Polymer crosslinking fracturing fluid suitable for acid-sensitive reservoirs and application thereof

Abstract

The application discloses a polymer cross-linking fracturing fluid suitable for acid-sensitive reservoirs and application thereof, and belongs to the field of oilfield chemicals, and comprises a multi-cross-linking interpenetrating system and a gel breaker; the multi-cross-linking interpenetrating system comprises a base fluid, a thickening agent, an alkaline cross-linking agent and other additives; the thickening agent comprises 0.25-0.3% of an anionic acrylamide modifier containing ortho-cis hydroxyl, 0.2-0.25% of a sulfone-bridged ortho-diamino poly-sulfone-isocyanate compound and 0.24-0.32% of cellulose fiber grafted beta-cyclodextrin, with the total amount of the base fluid as the benchmark; wherein the isocyanate is a semi-closed isocyanate; the alkaline cross-linking agent comprises 0.2-0.25% of triethanolamine titanium isopropyl titanate and 0.1-0.15% of magnesium oxide, with the total amount of the base fluid as the benchmark; the base fluid comprises deionized water, a sodium silicate solution and a surfactant, the pH of the sodium silicate solution is greater than 7.5, the addition amount of the sodium silicate solution is 20-25% of the mass of the deionized water, and the addition amount of the surfactant is 3-5% of the mass of the deionized water. The application effectively protects the acid formation.

Description

Technical Field

[0001] This invention belongs to the field of oilfield applied chemistry and relates to a polymer crosslinking fracturing fluid suitable for acid-sensitive reservoirs and its application. Background Technology

[0002] A certain shale oil reservoir has high calcium and magnesium content, as well as sulfides. The fluid entering the well must maintain an alkaline environment; otherwise, the calcium and magnesium in the reservoir will be released and crystallized, blocking the seepage channels. At the same time, an acidic environment will also cause the reservoir to release hydrogen sulfide, causing even greater destructive effects.

[0003] However, most fracturing fluids currently available are acidic fracturing fluids because they produce an acidic etching effect in the reservoir, which has a good effect on fracturing and plugging prevention. This is a technical effect that alkaline fracturing fluids or center fracturing fluids cannot achieve. Therefore, at present, there is a lack of an alkaline fracturing fluid with good fracturing and plugging prevention capabilities for acid-sensitive reservoirs such as certain shale oil reservoirs. Summary of the Invention

[0004] The purpose of this invention is to provide a polymer crosslinking fracturing fluid suitable for acid-sensitive reservoirs and its application, which solves the current problem of the lack of an alkaline fracturing fluid with good fracturing and anti-plugging capabilities for acid-sensitive reservoirs.

[0005] The technical solution adopted in this invention is as follows:

[0006] A polymer crosslinking fracturing fluid suitable for acid-sensitive reservoirs includes a multi-crosslinking interpenetrating system and a breaker; the multi-crosslinking interpenetrating system includes a base fluid, a thickener, an alkaline crosslinking agent, and other additives.

[0007] Based on the total amount of the base liquid, the thickener includes 0.25-0.3% of anionic acrylamide modified with ortho-cis hydroxyl groups, 0.2-0.25% of sulfone-bridged ortho-diamino-enhanced polysulfone-isocyanate complex, and 0.24-0.32% of cellulose fiber-grafted β-cyclodextrin; wherein the isocyanate is a semi-blocked isocyanate;

[0008] Based on the total amount of the base liquid, the alkaline crosslinking agent includes 0.2-0.25% of triethanolamine titanate isopropyl ester and 0.1-0.15% of magnesium oxide;

[0009] The base solution includes deionized water, sodium silicate solution, and surfactant. The pH of the sodium silicate solution is >7.5. The amount of sodium silicate solution added is 20-25% of the mass of deionized water, and the amount of surfactant added is 3-5% of the mass of deionized water.

[0010] Currently, alkaline fracturing fluids exhibit significantly weaker fracture-creating and anti-clogging performance compared to acidic fracturing fluids, resulting in a limited number of existing alkaline fracturing fluid systems. This application focuses on the two core aspects of fracture creation and anti-clogging, developing an alkaline fracturing fluid that not only possesses good fracture-creating and anti-clogging properties but also demonstrates excellent compatibility with acidic reservoirs. Furthermore, this application achieves a fracturing fluid pH of 7.5 or higher, and the pH of the broken fluid after gel breaking also reaches 7.5 or higher, effectively protecting acidic formations.

