Desorption agent, preparation method and application thereof and fracturing fluid

Abstract

The invention provides a desorption agent, a preparation method and application thereof and a fracturing fluid, the desorption agent is a stably dispersed nano-emulsion, and the desorption agent comprises the following components in percentage by weight: 1-4% of a sacrificial agent, 3-8% of a synergist, 12-28% of a surfactant, 5-10% of a dispersing solvent and the balance of water; wherein the sacrificial agent is nano silicon dioxide subjected to surface modification by a quaternary ammonium salt cationic surface active agent, and the mass ratio of the quaternary ammonium salt cationic surface active agent to the nano silicon dioxide is (0.01-0.2): 1. The desorption agent serves as an additive of the fracturing fluid and is injected into a stratum along with the fracturing fluid, construction is easy, cost is low, the seepage capacity of cracks and matrixes can be improved by reducing adsorption, the purposes of improving fracturing development and increasing the gas yield are finally achieved, and meanwhile damage of the fracturing fluid can be reduced.

Description

Technical Field

[0001] The invention relates to a desorbent and a preparation method and application thereof, and fracturing fluid, belonging 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 main form of extracting tight gas. At present, the water-based fracturing fluid used in this field mostly uses plant gums such as guar gum and / or modified polyacrylamide as thickeners to form polymer gels, which can transmit pressure, achieve the functions of forming cracks and transporting proppants, and finally complete reservoir transformation. Due to the existence of interaction forces such as static electricity, hydrogen bonds, and van der Waals forces, the thickener inside the fracturing fluid will be adsorbed in the cracks, proppant surfaces, and rock matrix, destroying the pores formed by proppant filling, blocking the gas flow channel, and part of the glue will be entangled in the cracks and aggregated to form residues, which seriously limit gas production. At the same time, the above-mentioned thickeners used in water-based fracturing fluids will cause a certain degree of damage to both core samples and proppants, and the recovery effect of permeability when flushed with brine or the like in the later stage is extremely limited. Therefore, it is necessary to reduce the reservoir damage caused by the adsorption of thickeners in fracturing fluids.

[0003] In order to reduce the adsorption of fracturing fluid, chemical agents can be added thereto. On the one hand, the chemical agent needs to be able to efficiently destroy the interaction between fracturing fluid and rock and proppant. On the other hand, it can not affect the seam-making and sand-carrying performance of fracturing fluid during construction, and will not bring additional reservoir damage, and the production and use costs are low. In this regard, CN113322057A discloses a kind of adsorption inhibitor, its preparation method and application, and the adsorption inhibitor can be first attached to the rock surface along with fluid injection, so as to suppress the adsorption and retention of guar gum. However, the silicon dioxide used therein is a solid phase, and has poor dispersibility in fracturing fluid, does not solve the problem of electrostatic adsorption and hydrogen bond adsorption, and is not suitable for polymer fracturing fluid system, and the effect and scope of 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 aims to solve the reservoir damage problem caused by severe adsorption of fracturing fluid on the surface of rock and proppant during the transformation of tight gas reservoirs, and in combination with the deficiencies of existing damage removal technologies, provides a desorbent, a preparation method and application thereof, and a fracturing fluid based on an accurate understanding of the interaction between fracturing fluid, rock and proppant.

[0006] In order to achieve the above objectives, on the one hand, 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%, it 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 by a quaternary ammonium cationic surfactant, wherein the mass ratio of the quaternary ammonium 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 by a quaternary ammonium cationic surfactant.

[0009] As a specific embodiment of the above 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 desorbent described above in 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 ion, nitrate, sulfate, phosphate, carbonate and sulfonate;

[0015] 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.

