Self-adaptive multi-scale water control agent for auxiliary fracturing of low-permeability reservoir and preparation method thereof

Abstract

The invention discloses a self-adaptive multi-scale water control agent for auxiliary fracturing of a low-permeability reservoir and a preparation method. The water control agent comprises the following components: clear water, a foaming agent, a scale regulator, a film-forming agent and a layering agent. The method comprises the following steps: firstly, respectively weighing the following components according to the mass ratio: the foaming agent: the scale regulator: the film-forming agent: the layering agent = (2.5-4): (5-10): (2-4): (0.8-1.5); the preparation method comprises the following steps: preparing a variable-frequency high-speed stirrer, adding 700-1350 mass ratio of clear water into a stirring cup of the variable-frequency high-speed stirrer, starting the stirrer, sequentially adding the foaming agent, the scale regulator, the film-forming agent and the layering agent, and continuously stirring for 15-20 minutes until the components are uniformly mixed, thereby obtaining the self-adaptive multi-scale water control agent for auxiliary fracturing of the low-permeability reservoir. According to the invention, the water production resistance in the stratum after the fracturing construction of the low-permeability reservoir can be greatly improved, and the auxiliary fracturing water control operation is realized.

Description

Technical Field

[0001] This invention belongs to the field of water control agent technology, specifically relating to an adaptive multi-scale water control agent for assisted fracturing in low-permeability reservoirs. This invention also relates to a method for preparing the above-mentioned water control agent. Background Technology

[0002] Water production control after reservoir commissioning has always been a challenging problem for engineers. Because the flow resistance of the water phase is much lower than that of the oil phase, once a water-dominant channel forms between the reservoir and the wellbore, the oil production energy in the same pressure system is significantly squeezed out, resulting in a substantial increase in surface water production and a corresponding significant decrease in oil production, thus harming the economic benefits of well commissioning. Simultaneously, the environmental impact of producing large amounts of formation water to the surface is also considerable. For low-permeability reservoirs, commissioning typically involves fracturing to create artificial fractures as formation fluid production channels. When the near-wellbore oil saturation is high, the oil phase production energy is sufficient, and water production is low. However, as near-wellbore oil production capacity decreases, water production capacity rapidly increases, and this fracture structure easily transforms into a water-dominant channel, inhibiting oil production in other areas. In this case, water control operations must be implemented.

[0003] However, both common mechanical and chemical water shut-off methods have a success rate of less than 30% based on current market application. The former requires extremely accurate identification of the water outlet location and is unsuitable for low-permeability reservoirs where oil and water co-exist. The latter consistently struggles to reconcile the conflict between water control intensity and oil production effectiveness. Excessive water control intensity inevitably damages oil production capacity, leading to a decline in both oil and water production; insufficient water control intensity fails to adequately suppress water production, and oil production cannot be significantly improved. In summary, water control after water production in low-permeability reservoirs presents significant challenges. Summary of the Invention

[0004] The purpose of this invention is to provide an adaptive multi-scale water control agent for assisted fracturing in low-permeability reservoirs, which can significantly improve the water production resistance in the formation after fracturing operations in low-permeability reservoirs and realize water control operations in assisted fracturing.

[0005] Another objective of this invention is to provide a method for preparing an adaptive multi-scale water control agent for assisted fracturing in low-permeability reservoirs.

[0006] The first technical solution adopted in this invention is an adaptive multi-scale water control agent for assisted fracturing of low-permeability reservoirs, comprising the following components: water, foaming agent, scale regulator, film-forming agent, and layering agent, wherein the mass ratio between the components is water, foaming agent: scale regulator: film-forming agent: layering agent = 700~1350, 2.5~4: 5~10: 2~4: 0.8~1.5.

[0007] The first technical solution of the present invention is further characterized in that,

[0008] The mass ratio of water, foaming agent, scale regulator, film-forming agent, and layering agent is water: foaming agent: scale regulator: film-forming agent: layering agent = 700~1350, 3~4: 5~10: 2~4: 0.8~1.5.

