Method for improving stratum plugging efficiency by anchoring hydrogel

Abstract

The invention discloses a method for improving stratum plugging efficiency by anchoring hydrogel, belongs to the field of heterogeneous reservoir exploitation, and aims to solve the problem that conventional polymer hydrogel is easy to shrink and migrate due to dehydration under complex stratum conditions, realize long-term stable plugging effect and improve recovery efficiency. The method for improving the stratum plugging efficiency by anchoring the hydrogel comprises the following steps: firstly, grafting an initiation site on the surface of a rock pore channel; taking acrylamide as a monomer, and forming a polyacrylamide molecular chain on the surface of the rock through atom transfer radical polymerization; and finally, injecting the acrylamide hydrogel precursor into the rock. And gelling the hydrogel precursor and the polyacrylamide molecular chain on the surface of the rock together to form the hydrogel anchored on the surface of the pore channel of the rock. The anchored hydrogel can significantly improve the long-term stability of the acrylamide hydrogel in a rock channel, so that the stratum plugging efficiency is improved, the improvement of the long-term recovery efficiency of a reservoir is facilitated, and the anchored hydrogel is widely applied to the field of heterogeneous reservoir exploitation.

Description

Technical Field

[0001] The invention discloses a method for improving formation plugging efficiency by anchoring hydrogel, and belongs to the field of heterogeneous oil reservoir exploitation. Background Art

[0002] Water flooding is one of the most cost-effective secondary oil recovery methods. However, with the continuous deepening of water injection development, a dominant water channel is formed in the high permeability layer in the reservoir, causing water to appear in the oil well too early, and a large amount of crude oil in the low permeability layer cannot be recovered. Therefore, in order to improve the efficiency of water injection development, it is necessary to inject plugging agents deep into the formation to block the dominant channels of the high permeability layer, forcing the subsequent injected water to flow to the unaffected low permeability oil-rich layer, thereby further improving the recovery rate. Practice has shown that taking profile control and water plugging measures is an effective way to improve the effect of water flooding development. Among many polymer plugging agents, acrylamide polymer gels are widely used in the control of water production due to their good performance. However, they are prone to dehydration, shrinkage and migration in complex formation environments, resulting in a gradual decrease in plugging performance or even complete loss.

[0003] In view of the above problems, the present invention discloses a method for anchoring hydrogel to improve formation plugging efficiency, wherein the hydrogel is fixed on the surface of rock pores, and a gel precursor is injected after grafting polymer treatment on the rock surface to form a hydrogel fixed on the rock surface, thereby achieving stable plugging and achieving the purpose of improving crude oil recovery. Summary of the invention

[0004] The present invention discloses a method for anchoring hydrogel to improve formation plugging efficiency. Firstly, polyacrylamide molecular chains are grafted on the surface of rock pores, and then a polyacrylamide gel precursor is injected into the rock pores. The gel precursor and the polyacrylamide chains on the surface of the rock pores are gelled together to form a hydrogel fixed on the surface of the rock pores, thereby achieving long-term effective and stable plugging.

[0005] In order to achieve the above object, the present invention provides a method for anchoring hydrogel to improve formation plugging efficiency, comprising the following steps: (1) Treatment of rock surface with grafted polyacrylamide Grafting polyacrylamide onto rock surfaces can be achieved via surface initiated atom transfer radical polymerization (SI-ATRP).

[0006] 2-bromo-2-methylpropionic acid 3-(triethoxysilyl)propyl ester or 2-bromo-2-methylpropionic acid 3-(trimethoxysilyl)propyl ester is injected into the formation along with the working fluid to react with the surface of the rock pores, and an initiation site containing alkyl bromide is introduced on the surface of the rock pores. Acrylamide monomer, CuBr, and 2,2′-bipyridine are then injected into the formation along with the working fluid, and surface-initiated atom transfer polymerization (SI-ATRP) is carried out on the initiation site on the surface of the rock pores, so that the polyacrylamide molecular chain is grafted on the surface of the rock pores.

