Desorbent, preparation method and application thereof and fracturing fluid

Abstract

The application provides a kind of desorption agent and its preparation method and application and fracturing fluid, wherein the desorption agent is stable dispersion nanoemulsion, comprising: 1-4% of sacrificial agent, 3-8% of synergist, 12-28% of surfactant, 5-10% of dispersion solvent and the rest of water, with the total weight of the desorption agent being 100%; wherein the sacrificial agent is nano-silica modified by quaternary ammonium salt cationic surfactant, and the mass ratio of quaternary ammonium salt cationic surfactant to nano-silica is 0.01-0.2:1. The desorption agent is used as an additive of fracturing fluid, and is injected into the formation with the fracturing fluid. The operation is simple and the cost is low. The permeability of the fracture and matrix can be improved by reducing adsorption, so as to improve the fracturing development and increase the gas production. Meanwhile, the fracturing fluid damage can also be reduced.

Description

Technical Field

[0001] The invention relates to a desorbent, a preparation method and application thereof, and a fracturing fluid, and belongs to the technical field of gas reservoir exploitation. Background Art

[0002] Tight gas is the main force in the development of unconventional natural gas. Hydraulic fracturing is the primary form of extracting tight gas. Currently, water-based fracturing fluids used in this field mostly use plant gums such as guar gum and / or modified polyacrylamide as thickeners to form a polymer gel that can transmit pressure, achieve the functions of forming cracks and transporting proppants, and ultimately complete reservoir transformation. Due to the existence of interaction forces such as static electricity, hydrogen bonds, and van der Waals forces, the thickener within the fracturing fluid will be adsorbed in the cracks, on the surface of the proppant, and in the rock matrix, destroying the pores formed by the proppant filling and blocking the gas flow channel. In addition, some of the gel will entangle in the cracks and aggregate to form residues, which seriously limit gas production. At the same time, the thickeners used in water-based fracturing fluids will cause a certain degree of damage to both core samples and proppants, and the effect of subsequent flushing with brine or the like on permeability recovery is extremely limited. Therefore, it is necessary to reduce the reservoir damage caused by the adsorption of thickeners in the fracturing fluid.

[0003] In order to reduce fracturing fluid adsorption, chemicals can be added thereto, on the one hand, the chemicals need to be able to efficiently destroy the interaction between fracturing fluid and rock and proppant, on the other hand, it can not also affect the cracking and sand carrying performance of fracturing fluid during construction, will not bring additional reservoir damage, and production and use costs are low. To this, CN113322057A discloses a kind of adsorption inhibitor, its preparation method and application, the adsorption inhibitor can be first attached to rock surface along with fluid injection, so as to suppress the adsorption retention of guar gum. But the silicon dioxide used therein is solid phase, poor dispersibility in fracturing fluid, unsolved electrostatic adsorption and hydrogen bond adsorption problems, and is not suitable for polymer fracturing fluid system, and effect and application are limited.

[0004] Therefore, providing a new type of desorbent to effectively reduce the interaction force between the fracturing fluid and the sandstone surface and efficiently reduce the damage to the reservoir during the fracturing process has become a technical problem that needs to be solved urgently in this field. Summary of the Invention

[0005] The present invention addresses the problem of reservoir damage caused by severe adsorption of fracturing fluid on the surface of rocks and proppants during the transformation of tight gas reservoirs. Combining the shortcomings of existing damage removal technologies, the present invention provides a desorbent, a preparation method and application thereof, and a fracturing fluid based on a precise understanding of the interaction between fracturing fluid, rocks and proppants.

[0006] In order to achieve the above objectives, in one aspect, the present invention provides a desorbent, wherein the desorbent is a stably dispersed nanoemulsion-like liquid, and based on the total weight of the desorbent being 100%, the desorbent comprises:

[0007] 1-4% sacrificial agent, 3-8% synergist, 12-28% surfactant, 5-10% dispersing solvent and the balance water;

[0008] The sacrificial agent is nano-silica surface-modified with a quaternary ammonium salt cationic surfactant, wherein the mass ratio of the quaternary ammonium salt cationic surfactant to the nano-silica is 0.01-0.2:1, that is, the desorbent is a stably dispersed nano-silica emulsion surface-modified with a quaternary ammonium salt cationic surfactant.

[0009] As a specific embodiment of the above-mentioned desorbent of the present invention, the average particle size of the nanoemulsion-like material is 20-200 nm.

[0010] As a specific embodiment of the above-mentioned desorbent of the present invention, the surface of the sacrificial agent is hydrophobic and carries a positive charge.

[0011] As a specific embodiment of the above-mentioned desorbent of the present invention, the average particle size of the sacrificial agent is 10-30 nm.

[0012] As a specific embodiment of the above-mentioned desorbent of the present invention, the structural formula of the quaternary ammonium salt cationic surfactant is shown in the following formula 1):

[0013]

[0014] In formula 1), X is selected from one of halide, nitrate, sulfate, phosphate, carbonate and sulfonate;

[0015] At least one R is an alkyl group with a carbon number of ≤4, and at least one R is an alkyl group with a carbon number of ≥6.