[0009] The foaming agent includes sodium dodecylbenzenesulfonate and dodecyl dimethyl betaine, with a mass ratio of sodium dodecylbenzenesulfonate to dodecyl dimethyl betaine of 1–3:0.5–2.5.

[0010] The scale regulators include hydroxymethyl starch and hydroxyethyl starch, and the mass ratio of hydroxymethyl starch to hydroxyethyl starch solution is 3.5–6.5:1–3.5.

[0011] Film-forming agents include hydroxyethyl cellulose and hydroxypropyl cellulose, with a mass ratio of hydroxyethyl cellulose to hydroxypropyl cellulose of 1–3.5:0.5–3.

[0012] The layering agent includes sodium hydroxyethyl cellulose and carboxymethyl chitosan, with a mass ratio of sodium hydroxyethyl cellulose to carboxymethyl chitosan of 8–15:0.03–0.15.

[0013] The mass ratio of sodium dodecylbenzenesulfonate to dodecyl dimethyl betaine is sodium dodecylbenzenesulfonate : dodecyl dimethyl betaine = 1.5~2.5 : 1~2;

[0014] The mass ratio of hydroxymethyl starch to hydroxyethyl starch solution is 4-6:1.5-3.

[0015] The mass ratio of hydroxyethyl cellulose to hydroxypropyl cellulose is 1.5–3.5:1–1.5.

[0016] The mass ratio of sodium hydroxyethyl cellulose to carboxymethyl chitosan is sodium hydroxyethyl cellulose: carboxymethyl chitosan = 10-14: 0.05-0.12.

[0017] The second technical solution adopted in this invention is a method for preparing an adaptive multi-scale water control agent for assisted fracturing in low-permeability reservoirs, specifically including the following steps:

[0018] Step 1: Weigh the following components according to their mass ratios:

[0019] Sodium dodecylbenzenesulfonate: Dodecyl dimethyl betaine: Hydroxymethyl starch: Hydroxyethyl starch: Hydroxyethyl cellulose: Hydroxypropyl cellulose: Sodium hydroxyethyl cellulose: Carboxymethyl chitosan = 1-3: 0.5-2.5: 3.5-6.5: 1-3.5: 1-3.5: 0.5-3: 8-15: 0.03-0.15;

[0020] Step 2: Take water with a mass ratio of 700-1350 and put it into the mixing cup of the variable frequency high-speed stirrer. Start the stirrer and add sodium dodecylbenzenesulfonate and dodecyl dimethyl betaine in sequence. Stir for 1 min to 2 min, then add hydroxymethyl starch and hydroxyethyl starch in sequence and continue stirring for 1 min to 2 min.

[0021] Step 3: Increase the speed of the stirrer and add hydroxyethyl cellulose, hydroxypropyl cellulose, sodium hydroxyethyl cellulose and carboxymethyl chitosan to the mixing cup in sequence;

[0022] Step 4: Stir continuously at a speed of 8000 r / min to 8500 r / min for 15 min to 20 min to obtain an adaptive multi-scale water control agent for assisted fracturing of low-permeability reservoirs.

[0023] The second technical solution of the present invention is further characterized in that,

[0024] In step 2, sodium dodecylbenzenesulfonate and dodecyl dimethyl betaine are added sequentially to the mixing vessel at a rate of 2 g / min to 3 g / min; in step 2, hydroxymethyl starch and hydroxyethyl starch are added sequentially to the mixing vessel at a rate of 2 g / min to 3 g / min.

[0025] When sodium dodecylbenzenesulfonate, dodecyl dimethyl betaine, hydroxymethyl starch and hydroxyethyl starch are added, the stirring speed of the variable frequency high-speed stirrer is 4000 r / min to 4500 r / min.

