Multifunctional polymer-free integrated reservoir modification mother liquor and preparation method and application thereof

Abstract

The present application relates to the technical field of oil and gas field development, in particular to a multifunctional polymer-free integrated reservoir modification mother liquor, a preparation method and application thereof. The mother liquor is a polymer-free high-density salt water-based ultra-low-density proppant suspension system, which realizes stable suspension of the proppant through physical density matching, and simultaneously pre-integrates anti-swelling, imbibition oil displacement (for oil wells) or natural gas desorption (for gas wells) functions. The mother liquor is transported to the site in the form of a pre-prepared suspension slurry, mixed with water through a hose pump or a diaphragm pump for quantitative pumping, and directly forms a pumpable working fluid, eliminating the need for a sand mixing link of a traditional sand tank truck, and greatly simplifies the construction process. The mother liquor does not contain any tackifying polymer, can reduce reservoir damage, and is suitable for fracturing modification of unconventional reservoirs such as coalbed methane and tight oil and gas, wherein the imbibition oil displacement rate of the mother liquor for oil wells is more than 40% in 120h, the mother liquor for gas wells can increase the Langmuir pressure of coal rock by more than 9%, and has significant reservoir modification effect and construction advantages.

Description

Technical Field

[0001] This invention relates to the field of oil and gas field development technology, specifically to an integrated reservoir stimulation mother liquor that is polymer-free and integrates proppant suspension and reservoir production enhancement functions, as well as its preparation method and application. Background Technology

[0002] Hydraulic fracturing is a key technology for developing unconventional oil and gas resources such as shale gas, tight oil, and coalbed methane. Traditional fracturing fluid systems are mainly divided into two categories: one is the slickwater system, which reduces drag and carries proppant by adding a small amount of drag-reducing polymers; the other is the gel system, which relies on cross-linking of high-molecular-weight polymers such as guar gum and its derivatives to form a high-viscosity gel to carry the proppant. However, both of these systems rely heavily on the use of water-soluble thickening polymers.

[0003] In recent years, to reduce fracturing costs and minimize polymer residue damage to reservoirs, "thickener-free" fracturing technology—using clean water or drag-reducing water containing only surfactants—has become an important direction for industry development. However, this technology faces a core challenge: low-viscosity clean water or polymer-free fluids have extremely poor sand-carrying capacity. Even ultra-low-density proppant settles rapidly in low-viscosity fluids, easily forming sand dikes in the horizontal section of the wellbore, leading to premature sand blockage, fracturing failure, or low fracture propping efficiency, severely restricting the widespread application of this technology.

[0004] Furthermore, traditional fracturing operations are complex, typically requiring various large pieces of equipment such as sand tankers, sand mixing trucks, instrument trucks, and fracturing pump trucks. During operation, proppant, various chemical additives, and water must be mixed in batches on-site in sand mixing tanks. This not only involves significant equipment investment and space occupation but also presents numerous on-site mixing steps, making it prone to errors and difficult to achieve precise real-time control. In particular, the concentration control of the proppant is crucial to the success of the operation, and traditional mechanical sand mixing methods cannot guarantee its absolute uniformity.

[0005] Therefore, how to achieve efficient and stable delivery of proppant without relying on polymers, while simplifying on-site construction procedures and accurately pre-setting reservoir protection and production enhancement functions, is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] The technical problem this invention aims to solve is to overcome the shortcomings of existing technologies and provide a multifunctional, polymer-free, integrated reservoir modification mother liquor, its preparation method, and its applications. This invention aims to fundamentally eliminate polymer damage, solve the sand-carrying problem using physical principles, and completely revolutionize traditional fracturing construction processes through a "factory prefabrication, simple on-site dilution" model.