[0011] Since alkaline fracturing fluids lack acid-corroding properties, increased pumping pressure is necessary to achieve good fracture creation during fracturing. This necessitates improving the shear-dilution resistance of the alkaline fracturing fluid, maintaining a certain viscosity even under increased pumping pressure to achieve optimal fracture creation. Furthermore, high and stable viscosity, coupled with strong sand-suspending capacity, enhances the fracturing fluid's anti-clogging ability, provided it is pumpable. Therefore, this application utilizes a multi-crosslinked system to maintain the viscosity stability of the alkaline fracturing fluid, ensuring high and stable viscosity even at higher pumping pressures, thus solving the problem of poor fracture creation and anti-clogging performance of alkaline fracturing fluids.

[0012] The base fluid of this application uses deionized water as the main substance and adds an alkaline sodium silicate solution to provide an alkaline basis for the entire fracturing fluid system. Combined with surfactants, this enhances the compatibility between the various components. Based on the aforementioned alkaline base fluid environment, the principle of forming a multi-crosslinked interpenetrating system in this application is as follows:

[0013] Triethanolamine titanate isopropyl triethanolamine has abundant hydroxyl groups, providing an alkaline crosslinking environment. Triethanolamine titanate isopropyl triethanolamine is a crosslinking agent for anionic acrylamide modified with ortho-cis-hydroxyl groups. The two form a basic crosslinking system for titanium crosslinking. However, it has poor shear dilution resistance. Compared with existing technologies, the viscosity decreases after increasing the pumping pressure, resulting in poor gap formation and anti-clogging effects. Therefore, this application incorporates a sulfone-bridged ortho-diamined polysulfone-isocyanate composite. The amino group in the sulfone-bridged ortho-diamined polysulfone forms a new chemical bond with the unblocked -NCO in the semi-blocked isocyanate, and the two are stably linked. When the blocked -NCO in the semi-blocked isocyanate is unblocked, the -NCO will further react with the sulfone-bridged ortho-diamined polysulfone, and some -NCO will also undergo crosslinking reactions with the basic crosslinking system containing hydroxyl groups. The existing cross-linked network structure interpenetrates to form a basic interpenetrating cross-linked network structure. However, the formed basic interpenetrating cross-linked network structure is unstable, especially under high pumping conditions, where the degree of entanglement of polymer chains is insufficient and not dense enough. Therefore, this application further introduces cellulose fiber grafted with β-cyclodextrin. By utilizing the water absorption and swelling of β-cyclodextrin in cellulose fiber grafted with β-cyclodextrin and the interlacing of cellulose fibers, the stability of the interpenetrating cross-linked structure and the degree of entanglement of polymer chains are enhanced. This effectively hooks and supports particles, which is not only beneficial for carrying sand but also for preventing blockage and avoiding particle settling and clogging. The resulting alkaline fracturing fluid has good high temperature resistance, high viscosity, pumpability, and shear dilution resistance in complex reservoirs with high pumping agents. While protecting acid-sensitive formations, it also has good fracture-creating ability and does not cause significant blockage.

[0014] Furthermore, the anionic acrylamide modified with ortho-cis hydroxyl groups is a konjac gum-grafted anionic acrylamide polymer, which is prepared by copolymerization of konjac gum and anionic acrylamide monomer, with the amount of anionic acrylamide monomer added being 8-10% of the mass of konjac gum.

[0015] Further, the sulfone-bridged ortho-diamino-modified polysulfone-isocyanate composite comprises sulfone-bridged ortho-diamino-modified polysulfone and semi-blocked isocyanate in a mass ratio of 1:3.5, and is prepared by the following method: at 60°C, the sulfone-bridged ortho-diamino-modified polysulfone-isocyanate is dissolved in dimethyl sulfoxide, and then the semi-blocked isocyanate is added at room temperature. After stirring evenly, dibutyltin dilaurate is added, and the reaction is continued to obtain the sulfone-bridged ortho-diamino-modified polysulfone-isocyanate composite.

[0016] Furthermore, the semi-blocked isocyanate is a semi-blocked isocyanate with 3,5-dimethylpyrazole as the end-capping agent.

