A nano-osmotic oil displacement agent, a preparation method and application thereof

Abstract

The application belongs to the technical field of oil field chemistry, and provides a nano imbibition oil displacement agent, a preparation method and application thereof. The nano imbibition oil displacement agent is obtained by polymerization reaction of acrylamide monomers and a surfactant; the acrylamide monomers include at least one of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, N-dodecyl acrylamide and 4-acryloyl morpholine; and the surfactant includes at least one of alpha-alkenyl sulfonate, alkylphenol polyoxyethylene ether and sodium dodecyl sulfate. The nano imbibition oil displacement agent solution can strengthen spontaneous imbibition in the fracturing process, improve the imbibition recovery rate of shale oil reservoirs, and ensure stable and increased production of shale oil development.

Description

Technical Field

[0001] This invention belongs to the field of oilfield chemical technology and relates to a nano-permeation displacement agent, its preparation method and application. Background Technology

[0002] Shale oil reservoirs have complex structures, characterized by strong heterogeneity of the rock matrix, low porosity (4.5%-11%), and ultra-low permeability ((0.001-0.1)×10⁻⁶). -3 μm 2 Shale oil reservoirs, characterized by their multi-micron to nano-scale pore throats, are often developed using horizontal well hydraulic fracturing. During fracturing and well-closing stages, spontaneous adsorption is a crucial mechanism in shale oil development. Given the complex pore and fracture structure of shale reservoirs, understanding how to enhance spontaneous adsorption and improve the effective utilization of shale oil is of significant guiding importance for achieving high and stable shale oil production.

[0003] Shale reservoir percolation is influenced by numerous factors, including reservoir wettability, permeability, pore characteristics, and crude oil fluidity. To effectively enhance reservoir percolation, suitable percolators need to be developed to alter the oil wettability caused by the self-generation and self-storage of shale reservoirs, providing a reasonably low interfacial tension, increasing capillary force, and improving the percolation-driven oil displacement. Simultaneously, given the poor porosity and permeability of shale oil reservoirs, it is also necessary to consider whether the injected fluid can pass through the reservoir's micro- and nano-pores.

[0004] Currently, commonly used fracturing and penetration aids are all single or compound surfactants, which can significantly reduce interfacial tension, easily lead to oil-water emulsification, affect capillary force, and are adsorbed in large quantities on the rock surface. They have little effect on changes in the oil-water mobility ratio, resulting in low sweep efficiency of the modifier.

[0005] Chinese invention patent application CN113717709A discloses a nanofluid permeator, which is mainly composed of amphiphilic grafted modified nano silica particles, betaine-type surfactants and nonionic surfactants, and has good salt resistance and fracturing fluid compatibility.

[0006] Chinese invention patent application CN113943411A discloses an oil displacement agent, which is mainly composed of nanomaterials modified with double bonds, acrylamide monomers and sodium α-olefin sulfonate synthesized from nanomaterials, and polyoxyethylene ether nonionic surfactants.

[0007] In the two nano-permeation displacement agents mentioned above, there are no chemical bonds between the nanomaterials and the surfactants, and the interaction is weak. During the formation migration process, the interaction is easily disrupted, leading to the aggregation of nanomaterials and affecting the permeation recovery rate.

[0008] Chinese invention patent CN113265022B discloses a percolation displacement agent and its preparation method. This percolation displacement agent is prepared from a polymer emulsion and a surfactant solution at a mass ratio of 1.5-9:1. The surface-active water-soluble polymer emulsion and the surfactant solution are mixed. The nonionic surfactant component in the surfactant solution is loaded onto the water-soluble polymer backbone, ensuring the entire system functions in a high-salt environment. With a suitable mixing ratio, the oil displacement efficiency of the entire agent system reaches over 10%. However, this percolation displacement agent requires an emulsifier to improve the compatibility of the polymer system during preparation and is not suitable for shale oil reservoirs with complex structures and ultra-low permeability.

