Composite surfactant for relieving damage of unconventional reservoir water seepage shield and preparation method and application thereof

Abstract

This invention belongs to the field of oilfield chemistry and enhanced oil recovery technology, specifically relating to a composite surfactant for mitigating water shield damage in unconventional reservoirs, its preparation method, and its application. The composite surfactant is composed of an amphoteric surfactant, anionic surfactant, and water; or an amphoteric surfactant, fluorocarbon surfactant, biological surfactant, and water; or a combination of an amphoteric surfactant, anionic surfactant, fluorocarbon surfactant, biological surfactant, and water. This invention reduces the oil-water interfacial tension to 10 at a composite surfactant concentration of 0.3wt%~0.5wt%. ‑3 mN / m, reverses the contact angle of the rock surface from <30° to 90°~120°, withstands temperatures up to 120℃, and has a mineralization resistance of up to 100,000mg / L. Effectively breaks down the water phase Jamin effect in the micro-nano pore throat, enabling the permeability recovery rate of dense rock cores to exceed 89%.

Description

Technical Field

[0001] This invention belongs to the field of oilfield chemistry and enhanced oil recovery technology, specifically involving a composite surfactant for resolving water-absorbing shield damage in unconventional oil reservoirs, its preparation method, and its application. The composite surfactant for resolving water-absorbing shield damage in unconventional oil reservoirs is an environmentally friendly nanocomposite surfactant that effectively treats the "water-absorbing shield" damage generated during hydraulic fracturing in unconventional oil reservoirs (tight oil, shale oil). This invention also relates to the preparation process of the composite surfactant and its application method in high-temperature and high-salinity oil reservoir environments. Background Technology

[0002] With the growth of global energy demand and the increasing depletion of conventional oil and gas resources, unconventional oil and gas resources, represented by tight oil and shale oil, have become an expansion area for energy development. The main characteristics of unconventional reservoirs are tight reservoirs, low porosity (typically <10%), extremely low permeability (typically <0.1 mD), and pore throat sizes mostly distributed in the nanometer to micrometer range. To obtain industrial oil flows, horizontal well staged multi-cluster volumetric fracturing has become an indispensable development method.

[0003] Technical Problem Analysis: During volumetric fracturing, tens of thousands of cubic meters of fracturing fluid, using water as the medium, are pumped into the formation under high pressure. During the initial well shutdown and reopening phases after fracturing, the extremely fine pores and throats of the reservoir matrix generate enormous capillary suction. A large amount of fracturing fluid filtrate spontaneously penetrates deep into the micropores of the matrix under capillary force. However, when the flowback production stage begins, this force that initially drove the water phase in instantly transforms into enormous resistance.

[0004] Water film retention and the Jamin effect: Due to the strong hydrophilicity (water-wet) of most dense rock surfaces, infiltrating water phases form a strong adsorbed water film on the pore throat walls, drastically reducing the effective pore throat radius. Formation of the immersion water shield: Retained water phases form continuous or discontinuous liquid phase barriers near fracture zones and deep within the matrix, the so-called "immersion water shield." This barrier cuts off the flow path of crude oil from the matrix to the fractures, leading to a decrease in oil phase permeability of 70%-90% or more, and even causing "water lock" in the well, resulting in production shutdown.

[0005] Limitations of existing technologies: Currently, the petroleum industry mainly relies on traditional surfactants and discharge aids to treat this type of aqueous phase damage, but these technologies have the following significant drawbacks: (1) Simple mechanism: Most commercially available drainage aids (such as polyethers and alcohols) reduce capillary resistance by reducing the interfacial tension (IFT) of gas / liquid or oil / liquid. However, in nanoscale pore throats, reducing the IFT to 20mN / m~30mN / m is far from enough to overcome the huge Jamin effect resistance.

[0006] (2) Weak wetting reversal ability: Traditional hydrocarbon surfactants are difficult to change the strong hydrophilicity of the rock surface and cannot destroy the water film attached to the pore wall, resulting in the water phase being "easy to enter but difficult to exit".

[0007] (3) The contradiction between environmental protection and cost: Fluorocarbon surfactants with excellent wetting and reversing ability (especially C8 long-chain structures, such as PFOS / PFOA) have been banned by major global environmental regulations (such as the Stockholm Convention) due to their bioaccumulation and toxicity. While short-chain fluorocarbon surfactants are environmentally friendly, they have low activity when used alone, require large amounts, and are extremely expensive.

[0008] (4) Poor temperature and salt resistance: Unconventional reservoirs are often accompanied by high temperature (>80℃) and high salinity (>50,000mg / L). Ordinary ionic surfactants are prone to precipitation or phase separation, leading to failure and even secondary damage. Summary of the Invention

[0009] To address the shortcomings of existing technologies, this invention provides a composite surfactant for overcoming the damage caused by the water absorption shield in unconventional oil reservoirs, along with its preparation method and applications. This invention offers a novel composite surfactant system capable of simultaneously achieving both "ultra-low interfacial tension" and "wetting reversal from hydrophilic to neutral / weakly hydrophobic," utilizing a dual mechanism of "ion-pair hydrophobic effect" and "competitive adsorption-wetting reversal." Furthermore, it possesses excellent temperature and salt resistance and environmental friendliness, thereby completely breaking down the "water absorption shield." This solves the industry pain point that existing drainage aids cannot simultaneously address deep-seated blockage removal and environmentally friendly, low-cost solutions, overcoming the technical deficiencies of traditional surfactant drainage aids in the aforementioned technologies.