[0016] As a specific embodiment of the above-mentioned desorbent of the present invention, the sacrificial agent is prepared by a preparation method comprising the following steps:

[0017] Monodisperse hydrophilic silica particles are added to a mixture of anhydrous ethanol and deionized water and uniformly dispersed, followed by addition of a quaternary ammonium salt cationic surfactant and reaction in a water bath at 60-80° C. for 4-6 hours to obtain an organosilicon emulsion, which is then subjected to reduced pressure distillation to obtain the sacrificial agent, i.e., nano-silica surface-modified with a quaternary ammonium salt cationic surfactant (i.e., hydrophobic nano-silica with a positively charged surface);

[0018] The mass ratio of the quaternary ammonium salt cationic surfactant to the monodisperse hydrophilic silica particles is 0.01-0.2:1.

[0019] The present invention does not impose any specific requirements on the ratio of anhydrous ethanol to deionized water in the mixture of anhydrous ethanol and deionized water. The ratio can be adjusted based on actual on-site operational needs, as long as the objectives of the present invention can be achieved. For example, in a preferred embodiment of the present invention, the volume ratio of anhydrous ethanol to deionized water can be 1:1.

[0020] As a specific embodiment of the above-mentioned desorbent of the present invention, the monodisperse hydrophilic silica particles are prepared by a sol-gel method, comprising:

[0021] A silica precursor is added to a mixture of alcohol and deionized water, stirred and heated to 30-45°C, and then a reaction catalyst is added to carry out hydrolysis and polycondensation until a jelly gel is produced. The jelly gel is dried and crushed, and then calcined at high temperature to obtain monodisperse hydrophilic silica particles.

[0022] Wherein, the alcohol includes one or a combination of methanol, ethanol, ethylene glycol, n-butanol and isopropanol;

[0023] The silicon dioxide precursor includes one or a combination of methyl orthosilicate, ethyl orthosilicate, tetraethyl orthosilicate and sodium silicate;

[0024] The reaction catalyst includes an acidic reaction catalyst or a basic reaction catalyst, etc. The acidic reaction catalyst includes one or a combination of hydrochloric acid, carbonic acid, acetic acid, lactic acid and ammonium acetate; the basic reaction catalyst includes one or a combination of ammonia water, sodium hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate and triethanolamine.

[0025] The present invention does not impose specific requirements on parameters such as the ratio of alcohol to deionized water in the mixture of alcohol and deionized water, the drying temperature, and the high-temperature calcination temperature. These parameters can be reasonably adjusted according to actual on-site operational needs, as long as the objectives of the present invention can be achieved. For example, in a preferred embodiment of the present invention, the volume ratio of alcohol (anhydrous ethanol) to deionized water can be 3:1, the drying temperature is 100°C, and the high-temperature calcination temperature is 300°C.

[0026] In the present invention, the reaction process for preparing the sacrificial agent is shown in the following formula 2):

[0027]

[0028]

[0029] It is difficult to accurately determine the number of initial hydroxyl groups on the surface of the monodisperse hydrophilic silica particles and the number of modified hydrophobic long chains in the present invention. Therefore, the number of hydroxyl groups and the number of hydrophobic long chains in formula 2) are only for reference, not actual numbers.

[0030] As a specific embodiment of the desorbent described above in the present invention, the synergist is a small molecule substance having a variety of hydrogen bond donors and acceptors, including one or a combination of trishydroxymethylaminomethane, ethanolamine, hydroxyethylethylenediamine and isopropanolamine.

[0031] As a specific embodiment of the above-mentioned desorbent of the present invention, the surfactant includes a non-ionic surfactant with an HLB value of 9-15.

[0032] As a specific embodiment of the above-mentioned desorbent of the present invention, the surfactant includes one or a combination of alkyl polyoxyethylene ether, Span, Tween and alkyl glycoside. In some embodiments of the present invention, the alkyl glycoside can be, for example, a rhamnolipid surfactant.

[0033] As a specific embodiment of the above desorbent of the present invention, wherein the dispersion solvent comprises C2-C 12 Alcohols and C2-C 12 One or a combination of alcohol ethers, etc.

[0034] As a specific embodiment of the above desorbent of the present invention, wherein C2-C 12 The alcohol includes one or a combination of isopropyl alcohol, glycerol, ethanol, etc.; C2-C 12 The alcohol ether includes one or a combination of ethylene glycol butyl ether, triethylene glycol butyl ether, propylene glycol methyl ether, ethylene glycol ethyl ether, etc.

[0035] On the other hand, the present invention also provides a method for preparing the above-mentioned desorbent, wherein the preparation method comprises:

[0036] Step (1): According to the nanoemulsion dispersion theory, a sacrificial agent (i.e., the hydrophobic nano-silica sacrificial agent with a positive surface charge) is used as an organic-like phase and mixed with water to obtain a first mixed solution;

[0037] Step (2): adding a surfactant and a dispersing solvent to the first mixed solution and mixing them uniformly to obtain a second mixed solution;

[0038] Step (3): adding a synergist to the second mixed solution and mixing uniformly to obtain a preformed solution;

[0039] Step (4): allowing the preformed liquid to stand for aging to obtain a stably dispersed nanoemulsion-like liquid, namely the desorbent.