[0017] Furthermore, the cellulose fiber grafted with β-cyclodextrin is a cellulose fiber grafted with β-cyclodextrin synthesized in an alkaline medium, wherein the content of β-cyclodextrin is 12-18%.

[0018] Furthermore, the de-gelling agent is a mixed alkaline microcapsule de-gelling agent, including a microcapsule-type oxidant and a microcapsule-type complex enzyme;

[0019] The shell of the microcapsule-type oxidant is a fluorosilicone resin shell, and the core material is sodium percarbonate and sodium perborate in a mass ratio of 1:1.

[0020] The shell of the microcapsule-type composite enzyme is a fluorosilicone resin shell, and the core material is a composite enzyme.

[0021] Furthermore, the core material of the microcapsule-type complex enzyme includes cellulase, hemicellulase, and broad-spectrum β-enzyme, with a mass ratio of cellulase, hemicellulase, and broad-spectrum β-enzyme of 2:1:2.

[0022] Furthermore, based on the total amount of the base solution, the other additives include 0.1% pH buffer and 0.25% hyperbranched polyamide-amine;

[0023] The pH buffer solution is an NH3·H2O-NH4Cl buffer solution with a pH of 7.5.

[0024] Furthermore, the surfactant in the base liquid is one of dodecyl dimethyl betaine and cocamidopropyl betaine.

[0025] An application of a polymer crosslinked fracturing fluid suitable for acid-sensitive reservoirs, used as a fracturing fluid system for acid-sensitive reservoirs.

[0026] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0027] 1. A polymer crosslinked fracturing fluid suitable for acid-sensitive reservoirs utilizes a multi-crosslinked system to maintain the viscosity stability of alkaline fracturing fluid, thereby achieving high and stable viscosity at high pumping pressures and solving the problem of poor fracture creation and anti-clogging performance of alkaline fracturing fluids.

[0028] 2. In this invention, the three components—anionic acrylamide modified with ortho-cis-hydroxyl groups, sulfone-bridged ortho-diamino polysulfone-isocyanate complex, and cellulose fiber grafted β-cyclodextrin—work synergistically to form a stable and dense multi-crosslinked three-dimensional network structure under the action of a crosslinking agent. The resulting alkaline fracturing fluid exhibits good high-temperature resistance, high viscosity, pumpability, and shear dilution resistance in complex reservoirs with high pumping agents. While protecting acid-sensitive formations, it also has good fracture-creating ability and does not cause significant blockage.

[0029] 3. The crosslinking agent in this invention uses triethanolamine titanate isopropyl ester as the synthetic component, combined with magnesium oxide as the alkali source, which helps to maintain a high pH of the crosslinking system, create a good alkaline crosslinking environment, and adapt to acid-sensitive reservoirs.

[0030] 4. The breaker in this invention is a mixed alkaline microcapsule breaker. The outer shell of the capsule is heat-resistant, which can ensure that it does not rupture prematurely during the fracturing process. After the fracturing is completed and the reservoir begins to close, the microcapsules are ruptured to release the sodium percarbonate, sodium perborate and complex enzyme inside. The enzymatic hydrolysis and oxidant action are used to achieve rapid rupture, which is conducive to the backflow of fracturing fluid.

[0031] 5. This invention not only ensures that the working fluid (fracturing fluid) is alkaline (pH>7.5), but also ensures that the pH value of the flowback fluid (breaking fluid) is maintained above 7.5. It realizes an alkaline environment throughout the entire process from injection, fracturing, sand carrying to flowback, and completely eliminates the risks of acid-sensitive mineral damage and secondary precipitation blockage caused by fluctuations in fluid pH value (especially from alkaline to acidic), providing comprehensive protection for acid-sensitive reservoirs. Attached Figure Description

[0032] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort, wherein:

[0033] Figure 1 This is a physical image of the fracturing fluid of this invention;

[0034] Figure 2 This is a physical image of the crosslinking agent of the present invention. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention; that is, the described embodiments are merely some embodiments of the invention, and not all embodiments. The components of the embodiments of the invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0036] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0037] It should be noted that relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0038] This invention provides a polymer crosslinking fracturing fluid suitable for acid-sensitive reservoirs, comprising a multi-crosslinking interpenetrating system and a breaker; the multi-crosslinking interpenetrating system includes a base fluid, a thickener, an alkaline crosslinking agent, and other additives;

