CN113072923B - Nano capsule gel breaker with controllable delivery and release, and preparation method and application thereof - Google Patents

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

A nanocapsule gel breaker with controllable delivery and release, its preparation method and application

technical field

The invention relates to a nanocapsule gel breaker with controllable delivery and release, a preparation method and application thereof, and belongs to the technical field of petroleum exploitation.

Background technique

The economical and effective development of low-permeability and tight oil reservoirs is a long-term and important task. Hydraulic fracturing is an important reservoir stimulation measure to improve the production of low-permeability and tight oil and gas fields, and the fracturing fluid used in the construction must completely break the gel after the proppant is laid in order to achieve a good production stimulation effect. If the gel is not completely broken and remains in the fracture or rock matrix, on the one hand, it will cause secondary damage to the formation, and on the other hand, the formed filter cake will reduce the conductivity of the fracture.

The most commonly used fracturing fluid system is acrylamide slick water fracturing fluid or guar gum and its derivatives fracturing fluid. Generally, after the fracturing is completed, the gel breaker is added to break the gel of the cross-linking system or degrade the polymer, so as to promote the effective flowback of the fracturing fluid residue and residue, and prevent the fractures and reservoir pores from being blocked and damaged. Potassium persulfate or ammonium persulfate are the most widely used breakers. There are two main methods of using the fracturing fluid breaker: one is that the breaker is injected into the fracturing fracture or fracture network at the same time as the cross-linked fracturing fluid; the other is that a part of the breaker (ammonium persulfate) The liquid is injected at the same time, and another part of the breaker (such as biological enzyme) is injected after the tail. During construction, the formula of gel breaker and the optimization of injection construction parameters are mainly used to control the gel breaking time and degree of cross-linked fracturing fluid, so that proppant can be effectively laid in artificial fractures. If the gel breaker and fracturing fluid are injected at the same time, there is a risk that the cross-linked fracturing fluid will break too fast, resulting in a rapid decrease in the viscosity of the fracturing fluid and the formation of sand plugs, which will affect the safety of fracturing construction and the migration and placement of proppants; The method of injecting the gel in two parts will make the concentration of the gel breaker uneven, and the gel breaking time of the fracturing fluid will be too slow or incomplete, resulting in a large amount of fracturing fluid residue remaining in the fracture and reducing the fracture conductivity.

At present, the effect of volume fracturing in tight oil reservoirs is unstable, and it is difficult to stabilize the production of tight oil. It can be seen that the existing methods and principles of adding gel breakers cannot fully meet the needs of fracturing in continental tight reservoirs in my country. Referring to the volume fracturing of tight oil in North America, in addition to achieving effective support of large-scale main fractures, how to further improve the conductivity of micro- and nano-scale complex fracture networks is one of the important directions of future research on tight reservoir fracturing. Therefore, in view of the particularity of tight reservoirs in my country, the gel breaker does not react with the sand-carrying fluid during the transportation process, and can be released in a controlled manner in the micro-nano fractures to effectively break the gel, which can effectively reduce the impact of residue blockage on the conductivity. It can improve the support effect of micro-nano fractures, thereby improving the effect of fracturing.

The delivery of the gel breaker and the precise control of the gel breaking time are always one of the key technical bottlenecks restricting various fracturing fluid systems and fracturing technologies. In order to solve the above contradictions, researchers have introduced microencapsulation technology in the pharmaceutical field. Capsules with a shell-core structure have a better encapsulation rate and can reduce the risk of premature release of the breaker, so they have received more attention.

At present, there are some bibliographical reports on the preparation of capsule gel breakers by encapsulation, mainly including physical encapsulation methods and chemical encapsulation methods; as Chinese patent document CN108251097A discloses a kind of microcapsule ammonium persulfate gel breaker prepared by polymer surface coagulation deposition The method of Chinese patent document CN105670598A discloses a kind of method that utilizes gelatin to solidify and wrap the ammonium sulfate of millimeter level; Chinese patent document CN107304356A discloses a kind of method that utilizes airgel of millimeter level to coat ammonium persulfate breaker; China Patent document CN109722236A discloses a method of encapsulating biological enzyme particles with a particle size of 1 mm by surface spraying; all of the above are physical encapsulation methods to prepare capsule breakers. Disclosed as Chinese patent document CN111961450A is a kind of preparation method utilizing free radical polymerization to prepare millimeter grade capsule ammonium persulfate breaker; Method; Chinese patent document CN106566 522A discloses a method for preparing a micron-level microcapsule ammonium persulfate breaker by using its own polymerized pyrrole monomer; all of the above are chemical encapsulation methods for preparing capsule breakers. At present, in the fracture network fracturing operation of tight reservoirs in horizontal wells, not only large-scale main fractures are required for effective support, but also the conductivity of micro-nano scale fractures needs to be improved (as shown in Figure 1). The size of the capsule breaker is above the micron level; the breaker above the micron level cannot enter the micro-nano level cracks and channels; therefore, the sanding and gel breaking of micro-nano scale fractures have become the bottleneck problem that restricts the improvement of fracturing effect.

