fluid, which also reduces the effectiveness of the fracturing. The factors listed above, as well as periodic cyclic loads associated with well closure and development and a long well closure period, can significantly reduce the strength of proppant packs.

The chemical compounds that make up resin proppants interact with gel breakers (for example, ammonium persulfate), reducing the concentration of breakers in the fracturing fluid. This affects the efficiency of cleaning the crack from the remnants of undecomposed polymer gel and significantly reduces the permeability of the crack.

In some cases, for example, with accelerated closing of the crack, the resin proppant does not have time to harden and acquire the calculated strength. This leads to an increase in the fraction of crushed proppant and a decrease in the conductivity of the crack.

A way to partially solve this problem is to create two-layer resin proppants (US patent 4585064, US patent 4717594). In this case, the inner resin coating directly adjacent to the surface of the proppant is completely cured, and the outer layer consists of an uncured resin material. Thus, the first layer of cured resin provides high proppant strength under external load conditions, and the outer layer is capable of solidifying (stitching) with adjacent proppant particles to form a strong package.

A known method (US patent 4888240, US patent 5422183, US patent 5597784), in which to strengthen the resin coating and enhance adhesion between the layers of the resin coating, as well as with the substrate (proppant), the inner resin layer is dusted with reinforcing compounds or composites :

talc, quartz flour, clay, as well as other minerals or polyisobutylene, copolymers of ethylene and vinyl acetate or ethylene and propylene. Reinforcing compounds are applied on top of the first layer and then it is cured, followed by a second fusible resin layer.

As noted above, a serious drawback of resin proppants is insufficient compatibility with hydraulic fracturing fluids and polymer destructors. A known method (US patent 5837656, US patent 5955144), aimed at improving the compatibility of the resin proppant with the chemical components that make up the fracturing fluid, which uses the same concept of a two-layer resin coating, but change the order of alternation of crosslinked and non-crosslinked coatings. As the first coating applied directly to the proppant particle, a fusible, curable composition is used, which is mainly novolac resin. The second coating, which has a protective function with respect to the fracturing fluid, is a predominantly cured resole resin. Laboratory tests showed good compatibility of the described proppant with fracturing fluids while maintaining the ability to form consolidated packaging in well conditions.

Further development of the resin proppant concept is described in US Pat. No. 7,153,575, which differs from US Pat. No. 5,837,656 and US 5,955,144 in that the proppant is coated with two or more curable resin layers.

The development of the known method can be recognized as the approach (US patent 7135231, US application 2007/0036977) for the manufacture of a multilayer proppant (consisting of mutually intersecting n-layers), which consists in sequentially applying a number of partially overlapping resin coatings in such a way that the resulting coating completely covers substrate surface. The patent also describes a method for producing proppant, which consists mainly in the application of a special spraying technology. The technology consists in applying a resin coating without any use of chemical solutions by spraying the powder of the desired chemical composition in air or other media using special nozzles.

The inventions disclosed in US 6114410 and US 6328105, describe an improved proppant, as well as a method for increasing the permeability of fractures in the reservoir. This proppant contains a mixture of particles capable of gluing (stitching) with each other, as well as removable (capable of dissolving in oil or water) particles.

Bonding particles can be coated with a curable polymer resin. Particles coated with polymer material in the formation adhere to similar particles located next to them, forming a permanent self-supporting matrix, from which, depending on the conditions existing in the fracture, the removed particles can exit. This increases fracture permeability as well as overall well productivity.

Known methods (US 7244492, US 2006/0035790), in which to limit the proppant use resin proppant particles coated with an additional layer consisting of elastomeric materials, as well as their combination of polymers with fibers.

A known method is in which to limit the removal of proppant placed in the formation, add fibrous material mixed with proppant material (US Patent 5330005), while the fibers are intertwined between the proppant particles, giving them increased strength and thereby limiting the return of proppant. In addition, the addition of fiber allows for a more efficient redistribution of loads by adding jumpers over a large area of proppant packing. The fiber structure is more flexible than vulcanized resin proppant, allowing proppant-fiber packing to move without losing its strength.

A known method of mixing proppant with a deformable material in the form of particles of a bead form (US patent 6059034). Deformable particles are made of a polymeric material. Deformable particles can also be spherical plastic balls or composite particles containing an undeformable core and a deformable coating. Typically, the volume of an undeformable core is approximately 50 to 95 vol. % of the total particle volume and may be quartz, cristobalite, graphite, gypsum or talc. In another embodiment (US Patent 6,330,916), the core consists of deformable materials and may include crushed or crushed materials, for example, nutshells, seedshells, fruit pits, and processed wood.