[0007] The technical solution adopted by this invention to solve its technical problem is: a multifunctional polymer-free integrated reservoir modification mother liquor, wherein the modification mother liquor is a high-density brine-based ultra-low density proppant suspension system, which is composed of high-density brine and ultra-low density proppant; the modification mother liquor does not contain any water-soluble thickening polymers used to increase the viscosity of the system; The density of the high-density brine is 1.01–1.60 g / cm³. 3 The dissolved salts are at least one of potassium chloride, sodium chloride, potassium formate, sodium formate, potassium bromide, sodium bromide, sodium nitrate, and potassium nitrate. The true density of the ultra-low density proppant is 1.0–1.55 g / cm³. 3 The bulk density is 0.65–0.80 g / cm³. 3 ; The volume concentration of the ultra-low density proppant in the mother liquor is 10-90%; Wherein, the density of the high-density brine is greater than or equal to the true density of the ultra-low-density proppant.

[0008] The modified mother liquor of this invention adopts a high-density saline-based ultra-low density proppant suspension system. Its core lies in utilizing the density matching or slight density difference between the high-density saline and the ultra-low density proppant to form a stable suspension state, thereby completely abandoning traditional polymer thickening methods.

[0009] In the technical solution of this invention, a high-density continuous phase is formed by selecting inorganic salts within a specific density range, which, in combination with a low-density dispersed phase (proppane), keeps the proppant particles in a suspended or quasi-suspended state in the mother liquor. When the density of the brine is higher than the true density of the proppant, the proppant may even exhibit a floating tendency, which also facilitates its uniform distribution under static conditions and avoids the rapid sedimentation and caking of proppant in traditional low-viscosity fluids. This physical suspension mechanism is the cornerstone of the entire technical solution.

[0010] Furthermore, the high-density brine also contains 0.1% to 10.0% by weight of a clay stabilizer, wherein the clay stabilizer is at least one of polyamines or quaternary ammonium salts. The clay stabilizer can prevent the water-based working fluid from entering the reservoir and causing the clay minerals to hydrate and expand, thus preventing a decrease in reservoir permeability.

[0011] Furthermore, the high-density brine also contains 0.1% to 10.0% by weight of a drag-reducing surfactant. This surfactant forms worm-like micelles in the aqueous system, effectively reducing friction.

[0012] Furthermore, the high-density brine also contains functional additives pre-added according to the well type: For oil well reservoirs, the functional additive is a permeation displacement agent comprising 0.05–10% of the brine weight; For gas well reservoirs, the functional additive is a natural gas desorbent comprising 0.05 to 10% of the brine weight.

[0013] The percolation displacement agent comprises the following components by weight percentage: 10-30% sulfonic acid betaine surfactant, 20-30% fatty alcohol polyoxyethylene ether surfactant, 2-10% fluorocarbon surfactant, 20-40% ethylene glycol butyl ether, and 1-5% rhamnose. The function of the percolation displacement agent is to reduce the interfacial tension between oil and water in the reservoir, improve the water-phase oil displacement effect, and increase the oil recovery rate.

[0014] The natural gas desorbent comprises the following components by mass percentage: 20-30% betaine surfactant, 20-30% fatty alcohol ether carboxylate surfactant, and 40-60% amine oxide surfactant. The natural gas desorbent functions by adsorbing onto rock surfaces (such as coal, shale), increasing the Ranvin pressure, enhancing the natural gas desorption capacity, and thus increasing natural gas production capacity.

[0015] Furthermore, the ultra-low density proppant is a 6-400 mesh spherical particle constructed using a thermosetting resin. This type of proppant not only has low density but also high strength and good chemical stability, meeting the support requirements of deep, high-pressure reservoirs. The thermosetting resin material is a three-dimensional network polymer structure formed by copolymerizing at least one monofunctional monomer (monovinyl monomer, monoacrylate monomer) with at least one difunctional monomer (divinyl monomer, diacrylate monomer); or a three-dimensional network polymer structure formed by copolymerizing at least one of the above monofunctional and difunctional monomers with an unsaturated polyester.

[0016] A method for preparing the multifunctional polymer-free integrated reservoir modification mother liquor as described above comprises the following steps: Step S1: Dissolve the salts in water to prepare a solution with a density of 1.01–1.60 g / cm³. 3 High-density brine; Step S2: According to the target well type, add the corresponding functional additives, clay stabilizers and drag-reducing surfactants to the high-density brine prepared in step S1, and mix evenly to obtain a brine mixture. Step S3: Add the ultra-low density proppant to the brine mixture obtained in step S2 at a volume concentration of 10-90%, and stir at low speed to form a homogeneous suspension mother liquor.