[0039] Based on the total amount of the base liquid, the thickener includes 0.25-0.3% of anionic acrylamide modified with ortho-cis hydroxyl groups, 0.2-0.25% of sulfone-bridged ortho-diamino-enhanced polysulfone-isocyanate complex, and 0.24-0.32% of cellulose fiber-grafted β-cyclodextrin; wherein the isocyanate is a semi-blocked isocyanate;

[0040] Based on the total amount of the base liquid, the alkaline crosslinking agent includes 0.2-0.25% of triethanolamine titanate isopropyl ester and 0.1-0.15% of magnesium oxide;

[0041] The base solution includes deionized water, sodium silicate solution, and surfactant. The pH of the sodium silicate solution is >7.5. The amount of sodium silicate solution added is 20-25% of the mass of deionized water, and the amount of surfactant added is 3-5% of the mass of deionized water.

[0042] Specifically, the anionic acrylamide modified with ortho-cis hydroxyl groups is a konjac gum-grafted anionic acrylamide polymer, which is prepared by copolymerization of konjac gum and anionic acrylamide monomer, with the amount of anionic acrylamide monomer added being 8-10% of the mass of konjac gum.

[0043] Specifically, the sulfone-bridged ortho-diamino-enhanced polysulfone-isocyanate composite comprises sulfone-bridged ortho-diamino-enhanced polysulfone and semi-blocked isocyanate in a mass ratio of 1:3.5, and is prepared by the following method: at 60°C, the sulfone-bridged ortho-diamino-enhanced polysulfone-isocyanate is dissolved in dimethyl sulfoxide, and then the semi-blocked isocyanate is added at room temperature. After stirring evenly, dibutyltin dilaurate is added, and the reaction is continued to obtain the sulfone-bridged ortho-diamino-enhanced polysulfone-isocyanate composite.

[0044] Specifically, the semi-blocked isocyanate is a semi-blocked isophorone diisocyanate with 3,5-dimethylpyrazole as the end-capping agent.

[0045] Specifically, the cellulose fiber grafted with β-cyclodextrin is a cellulose fiber grafted with β-cyclodextrin synthesized in an alkaline medium, wherein the content of β-cyclodextrin is 12-18%.

[0046] Specifically, the de-gelling agent is a mixed alkaline microcapsule de-gelling agent, including a microcapsule-type oxidant and a microcapsule-type complex enzyme;

[0047] The shell of the microcapsule-type oxidant is a fluorosilicone resin shell, and the core material is sodium percarbonate and sodium perborate in a mass ratio of 1:1.

[0048] The shell of the microcapsule-type composite enzyme is a fluorosilicone resin shell, and the core material is a composite enzyme.

[0049] Specifically, the core material of the microcapsule-type complex enzyme includes cellulase, hemicellulase and broad-spectrum β-enzyme, with a mass ratio of cellulase, hemicellulase and broad-spectrum β-enzyme of 2:1:2.

[0050] Cellulase and hemicellulase are both alkaline cellulase and alkaline hemicellulase. Alkaline cellulase includes alkaline cellulase produced by Bacillus sp., and alkaline hemicellulase includes alkaline xylanase and alkaline β-mannanase produced by Bacillus alkaliphilus. A broad-spectrum β-enzyme developed by Liaohe Oilfield has a pH range of 6-11.

[0051] Specifically, based on the total amount of the base solution, the other additives include 0.1% pH buffer and 0.25% hyperbranched polyamide-amine;

[0052] The pH buffer solution is an NH3·H2O-NH4Cl buffer solution with a pH of 7.5.

[0053] Specifically, the surfactant in the base liquid is one of dodecyl dimethyl betaine and cocamidopropyl betaine.

[0054] The aforementioned application of a polymer crosslinked fracturing fluid suitable for acid-sensitive reservoirs is described, and it is used as a fracturing fluid system for acid-sensitive reservoirs.

[0055] The features and performance of the present invention will be further described in detail below with reference to specific embodiments.