[0040] According to the preparation method described above, the desorbent provided by the present invention is a stably dispersed nanoemulsion prepared by emulsifying an organic-phase-like sacrificial agent, a synergist, a surfactant, a dispersing solvent and water.

[0041] As a specific embodiment of the preparation method described above of the present invention, in step (2), the uniform mixing is achieved by mechanical stirring, and the conditions of the mechanical stirring include: a temperature of 30-60° C. and a mechanical stirring time of more than 0.5 h.

[0042] As a specific embodiment of the above-mentioned preparation method of the present invention, in step (4), the static aging time is greater than 2 hours.

[0043] As a specific embodiment of the above-mentioned preparation method of the present invention, the uniform mixing in step (1) and step (3) can also be achieved by mechanical stirring.

[0044] In another aspect, the present invention also provides the use of the aforementioned desorbent in the fracturing and reconstruction of tight gas reservoirs. During this application, the desorbent is injected into the formation along with the fracturing fluid as an additive to the fracturing fluid. This simple and low-cost method improves the permeability of fractures and the matrix by reducing adsorption, ultimately improving fracturing development and increasing gas production, while also reducing damage from the fracturing fluid.

[0045] In some embodiments of the present invention, the tight gas reservoir may be, for example, a tight sandstone gas reservoir.

[0046] During application, after the desorbent enters the reservoir / formation along with the fracturing fluid, the sacrificial agent in the desorbent is a positively charged nano-scale fine particle. Compared with the thickener molecules used in existing conventional fracturing fluids (such as plant gums such as guar gum and / or modified polyacrylamide), the sacrificial agent has a stronger adsorption effect on the rock. Under the action of electrostatics, it can quickly penetrate into the tiny pores and stably adsorb on the surface of the negatively charged sand particles. At the same time, the sacrificial agent exposes hydrophobic groups, which can utilize its large specific surface area to form a hydrophobic film in the formation as a shielding layer; the small molecule enhancer in the desorbent can enter the thickener group, forming hydrogen bonds and ion pairs with the residual hydroxyl and amide groups, which can destroy the intramolecular force, prevent the molecular chain from curling or entangled to cause pore blockage, and can further shield the residual adsorption groups in the fracturing fluid; the surfactant in the desorbent can achieve low surface tension and increase the flow capacity of the fracturing fluid; the dispersing solvent in the desorbent can dissolve reservoir organic matter and dredge pores. In summary, the components in the desorbent provided by the present invention work synergistically to effectively protect the reservoir and reduce the adsorption damage of residual fracturing fluid.

[0047] In still another aspect, the present application also provides a fracturing fluid, wherein the fracturing fluid comprises the desorbent as described above.

[0048] As a specific embodiment of the fracturing fluid as described above, the amount of the desorbent is 0.1-0.5% based on 100% of the total weight of the fracturing fluid.

[0049] Compared with the prior art, the desorbent provided by the present application can achieve the following beneficial technical effects:

[0050] 1. The desorbent is a stable dispersed nanoemulsion, which can reach all areas affected by the fracturing fluid, has multiple functions in one agent, and can effectively destroy the electrostatic, van der Waals force, hydrogen bond and other interaction forces between the fracturing fluid and the surface of sandstone and proppant, reduce the adsorption and retention of the fracturing fluid in the reservoir, reduce the damage to the reservoir, and restore the gas production capacity.

[0051] 2. The raw materials of the desorbent have a wide selection range, the preparation method is simple, the desorbent can be quickly dissolved in the fracturing fluid, the use amount of the thickening agent can be reduced by desorption, the process requirement is low, the cost reduction effect is good, and industrial production and application can be realized.

[0052] 3. The desorbent has stable performance, the standard curve of vegetable guar gum and polymer is established by anthrone-colorimetric method and starch-cadmium iodide method, the performance of the fracturing fluid under the action of the desorbent is determined according to the petroleum industry standard SY / T5107-2016 "Method for evaluating the performance of water-based fracturing fluid", and the performance indexes measured are as follows: the residue content of the fracturing fluid is less than 20 mg / L, the adsorption amount on the surface of quartz sand is less than 3 mg / g, the adsorption reduction rate is more than 70%, the contact angle of the rock surface after adsorption is greater than 85°, and the damage degree to the rock matrix is less than 18%. BRIEF DESCRIPTION OF DRAWINGS

[0053] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0054] Figure 1 The process schematic diagram of the preparation method of the desorbent in the embodiments of the present application. DETAILED DESCRIPTION

[0055] It should be noted that the term "comprise" and any variations thereof in the description and claims of the present invention are intended to cover non-exclusive inclusions. For example, a process, method, system, product or apparatus comprising a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units that are not explicitly listed or are inherent to these processes, methods, products or apparatus.