[0007] Wherein: the concentration of 3-(triethoxysilyl)propyl 2-bromo-2-methylpropionate or 3-(trimethoxysilyl)propyl 2-bromo-2-methylpropionate in the working fluid is 0.001wt% to 10wt%, the formation temperature is 40°C to 200°C, and the reaction time is 5 minutes to 120 hours.

[0008] The concentration of acrylamide monomer in the working solution is 0.1wt% to 20wt%, the concentration of CuBr or CuCl in the working solution is 0.01wt% to 10wt%, the concentration of 2,2′-bipyridine in the working solution is 0.01wt% to 10wt%, the formation temperature is 40°C to 200°C, and the reaction time is 5 minutes to 240 hours.

[0009] (2) Anchoring polyacrylamide hydrogel on rock surface An acrylamide polymer hydrogel precursor containing a polymer and a cross-linking agent is injected into the rock treated in step (1). The hydrogel precursor and the polyacrylamide molecular chains on the surface of the rock pores are gelled together to form a polyacrylamide hydrogel anchored on the surface of the rock pores.

[0010] Wherein: the polymer in the acrylamide polymer hydrogel precursor is polyacrylamide or partially hydrolyzed polyacrylamide, the crosslinking agent in the acrylamide polymer hydrogel precursor is N,N'-methylenebisacrylamide crosslinking agent, phenolic resin crosslinking agent, polyethyleneimine crosslinking agent or a mixture of the above crosslinking agents; the gelling reaction temperature is 40°C ~ 200°C, and the gelling reaction time is 30 minutes ~ 360 hours.

[0011] The beneficial effects of the present invention are: 1. The method for improving formation plugging efficiency by anchoring hydrogel provided by the present invention can achieve long-term and effective plugging of high-permeability layers of reservoirs, significantly improve the sweep efficiency of low-permeability reservoirs, and improve oil reservoir recovery.

[0012] 2. The method of anchoring hydrogel to improve formation plugging efficiency provided by the present invention has the advantages of high plugging efficiency, long plugging time, wide application range, etc., and is widely applicable to the plugging treatment of heterogeneous oil reservoirs. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 A schematic diagram of the method for improving formation plugging efficiency by anchoring hydrogel provided by the present invention.

[0014] Figure 2 This is the Fourier transform infrared spectrum of the rock before and after polyacrylamide is grafted on the rock pore surface.

[0015] Figure 3 The invention compares the oil recovery enhancement effect of the hydrogel anchored on the surface of the rock pores provided by the present invention with the oil recovery enhancement effect of the unfixed free hydrogel under different gel aging time conditions. DETAILED DESCRIPTION Example

[0016] A working solution containing 1wt% 2-bromo-2-methylpropionic acid 3-(triethoxysilyl)propyl ester was injected into a sandstone rock at 110°C and kept at 110°C for 12 hours. After the reaction was completed, the working solution was injected to drive out the unreacted 2-bromo-2-methylpropionic acid 3-(triethoxysilyl)propyl ester. Subsequently, a working solution containing 15wt% acrylamide monomer, 0.1wt% CuBr and 0.2wt% 2,2′-bipyridine was injected into the rock and reacted at 110°C for 12 hours. After the reaction was completed, the working solution was injected to drive out the unreacted substances to obtain a rock with polyacrylamide grafted on the pore surface. Figure 2 Shown is the Fourier transform infrared spectrum of the rock before and after polyacrylamide is grafted onto the rock pore surface.

[0017] Finally, a polyacrylamide hydrogel precursor solution containing phenolic resin as a crosslinking agent is injected into the rock with polyacrylamide grafted on the pore surface, and reacted at 110°C for 8 hours. The hydrogel precursor and the polyacrylamide molecular chains on the rock pore surface are gelled together to form a polyacrylamide hydrogel anchored on the rock pore surface. The results of the simulated heterogeneous oil reservoir oil recovery experiment show that compared with the unanchored free hydrogel, under different gel aging time conditions, the hydrogel anchored on the rock pore surface provided by the present invention can more significantly improve the oil recovery rate ( Figure 3 ). Example

[0018] A working fluid containing 2wt% 3-(trimethoxysilyl)propyl 2-bromo-2-methylpropionate is injected into a formation rock at 90°C and reacted at 90°C for 8 hours; after the reaction is completed, the working fluid is injected to drive out the unreacted substances; subsequently, a working fluid containing 20wt% acrylamide monomer, 0.5wt% CuCl, and 2wt% 2,2′-bipyridine is injected into the formation rock, and after reacting at 90°C for 48 hours, the working fluid is injected to drive out the unreacted substances to obtain a formation rock with polyacrylamide grafted on the pore surface.

