A Multifunctional Anti-scaling Supramolecular Fracturing Fluid System for Unconventional Oil Reservoirs and Its Application

Abstract

This invention discloses a multifunctional scale-inhibiting supramolecular fracturing fluid system for unconventional oil reservoirs and its application, belonging to the field of oil and gas field fracturing technology. The fracturing fluid, by weight percentage, comprises 0.4-1.0% viscosifier, 0.05-1.5% clay stabilizer, 0.08-0.6% breaker, 0.5-0.8% scale inhibitor, and the balance being water. The viscosifier is a supramolecular fracturing fluid viscosifier with host-guest inclusion properties, and the scale inhibitor is a W / O type microemulsion scale inhibitor with amphiphilic modified graphene oxide as the main component. This invention can construct a reversible supramolecular network and improve drag reduction and proppant carrying capacity; the high association strength makes the system insensitive to high-valence salt ions, resulting in strong reservoir adaptability; the W / O type microemulsion scale inhibitor enables the reservoir to become hydrophilic, allowing the fracturing fluid to penetrate deep into the reservoir through percolation, while adsorption at the reservoir interface reduces scale growth sites, and the release of the scale inhibitor after demulsification inhibits scale formation.

Description

Technical Field

[0001] This invention relates to the field of oil and gas field fracturing technology, and in particular to a multifunctional anti-scaling supramolecular fracturing fluid system for unconventional oil reservoirs and its application. Background Technology

[0002] Unconventional oil reservoirs (such as shale oil and gas, tight sandstone gas, and coalbed methane) are generally characterized by low porosity and permeability, small pore throats, and well-developed natural fractures and clay minerals. Conventional development is unlikely to achieve industrial production capacity, and large-scale hydraulic fracturing is usually required for production enhancement. As the core working fluid of hydraulic fracturing, fracturing fluid must reduce the friction between the tubing and the surface under high flow rate and high shear conditions, maintain stable rheology and proppant carrying capacity in complex formation water environments, and achieve effective gel breaking and low residue flowback after fracturing to reduce damage to reservoir seepage channels.

[0003] Existing fracturing fluid systems mainly include slickwater, guar gum / crosslinked gum, synthetic polymer thickening systems, and some surfactant viscoelastic systems. Slickwater has low friction and is easy to prepare, but its low viscosity limits proppant carrying capacity. Crosslinked guar gum has high viscosity and good proppant carrying capacity, but it easily produces residues and may cause reservoir damage. Furthermore, its stability and controllability in breaking the gel are insufficient under high temperature and high salinity conditions. At the same time, high salinity and divalent / polyvalent ions can easily cause viscosity decay, shear degradation, and poor compatibility of polymer systems. Clay minerals may also clog pore throats due to hydration swelling and dispersion migration upon contact with water, requiring the use of clay stabilizers (such as potassium chloride, quaternary ammonium salts, or polyquaternary ammonium salts) to suppress sensitive damage. In addition, oxidizing gelling agents such as persulfate are often used after fracturing to reduce viscosity and facilitate flowback, but the gelling efficiency and residue control are still affected by the system structure and formation conditions.

[0004] Furthermore, scaling is a common risk during fracturing in unconventional reservoirs: the mixing of fracturing fluid with formation water / flowback fluid and sudden changes in temperature, pressure, and ionic environment can easily induce the deposition of inorganic scale such as carbonate and sulfate scale in fractures, near-wellbore areas, and surface processes, resulting in reduced conductivity, pore throat blockage, and equipment scaling. Current methods mostly involve the independent addition of scale inhibitors (such as phosphonates and polycarboxylates), but in high-flow-rate, high-shear, and complex formulation systems, the deep transport and effective action distance of scale inhibitors are limited, and they may interact with thickeners, surfactants, and salt additives, leading to a decrease in scale inhibitor effectiveness or the introduction of new compatibility risks.

[0005] Therefore, how to achieve multi-functional synergy of "viscosity enhancement and drag reduction, sand carrying, clay stabilization, scale prevention and gel breaking" in fracturing fluid systems, while taking into account stability in high temperature, high salinity and multivalent ion environments, has become an important development direction for fracturing fluid technology in unconventional reservoirs. Summary of the Invention

[0006] To address the aforementioned problems, this invention aims to provide a multifunctional anti-scaling supramolecular fracturing fluid system for unconventional oil reservoirs and its application.