[0009] Therefore, considering the complex pore and fracture structure of shale oil reservoirs, and taking into account factors such as reservoir wettability, permeability, pore characteristics, and crude oil fluidity, developing suitable permeabilizers to effectively enhance the spontaneous permeation of shale reservoirs is currently the key to high and stable shale oil production. Summary of the Invention

[0010] This invention addresses the lack of suitable percolation displacement agents for shale oil reservoir fracturing, as well as the problems of weak interaction between nanomaterials and surfactants and easy aggregation in existing shale oil reservoir fracturing percolation displacement agents. It provides a nano-percolation displacement agent, its preparation method, and its application. Using acrylamide as the backbone structure (and possibly supplemented with other acrylamide monomers), the nano-percolation displacement agent is polymerized with a surfactant. Under the combined action of acrylamide monomers and surfactants, the percolation displacement agent exhibits excellent spontaneous percolation effect, allowing it to be injected into the micro- and nano-pore throats of shale oil reservoirs, effectively improving the percolation recovery rate of shale oil reservoirs.

[0011] One of the technical solutions of this invention is:

[0012] A nano-permeable oil displacement agent is provided, which is obtained by polymerization reaction of acrylamide monomers and surfactants; the acrylamide monomers include at least one of acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, N-dodecylacrylamide and 4-acryloylmorpholine; the surfactants include at least one of α-alkenylsulfonate, alkylphenol polyoxyethylene ether and sodium dodecyl sulfate.

[0013] Preferably, the acrylamide monomer includes at least acrylamide, and the surfactant is an α-olefin sulfonate.

[0014] In some embodiments of the present invention, when there is only one acrylamide monomer, acrylamide is selected, that is, acrylamide is used as the backbone structure.

[0015] In some embodiments of the present invention, the acrylamide monomer is acrylamide and 2-acrylamido-2-methylpropanesulfonic acid.

[0016] In some embodiments of the present invention, the acrylamide monomers are acrylamide and N-dodecylacrylamide.

[0017] In some embodiments of the present invention, the acrylamide monomer is acrylamide and 4-acryloylmorpholine.

[0018] More preferably, the acrylamide monomers are used in the following amounts: 10-30 wt% acrylamide, 0-15 wt% 2-acrylamido-2-methylpropanesulfonic acid, 0-10 wt% N-dodecylacrylamide and 0-10 wt% 4-acryloylmorpholine.

[0019] Preferably, the amount of surfactant used is 5-20 wt%.

[0020] More preferably, the α-alkenylsulfonate is sodium α-alkenylsulfonate.

[0021] In some embodiments of the present invention, the general structural formula of the nano-penetrating oil displacement agent is as follows:

[0022]

[0023] Wherein, R is a C11-13 alkyl group; M is either Na or K; x:y:z:m:n = 2-8:0-5:1-5:0-5:0-5.

[0024] Furthermore, the nano-permeation oil displacement agent has a particle size of 1-100 nm.

[0025] The second technical solution of the present invention is:

[0026] A method for preparing the above-mentioned nano-permeation displacement agent is provided, comprising the following steps:

[0027] (1) Add acrylamide monomers and surfactants to the reaction apparatus;

[0028] (2) Under nitrogen protection, add water to dissolve completely and adjust the pH;

[0029] (3) Heat up, add initiator, and carry out polymerization reaction to obtain the product.

[0030] Furthermore, the amount of the initiator is 0.08-1.0 wt% of the total amount of acrylamide monomers and surfactants.

[0031] Furthermore, the initiator comprises an oxidant and a reducing agent; the mass ratio of the oxidant to the reducing agent is 1:0.7-0.8.

[0032] Furthermore, the oxidant is selected from at least one of ammonium persulfate, sodium persulfate, and potassium persulfate; the reducing agent is selected from sodium sulfite or sodium bisulfite.

[0033] Furthermore, in step (2), the pH value is 6.0-8.0.

[0034] Furthermore, in step (3), the polymerization reaction temperature is 50-70℃; the polymerization time is 3-5h.