[0026] In step 3, when adding hydroxyethyl cellulose, hydroxypropyl cellulose, sodium hydroxyethyl cellulose and carboxymethyl chitosan to the mixing cup in sequence, the stirring speed is 8000 r / min to 8500 r / min, and hydroxyethyl cellulose, hydroxypropyl cellulose, sodium hydroxyethyl cellulose and carboxymethyl chitosan are added to the mixing cup at a rate of 2 g / min to 3 g / min.

[0027] The beneficial effects of this invention are:

[0028] The adaptive multi-scale water control agent for low-permeability reservoir fracturing of this invention is based on a foam system. It introduces a foaming agent and a scale modifier as surfactant and macromolecular components, respectively, to form a structure with randomly distributed scales. The scale modifier stabilizes the vesicle structure formed by the foaming agent, ensuring stable suspension and preventing rupture even after deformation. This meets the injection requirements of different scales of formation pores and fracture channels. Simultaneously, the spherical structure of the formed vesicles provides a large specific surface area, carrying more water-enhancing components into the formation and adsorbing them onto the rock surface at the fracture end after fracturing. This significantly increases the water production resistance in the formation after fracturing, with almost no impact on the oil phase flow resistance, thus achieving water control in fracturing operations. Detailed Implementation

[0029] The present invention will now be described in detail with reference to specific embodiments.

[0030] Once water is produced in a low-permeability reservoir, a dominant water-producing channel is formed, making water control difficult and posing high operational risks. Therefore, before fracturing production begins and a dominant water-producing channel has yet to form in the reservoir, injecting the adaptive multi-scale water-control agent for low-permeability reservoir fracturing (as per this invention) can significantly increase the resistance to water production, creating a preventative water control effect that better meets the water control requirements of low-permeability reservoirs.

[0031] This invention relates to an adaptive multi-scale water control agent for assisted fracturing in low-permeability reservoirs, comprising the following components: water, foaming agent, scale regulator, film-forming agent, and layering agent. The mass ratio of each component is water: foaming agent: scale regulator: film-forming agent: layering agent = 700-1350: 2.5-4: 5-10: 2-4: 0.8-1.5.

[0032] Furthermore, the mass ratio of water, foaming agent, scale regulator, film-forming agent, and layering agent is foaming agent: scale regulator: film-forming agent: layering agent = 700~1350: 3~4: 5~10: 2~4: 0.8~1.5.

[0033] The foaming agent includes sodium dodecylbenzenesulfonate and dodecyl dimethyl betaine, with a mass ratio of sodium dodecylbenzenesulfonate to dodecyl dimethyl betaine of 1–3:0.5–2.5.

[0034] The scale regulators include hydroxymethyl starch and hydroxyethyl starch, and the mass ratio of hydroxymethyl starch to hydroxyethyl starch solution is 3.5–6.5:1–3.5.

[0035] Film-forming agents include hydroxyethyl cellulose and hydroxypropyl cellulose, with a mass ratio of hydroxyethyl cellulose to hydroxypropyl cellulose of 1–3.5:0.5–3.

[0036] The layering agent includes sodium hydroxyethyl cellulose and carboxymethyl chitosan, with a mass ratio of sodium hydroxyethyl cellulose to carboxymethyl chitosan of 8–15:0.03–0.15.

[0037] Preferably, the mass ratio of sodium dodecylbenzenesulfonate to dodecyl dimethyl betaine is sodium dodecylbenzenesulfonate: dodecyl dimethyl betaine = 1.5-2.5: 1-2;

[0038] Preferably, the mass ratio of hydroxymethyl starch to hydroxyethyl starch solution is 4-6:1.5-3.

[0039] Preferably, the mass ratio of hydroxyethyl cellulose to hydroxypropyl cellulose is 1.5–3.5:1–1.5.

[0040] Preferably, the mass ratio of sodium hydroxyethyl cellulose to carboxymethyl chitosan is sodium hydroxyethyl cellulose: carboxymethyl chitosan = 10-14: 0.05-0.12.