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

[0017] Adding monodisperse hydrophilic silica particles to a mixture of anhydrous ethanol and deionized water and uniformly dispersing the particles, then adding a quaternary ammonium salt cationic surfactant and reacting the particles in a water bath at 60-80° C. for 4-6 hours to obtain an organosilicon emulsion, and subjecting the organosilicon emulsion 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] Wherein, 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 make specific requirements on the ratio of anhydrous ethanol to deionized water in the mixture of anhydrous ethanol and deionized water, and can be reasonably adjusted according to the actual needs of the on-site operation, as long as the purpose of the present invention can be achieved. For example, in a more 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 desorbent of the present invention, the monodisperse hydrophilic silica particles are prepared by a sol-gel method, comprising:

[0021] Adding a silica precursor to a mixture of alcohol and deionized water, stirring and heating to 30-45°C, then adding a reaction catalyst for hydrolysis and polycondensation until a jelly gel is produced, drying and crushing the jelly gel, and then calcining 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 an alkaline reaction catalyst, etc. The acidic reaction catalyst includes one or a combination of hydrochloric acid, carbonic acid, acetic acid, lactic acid and ammonium acetate, etc.; the alkaline reaction catalyst includes one or a combination of ammonia water, sodium hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate and triethanolamine, etc.

[0025] Among them, the present invention does not make specific requirements on the parameters such as the ratio of alcohol to deionized water in the mixed solution of alcohol and deionized water, the drying temperature, and the high-temperature calcination temperature, which can be reasonably adjusted according to the actual needs of the on-site operation, as long as the purpose of the present invention can be achieved. For example, in a more 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 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 illustration, not actual number.

[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 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 desorbent described above, the surfactant comprises one or a combination of alkyl polyoxyethylene ether, Span, Tween and alkyl glycoside, etc. In some embodiments of the present invention, the alkyl glycoside may be, for example, a rhamnolipid surfactant, etc.

[0033] As a specific embodiment of the desorbent described above in the present invention, the dispersing 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 desorbent described above in the present invention, wherein C2-C 12 The alcohol includes one or a combination of isopropanol, 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 charge on the surface) is used as an organic-like phase and mixed evenly 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 the mixture evenly to obtain a preformed solution;

[0039] Step (4): allowing the preformed liquid to stand for aging to obtain a stably dispersed nanoemulsion, i.e., 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 preparation method described above in 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 above-mentioned desorbent in the fracturing transformation of tight gas reservoirs. During the application process, the desorbent is used as an additive of the fracturing fluid and injected into the formation together with the fracturing fluid. The construction is simple and the cost is low. The permeability of the fracture and matrix can be improved by reducing adsorption, and finally the purpose of improving fracturing development and increasing gas production can be achieved. At the same time, it can also reduce the damage of 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 the application process, after the desorbent enters the reservoir / formation with the fracturing fluid, the sacrificial agent in the desorbent is a positively charged nano-scale fine particle. Compared with the thickener molecules (such as guar gum and / or modified polyacrylamide) used in existing conventional fracturing fluids, 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 negatively charged sand particles. At the same time, the sacrificial agent exposes hydrophobic groups, and can use 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, form hydrogen bonds and ion pairs with the residual hydroxyl and amide groups, destroy the intramolecular force, avoid the molecular chain curling or entanglement to cause pore blockage, and 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 the pores. In summary, the components in the desorbent provided by the present invention have multiple effects synergistically, which can effectively protect the reservoir and reduce the adsorption damage of residual fracturing fluid.

[0047] In yet another aspect, the present invention further provides a fracturing fluid, wherein the fracturing fluid comprises the above-mentioned desorbent.

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

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

[0050] 1. The desorbent is a stably dispersed nanoemulsion that can reach all areas affected by the fracturing fluid. It has multiple effects. The sacrificial agent, synergist, surfactant and dispersing solvent can effectively destroy the electrostatic, van der Waals force, hydrogen bond and other interaction forces between the fracturing fluid and the sandstone and proppant surfaces, reduce the adsorption and retention of the fracturing fluid in the reservoir, reduce reservoir damage, and restore gas production capacity.

[0051] 2. The desorbent has a wide range of raw materials to choose from, a simple preparation method, can be quickly dissolved in the fracturing fluid, can reduce the amount of thickener through desorption, has low process requirements, good cost reduction effect, and can achieve industrial production and application.