[0056] The "range" disclosed in the present invention is given in the form of a lower limit and an upper limit. It can be one or more lower limits, and one or more upper limits respectively. A given range is defined by selecting a lower limit and an upper limit. The selected lower limit and upper limit define the boundaries of a particular range. All ranges defined in this way are combinable, i.e., any lower limit can be combined with any upper limit to form a range. For example, a range of 60-120 and 80-110 is listed for a particular parameter, and it is understood that a range of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​listed are 1 and 2, and the maximum range values ​​listed are 3, 4, and 5, then the following ranges can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5.

[0057] In the present invention, unless otherwise specified, the numerical range "ab" is an abbreviation for any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" are listed in this invention, and "0-5" is merely an abbreviation for these numerical combinations.

[0058] In the present invention, unless otherwise specified, all embodiments and preferred embodiments mentioned in the present invention can be combined with each other to form a new technical solution.

[0059] In the present invention, unless otherwise specified, all technical features and preferred features mentioned in the present invention can be combined with each other to form a new technical solution.

[0060] In the present invention, unless otherwise specified, all steps mentioned herein may be performed sequentially or randomly, but are preferably performed sequentially. For example, the method comprising steps (a) and (b) indicates that the method may comprise steps (a) and (b) performed sequentially, or may comprise steps (b) and (a) performed sequentially. For example, the method further comprising step (c) indicates that step (c) may be added to the method in any order, for example, the method may comprise steps (a), (b) and (c), or may comprise steps (a), (c) and (b), or may comprise steps (c), (a) and (b), etc.

[0061] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below in conjunction with the attached table, drawings and examples. The following embodiments are some embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention. If specific conditions are not specified in the examples, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0062] Example 1

[0063] This embodiment provides a desorbent, which is prepared by a preparation method comprising the following specific steps:

[0064] Step (1): using a nano-silica sacrificial agent surface-modified with dioctadecyldimethylammonium chloride as an organic-like phase, adding 69 g of clean water and 2 g of the sacrificial agent into a reaction container, and mechanically stirring for 5 minutes to obtain a first mixed solution;

[0065] Step (2): adding 18 g of a surfactant (10 g of lauryl glucoside and 8 g of octyl glucoside) and 5 g of a dispersing solvent (propylene glycol methyl ether) to the first mixed solution under stirring, and mechanically stirring the mixture at 30° C. for 2 h to obtain a second mixed solution;

[0066] Step (3): adding 6 g of a synergist (tris(hydroxymethyl)aminomethane)) to the second mixed solution and mixing uniformly to obtain a preformed solution;

[0067] Step (4): The preformed liquid was allowed to stand for aging for 6 hours to obtain a stably dispersed nanoemulsion, i.e., the desorbent. The average particle size thereof was measured to be 80 nm using a Malvern laser particle size analyzer.

[0068] The process diagram of the desorbent preparation method is as follows Figure 1 As shown, from Figure 1 It can be seen that after mixing the sacrificial agent and clean water to obtain a first mixed liquid, after adding a surfactant and a dispersing solvent to the first mixed liquid, the sacrificial agent can act as an organic solvent-like agent and be emulsified and wrapped in the aqueous phase by the surfactant and the dispersing solvent, so as to facilitate the final formation of a stable dispersed nanoemulsion-like liquid.

[0069] Based on the total weight of the desorbent as 100%, it comprises:

[0070] 2% sacrificial agent, 6% synergist, 18% surfactant, 5% dispersing solvent and 69% water;

[0071] The sacrificial agent, that is, nano-silica surface-modified with dioctadecyldimethylammonium chloride, is prepared by a sol-gel method comprising the following specific steps:

[0072] Step 1: In a reaction vessel, 750 mL of anhydrous ethanol and 250 mL of deionized water were stirred uniformly, and a silica precursor (70 g of tetraethyl orthosilicate, TEOS) was added to the resulting mixture. After stirring and heating to 35°C, 10 wt% ammonia was added for hydrolysis and polycondensation until a jelly gel was produced. The jelly gel was dried at 100°C and crushed, and then calcined at 300°C for 20 minutes to produce monodisperse hydrophilic silica particles.

[0073] Step 2: In a reaction vessel, 100 mL of anhydrous ethanol and 100 mL of deionized water were stirred evenly, 20 g of the monodisperse hydrophilic silica particles obtained in step 1 were added to the resulting mixture and uniformly dispersed by ultrasound, followed by addition of 1 g of dioctadecyl dimethyl ammonium chloride, and the mixture was reacted in a 75°C water bath for 6 h to obtain an organosilicon emulsion, which was then subjected to reduced pressure distillation to obtain nano-silica surface-modified with dioctadecyl dimethyl ammonium chloride, the surface of which was hydrophobic and positively charged.

[0074] The average particle size of the sacrificial agent was measured by a nanoparticle size and Zeta potential analyzer and was found to be 18 nm.