[0041] The preparation method of the adaptive multi-scale water control agent for assisted fracturing in low-permeability reservoirs of the present invention specifically includes the following steps:

[0042] Step 1: Weigh the following components according to their mass ratios:

[0043] Foaming agent: Scale regulator: Film-forming agent: Layering agent = 2.5~4: 5~10: 2~4: 0.8~1.5.

[0044] Step 2: Take water with a mass ratio of 700 to 1350 and put it into the mixing cup of the variable frequency high-speed stirrer. Set the stirring speed of the variable frequency high-speed stirrer to 4000 r / min to 4500 r / min. Add sodium dodecylbenzenesulfonate and dodecyl dimethyl betaine in sequence at a speed of 2 g / min to 3 g / min. Stir for 1 min to 2 min. Then add hydroxymethyl starch and hydroxyethyl starch in sequence at a speed of 2 g / min to 3 g / min. Stir for 1 min to 2 min.

[0045] Step 3: Adjust the stirring speed to 8000r / min~8500r / min, and add hydroxyethyl cellulose, hydroxypropyl cellulose, sodium hydroxyethyl cellulose and carboxymethyl chitosan in sequence at a speed of 2g / min~3g / min;

[0046] Step 4: After all components have been added, stir continuously for 15-20 minutes at a speed of 8000-8500 r / min to obtain an adaptive multi-scale water control agent for assisted fracturing of low-permeability reservoirs.

[0047] Furthermore, the ratio of foaming agent: scale regulator: film-forming agent: layering agent = 2.5~4: 5~10: 2~4: 0.8~1.5 in step 1 can also be converted to sodium dodecylbenzenesulfonate: dodecyl dimethyl betaine: hydroxymethyl starch: hydroxyethyl starch: hydroxyethyl cellulose: hydroxypropyl cellulose: sodium hydroxyethyl cellulose: carboxymethyl chitosan = 1~3: 0.5~2.5: 3.5~6.5: 1~3.5: 1~3.5: 0.5~3: 8~15: 0.03~0.15;

[0048] In the preparation of the adaptive multi-scale water control agent for assisted fracturing of the above-mentioned low-permeability reservoirs, the clean water is taken from the site, which is convenient to obtain and economical.

[0049] Secondly, the adaptive multi-scale water control agent for assisted fracturing in low-permeability reservoirs prepared according to the above-mentioned proportions achieves the desired target performance. Specifically, the density of this adaptive multi-scale water control agent is 0.55 g / cm³. 3 ~0.95g / cm 3 The apparent viscosity is 15.5 mPa·s to 32.5 mPa·s, the plastic viscosity is 7.5 mPa·s to 22.5 mPa·s, and the dynamic-plastic ratio is 0.7 Pa / (mPa·s) to 1.10 Pa / (mPa·s), enabling rapid on-site pumping.

[0050] Example 1

[0051] In this embodiment, water at a mass ratio of 13:50 was placed in a mixing cup. While stirring at 4000 rpm, 2.5 g of sodium dodecylbenzenesulfonate and 2.5 g of dodecyl dimethyl betaine were added at a rate of 2 g / min. After stirring for 1 minute, 6 g of hydroxymethyl starch and 3 g of hydroxyethyl starch were added at a rate of 3 g / min. After stirring for 2 minutes, the stirring speed was adjusted to 8500 rpm, and 2.5 g of hydroxyethyl cellulose, 1.5 g of hydroxypropyl cellulose, 13 g of sodium hydroxyethyl cellulose, and 0.11 g of carboxymethyl chitosan were added sequentially to the beaker. All components were added at mass ratios. Stirring was continued for 15 minutes until all parts were uniformly mixed, yielding an adaptive multi-scale water control agent for assisted fracturing in low-permeability reservoirs. The density of the prepared water control agent was directly measured using a density balance, and the final density was 0.82 g / cm³. 3 .