[0007] The technical solution of the present invention is as follows:

[0008] On the one hand, a multifunctional anti-scaling supramolecular fracturing fluid system for unconventional reservoirs is provided, comprising, by weight percentage, 0.4-1.0% of a viscosity modifier, 0.05-1.5% of a clay stabilizer, 0.08-0.6% of a breaker, 0.5-0.8% of a scale inhibitor, and the balance being water. The viscosity modifier is a supramolecular fracturing fluid viscosity modifier with host-guest inclusion effect, and the scale inhibitor is a W / O type microemulsion scale inhibitor with amphiphilic modified graphene oxide as the main component.

[0009] Preferably, the supramolecular fracturing fluid thickener comprises 50-75 parts by weight of a host thickener and 25-50 parts by weight of a guest thickener, wherein the host thickener is a cyclic host compound having hydrophobic cavities / hydrophobic recognition sites, and the guest thickener is a water-soluble associative polymer containing hydrophobic groups.

[0010] Preferably, the cyclic host compound having hydrophobic cavities / hydrophobic recognition sites is a cyclodextrin host and / or a soluble derivative / polymer of a cyclodextrin host, and the water-soluble associative polymer containing hydrophobic groups is any one or more of hydrophobic associative polyacrylamides, hydrophobically modified polycarboxylic acids, and hydrophobically modified natural / semi-synthetic polymers.

[0011] Preferably, the cyclodextrin-based matrix and its soluble derivatives / polymers include β-cyclodextrin, hydroxypropyl-β-cyclodextrin, and cyclodextrin-epoxychloropropane polymers.

[0012] Preferably, the clay stabilizer is any one or more of potassium chloride, small molecule quaternary ammonium salts, and polyquaternary ammonium salt organic clay stabilizers.

[0013] Preferably, the breaker is a persulfate breaker, which is any one or more of ammonium persulfate, sodium persulfate, and potassium persulfate.

[0014] Preferably, the W / O type microemulsion antiscalant comprises 30-50 parts by weight of an aqueous solution of amphiphilic modified graphene oxide, 35-50 parts by weight of saturated alkane, 5-10 parts by weight of a main surfactant and 3-8 parts by weight of a co-surfactant, wherein the mass fraction of the solute in the aqueous solution of the amphiphilic modified graphene oxide is 0.5-1%.

[0015] Preferably, the saturated alkane is a medium- or long-chain alkane, the main surfactant is a surfactant with an HLB value of less than 6, and the co-surfactant is a short-chain alcohol and / or a branched-chain alcohol.

[0016] Preferably, the saturated alkane is any one or more of n-octane, n-nonane, and n-decane; the main surfactant is any one or more of glycerol fatty acid ester, polyglycerol fatty acid ester, and dehydrated sorbitan fatty acid ester; and the co-surfactant is any one or more of n-butanol, n-pentanol, n-hexanol, isopropanol, and isoamyl alcohol.

[0017] On the other hand, it also provides the application of the unconventional reservoir multifunctional anti-scaling supramolecular fracturing fluid system described in any of the above-mentioned methods in the fracturing and exploitation of unconventional reservoirs.

[0018] The beneficial effects of this invention are:

[0019] (1) The present invention uses a supramolecular fracturing fluid viscosity enhancer with host-guest encapsulation, which can construct a reversible supramolecular network by utilizing host-guest encapsulation, resulting in more robust association. Compared with the traditional fracturing fluid system, its viscosity can be increased by more than 30%, its temperature resistance and shear resistance can be increased by more than 20%, and its drag reduction rate is about 75%, effectively improving the sand carrying capacity and drag reduction performance.

[0020] (2) The main supramolecular structure of this invention provides stronger reservoir adaptability through host-guest encapsulation, is insensitive to high-valence salt ions, and the W / O type microemulsion isolates the interaction between the scale inhibitor and the supramolecular thickener through the shielding effect of saturated alkanes. By integrating thickening and drag reduction, sand carrying, clay stabilization, scale prevention, and gel breaking into a single system framework, the compatibility risks and process complexity caused by the use of multiple agents in the field are reduced.

