CN113072923B - Nano capsule gel breaker with controllable delivery and release, and preparation method and application thereof - Google Patents
Nano capsule gel breaker with controllable delivery and release, and preparation method and application thereof Download PDFInfo
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- C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
- C09K8/00—Compositions for drilling of boreholes or wells; Compositions for treating boreholes or wells, e.g. for completion or for remedial operations
- C09K8/60—Compositions for stimulating production by acting on the underground formation
- C09K8/62—Compositions for forming crevices or fractures
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Abstract
The invention relates to a nano-capsule gel breaker with controllable delivery and release, a preparation method and application thereof, wherein the nano-capsule gel breaker is prepared by carrying out microemulsion evaporation and then surface modification on a hydrophobic polymer wall material, a gel breaker, dichloromethane (DCM), a non-solvent oil phase or an external water phase and a surface modification material: the nano-capsule gel breaker disclosed by the invention is small in size, has the particle size of 50-500 nanometers, can enter a micro-nano crack along with fracturing fluid after entering a reservoir, and can release the gel breaker to help a thickening agent in the fracturing fluid break gel, assist in laying of a propping agent and remove polymer residues, so that the flow conductivity of the micro-nano crack is increased. The fracturing fluid can be conveyed and accurately released in micro-nano level cracks and pore passages, the gel breaking time of a thickening agent in the fracturing fluid is delayed, the laying effect of the propping agent is improved, and the flow conductivity of the micro-nano cracks is improved.
Description
Technical Field
The invention relates to a nano-capsule gel breaker with controllable delivery and release, a preparation method and application thereof, belonging to the technical field of oil exploitation.
Background
The cost-effective development of hypotonic and tight reservoirs is a long-term and important task. Hydraulic fracturing is an important reservoir transformation measure for improving the yield of low-permeability and compact oil and gas fields, and the fracturing fluid used in construction needs to thoroughly break gel after the proppant is laid, so that a good yield-increasing effect can be achieved. If the gel breaking is not completely remained in the cracks or rock matrixes, secondary damage can be caused to the stratum on one hand, and the formed filter cake can reduce the flow conductivity of the cracks on the other hand.
The most commonly used fracturing fluid systems are acrylamide slick water fracturing fluids or guanidine gum and derivatives thereof. In general, a gel breaker is added to break gel or degrade a polymer of a crosslinking system after fracturing modification is completed, so that residual fracturing fluid and residues are effectively drained, and cracks and reservoir pores are prevented from being damaged by blocking. Potassium persulfate or ammonium persulfate are the most widely used breakers. The application methods of the fracturing fluid gel breaker mainly comprise two methods: firstly, the gel breaker is injected into a fracturing crack or a fracture network simultaneously along with the crosslinking fracturing fluid; and secondly, injecting one part of gel breaker (ammonium persulfate) along with the crosslinking fracturing fluid at the same time, and injecting the other part of gel breaker (such as biological enzyme) in a tail-chasing way. During construction, the gel breaking time and the gel breaking degree of the cross-linked fracturing fluid are regulated and controlled mainly by using a gel breaker formula and injection construction parameter optimization, so that the propping agent is effectively paved in the artificial fractures. The gel breaker and the fracturing fluid are injected simultaneously, so that the risk of too fast gel breaking of the cross-linked fracturing fluid exists, the viscosity of the fracturing fluid is rapidly reduced to form sand blockage, and the fracturing construction safety and the migration and laying of the propping agent are influenced; the method of injecting the gel breaker into two parts can lead the concentration of the gel breaker to be uneven, lead the gel breaking time of the fracturing fluid to be too slow or lead the gel breaking to be incomplete, lead a large amount of fracturing fluid residues to be retained in cracks and reduce the flow conductivity of the cracks.
At the present stage, the volume fracturing effect of the compact reservoir is unstable, the stable production difficulty of the compact oil is high, and therefore, the existing gel breaker addition mode and principle cannot completely meet the fracturing modification requirements of continental facies compact reservoirs in China. By taking the North America tight oil volume fracturing as a reference, the method not only realizes effective support of a larger-scale main seam, but also further improves the flow conductivity of a micro-nano-scale complex seam network, and is one of important future efforts in tight reservoir fracturing research. Therefore, according to the particularity of compact reservoirs in China, the gel breaker is not reacted with a sand carrying liquid in the conveying process, can be controllably released and efficiently broken in the micro-nano cracks, the influence of residue blockage on the flow conductivity can be effectively reduced, the supporting effect of the micro-nano cracks is improved, and the fracturing modification effect is improved.
The delivery of the gel breaker and the accurate control of gel breaking time are always one of the key technical bottlenecks limiting various fracturing fluid systems and fracturing technologies. To solve the above-mentioned contradictions, researchers have introduced microcapsule technology in the pharmaceutical field. The capsule with the shell-core structure has a better encapsulation rate, and can reduce the risk of premature release of the gel breaker, so that the capsule is more widely concerned.