[0052] 3. The performance of the desorbent is stable. The standard curves of plant guar gum and polymer are established by anthrone-colorimetry 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". The measured performance indicators 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 degree of damage to the core matrix is ​​less than 18%. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0054] Figure 1 Schematic diagram of the process of preparing a desorbent in an embodiment of the present invention. DETAILED DESCRIPTION

[0055] It should be noted that the term "comprises" and any variations thereof in the specification and claims of the present invention are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes 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 inherent to these processes, methods, products or devices.

[0056] "Scope" disclosed in the present invention is given in the form of lower limit and 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, for a specific parameter, a range of 60-120 and 80-110 is listed, 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" represents an abbreviation of any real number combination between a and b, where a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been listed in the present invention, and "0-5" is just an abbreviation of 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 includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0061] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with the attached table, drawings and examples. The following described 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 ordinary technicians in the field without making creative work are within the scope of protection of the present invention. If the specific conditions are not specified in the embodiments, they are carried out according to the normal conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified in 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 min 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): Add 6 g of a synergist (trishydroxymethylaminomethane) to the second mixed solution and mix well to obtain a preformed solution;

[0067] Step (4): The preformed liquid is allowed to stand for 6 hours to age, and a stably dispersed nanoemulsion-like liquid, i.e., the desorbent, is obtained. The average particle size thereof is measured by a Malvern laser particle size analyzer to be 80 nm.

[0068] The process diagram of the desorbent preparation method is shown in 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 be used as a quasi-organic solvent 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 quasi-nanoemulsion.

[0069] Taking 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 dioctadecyl dimethyl ammonium chloride, is prepared by a sol-gel method comprising the following specific steps:

[0072] Step 1: In a reaction container, 750 mL of anhydrous ethanol and 250 mL of deionized water were stirred evenly, 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 % of ammonia water 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 min to obtain monodisperse hydrophilic silica particles;

[0073] Step 2: In a reaction container, stir 100 mL of anhydrous ethanol and 100 mL of deionized water, add 20 g of the monodisperse hydrophilic silica particles obtained in step 1 to the resulting mixture and disperse them uniformly by ultrasound, then add 1 g of dioctadecyl dimethyl ammonium chloride, and react for 6 h in a 75°C water bath to obtain an organosilicon emulsion, and then perform reduced pressure distillation on the organosilicon emulsion to obtain nano-silica surface-modified with dioctadecyl dimethyl ammonium chloride, the surface of which is hydrophobic and has a positive charge.

[0074] The average particle size of the sacrificial agent measured by a nanoparticle size and Zeta potential analyzer is 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 whose surface is modified by hexadecyltrimethylammonium chloride as an organic-like phase, adding 66 g of clean water and 3 g of the sacrificial agent into a reaction container, 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 at a temperature of 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 well to obtain a preformed solution;

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

[0081] The process diagram of the desorbent preparation method is shown in 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 be used as a quasi-organic solvent 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 quasi-nanoemulsion.

[0082] Taking 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, that is, nano-silicon dioxide surface-modified with hexadecyltrimethylammonium chloride, is prepared by a sol-gel method comprising the following specific steps:

[0085] Step 1: In a reaction container, 750 mL of anhydrous ethanol and 250 mL of deionized water were stirred evenly, and a silica precursor (35 g of tetraethyl 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 container, stir 100 mL of anhydrous ethanol and 100 mL of deionized water, add 10 g of the monodisperse hydrophilic silica particles obtained in step 1 to the resulting mixture and disperse them evenly by ultrasound, then add 0.8 g of hexadecyltrimethylammonium chloride, and react for 4 h in a 60°C water bath to obtain an organosilicon emulsion, and then perform reduced pressure distillation on the organosilicon emulsion to obtain nano-silica surface-modified with hexadecyltrimethylammonium chloride, the surface of which is hydrophobic and has a positive charge.