Chinese patent document CN107033869 discloses a method of using porous silica particles to carry an ammonium persulfate breaker. However, since there is no shell-core structure, the loading rate of ammonium persulfate is low (5-10%). Moreover, due to the porous structure of the particle surface, ammonium persulfate and the thickener still have the risk of contact reaction in advance. Li Xiaodan (2020), Zhou (2017), etc. prepared persulfate nanocapsules with a size of 50-750 nm by free radical polymerization. This preparation method relies on persulfate to initiate free radical polymerization, and forms a layer of poly(styrene-acrylamide) or polypyrrole shell on the surface of the dispersed phase to achieve the purpose of encapsulation. However, due to 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 monomers cannot participate in the reaction and are lost. At the same time, part of the persulfate will be consumed during free radical polymerization, which greatly reduces the utilization rate of raw materials. The study also found that the low-thickness poly(styrene-acrylamide) or polypyrrole shell grown on the surface will lead to incomplete encapsulation of persulfate, so that the sustained release time of the capsule cannot be too long, which can only reach 8 hours at most at present.

Therefore, it is necessary to develop a new, simpler, and environmentally friendly encapsulation technology to prepare a capsule breaker with a smaller size (micro-nano level), higher encapsulation rate, and high-efficiency release. Nanoscale crack and channel delivery and precise release.

Contents of the invention

Aiming at the deficiencies of the prior art, the first object of the present invention is to provide a nanocapsule breaker with controllable delivery and release.

The nanocapsule gel breaker of the present invention has a small size and a particle size of 50 nm to 500 nm. After entering the reservoir, it can enter micro-nano fractures with the fracturing fluid and release the gel breaker to help the thickener in the fracturing fluid break the gel. , to assist the laying of proppant, remove polymer residues, thereby increasing the conductivity of micro-nano fractures.

The second object of the present invention is to provide a method for preparing a nanocapsule breaker with controllable delivery and release. The preparation method is simple, complete in encapsulation, high in encapsulation rate, and greatly improves the utilization rate of raw materials.

The third object of the present invention is to provide an application of nanocapsule gel breaker with controllable delivery and release, which can be delivered and precisely released in micro-nano level cracks and pores, and delay the gel breaking of the viscosifier in the fracturing fluid time, improve the effect of proppant laying, and improve the conductivity of micro-nano fractures.

To achieve the above object, the present invention is achieved through the following technical solutions:

A nanocapsule gel breaker with controllable delivery and release, which is prepared by evaporating the microemulsion and then modifying the surface of the following components by mass percentage:

Preferably according to the present invention, the hydrophobic polymer wall material is selected from polyethylene lactide (PLGA), polycaprolactone (PCL), polymethyl methacrylate (PMMA), polymethyl acrylate (PMA) , polytert-butyl methacrylate (PtBMA) or polyisobutyl acrylate (PtBA).

Preferably according to the present invention, the gel breaker is selected from one of sodium persulfate, potassium persulfate, pectinase, hydrochloric acid, citric acid and acetic acid.

Preferably according to the present invention, the non-solvent oil phase is selected from one of n-hexane, cyclohexane, n-heptane, toluene and p-xylene.

Preferably according to the present invention, the emulsifier is selected from emulsifier Pluronic 17R4, emulsifier Brij L-4, emulsifier Brij 72, emulsifier Pluronic L-121, emulsifier Triton X-45, emulsifier Tergitol NP-4 , Span80, cetyltrimethylammonium bromide (CTAB) or a combination of two or more.

Pluronic 17R4, emulsifier Brij L-4, and emulsifier Brij 72 are available from Sigma-Aldrich Co., Ltd. in the United States.

Emulsifier Pluronic L-121, emulsifier Triton X-45, and emulsifier Tergitol NP-4 are available from US DOW.