At present, some literature reports on the preparation of capsule breakers by an encapsulation method mainly comprise a physical encapsulation method and a chemical encapsulation method; for example, chinese patent document CN108251097A discloses a method for preparing microcapsule ammonium persulfate gel breaker by polymer surface coagulation deposition; chinese patent document CN105670598A discloses a method of curing and wrapping millimeter-grade ammonium sulfate with gelatin; chinese patent document CN107304356A discloses a method for coating an ammonium persulfate breaker with millimeter-grade aerogel; chinese patent document CN109722236A discloses a method for coating biological enzyme granules with the grain diameter of 1mm by surface spraying; the capsule gel breaker is prepared by a physical packaging method. For example, chinese patent document CN111961450A discloses a method for preparing millimeter-grade encapsulated ammonium persulfate gel breaker by using radical polymerization; chinese patent document CN 11187614A discloses a method for preparing a millimeter-sized high-temperature-resistant capsule gel breaker by free radical polymerization; chinese patent document CN106566 522A discloses a method for preparing a micron-grade microcapsule ammonium persulfate gel breaker by utilizing own polymerized pyrrole monomer; the capsule gel breaker is prepared by a chemical encapsulation method. At present, when fracture network fracturing construction of a compact reservoir of a horizontal well is carried out, not only is a main fracture with a larger size effectively supported, but also the flow conductivity of a micro-nano-scale fracture needs to be improved (as shown in figure 1), but the capsule gel breaker prepared by the wrapping method has the size above the micron level; the gel breaker with the micron level or above cannot enter the cracks and the pore passages with the micron level or above; therefore, the sand laying and gel breaking of the micro-nano scale cracks become bottleneck problems which restrict the improvement of the fracturing effect.
Chinese patent document CN107033869 discloses a method for carrying ammonium persulfate breaker by using porous silica particles. But because of no shell-core structure, the ammonium persulfate loading rate is low (5-10%). Moreover, because the surface of the particles is of a porous structure, the ammonium persulfate and the thickening agent still have the risk of contact reaction in advance. Lixiaodan (2020), zhou (2017) and the like prepare persulfate nanocapsules with the particle size of 50-750 nm in a free radical polymerization mode. The preparation method is characterized in that persulfate is used for initiating free radical polymerization, and a layer of poly (styrene-acrylamide) or polypyrrole shell is formed on the surface of a disperse phase to achieve the purpose of wrapping. However, because of the limited contact surface, only monomers in contact with persulfate can undergo polymerization to form long-chain polymers, and only a thin polymer shell can be formed on the surface of persulfate. Most of the monomers are lost without participating in the reaction. Meanwhile, partial persulfate is consumed during free radical polymerization, so that the utilization rate of raw materials is greatly reduced. The research also finds that the low-thickness poly (styrene-acrylamide) or polypyrrole shell growing on the surface can cause incomplete persulfate coating, so that the slow release time of the capsule cannot be too long, and at present, the slow release time can only reach 8 hours at most.
Therefore, a novel, simpler and environment-friendly encapsulation technology needs to be developed to prepare a capsule gel breaker with smaller size (micro-nano level), higher encapsulation efficiency and high-efficiency release, so that the gel breaker can be conveyed and accurately released in cracks and pores of the micro-nano level.
Disclosure of Invention
In view of the deficiencies of the prior art, it is a first object of the present invention to provide a nanocapsule breaker with controlled delivery and release.
The nano-capsule gel breaker disclosed by the invention is small in size, has the particle size of 50-500 nanometers, can enter a micro-nano crack along with fracturing fluid after entering a reservoir, and can release the gel breaker to help a thickening agent in the fracturing fluid break gel, assist in laying of a propping agent and remove polymer residues, so that the flow conductivity of the micro-nano crack is increased.
The second purpose of the invention is to provide a preparation method of the nano capsule gel breaker with controllable delivery and release, which has the advantages of simple preparation method, complete coating, high coating rate and greatly improved utilization rate of raw materials.
The third purpose of the invention is to provide the application of the nano capsule gel breaker with controllable delivery and release, which can be delivered and accurately released in micro-nano level cracks and ducts, delay the gel breaking time of a thickening agent in fracturing fluid, improve the laying effect of a propping agent and realize the improvement of the flow conductivity of micro-nano cracks.
In order to achieve the above purpose, the invention is realized by the following technical scheme:
a nano capsule gel breaker with controllable delivery and release is prepared by the following components in percentage by mass through microemulsion evaporation and surface modification:
according to a preferred embodiment of the present invention, the hydrophobic polymer wall material is selected from one of poly (lactide-co-glycolide) (PLGA), polycaprolactone (PCL), polymethyl methacrylate (PMMA), polymethyl acrylate (PMA), poly (tert-butyl methacrylate) (PtBMA), or poly (isobutyl acrylate) (PtBA).