[0017] The core of the preparation method lies in "factory prefabrication." All complex additives requiring precise measurement, including functional percolation displacement agents / desorbents, are pre-added to high-density brine in a controlled factory environment, ensuring consistent product quality and reliable functionality. The final product is a "concentrated suspension" that can be directly canned and transported.

[0018] Furthermore, in step S2, adding the corresponding functional additive according to the target well type specifically involves: For oil well reservoirs, the functional additive is a permeation displacement agent comprising 0.05–10% of the brine weight; For gas well reservoirs, the functional additive is a natural gas desorbent comprising 0.05 to 10% of the brine weight.

[0019] An application of a multifunctional polymer-free integrated reservoir stimulation mother fluid as described above, wherein the mother fluid is used in the fracturing stimulation of unconventional reservoirs; the unconventional reservoirs include coalbed methane reservoirs (gas wells) and tight oil and gas reservoirs (oil wells); for oil well reservoirs, a mother fluid pre-added with a permeation displacement agent is used; for gas well reservoirs, a mother fluid pre-added with a natural gas desorbent is used.

[0020] Furthermore, when the modified mother liquor is used on-site, the following steps are included: Step (1): Transport the pre-prepared suspension modification mother liquor to the fracturing construction site; Step (2): The suspension modification mother liquor is quantitatively pumped in using a hose pump or diaphragm pump and mixed and diluted with on-site water at a volume ratio of 1:1 to 1:100 to form a fracturing fluid that can be directly pumped in. Step (3): The diluted fracturing fluid is injected into the target reservoir through a high-pressure fracturing pump truck unit to carry out fracturing operations.

[0021] Furthermore, in step (2), the mixing and dilution process is completed by an online dynamic mixing device, which is a high-shear mixer or a static mixer, to ensure that the high-viscosity concentrated mother liquor and the low-viscosity dilution water are uniformly mixed at the molecular level in a very short time, and to prevent uneven local proppant concentration; the on-site water source is at least one of clean water, seawater, formation water or fracturing flowback fluid, which greatly broadens the applicable range of water sources.

[0022] The beneficial effects of this invention are that it is rationally designed and has the following advantages: 1. Eliminate polymer damage at the source: The system contains no thickening polymers at all, which completely avoids the blockage of reservoir pore throats by polymer residues, unbroken glue and other solid substances, thus protecting reservoir permeability to the maximum extent. Experimental data show that the permeability recovery rate can reach more than 93%. 2. Achieving efficient suspension by physical method: Utilizing the density matching principle between high-density brine and ultra-low density proppant, the proppant achieves statically stable suspension in the mother liquor (sedimentation rate less than 2% in 24 hours) without increasing any viscosity. This solves the problem of stratification during transportation and storage of ultra-low density proppant and fundamentally improves its dynamic sand-carrying performance in low-viscosity diluents. 3. Simplify on-site construction process: The complex liquid preparation and sand mixing process is moved to the factory, and only two simple actions are required on site: "pumping mother liquor + online dilution". This completely eliminates large equipment such as sand tank trucks and sand mixing trucks and complicated on-site operations, greatly reducing equipment dependence, labor costs and work preparation time, and improving the safety and accuracy of construction. 4. Precise pre-setting of functions: Complex functions such as percolation oil displacement and natural gas desorption are pre-integrated into the modification mother liquid, eliminating the need for any additional additions on site. This avoids potential errors in on-site liquid preparation and ensures precise and controllable functional effects. Experiments have shown that the percolation oil displacement rate of the mother liquid for oil wells exceeds 40% after 120 hours, and the mother liquid for gas wells can increase the Randolph pressure of coal and rock by more than 9%. 5. Excellent compatibility and universality: The high-mineralization brine matrix has good chemical compatibility with various on-site water sources (including high-salinity formation water and backflow fluid). It is not easy to produce precipitation or flocculation when mixed, which is conducive to water resource recycling and environmental protection. Attached Figure Description

[0023] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0024] Figure 1 This is a graph showing the relationship between the settling time and sedimentation rate for each sample in Example 1. Figure 2 This is a graph showing the permeation rate of experimental solution A and control solution C in Example 3. Detailed Implementation

[0025] The present invention will now be described in further detail with reference to the accompanying drawings. These drawings are simplified schematic diagrams, illustrating only the basic structure of the invention, and therefore only show the components relevant to the invention.