Preferably according to the present invention, the stabilizer is sodium dodecylsulfonate (SDS), cetyltrimethylammonium bromide (CTAB), Tween40, Tween60, partially hydrolyzed with a degree of hydrolysis of 10-35%. One of polyacrylamide (HPAM), polyvinyl alcohol (PVA), or a combination of two or more.

Preferably according to the present invention, the crosslinking agent is N,N-methylenebisacrylamide, polyethylene glycol acrylate, chromium acetate, aluminum citrate, trialkylamine, glutaraldehyde, polyethylene glycol One or more combination of amines.

Preferably according to the present invention, said surface modification material is branched chain polyethyleneimine (PEI), amphoteric aminopropyl benzyl carbonyl, chitosan, polypyrrole, partially hydrolyzed polymer with a degree of hydrolysis of 10-35%. Acrylamide (HPAM), cetyltrimethylammonium bromide (CTAB) or a combination of two or more.

Further preferably, the general formula of the amphoteric aminopropyl benzyl carbonyl is as follows: R-ONHC3H6N(CH3)2CH2CO2, wherein R is C12-14.

Furthermore, R is C18 or C22.

According to the present invention, preferably, a nanocapsule gel breaker with controllable delivery and release, the mass percentage of raw material components is as follows:

According to the present invention, preferably, a finished nanocapsule breaker with controllable delivery and release, the mass percent component is selected from one of the following:

a. Polyethylene lactide (PLGA) 55%, ammonium persulfate 23%, Brij72 0.07%, glutaraldehyde (GA) 0.1%, branched polyethyleneimine (PEI) 5%, and the balance is water; or

b. Polycaprolactone (PCL) 40%, potassium persulfate 20%, Tergitol NP-4 0.05%, Brij L-40.05%, branched polyethyleneimine (PEI) 6%, and the balance is water; or

c. Polymethylmethacrylate (PMMA) 50%, pectinase 30%, Brij72 0.15%, polypyrrole 10%, and the balance is water; or

d. Polyisobutyl acrylate (PtBA) 60%, hydrochloric acid 10%, Poloxmar 182 0.05%, Brij L-40.1%, and the balance is water; or

e. Polyisobutyl acrylate (PtBA) 55%, pectinase 35%, Brij72 0.07%,

R-ONHC3H6N(CH3)2CH2CO2(R=C12) 0.03%, polyacrylamide 7%, and the balance is water.

The nanocapsule breaker of the present invention is a nanoscale capsule composed of a water-based inner core, gel breaker components in the aqueous solution of the inner core, a hydrophobic polymer shell, and a hydrophilic or amphiphilic polymer outer layer structure. diameter size. In the present invention, the particle size of the nanocapsule is preferably 50 nanometers to 500 nanometers.

The nanocapsule breaker with controllable delivery and release is obtained through two steps: emulsion evaporation to prepare the nanocapsule breaker with the hydrophobic polymer as the wall material; surface modification and modification of the nanocapsule breaker.

A method for preparing a delivery and release controllable nanocapsule breaker, comprising the steps of:

(1) Preparation of nanocapsule gel breaker by emulsion evaporation

1) Add the gel breaker to the water according to the ratio to prepare the gel breaker water phase solution, adjust the pH value of the water phase solution to 2.0-5.5, use the gel breaker water phase solution as the inner water core, add the hydrophobic polymer wall material dissolved in methyl chloride to obtain a hydrophobic polymer oil phase;

2) Add the water phase solution of the gel breaker to the oil phase of the hydrophobic polymer, add an emulsifier and/or stabilizer according to the ratio, and stir at high speed to emulsify to obtain an intermediate emulsion. The volume ratio of the water phase solution to the oil phase is 1:150 -1:20;

3) adding the intermediate emulsion into the non-solvent oil phase or the external water phase for secondary emulsification to form a microemulsion;

4) stirring and evaporating the microemulsion at 40-100° C. for 6-12 hours to remove dichloromethane to obtain a dispersion of nanocapsule breakers with hydrophobic polymer shells in the oil phase;

5) separating the nanocapsule breaker from the oil phase, washing, drying, and then secondary dispersion in water to obtain a nanocapsule dispersion;

(2) Surface modification of nanocapsules

6) Dissolving the surface modification material with a dissolved amount of water to prepare a surface modification material solution, adding the surface modification material solution to the nanocapsule dispersion, adding or not adding a crosslinking agent, and acting on the surface through crosslinking and evaporation deposition The modified material is embedded on the outer surface of the nanocapsule to obtain a nanocapsule breaker with controllable delivery and release.