[0010] The primary objective of this invention is to provide a composite surfactant that can overcome the damage caused by the water shield in unconventional reservoirs. This composite surfactant can achieve ultra-low interfacial tension (10 wt%) at extremely low concentrations (0.3wt%-0.5wt%). -3 The invention also aims to provide a method for preparing this composite surfactant and its application in oilfields. The contact angle of the rock surface is completely reversed from strongly hydrophilic (<30°) to neutral / weakly hydrophobic (90°~120°).

[0011] To achieve the above technical objectives, this invention employs a molecular structure design and a multi-component compound synergistic strategy. The specific technical solution is as follows:

[0012] This invention protects a composite surfactant for relieving water shield damage in unconventional oil reservoirs. The composite surfactant for relieving water shield damage in unconventional oil reservoirs comprises the following raw materials in the following mass percentages: 0.1%~0.8% amphoteric surfactant, 0.05%~0.6% anionic surfactant, and water, wherein the sum of the mass percentages of each raw material is 100%.

[0013] Alternatively, the composite surfactant that relieves the damage caused by water seepage shield in unconventional reservoirs may consist of the following raw materials by mass percentage: 0.1% to 0.8% amphoteric surfactant, 0.01% to 0.4% fluorocarbon surfactant, 0.01% to 0.3% bio-surfactant, and water, with the sum of the mass percentages of each raw material being 100%.

[0014] Alternatively, the composite surfactant that can resolve the damage caused by water seepage shield in unconventional reservoirs may consist of the following raw materials by mass percentage: 0.1%~0.8% amphoteric surfactant, 0.05%~0.6% anionic surfactant, 0.01%~0.4% fluorocarbon surfactant, 0.01%~0.3% bio-surfactant, and water, with the sum of the mass percentages of each raw material being 100%.

[0015] The aforementioned composite surfactant, which relieves the damage caused by the water seepage shield in unconventional reservoirs, can reduce the interfacial tension between oil and water to below 0.05 mN / m within a temperature range of 25°C to 90°C, and transform the contact angle of water-wettable rock surfaces from less than 30° to a neutral or weakly hydrophobic state within the range of 90° to 120°.

[0016] Preferably, the mass ratio of amphoteric surfactant to anionic surfactant is 1 to 6:1. More specifically, the mass ratio of amphoteric surfactant to anionic surfactant is 2 to 4:1. At this ratio, the two surfactants attract each other electrostatically to form a tightly packed pseudo-gemini surfactant complex.

[0017] Preferably, the amphoteric surfactant is selected from at least one of amine oxide compounds, betaine compounds, and imidazoline compounds; specifically, it is selected from at least one of dodecyl dimethylamine oxide (DDAO), tetradecyl dimethylamine oxide (TDAO), cocamidopropyl hydroxysulfonyl betaine (CHSB), and dodecyl betaine (BS-12). More specifically, the amphoteric surfactant is dodecyl dimethylamine oxide (DDAO), with the structural formula C... 12 H 25 N + (CH3)2O - It can be protonated and exhibit cationic characteristics in weakly acidic to neutral formation water environments.

[0018] Preferably, the anionic surfactant is a branched secondary alkyl sulfonate (SAS); specifically, the anionic surfactant is selected from sodium branched secondary alkyl sulfonate (SATRO), sodium dodecyl sulfate (SDS), or sodium fatty alcohol polyoxyethylene ether sulfate (AES). Further, the anionic surfactant has a carbon chain length of C0.05. 13 ~C 17 Sodium secondary alkyl sulfonate (SAS-60) within the range, this molecule has a multi-point hydrophobic branched structure, used to maintain the microemulsion phase behavior of the system under high mineralization.

[0019] Preferably, the fluorocarbon surfactant is selected from short-chain perfluoroalkyl sulfonamide derivatives, perfluoroalkyl carboxylates, or perfluoroalkyl betaines, and its perfluorocarbon chain length C0 is [not specified]. n F 2n+1 In this context, n ≤ 4. Furthermore, the fluorocarbon surfactant is sodium perfluorobutyl sulfonyl aminopropionate (FC-1) or perfluorobutyl sulfonyl polyoxyethylene ether; the fluorocarbon surfactant of this invention does not contain perfluorooctane sulfonic acid (PFOS) or perfluorooctanoic acid (PFOA) and their salts, and complies with environmental emission standards.

[0020] Preferably, the biosurfactant is a glycolipid biosurfactant; specifically, it is selected from sophorolipid, rhamnolipid, or trehalolipid; further, the biosurfactant is sophorolipid (BS-2), and is a mixture of acidic sophorolipid and lactone sophorolipid, wherein the mass percentage of lactone sophorolipid is not less than 60%.