[0075] Example 2

[0076] This embodiment provides a desorbent, which is prepared by a preparation method comprising the following specific steps:

[0077] Step (1): using a nano-silica sacrificial agent surface-modified with hexadecyltrimethylammonium chloride as an organic-like phase, adding 66 g of clean water and 3 g of the sacrificial agent into a reaction vessel, and mechanically stirring for 5 minutes to obtain a first mixed solution;

[0078] Step (2): adding 20 g of a rhamnolipid surfactant and 6 g of a dispersing solvent (3 g of ethanol and 3 g of triethylene glycol butyl ether) to the first mixed solution under stirring, and mechanically stirring the mixture at 40° C. for 2 h to obtain a second mixed solution;

[0079] Step (3): adding 5 g of a synergist (hydroxyethylethylenediamine) to the second mixed solution and mixing uniformly to obtain a preformed solution;

[0080] Step (4): The preformed liquid was allowed to stand for 5 hours to age, and a stably dispersed nanoemulsion-like liquid, namely the desorbent, was obtained. The average particle size thereof was measured to be 95 nm using a Malvern laser particle size analyzer.

[0081] The process diagram of the desorbent preparation method is as follows Figure 1 As shown, from Figure 1It can be seen that after mixing the sacrificial agent and clean water to obtain a first mixed liquid, after adding a surfactant and a dispersing solvent to the first mixed liquid, the sacrificial agent can act as an organic solvent-like agent and be emulsified and wrapped in the aqueous phase by the surfactant and the dispersing solvent, so as to facilitate the final formation of a stable dispersed nanoemulsion-like liquid.

[0082] Based on the total weight of the desorbent as 100%, it comprises:

[0083] 3% sacrificial agent, 5% synergist, 20% surfactant, 6% dispersing solvent and 66% water;

[0084] The sacrificial agent, i.e., nano-silica surface-modified with hexadecyltrimethylammonium chloride, is prepared by a sol-gel method comprising the following specific steps:

[0085] Step 1: In a reaction vessel, 750 mL of anhydrous ethanol and 250 mL of deionized water were stirred uniformly, and a silica precursor (35 g of ethyl orthosilicate and 35 g of sodium silicate) was added to the resulting mixture. After stirring and heating to 35° C., a mixture of 10 wt % acetic acid and 5 wt % ammonium acetate was added dropwise thereto for hydrolysis and polycondensation until a jelly gel was produced. The jelly gel was dried at 100° C. and crushed, and then calcined at 300° C. for 15 min to obtain monodisperse hydrophilic silica particles.

[0086] Step 2: In a reaction vessel, 100 mL of anhydrous ethanol and 100 mL of deionized water were stirred evenly, 10 g of the monodisperse hydrophilic silica particles obtained in step 1 were added to the resulting mixture and uniformly dispersed by ultrasound, and then 0.8 g of hexadecyltrimethylammonium chloride was added, and the mixture was reacted in a 60°C water bath for 4 h to obtain an organosilicon emulsion, which was then subjected to reduced pressure distillation to obtain nano-silica surface-modified with hexadecyltrimethylammonium chloride, the surface of which was hydrophobic and had a positive charge.

[0087] The average particle size of the sacrificial agent was measured by a nanoparticle size and Zeta potential analyzer and was found to be 15 nm.

[0088] Example 3

[0089] This embodiment provides a desorbent, which is prepared by a preparation method comprising the following specific steps:

[0090] Step (1): using a nano-silica sacrificial agent surface-modified with hexadecyldimethylbenzylammonium chloride as an organic-like phase, adding 71 g of clean water and 2 g of the sacrificial agent into a reaction vessel, and mechanically stirring for 10 minutes to obtain a first mixed solution;

[0091] Step (2): adding 15 g of a surfactant (10 g of lauryl glucoside and 5 g of octyl glucoside) and 7 g of a dispersing solvent (4 g of isopropyl alcohol and 3 g of triethylene glycol butyl ether) to the first mixed solution under stirring, and mechanically stirring the mixture at 35° C. for 2 h to obtain a second mixed solution;

[0092] Step (3): adding 5 g of a synergist (isopropanolamine) to the second mixed solution and mixing uniformly to obtain a preformed solution;

[0093] Step (4): The preformed liquid was allowed to stand for 5 hours to age, and a stably dispersed nanoemulsion-like liquid, namely the desorbent, was obtained. The average particle size thereof was measured to be 72 nm using a Malvern laser particle size analyzer.

[0094] The process diagram of the desorbent preparation method is as follows Figure 1 As shown, from Figure 1 It can be seen that after mixing the sacrificial agent and clean water to obtain a first mixed liquid, after adding a surfactant and a dispersing solvent to the first mixed liquid, the sacrificial agent can act as an organic solvent-like agent and be emulsified and wrapped in the aqueous phase by the surfactant and the dispersing solvent, so as to facilitate the final formation of a stable dispersed nanoemulsion-like liquid.