Preferably, the gel breaker is selected from one of sodium persulfate, potassium persulfate, pectinase, hydrochloric acid, citric acid and acetic acid.
Preferably according to the invention, the non-solvent oily phase is selected from one of n-hexane, cyclohexane, n-heptane, toluene, p-xylene.
According to the invention, the emulsifier is preferably selected from one or more of emulsifier Pluronic 17R4, emulsifier Brij L-4, emulsifier Brij72, emulsifier Pluronic L-121, emulsifier Triton X-45, emulsifier Tergitol NP-4, span80 and Cetyl Trimethyl Ammonium Bromide (CTAB).
Pluronic 17R4, emulsifier Brij L-4, emulsifier Brij72, available from Sigma-Aldrich, inc., USA.
Emulsifier Pluronic L-121, emulsifier Triton X-45, emulsifier Tergitol NP-4 available from Dow corporation, USA.
According to the invention, the stabilizer is one or the combination of more than two of Sodium Dodecyl Sulfate (SDS), cetyl Trimethyl Ammonium Bromide (CTAB), tween40, tween60, partially Hydrolyzed Polyacrylamide (HPAM) with the hydrolysis degree of 10-35 percent and polyvinyl alcohol (PVA).
According to the invention, the cross-linking agent is preferably one or the combination of more than two of N, N-methylene-bisacrylamide, polyethylene glycol acrylate, chromium acetate, aluminum citrate, trialkylamine, glutaraldehyde and polyethyleneimine.
According to the invention, the surface modification material is preferably one or more of branched Polyethyleneimine (PEI), amphoteric aminopropyl benzyl carbon base, chitosan, polypyrrole, partially Hydrolyzed Polyacrylamide (HPAM) with the hydrolysis degree of 10-35%, and Cetyl Trimethyl Ammonium Bromide (CTAB).
Further preferred, the amphoteric aminopropyl benzylic carbon radical has the general formula: R-ONHC3H6N (CH 3) 2CH2CO2, wherein R is C12-14.
Further, R is C18 or C22.
According to the invention, the preferable delivery and release controllable nano capsule gel breaker comprises the following raw material components in percentage by mass:
according to the invention, preferably, the finished product of the nano capsule gel breaker with controllable delivery and release comprises the following components in percentage by mass:
a. 55% of poly (lactic-co-glycolic acid) (PLGA), 23% of ammonium persulfate, 0.07% of Brij72, 0.1% of Glutaraldehyde (GA), 5% of branched Polyethyleneimine (PEI) and the balance of water; or
b. 40% of Polycaprolactone (PCL), 20% of potassium persulfate, 0.05% of Tergitol NP-4, 0.05% of Brij L-4, 6% of branched Polyethyleneimine (PEI), and the balance of water; or
c. 50% of polymethyl methacrylate (PMMA), 30% of pectinase, 0.15% of Brij72, 10% of polypyrrole and the balance of water; or
d. 60% of polyisobutyl acrylate (PtBA), 10% of hydrochloric acid, 0.05% of Poloxmar 182, 0.1% of Brij L-4, and the balance of water; or
e. 55% of isobutyl polyacrylate (PtBA), 35% of pectinase, 72.07% of Brij,
R-ONHC3H6N (CH 3) 2CH2CO2 (R = C12) 0.03%, polyacrylamide 7%, the balance water.
The nano-capsule gel breaker is a nano-level capsule which is composed of a water-based core, gel breaker components in an aqueous solution of the core, a hydrophobic polymer shell and a hydrophilic or amphiphilic polymer outer layer structure, and the particle size is determined according to application requirements. The preferable particle size of the nanocapsule is 50 nm-500 nm.
The nano capsule gel breaker with controllable delivery and release is obtained through two steps: preparing a nano-capsule gel breaker with a hydrophobic polymer as a wall material by emulsion evaporation; and (3) modifying and modifying the surface of the nano-capsule gel breaker.
A preparation method of a nano capsule gel breaker with controllable delivery and release comprises the following steps:
(1) Preparation of nano capsule gel breaker by emulsion evaporation
1) Adding the gel breaker into water according to a ratio to prepare a gel breaker aqueous phase solution, adjusting the pH value of the aqueous phase solution to 2.0-5.5, taking the gel breaker aqueous phase solution as an inner water core, and adding a hydrophobic polymer wall material into dichloromethane for dissolving to prepare a hydrophobic polymer oil phase;
2) Adding the aqueous phase solution of the gel breaker into the oil phase of the hydrophobic polymer, adding an emulsifier and/or a stabilizer according to the proportion, stirring at a high speed for emulsification to obtain an intermediate emulsion, wherein the volume ratio of the aqueous phase solution to the oil phase is 1-150-1;
3) Adding the intermediate emulsion into a non-solvent oil phase or an external water phase, and carrying out secondary emulsification to form a microemulsion;
4) Stirring the microemulsion at 40-100 ℃ for evaporation reaction for 6-12 hours to remove dichloromethane, and obtaining a dispersion liquid of the nano capsule gel breaker with the hydrophobic polymer shell in the oil phase;
5) Separating the nano-capsule gel breaker from the oil phase, washing, drying, and then dispersing in water for the second time to obtain a nano-capsule dispersion liquid;
(2) Nanocapsule surface modification
6) Dissolving the surface modification material with a dissolving amount of water to prepare a surface modification material solution, adding the surface modification material solution into the nano-capsule dispersion liquid, adding or not adding a cross-linking agent, and embedding the surface modification material on the outer surface of the nano-capsule through cross-linking and evaporation deposition to obtain the nano-capsule gel breaker with controllable conveying and release.