[0021] Preferably, the composite surfactant for relieving damage from the water-absorbing shield in unconventional reservoirs further includes a synergist selected from at least one of acetylenic diol nonionic surfactants, short-chain alcohols, and inorganic salts. The synergist accounts for 0.05% to 0.3% by mass of the composite surfactant for relieving damage from the water-absorbing shield in unconventional reservoirs. Specifically, the synergist is selected from 2,4,7,9-tetramethyl-5-decyn-4,7-diol (TMDD) or its ethoxylated derivative, used to reduce the dynamic surface tension of the system and eliminate microfoam clogging.

[0022] This invention also protects a method for preparing a composite surfactant that can mitigate the damage caused by the water shield in unconventional reservoirs, comprising the following steps: Base solution preparation: Add 60% to 80% of the total mass of the formula of deionized water to the reaction vessel, heat to 45℃ to 55℃, and start stirring (300 rpm to 500 rpm).

[0023] Main agent formulation: Slowly add the anionic surfactant and amphoteric surfactant sequentially, stirring continuously for 30-60 minutes until the solution is completely clear and transparent, forming a homogeneous ion-pair micelle solution. If both are added simultaneously or mixed too quickly, the high concentration of positive and negative charges will instantly "clump together," forming insoluble white flocculent precipitates or high-viscosity gel clusters; for example, milk poured instantly into lemon juice will clump.

[0024] Post-treatment: Add the remaining water, adjust the pH of the ion-pair micelle solution to 6.5~8.0, and filter through a 0.5μm~1.0μm filter element to obtain a composite surfactant that can relieve the damage caused by the non-conventional reservoir water absorption shield.

[0025] The purpose of adjusting the pH value is to "balance chemical stability" and "maintain active structure," specifically: 1) Preventing the decomposition of anionic surfactants (specifically for SDS): Sodium dodecyl sulfate (SDS) in the formulation is a sulfate ester salt. If the pH is too low (strongly acidic, <5), SDS is highly susceptible to acid-catalyzed hydrolysis, decomposing into dodecyl alcohol and sodium bisulfate, leading to product stratification and failure. 2) Ensuring the protonation potential of DDAO: DDAO requires a neutral / slightly acidic environment to protonate and become positively charged. Controlling the pH of the finished product at 6.5~8.0 ensures that after injection into the formation (typically, formation water pH is 6~7), the product can quickly respond to environmental changes and activate the "ion pairing" mechanism.

[0026] The advantage of obtaining small particle size is to ensure "injectability" and "harmless passage capability" in tight reservoirs, specifically: 1) Matching nanoscale pore throats: The pore throat diameter of rocks in unconventional oil reservoirs (tight oil, shale oil) is very small, usually between tens of nanometers and a few micrometers. If the fluid contains large particles larger than 1.0 μm, these particles will block the pores on the rock surface during injection, preventing the agent from penetrating deep into the formation. 2) Eliminating the physical premise of the "Jamin effect": The core function of the product of this invention includes reducing the Jamin effect (bubble / droplet blockage). If the agent itself contains large-diameter impurities, it will artificially cause solid particle blockage, which runs counter to the original intention of "unblocking".

[0027] This invention also protects a method for preparing a composite surfactant that can mitigate the damage caused by the water shield in unconventional reservoirs, comprising the following steps: Base solution preparation: Add 60% to 80% of the total mass of the formula of deionized water to the reaction vessel, heat to 45℃ to 55℃, and start stirring (300 rpm to 500 rpm).

[0028] Main agent compounding: Lower the temperature to below 40℃, add fluorocarbon surfactants and biological surfactants to the water, and mix evenly.

[0029] Post-treatment: Add the remaining water, adjust the pH to 6.5~8.0, and filter through a 0.5μm~1.0μm filter element to obtain a composite surfactant that can relieve the damage caused by the non-conventional reservoir water absorption shield.

[0030] This invention also protects a method for preparing a composite surfactant that can mitigate the damage caused by the water shield in unconventional oil reservoirs. The preparation method is summarized as follows: heating the solvent → cooling → adding biological / auxiliary agents → adding fluorocarbons → adjusting pH. It encompasses the most complex "full-component" formulation design and includes the following steps: Base solution preparation: Add 60% to 80% of the total mass of the formula of deionized water to the reaction vessel, heat to 45℃ to 55℃, and start stirring (300 rpm to 500 rpm).

[0031] Main agent compounding: Slowly add anionic surfactant and amphoteric surfactant in sequence, and stir continuously for 30 min to 60 min until the solution is completely clear and transparent, forming a homogeneous ion-pair micelle solution.

[0032] Functional modification: The temperature is lowered to below 40℃, and a bio-based surfactant and synergist are added to the ion-pair micelle solution. The mixture is stirred at low speed (100-200 rpm) for 15-30 minutes to obtain a functionalized ion-pair micelle solution. Here, "modification" does not refer to a chemical reaction to generate new substances, but rather to the physical restructuring of the microstructure. The added bio-based surfactant (macromolecule head group) and synergist (rigid spacer group) act like "parts," inserting / embedding themselves into the interstices of the ion-pair micelles, thus forming a "hybrid micelle." This new micelle retains the "ultra-low tension" of the ion pair while acquiring the "wetting reversal" function of the biomolecule and the "dynamic wetting" speed of the synergist (acetylenic diol), achieving multiple benefits that a single molecule cannot.