[0026] In this invention, the ultra-low density proppant used is at least one of Chinese patents CN121108415A, CN103965390B, and CN103980404B.

[0027] Example 1: Preparation and Static Stability Testing of Mother Solutions in Different Salt Water Systems This embodiment aims to verify the suspending ability of high-density brine with different densities and salt types on ultra-low density proppant.

[0028] Prepare solutions with a density of 1.01 g / cm³. 3 KCl solution, 1.18 g / cm³ 3 Potassium formate solution, 1.30 g / cm³ 3 Sodium nitrate solution and 1.60 g / cm 3A potassium bromide solution was used as the high-density brine base. To each brine sample, 0.5% by weight of a clay stabilizer (polyamine) and 1.0% by weight of a drag-reducing surfactant (erucamide propyltrimethylammonium chloride) were added. Furthermore, at a concentration of 1.20 g / cm³... 3 and 1.32 g / cm 3 Add 0.1% of a permeation displacement agent (for simulated oil wells) to the brine at a concentration of 1.50 g / cm³. 3 Add 0.2% natural gas desorbent (for simulated gas wells) to the brine.

[0029] Take a certain amount of each of the three prepared high-density saline solutions and mix them separately with ultra-low-density proppant at a volume concentration of 30%. Stir the mixture using a paddle mixer at 60 rpm for 30 minutes to form homogeneous suspensions, which are denoted as follows: Sample A (1.01 g / cm³) 3 The brine, for oil wells, KCl, ultra-low density proppant with a true density of 1.0 g / cm³ 3 ); Sample B (1.18 g / cm³) 3 The brine, for use in oil wells, potassium formate, ultra-low density proppant with a true density of 1.15 g / cm³ 3 ); Sample C (1.30 g / cm³) 3 The brine, used in gas wells, contains sodium nitrate and ultra-low density proppant with a true density of 1.27 g / cm³. 3 ) Sample D (1.60 g / cm³) 3 The brine, used in gas wells, contains potassium bromide and ultra-low density proppant with a true density of 1.55 g / cm³. 3 ).

[0030] In this embodiment, the ultra-low density proppant is a bulk cross-linked high-strength polymer material obtained by suspension polymerization of styrene and ethylene diacrylate.

[0031] Two comparative examples were set up: Comparative Example 1 consisted of a 1.0% concentration polyacrylamide (PAM) solution and an ultra-low density proppant (true density 1.15 g / cm³). 3 The polymer-based suspension mother liquor was formed by mixing water and an ultra-low density proppant (true density 1.15 g / cm³). Comparative Example 2 consisted of water and an ultra-low density proppant (true density 1.15 g / cm³). 3 Mix directly.

[0032] All the above samples were stored at room temperature, and the sedimentation of the proppant and the state of the system were recorded after 24 hours and 7 days. The experimental results are shown in Table 1 and... Figure 1 .

[0033] Table 1 Comparison of static stability of different suspension systems

[0034] From Table 1 and Figure 1 It can be seen that samples A, B, and C (all with brine densities greater than the true density of the ultra-low density proppant in the system) exhibit excellent static stability under polymer-free conditions, with a 24-hour sedimentation rate of less than 2%. Samples B and C showed almost no clarification layer, performing similarly to the high-viscosity polymer control example 1, and far superior to the clear water control example 2 (complete sedimentation). This indicates that the suspension strategy based on physical density matching is entirely feasible, and the addition of functional additives did not affect the stability of the system.