According to the invention, the pH regulator for regulating the pH value of the aqueous phase solution is preferably a 1M hydrochloric acid solution or a 1M sodium hydroxide solution.
Preferably, according to the invention, in step 3), when the external aqueous phase is added, a W/O/W microemulsion is prepared, and when the non-solvent oil phase is added, a W/O reverse microemulsion is prepared.
The nano capsule gel breaker with controllable delivery and release, prepared by the invention, has a good gel breaking effect when being applied to a fracturing process of a tight reservoir fracture network, and particularly has a good effect of breaking a thickening agent and cleaning a polymer with fluid loss in a micro-nano fracture.
According to the invention, the preferable specific application method is as follows:
preparing a suspension with the weight percentage content of 0.01-5% by using water for the nano capsule gel breaker, mixing the suspension with other components of the fracturing fluid, and pumping the mixture into a stratum; under the micro-nano fracture after volume fracturing, the nano capsule gel breaker can control the release time of the gel breaker, delay the gel breaking time of a thickening agent in a fracturing fluid, improve the laying effect of a propping agent and realize the improvement of the flow conductivity of the micro-nano fracture.
The water for preparing the suspension can be clear water, prepared saline water, injection water or reinjection water.
The wall material of the nano-capsule gel breaker is formed by deposition and winding of a hydrophobic polymer, and the influence on temperature, pH and the like is responded to cause the release of the core material gel breaker triggered by a physical method, and the nano-capsule gel breaker mainly comprises four modes: shell collapse due to pressure, shell melting and dissolution due to temperature, pH and ionic strength, porosity change due to shell material shrinkage and thermal degradation of the shell material. For example, the dissolution temperature of the wall material polymethyl methacrylate (PMMA) is 45-110 ℃, and the shell is melted and dissolved in the range, so that the release of the gel breaker from the inner water phase can be delayed to different degrees, and the effect of delaying the gel breaking time of the thickening agent is achieved.
The invention has the technical characteristics and excellent effects that:
1. according to the nano-capsule gel breaker, the gel breaker is released under the stimulation of formation conditions at the micro-nano cracks of a reservoir layer, so that the viscosity of a fracturing fluid is reduced, and a propping agent is assisted to be effectively paved; meanwhile, the micro-nano cracks or residual polymers in pores are cleaned, the flow conductivity of the micro-nano cracks is improved, and the matrix seepage capability is improved.
2. When the nano capsule gel breaker is mixed with fracturing fluid, the nano capsule gel breaker is uniformly dispersed in a fracturing fluid system in a suspension form, and after the nano capsule gel breaker is injected into a stratum, if the nano capsule gel breaker enters a large crack and a large pore channel, the dispersion form of the nano capsule cannot be changed, and the problem of filtration or adsorption cannot occur; if the fracturing fluid enters the micro-nano cracks and the small-size pore passages, the nanocapsules are adsorbed on the surface of the rock due to the reduction of the flow velocity, the gel breaker is released in the micro-nano cracks, the fracturing fluid is promoted to break the gel, the residual polymer on the surface of the rock is cleaned, and the flow conductivity of the micro-nano cracks and the matrix pore seepage capacity are improved.
3. The nano-capsule gel breaker is preferably subjected to surface modification, so that the dispersing capacity of nano-capsules is improved, the nano-capsules have the effect of reversely wetting the surface of rock, and the capillary imbibition, drainage and flooding are promoted.
4. The nano capsule gel breaker can adjust the structure and the particle size according to the oil reservoir conditions, adjust the release time of the gel breaker and has strong adaptability.
5. The invention does not increase the operation time, does not need additional field workers and has better economic benefit.
Drawings
Fig. 1 is a schematic illustration of the delivery and release of a nanocapsule breaker.
FIG. 2 is a schematic diagram of the W/O/W double emulsion evaporation method for preparing the nano-capsule breaker in examples 1 and 2.
FIG. 3 is a schematic diagram of the W/O reverse microemulsion evaporation method and the principle of surface cross-linking modification in examples 3, 4 and 5.
FIG. 4 is a photograph of a dispersion of ammonium persulfate nanocapsules prepared in example 1.