[0033] Fluorocarbon synergistic effect: Add fluorocarbon surfactants dropwise to the functionalized ion-pair micelle solution and stir for 20-40 minutes to ensure no oil floating or precipitation occurs.

[0034] Post-treatment: Add the remaining water, adjust the pH to 6.5~8.0, and filter through a 0.5μm~1.0μm filter element to obtain a composite surfactant that can relieve the damage caused by the non-conventional reservoir water absorption shield.

[0035] This invention also protects the application of composite surfactants that can overcome the damage caused by water seepage shields in unconventional reservoirs in enhancing production in unconventional reservoirs.

[0036] Preferred method for applying composite surfactants that overcome water shield damage in unconventional reservoirs to enhance production includes the following steps: Obtain core samples and formation water samples from the target reservoir, and determine formation temperature, formation water salinity, and original rock wettability.

[0037] The permeability recovery value was measured by core displacement experiments, and the permeability recovery rate was calculated. The response surface methodology was used to establish a mathematical model of the permeability recovery rate of the core sample and the concentration, temperature, and salinity of the composite surfactant for solving the water absorption shield damage of unconventional reservoirs. The optimal concentration of the composite surfactant for the target reservoir was calculated, which is usually between 0.3wt% and 0.7wt%.

[0038] Composite surfactants that can resolve the damage caused by water seepage shields in unconventional reservoirs are injected into the formation as pre-flush fluids, slickwater fracturing fluid additives, or well-clogging replacement fluids.

[0039] After injection, a well-shutting operation is carried out for 24 to 72 hours. The spontaneous diffusion and adsorption of composite surfactant molecules that can remove the "water-absorbing shield" in the pore throat are utilized to remove the damage caused by the non-conventional reservoir water-absorbing shield.

[0040] Wells were opened and the wastewater was returned to the source to restore production capacity.

[0041] Preferably, the target reservoir has a permeability of less than 1×10⁻⁶. -3 μm 2 Tight sandstone reservoirs, shale reservoirs, or tight carbonate reservoirs; formation water salinity ranges from 10,000 mg / L to 150,000 mg / L.

[0042] The composite surfactant, used at a concentration of 0.3wt%-0.5wt%, reduces the oil-water interfacial tension to 10. -3 mN / m, and reversed the contact angle of the rock surface from <30° to 90°~120°, with a temperature resistance of up to 120℃ and a mineralization resistance of up to 100,000mg / L, breaking down the water phase Jamin effect in the micro-nano pore throat, and enabling the permeability recovery rate of dense rock cores to exceed 89%.

[0043] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The composite surfactant of this invention, which solves the damage of water-absorbing shield in unconventional reservoirs, is based on molecular dynamics simulation and response surface optimization design. It is composed of amphoteric surfactants, anionic surfactants and water. Based on molecular dynamics simulation and response surface optimization design, it was first verified how amphoteric surfactants (such as DDAO) and anionic surfactants (such as SDS or SAS) overcome repulsion through electrostatic attraction. Thus, the feasibility of this closely arranged "pseudo-gemini" supramolecular structure was theoretically established, and then the surfactant combination was carried out.

[0044] In this invention, the principle of component selection and the synergistic mechanism are as follows: 1) Synergistic effect of zwitterionic-anion pairs (DDAO+SAS): The dodecyl dimethylamine oxide (DDAO) selected in this invention undergoes partial protonation under reservoir conditions (typically pH 5-7), becoming positively charged and exhibiting strong electrostatic attraction with negatively charged branched secondary alkyl sulfonate sodium (SAS). This interaction eliminates the repulsive force between like-charged head groups, resulting in an extremely close molecular arrangement at the oil-water interface, forming a structure similar to a "pseudo-Gemini." Here, the "molecule" in "pseudo-Gemini" does not refer to a single raw material molecule, but rather a supramolecular structural unit, an ion-pair complex formed by the electrostatic attraction between protonated DDAO and SAS anions.

[0045] Effect: This dense interfacial film can significantly reduce the oil-water interfacial tension (IFT) from the conventional 1mN / m~10mN / m to 10mN / m. -3 The ultra-low mN / m level greatly reduces capillary resistance, making it easier for oil droplets to deform and pass through narrow pore throats.

[0046] The special characteristics of SAS: Branched SAS is chosen instead of straight-chain sulfonates because the branched structure not only has better solubility, but also is more resistant to high-valence cations (Ca) under the steric hindrance of macromolecules. 2+ Mg 2+ This prevents precipitation under high mineralization conditions.