Preferably according to the present invention, the pH regulator for adjusting the pH value of the aqueous phase solution is 1M hydrochloric acid solution or 1M sodium hydroxide solution.

Preferably according to the present invention, in step 3), when the external water phase is added, a W/O/W microemulsion is prepared, and when the non-solvent oil phase is added, a W/O reverse phase microemulsion is prepared.

A nanocapsule gel breaker with controllable delivery and release prepared by the invention has a good gel breaking effect when applied to the fracture network fracturing process of tight oil reservoirs, especially in micro-nano fractures to break the gel of the thickener and clean the filter. Lost polymer works well.

Preferably according to the present invention, specific application method is as follows:

The nanocapsule gel breaker is prepared with water into a suspension with a mass percentage of 0.01% to 5%, mixed with other components of the fracturing fluid, and then pumped into the formation together; under the micro-nano fractures after volume fracturing, the nanocapsules break The glue can control the release time of the breaker, delay the breaking time of the thickener in the fracturing fluid, improve the effect of proppant laying, and realize the improvement of the conductivity of micro-nano fractures.

The above-mentioned water for preparing the suspension can be clear water, prepared brine, injection water or re-injection water.

The wall material of the nanocapsule breaker of the present invention is formed by the deposition and winding of hydrophobic polymers, and responds to the influence of temperature and pH to cause physical methods to trigger the release of the core material breaker, which mainly includes four methods: the shell collapse caused by pressure, Shell melting and dissolution due to temperature, pH, and ionic strength, porosity changes due to shell material shrinkage, and thermal degradation of shell material. For example, the melting temperature of the wall material polymethyl methacrylate (PMMA) is 45-110 °C. In this range, the shell can be melted and dissolved, which can delay the release of the breaker from the inner water phase to varying degrees, so as to delay the thickening agent. Effect of break time.

Technical characteristics of the present invention and good effect are:

1. The nanocapsule gel breaker of the present invention releases the gel breaker in the micro-nano fractures of the reservoir due to formation conditions, thereby reducing the viscosity of the fracturing fluid and assisting the effective laying of the proppant; at the same time, it cleans the micro-nano cracks or pores The residual polymer can improve the conductivity of micro-nano cracks and improve the seepage capacity of the matrix.

2. The nanocapsule gel breaker of the present invention, when mixed with fracturing fluid, allows the nanocapsule gel breaker to be evenly dispersed in the fracturing fluid system in the form of a suspension. After injecting into the formation, if it enters a large fracture, For large pores, the dispersed form of nanocapsules will not change, and there will be no problems of filtration or adsorption; if they enter micro-nano cracks or small-sized pores, due to the reduced flow rate, nanocapsules will be adsorbed on the rock surface. The gel breaker is released in the fracture, which promotes the fracturing fluid to break the gel, and removes the residual polymer on the rock surface, improving the conductivity of micro-nano fractures and matrix pore seepage.

3. The nanocapsule gel breaker of the present invention is preferably surface modified or modified, which improves the dispersion ability of the nanocapsules, and allows the nanocapsules to have the effect of reverse wetting on the rock surface, and promotes capillary imbibition and displacement .

4. The nanocapsule breaker of the present invention can adjust its structure and particle size according to the oil reservoir conditions, adjust the release time of the breaker, and has strong adaptability.

5. The present invention does not increase the operating time, does not require additional on-site staff, and has better economic benefits.

Description of drawings

Figure 1 is a schematic diagram of the delivery and release of nanocapsule breakers.

Fig. 2 is a schematic diagram of the principle of preparing nanocapsule breakers by W/O/W double emulsion evaporation method in Examples 1 and 2.

Fig. 3 is a schematic diagram of the W/O inverse microemulsion evaporation method and the principle of surface cross-linking modification in Examples 3, 4 and 5.

Fig. 4 is the photo of the ammonium persulfate nanocapsule dispersion prepared in Example 1.

Fig. 5 is the SEM photo of the dried nanocapsules prepared in Examples 1, 2 and 3. (a) Example 1; (b) Example 2; (c) Example 3.

Fig. 6 viscosity change curve of ammonium persulfate nanocapsule polyacrylamide aqueous solution. (a) The viscosity change curve (experimental example 1) of solution standard viscosity, blank control sample and 0.1% ammonium persulfate nanocapsule sample; (b) the viscosity change of 0.1% ammonium persulfate nanocapsule polyacrylamide solution at different temperatures Curve (experimental example 2).