[0087] The average particle size of the sacrificial agent measured by a nanoparticle size and Zeta potential analyzer is 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 container, and mechanically stirring for 10 min 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 isopropanol 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 well to obtain a preformed solution;

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

[0094] The process diagram of the desorbent preparation method is shown in 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 be used as a quasi-organic solvent 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 quasi-nanoemulsion.

[0095] Taking 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 container, 750 mL of anhydrous ethanol and 250 mL of deionized water were stirred evenly, 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 min to obtain monodisperse hydrophilic silica particles;

[0099] Step 2: In a reaction container, stir 100 mL of anhydrous ethanol and 100 mL of deionized water, add 10 g of the monodisperse hydrophilic silica particles obtained in step 1 to the resulting mixture and disperse them uniformly by ultrasound, then add 0.9 g of hexadecyldimethylbenzylammonium chloride, and react for 6 h in a 75°C water bath to obtain an organosilicon emulsion, and then perform reduced pressure distillation on the organosilicon emulsion to obtain nano-silica surface-modified with hexadecyldimethylbenzylammonium chloride, the surface of which is hydrophobic and has a positive charge.

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

[0101] Example 4

[0102] This embodiment provides a desorbent, which is different from the embodiment 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 is different from the embodiment 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 is different from the embodiment 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 by 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 sacrificial nano-silica agent whose surface is modified by dioctadecyl dimethyl ammonium chloride and 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 sacrificial nano-silica agent and a surfactant whose surface is modified by dioctadecyldimethylammonium chloride.

[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 the monodisperse hydrophilic silica particles prepared in step 1 of Example 1, that is, the sacrificial agent in this comparative example is not surface-modified using dioctadecyl dimethyl ammonium 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 nano-silica surface-modified with tetramethylammonium chloride, that is, the quaternary ammonium salt cationic surfactant used in this comparative example does not meet the requirements that 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.

[0134] Comparative Example 9

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

[0136] The amount of the sacrificial agent is 5 g, the amount of the synergist is 10 g, the amount of the surfactant is 10 g, the amount of the dispersing solvent is 15 g and the amount of clean water is 60 g, that is, based on the total weight of the desorbent as 100%, it comprises:

[0137] 5% sacrificial agent, 10% synergist, 10% surfactant, 15% dispersing solvent and 60% clean 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 remainder 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% of sacrificial agent, 6% of synergist, 18% of surfactant, 5% of dispersing solvent and 70.5% of 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% of sacrificial agent, 6% of synergist, 18% of surfactant, 5% of dispersing solvent and 64% of 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] Silicon dioxide is a solid particle insoluble in water, and its surface is modified to be a quasi-organic solvent after hydrophobic modification. At this time, after mixing it with water, it can form a stably dispersed quasi-nanoemulsion by relying on the emulsifying medium, that is, the surfactant and the dispersing solvent, that is, the desorbent provided by the present invention. Therefore, due to the lack of emulsifying substances, Comparative Examples 3 and 4 will produce solid-liquid separation and cannot form a stable desorbent product; and the sacrificial agent used in Comparative Example 7 is hydrophilic silicon dioxide, which cannot be stably dispersed in water as a quasi-organic solvent, and thus cannot form a stable desorbent product; in Comparative Example 9, due to the incompatibility of the ratio of water, quasi-organic solvent, synergist and emulsifying medium, a stable desorbent product cannot be formed; in Comparative Example 11, since the sacrificial agent used in the present invention is a solid, when the amount added exceeds 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 desorbent provided by Examples 1 to 6 of the present invention and the desorbent provided by 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", and firstly uses the above-mentioned desorbent to prepare guar fracturing fluid, including: adding 0.3g of guar gum and 0.03g of ammonium persulfate, a gel breaker, to 99.67g of water and mixing them evenly, adding 0.3g of the above-mentioned desorbent to the obtained mixed solution (100g) to prepare guar fracturing fluid, and then testing the residue content of the mixed solution (corresponding to the blank example) and the guar fracturing fluid, the adsorption amount on the quartz sand surface, the contact angle with the rock surface and the degree of damage to the core, etc., and the obtained experimental data 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 amount of guar gum fracturing fluid per gram of quartz sand 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 amount 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 angle increased from 27.1° to 85.5°, 86.3°, 87.7°, 88.4°, 85.9° and 89.2° respectively, which was conducive to liquid return; 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 fluid prepared by adding the desorbent provided in Comparative Examples 1-2, 5-6, 8 and 10 respectively showed different degrees of reduction, which means 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 contact angle of the rock surface after adsorption is greater than 85°, and the degree of damage to the core matrix is ​​less than 18%.

