A temperature-resistant and salt-resistant nano-fracture imbibition agent and preparation method thereof

Abstract

The invention discloses a heat-resistant and salt-resistant nano-fracturing imbibition agent and a preparation method thereof, and belongs to the technical field of oil and gas exploitation. A heat-resistant and salt-resistant nano-fracturing imbibition agent is composed of the following components: starch, acrylic acid, ammonium persulfate, sodium bisulfite, quaternary ammonium salt, interfacial tension reducer, and deionized water. The heat-resistant and salt-resistant nano-fracturing imbibition agent provided by the invention has a hydrophobic associating polymer and an interfacial tension reducer as the main components, and has excellent heat resistance, salt resistance, and shear resistance; the formation adsorption loss is small, the oil-water interfacial tension is low, and it can penetrate into the deep part of the low-permeability reservoir, change the wettability of the rock, and through a certain period of well sealing after fracturing, the surfactant is absorbed into the pore throat of the ultra-low permeability reservoir, and more crude oil is absorbed and replaced, thereby improving the fracturing effect of the tight oil layer, delaying the production decline rate, and improving the single well production and recovery rate; the raw materials are widely available, the cost is low, the method is simple and easy to operate, and it is suitable for industrial production.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas exploitation, and in particular to a temperature-resistant and salt-resistant nano-fracturing imbibition agent and a preparation method thereof. Background Art

[0002] Fracturing is to "break up" the reservoir matrix by artificial means to form a reservoir fracture network, increase the contact area between the fracture wall and the reservoir matrix, shorten the seepage distance of oil and gas in the matrix, and reduce the driving pressure difference required for oil and gas, thereby improving the reservoir seepage capacity. After years of development, with the continuous updating and improvement of the theory and practice of volume fracturing production increase technology, reservoir volume fracturing transformation technology has become one of the important production and injection increase technologies in modern unconventional oil and gas fields.

[0003] During the hydraulic fracturing process, a large amount of fracturing fluid is injected into unconventional reservoirs. In traditional fracturing reconstruction, the main function of fracturing fluid is to create cracks. For unconventional oil reservoirs, large-scale injection of fracturing fluid can increase formation energy, transfer fluid pressure to the remote end, and improve the fracturing effect.

[0004] my country's fossil energy consumption accounts for a high proportion, and its self-sufficiency capacity is seriously insufficient. In addition, the exploration level of onshore oil resources is already very high, and the newly discovered geological reserves are gradually declining. In recent years, the newly discovered reserves are mainly ultra-low permeability oil reservoirs, which have low reservoir abundance, poor quality, poor physical properties, deep burial, dense lithology, and great development difficulties. Fracture network fracturing is often used to increase production. In the early stage, a good oil increase effect was achieved, but with the extension of production time, the reservoir energy gradually decreased and could not be effectively supplemented, and the production capacity decreased rapidly in the later period. In addition, conventional fracturing fluids cannot penetrate deep into the formation and are easily adsorbed on the rock surface, which seriously affects the efficiency of oil absorption and washing.

[0005] Domestic and foreign research has found that combining fracturing with imbibition technology can play a synergistic role in increasing tight oil production and delaying decline. This technology is to add an appropriate amount of nano-surfactant to the fracturing fluid, which will enter the high oil saturation matrix or natural fracture area with the fracturing fluid during the fracturing process and the well blocking stage after fracturing, and accelerate in-situ oil production through rapid imbibition.

[0006] By using active substances that enhance imbibition displacement, the oil-water interfacial tension is reduced, the lipophilicity of the reservoir pore wall is reduced, the driving effect of capillary force is increased, and the displacement efficiency of crude oil in micro-nano pores is improved. This "fracture network production increase and oil-water imbibition displacement" oil recovery attempt is referred to as the "fracture network production increase + imbibition displacement" technology. On the one hand, a large-area fracture network is formed in the reservoir after fracturing, and the fracturing fluid carries the proppant into the fracture network; on the other hand, the fracturing fluid spontaneously penetrates into the pores under the action of capillary pressure, displacing the oil phase and improving the oil and gas recovery efficiency. The research and development and application of imbibition oil-displacing fracturing fluids are of great significance to the increase of oil and gas production in tight reservoirs.