[0035] Example 2: Simulation Experiment of Dynamic Mixing and Transport of Mother Liquor This embodiment aims to simulate the effect of online mixing of the mother liquor and water under field conditions, as well as the dynamic proppant carrying stability of the diluted fracturing fluid.

[0036] Sample B (potassium formate mother liquor, proppant concentration 30%, containing percolation displacement agent) prepared in Example 1 was used as the test object. The proppant concentration was increased to 50% and used as a concentrated mother liquor for later use.

[0037] An experimental setup was constructed to simulate the on-site mixing and pumping process, including: a mother liquor tank, a clear water tank, a high-shear online mixer, and a transparent pipeline circulation system.

[0038] Experimental procedure: 1. Mixing Uniformity Test: The pump flow rate ratio of mother liquor to water was set at 1:5 (the target diluted proppant concentration is approximately 8.3%). The mother liquor and water were metered into a high-shear dynamic mixer using a flexible pump. After the system stabilized, 100ml samples were continuously taken from the mixer outlet each time. The samples were filtered, dried, and weighed to calculate the actual proppant concentration.

[0039] 2. Dynamic Settlement Observation: The above-mentioned online mixed and diluted fracturing fluid is introduced into the transparent pipeline circulation system to circulate at an average flow velocity of 0.5 m / s, simulating the wellbore. Observe continuously for 30 minutes and record whether sand embankments form or proppant deposits are deposited at the bottom of the pipeline.

[0040] Two control groups were set up: Control group A involved mixing the mother liquor and water in a 1:5 ratio in a mixing tank using simple mechanical stirring, followed by circulation and observation; Control group B involved adding the proppant directly to water, mixing it using a high-shear mixer (also diluted to 8.3%), and immediately conducting circulation and observation. The experimental results are shown in Table 2.

[0041] Table 2. Test Results of Dynamic Mixing and Conveying Performance

[0042] As shown in Table 2: 1. In terms of mixing uniformity: The combination of a hose pump for metered injection and high-shear dynamic mixing ensures that the measured value of the proppant concentration deviates from the theoretical value by only ±0.4%, resulting in excellent mixing uniformity and guaranteeing stable proppant concentration during construction. In contrast, the mixing method of simple mechanical stirring can result in a proppant concentration deviation of up to ±3.2%, which is poor and can easily lead to excessively high or low local proppant concentrations, affecting the construction effect.

[0043] 2. In terms of delivery stability: After the fracturing fluid mixed using the process of this invention circulates in the pipeline for 30 minutes, no sand bed forms, the proppant is always evenly distributed, and there is no risk of sand blockage; while the mixture with simple mechanical stirring produces discontinuous sand clumps and obvious local flow velocity fluctuations; compared with the water-sand mixed system of Example 2, even with high shear mixing, a stable sand embankment still forms within 10 minutes, which cannot meet the requirements of continuous construction.

[0044] Conclusion: The high-concentration brine suspension mother liquor of this invention, combined with quantitative pumping using a flexible hose pump and a high-shear online dynamic mixing process, can achieve rapid and uniform mixing with clean water, and effectively delay the dynamic sedimentation of proppant in low-viscosity fracturing fluid, thus avoiding sand blockage. Simple mechanical stirring cannot meet the uniformity requirements, and this process eliminates the need for sand tanker trucks for sand mixing, significantly simplifying the operation.

[0045] Example 3: Reservoir Suitability and Functional Evaluation Experiment This embodiment aims to evaluate the degree of damage to the reservoir caused by the mother liquor of the present invention and the actual effect of its preset functions.

[0046] Experiments were conducted using low-permeability coal cores (i.e., tight sandstone cores with a permeability of approximately 0.1 mD, simulating oil wells) and coal cores from gas well reservoirs (i.e., coal-gas well cores, simulating gas wells).

[0047] Experimental procedure: 1. Preparation of experimental solution Experimental solution A (for oil wells in this invention): Dilute sample A (containing 0.1% percolation displacement agent) from Example 1 with water at a ratio of 1:10.

[0048] Experimental solution B (for gas wells in this invention): Dilute sample C (containing 0.2% natural gas desorbent) from Example 1 with water at a ratio of 1:10.