[0047] 2) Fluorocarbon-biological dual wetting regulation (FC-1+BS-2): FC-1 (C4 Fluorocarbon): Utilizing a short-chain C4 perfluorobutyl derivative, it meets environmental requirements while retaining the extremely low surface energy characteristic of fluorocarbon chains. FC-1 molecules preferentially adsorb onto high-energy sites on rock surfaces, forming a fluorinated hydrophobic film that significantly improves the contact angle.

[0048] BS-2 (Sophorolipid): As a glycolipid biosurfactant, sophorolipid has a unique lactone ring structure and hydroxy fatty acid chain. It is not only environmentally friendly, but also capable of co-adsorption with fluorocarbon molecules at the solid-liquid interface, filling the gaps between fluorocarbon molecules and making the wetting reversal layer denser and more stable.

[0049] Effect: Through the synergy of both, the rock surface is transformed from strongly hydrophilic (contact angle <30°) to neutral to weakly hydrophobic (contact angle 90°-120°). This change in wettability disrupts the continuity of the water film, causing it to shrink into discrete water droplets, eliminating the self-absorption force of the aqueous phase, and making it easier for water to be carried away by the oil flow.

[0050] 3) Synergistic adjuvants: The introduction of thyne diol (TMDD) is to address the dynamic surface tension problem. In the high-speed flow of fracturing flowback, the interface is constantly being renewed. TMDDD molecules are small and diffuse rapidly, quickly occupying the newly formed interface and preventing microbubble blockage (microfoam damage) caused by the delayed diffusion of composite surfactants.

[0051] 2. This invention innovatively utilizes a dual mechanism of "ion-pair hydrophobic effect" and "competitive adsorption-wetting reversal" to reduce the oil-water interfacial tension to 10 at extremely low concentrations (0.3wt%-0.5wt%). -3 The surfactant exhibits an ultra-low mN / m concentration and completely reverses the contact angle of the rock surface from strongly hydrophilic (<30°) to neutral to slightly hydrophobic (90°-120°). Experiments have confirmed that this composite surfactant is temperature resistant up to 120℃ and mineralization resistant up to 100,000 mg / L, effectively breaking down the Jamin effect in the aqueous phase of micro- and nano-pore throats, resulting in a permeability recovery rate exceeding 89% for dense cores. This invention addresses the industry pain point of existing drainage aids failing to simultaneously address deep unblocking and environmentally friendly, low-cost operations, and has significant industrial value for improving unconventional oil and gas recovery.

[0052] Dual-effect combined, with a thorough mechanism: This invention simultaneously achieves "reducing capillary resistance (reducing tension)" and "eliminating self-absorption power (wetting reversal)," fundamentally destroying the physicochemical basis of the existence of the seepage and absorption shield.

[0053] Environmental compliance: The entire formula is free of APEO (alkylphenol polyoxyethylene ether) and long-chain fluorocarbons (PFOS / PFOA), has good biodegradability (LD50>2000mg / kg), and complies with increasingly stringent oilfield environmental regulations.

[0054] High tolerance: The composite surfactant can withstand high temperatures of 120℃ and a mineralization of 100,000 mg / L (containing Ca). 2+ Mg 2+ It remains clear and transparent under certain conditions, and its interfacial activity does not decrease, thus solving the problem that traditional agents are not resistant to temperature and salt.

[0055] Significantly increased production: Core experiments show that the permeability recovery value of dense cores treated with the composite surfactant of this invention can reach more than 89.7%, which is significantly higher than that of conventional drainage aids (usually 50%~70%). Attached Figure Description

[0056] Figure 1 A comparison diagram of the mechanism of wettability reversal on rock surface and droplet morphology.

[0057] Figure 2 Diagram illustrating the damage mechanism of a water-absorbing shield. Detailed Implementation

[0058] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0059] Raw material description: DDAO: Dodecyl dimethylamine oxide, industrial grade, solid content 30%.

[0060] SATRO (SAS-60): Branched secondary alkyl sulfonate sodium salt, carbon chain C 14 ~C 17 Industrial grade, 60% solids content.

[0061] SDS: Sodium dodecyl sulfate, chemically pure.

[0062] FC-1: Sodium perfluorobutylsulfonylaminopropionate, self-made or purchased from DuPont / 3M alternatives, 25% solids content.

[0063] BS-2: Sophorolipid, purified from fermentation products, with 65% lactone content and 50% solid content.

[0064] Alkyne diol: Surfynol 104 or similar products.

[0065] The technical solution of the present invention will be studied below with reference to experimental examples. The specific research methods and results are as follows: This invention aims to resolve two core contradictions: "ultra-low interfacial tension" vs. "wetting reversal," and "high performance" vs. "low cost / environmental friendliness." To demonstrate that each component indeed achieves the aforementioned effects, experimental examples and test cases were designed to target specific "functional modules," rather than adding everything each time, as shown in Table 1.

[0066] Table 1. Experimental Examples and Reasons for Experimental Example Design The processes in Experimental Example 1 and Example 2 were tailored to the specific materials added. In Experimental Example 1 and Example 2, since the formulation did not contain heat-sensitive bio-surfactants (BS-2) and poorly dispersible fluorocarbons (FC-1), the process ended after the solution became clear, without the need for subsequent complex low-temperature steps. In Experimental Example 2, since the formulation did not contain amphoteric surfactants (DDAO), the "amphoteric-anionic compounding" step was not required, and the anionic surfactant (SATRO) could be dissolved directly. However, since it contained heat-sensitive components, the core temperature control logic of "cooling down - adding bio- / fluorocarbons" was retained.