Fig. 5 is an SEM photograph of the nanocapsules prepared in examples 1, 2 and 3 after drying. (a) example 1; (b) example 2; (c) example 3.
FIG. 6 is a change curve of the viscosity of the polyacrylamide aqueous solution of the ammonium persulfate nanocapsule. (a) Viscosity profiles of the solution base viscosity, blank control sample and 0.1% ammonium persulfate nanocapsule sample (Experimental example 1); (b) Viscosity change curves of 0.1% ammonium persulfate nanocapsule polyacrylamide solutions at different temperatures (Experimental example 2).
Detailed Description
Reference will now be made in detail to various exemplary embodiments of the invention, the detailed description should not be construed as limiting the invention but rather as a more detailed description of certain aspects, features and embodiments of the invention. All percentages in the examples are by mass, unless otherwise specified, and all raw materials used are commercially available materials.
Example 1
A preparation method of a nano capsule gel breaker with controllable delivery and release comprises the following steps:
(1) Preparation of nano capsule gel breaker by emulsion evaporation
1) Adding 0.1g of ammonium persulfate into 0.5ml of water to prepare an ammonium persulfate aqueous phase solution (inner water core), and adding 1.1g of poly (glycolide-lactide) into 10ml of dichloromethane for dissolving to prepare a hydrophobic polymer oil phase;
2) Adding 0.5ml of gel breaker aqueous phase solution into 5ml of hydrophobic polymer oil phase, adding Brij 72.05 ml, emulsifying by using a high-speed stirring paddle, and stirring at the rotating speed of 12000rpm for 5min to obtain an intermediate emulsion;
3) Adding the intermediate emulsion into 10ml of 1wt% polyvinyl alcohol (PVA) solution, performing secondary emulsification to form microemulsion, stirring at 55 ℃ (350 rpm) to evaporate for 8 hours, separating the nano-capsule gel breaker from an oil phase, washing, drying, and performing secondary dispersion in water to obtain 2wt.% nano-capsule dispersion liquid;
(2) Surface modification:
2wt.% of the nanocapsule dispersion was added with 2ml of branched polyethyleneimine (PEI, 95%, molecular weight 35 k) and 0.35ml of 50wt.% Glutaraldehyde (GA), and reacted at 55 ℃ for 8 hours with stirring at 200rpm to obtain an ammonium persulfate nanocapsule surface-modified by PEI crosslinking.
FIG. 4 is the final ammonium persulfate nanocapsule dispersion. Fig. 5 (a) is a Scanning Electron Microscope (SEM) photograph of the dried nanocapsules.
The delivery and release of the prepared nanocapsule breaker in the fracture is shown in fig. 1.
Example 2
A preparation method of a nano capsule gel breaker with controllable delivery and release comprises the following steps:
(1) Preparation of nano capsule gel breaker by emulsion evaporation
1) Adding 0.1g ammonium persulfate into 0.5ml water to prepare ammonium persulfate aqueous phase solution (inner water core), adding 0.9g polycaprolactone into 10ml dichloromethane for dissolving to prepare hydrophobic polymer oil phase;
2) Adding 0.5ml of gel breaker aqueous phase solution into 5ml of hydrophobic polymer oil phase, adding 0.05ml of Tergitol NP-4.05ml and 0.05ml of Brij L-4, emulsifying by using a high-speed stirring paddle, stirring at the rotating speed of 12000rpm for 5min to obtain an intermediate emulsion;
3) Adding the intermediate emulsion into 10ml of 1wt% polyvinyl alcohol (PVA) solution, performing secondary emulsification to form microemulsion, stirring at 50 ℃ (350 rpm) to evaporate for 8 hours, separating the nano-capsule gel breaker from an oil phase, washing, drying, and performing secondary dispersion in water to obtain 2wt.% nano-capsule dispersion liquid;
(2) Surface modification:
and adding 3ml of branched polyethyleneimine (PEI, 95 percent and the molecular weight of 35 k) into 2wt.% of the nano-capsule dispersion, and reacting at 55 ℃ for 8 hours by stirring at 200rpm to obtain the ammonium persulfate nano-capsules with surfaces deposited by PEI. Fig. 5 (b) is a Scanning Electron Microscope (SEM) photograph of the dried nanocapsules.