[0052] Example 2

[0053] The preparation steps in this embodiment are the same as in Example 1, except that the amounts of each component are changed. The mass ratio is as follows: 700 parts water, 1 part sodium dodecylbenzenesulfonate, 1.3 parts dodecyl dimethyl betaine, 3.5 parts hydroxymethyl starch, 1 part hydroxyethyl starch, 1 part hydroxyethyl cellulose, 0.5 parts hydroxypropyl cellulose, 8 parts sodium hydroxyethyl cellulose, and 0.15 parts carboxymethyl chitosan. The mixture is stirred until all parts are homogeneous, and the final density of the water-controlling agent is 0.76 g / cm³. 3 .

[0054] Example 3

[0055] In this embodiment, the water-controlling agent is prepared using the same steps as in Example 1. While keeping other component parameters unchanged, the amount of foaming agent added is adjusted in a gradient manner, as described below.

[0056] Five water-controlling agents were prepared, with all other components remaining constant except for the mass ratio of the foaming agent. These five experiments were designated A, B, C, D, and E. In experiment A, the components were weighed according to the following mass ratios: 1000 parts water, 2.6 parts sodium dodecylbenzenesulfonate, 0.5 parts dodecyl dimethyl betaine, 6.5 parts hydroxymethyl starch, 3.5 parts hydroxyethyl starch, 3.5 parts hydroxyethyl cellulose, 3 parts hydroxypropyl cellulose, 15 parts sodium hydroxyethyl cellulose, and 0.03 parts carboxymethyl chitosan.

[0057] The amounts of sodium dodecylbenzenesulfonate and dodecyl dimethyl betaine in the foaming agent were gradually increased at 0.1 mass intervals. Specifically, the foaming agent in experiment B was 2.7% sodium dodecylbenzenesulfonate and 0.6% dodecyl dimethyl betaine; the foaming agent in experiment C was 2.8% sodium dodecylbenzenesulfonate and 0.7% dodecyl dimethyl betaine; the foaming agent in experiment D was 2.9% sodium dodecylbenzenesulfonate and 0.8% dodecyl dimethyl betaine; and the foaming agent in experiment E was 3% sodium dodecylbenzenesulfonate and 0.9% dodecyl dimethyl betaine.

[0058] The density of the adaptive multi-scale water control agent for assisted fracturing of low-permeability reservoirs prepared in experiments A, B, C, D and E was measured using a density balance. The density distribution of the water control agent in the five experiments is shown in Table 1.

[0059] Table 1 shows the densities of the water-controlling agents prepared from A, B, C, D, and E.

[0060]

[0061] Example 4

[0062] This embodiment is based on Example 3. The amount of water added is adjusted in a gradient manner. Based on the above-mentioned Experiment A, the amount of water added is gradually increased at intervals of 50 to dilute the water-controlling agent in Experiment A. The results of four experiments (F, G, H, and J) are recorded continuously (the amount of water added is 1050, 1100, 1150, and 1200 respectively). The density of the water-controlling agents prepared in Experiments F, G, H, and J is measured using a density scale. The density distribution of the five experiments is compared and shown in Table 2.

[0063] Table 2 shows the densities of the water-controlling agents prepared by A, F, G, H, and J.

[0064]

[0065]

[0066] Since the structure content in the adaptive multi-scale water control agent for assisted fracturing in low-permeability reservoirs of this invention characterizes the water control performance of the system, and considering the difficulty in accurately measuring the structure content, the content is indirectly characterized by density values. Lower density indicates higher content, and higher density indicates lower content.

[0067] As can be seen from Examples 1 to 4, the density of the adaptive multi-scale water control agent for assisted fracturing in low-permeability reservoirs can be adjusted by changing the composition ratio. Specifically, as shown in Table 1, increasing the proportion of foaming agent in the water control agent reduces its density; as shown in Table 2, increasing the proportion of water in the water control agent increases its density. Furthermore, with the addition of foaming agent, the density change of the prepared water control agent becomes stable, making it easy to control and obtain an adaptive multi-scale water control agent with the target density.