[0007] At present, there are two main types of imbibition-type fracturing fluids: one is a clean fracturing fluid system composed of VES, which remains in the formation pores after breaking the gel, thereby enhancing the imbibition-type oil recovery effect; the other is to add an imbibition agent (such as a surfactant, etc.) to the fracturing fluid, so that the imbibition agent exists in the pre-fluid, displacement fluid or low-viscosity fluid, thereby enhancing the imbibition-type oil recovery effect.

[0008] Cao et al. used high-pressure mercury injection and nuclear magnetic resonance technology to measure the pore size distribution of dense sandstone, and divided the pores into three types according to the pore size: micropores, mesopores and macropores. Surfactants were used to conduct spontaneous and forced imbibition oil recovery experiments in these three types of pores. The experiments confirmed that the oil in the micropores contributes more than 50% to the imbibition recovery rate. Qi Shulei et al. used Br(CH2) m COOC2H5, N-methylimidazole, R1(Me)SiHO[(Me)2SiO] n R2 was used as the reaction raw material and ionic liquid as the catalyst to produce a heat-resistant and salt-resistant fracturing imbibition agent, which was applied on site at HH12P132 in the North China Oilfield and had a significant oil-increasing effect.

[0009] It can be seen that the combination of fracturing and imbibition technology has a significant effect on increasing production. However, the use of conventional surfactants as imbibition agents has poor oil washing performance and limited imbibition effect. The production increase effect has a large room for improvement. In addition, there are problems such as large adsorption loss to the formation (for example, the cationic surfactant hexadecyltrimethylammonium bromide studied by Wang Xiaoxiang et al.), relatively harsh preparation reaction conditions, difficult operation, and unstable structure. Summary of the invention

[0010] The purpose of the present invention is to provide a temperature-resistant and salt-resistant nano-fracturing imbibing agent and a preparation method thereof, so as to solve the problems of existing imbibing agents such as large formation adsorption loss, limited imbibing effect, unsatisfactory production increase effect, relatively harsh preparation conditions, difficult operation, poor stability of the prepared compounds, and easy failure.

[0011] To achieve the above purpose, the present invention provides a temperature-resistant and salt-resistant nano-fracture imbibition agent and a preparation method thereof. A temperature-resistant and salt-resistant nano-fracture imbibition agent is composed of the following components: starch, acrylic acid, ammonium persulfate, sodium bisulfite, quaternary ammonium salt, interfacial tension reducer, and deionized water.

[0012] Preferably, the mass volume ratio of starch to acrylic acid is 100:(6-10); the mass volume ratio of starch to deionized water is 1:8; the amount of quaternary ammonium salt is 5% to 10% of the mass of the starch; and the interfacial tension reducer is 3% to 6% of the mass of the starch.

[0013] Preferably, the mass volume ratio of starch to acrylic acid is 10:1; the amount of quaternary ammonium salt is 10% of the mass of the starch; and the amount of interfacial tension reducer is 6% of the mass of the starch.

[0014] Preferably, the quaternary ammonium salt is one of dimethyl octadecyl allyl ammonium bromide and dimethyl docosyl allyl ammonium bromide, or a mixture of the two; and the interfacial tension reducer is BGF.

[0015] Preferably, the starch is one of cassava starch and banana taro starch or a mixture of the two; and the acrylic acid is a chemically pure reagent from which the inhibitor has been removed.

[0016] A method for preparing the temperature-resistant and salt-resistant nano-fracturing imbibing agent as described above comprises the following steps:

[0017] S1. Accurately weigh / measure starch and deionized water, add them into a stirrer, stir and mix them under nitrogen protection, and gelatinize them at a constant temperature of 70-80°C for 30-40 minutes;

[0018] S2, after cooling the reaction system to a certain temperature, adding an aqueous solution of ammonium persulfate, stirring the reaction for a certain period of time, and then adding dropwise an acrylic acid solution while stirring;

[0019] S3, after the dropwise addition is completed, add sodium bisulfite solution to react for a certain period of time, add a certain amount of 95% by volume ethanol to the obtained product, stir, let stand, filter, and then add anhydrous ethanol to wash once;

[0020] S4, adding quaternary ammonium salt and interfacial tension reducing agent to the product obtained in step S3 and stirring evenly;

[0021] The reaction formula is:

[0022]

[0023] Wherein R is octadecyl or docosyl.