Example 3
A preparation method of a nano capsule gel breaker with controllable delivery and release comprises the following steps:
(1) Preparation of nano capsule gel breaker by emulsion evaporation
1) Adding 0.3g of pectinase into 0.6ml of water to prepare a pectinase aqueous phase solution (inner water core), and adding 0.6g of polymethyl methacrylate (PMMA) into 10ml of dichloromethane to dissolve to prepare a hydrophobic polymer oil phase;
2) Adding 0.5ml of gel breaker aqueous phase solution into 5ml of hydrophobic polymer oil phase, adding Brij 72.1 ml, and emulsifying by using a high-speed stirring paddle (12000rpm, 5 min) to obtain an intermediate emulsion;
3) Adding the intermediate emulsion into 20ml of hexane solution, carrying out secondary emulsification to form microemulsion, stirring at 50 ℃ (300 rpm) for evaporation for 8 hours, separating the nano-capsule gel breaker from the oil phase, washing, drying, and then carrying out secondary dispersion in water to obtain 2wt.% nano-capsule dispersion liquid;
(2) Surface modification:
2wt.% of the nanocapsule dispersion was added to 20ml of 2% polypyrrole solution, and reacted at 60 ℃ for 8 hours with stirring at 500rpm to obtain nanocapsules. Fig. 5 (c) is a Scanning Electron Microscope (SEM) photograph of the dried nanocapsules.
Example 4
A preparation method of a nano capsule gel breaker with controllable delivery and release comprises the following steps:
(1) Preparation of nano capsule gel breaker by emulsion evaporation
1) Preparing 0.5ml of a 3wt.% hydrochloric acid (HCl) solution as an internal water phase, and adding 0.5g of polymethyl methacrylate (PtBA) into 10ml of dichloromethane for dissolving to prepare a hydrophobic polymer oil phase;
2) Adding 0.5ml of internal water phase into 5ml of hydrophobic polymer oil phase, adding 0.05ml of Poloxmar 182 and 0.05ml of Brij L-40.075ml, and emulsifying by using a high-speed stirring paddle (12000rpm, 5 min) to obtain an intermediate emulsion;
3) Adding the intermediate emulsion into 20ml of hexane solution, carrying out secondary emulsification to form microemulsion, stirring at 50 ℃ (300 rpm) for evaporation for 8 hours, separating the nano-capsule gel breaker from the oil phase, washing, drying, and then carrying out secondary dispersion in water to obtain 2wt.% nano-capsule dispersion liquid;
(2) Surface modification:
2wt.% of the nanocapsule dispersion was added to 20ml of 2% polypyrrole solution, and reacted at 60 ℃ for 8 hours with stirring at 500rpm to obtain nanocapsules.
Example 5
A preparation method of a nano capsule gel breaker with controllable delivery and release comprises the following steps:
(1) Preparation of nano capsule gel breaker by emulsion evaporation
1) Adding 0.5g pectinase into 0.75ml water to obtain pectinase aqueous phase solution (inner water core), adding 0.5g polymethyl methacrylate (PtBA) into 15ml dichloromethane, and dissolving to obtain hydrophobic polymer oil phase;
2) Adding 0.5ml of gel breaker aqueous phase solution into 5ml of hydrophobic polymer oil phase, adding Brij 72.1 ml, and emulsifying by using a high-speed stirring paddle (12000rpm, 5min) to obtain an intermediate emulsion;
3) Adding the intermediate emulsion into 20ml of hexane solution, performing secondary emulsification to form a microemulsion, stirring at 50 ℃ (300 rpm) for 8 hours, separating the nano-capsule gel breaker from the oil phase, washing, drying, and performing secondary dispersion in 1wt.% polyacrylamide (HPAM) to obtain 2wt.% nano-capsule dispersion liquid;
(2) Surface modification:
2wt.% of the nanocapsule dispersion was added to 20ml of 0.05% R-ONHC3H6N (CH 3) 2CH2CO2 (R = C12), and reacted at 60 ℃ for 8 hours using 500rpm stirring to obtain surface-modified ammonium persulfate nanocapsules.
Experimental example gel breaking time comparison
The molecular weight of the polyacrylamide polymer (HPAM) for experiments is 12x10 4 Da。
The gel breaking experiment steps are as follows:
HPAM aqueous solution with mass fraction of 0.5%. The ammonium persulfate nanocapsules prepared in example 1 and the aqueous ammonium persulfate solution each having a mass fraction of 0.1% were prepared using 0.5% hpam aqueous solution, respectively.
Experimental example 1
The viscosity was measured by a Brookfield DV III viscometer for 0, 1, 2, 4, 6, 8, and 10h of degradation at 80 ℃ using a polyacrylamide-ammonium persulfate solution as a blank comparison sample and 0.5% HPAM as a solution reference viscosity comparison, and the viscosity change curves were plotted and compared.
Experimental example 2:
the viscosity of 0.1 percent ammonium persulfate nanocapsule polyacrylamide aqueous solution degraded for 0, 1, 2, 4, 6, 8 and 10 hours is measured by a Brookfield DV III viscometer at 40 ℃, 60 ℃, 80 ℃ and 110 ℃, and a viscosity change curve is drawn and compared.
The HPAM solution baseline viscosity in fig. 6 (a) decreased slowly at 80 ℃ due to the slow temperature increase. Meanwhile, as the number of measurements increases, the three-dimensional network structure of the polymer is destroyed by shear force, resulting in a slight decrease in viscosity.