[0021] (3) The present invention uses a W / O type microemulsion anti-scaling agent, which integrates "anti-scaling + wetting reversal + deep delivery". The W / O type microemulsion anti-scaling agent is not only used to inhibit scale, but also improves wettability to make the reservoir more hydrophilic, and allows the fracturing fluid to enter deeper through percolation, thereby expanding the fracturing operation range.

[0022] (4) The fracturing fluid of the present invention has a residue content of less than 25 mg / L after gel breaking, the residue amount is small, and the microemulsion structure can reduce the interfacial tension to 10. -3 The ultra-low level of mN / m can effectively reduce the impact of the Jamin effect during the flowback process, resulting in low damage to the reservoir. Detailed Implementation

[0023] The present invention will be further described below with reference to embodiments. It should be noted that, unless otherwise specified, the embodiments and technical features described in this application can be combined with each other. It should also be pointed out that, unless otherwise specified, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. The terms "comprising" or "including" and similar words used in this invention refer to elements or objects preceding the word that encompass the elements or objects listed following the word and their equivalents, without excluding other elements or objects.

[0024] On the one hand, the present invention provides a multifunctional anti-scaling supramolecular fracturing fluid system for unconventional reservoirs, comprising, by weight percentage, 0.4-1.0% of a viscosity modifier, 0.05-1.5% of a clay stabilizer, 0.08-0.6% of a breaker, 0.5-0.8% of a scale inhibitor, and the balance being water. The viscosity modifier is a supramolecular fracturing fluid viscosity modifier with host-guest inclusion effect, and the scale inhibitor is a W / O type microemulsion scale inhibitor with amphiphilic modified graphene oxide as the main component.

[0025] It should be noted that the amphiphilic modified graphene oxide described in this invention is prior art, specifically the amphiphilic modified graphene oxide TAS-GO in CN119709153A, with the following structural formula:

[0026]

[0027] In this invention, a supramolecular fracturing fluid viscosity enhancer with host-guest inclusion interaction is used as the viscosity enhancer. This viscosity enhancer can construct a reversible supramolecular network through host-guest inclusion interaction, and rely on this interaction to strengthen association, thereby improving drag reduction and proppant carrying capacity. High association strength makes the system insensitive to high-valence salt ions, enhancing reservoir adaptability. A W / O type microemulsion scale inhibitor is used, which improves reservoir wettability, allowing the reservoir to become hydrophilic and enabling the fracturing fluid to penetrate deep into the reservoir through percolation. Simultaneously, adsorption at the reservoir interface reduces scale growth sites, and the release of the scale inhibitor after demulsification inhibits scale formation.

[0028] In one specific embodiment, the supramolecular fracturing fluid thickener comprises 50-75 parts by weight of a host thickener and 25-50 parts by weight of a guest thickener. The host thickener is a cyclic host compound having hydrophobic cavities / hydrophobic recognition sites, and the guest thickener is a water-soluble associative polymer containing hydrophobic groups.

[0029] In one specific embodiment, the cyclic host compound having hydrophobic cavities / hydrophobic recognition sites is a cyclodextrin host and / or a soluble derivative / polymer of a cyclodextrin host, and the water-soluble associative polymer containing hydrophobic groups is any one or more of hydrophobic associative polyacrylamides, hydrophobically modified polycarboxylic acids, and hydrophobically modified natural / semi-synthetic polymers.

[0030] Optionally, the cyclodextrin-based matrix and its soluble derivatives / polymers include β-cyclodextrin, hydroxypropyl-β-cyclodextrin, and cyclodextrin-epoxychloropropane polymers. It should be noted that the reagents in this embodiment are only preferred cyclodextrin-based matrices and their soluble derivatives / polymers according to the present invention; other cyclodextrin-based matrices and their soluble derivatives / polymers in the prior art are also applicable to the present invention.

[0031] In one specific embodiment, the clay stabilizer is any one or more of potassium chloride, small molecule quaternary ammonium salts (non-polymers without repeating segments, typically with a molecular weight less than 500), and polyquaternary ammonium salt organic clay stabilizers; the breaker is a persulfate breaker, specifically any one or more of ammonium persulfate, sodium persulfate, and potassium persulfate.