[0024] Preferably, the certain temperature in step S2 refers to 30-40° C., the stirring reaction time refers to 8-15 min; the reaction time in step S3 refers to 0.5-1 h, and the amount of 95% ethanol added is based on the amount of the product being covered.

[0025] Application of the temperature-resistant and salt-resistant nano-fracturing imbibing agent as described above in oil production.

[0026] The results of the imbibition experiment on low permeability sandstone reservoirs conducted by scholars show that wettability is an important factor affecting imbibition. Imbibition in hydrophilic and weakly hydrophilic low permeability reservoirs is beneficial to improving the recovery rate. The imbibition rate depends on the pore structure of the porous medium, the fluid properties and the interfacial tension between the fluids, and the interaction between the fluid and the solid.

[0027] By studying the imbibition sensitive factors, it was found that the chemical solution system that reduces the oil-water interfacial tension can make the remaining oil become mobile oil, which is beneficial to the displacement and migration of oil droplets in the porous medium, thereby improving the imbibition recovery rate of hydrophilic low permeability reservoirs.

[0028] Studies have shown that introducing a small amount of hydrophobic groups or chains into the hydrophilic macromolecular chain of the polymer to prepare a hydrophobic associating polymer can form a reversible physical cross-linked three-dimensional spatial network structure in water, making the polymer perform outstandingly in terms of viscosity increase, temperature resistance, salt resistance and shear resistance.

[0029] Therefore, the temperature-resistant and salt-resistant nano-fracturing imbibition agent and the preparation method thereof provided by the present invention have the following beneficial effects:

[0030] 1. The present invention forms a hydrophobic associating polymer with a reversible physical cross-linked three-dimensional network structure by adding a small amount (about 2%) of hydrophobic groups, namely propionic acid-quaternary ammonium salt residues, to the hydrophilic macromolecular chain, namely starch, so that the prepared absorbing agent has excellent temperature resistance, salt resistance and shear resistance.

[0031] 2. The salt-resistant nano-fracture imbibition agent provided by the present invention has low interfacial tension and capillary self-imbibition height, and does not change significantly in the temperature and salt resistance tests. It can be used as a heat-resistant and fracturing imbibition agent and applied in various temperature change and high-salt operating environments. It can be combined with fracturing technology and post-fracturing well sealing to play a synergistic role, thereby increasing the production of tight oil and delaying the rate of production decline;

[0032] 3. The main components of the imbibition agent provided by the present invention are hydrophobic associating polymers and interfacial tension reducers. The formation adsorption loss is small, the oil-water interfacial tension is low, and the imbibition agent can penetrate into the deep part of the low permeability reservoir to change the wettability of the rock. The imbibition agent has a strong imbibition effect. By sealing the well for a certain period after fracturing, the surfactant can be imbibed into the pore throat of the ultra-low permeability reservoir, and the in-situ oil production can be accelerated by rapid imbibition, and more crude oil can be imbibed and replaced, thereby improving the fracturing effect of the tight oil layer, delaying the rate of production decline, and increasing the single well production and recovery rate;

[0033] 4. The hydrophobic associating polymer in the imbibition agent provided by the present invention, and the acrylic acid and quaternary ammonium salt copolymer byproduct generated during the reaction process, can be used as a polyquaternary ammonium salt anti-swelling agent, which can effectively prevent the pore throat blockage caused by the expansion and migration of formation clay minerals, thereby causing the problem of decreased reservoir matrix permeability, water-sensitive damage, and reduced oil and gas production;

[0034] 5. The imbibition agent provided by the present invention has a stable connection between the hydrophobic group and the hydrophilic macromolecular chain, and will not lose its function due to changes in environmental acidity and alkalinity and temperature during operation, and can be applied to formation environments of various properties;