To fix the proppant and limit its removal, a proppant mixture with adhesive polymeric materials can be used (US Patent 5,582,249). Adhesive compounds come into mechanical contact with the proppant particles, envelop and cover them with a thin sticky layer. This leads to the bonding of particles with each other, as well as with sand or fragmented proppant fragments, which leads to a significant or complete cessation of the removal of solid particles from the crack. A characteristic feature of adhesive compounds is the ability to maintain stickiness for a long time and at elevated borehole temperatures, without leading to their crosslinking or curing.

A known method of wedging cracks using adhesive compounds and resin proppants (US patent 7032667). US Pat. No. 6742590 discloses a method for protecting a crack from proppant removal in a mixture of adhesive materials with deformable particles, which in themselves are effective proppant-preventing additives.

Another variety of materials used to combat proppant removal are thermoplastic materials (US Patent 5,501,274, EP, Application 0735235). Thermoplastic materials mixed with a proppant have the ability to soften under the influence of high temperature of the rock and then stick together with it to form glued aggregates, including the plural proppant.

A known method of using thermoplastic materials in a mixture with a resin proppant (US patent 5697440). In a number of methods, the thermoplastic material is mixed with the proppant in a liquid state or in the form of a solution in a suitable solvent (US Patent 6830105). In this case, the elastomer-forming compound can cure on its own or under the action of special additional reagents with the formation of a thermoplastic material.

A known method of using hydraulic fracturing fluid, which is a self-degradable cement (patent application US 2006/0169448), consisting of acidic and basic components, the interaction between which leads to the formation of a cement material, as well as a degradable component, capable of decomposition under crack conditions and providing the formation of voids inside the cement.

A known method of hydraulic fracturing using a new type of proppant particles, as well as the composition of a new material for creating gravel filters using hydrated cement particles having an average size ranging from about 5 micrometers to about 2.5 centimeters (patent applications US 2006 / 0162926, US 2006/0166834).

The technical problem solved by the developed invention is to increase the efficiency of the fracturing method of the reservoir.

The technical result obtained by the implementation of the developed technical solution consists in improving the compatibility of the resin proppant with hydraulic fracturing fluid and preventing the degradation of the polymer breaker and the surface of the resin proppant, which preserves the required viscosity of the polymer fluid throughout the hydraulic fracturing process, preventing premature proppant sedimentation in the fracture , increasing the strength of the consolidated proppant pack, as well as more complete cleaning of the crack from the remainder in polymer gel.

The factors listed above lead to a decrease in proppant removal during the washing, well development, and also during production while preserving the permeability of the proppant pack at the production stage and long-term operation of the well.

To achieve the technical result, it is proposed to apply at least one additional layer 3 (Fig. 1) on the external resin surface 2 of the substrate 1, which performs protective functions by partially and / or completely preventing adverse reactions of the resin coating with chemical compounds that make up the liquid fracturing and polymer breaker.

The developed method consists in creating a protective layer 3 on the outer surface of the resin proppant, mainly based on polymers, surface-active compounds, waxes, paraffins and mixtures thereof.

The advantages of the proposed approach are formulated below:

1. The proposed approach can significantly simplify and reduce the cost of the production of resin proppants in comparison with the classical approaches of creating additional layers of cured resin, described, for example, in patents US 5837656, US 5955144, US 7135231, US 7153575.

2. Resin proppant containing an additional protective layer does not interact with the hydraulic fracturing fluid at the stage of the hydraulic fracturing operation and during the closing of the fracture and does not impair the rheological characteristics of the hydraulic fracturing fluid and its transport properties. This positively affects the efficiency of the proppant injection procedure, reduces the likelihood of a premature stop of work (stop proppant), and also provides a more uniform distribution of proppant along the crack height.

3. Resin proppant containing an additional protective layer 3 does not interact with chemicals that make up the gel destructors. This increases their effectiveness, contributes to a more complete cleansing of the crack from gel residues, thereby increasing the conductivity and oil recovery.

4. The above factors 2, 3 ensure the preservation of the quality of the resin coating. The cured coating is characterized by higher strength compared to the proppants described in US patents 5218038, US 4585064, US 4717594.

5. The additional coating applied to the surface of the resin proppant is capable of dissolving in water or oily liquids and gas condensate, and therefore does not reduce the permeability of the proppant pack, as is the case with proppants coated with an additional protective layer of cured resin (US, U.S. Patent 4,585,064; U.S. Patent 4,717,594)

A method has been developed for conducting hydraulic fracturing, according to which a crosslinkable proppant is pumped into the fracture based on a known resin proppant, characterized by the presence of at least one additional layer, which performs protective functions by partially and / or completely preventing side reactions of the resin coating with chemical compounds that make up fracturing fluid and polymer breaker.