[0049] Control solution C: Dilute 1.0% PAM stock solution (Comparative Example 1) with water at a ratio of 1:10.

[0050] 2. Core damage assessment Oil well core damage: Using tight sandstone cores, the original permeability K1 was measured. Then, experimental fluid A (0.5 times the pore volume) was injected into the tight sandstone core, and it was cured at reservoir temperature for 24 hours. Simulated formation water was used for reverse displacement, and the permeability K2 after damage was measured. The permeability recovery rate (K2 / K1) was calculated. Using the same method, control fluid C was used to evaluate the damage to the tight sandstone cores.

[0051] Damage to gas well cores: Using coal and rock gas well cores, the same method was used to evaluate the damage to the coal and rock gas well cores with experimental solution B and control solution C, respectively.

[0052] 3. Functional evaluation Percolation Displacement Rate (Oil Well): Static percolation displacement experiments were conducted using Amott bottles, and the displacement rate was measured over 120 hours. Specifically, the Amott bottle static percolation displacement experiment involved saturating the core with formation crude oil and then soaking the core in an Amott bottle with either experimental solution A or control solution C. The volume percentage of the oil phase percolated was recorded every 12 hours. The test results are shown below. Figure 2 .

[0053] Ransworth pressure rise rate (gas well): Ransworth pressure was tested using methane (purity ≥99.99%) and 80-100 mesh coal samples. After the coal samples and experimental fluid B were cured at the reservoir temperature for 24 hours, the methane adsorption curve was tested using a high-pressure adsorption instrument, and the Ransworth pressure rise rate was calculated.

[0054] The experimental results are shown in Table 3.

[0055] Table 3. Experimental Results of Core Damage Assessment and Functional Effects

[0056] Depend on Figure 2 As shown in Table 3, compared with the polymer-containing control solution C, the experimental solutions A and B of this invention exhibited lower damage to both oil well cores and gas well cores, and higher permeability recovery rates. Meanwhile, the mother solution for oil wells demonstrated excellent percolation and oil displacement capabilities (42.5%), while the mother solution for gas wells significantly increased the Randolph pressure of coal and rock (9.2%), proving that its pre-set functions were effectively utilized.

[0057] Example 4: Field Application Simulation This embodiment simulates the entire fracturing process of a coalbed methane well to verify the field operability of the present invention.

[0058] A target coalbed methane well, the target layer is a brittle coal seam with well-developed fractures.

[0059] 1. Preparation: Prepare 200 cubic meters of potassium formate high-density brine-based mother liquor (supporting agent concentration 40%, true density 1.22 g / cm³) in advance at the chemical plant. 3 (0.3% natural gas desorbent was added beforehand) and transported to the well site.

[0060] 2. On-site construction: Connect the high-shear online mixer and use a diaphragm pump to quantitatively pump the mother liquor and the fracturing flowback fluid collected on-site to mix in real time at a ratio of 1:8.

[0061] 3. Pumping procedure: at a rate of 4-6 m 3 The mixed fracturing fluid was pumped into the well at a flow rate of / min. The entire operation used 200 cubic meters of mother fluid, 1600 cubic meters of flowback fluid, and 80 cubic meters of proppant. The pressure remained stable throughout the operation without abnormal fluctuations, and the post-operation pressure drop curve showed good fracture closure.

[0062] In summary, the multifunctional polymer-free integrated reservoir stimulation mother liquor and its application method provided by this invention can safely, efficiently, and stably complete the fracturing stimulation of unconventional reservoirs without using any polymers. This solution demonstrates significantly superior performance compared to existing technologies in terms of simplifying the construction process, reducing reservoir damage, and precisely achieving enhanced production, possessing extremely high industrial application value and promising prospects for widespread adoption.