[0032] It should be noted that the clay stabilizer is used to inhibit the hydration and expansion of reservoir clay minerals caused by water during supramolecular fracturing, and the breaker is used to break the supramolecular fracturing fluid after fracturing fluid application to facilitate flowback. The agents in the above embodiments are only preferred agents of the present invention, and other clay stabilizers and breaker agents with the same function in the prior art can also be applied to the present invention.

[0033] In one specific embodiment, the W / O type microemulsion antiscalant comprises 30-50 parts by weight of an aqueous solution of amphiphilic modified graphene oxide, 35-50 parts by weight of saturated alkane, 5-10 parts by weight of a main surfactant and 3-8 parts by weight of a co-surfactant, wherein the mass fraction of the solute in the aqueous solution of the amphiphilic modified graphene oxide is 0.5-1%.

[0034] In the above embodiments, the saturated alkane is added to enable the scale inhibitor to form a W / O type microemulsion. If the saturated alkane is not added, the scale inhibitor cannot form a W / O type microemulsion, which will cause the scale inhibitor to diffuse in the system under high shear, thereby weakening the host-guest inclusion effect of the supramolecular fracturing fluid thickener and reducing the temperature resistance, shear resistance and drag reduction performance of the supramolecular fracturing fluid.

[0035] In one specific embodiment, the saturated alkane is a medium- to long-chain alkane (C10-C16), the main surfactant is a surfactant with an HLB value less than 6, and the co-surfactant is a short-chain alcohol (C3-C7) and / or a branched-chain alcohol.

[0036] In this invention, a surfactant with an HLB value less than 6 is used as the main surfactant to enable the scale inhibitor to form a stable W / O microemulsion. If a surfactant with an HLB value greater than or equal to 6 is added as the main surfactant, the scale inhibitor will not be able to form a stable W / O microemulsion. This will also cause the scale inhibitor to diffuse in the system under high shear, thereby weakening the host-guest inclusion effect of the supramolecular fracturing fluid thickener and reducing the temperature resistance, shear resistance and drag reduction performance of the supramolecular fracturing fluid.

[0037] In one specific embodiment, the saturated alkane is any one or more of n-octane, n-nonane, and n-decane; the main surfactant is any one or more of glycerol fatty acid esters (such as glyceryl monooleate, glyceryl monostearate, etc.), polyglycerol fatty acid esters (such as polyglyceryl-2 oleate, polyglyceryl-3 diisostearate, etc.), and sorbitan fatty acid esters (such as sorbitan monostearate (Span60), sorbitan monooleate (Span80), etc.); and the co-surfactant is any one or more of n-butanol, n-pentanol, n-hexanol, isopropanol, and isoamyl alcohol.

[0038] In one specific embodiment, the W / O type microemulsion antiscalant is prepared by the following steps: using an aqueous solution of amphiphilic modified graphene oxide TAS-GO as the main component, supplemented with main and co-surfactants and saturated alkanes, and obtaining the W / O type microemulsion antiscalant after standing for 12 hours (or magnetic stirring for 30 minutes).

[0039] On the other hand, the present invention also provides the application of the unconventional reservoir multifunctional anti-scaling supramolecular fracturing fluid system described in any one of the above-mentioned claims in the fracturing and exploitation of unconventional reservoirs.

[0040] In this invention, when the multifunctional anti-scaling supramolecular fracturing fluid system for unconventional reservoirs is applied to fracturing and exploitation of unconventional reservoirs, it can utilize the strong association effect of the viscosifier to endow the system with excellent drag reduction, proppant carrying and reservoir adaptability. The presence of the W / O type microemulsion anti-scaling agent not only achieves excellent anti-scaling effect, but also improves reservoir wettability and makes the reservoir hydrophilic. The fracturing fluid enters the deep reservoir under the action of percolation and adsorption. After the system breaks down, the viscosity and residue are extremely low, which is more conducive to flowback.

[0041] Example 1

[0042] A multifunctional anti-scaling supramolecular fracturing fluid system for unconventional oil reservoirs is prepared through the following steps:

[0043] (1) Preparation of W / O type microemulsion scale inhibitor

[0044] By mass percentage, 35% of amphiphilic modified graphene oxide TAS-GO aqueous solution (solute mass fraction of 0.6%), 50% of n-octane, 8% of dehydrated sorbitan monooleate (main surfactant), and 7% of n-butanol (co-surfactant) were taken and magnetically stirred for 30 min to obtain a W / O type microemulsion antiscalant.