A method for producing a crosslinkable proppant has been developed, which consists in creating at least one protective layer 3 on the outer surface of the resin proppant.

As the protective layer 3, partially and / or completely water-soluble and / or organo-soluble and / or degraded under well conditions, mainly polymers, surface-active compounds, waxes, paraffins and mixtures thereof can be used.

As a protective layer 3 can also be used and insoluble in well conditions.

As the protective layer 3, polyolefins, polysaccharides, polylactides, polyglycols, polyacids, polyacrylamides, polyamino acids, fluoropolymers, polyacrylates, polyamides, polyvinyls, polyimides, polyurethanes, polycarbonates, polysulfones, polyesters, waxes, paraffins, and paraffins thereof can be used. mixtures, except those capable of curing resins.

Inorganic compounds may be used as the protective layer 3.

The thickness of the protective layer 3 is in the range from 10 nm to 1 mm.

As the resin coating 2, compounds capable of partial and / or full cure under well conditions can be used.

Resin coating 2 may consist of at least one layer.

Resin coating 2 can be a combination of two or more alternating sublayers, consisting of both cured and capable of curing resin sublayers.

As the material of the substrate 1, all known types of proppants, mainly spherical, ellipsoid, angular, elongated, having a minimum linear size, passing into the cell with a size lying in the range of 1-100 mesh, are applicable.

The substrate 1 can be made of sand, ceramic, polymer, composite materials, metal, glass, as well as their combination.

The substrate 1 may be made of wood materials.

The protective layer 3 can be applied to the resin coating 2 by immersing the proppant in a solution of the protective layer material in a suitable solvent (dipping method) and then drying the proppant under conditions (temperature and duration of drying) under which the resin coating 2 does not completely cure.

The protective layer 3 can be applied to the resin coating 2 by the mechanical activation method, which is the mechanical processing of proppant with finely ground powder of the material of the protective layer using planetary mills.

The protective layer 3 can be applied to the resin coating 2 by a gas-dynamic method, in which the applied material of the protective layer is introduced into the air flow, striking the surface to be coated. The temperature of the air flow is selected so that there is no complete curing of the resin coating 2.

The protective layer 3 can be applied to the resin coating 2 of supercritical carbon dioxide. The undoubted advantages of this approach are the possibility of forming ultrathin coatings with a high degree of uniformity and low roughness; the possibility of implementing the optimal dynamics of the process of deposition of the protective layer, mainly polymer; the absence of a liquid phase at atmospheric pressure, which eliminates the reorganization of molecules deposited on the substrate due to the influence of surface tension forces; the absence _{of a} liquid phase in CO ₂ at atmospheric pressure allows us to solve the problem of residual solvent in the obtained surface films; high solubility of most materials of the protective layer 3 in supercritical carbon dioxide; the absence of unwanted curing of the resin coating 2 in the selected conditions for applying the protective coating 3.

The protective layer 3 can be applied to the resin coating 2 using liquid solutions of tetrafluoroethylene telomers. The essence of the method consists in dissolving gaseous tetrafluoroethylene in a suitable solvent, applying the solution to the proppant and further radiation treatment with gamma rays. Solvent removal and proppant drying are accompanied by agglomeration of oligomers on the surface to form a strong film firmly bound to the surface.

The protective layer 3 can be applied to the resin coating 2 by gas phase surface polymerization from cyclic di-n-xylylene. The method consists in the fact that in vacuum the molecules of n-cyclophane or its derivatives, passing through the pyrolysis zone of ~ 600 ° C, turn into an active intermediate, which condenses and polymerizes on a cold substrate (proppant). A detailed description of the method was described by Gorham W.F., J. Polymer ScL, A-1, 1966. V.4. No. 12. P.3027. By varying the parameters of the processes of sublimation, pyrolysis, evaporation and polymerization, it is possible to control the thickness and composition of the protective layer 3.

Under the influence of reservoir temperature and pressure, a crosslinking proppant is cured, which forms a uniform solid mass that prevents crack closure and prevents proppant removal. In this case, the protective layer 3 does not have a noticeable effect on the crosslinking process of adjacent proppant granules.

In the proposed method, a crosslinkable proppant can be used throughout the hydraulic fracturing stage or only at the final stage.

The industrial applicability of the developed method was tested in experiments showing the effect of fracturing fluid and polymer breaker on the strength of samples under uniaxial compression, as well as the proppant compatibility with the polymer breaker. Two resin proppant samples were tested.

Sample 1 (reference sample) is a commercially available resin proppant consisting of one crosslinkable resin layer. The weight of the resin coating according to the combustion test was 3.8%. The proppant size is 16/20 mesh.