Detailed ways

Various exemplary embodiments of the present invention will now be described in detail. The detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features and embodiments of the present invention. Unless otherwise specified, all percentages in the examples are percentages by mass, and all raw materials used are commercially available materials.

Example 1

A method for preparing a delivery and release controllable nanocapsule breaker, comprising the steps of:

(1) Preparation of nanocapsule gel breaker by emulsion evaporation

1) Add 0.1g of ammonium persulfate to 0.5ml of water to prepare an aqueous solution of ammonium persulfate (inner water core), and dissolve 1.1g of polyglycolide in 10ml of dichloromethane to obtain a hydrophobic polymer oil phase ;

2) Add 0.5ml of gel breaker aqueous phase solution into 5ml of hydrophobic polymer oil phase, add 0.05ml of Brij72, and emulsify with a high-speed stirring paddle at a stirring speed of 12000rpm for 5min to obtain an intermediate emulsion;

3) Add the intermediate emulsion to 10ml 1wt% polyvinyl alcohol (PVA) solution, carry out secondary emulsification, form a microemulsion, stir (350rpm) at 55°C for 8 hours, separate the nanocapsule breaker from the oil phase, and wash , dried, and then secondarily dispersed in water to obtain a 2wt.% nanocapsule dispersion;

(2) Surface modification:

2wt.% nanocapsule dispersion, add 2ml branched polyethyleneimine (PEI, 95%, molecular weight 35k) and 0.35ml 50wt.% glutaraldehyde (GA), use 200rpm stirring at 55 ℃ for 8 hours to obtain Ammonium persulfate nanocapsules whose surface is cross-linked with PEI.

Fig. 4 is the finally obtained ammonium persulfate nanocapsule dispersion. Figure 5(a) is a scanning electron microscope (SEM) photo of the dried nanocapsules.

The delivery and release of the prepared nanocapsule breaker in the crack is shown in Fig. 1.

Example 2

A method for preparing a delivery and release controllable nanocapsule breaker, comprising the steps of:

(1) Preparation of nanocapsule gel breaker by emulsion evaporation

1) Add 0.1g of ammonium persulfate to 0.5ml of water to obtain an aqueous solution of ammonium persulfate (inner water core), and dissolve 0.9g of polycaprolactone in 10ml of dichloromethane to obtain a hydrophobic polymer oil phase ;

2) Add 0.5ml of gel breaker aqueous phase solution into 5ml of hydrophobic polymer oil phase, add Tergitol NP-40.05ml and Brij L-4 0.05ml, use high-speed stirring paddle for emulsification, stirring speed 12000rpm, stirring time 5min, get intermediate emulsion;

3) Add the intermediate emulsion to 10ml 1wt% polyvinyl alcohol (PVA) solution, perform secondary emulsification to form a microemulsion, stir (350rpm) at 50°C for 8 hours, separate the nanocapsule breaker from the oil phase, and wash , dried, and then secondarily dispersed in water to obtain a 2wt.% nanocapsule dispersion;

(2) Surface modification:

With 2wt.% nanocapsule dispersion, add 3ml branched polyethyleneimine (PEI, 95%, molecular weight 35k), use 200rpm to stir and react at 55 ℃ for 8 hours to obtain the ammonium persulfate nanocapsule formed by the surface deposition of PEI . Figure 5(b) is a scanning electron microscope (SEM) photo of the dried nanocapsules.

Example 3

A method for preparing a delivery and release controllable nanocapsule breaker, comprising the steps of:

(1) Preparation of nanocapsule gel breaker by emulsion evaporation

1) Add 0.3g of pectinase to 0.6ml of water to prepare a pectinase aqueous phase solution (inner water core), add 0.6g of polymethyl methacrylate (PMMA) to dissolve in 10ml of dichloromethane to obtain a hydrophobic polymer oil phase;

2) Add 0.5ml of gel breaker aqueous phase solution into 5ml of hydrophobic polymer oil phase, add 0.1ml of Brij72, and emulsify with a high-speed stirring paddle (12000rpm, 5min) to obtain an intermediate emulsion;

3) Add the intermediate emulsion into 20ml of hexane solution for secondary emulsification to form a microemulsion, stir (300rpm) at 50°C for 8 hours to evaporate, separate the nanocapsule breaker from the oil phase, wash, dry, and then dissolve in water Secondary dispersion to obtain 2wt.% nanocapsule dispersion;

(2) Surface modification:

Add 20ml of 2% polypyrrole solution to 2wt.% nanocapsule dispersion, stir at 500rpm and react at 60°C for 8 hours to obtain nanocapsules. Figure 5(c) is a scanning electron microscope (SEM) photo of the dried nanocapsules.