[0045] (2) Preparation of a multifunctional anti-scaling supramolecular fracturing fluid system for unconventional oil reservoirs

[0046] Dissolve the guest thickener in the prepared water at room temperature for 5-10 minutes, add the main thickener and continue stirring for 5-10 minutes, then add the clay stabilizer and W / O microemulsion antiscalant in sequence and stir evenly, and finally add the breaker to obtain the fracturing fluid system.

[0047] In this embodiment, the fracturing fluid system, based on its total mass of 100%, includes 0.8% supramolecular fracturing fluid thickener (0.53% hydroxypropyl-β-cyclodextrin (HP-β-CD) + 0.27% hydrophobic associating polyacrylamide (HAPAM)), 0.8% clay stabilizer (KCl), 0.15% breaker (ammonium persulfate), 0.7% W / O type microemulsion scale inhibitor, and the balance being water.

[0048] Example 2

[0049] A multifunctional anti-scaling supramolecular fracturing fluid system for unconventional oil reservoirs is prepared through the following steps:

[0050] (1) Preparation of W / O type microemulsion scale inhibitor

[0051] By mass percentage, 40% of amphiphilic modified graphene oxide TAS-GO aqueous solution (solute mass fraction of 0.6%), 50% of n-nonane, 6% of glycerol monooleate (main surfactant), and 4% of n-pentanol (co-surfactant) were taken and magnetically stirred for 30 min to obtain a W / O type microemulsion antiscalant.

[0052] (2) Preparation of a multifunctional anti-scaling supramolecular fracturing fluid system for unconventional oil reservoirs

[0053] Dissolve the guest thickener in the prepared water at room temperature for 5-10 minutes, add the main thickener and continue stirring for 5-10 minutes, then add the clay stabilizer and W / O microemulsion antiscalant in sequence and stir evenly, and finally add the breaker to obtain the fracturing fluid system.

[0054] In this embodiment, the fracturing fluid system, based on its total mass of 100%, includes 1.0% supramolecular fracturing fluid thickener (0.60% hydroxypropyl-β-cyclodextrin (HP-β-CD) + 0.40% hydrophobic associating polyacrylamide (HAPAM)), 0.8% clay stabilizer (KCl), 0.2% breaker (ammonium persulfate), 0.5% W / O type microemulsion scale inhibitor, and the balance being water.

[0055] Example 3

[0056] A multifunctional anti-scaling supramolecular fracturing fluid system for unconventional oil reservoirs is prepared through the following steps:

[0057] (1) Preparation of W / O type microemulsion scale inhibitor

[0058] By mass percentage, 38% of amphiphilic modified graphene oxide TAS-GO aqueous solution (solute mass fraction of 0.7%), 50% of n-decane, 7% of glycerol monostearate (main surfactant), and 5% of n-pentanol (co-surfactant) were taken and magnetically stirred for 30 min to obtain a W / O type microemulsion antiscalant.

[0059] (2) Preparation of a multifunctional anti-scaling supramolecular fracturing fluid system for unconventional oil reservoirs

[0060] Dissolve the guest thickener in the prepared water at room temperature for 5-10 minutes, add the main thickener and continue stirring for 5-10 minutes, then add the clay stabilizer and W / O microemulsion antiscalant in sequence and stir evenly, and finally add the breaker to obtain the fracturing fluid system.

[0061] In this embodiment, the fracturing fluid system, based on its total mass of 100%, includes 0.7% supramolecular fracturing fluid thickener (0.4% β-cyclodextrin-epoxychloropropane condensate (β-CDP) + 0.3% hydrophobically modified polyacrylic acid (HM-PAA)), 0.75% clay stabilizer (NH4Cl), 0.25% breaker (sodium persulfate), 0.6% W / O type microemulsion scale inhibitor, and the balance being water.

[0062] Example 4

[0063] A multifunctional anti-scaling supramolecular fracturing fluid system for unconventional oil reservoirs is prepared through the following steps:

[0064] (1) Preparation of W / O type microemulsion scale inhibitor

[0065] By mass percentage, 36% of amphiphilic modified graphene oxide TAS-GO aqueous solution (solute mass fraction of 0.6%), 50% of n-octane, 8% of triglyceride diisostearate (main surfactant), and 6% of isopropanol (co-surfactant) were taken and magnetically stirred for 30 min to obtain a W / O type microemulsion antiscalant.