[0056] Example 1:

[0057] A preferred embodiment of the present invention provides a polymer crosslinking fracturing fluid suitable for acid-sensitive reservoirs, which is prepared by the following method:

[0058] S1. Prepare the base solution: Take 200ml of deionized water, add 40g of 1% (mass fraction) sodium silicate aqueous solution (pH 11) and 6g of dodecyl dimethyl betaine to the deionized water, stir evenly to obtain the base solution, the pH of the base solution is greater than 7.5;

[0059] S2. Take 150ml of base solution, add 0.62g of konjac gum grafted anionic acrylamide polymer (the amount of anionic acrylamide monomer added is 9% of the mass of konjac gum), 0.5g of sulfone-bridged ortho-diamino-enhanced polysulfone-isocyanate complex (liquid), and 0.6g of cellulose fiber grafted β-cyclodextrin (the content of β-cyclodextrin is 18%) to the base solution, and stir at high speed until uniform to obtain the gel solution;

[0060] S3. Add 0.5g of triethanolamine titanate isopropyl ester and 0.25g of magnesium oxide to the remaining base solution, stir evenly to obtain the crosslinking solution;

[0061] S4. Mix the adhesive and crosslinking liquid, stir evenly, add microcapsule oxidant, microcapsule complex enzyme and other additives, and continue stirring to obtain fracturing fluid; wherein, the core material of microcapsule oxidant is added at 0.025% of the total amount of adhesive and crosslinking liquid, and the core material of microcapsule complex enzyme is added at 0.025% of the total amount of adhesive and crosslinking liquid.

[0062] Example 2:

[0063] A preferred embodiment of the present invention provides a polymer crosslinking fracturing fluid suitable for acid-sensitive reservoirs, which is prepared by the following method:

[0064] S1. Prepare the base solution: Take 200ml of deionized water, add 46g of 1% (mass fraction) sodium silicate aqueous solution (pH 11) and 8g of dodecyl dimethyl betaine to the deionized water, stir evenly to obtain the base solution, the pH of the base solution is greater than 7.5;

[0065] S2. Take 150ml of base solution, add 0.73g of konjac gum grafted anionic acrylamide polymer (the amount of anionic acrylamide monomer added is 9% of the mass of konjac gum), 0.59g of sulfone-bridged ortho-diamino-modified polysulfone-isocyanate complex (liquid), and 0.76g of cellulose fiber grafted β-cyclodextrin (the content of β-cyclodextrin is 15%) to the base solution, and stir at high speed until uniform to obtain the gel solution;

[0066] S3. Add 0.6g of triethanolamine titanate isopropyl ester and 0.33g of magnesium oxide to the remaining base solution, stir evenly to obtain the crosslinking solution;

[0067] S4. Mix the adhesive and crosslinking solution, stir evenly, then add the microencapsulated oxidant, microencapsulated composite enzyme, and other additives, and continue stirring to obtain the fracturing fluid. The core material of the microencapsulated oxidant is added at 0.025% of the total amount of the adhesive and crosslinking solution, and the core material of the microencapsulated composite enzyme is added at 0.025% of the total amount of the adhesive and crosslinking solution.

[0068] fracturing fluid Figure 1 As shown, it is a translucent, pale yellow, viscous substance. The cross-linking agent is as follows: Figure 2 As shown.

[0069] Example 3:

[0070] A preferred embodiment of the present invention provides a polymer crosslinking fracturing fluid suitable for acid-sensitive reservoirs, which is prepared by the following method:

[0071] S1. Prepare the base solution: Take 200ml of deionized water, add 50g of 1% (mass fraction) sodium silicate aqueous solution (pH 11) and 10g of dodecyl dimethyl betaine to the deionized water, stir evenly to obtain the base solution, the pH of the base solution is greater than 7.5;

[0072] S2. Take 150ml of base solution, add 0.78g of konjac gum grafted anionic acrylamide polymer (the amount of anionic acrylamide monomer added is 9% of the mass of konjac gum), 0.65g of sulfone-bridged ortho-diamino-enhanced polysulfone-isocyanate complex (liquid), and 0.83g of cellulose fiber grafted β-cyclodextrin (the content of β-cyclodextrin is 12%) to the base solution, and stir at high speed until uniform to obtain the gel solution;

[0073] S3. Add 0.65g of triethanolamine titanate isopropyl ester and 0.39g of magnesium oxide to the remaining base solution, stir evenly to obtain the crosslinking solution;

[0074] S4. Mix the adhesive and crosslinking liquid, stir evenly, add microcapsule oxidant, microcapsule complex enzyme and other additives, and continue stirring to obtain fracturing fluid; wherein, the core material of microcapsule oxidant is added at 0.025% of the total amount of adhesive and crosslinking liquid, and the core material of microcapsule complex enzyme is added at 0.025% of the total amount of adhesive and crosslinking liquid.