[0068] Because the adaptive multi-scale water control agent for low-permeability reservoir fracturing of this invention exhibits relatively stable foam performance and viscosity properties during preparation, it can meet the formation sealing performance requirements. Pressure tests were conducted on the water control agents prepared in Examples 1-4. In an indoor laboratory setting, 25mm diameter sand-filled tubes were filled with 40-120 mesh quartz sand until the gas permeability was between 800-1200 mD. First, clean water was injected at a stable displacement rate of 0.5 mL / min, and the displacement pressure value P1 was tested when the injection stabilized. Then, the water control agent prepared according to this invention was injected stably at the same flow rate for 2 hours. Afterward, clean water was replaced, and the injection was repeated at a displacement rate of 0.5 mL / min until stable, and the displacement pressure value P2 was tested. The difference between P2 and P1 characterizes the distribution of the water control agent's improvement on the pressure-bearing capacity of the sand-filled tube. The experimental results are shown in Table 3.

[0069] Table 3. Experimental results of adaptive multi-scale water-controlling agent improving formation pressure bearing capacity.

[0070]

[0071] It can be seen that the adaptive multi-scale water control agent for low-permeability reservoir fracturing of the present invention, after being injected into a sand-packed pipe with a permeability of close to 1000mD, increases the pressure bearing capacity by ≥5MPa and has good water control performance.

[0072] Because the adaptive multi-scale water control agent for low-permeability reservoir fracturing of the present invention has no solid phase, the surfactant and macromolecules have self-degradability, and it has good reservoir damage control capabilities.

[0073] Protective experiments were conducted on the water-controlling agents prepared in Examples 1-4. In an indoor environment, a 25mm diameter sand-filled pipe was filled with 20-40 mesh quartz sand until the gas permeability was approximately 20mD. The initial liquid permeability K1 was first tested with formation water. Then, the water-controlling agent prepared according to this invention was injected with the same fluid for 2 hours. Nitrogen gas was then used to displace the liquid until no liquid returned from the outlet. The permeability K2 of the sand-filled pipe was then tested again with clean water. The permeability recovery rate K2 / K1 of the sand-filled pipe was calculated. The experimental results are shown in Table 4.

[0074] Table 4. Experimental Results of Adaptive Multi-Scale Water Control Agent Damage Rate Recovery Evaluation

[0075] Initial penetration rate K1 Permeability K2 after displacement Permeability recovery rate 23mD 21.4mD 93.04％

[0076] It can be seen that the permeability recovery rate of the adaptive multi-scale water control agent for low-permeability reservoir fracturing of the present invention is >90% after displacement, which shows good reservoir protection performance.

Claims

1. An adaptive multi-scale water control agent for assisted fracturing in low-permeability reservoirs, characterized in that, It includes the following components: water, foaming agent, scale regulator, film-forming agent and layering agent. The mass ratio of each component is water, foaming agent: scale regulator: film-forming agent: layering agent = 700~1350, 2.5~4: 5~10: 2~4: 0.8~1.

5.

2. The adaptive multi-scale water control agent for assisted fracturing of low-permeability reservoirs according to claim 1, characterized in that, The mass ratio of water, foaming agent, scale regulator, film-forming agent and layering agent is water, foaming agent: scale regulator: film-forming agent: layering agent = 700~1350, 3~4: 5~10: 2~4: 0.8~1.

5.

3. The adaptive multi-scale water control agent for assisted fracturing of low-permeability reservoirs according to claim 1 or 2, characterized in that, The foaming agent comprises sodium dodecylbenzenesulfonate and dodecyl dimethyl betaine, wherein the mass ratio of sodium dodecylbenzenesulfonate to dodecyl dimethyl betaine is sodium dodecylbenzenesulfonate: dodecyl dimethyl betaine = 1-3: 0.5-2.5; The scale regulator includes hydroxymethyl starch and hydroxyethyl starch, and the mass ratio of the hydroxymethyl starch and hydroxyethyl starch solution is hydroxymethyl starch: hydroxyethyl starch solution = 3.5~6.5: 1~3.5; The film-forming agent includes hydroxyethyl cellulose and hydroxypropyl cellulose, wherein the mass ratio of hydroxyethyl cellulose to hydroxypropyl cellulose is 1-3.5:0.5-3. The layering agent includes sodium hydroxyethyl cellulose and carboxymethyl chitosan, wherein the mass ratio of sodium hydroxyethyl cellulose to carboxymethyl chitosan is 8-15:0.03-0.