[0152] The above is only a specific embodiment of the present invention, and cannot be used to limit the scope of the invention. Therefore, the replacement of equivalent components, or equivalent changes and modifications made according to the protection scope of the patent of the present invention, should still fall within the scope of this patent. In addition, the technical features of the present invention can be freely combined with each other, with each other and with each other, and with each other.

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-silicon dioxide whose surface is modified by a quaternary ammonium salt cationic surfactant, wherein the mass ratio of the quaternary ammonium salt cationic surfactant to the nano-silicon dioxide is 0.01-0.2:

1.

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 surface of the sacrificial agent is hydrophobic and has a positive charge.

4. The desorbent according to claim 1, characterized in that The average particle size of the sacrificial agent is 10-30 nm.

5. The desorbent according to claim 1, characterized in that The structural formula of the quaternary ammonium salt cationic surfactant is shown in the following 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.

6. The desorbent according to claim 1 or 5, characterized in that: The sacrificial agent is prepared by a preparation method comprising the following steps: Adding monodisperse hydrophilic silica particles to a mixture of anhydrous ethanol and deionized water and uniformly dispersing the particles, then adding a quaternary ammonium salt cationic surfactant and reacting the mixture in a water bath at 60-80° C. for 4-6 hours to obtain an organosilicon emulsion, and performing reduced pressure distillation on the organosilicon emulsion to obtain the sacrificial agent; Wherein, the mass ratio of the quaternary ammonium salt cationic surfactant to the monodisperse hydrophilic silica particles is 0.01-0.2:

1.

7. The desorbent according to claim 6, characterized in that The monodisperse hydrophilic silica particles are prepared by a sol-gel method, comprising: Adding a silica precursor to a mixture of alcohol and deionized water, stirring and heating to 30-45°C, then adding a reaction catalyst for hydrolysis and polycondensation until a jelly gel is produced, drying and crushing the jelly gel, and then calcining 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 an alkaline reaction catalyst. The acidic reaction catalyst includes one or a combination of hydrochloric acid, carbonic acid, acetic acid, lactic acid and ammonium acetate; the alkaline reaction catalyst includes one or a combination of ammonia water, sodium hydroxide, potassium hydroxide, sodium carbonate, sodium bicarbonate and triethanolamine.

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

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

10. The desorbent according to claim 9, characterized in that The surfactant includes one or a combination of alkyl polyoxyethylene ether, Span, Tween and alkyl glycoside.

11. 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.

12. The desorbent according to claim 11, characterized in that C2-C 12 The alcohol includes one or a combination of isopropanol, 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.

13. The method for preparing the desorbent according to any one of claims 1 to 12, characterized in that: The preparation method comprises: Step (1): mixing the sacrificial agent and water uniformly 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 the mixture evenly to obtain a preformed solution; Step (4): allowing the prefabricated liquid to stand for aging to obtain the desorbent.

14. The preparation method according to claim 13, 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.

15. The preparation method according to claim 13 or 14, characterized in that: In step (4), the static aging time is greater than 2 hours.

16. Use of the desorbent according to any one of claims 1 to 12 in the fracturing reconstruction of tight gas reservoirs.

17. A fracturing fluid, characterized in that: The fracturing fluid comprises the desorbent according to any one of claims 1 to 12.

18. The fracturing fluid according to claim 17, characterized in that: Based on the total weight of the fracturing fluid being 100%, the dosage of the desorbent is 0.1-0.5%.

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