FIG. 6 (a) shows that the ammonium persulfate nanocapsule of the present invention can delay gel breaking for 2 hours at 80 ℃, and compared with the viscosity of a 0.1% ammonium persulfate polyacrylamide aqueous solution, the time for gel breaking of the ammonium persulfate nanocapsule is significantly delayed; the ammonium sulfate nanocapsule has high gel breaking speed at 80 ℃, the viscosity of the aqueous solution is reduced to be less than 5mPa & s specified in general technical conditions for fracturing fluid (SY 6376-2008) within 1h, and the flowback standard is met.
FIG. 6 (b) shows that the gel breaking rate and effect of the ammonium persulfate nanocapsules of the present invention are significantly affected by temperature. The viscosity of the sample at 40 ℃ is basically unchanged within 10 h; the viscosity of the sample begins to decrease after 1 hour at 60 ℃, and after 8 hours, the viscosity is lower than 5mPa & s specified by the fracturing fluid in general technical conditions of fracturing fluid (SY 6376-2008), so that the requirement of site fracturing construction is met (the longest gel breaking time of the fracturing fluid is 12 hours); the viscosity of the sample begins to decrease after 1 hour at 80 ℃, and is lower than 5mPa & s after 6 hours, so that the requirement of site fracturing construction is met; the initial viscosity of the sample at 110 ℃ is lower than that of the sample at other temperatures, and the sample proves that part of ammonium persulfate starts to be released, the viscosity in 2h is lower than 5mPa & s, and the requirement of delaying gel breaking at high temperature in site fracturing construction is met.
The results of experimental examples 1 and 2 show that the nano-capsule gel breaker prepared by the invention has a good gel breaking effect when being applied to the fracturing modification process of a deep layer or a compact reservoir, particularly has a good effect of promoting the gelling agent to break gel and cleaning the polymer of fluid loss in a micro-nano crack, and simultaneously has a gel breaking delaying function under a high-temperature condition.
It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. Further, for numerical ranges in this disclosure, it is understood that each intervening value, between the upper and lower limit of that range, is also specifically disclosed. Every smaller range between any stated value or intervening value in a stated range and any other stated or intervening value in a stated range is encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included or excluded in the range.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference herein for the purpose of disclosing and describing the methods and/or materials associated with the documents. In case of conflict with any incorporated document, the present specification will control.
It will be apparent to those skilled in the art that various modifications and variations can be made in the specific embodiments of the present disclosure without departing from the scope or spirit of the disclosure. Other experimental modes which can be derived from the description of the invention will be apparent to the skilled person. The specification and examples are exemplary only.
As used herein, the terms "comprising," "including," "having," "containing," and the like are open-ended terms that mean including, but not limited to.
Claims (6)
1. A nano capsule gel breaker with controllable delivery and release is prepared by the following components in percentage by mass through microemulsion evaporation and surface modification:
0.2 to 1 percent of hydrophobic polymer wall material,
0.05 to 0.5 percent of gel breaker,
0.2 to 2 percent of water,
20 to 40 percent of dichloromethane DCM,
50-75% of non-solvent oil phase or external water phase,
0.01 to 0.1 percent of emulsifier,
0 to 5 percent of stabilizing agent,
0 to 1 percent of cross-linking agent,
0.02-1% of surface modification material;
the hydrophobic polymer wall material is selected from one of poly (lactic-co-glycolic acid) (PLGA), polycaprolactone (PCL), polymethyl methacrylate (PMMA), polymethyl acrylate (PMA), poly (tert-butyl methacrylate) (PtBMA) or poly (isobutyl acrylate) (PtBA);
the gel breaker is selected from one of sodium persulfate, potassium persulfate, pectinase, hydrochloric acid, citric acid and acetic acid; the non-solvent oil phase is selected from one of n-hexane, cyclohexane, n-heptane, toluene and p-xylene;
the surface modification material is one or the combination of more than two of branched Polyethyleneimine (PEI), amphoteric aminopropyl benzyl carbon group, chitosan, polypyrrole, partially Hydrolyzed Polyacrylamide (HPAM) with the hydrolysis degree of 10-35 percent and hexadecyl trimethyl ammonium bromide (CTAB); the amphoteric aminopropyl benzylic carbon group has the general formula: R-ONHC3H6N (CH 3) 2CH2CO2, wherein R is C12-14;
the nano capsule gel breaker with controllable delivery and release is prepared by the following method:
(1) Preparation of nano capsule gel breaker by emulsion evaporation
1) Adding the gel breaker into water according to the proportion to prepare aqueous phase solution of the gel breaker, adjusting the pH value of the aqueous phase solution to 2.0-5.5,
taking the gel breaker aqueous phase solution as an inner water core, and adding the hydrophobic polymer wall material into dichloromethane for dissolving to prepare a hydrophobic polymer oil phase;
2) Adding the aqueous phase solution of the gel breaker into the oil phase of the hydrophobic polymer, adding an emulsifier and/or a stabilizer according to a ratio, stirring at a high speed for emulsification to obtain an intermediate emulsion, wherein the volume ratio of the aqueous phase solution to the oil phase is (1-1);
3) Adding the intermediate emulsion into a non-solvent oil phase or an external water phase, and carrying out secondary emulsification to form a microemulsion;
4) Stirring the microemulsion at 40-100 ℃ for evaporation reaction for 6-12 hours to remove dichloromethane, and obtaining a dispersion liquid of the nano capsule gel breaker with the hydrophobic polymer shell in the oil phase;
5) Separating the nano-capsule gel breaker from the oil phase, washing, drying, and then dispersing in water for the second time to obtain a nano-capsule dispersion liquid;
(2) Nanocapsule surface modification
6) Dissolving the surface modification material with a dissolving amount of water to prepare a surface modification material solution, adding the surface modification material solution into the nano-capsule dispersion liquid, adding or not adding a cross-linking agent, and embedding the surface modification material on the outer surface of the nano-capsule through cross-linking and evaporation deposition to obtain the nano-capsule gel breaker with controllable conveying and release.