[0066] (2) Preparation of a multifunctional anti-scaling supramolecular fracturing fluid system for unconventional oil reservoirs

[0067] Dissolve the guest thickener in the prepared water at room temperature for 5-10 minutes, add the main thickener and continue stirring for 5-10 minutes, then add the clay stabilizer and W / O microemulsion antiscalant in sequence and stir evenly, and finally add the breaker to obtain the fracturing fluid system.

[0068] In this embodiment, the fracturing fluid system, based on its total mass of 100%, includes 0.7% supramolecular fracturing fluid thickener (0.5% carboxymethyl-β-cyclodextrin (CM-β-CD) + 0.2% hydrophobically modified polyaspartic acid), 0.95% clay stabilizer (NH4Cl), 0.2% breaker (potassium persulfate), 0.7% W / O type microemulsion scale inhibitor, and the balance being water.

[0069] Example 5

[0070] A multifunctional anti-scaling supramolecular fracturing fluid system for unconventional oil reservoirs is prepared through the following steps:

[0071] (1) Preparation of W / O type microemulsion scale inhibitor

[0072] By mass percentage, 33% of amphiphilic modified graphene oxide TAS-GO aqueous solution (solute mass fraction of 0.5%), 50% n-nonane, 9% diglycerol monooleate (main surfactant), and 8% isoamyl alcohol (co-surfactant) were taken and magnetically stirred for 30 min to obtain a W / O type microemulsion antiscalant.

[0073] (2) Preparation of a multifunctional anti-scaling supramolecular fracturing fluid system for unconventional oil reservoirs

[0074] Dissolve the guest thickener in the prepared water at room temperature for 5-10 minutes, add the main thickener and continue stirring for 5-10 minutes, then add the clay stabilizer and W / O microemulsion antiscalant in sequence and stir evenly, and finally add the breaker to obtain the fracturing fluid system.

[0075] In this embodiment, the fracturing fluid system, based on its total mass of 100%, includes 0.6% supramolecular fracturing fluid thickener (0.3% carboxymethyl-β-cyclodextrin (CM-β-CD) + 0.3% hydrophobically modified polyacrylic acid (HM-PAA)), 1% clay stabilizer (quaternary ammonium salt organic clay stabilizer), 0.15% breaker (sodium persulfate), 0.8% W / O type microemulsion scale inhibitor, and the balance being water.

[0076] Example 6

[0077] A multifunctional anti-scaling supramolecular fracturing fluid system for unconventional oil reservoirs is prepared through the following steps:

[0078] (1) Preparation of W / O type microemulsion scale inhibitor

[0079] By mass percentage, 36% of amphiphilic modified graphene oxide TAS-GO aqueous solution (solute mass fraction of 0.6%), 50% n-decane, 8% dehydrated sorbitan monostearate (main surfactant), and 6% n-hexanol (co-surfactant) were taken and magnetically stirred for 30 min to obtain a W / O type microemulsion antiscalant.

[0080] (2) Preparation of a multifunctional anti-scaling supramolecular fracturing fluid system for unconventional oil reservoirs

[0081] Dissolve the guest thickener in the prepared water at room temperature for 5-10 minutes, add the main thickener and continue stirring for 5-10 minutes, then add the clay stabilizer and W / O microemulsion antiscalant in sequence and stir evenly, and finally add the breaker to obtain the fracturing fluid system.

[0082] In this embodiment, the fracturing fluid system, based on its total mass of 100%, includes 0.6% supramolecular fracturing fluid thickener (0.4% methyl-β-cyclodextrin (Me-β-CD) + 0.2% hydrophobically modified polyacrylic acid (HM-PAA)), 1.2% clay stabilizer (quaternary ammonium salt organic clay stabilizer), 0.15% breaker (potassium persulfate), 0.7% W / O type microemulsion scale inhibitor, and the balance being water.

[0083] Comparative Example 1

[0084] Unlike Example 1, in step (2) of this comparative example, the thickener in the fracturing fluid system does not include the main thickener, but only the guest thickener, that is, the thickener in this comparative example is 0.8% hydrophobic associating polyacrylamide (HAPAM).