[0035] The third technical solution of the present invention is:

[0036] A nano-permeable oil displacement agent solution is provided, wherein the nano-permeable oil displacement agent solution comprises the above-mentioned nano-permeable oil displacement agent or the nano-permeable oil displacement agent prepared by the above-mentioned preparation method.

[0037] Furthermore, the solvent of the solution is deionized water or formation water.

[0038] Furthermore, the concentration of the nano-permeation displacement agent in the nano-permeation displacement agent solution is 0.1-2.0 wt%.

[0039] The fourth technical solution of the present invention is:

[0040] The application of the above-mentioned nano-permeable displacement agent or the above-mentioned nano-permeable displacement agent solution in fracturing and displacement of shale oil reservoirs is provided.

[0041] Furthermore, the shale oil reservoir has a formation temperature ≤100℃, formation water salinity of 0-10000 mg / L, and permeability of (0.01-1.0)×10⁻⁶. -3 μm 2 .

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] (1) The nano-permeable oil displacement agent of this invention, obtained by combining acrylamide monomers as the backbone structure with surfactants, has a low usage concentration. When combined with an aqueous phase with a mineralization of 0-10000 mg / L, it can effectively reduce the interfacial tension of the nano-permeable oil displacement agent solution (interfacial tension ≤ 0.07 mN·m). -1The nano-permeable oil displacement agent has a contact angle (≤33.66°), which can reduce the oil-water interfacial tension and start-up pressure, increase capillary force, improve the spreading coefficient, and enhance the permeable oil displacement power and the degree of crude oil stripping on the core surface. It can also improve the adhesion work reduction rate and spontaneous permeable recovery rate, with an adhesion work reduction rate ≥98% and permeation efficiency ≥30.34%. It can also effectively avoid the adsorption and chromatographic separation problems of permeable oil displacement agents on the rock surface during formation migration. The bimolecular adsorption effect of the nano-permeable oil displacement agent on the rock surface can change the oil wettability caused by the self-generation and self-storage of shale reservoirs, thereby reducing the adhesion work of shale oil and utilizing the residual oil in the large, medium and small pores of shale reservoirs, and strengthening the spontaneous permeable oil displacement effect.

[0044] (2) When other acrylamide monomers are further combined with the acrylamide skeleton structure, and after further optimizing the ratio of acrylamide monomers to surfactants, polymers with specific structural units and degree of polymerization ratios are obtained, which further improves their comprehensive oil displacement performance.

[0045] (3) The nano-permeation oil displacement agent of the present invention can be dispersed to form a nano-scale solution with a particle size of only 1-10nm. It can penetrate into the small and complex pore throats of shale reservoirs to replace crude oil, improve the sweeping degree, and enhance the spontaneous permeation effect.

[0046] (4) The nano-permeation oil displacement agent solution of the present invention is used for energy-enhancing fracturing. As the artificial fractures formed by fracturing enter the micro fractures of the reservoir matrix, the spontaneous permeation effect is enhanced during the later well simmering process, thereby improving the permeation recovery rate of shale oil reservoirs and ensuring stable and increased production of shale oil.

[0047] (5) The method for preparing nano-permeation oil displacement agent provided by the present invention has a high monomer conversion rate and a simple preparation process. Attached Figure Description

[0048] Figure 1 The particle size distribution of nano-permeable oil displacement agent solutions SXY-1, SXY-7, and SXY-8 prepared in Examples 1, 3, and 4 with a concentration of 0.3 wt.% is shown.

[0049] Figure 2 Interfacial tension diagrams of 0.3 wt.% nano-permeation displacement agent solutions SXY-1, SXY-7, and SXY-8 from Examples 1, 3, and 4;

[0050] Figure 3 The results of spontaneous adsorption recovery of nano-permeation oil displacement agent solutions SXY-1 to SXY-4 prepared in Examples 5-8 of this invention, as well as surfactant AOS and water in shale oil reservoirs;

[0051] Figure 4The results show the spontaneous adsorption recovery rates of the nano-adsorption oil displacement agent solutions SXY-7 and SXY-8 prepared in Comparative Examples 3 and 4 of this invention in shale oil reservoirs. Detailed Implementation

[0052] The following non-limiting embodiments are intended to enable those skilled in the art to gain a more comprehensive understanding of the present invention, but do not limit the invention in any way. The following content is merely an exemplary description of the scope of protection of the present invention, and those skilled in the art can make various changes and modifications to the invention based on the disclosed content, which should also fall within the scope of protection of the present invention.