[0075] Example 4:

[0076] Based on Example 2, the difference between this example and Example 2 is that in step S2, the amount of anionic acrylamide monomer added to the konjac gum grafted anionic acrylamide polymer is 8% of the mass of konjac gum.

[0077] Example 5:

[0078] Based on Example 2, the difference between this example and Example 2 is that in step S2, the amount of anionic acrylamide monomer added to the konjac gum grafted anionic acrylamide polymer is 10% of the mass of konjac gum.

[0079] Comparative Example 1:

[0080] Based on Example 2, the difference from Example 2 is that the base liquid in this comparative example does not include an aqueous solution of sodium silicate.

[0081] Comparative Example 2:

[0082] Based on Example 2, the difference from Example 2 is that the base liquid of this comparative example does not contain dodecyl dimethyl betaine.

[0083] Comparative Example 3:

[0084] Based on Example 2, the difference from Example 2 is that the thickener in this comparative example only includes konjac gum grafted anionic acrylamide polymer (the amount of anionic acrylamide monomer added is 9% of the mass of konjac gum).

[0085] Comparative Example 4:

[0086] Based on Example 2, the difference from Example 2 is that the konjac gum in this comparative thickener is not grafted with anionic acrylamide polymer, and includes konjac gum, sulfone-bridged ortho-diaminolated polysulfone-isocyanate complex (liquid), and cellulose fiber grafted with β-cyclodextrin (β-cyclodextrin content is 15%).

[0087] Comparative Example 5:

[0088] Based on Example 2, the difference from Example 2 is that the thickener in this comparative example does not include a sulfone-bridged ortho-diamino-substituted polysulfone-isocyanate complex.

[0089] Comparative Example 6:

[0090] Based on Example 2, the difference from Example 2 is that the thickener in this comparative example includes anionic acrylamide modified with ortho-cis hydroxyl groups, sulfone-bridged ortho-diamino-modified polysulfone, and cellulose fiber grafted β-cyclodextrin.

[0091] Comparative Example 7:

[0092] Based on Example 2, the difference from Example 2 is that the thickener in this comparative example includes anionic acrylamide modified with ortho-cis hydroxyl groups, semi-blocked isophorone diisocyanate with 3,5-dimethylpyrazole as the end-capping agent, and cellulose fiber grafted β-cyclodextrin.

[0093] Comparative Example 8:

[0094] Based on Example 2, the difference from Example 2 is that the isocyanate in the sulfone-bridged ortho-diamino polysulfone-isocyanate complex in this comparative thickener is an unblocked isophorone diisocyanate without an end-capping agent.

[0095] Comparative Example 9:

[0096] Based on Example 2, the difference from Example 2 is that the thickener in this comparative example does not include cellulose fiber grafted β-cyclodextrin.

[0097] Comparative Example 10:

[0098] Based on Example 2, the difference from Example 2 is that the crosslinking agent in this comparative example does not include magnesium oxide.

[0099] Comparative Example 11:

[0100] Based on Example 2, the difference from Example 2 is that this comparative degreasing agent does not contain capsule-type complex enzymes.

[0101] Comparative Example 12:

[0102] Based on Example 2, the difference from Example 2 is that this comparative degreasing agent does not contain a capsule-type oxidant.

[0103] Comparative Example 13:

[0104] Based on Example 2, the difference from Example 2 is that the compound enzyme and oxidant in this comparative degreasing agent are used directly without encapsulation.

[0105] Experimental Example 1:

[0106] The gelling properties of the preparation methods in Examples 1-5 and Comparative Examples 1-13, as well as the pH, viscosity, and viscosity and pH of the gelled fracturing fluid after gel breaking, were tested. The results are shown in Table 1.

[0107] Gel-forming property: If a gel can form a uniform, high-viscosity colloid, it is considered gel-forming; conversely, if a gel cannot form a uniform and high-viscosity colloid, it is considered non-gel-forming.