[0035] 6. The imbibition agent provided by the present invention uses starch as the main material. Starch contains a large number of hydrophilic groups - hydroxyl groups, while the amount of introduced hydrophobic groups is small. The large number of hydroxyl groups retained can improve the wettability of the imbibition agent, thereby reducing damage to the reservoir and improving the oil recovery rate;

[0036] 7. The materials used in the imbibition agent provided by the present invention are widely available, the preparation conditions are simple and easy to operate, the preparation cost is low, and it is suitable for large-scale production.

[0037] The technical solution of the present invention is further described in detail below through embodiments. DETAILED DESCRIPTION

[0038] The technical solution of the present invention is further illustrated by the following examples.

[0039] In order to enable those skilled in the art to understand the characteristics and effects of the present invention, the following is a general description and definition of the terms and expressions mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used in the text are the common meanings understood by those skilled in the art for the present invention. In the event of a conflict, the definition in this specification shall prevail.

[0040] The theories or mechanisms described and disclosed herein, whether correct or incorrect, should not limit the scope of the present invention in any way, that is, the present invention can be implemented without being limited by any specific theory or mechanism.

[0041] Herein, all features such as values, quantities, contents and concentrations defined in the form of numerical ranges or percentage ranges are for simplicity and convenience only. Accordingly, the description of numerical ranges or percentage ranges should be considered to have included and specifically disclosed all possible secondary ranges and individual values ​​within the range (including integers and fractions).

[0042] In this document, unless otherwise specified, “includes,” “including,” “contains,” “has,” or similar terms cover the meanings of “consisting of” and “mainly consisting of,” for example, “A includes a” covers the meanings of “A includes a and other” and “A only includes a.”

[0043] In this document, in order to make the description concise, not all possible combinations of various technical features in various embodiments or examples are described. Therefore, as long as there is no contradiction in the combination of these technical features, the various technical features in various embodiments or examples can be combined arbitrarily, and all possible combinations should be considered to be within the scope of this specification.

[0044] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0045] The materials, reagents and instruments used in the examples were obtained from commercial sources.

[0046] Embodiment 1

[0047] A temperature-resistant and salt-resistant nano-fracturing imbibition agent is prepared by the following method:

[0048] S1. Accurately weigh 5 g of cassava starch, measure 40 mL of deionized water, add into a stirrer, stir and mix under nitrogen protection, and gelatinize at 70°C for 30 min;

[0049] S2, after cooling the reaction system to 40°C, add 10 mL of ammonium persulfate aqueous solution (concentration of 10%), stir the reaction for 10 min, and then add 300 μL of acrylic acid solution dropwise while stirring;

[0050] S3, after the dropwise addition is completed, add sodium bisulfite solution (concentration is 5%) and react for 0.5h, add 40mL 95% volume fraction ethanol to the obtained product, stir, let stand, filter, and then add anhydrous ethanol to wash once;

[0051] S4. Add 0.5 g of dimethyloctadecyl allyl ammonium bromide and 0.3 g of BGF to the product obtained in step S3 and stir evenly.

[0052] Embodiment 2

[0053] A temperature-resistant and salt-resistant nano-fracture imbibition agent was prepared in the same manner as in Example 1, except that:

[0054] In step S1, the reaction was carried out at 75° C. for 40 min;

[0055] In step S2, the mixture is cooled to 30° C. and subjected to gelatinization reaction for 15 minutes;

[0056] The reaction time in step S3 is 0.7 h.

[0057] Embodiment 3

[0058] A temperature-resistant and salt-resistant nano-fracturing imbibition agent was prepared in the same manner as in Example 1, except that:

[0059] In step S1, the reaction was carried out at 80° C. for 35 min;

[0060] In step S2, the mixture is cooled to 35° C. and subjected to gelatinization reaction for 8 minutes;

[0061] The reaction in step S3 was carried out for 1 h.