[0067] Example 1 A method for preparing a composite surfactant to resolve water absorption shield damage in unconventional reservoirs, with preferred formulation L1 (focusing on stress reduction), includes the following steps: Formulation composition (by weight percentage): DDAO: 0.3%, SDS: 0.05%, acetylacetonate diol: 0.1%, water: balance (99.55%).

[0068] Preparation process: Add water to the reactor and heat to 45°C; then add SDS and stir to dissolve for 20 minutes; then add DDAO and stir for 30 minutes until the solution is clear; cool to 30°C, add acetylacetonate diol, and stir until homogeneous to obtain the final product. This formulation has extremely low cost and is suitable for low-water-content oil reservoirs.

[0069] Example 2 A method for preparing a composite surfactant to resolve water shield damage in unconventional reservoirs, with preferred formulation L2 (comprehensive performance + tolerance), includes the following steps: Formula composition (by weight): DDAO: 0.2%, SATRO (SAS-60): 0.3%, SDS: 0.05%, Water: balance (99.45%).

[0070] Preparation process: Water is added to the reactor and heated to 45°C; then SDS is added and stirred to dissolve for 20 min; DDAO is then added and stirred for 30 min until the solution is clear; the temperature is lowered to 30°C, SATRO (SAS-60) is added, and the mixture is stirred until homogeneous. This formulation introduces SATRO (SAS-60), which has better salt tolerance, to replace acetylacetonate diol and part of DDAO, enhancing stability at a mineralization of 40,000 mg / L, and further reducing IFT by utilizing its branched structure.

[0071] Experimental Example The preparation method of the composite surfactant, L3 (focusing on wetting reversal and environmental protection), includes the following steps: Formulation composition (by weight percentage): FC-1 (fluorocarbon): 0.05%, BS-2 (sophorolipid): 0.2%, SATRO: 0.3%, water: balance (99.45%).

[0072] Preparation process: Add water to the reaction vessel and heat to 45°C; then add SATRO and stir to dissolve for 20 minutes until the solution is clear; cool to 30°C, add BS-2 and FC-1, and stir until homogeneous to obtain the final product.

[0073] Example 3 A method for preparing a composite surfactant to resolve water absorption shield damage in unconventional reservoirs, comprising the following steps: Formulation composition (by weight percentage): DDAO: 0.2%, SATRO (SAS-60): 0.3%, SDS: 0.05%, FC-1 (fluorocarbon): 0.05%, BS-2 (sophorolipid): 0.2%, acetylacetonate: 0.1%, water: balance (0.91%).

[0074] Preparation process: Water is heated to 40℃ and then mixed evenly with DDAO, SATRO and SDS to form a homogeneous ion-pair micelle solution; the temperature is lowered to below 40℃, sophorolipid and acetylacetic diol are added to the ion-pair micelle solution and mixed evenly to obtain a functionalized modified ion-pair micelle solution; FC-1 is added dropwise to the functionalized modified ion-pair micelle solution, mixed evenly, and the pH value is adjusted to 8.0. The solution is then filtered through a 1.0μm filter to obtain a composite surfactant that can relieve the damage caused by the non-conventional reservoir water absorption shield.

[0075] Example 4 A method for preparing a composite surfactant to resolve water shield damage in unconventional reservoirs, with preferred formulation L3 (emphasizing wetting reversal and environmental friendliness), includes the following steps: Formula composition (by weight percentage): DDAO: 0.3%, FC-1 (fluorocarbon): 0.05%, BS-2 (sophorolipid): 0.2%, water: balance (99.45%).

[0076] Preparation process: Add water to the reactor and heat to 45℃; then add DDAO and stir to dissolve for 20 minutes until the solution is clear; cool to 30℃, add BS-2 and FC-1, and stir until homogeneous. This formulation is specifically designed for the wettability modification of strongly hydrophilic rocks while maintaining good environmental performance.

[0077] The following is a performance evaluation of composite surfactants for relieving water shield damage in unconventional reservoirs: Test conditions: Simulated formation water: mineralization 40,141 mg / L (CaCl2 type water quality), containing Ca 2+ The amount was 1935 mg / L.

[0078] Simulated oil: a mixture of degassed crude oil and kerosene, with a viscosity of 11.0 mPa·s at 70°C.

[0079] Temperature: 70℃.

[0080]

Test Example 1

[0081] Table 2. Results of interfacial tension test (70℃) The results show that Examples 1 and 2 successfully reduced the interfacial tension to 10 by utilizing the ion-pairing effect of DDAO and the anionic surfactant. -2 The order of magnitude. While the experimental examples using only fluorocarbon surfactants and biological surfactants showed high surface activity, they were not as effective as the combined systems of Examples 1 and 2 in reducing oil-water interfacial tension.