Example 4

A method for preparing a delivery and release controllable nanocapsule breaker, comprising the steps of:

(1) Preparation of nanocapsule gel breaker by emulsion evaporation

1) Prepare 0.5ml of 3wt.% hydrochloric acid (HCl) solution as the internal water phase, add 0.5g of polymethyl methacrylate (PtBA) into 10ml of dichloromethane to dissolve, and obtain a hydrophobic polymer oil phase;

2) Add 0.5ml of the internal water phase to 5ml of the hydrophobic polymer oil phase, add 0.05ml of Poloxmar 182 and 0.075ml of BrijL-4, and emulsify with a high-speed stirring paddle (12000rpm, 5min) to obtain an intermediate emulsion;

3) Add the intermediate emulsion into 20ml of hexane solution for secondary emulsification to form a microemulsion, stir (300rpm) at 50°C for 8 hours to evaporate, separate the nanocapsule breaker from the oil phase, wash, dry, and then dissolve in water Secondary dispersion to obtain 2wt.% nanocapsule dispersion;

(2) Surface modification:

Add 20ml of 2% polypyrrole solution to 2wt.% nanocapsule dispersion, stir at 500rpm and react at 60°C for 8 hours to obtain nanocapsules.

Example 5

A method for preparing a delivery and release controllable nanocapsule breaker, comprising the steps of:

(1) Preparation of nanocapsule gel breaker by emulsion evaporation

1) Add 0.5g of pectinase to 0.75ml of water to prepare a pectinase aqueous phase solution (inner water core), add 0.5g of polymethyl methacrylate (PtBA) to dissolve in 15ml of dichloromethane to obtain a hydrophobic polymer oil phase;

2) Add 0.5ml of gel breaker aqueous phase solution into 5ml of hydrophobic polymer oil phase, add 0.1ml of Brij72, and emulsify with a high-speed stirring paddle (12000rpm, 5min) to obtain an intermediate emulsion;

3) Add the intermediate emulsion into 20ml of hexane solution for secondary emulsification to form a microemulsion, stir (300rpm) at 50°C for 8 hours to evaporate, separate the nanocapsule breaker from the oil phase, wash, dry, and then dissolve in 1wt .% secondary dispersion in polyacrylamide (HPAM) to obtain 2wt.% nanocapsule dispersion;

(2) Surface modification:

Add 20ml of 0.05% R-ONHC3H6N(CH3)2CH2CO2(R=C12) to 2wt.% nanocapsule dispersion, stir at 500rpm and react at 60°C for 8 hours to obtain surface-modified ammonium persulfate nanocapsules.

Experimental example gel breaking time comparison

The experimental polyacrylamide polymer (HPAM) has a molecular weight of 12x10 ⁴ Da.

The gel breaking experiment steps are as follows:

The mass fractions are all 0.5% HPAM aqueous solutions. The ammonium persulfate nanocapsules prepared in Example 1 and the ammonium persulfate aqueous solution with a mass fraction of 0.1% were prepared respectively with 0.5% HPAM aqueous solution.

Experimental example 1

Using polyacrylamide-ammonium persulfate solution as a blank comparison sample, and using 0.5% HPAM as a solution benchmark viscosity comparison, the Brookfield DVⅢ viscometer was used to measure its degradation at 80°C for 0, 1, 2, 4, 6, 8, 10h Viscosity at time, draw the viscosity change curve and compare.

Experimental example 2:

Use a Brookfield DVⅢ viscometer to measure the viscosity of 0.1% ammonium persulfate nanocapsule polyacrylamide aqueous solution at 40°C, 60°C, 80°C, and 110°C for 0, 1, 2, 4, 6, 8, and 10 hours, and draw Viscosity curves and comparisons.

The base viscosity of HPAM solution in Figure 6(a) decreases slowly at 80°C because of the slow temperature rise. At the same time, as the number of measurements increases, the three-dimensional network structure of the polymer is destroyed by the shear force, resulting in a slight decrease in viscosity.