Sample 2 - is the same proppant as the reference sample, on which a protective layer consisting of a mixture of low density polyethylene and paraffin in a mass ratio of 7: 3 is applied by dipping. The thickness of the protective layer was 20 ± 5 μm.

Experiment 1: determination of the strength of the packaging of the proppant with a resin coating during crosslinking in simulated well conditions under uniaxial compression.

A sample of 100 g of proppant (samples 1 and 2) was added to a 500 ml plastic cup containing 100 ml of a linear gel based on guar gum (5 g / l), 0.1 g of ammonium persulfate (polymer breaker) and then thoroughly mixed with a mechanical stirrer at room temperature for 1 minute at a speed of 500 rpm. Next, the gel was crosslinked using an alkaline solution of boric acid and stirring was continued for 30 seconds; the pH of the crosslinked gel was 12.3. The resulting suspension was placed in a steel form for crosslinking, which is a hollow cylinder and two pistons. The crosslinking mold is equipped with a temperature control system with an accuracy of ± 1 ° C. Crosslinking of resin proppant took place at a pressure of 6895 kPa and a temperature of 100 ° C. The crosslinking time was 1 hour. During stitching, it is necessary to maintain the temperature and pressure on the proppant pack. The closing pressure was maintained with an accuracy of ± 5%. The resulting samples were dried in air at room temperature for 24 hours. The strength of the proppant pack under uniaxial compression was determined on an Instron apparatus according to GOST 21153.2-84, ASTM D 3148-02.

It was shown that the strength of the crosslinked proppant pack of sample 2 is 170 ± 10% of the strength of reference sample 1. This result demonstrates the absence of the effect of the crosslinked fracturing fluid and polymer breakers on the quality of the resin coating having a protective layer.

Experiment 2: study of the compatibility of proppant with a polymer breaker.

In a 500 ml glass jar, weighed 100 g of proppant (samples 1 and 2) and 100 ml of distilled water containing 0.1 g of ammonium persulfate (polymer breaker) were added. Samples 1 and 2 were thoroughly mixed using an electromechanical shaker at room temperature for 4 hours. Every 30 min, samples were taken to determine the content of ammonium persulfate. The concentration of polymer breaker was determined by UV-visible spectroscopy using a technique described in detail in the literature (Lo S., Miller M.J., Li J., "Encapsulated breaker release at hydrostatic pressure and elevated temperatures", SPE 77744). The temperature of the experiment was chosen so that the natural thermal destruction of ammonium persulfate was absent. The experiment showed that after 4 hours in samples 1 and 2, the content of ammonium persulfate is 0.015 and 0.097%, respectively. In other words, a sample of commercially available proppant 1 absorbed (destroyed) 84.5% of the polymer breaker. Moreover, the resin proppant sample with an additional coating practically does not interact with ammonium persulfate.

Claims (10)

1. A proppant granule containing a base - a substrate and a resin coating - a resin layer, on the outer surface of which at least one additional coating is applied - an additional layer consisting of a mixture of low density polyethylene and paraffin in a ratio of 7: 3, which performs a protective function , by at least partially preventing adverse reactions of the resin layer with the chemical compounds that make up the fracturing fluid and the polymer breaker, the thickness of the additional layer is from 10 to 30 microns. 2. The proppant granule according to claim 1, characterized in that compounds capable of at least partially curing under well conditions are used as the resin layer. 3. The proppant granule according to claim 1, characterized in that the resin layer is a cured resin. 4. The proppant granule according to claim 1, characterized in that the resin layer consists of at least one layer. 5. The proppant granule according to claim 1, characterized in that the resin layer is a combination of two or more alternating layers consisting of both cured and capable of curing resins. 6. The proppant granule according to claim 1, characterized in that all known types of proppants having a minimum linear size of 1-100 mesh are applicable as a substrate. 7. The proppant granule according to claim 1, characterized in that the substrate has a spherical, ellipsoidal, angular, elongated shape. 8. The proppant granule according to claim 1, characterized in that sand, ceramic, polymer, composite materials, metal, glass, and also combinations thereof are used as the substrate material. 9. The proppant granule according to claim 1, characterized in that wood material is used as the substrate material. 10. The method of hydraulic fracturing, including pumping proppant granules into the hydraulic fracture — proppant granules containing a base — a substrate and a resin coating — a resin layer, on the outer surface of which at least one additional coating is applied — an additional layer consisting of a mixture of polyethylene low density and paraffin in a ratio of 7: 3, performing a protective function, by at least partially preventing adverse reactions of the resin layer with chemical compounds included in The remaining liquid fracturing destroyer and polymer, the thickness of the additional layer is from 10 to 30 microns.

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