15.

4. The adaptive multi-scale water control agent for assisted fracturing of low-permeability reservoirs according to claim 3, characterized in that, The mass ratio of sodium dodecylbenzenesulfonate to dodecyl dimethyl betaine is sodium dodecylbenzenesulfonate: dodecyl dimethyl betaine = 1.5~2.5: 1~2; The mass ratio of the hydroxymethyl starch and hydroxyethyl starch solution is hydroxymethyl starch: hydroxyethyl starch solution = 4-6: 1.5-3; The mass ratio of hydroxyethyl cellulose to hydroxypropyl cellulose is 1.5–3.5:1–1.

5. The mass ratio of sodium hydroxyethyl cellulose to carboxymethyl chitosan is sodium hydroxyethyl cellulose: carboxymethyl chitosan = 10-14: 0.05-0.

12.

5. A method for preparing an adaptive multi-scale water control agent for assisted fracturing in low-permeability reservoirs, characterized in that, Specifically, the following steps are included: Step 1: Weigh the following components according to their mass ratios: Sodium dodecylbenzenesulfonate: Dodecyl dimethyl betaine: Hydroxymethyl starch: Hydroxyethyl starch: Hydroxyethyl cellulose: Hydroxypropyl cellulose: Sodium hydroxyethyl cellulose: Carboxymethyl chitosan = 1-3: 0.5-2.5: 3.5-6.5: 1-3.5: 1-3.5: 0.5-3: 8-15: 0.03-0.15; Step 2: Take water with a mass ratio of 700-1350 and put it into the mixing cup of the variable frequency high-speed stirrer. Start the stirrer and add sodium dodecylbenzenesulfonate and dodecyl dimethyl betaine in sequence. Stir for 1 min to 2 min, then add hydroxymethyl starch and hydroxyethyl starch in sequence and continue stirring for 1 min to 2 min. Step 3: Increase the speed of the stirrer and add hydroxyethyl cellulose, hydroxypropyl cellulose, sodium hydroxyethyl cellulose and carboxymethyl chitosan to the mixing cup in sequence; Step 4: Stir continuously at a speed of 8000 r / min to 8500 r / min for 15 min to 20 min to obtain an adaptive multi-scale water control agent for assisted fracturing of low-permeability reservoirs.

6. The preparation method of the adaptive multi-scale water control agent for assisted fracturing in low-permeability reservoirs according to claim 5, characterized in that, In step 2, sodium dodecylbenzenesulfonate and dodecyl dimethyl betaine are added sequentially to the mixing vessel at a rate of 2 g / min to 3 g / min; in step 2, hydroxymethyl starch and hydroxyethyl starch are added sequentially to the mixing vessel at a rate of 2 g / min to 3 g / min. When sodium dodecylbenzenesulfonate, dodecyl dimethyl betaine, hydroxymethyl starch and hydroxyethyl starch are added, the stirring speed of the variable frequency high-speed stirrer is 4000 r / min to 4500 r / min.

7. The preparation method of the adaptive multi-scale water control agent for assisted fracturing in low-permeability reservoirs according to claim 5, characterized in that, In step 3, when hydroxyethyl cellulose, hydroxypropyl cellulose, sodium hydroxyethyl cellulose and carboxymethyl chitosan are added to the mixing cup in sequence, the stirring speed is 8000 r / min to 8500 r / min, and hydroxyethyl cellulose, sodium hydroxyethyl cellulose and carboxymethyl chitosan are added to the mixing cup at a rate of 2 g / min to 3 g / min.

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