[0095] Based on the total weight of the desorbent as 100%, it comprises:

[0096] 2% sacrificial agent, 5% synergist, 15% surfactant, 7% dispersing solvent and 71% water;

[0097] The sacrificial agent, i.e., nano-silica surface-modified with hexadecyldimethylbenzyl ammonium chloride, is prepared by a sol-gel method comprising the following specific steps:

[0098] Step 1: In a reaction vessel, 750 mL of anhydrous ethanol and 250 mL of deionized water were stirred uniformly, and a silica precursor (70 g of tetraethyl orthosilicate) was added to the resulting mixture. After stirring and heating to 38°C, a 12% sodium carbonate solution was added dropwise thereto for hydrolysis and polycondensation until a jelly gel was produced. The jelly gel was dried at 100°C and crushed, and then calcined at 300°C for 20 minutes to produce monodisperse hydrophilic silica particles.

[0099] Step 2: In a reaction vessel, 100 mL of anhydrous ethanol and 100 mL of deionized water were stirred evenly, 10 g of the monodisperse hydrophilic silica particles obtained in step 1 were added to the resulting mixture and uniformly dispersed by ultrasound, followed by addition of 0.9 g of hexadecyldimethylbenzylammonium chloride, and the mixture was reacted in a 75°C water bath for 6 h to obtain an organosilicon emulsion, which was then subjected to reduced pressure distillation to obtain nano-silica surface-modified with hexadecyldimethylbenzylammonium chloride, the surface of which was hydrophobic and positively charged.

[0100] The average particle size of the sacrificial agent was measured by nanoparticle size and Zeta potential analyzer and was found to be 23 nm.

[0101] Example 4

[0102] This embodiment provides a desorbent, which differs from Example 1 only in that:

[0103] When preparing the sacrificial agent, the quaternary ammonium salt cationic surfactant used in step 2 is octadecyl dimethyl hydroxyethyl quaternary ammonium nitrate.

[0104] Example 5

[0105] This embodiment provides a desorbent, which differs from Example 1 only in that:

[0106] When preparing the sacrificial agent, the reaction catalyst used in step 1 is a 5 wt % sodium hydroxide aqueous solution.

[0107] Example 6

[0108] This embodiment provides a desorbent, which differs from Example 1 only in that:

[0109] The synergist used in the desorbent was a combination of 3 g of tris(hydroxymethyl)aminomethane and 3 g of isopropanolamine.

[0110] Comparative Example 1

[0111] This comparative example provides a desorbent, which differs from Example 1 only in that:

[0112] The desorbent does not contain a sacrificial nano-silica agent whose surface is modified with dioctadecyldimethylammonium chloride.

[0113] Comparative Example 2

[0114] This comparative example provides a desorbent, which differs from Example 1 only in that:

[0115] The desorbent does not contain a synergist.

[0116] Comparative Example 3

[0117] This comparative example provides a desorbent, which differs from Example 1 only in that:

[0118] The desorbent does not contain a surfactant.

[0119] Comparative Example 4

[0120] This comparative example provides a desorbent, which differs from Example 1 only in that:

[0121] The desorbent does not contain a dispersing solvent.

[0122] Comparative Example 5

[0123] This comparative example provides a desorbent which differs from Example 1 only in that:

[0124] The desorbent does not contain a dispersing solvent.

[0125] Comparative Example 6

[0126] This comparative example provides a desorbent which differs from Example 1 only in that:

[0127] The desorbent does not contain a dispersing solvent.

[0128] Comparative Example 7

[0129] This comparative example provides a desorbent which differs from Example 1 only in that:

[0130] The desorbent contains a sacrificial agent, but the sacrificial agent is a monodisperse hydrophilic silica particle made in Step 1 of Example 1, i.e. the sacrificial agent in this comparative example is not surface modified with dioctadecyldimethylammonium chloride.

[0131] Comparative Example 8

[0132] This comparative example provides a desorbent which differs from Example 1 only in that:

[0133] The desorbent contains a sacrificial agent, but the sacrificial agent is a tetramethylammonium chloride surface modified nano-silica, i.e. the quaternary ammonium salt cationic surfactant used in this comparative example does not meet the requirement that at least one R is an alkyl group having a carbon number of < 4 and at least one R is an alkyl group having a carbon number of > 6.

[0134] Comparative Example 9

[0135] This comparative example provides a desorbent which differs from Example 1 only in that:

[0136] The sacrificial agent is used in an amount of 5 g, the synergist is used in an amount of 10 g, the surfactant is used in an amount of 10 g, the dispersing solvent is used in an amount of 15 g and the water is used in an amount of 60 g, i.e. based on the total weight of the desorbent being 100%, it comprises:

[0137] 5% sacrificial agent, 10% synergist, 10% surfactant, 15% dispersing solvent and 60% water; the desorbent provided in this comparative example does not meet the ratio requirements of 1-4% sacrificial agent, 3-8% synergist, 12-28% surfactant, 5-10% dispersing solvent and the balance water.

[0138] Comparative Example 10

[0139] This comparative example provides a desorbent, which differs from Example 1 only in that:

[0140] The amount of sacrificial agent used is 0.5g and the amount of clean water used is 70.5g, that is, based on the total weight of the desorbent as 100%, it contains 0.5% sacrificial agent, 6% synergist, 18% surfactant, 5% dispersing solvent and 70.5% water; in the desorbent provided in this comparative example, the amount of the main component sacrificial agent added is less than the required ratio of the formula.