[0053] The chemical formula of the main component of surfactant AOS: C 14 H 27 SO3Na, structural formula as follows:

[0054]

[0055] Example 1

[0056] Preparation of nano-permeation displacement agent SX-1:

[0057] (1) Place 15g acrylamide, 10g 2-acrylamido-2-methylpropanesulfonic acid and 5g surfactant AOS in a 250mL round-bottom flask with a mechanical stirrer on top, and continuously purge with nitrogen to maintain an inert environment;

[0058] (2) Add 70g of deionized water to the flask to keep the total monomer (including acrylamide monomer and surfactant) concentration of the solution at 30wt%, and set the stirring speed to 500rpm; after the monomer is completely dissolved, adjust the pH of the system to neutral with sodium hydroxide aqueous solution.

[0059] (3) After heating the system to 50°C, 0.011 g of Na2SO3 and 0.013 g of Na2S2O8 (accounting for 0.08 wt% of the total mass fraction of monomers) were added as initiators. After reacting at 50°C for 5 h, the mixture was cooled to 25°C to obtain a pale yellow, oily, viscous liquid.

[0060] (4) Add 10 mL of NaOH / Na2CO3 solution (NaOH / Na2CO3 mass ratio = 1:1) to the liquid, wash with ethanol, dry, pulverize, and obtain the final product, nano-permeation displacement agent SX-1.

[0061] Example 2

[0062] The preparation method is the same as in Example 1, except that in step (1), 15g of acrylamide monomer, 10g of 4-acryloylmorpholine and 5g of surfactant AOS are added to prepare nano-permeation oil displacement agent SX-2.

[0063] Example 3

[0064] The preparation method is the same as in Example 1, except that in step (1), 15g of acrylamide monomer, 10g of N-dodecylacrylamide and 5g of surfactant AOS are added to prepare nano-permeation oil displacement agent SX-3.

[0065] Example 4

[0066] The preparation method is the same as in Example 1, except that in step (1), 15g of acrylamide, 5g of 2-acrylamido-2-methylpropanesulfonic acid and 10g of surfactant AOS are added to prepare nano-permeation oil displacement agent SX-4.

[0067] Examples 5-8

[0068] Preparation of nano-permeation oil displacement agent solutions SXY-1~SXY4:

[0069] Weigh 0.3g of the nano-permeation oil displacement agent from Examples 1-4 respectively, place them in a 200mL beaker, add 99.7g of deionized water, and prepare nano-permeation oil displacement agent solutions SXY-1 to SXY-4 with a mass concentration of 0.3wt%.

[0070] Comparative Example 1

[0071] The preparation method is the same as in Example 1, except that in step (1), 15g of acrylamide, 10g of N-dodecylacrylamide and 20g of sodium α-carbamoyl sulfonate are added to prepare nano-permeation displacement agent SX-5.

[0072] Comparative Example 2

[0073] The preparation method is the same as in Example 1, except that in step (1), 25g of acrylamide and 5g of surfactant AOS are added to obtain nano-permeation oil displacement agent SX-6.

[0074] Comparative Example 3

[0075] The preparation method is the same as in Example 1, except that in step (1), 25g of 2-acrylamido-2-methylpropanesulfonic acid and 5g of surfactant AOS are added to obtain nano-permeation oil displacement agent SX-7.

[0076] Comparative Example 4

[0077] The preparation method is the same as in Example 1, except that in step (1), the surfactant used is dodecylphenol polyoxyethylene ether OP-10 to prepare nano-permeation oil displacement agent SX-8.