[0019] Finally, a partially hydrolyzed polyacrylamide hydrogel precursor solution containing N,N'-methylenebisacrylamide as a cross-linker is injected into the formation rock with polyacrylamide grafted on the pore surface along with the working fluid. The solution is reacted at 90°C for 24 hours. The hydrogel precursor and the polyacrylamide molecular chains on the surface of the rock pores form a gel together to form a polyacrylamide hydrogel anchored on the surface of the rock pores, thereby achieving a long-term and effective plugging effect on the formation.

[0020] Although the specific implementation of the present invention is described in detail in conjunction with the drawings, it should not be understood as limiting the scope of protection of this patent. Within the scope described in the claims, various modifications and variations that can be made by those skilled in the art without creative work still fall within the scope of protection of this patent.

Claims

1. A method for anchoring hydrogel to improve formation plugging efficiency, characterized in that: The method comprises the following steps: (1) 2-bromo-2-methylpropionic acid 3-(triethoxysilyl)propyl ester or 2-bromo-2-methylpropionic acid 3-(trimethoxysilyl)propyl ester is injected into the formation along with the working fluid to react with the surface of the rock pores, so that the initiation sites containing alkyl bromide are grafted onto the surface of the rock pores. Then, acrylamide monomer, CuBr or CuCl, and 2,2′-bipyridine are injected into the formation along with the working fluid, and surface-initiated atom transfer polymerization (SI-ATRP) is carried out on the initiation sites on the surface of the rock pores, so that the polyacrylamide molecular chains are grafted onto the surface of the rock pores; (2) Injecting an acrylamide hydrogel precursor containing a polymer and a cross-linking agent into the rock pores treated in step (1), the acrylamide polymer hydrogel precursor and the polyacrylamide molecular chains on the surface of the rock pores form a gel to form a polyacrylamide hydrogel anchored on the surface of the rock pores, thereby achieving a long-term stable plugging effect, thereby improving the long-term recovery rate of the heterogeneous oil reservoir.

2. The method for improving formation plugging efficiency by anchoring hydrogel according to claim 1, characterized in that: In the step (1), the concentration of 3-(triethoxysilyl)propyl 2-bromo-2-methylpropionate or 3-(trimethoxysilyl)propyl 2-bromo-2-methylpropionate in the working fluid is 0.001wt% to 10wt%, the formation temperature is 40°C to 200°C, and the reaction time is 5 minutes to 120 hours.

3. The method for improving formation plugging efficiency by anchoring hydrogel according to claim 1, characterized in that: In the step (1), the concentration of acrylamide monomer in the working solution is 0.1wt% to 20wt%, the concentration of CuBr or CuCl in the working solution is 0.01wt% to 10wt%, the concentration of 2,2′-bipyridine in the working solution is 0.01wt% to 10wt%, the formation temperature is 40°C to 200°C, and the reaction time is 5 minutes to 240 hours.

4. The method for improving formation plugging efficiency by anchoring hydrogel according to claim 1, characterized in that: In the step (2), the polymer in the acrylamide polymer hydrogel precursor is polyacrylamide or partially hydrolyzed polyacrylamide, and the crosslinking agent in the acrylamide polymer hydrogel precursor is N,N'-methylenebisacrylamide crosslinking agent, phenolic resin crosslinking agent, polyethyleneimine crosslinking agent or a mixture of the above crosslinking agents.

5. The method for improving formation plugging efficiency by anchoring hydrogel according to claim 1, characterized in that: In the step (2), the formation temperature for the gelation of the acrylamide polymer hydrogel precursor and the polyacrylamide molecular chains on the surface of the rock pores is 40°C to 200°C, and the gelation time is 30 minutes to 360 hours.

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