Figure 6 (a) shows that the ammonium persulfate nanocapsules of the present invention can delay gel breaking for 2h at 80° C., compared with the viscosity of 0.1% ammonium persulfate polyacrylamide aqueous solution, the gel breaking time of ammonium persulfate nanocapsules obviously lags behind; ammonium sulfate The gel breaking speed of the nanocapsules is fast at 80°C, and the viscosity of the aqueous solution is reduced to below 5mPa·s specified in the "General Technical Conditions for Fracturing Fluids" (SY6376-2008) within 1 hour, meeting the flowback standard.

Figure 6(b) shows that the gel breaking rate and effect of the ammonium persulfate nanocapsules of the present invention are significantly affected by temperature. At 40°C, the viscosity of the sample basically does not change within 10 hours; at 60°C, the viscosity of the sample begins to decrease after 1 hour, and after 8 hours, the viscosity is lower than the 5mPa·s stipulated in the "General Technical Conditions for Fracturing Fluids" (SY6376-2008) for fracturing fluids Below, it meets the needs of on-site fracturing construction (the longest gel breaking time of fracturing fluid is 12h); at 80°C, the viscosity of the sample begins to decrease after 1h, and after 6h, the viscosity is lower than 5mPa·s, which meets the needs of on-site fracturing construction; at 110°C The initial viscosity of the sample is lower than that of the samples at other temperatures, which proves that part of the ammonium persulfate begins to be released, and the viscosity is lower than 5mPa·s within 2 hours, which meets the needs of delaying gel breaking under high temperature in on-site fracturing construction.

The results of Experimental Examples 1 and 2 show that the nanocapsule gel breaker prepared by the present invention has a good gel-breaking effect when applied to deep or dense reservoir fracturing, especially in micro-nano fractures to promote gel-breaking of the thickener and It has a good effect on cleaning the fluid loss polymer, and it also has the function of delaying gel breaking under high temperature conditions.

It should be understood that the terminology described in the present invention is only used to describe specific embodiments, but not to limit the present invention. In addition, regarding the numerical ranges in the present invention, it should be understood that each intermediate value between the upper limit and the lower limit of the range is also specifically disclosed. Each smaller range between any stated value or intervening value in a stated range and any other stated value 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 from 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 the 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 to disclose and describe the methods and/or materials in connection with which the documents are described. In case of conflict with any incorporated document, the contents of this specification control.

It will be apparent to those skilled in the art that various modifications and changes can be made in the specific embodiments of the present invention described herein without departing from the scope or spirit of the present invention. Other experimental modes will be apparent to the skilled person from the description of the present invention. The specification and examples in this application are exemplary only.

Descriptions such as "comprising", "including", "having", and "containing" used herein are all open terms, meaning including but not limited to.

Claims (6)