[0078] Comparative Examples 5-8

[0079] Preparation of nano-permeation oil displacement agent solutions SXY-5~SXY-8:

[0080] Weigh 0.3g of each of the comparative examples 1-4 and place them in a 200mL beaker. Add 99.7g of deionized water to prepare nano-permeation oil displacement agent solutions SXY-5 to SXY-8 with a mass concentration of 0.3wt%.

[0081] Test Example: Performance Evaluation of Nano-Permeation Oil Displacement Agent Solution:

[0082] (1) Particle size distribution of nano-permeable oil displacement agent solution

[0083] The nano-permeation oil displacement agent can be dispersed in deionized water to form a nanoscale solution, and its particle size distribution is tested using a Malvern laser particle size analyzer.

[0084] (2) Interfacial tension of nano-permeable oil displacement agent solution

[0085] The interfacial tensions of nano-permeation displacement agent solution, conventional surfactant solution (0.3 wt% AOS) solution, deionized water and Jimsar shale oil were measured using an interfacial tensiometer.

[0086] (3) Improvement of wettability of nano-permeable oil displacement agent solution

[0087] (a) Cut the Jimsar core into 5mm thick slices and measure the wetting angle of the core slices;

[0088] (b) The above core sections were immersed in nano-permeation displacement agent solution and conventional surfactant solution (0.3wt% AOS) respectively, soaked at room temperature for 24 hours, and then removed and dried.

[0089] (c) The contact angle between deionized water and core samples was measured using a JY-82C-N2 contact angle meter. The contact angles of core samples soaked in different solutions were compared with those of core samples not treated with the sample solution.

[0090] (4) Adhesion work reduction ability of nano-permeable oil displacement agent solution

[0091] The adhesion work of the nano-permeation displacement agent solution is calculated using the following formula, and its adhesion work reduction rate is calculated to evaluate its adhesion work reduction capability:

[0092] W = σ ow (1-cosθ)

[0093] Where, σ ow θ represents the interfacial tension between Jimsar shale oil and different solutions; θ represents the contact angle between the core and different solutions.

[0094] (5) Spontaneous adsorption recovery rate of nano-adsorption oil displacement agent solution

[0095] The prepared nano-permeation displacement agent solution, a conventional surfactant solution (0.3 wt% AOS), and deionized water were mixed at a concentration of 0.1 × 10⁻⁶. -3 μm 2 Spontaneous infiltration experiments were conducted in the core sample at room temperature, using Jimsar shale oil.

[0096] The interfacial tension, contact angle, adhesion work, and spontaneous adsorption recovery rate of Examples 5-8, Comparative Examples 5-8, and conventional surfactant solutions (0.3wt% AOS) and deionized water were tested according to the above method. The test results are shown in Table 1.

[0097] Table 1 Performance test results of different solution systems

[0098]

[0099] Test results:

[0100] The particle size distribution of 0.3wt% nano-permeation displacement agent solutions SXY-1, SXY-7, and SXY-8 is as follows: Figure 1 As shown, the nano-permeation displacement agent SX-1 prepared in Example 1 of this invention has a particle size of 2-6 nm, which can penetrate deep into the small and complex pore throats of shale reservoirs to replace crude oil, improve the sweepability, and enhance the spontaneous permeation effect; while the nano-permeation displacement agents XS-7 and XS-8 prepared in the comparative example have particle sizes greater than 5 nm, with a maximum of 30 nm, and the spontaneous permeation effect will be greatly reduced.

[0101] The interfacial tension diagram of 0.3wt% nano-permeation displacement agent solution A is shown below. Figure 2 As shown, the nano-permeation displacement agent solution SXY-1 prepared in this embodiment of the invention and Jimsar shale oil reached an equilibrium interfacial tension value of 0.07 mN·m in a short time. -1 It has a moderate ability to reduce the starting pressure of oil-water interfacial tension, which can increase capillary force, improve the spreading coefficient, and enhance the percolation displacement power and the degree of crude oil stripping on the core surface; while the equilibrium interfacial tension values ​​of the nano-percolation displacement agent solutions XSY-7 and XSY-8 prepared in the comparative proportion are higher than 0.1 mN·m -1 The equilibrium interfacial tension value of a conventional surfactant solution is 0.1837 mN·m. -1 .