[0108] pH testing: pH testing was performed using a pH meter in accordance with the SY / T 5107-2005 standard;

[0109] Viscosity: Follow the procedure in SY / T 6074-94, section 6.4. Take 350 ml of sample heated to 30℃ (the preparation volume can be scaled up proportionally according to the required testing volume; this is the cross-linked fracturing fluid). Measure the viscosity using a Fann-35 viscometer at a rotation speed of 100 r / min (shear rate of 170 s). -1 ), viscosity at 30℃ (apparent viscosity), the recorded value is the range of the point value (excluding the endpoint value);

[0110] Breakage performance test: SY / T 5107-2005 (6.13 Determination of breaking performance of fracturing fluid); The microcapsule rupture of this application is mainly based on pressure rather than temperature. Therefore, it is not necessary to test the breaking temperature and the breaking time at the corresponding temperature. The apparent viscosity of the breaking fluid is directly tested after the capsule is broken.

[0111] Table 1. Basic constructability test of fracturing fluid

[0112]

[0113] The breaking mechanism of this application relies on pressure to disrupt the capsule structure and release the internal breaking agent. In high-temperature reservoirs, breaking mainly depends on oxidants, while in low-temperature reservoirs, oxidants and complex enzymes work synergistically. Therefore, the breaking mechanism of this application is suitable for reservoirs at different temperatures.

[0114] Experimental Example 2:

[0115] The sand-suspending properties, temperature resistance, and shear resistance of the gelled fracturing fluids in Examples 1-5 and Comparative Examples 1-10 were tested, and the results are shown in Table 2.

[0116] Suspension property: Sinking speed of a φ6mm steel ball at 90℃;

[0117] Temperature resistance: According to SY / T 5107-2005 standard, after filling the viscometer sample cup with fracturing fluid, the sample was heated; the heating rate was controlled at 3℃ / min ± 0.2℃ / min, starting the test at 30℃, while the rotor was operated at a shear rate of 170s. -1 The fracturing fluid was subjected to continuous shearing under heating conditions, and the temperature at which the apparent viscosity dropped to 50 mPa·s was used to characterize the temperature resistance of the sample.

[0118] Temperature and shear resistance: According to SY / T 5107-2005 standard, at 120℃, the shear rate is 170 s⁻¹. -1 Viscosity after 2 hours of shearing.

[0119] Table 2. Basic Performance Testing of Fracturing Fluids

[0120] Suspended sand Temperature resistance Shear resistance Example 1 0.7-0.8 m / min ＞120℃ >150 mPa·s Example 2 0.4-0.5 m / min ＞120℃ >150 mPa·s Example 3 0.7-0.8 m / min ＞120℃ >150 mPa·s Example 4 0.8-0.9 m / min ＞120℃ >150 mPa·s Example 5 0.5-0.6 m / min ＞120℃ >150 mPa·s Comparative Example 3 2.5-2.6 ＞120℃ 80-90 mPa·s Comparative Example 4 1.4-1.5 ＞120℃ 120-130 mPa·s Comparative Example 5 1.8-1.9 ＞120℃ 100-110 mPa·s Comparative Example 7 1.7-1.8 ＞120℃ 100-110 mPa·s Comparative Example 9 1.2-1.3 ＞120℃ 80-90 mPa·s

[0121] This application has strong sand-suspending capacity and good temperature and shear resistance.

[0122] Experimental Example 3:

[0123] The fracturing fluids prepared in Examples 1-5 were tested and their application effects were evaluated in field test wells (based on the field usage and the preparation volume was scaled up proportionally). The results are shown in Table 3.

[0124] Table 3. On-site test construction results

[0125] Compatibility of fracturing fluid system with geological conditions of a shale oil block Construction success rate Reverse displacement situation Example 1 Suitable for acid-sensitive reservoirs and does not harm them. 100% Timely return and drainage, no blockage. Example 2 Suitable for acid-sensitive reservoirs and does not harm them. 100% Timely return and drainage, no blockage. Example 3 Suitable for acid-sensitive reservoirs and does not harm them. 100% Timely return and drainage, no blockage. Example 4 Suitable for acid-sensitive reservoirs and does not harm them. 100% Timely return and drainage, no blockage. Example 5 Suitable for acid-sensitive reservoirs and does not harm them. 100% Timely return and drainage, no blockage.

[0126] This invention has been successfully applied to acid-sensitive reservoirs in a shale oil field. The fracturing fluid formulated in this invention, before cross-linking, achieves a drag reduction rate of over 80% in its low-viscosity state.