2. The nanocapsule breaker of claim 1, wherein the emulsifier is selected from the group consisting of Pluronic 17R4, brij L-4, brij72, pluronic L-121, triton X-45, tergitol NP-4, span80, cetyl trimethylammonium bromide (CTAB), and combinations thereof.
3. The nanocapsule breaker of claim 1, wherein the stabilizer is one or a combination of two or more of Sodium Dodecyl Sulfate (SDS), cetyl Trimethyl Ammonium Bromide (CTAB), tween40, tween60, partially Hydrolyzed Polyacrylamide (HPAM) with a hydrolysis degree of 10-35%, and polyvinyl alcohol (PVA);
the cross-linking agent is one or the combination of more than two of N, N-methylene bisacrylamide, polyethylene glycol acrylate, chromium acetate, aluminum citrate, trialkylamine, glutaraldehyde and polyethyleneimine.
4. The nano-capsule gel breaker of claim 1, which is characterized by comprising the following raw material components in percentage by mass:
0.25 to 0.5 percent of hydrophobic polymer wall material,
0.05 to 0.25 percent of gel breaker,
0.2-1% of water,
20-30% of dichloromethane DCM,
55-65% of non-solvent oil phase or external water phase,
0.01 to 0.05 percent of emulsifier,
0.1 to 2 percent of stabilizing agent,
0.001 to 0.02 percent of cross-linking agent,
0.05-0.5% of surface modified material.
5. The nanocapsule breaker of claim 1 wherein the composition is selected from one of the following:
a. 55% of poly (lactic-co-glycolic acid) (PLGA), 23% of ammonium persulfate, 0.07% of Brij72, 0.1% of Glutaraldehyde (GA), 5% of branched Polyethyleneimine (PEI) and the balance of water; or alternatively
b. 40% of Polycaprolactone (PCL), 20% of potassium persulfate, 0.05% of Tergitol NP-4, 0.05% of Brij L-4, 6% of branched Polyethyleneimine (PEI), and the balance of water; or
c. 50% of polymethyl methacrylate (PMMA), 30% of pectinase, 0.15% of Brij72, 10% of polypyrrole and the balance of water; or alternatively
d. 60% of polyisobutyl acrylate (PtBA), 10% of hydrochloric acid, 0.05% of Poloxmar 182, 0.1% of Brij L-4, and the balance of water; or
e. 55% of isobutyl polyacrylate (PtBA), 35% of pectinase, 72.07% of Brij,
R-ONHC3H6N (CH 3) 2CH2CO2, R = C12.03%, polyacrylamide 7%, and water in balance.
6. The application of the nano capsule gel breaker with controllable delivery and release, which is applied to the gel breaking in the fracturing process of tight reservoir fracture network, of any one of claims 1 to 5,
the specific application method comprises the following steps:
preparing a suspension with the weight percentage of 0.01-5% by using water for the nano capsule gel breaker, mixing the suspension with other components of a fracturing fluid, and pumping the mixture into a stratum; under the micro-nano fracture after volume fracturing, the nano capsule gel breaker can control the release time of the gel breaker, delay the gel breaking time of a thickening agent in a fracturing fluid, improve the laying effect of a propping agent and realize the improvement of the flow conductivity of the micro-nano fracture.
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| CN114790379A (en) * | 2022-04-24 | 2022-07-26 | 西南石油大学 | Double-chamber microcapsule for drilling fluid and preparation method and application thereof |
| CN115612477A (en) * | 2022-10-31 | 2023-01-17 | 陕西科技大学 | Silica aerogel loaded gel breaker and preparation method and application thereof |
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| CN111876142A (en) * | 2020-07-27 | 2020-11-03 | 西安奥德石油工程技术有限责任公司 | High-temperature-resistant capsule gel breaker for fracturing and preparation method thereof |
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