[0102] The spontaneous adsorption recovery results of the nano-adsorption displacement agent solutions prepared in Examples 5-8 of this invention, as well as the surfactant AOS and water in shale oil reservoirs, are as follows: Figure 3 As shown, the spontaneous adsorption recovery results of the nano-adsorption oil displacement agent solutions prepared in Comparative Examples 7 and 8 in shale oil reservoirs are as follows: Figure 4 As shown; the spontaneous adsorption recovery rate of the nano-permeable oil displacement agent solution (0.3wt%) prepared in Examples 5-8 is as high as 30% or more, which is higher than that of Comparative Examples 7 and 8; and is much higher than the spontaneous adsorption recovery rate (25%) of conventional surfactant (0.3wt% AOS) solution and the spontaneous adsorption recovery rate (13%) of deionized water.

[0103] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, and is not intended to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions made by those skilled in the art to the technical solution of the present invention do not depart from the essence and scope of the technical solution of the present invention.

Claims

1. A nano-permeable displacement agent for fracturing and displacement in shale oil reservoirs, characterized in that, The nano-permeable oil displacement agent is obtained by polymerization reaction of acrylamide monomers and surfactants; the acrylamide monomers include at least acrylamide, and also include at least one of 2-acrylamido-2-methylpropanesulfonic acid, N-dodecylacrylamide and 4-acryloylmorpholine; the surfactants include α-alkenyl sulfonate. The acrylamide monomers are used in the following amounts: acrylamide 10-30 wt%, 2-acrylamido-2-methylpropanesulfonic acid 0-15 wt%, N-dodecylacrylamide 0-10 wt%, and 4-acryloylmorpholine 0-10 wt%; the surfactant is used in the following amounts: 5-20 wt%. The nano-permeable oil displacement agent has a particle size of 1-10 nm.

2. The preparation method of the nano-permeation displacement agent according to claim 1, characterized in that, Includes the following steps: (1) Add acrylamide monomers and surfactants to the reaction apparatus; (2) Under an inert atmosphere, dissolve completely in water and adjust the pH. (3) Heat up, add initiator, and carry out polymerization reaction to obtain the product.

3. The preparation method according to claim 2, characterized in that, The amount of the initiator is 0.08-1.0 wt% of the total amount of acrylamide monomers and surfactants.

4. The preparation method according to claim 2, characterized in that, The initiator comprises an oxidant and a reducing agent; the mass ratio of the oxidant to the reducing agent is 1:0.7-0.8; the oxidant is selected from at least one of ammonium persulfate, sodium persulfate, and potassium persulfate; the reducing agent is selected from sodium sulfite or sodium bisulfite.

5. The preparation method according to claim 2, characterized in that, In step (2), the pH value is 6.0-8.0; in step (3), the polymerization reaction temperature is 50-70℃; and the polymerization time is 3-5h.

6. A nano-penetrating oil displacement agent solution, characterized in that, This includes the nano-permeation oil displacement agent according to claim 1 or the nano-permeation oil displacement agent prepared by any of the preparation methods according to claims 2-5.

7. The nano-permeation oil displacement agent solution according to claim 6, characterized in that, The solvent of the solution is deionized water or formation water; the concentration of the nano-permeation displacement agent in the nano-permeation displacement agent solution is 0.1-2.0 wt%.

8. The application of a nano-permeable displacement agent or a nano-permeable displacement agent solution in fracturing and displacement of shale oil reservoirs, characterized in that, The nano-permeable oil displacement agent is the nano-permeable oil displacement agent according to claim 1 or the nano-permeable oil displacement agent prepared by any of the preparation methods according to claims 2-5; the nano-permeable oil displacement agent solution is the nano-permeable oil displacement agent solution according to claim 6 or 7.

9. The application according to claim 8, characterized in that, The shale oil reservoir has a formation temperature ≤100℃, formation water salinity of 0-10000 mg / L, and permeability of (0.01-1.0)×10⁻⁶. -3 μm 2 .

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