[0141] Comparative Example 11

[0142] This comparative example provides a desorbent, which differs from Example 1 only in that:

[0143] The amount of sacrificial agent used is 7g and the amount of clean water used is 64g, that is, based on the total weight of the desorbent as 100%, it contains 7% sacrificial agent, 6% synergist, 18% surfactant, 5% dispersing solvent and 64% water; in the desorbent provided in this comparative example, the amount of the main component sacrificial agent added is greater than the required ratio of the formula.

[0144] Silica is a water-insoluble solid particle whose surface, after hydrophobic modification, becomes an organic solvent-like substance. When mixed with water, it forms a stably dispersed nanoemulsion-like substance, relying on the action of an emulsifying medium, namely a surfactant and a dispersing solvent, which is the desorbent provided by the present invention. Therefore, due to the lack of an emulsifying substance, Comparative Examples 3 and 4 experience solid-liquid separation and fail to form a stable desorbent product. The sacrificial agent used in Comparative Example 7 is hydrophilic silica, which cannot be stably dispersed in water as an organic solvent-like substance, thus failing to form a stable desorbent product. Comparative Example 9 also fails to form a stable desorbent product due to the mismatched ratios of water, organic solvent-like substance, synergist, and emulsifying medium. In Comparative Example 11, because the sacrificial agent used in the present invention is a solid, when added in an amount exceeding 4%, it cannot be stably suspended in the liquid to form a desorbent product.

[0145] Test Example 1

[0146] In order to further determine the performance of the desorbents provided in Examples 1 to 6 of the present invention and the desorbents provided in Comparative Examples 1 to 2, 5 to 6, 8, and 10, this test example refers to the industry standard SY / T5107-2016 "Water-based Fracturing Fluid Performance Evaluation Method". The guar gum fracturing fluid is first prepared using the above-mentioned desorbent, comprising: adding 0.3 g of guar gum and 0.03 g of ammonium persulfate, a gel breaker, to 99.67 g of water and mixing them uniformly, and adding 0.3 g of the above-mentioned desorbent to the resulting mixed solution (100 g) to prepare a guar gum fracturing fluid. The mixed solution (corresponding to the blank) and the guar gum fracturing fluid are tested for performance indicators such as the residue content, the adsorption amount on the quartz sand surface, the contact angle with the rock surface, and the degree of damage to the core. The experimental data obtained are shown in Table 1 below.

[0147] Table 1 Performance indicators of guar gum fracturing fluid containing different desorbents

[0148]

[0149] Note: The adsorption reduction rates in Table 1 are calculated based on the adsorption capacity per gram of quartz sand of the guar gum fracturing fluid provided in the blank example.

[0150] It can be seen from the experimental data in Table 1 that, compared with the blank example, the guar gum fracturing fluid prepared by adding the desorbent provided by Examples 1 to 6 of the present invention has a thickener residue content reduced from 50 mg / L to 15.2 mg / L, 12.3 mg / L, 14.2 mg / L, 11.4 mg / L, 13.8 mg / L and 14.5 mg / L, respectively, which can reduce reservoir pore blockage; the adsorption capacity per gram of quartz sand is reduced from 9.660 mg.g -1 Reduced to 2.440mg.g -1 , 2.782mg.g -1 , 2.386mg.g -1 , 2.559mg.g -1 , 2.492mg.g -1 and 2.627mg.g -1 The adsorption reduction rates were 74.7%, 71.2%, 75.3%, 73.5%, 74.2% and 72.8% respectively; the contact angles increased from 27.1° to 85.5°, 86.3°, 87.7°, 88.4°, 85.9° and 89.2° respectively, which was beneficial to liquid flowback; the comprehensive damage rate was reduced from 41.3% to 12.3%, 13.5%, 12.8%, 15.3%, 11.9% and 13.8% respectively.

[0151] In addition, it can be seen from Table 1 that compared with the guar gum fracturing fluid prepared by adding the desorbent provided in Example 1 of the present invention, the various performance indicators of the guar gum fracturing fluids prepared by adding the desorbents provided in Comparative Examples 1-2, 5-6, 8 and 10, respectively, were reduced to varying degrees. This shows that only the various performance indicators of the guar gum fracturing fluid prepared by using the desorbent that meets the requirements of the present invention can meet the performance indicators required by the present invention as follows: the residue content of the fracturing fluid is less than 20 mg / L, the adsorption amount on the quartz sand surface is less than 3 mg / g, the adsorption reduction rate is more than 70%, the rock surface contact angle after adsorption is greater than 85°, and the degree of damage to the core matrix is ​​less than 18%.

[0152] The above description is merely a specific embodiment of the present invention and should not be construed as limiting the scope of the invention. Therefore, substitutions of equivalent components, or equivalent changes and modifications made within the scope of patent protection, should still fall within the scope of this patent. Furthermore, the technical features of this invention may be freely combined with one another, with other technical inventions, and with other technical inventions.