[0085] Comparative Example 2

[0086] Unlike Example 2, this comparative example does not include step (1), and the fracturing fluid system in step (2) does not include W / O type microemulsion antiscalant, and the amount of the agent is made up with water.

[0087] Comparative Example 3

[0088] Unlike Example 6, step (1) of this comparative example only includes the main surfactant and does not include the co-surfactant, that is, the surfactant of this comparative example is 14% Span60.

[0089] Comparative Example 4

[0090] Unlike Example 6, step (1) of this comparative example only includes a co-surfactant and does not include a main surfactant, that is, the surfactant in this comparative example is 14% n-hexanol.

[0091] Test case

[0092] According to the testing standard SY / T 5107-2016 "Performance Evaluation Method of Water-based Fracturing Fluids", the fracturing fluid systems prepared in the above embodiments and comparative examples were tested for their temperature and shear resistance (100℃, 170s). -1 Under the specified conditions (shear for 90 min), formation water compatibility, drag reduction rate, fracturing fluid rupture viscosity, residue, and interfacial tension were tested. The results were compared with conventional guar gum fracturing fluid (0.4% HPG + 0.3% crosslinking agent + 1% KCl + 0.35% ammonium persulfate + 0.1% bactericide + 0.1% drainage aid) and slickwater fracturing fluid (0.3% polymer drag reducer + 2.5% clay stabilizer + 0.3% drainage aid + 0.1% bactericide + 0.2% potassium persulfate). Scale prevention tests were performed on the fracturing fluid systems prepared in each example and comparative example according to SY / T 5673-2020 "General Technical Conditions for Scale Inhibitors for Oilfield Use". Furthermore, a contact angle meter was used to test the water droplet contact angle of oleophilic core thin sections before and after the fracturing fluid system was applied. The test results are shown in Table 1.

[0093] Table 1 Performance parameters of various fracturing fluid systems

[0094]

[0095] As can be seen from the data in Table 1, the comparison between Example 1 and Comparative Example 1 shows that the supramolecular fracturing fluid formed by the host-guest encapsulation interaction in this invention has significantly stronger temperature and shear resistance, drag reduction rate, and rupture properties than the traditional hydrophobic associative supramolecular fracturing fluid.

[0096] The comparison between Example 2 and Comparative Example 2 shows that the W / O type microemulsion antiscalant has excellent antiscaling effect, and the presence of the microemulsion reduces the interfacial tension to 10. -3The mN / m interface changes from oleophilic to hydrophilic, which allows the fracturing fluid to penetrate deep into the reservoir through percolation and significantly reduces the influence of the Jamin effect during the rupture and flowback.

[0097] Comparing Example 6 with Comparative Examples 3 and 4, the W / O microemulsion scale inhibitor in Comparative Example 3 contained only Span60 surfactant, while Comparative Example 4 contained only n-hexanol. In terms of fracturing fluid performance, Comparative Examples 3 and 4 showed significantly lower temperature and shear resistance, and drag reduction rate compared to Example 6. This is because the lack of n-butanol (co-surfactant) weakens the interfacial film strength of the microemulsion scale inhibitor, leading to demulsification during high shear processes. The scale inhibitor, originally encapsulated by n-decane (oil phase), dispersed in the fracturing fluid system affects the strength of the host-guest encapsulation relationship, thus reducing the temperature and shear resistance and drag reduction rate of the supramolecular fracturing fluid. Furthermore, the lack of Span60 (the main surfactant) prevents the construction of a microemulsion system, making the impact of the scale inhibitor on the host-guest encapsulation relationship even more pronounced. Similarly, in Comparative Examples 3 and 4, due to the lack of complete surfactant components, the scale inhibitor could not function in a microemulsion structure. Its ability to reduce interfacial tension and wettability could only rely on the action of surfactants, and scale prevention could only be achieved by the inhibitory effect of the scale inhibitor. It could not form a microemulsion film on the surface to isolate scale growth.

[0098] In addition, compared with traditional guar gum and slickwater fracturing fluid, this invention integrates multiple functions such as viscosity enhancement, drag reduction, sand carrying, scale prevention, wetting reversal, and deep fracturing fluid delivery, providing a new and feasible solution for the efficient development of unconventional oil and gas reservoirs.