[0062] Performance Testing

[0063] The interfacial tension, self-priming performance and surface tension of the imbibition agents prepared in Examples 1 to 3 were measured with reference to GB / T 38722-2020 Determination of interfacial tension of surfactants (pulling up liquid film method), JB / T 6664.3-2004 Self-priming pump Part 3: Self-priming performance test method, and GB / T5549-2010 Surfactant using the pulling up liquid film method. The results are shown in Table 1.

[0064] Table 1

[0065]

[0066] It can be seen from Table 1 that the imbibition agents for fracturing prepared in Examples 1 to 3 of the present invention all have lower interfacial tension and capillary self-imbibition height, and have no significant changes in the temperature resistance and salt resistance tests. The imbibition agents prepared by the parameters of Examples 1 and 3 have better effects than the imbibition agent prepared in Example 2.

[0067] Therefore, the main components of a temperature-resistant and salt-resistant nano-fracturing imbibition agent provided by the present invention are a hydrophobic associating polymer and an interfacial tension reducer, and the agent has excellent temperature resistance, salt resistance and shear resistance; the formation adsorption loss is small, the oil-water interfacial tension is low, and the agent can penetrate into the deep low-permeability reservoir to change the wettability of the rock, and by sealing the well for a certain period after fracturing, the surfactant is absorbed into the pore throat of the ultra-low permeability reservoir to replace more crude oil, thereby improving the fracturing effect of the tight oil layer, delaying the rate of production decline, and increasing the single well production and recovery rate; the salt-resistant raw materials are widely available, the cost is low, the method is simple and easy to operate, and the agent is suitable for industrial production.

[0068] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A temperature-resistant and salt-resistant nano-fracturing imbibition agent, characterized in that: The temperature-resistant and salt-resistant nano-fracturing imbibition agent is composed of the following components: starch, acrylic acid, ammonium persulfate, sodium bisulfite, quaternary ammonium salt, interfacial tension reducer, and deionized water; The quaternary ammonium salt is one of dimethyl octadecyl allyl ammonium bromide and dimethyl docosyl allyl ammonium bromide or a mixture of the two; the interfacial tension reducer is BGF; The starch is one of cassava starch and banana starch or a mixture of the two; the acrylic acid is a chemically pure reagent from which the inhibitor has been removed; The preparation method of the above-mentioned temperature-resistant and salt-resistant nano-fracturing imbibing agent comprises the following steps: S1. Accurately weigh / measure starch and deionized water, add them into a stirrer, stir and mix them under nitrogen protection, and gelatinize them at a constant temperature of 70-80°C for 30-40 min; S2, after cooling the reaction system to a certain temperature, adding an aqueous solution of ammonium persulfate, stirring the reaction for a certain period of time, and then adding dropwise an acrylic acid solution while stirring; S3, after the dropwise addition is completed, add sodium bisulfite solution to react for a certain period of time, add a certain amount of 95% by volume ethanol to the obtained product, stir, let stand, filter, and then add anhydrous ethanol to wash once; S4, adding quaternary ammonium salt and interfacial tension reducing agent to the product obtained in step S3 and stirring evenly; The mass volume ratio of starch to acrylic acid is 100g:(6-10)mL; the mass volume ratio of starch to deionized water is 1g:8mL; the amount of quaternary ammonium salt is 5%-10% of the mass of the starch; the interfacial tension reducer is 3%-6% of the mass of the starch; The reaction formula is: ； Wherein R is octadecyl or docosyl; The certain temperature in step S2 refers to 30-40° C., the certain time of stirring reaction refers to 8-15 min; the certain time of reaction in step S3 refers to 0.5-1 h, and the amount of 95% ethanol added is based on the amount of the product being covered.

2. The temperature-resistant and salt-resistant nano-fracturing imbibing agent according to claim 1, characterized in that: The mass volume ratio of starch to acrylic acid is 10 g:1 mL; the amount of quaternary ammonium salt is 10% of the mass of the starch; and the amount of interfacial tension reducer is 6% of the mass of the starch.

3. Use of the temperature-resistant and salt-resistant nano-fracturing imbibition agent according to any one of claims 1 to 2 in oil production.

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