[0127] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A polymer crosslinking fracturing fluid suitable for acid-sensitive reservoirs, characterized in that: It includes a multi-crosslinking interpenetrating polymer system and a debonding agent; the multi-crosslinking interpenetrating polymer system includes a base liquid, a thickener, an alkaline crosslinking agent, and other additives; Based on the total amount of the base liquid, the thickener includes 0.25-0.3% of anionic acrylamide modified with ortho-cis hydroxyl groups, 0.2-0.25% of sulfone-bridged ortho-diamino-enhanced polysulfone-isocyanate complex, and 0.24-0.32% of cellulose fiber-grafted β-cyclodextrin; wherein the isocyanate is a semi-blocked isocyanate; Based on the total amount of the base liquid, the alkaline crosslinking agent includes 0.2-0.25% of triethanolamine titanate isopropyl ester and 0.1-0.15% of magnesium oxide; The base solution includes deionized water, sodium silicate solution, and surfactant. The pH of the sodium silicate solution is >7.

5. The amount of sodium silicate solution added is 20-25% of the mass of deionized water, and the amount of surfactant added is 3-5% of the mass of deionized water. The de-gelatinizing agent is a mixed alkaline microcapsule de-gelatinizing agent, including microcapsule-type oxidants and microcapsule-type complex enzymes; The shell of the microcapsule-type oxidant is a fluorosilicone resin shell, and the core material is sodium percarbonate and sodium perborate in a mass ratio of 1:

1. The shell of the microcapsule-type composite enzyme is a fluorosilicone resin shell, and the core material is a composite enzyme. The core material of the microcapsule-type complex enzyme includes cellulase, hemicellulase, and broad-spectrum β-enzyme, with a mass ratio of 2:1:

2.

2. The polymer crosslinking fracturing fluid suitable for acid-sensitive reservoirs according to claim 1, characterized in that: The anionic acrylamide modified with ortho-cis hydroxyl groups is a konjac gum-grafted anionic acrylamide polymer, which is prepared by copolymerization of konjac gum and anionic acrylamide monomers, with the amount of anionic acrylamide monomer added being 8-10% of the mass of konjac gum.

3. The polymer crosslinking fracturing fluid suitable for acid-sensitive reservoirs according to claim 1, characterized in that: The sulfone-bridged ortho-diamino-enhanced polysulfone-isocyanate composite comprises sulfone-bridged ortho-diamino-enhanced polysulfone and semi-blocked isocyanate in a mass ratio of 1:3.5, and is prepared by the following method: at 60°C, the sulfone-bridged ortho-diamino-enhanced polysulfone-isocyanate is dissolved in dimethyl sulfoxide, and then the semi-blocked isocyanate is added at room temperature. After stirring evenly, dibutyltin dilaurate is added, and the reaction is continued to obtain the sulfone-bridged ortho-diamino-enhanced polysulfone-isocyanate composite.

4. The polymer crosslinking fracturing fluid suitable for acid-sensitive reservoirs according to claim 3, characterized in that: The semi-blocked isocyanate is a semi-blocked isocyanate with 3,5-dimethylpyrazole as the end-capping agent.

5. The polymer crosslinking fracturing fluid suitable for acid-sensitive reservoirs according to claim 1, characterized in that: The cellulose fiber grafted with β-cyclodextrin is a cellulose fiber grafted with β-cyclodextrin synthesized in an alkaline medium, wherein the content of β-cyclodextrin is 12-18%.

6. The polymer crosslinking fracturing fluid suitable for acid-sensitive reservoirs according to claim 1, characterized in that: Based on the total amount of the base solution, the other additives include 0.1% pH buffer and 0.25% hyperbranched polyamide-amine; The pH buffer solution is an NH3·H2O-NH4Cl buffer solution with a pH of 7.

5.

7. The polymer crosslinking fracturing fluid suitable for acid-sensitive reservoirs according to claim 1, characterized in that: The surfactant in the base liquid is one of dodecyl dimethyl betaine and cocamidopropyl betaine.

8. The application of a polymer crosslinking fracturing fluid suitable for acid-sensitive reservoirs according to any one of claims 1-7, characterized in that: Used as a fracturing fluid system for acid-sensitive reservoirs.

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