Claims

1. A desorbent, characterized in that: The desorbent is a stably dispersed nanoemulsion-like liquid, and based on the total weight of the desorbent being 100%, it comprises: 1-4% sacrificial agent, 3-8% synergist, 12-28% surfactant, 5-10% dispersing solvent and the balance water; Wherein, the sacrificial agent is nano-silica surface-modified with a quaternary ammonium salt cationic surfactant, wherein the mass ratio of the quaternary ammonium salt cationic surfactant to the nano-silica is 0.01-0.2:1, and the structural formula of the quaternary ammonium salt cationic surfactant is shown in the following formula 1): Formula 1) In formula 1), X is selected from one of halide, nitrate, sulfate, phosphate, carbonate and sulfonate; At least one R is an alkyl group with a carbon number ≤ 4, and at least one R is an alkyl group with a carbon number ≥ 6; The surface of the sacrificial agent is hydrophobic and has a positive charge; The average particle size of the sacrificial agent is 10-30 nm.

2. The desorbent according to claim 1, characterized in that The average particle size of the nanoemulsion is 20-200 nm.

3. The desorbent according to claim 1, characterized in that The sacrificial agent is prepared by a preparation method comprising the following steps: Monodisperse hydrophilic silica particles are added to a mixture of anhydrous ethanol and deionized water and uniformly dispersed, followed by addition of a quaternary ammonium salt cationic surfactant and reaction in a water bath at 60-80° C. for 4-6 hours to obtain an organosilicon emulsion, and the organosilicon emulsion is subjected to reduced pressure distillation to obtain the sacrificial agent; The mass ratio of the quaternary ammonium salt cationic surfactant to the monodisperse hydrophilic silica particles is 0.01-0.2:

1.

4. The desorbent according to claim 3, characterized in that The monodisperse hydrophilic silica particles are prepared by a sol-gel method, comprising: A silica precursor is added to a mixture of alcohol and deionized water, stirred and heated to 30-45°C, and then a reaction catalyst is added to perform hydrolysis and polycondensation until a jelly gel is produced. The jelly gel is dried and crushed, and then calcined at high temperature to obtain monodisperse hydrophilic silica particles. Wherein, the alcohol includes one or a combination of methanol, ethanol, ethylene glycol, n-butanol and isopropanol; The silicon dioxide precursor includes one or a combination of methyl orthosilicate, ethyl orthosilicate, tetraethyl orthosilicate and sodium silicate; The reaction catalyst includes an acidic reaction catalyst or a basic reaction catalyst. The acidic reaction catalyst includes one or a combination of hydrochloric acid, carbonic acid, acetic acid, lactic acid and ammonium acetate; the basic reaction catalyst includes one or a combination of ammonia water, sodium hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate and triethanolamine.

5. The desorbent according to claim 1 or 2, characterized in that The synergist includes one or a combination of trishydroxymethylaminomethane, ethanolamine, hydroxyethylethylenediamine and isopropanolamine.

6. The desorbent according to claim 1 or 2, characterized in that The surfactant includes a nonionic surfactant with an HLB value of 9-15.

7. The desorbent according to claim 6, characterized in that The surfactant includes one or a combination of alkyl polyoxyethylene ether, Span, Tween and alkyl glycoside.

8. The desorbent according to claim 1 or 2, characterized in that The dispersing solvent includes C2-C 12 Alcohols and C2-C 12 One or a combination of several alcohol ethers.

9. The desorbent according to claim 8, characterized in that C2-C 12 The alcohol includes one or a combination of isopropyl alcohol, glycerol, and ethanol; C2-C 12 The alcohol ether includes one or a combination of ethylene glycol butyl ether, triethylene glycol butyl ether, propylene glycol methyl ether, and ethylene glycol ethyl ether.

10. The method for preparing the desorbent according to any one of claims 1 to 9, characterized in that: The preparation method comprises: Step (1): uniformly mixing the sacrificial agent and water to obtain a first mixed solution; Step (2): adding a surfactant and a dispersing solvent to the first mixed solution and mixing them uniformly to obtain a second mixed solution; Step (3): adding a synergist to the second mixed solution and mixing uniformly to obtain a preformed solution; Step (4): allowing the prefabricated liquid to stand for aging to obtain the desorbent.

11. The preparation method according to claim 10, characterized in that: In step (2), the uniform mixing is achieved by mechanical stirring, and the conditions of the mechanical stirring include: a temperature of 30-60° C. and a mechanical stirring time of more than 0.5 h.

12. The preparation method according to claim 10 or 11, characterized in that: In step (4), the static aging time is greater than 2 hours.

13. Use of the desorbent according to any one of claims 1 to 9 in the fracturing reconstruction of tight gas reservoirs.

14. A fracturing fluid, characterized in that: The fracturing fluid comprises the desorbent according to any one of claims 1 to 9.

15. The fracturing fluid according to claim 14, characterized in that Based on the total weight of the fracturing fluid as 100%, the amount of the desorbent is 0.1-0.5%.

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