[0082]

Test Example 2

[0083] Table 3 Contact Angle Test Results The results in Table 3 show that Example 1 increased the contact angle from 23° to 104.99°, which is the ideal wetting state for removing the water absorption shield (neutral wetting, neither strongly hydrophilic nor strongly oleophilic, with minimal fluid flow resistance).

[0084] [Test Example 3] Core Permeability Recovery Experiment: According to the provisions of GB / T29172-2012 "Core Analysis Methods", tight cores with similar permeability were selected. First, a "water shield" damage model was established by high-pressure displacement with simulated formation water for 24 hours, and the permeability K2 after damage was measured. Then, a water shield removal agent was used for displacement, and the permeability K3 after recovery was measured. The measurement results are shown in Table 3.

[0085] Table 4 Comparison of Core Permeability Recovery Rate Table 4 Conclusion: The data irrefutably proves that water displacement alone cannot remove the water shield (recovery rate is only 21%). However, Example 2 (L2 formulation) of the present invention can restore the permeability to 89.7% of the original level, proving that it can effectively destroy the water film and liquid plug in the pore throat and clear the oil and gas channels.

[0086]

Test Example 4

[0087] Experimental conditions: The formulation solution was sealed in a deoxygenated high-temperature and high-pressure ampoule and aged continuously for 30 days in a 120°C constant temperature oven.

[0088] Evaluation criteria: Observe the changes in appearance and measure the oil-water interfacial tension (IFT) before and after aging.

[0089] Table 5. High-temperature aging test data of the composite surfactant in Example 2 at 120℃ Table 6. High-temperature aging test data of the composite surfactant in Example 1 at 120℃ Table 7. High-temperature aging test data of the composite surfactant in the experimental example at 120℃ Experiments have shown that all three formulations can withstand temperatures up to 120℃.

[0090]

Test Example 5

[0091] Experimental conditions: Prepare simulated water with different mineralization (NaCl + CaCl2).

[0092] Evaluation indicators: Whether the formulation solution of Example 2 is turbid / precipitated (phase stability) and interfacial tension value.

[0093] Table 8. Solubility and interfacial activity of the composite surfactant in brine with different salinity in Example 2 [Application Example] Process optimization using response surface methodology: To guide field applications, this invention further utilizes the Box-Behnken Response Surface Method (RSM) to establish a second-order regression model between the permeability recovery value (Y) and formation mineralization (A), temperature (B), and reagent concentration (C) using the formulation of Example 2.

[0094] The model equations are: Y=-863.0611+0.000973×A+25.34961×B+189.87095×C-2.71820×10 -7 ×A×B+3.74065×10 -7 ×A×C-0.000748×B×C-1.50761×10 -8 ×A 2 -0.180304×B2 -187.33167×C 2 ; The optimal on-site construction process parameters calculated based on this model are: Drug concentration: 0.43wt% (ensuring effectiveness while saving costs).

[0095] Applicable temperature range: 65℃~75℃ (optimal point 74.8℃).

[0096] Applicable mineralization: 30,000-40,000 mg / L (optimal point: 34,724 mg / L).

[0097] Under these conditions, the predicted permeability recovery value can reach 90.5%.

[0098] This optimization provides precise guidance for oilfield engineers in preparing solutions, avoiding the cost waste caused by blindly increasing the concentration.

[0099] In summary, this invention provides a "water absorption shield" treatment technology with a clear mechanism, scientific formulation, detailed data, and high environmental efficiency. Through special molecular structure design and compounding, it successfully overcomes the problems of difficult and short-lasting treatment of water phase damage in tight oil reservoirs, demonstrating broad prospects for industrial application. Based on the technical inspiration provided by this invention, and as common knowledge in the field, any changes, modifications, additions, or substitutions made by those skilled in the art within the scope of this invention should also be considered within the protection scope of this invention.

Claims

1. A composite surfactant for relieving water shield damage in unconventional oil reservoirs, characterized in that, The composite surfactant for mitigating water shield damage in unconventional reservoirs comprises the following raw materials by mass percentage: The ingredients are 0.1%~0.8% amphoteric surfactant, 0.05%~0.6% anionic surfactant, and water, with the sum of the mass percentages of each ingredient being 100%; wherein the mass ratio of amphoteric surfactant to anionic surfactant is 1~6:

1. Alternatively, a complex surfactant that resolves water shield damage from unconventional reservoirs may consist of the following raw materials by mass percentage: The ingredients are: 0.1%~0.8% amphoteric surfactant, 0.01%~0.4% fluorocarbon surfactant, 0.01%~0.3% bio-surfactant, and water, with the sum of the mass percentages of all ingredients being 100%. Alternatively, a complex surfactant that resolves damage from water-absorbing shields in unconventional reservoirs may comprise the following raw materials by mass percentage: The ingredients are: 0.1%~0.8% amphoteric surfactant, 0.05%~0.6% anionic surfactant, 0.01%~0.4% fluorocarbon surfactant, 0.01%~0.3% bio-surfactant, and water, with the sum of the mass percentages of all raw materials being 100%; wherein the mass ratio of amphoteric surfactant to anionic surfactant is 1~6:

1. The amphoteric surfactant is at least one of amine oxide compounds, betaine compounds, and imidazoline compounds; the anionic surfactant is selected from secondary alkyl sulfonates with branched chain structures.