1. A nanocapsule gel breaker with controllable delivery and release, which is prepared by evaporating the microemulsion and then surface-modifying the components in the following mass percentages: Hydrophobic polymer wall material 0.2-1%, Gel breaker 0.05-0.5%, Water 0.2-2%, Dichloromethane DCM 20-40%, Non-solvent oil phase or external water phase 50-75%, Emulsifier 0.01-0.1%, Stabilizer 0-5%, Cross-linking agent 0-1%, Surface modification materials 0.02-1%; The hydrophobic polymer wall material is selected from polylactide (PLGA), polycaprolactone (PCL), polymethylmethacrylate (PMMA), polymethylacrylate (PMA), polytert-butylmethacrylate (PtBMA) or polyisobutyl acrylate (PtBA); The gel breaker is selected from one of sodium persulfate, potassium persulfate, pectinase, hydrochloric acid, citric acid, acetic acid; the non-solvent oil phase is selected from normal hexane, cyclohexane, normal heptane, toluene, One of p-xylene; The surface modification materials are branched polyethyleneimine (PEI), amphoteric aminopropylbenzyl carbonyl, chitosan, polypyrrole, partially hydrolyzed polyacrylamide (HPAM) with a degree of hydrolysis of 10-35%, One or more combinations of cetyltrimethylammonium bromide (CTAB); amphoteric aminopropyl benzyl carbonyl has the following general formula: R-ONHC3H6N(CH3)2CH2CO2, where R is C12-14; The nanocapsule breaker with controllable delivery and release is prepared as follows: (1) Preparation of nanocapsule gel breaker by emulsion evaporation 1) Add the gel breaker to water according to the ratio to prepare the gel breaker aqueous solution, adjust the pH value of the aqueous phase solution to 2.0-5.5, The aqueous phase solution of the gel breaker is used as the inner water core, and the hydrophobic polymer wall material is dissolved in dichloromethane to obtain the hydrophobic polymer oil phase; 2) Add the water phase solution of the gel breaker to the oil phase of the hydrophobic polymer, add an emulsifier and/or stabilizer according to the ratio, and stir at high speed to emulsify to obtain an intermediate emulsion. The volume ratio of the water phase solution to the oil phase is 1:150 -1:20; 3) Add the intermediate emulsion into the non-solvent oil phase or the external water phase for secondary emulsification to form a microemulsion; 4) Stir and evaporate the microemulsion at 40-100°C for 6-12 hours to remove dichloromethane to obtain a dispersion of nanocapsule breaker in the oil phase with a hydrophobic polymer shell; 5) Separating the nanocapsule breaker from the oil phase, washing, drying, and then redispersing in water to obtain a nanocapsule dispersion; (2) Surface modification of nanocapsules 6) Dissolve the surface modification material with a dissolved amount of water to prepare a surface modification material solution, add the surface modification material solution to the nanocapsule dispersion, add or not add a cross-linking agent, and act on the surface through cross-linking and evaporation deposition The modified material is embedded on the outer surface of the nanocapsule to obtain a nanocapsule breaker with controllable delivery and release. 2. The nanocapsule breaker according to claim 1, wherein the emulsifier is selected from emulsifier Pluronic 17R4, emulsifier Brij L-4, emulsifier Brij 72, emulsifier Pluronic L-121, emulsifier Agent TritonX-45, emulsifier Tergitol NP-4, Span80, cetyltrimethylammonium bromide (CTAB) or a combination of two or more. 3. The nanocapsule gel breaker according to claim 1, wherein the stabilizer is sodium dodecylsulfonate (SDS), cetyltrimethylammonium bromide (CTAB), Tween40 , Tween60, one or more combinations of partially hydrolyzed polyacrylamide (HPAM) and polyvinyl alcohol (PVA) with a degree of hydrolysis of 10-35%; The crosslinking agent is one of N, N-methylenebisacrylamide, polyethylene glycol acrylate, chromium acetate, aluminum citrate, trialkylamine, glutaraldehyde, polyethyleneimine or A combination of two or more. 4. according to the described nanocapsule breaker of claim 1, it is characterized in that, raw material component mass percent is as follows: Hydrophobic polymer wall material 0.25-0.5%, Gel breaker 0.05-0.25%, Water 0.2-1%, Dichloromethane DCM 20-30%, Non-solvent oil phase or external water phase 55-65%, Emulsifier 0.01-0.05%, Stabilizer 0.1-2%, Cross-linking agent 0.001-0.02%, Surface modifying materials 0.05-0.5%. 5. The nanocapsule gel breaker according to claim 1, wherein the mass percent component is selected from one of the following: a. Polyethylene lactide (PLGA) 55%, ammonium persulfate 23%, Brij72 0.07%, glutaraldehyde (GA) 0.1%, branched polyethyleneimine (PEI) 5%, the balance is water; or b. Polycaprolactone (PCL) 40%, potassium persulfate 20%, Tergitol NP-4 0.05%, Brij L-4 0.05%, branched polyethyleneimine (PEI) 6%, and the balance is water; or c. Polymethyl methacrylate (PMMA) 50%, pectinase 30%, Brij72 0.15%, polypyrrole 10%, the balance is water; or d. Polyisobutyl acrylate (PtBA) 60%, hydrochloric acid 10%, Poloxmar 182 0.05%, Brij L-4 0.1%, and the balance is water; or e. Polyisobutyl acrylate (PtBA) 55%, pectinase 35%, Brij72 0.07%, R-ONHC3H6N(CH3)2CH2CO2, R=C12 0.03%, polyacrylamide 7%, the balance is water. 6. The application of any delivery and release controllable nanocapsule gel breaker according to claim 1-5, which is applied to the gel breaking in the fracture network fracturing process of tight oil reservoirs, The specific application method is as follows: The nanocapsule gel breaker is prepared into a suspension with a mass percentage of 0.01%~5% with water, mixed with other components of the fracturing fluid, and then pumped into the formation together; The glue can control the release time of the breaker, delay the breaking time of the thickener in the fracturing fluid, improve the effect of proppant laying, and realize the improvement of the conductivity of micro-nano fractures.

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