[0063] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A multifunctional polymer-free integrated reservoir modification mother liquor, characterized in that: The modified mother liquor is a high-density saline-based ultra-low-density proppant suspension system, which is composed of high-density saline and ultra-low-density proppant. The density of the high-density brine is 1.01–1.60 g / cm³. 3 The dissolved salts are at least one of potassium chloride, sodium chloride, potassium formate, sodium formate, potassium bromide, sodium bromide, sodium nitrate, and potassium nitrate. The true density of the ultra-low density proppant is 1.0–1.55 g / cm³. 3 The bulk density is 0.65–0.80 g / cm³. 3 ; The volume concentration of the ultra-low density proppant in the mother liquor is 10-90%; Wherein, the density of the high-density brine is greater than or equal to the true density of the ultra-low-density proppant.

2. The multifunctional polymer-free integrated reservoir modification mother liquor according to claim 1, characterized in that: The high-density brine also contains 0.1 to 10.0% clay stabilizer by weight of the brine, wherein the clay stabilizer is at least one of polyamines and quaternary ammonium salts.

3. The multifunctional polymer-free integrated reservoir modification mother liquor according to claim 1, characterized in that: The high-density brine also contains drag-reducing surfactants at a weight of 0.1% to 10.0% of the brine.

4. The multifunctional polymer-free integrated reservoir modification mother liquor according to claim 1, characterized in that: The high-density brine also contains functional additives pre-added according to the well type: For oil well reservoirs, the functional additive is a permeation displacement agent comprising 0.05–10% of the brine weight; For gas well reservoirs, the functional additive is a natural gas desorbent comprising 0.05 to 10% of the brine weight.

5. The multifunctional polymer-free integrated reservoir modification mother liquor according to claim 1, characterized in that: The ultra-low density proppant is composed of 6-400 mesh spherical particles constructed using thermosetting resin.

6. A method for preparing a multifunctional polymer-free integrated reservoir modification mother liquor as described in any one of claims 1 to 5, characterized in that: Specifically, the steps include the following: Step S1: Dissolve the salts in water to prepare a solution with a density of 1.01–1.60 g / cm³. 3 High-density brine; Step S2: According to the target well type, add the corresponding functional additives, clay stabilizers and drag-reducing surfactants to the high-density brine prepared in step S1, and mix evenly to obtain a brine mixture. Step S3: Add the ultra-low density proppant to the brine mixture obtained in step S2 at a volume concentration of 10-90%, and stir at low speed to form a homogeneous suspension mother liquor.

7. The method for preparing a multifunctional polymer-free integrated reservoir modification mother liquor according to claim 6, characterized in that: In step S2, the addition of the corresponding functional additive according to the target well type specifically involves: For oil well reservoirs, the functional additive is a permeation displacement agent comprising 0.05–10% of the brine weight; For gas well reservoirs, the functional additive is a natural gas desorbent comprising 0.05 to 10% of the brine weight.

8. The application of a multifunctional polymer-free integrated reservoir modification mother liquor as described in any one of claims 1 to 5, characterized in that: The application of the modified mother liquor in fracturing of unconventional reservoirs; the unconventional reservoirs include coalbed methane reservoirs and tight oil and gas reservoirs; for oil well reservoirs, a modified mother liquor pre-added with a permeation displacement agent is used; for gas well reservoirs, a modified mother liquor pre-added with a natural gas desorbent is used.

9. The application of the multifunctional polymer-free integrated reservoir modification mother liquor according to claim 8, characterized in that: When the modified mother liquor is used on-site, the following steps are included: Step (1): Transport the pre-prepared suspension modification mother liquor to the fracturing construction site; Step (2): The suspension modification mother liquor is quantitatively pumped in using a hose pump or diaphragm pump and mixed and diluted with on-site water at a volume ratio of 1:1 to 1:100 to form a fracturing working fluid that can be directly pumped in. Step (3): The diluted fracturing working fluid is injected into the target reservoir through a high-pressure fracturing pump truck unit to carry out fracturing operations.

10. The application of the multifunctional polymer-free integrated reservoir modification mother liquor according to claim 9, characterized in that: In step (2), the mixing and dilution process is completed by an online dynamic mixing device, which is a high-shear mixer or a static mixer; the on-site water source is at least one of clean water, seawater, formation water or fracturing flowback fluid.

Images