2. The composite surfactant for resolving water shield damage in unconventional reservoirs according to claim 1, characterized in that, The amphoteric surfactant is selected from dodecyl dimethylamine oxide, tetradecyl dimethylamine oxide, cocamidopropyl hydroxysulfonate betaine, or dodecyl betaine.

3. The composite surfactant for resolving water shield damage in unconventional reservoirs according to claim 1, characterized in that, The anionic surfactant is selected from branched secondary alkyl sulfonate sodium, dodecyl sulfate sodium, or fatty alcohol polyoxyethylene ether sulfate sodium.

4. The composite surfactant for resolving water shield damage in unconventional reservoirs according to claim 1, characterized in that, Fluorocarbon surfactants are selected from short-chain perfluoroalkyl sulfonamide derivatives, perfluoroalkyl carboxylates, or perfluoroalkyl betaines, and their perfluorocarbon chain length C0 is [not specified]. n F 2n+1 In this case, n ≤ 4.

5. The composite surfactant for resolving water shield damage in unconventional reservoirs according to claim 1, characterized in that, Biological surfactants are glycolipid biological surfactants.

6. The composite surfactant for resolving water shield damage in unconventional reservoirs according to claim 1, characterized in that, The composite surfactant that relieves the damage of water seepage shield in unconventional reservoirs also includes a synergist. The synergist is selected from at least one of acetylenic diol nonionic surfactants, short-chain alcohols, and inorganic salts. The mass percentage of the synergist in the composite surfactant that relieves the damage of water seepage shield in unconventional reservoirs is 0.05% to 0.3%.

7. A method for preparing the composite surfactant according to claim 1 for resolving water absorption shield damage in unconventional oil reservoirs, characterized in that, Includes the following steps: Heat the water to 40℃~45℃, then mix it evenly with the main agent to form a homogeneous ion-pair micelle solution; The main agent consists of anionic surfactants and amphoteric surfactants; The pH of the ion-pair micelle solution was adjusted to 6.5-8.0, and then filtered through a 0.5μm-1.0μm filter element to obtain a composite surfactant that can relieve the damage caused by the non-conventional reservoir water absorption shield.

8. A method for preparing a composite surfactant as described in claim 1 for resolving water shield damage in unconventional oil reservoirs, characterized in that, Includes the following steps: Water is heated to 40℃~45℃, then mixed evenly with an amphoteric surfactant. The temperature is then lowered to below 40℃, and the mixture is further mixed evenly with fluorocarbon surfactants and biological surfactants. The pH value is adjusted to 6.5~8.0, and the mixture is filtered through a 0.5μm~1.0μm filter element to obtain a composite surfactant that can relieve the damage caused by the seepage shield of unconventional oil reservoirs.

9. A method for preparing the composite surfactant according to claim 1 for resolving water shield damage in unconventional oil reservoirs, characterized in that, Includes the following steps: Heat the water to 40℃~45℃, then mix it evenly with the main agent to form a homogeneous ion-pair micelle solution; The main agent consists of anionic surfactants and amphoteric surfactants; The temperature was lowered to below 40℃, and a biological surfactant was added to the ion-pair micelle solution and mixed evenly to obtain a functionalized modified ion-pair micelle solution. Fluorocarbon surfactants were added dropwise to a functionalized ion-pair micelle solution, mixed thoroughly, and the pH was adjusted to 6.5-8.

0. The solution was then filtered through a 0.5-1.0 μm filter to obtain a composite surfactant that could relieve the damage caused by the non-conventional reservoir water absorption shield.

10. The application of the composite surfactant described in claim 1 for resolving water shield damage in unconventional reservoirs in enhancing production in unconventional reservoirs, characterized in that, The application method includes the following steps: Obtain core samples and formation water samples from the target reservoir, and determine formation temperature, formation water salinity, and original rock wettability; A mathematical model of the concentration, temperature, and salinity of a composite surfactant was established using the response surface methodology to determine the permeability recovery rate and the solution of water absorption shield damage in unconventional reservoirs. The optimal concentration for this target reservoir was then calculated. Composite surfactants that can resolve the damage caused by water seepage shields in unconventional reservoirs are injected into the formation as pre-flush fluids, slickwater fracturing fluid additives, or well-clogging replacement fluids. After injection, a well-shutting operation is carried out, with a shutting time of 24h~72h. The spontaneous diffusion and adsorption of composite surfactant molecules that can remove the water-absorbing shield in the pore throat are utilized to remove the water-absorbing shield in the pore throat. Well opening and drainage to restore production capacity; The target reservoirs are those with a permeability of less than 1×10⁻⁶. -3 μm 2 Tight sandstone reservoirs, shale reservoirs, or tight carbonate reservoirs; formation water salinity ranges from 10,000 mg / L to 150,000 mg / L.

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