[0099] In summary, this invention combines host-guest encapsulation supramolecular fracturing fluid technology with scale inhibitor microemulsification technology to provide a multifunctional scale-inhibiting supramolecular fracturing fluid system with excellent drag reduction and proppant carrying performance, capable of forming complex fracture networks during fracturing. The addition of a W / O type microemulsion scale inhibitor not only prevents scale buildup within the fracture network, but the W / O microemulsion structure also improves reservoir wettability, making the reservoir more hydrophilic. This allows the fracturing fluid to penetrate deeper into the reservoir through percolation, increasing the fracturing range. Compared with existing technologies, this invention represents a significant advancement.

[0100] The above description is merely a representative embodiment of the present invention and is not intended to limit the present invention in any way. Any embodiment made by those skilled in the art without departing from the scope of the present invention and utilizing the disclosed technical content is an equivalent embodiment of the present invention. Any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A multifunctional anti-scaling supramolecular fracturing fluid system for unconventional oil reservoirs, characterized in that, By weight percentage, it includes 0.4-1.0% thickener, 0.05-1.5% clay stabilizer, 0.08-0.6% breaker, 0.5-0.8% scale inhibitor, and the balance being water; The thickener is a supramolecular fracturing fluid thickener with host-guest inclusion effect. The supramolecular fracturing fluid thickener includes a host thickener and a guest thickener. The host thickener is any one or more of β-cyclodextrin, hydroxypropyl-β-cyclodextrin, and cyclodextrin-epoxychloropropane polymer. The guest thickener is a water-soluble associative polymer containing hydrophobic groups. The scale inhibitor is a W / O type microemulsion scale inhibitor with amphiphilic modified graphene oxide as the main component. The W / O type microemulsion scale inhibitor comprises 30-50 parts by weight of an aqueous solution of amphiphilic modified graphene oxide, 35-50 parts by weight of saturated alkane, 5-10 parts by weight of a main surfactant, and 3-8 parts by weight of a co-surfactant. The mass fraction of the solute in the aqueous solution of amphiphilic modified graphene oxide is 0.5-1%. The structural formula of the amphiphilic modified graphene oxide is: The main surfactant is any one or more of the following: sorbitan monooleate, glycerol monooleate, glycerol monostearate, polyglycerol diisostearate, diglycerol monooleate, and sorbitan monostearate. The co-surfactant is any one or more of n-butanol, n-pentanol, isopropanol, isoamyl alcohol, and n-hexanol; The clay stabilizer is any one or more of inorganic salts, cationic copolymers, and cationic compounds; The breaker is a persulfate-based breaker.

2. The unconventional reservoir multifunctional anti-scaling supramolecular fracturing fluid system according to claim 1, characterized in that, The supramolecular fracturing fluid thickener comprises 50-75 parts by weight of a main thickener and 25-50 parts by weight of a guest thickener.

3. The unconventional reservoir multifunctional anti-scaling supramolecular fracturing fluid system according to claim 1, characterized in that, The water-soluble associative polymer containing hydrophobic groups is any one or more of hydrophobic associative polyacrylamides, hydrophobic modified polycarboxylic acids, and hydrophobic modified natural / semi-synthetic polymers.

4. The unconventional reservoir multifunctional anti-scaling supramolecular fracturing fluid system according to claim 1, characterized in that, The inorganic salt clay stabilizer is potassium chloride, the cationic copolymer clay stabilizer is a polyquaternary ammonium salt organic clay stabilizer, and the cationic compound clay stabilizer is a small molecule quaternary ammonium salt.

5. The unconventional reservoir multifunctional anti-scaling supramolecular fracturing fluid system according to claim 1, characterized in that, The persulfate-based degreasing agent is any one or more of ammonium persulfate, sodium persulfate, and potassium persulfate.

6. The unconventional reservoir multifunctional anti-scaling supramolecular fracturing fluid system according to claim 1, characterized in that, The saturated alkane is a medium- or long-chain alkane.

7. The unconventional reservoir multifunctional anti-scaling supramolecular fracturing fluid system according to claim 6, characterized in that, The saturated alkane is any one or more of n-octane, n-nonane, and n-decane.

8. The application of the unconventional reservoir multifunctional anti-scaling supramolecular fracturing fluid system as described in any one of claims 1-7 in the fracturing and exploitation of unconventional reservoirs.

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