In-situ crosslinking-self-degradation high-strength gel temporary plugging agent and preparation method thereof

Abstract

The invention discloses an in-situ crosslinking-self-degradation high-strength gel temporary plugging agent and a preparation method thereof, and belongs to the technical field of oil-gas field development. The gel temporary plugging agent is prepared from the following substances in parts by weight: 0.33 to 2.33 parts of polyvinyl alcohol, 0.67 to 4.67 parts of corn amylopectin, 2.8 to 7.0 parts of acrylamide, 1.2 to 3.0 parts of N-vinyl pyrrolidone, 0.05 to 1.05 parts of a cross-linking agent, 0.001 to 0.06 part of an initiator, 0.3 to 2.1 parts of glycerol, 0.02 to 0.14 part of calcium chloride and the balance of water, and the sum of the parts by weight of the substances is 100 parts. The preparation method is simple and convenient to operate, raw materials are low in price and easy to obtain, the preparation process is controllable, and huge industrial popularization prospects are shown. The gel temporary plugging agent is used for a reservoir temporary plugging steering process, can be self-degraded under the condition of constant temperature of a stratum, and has important significance for realizing efficient development of an oil field and improving the oil and gas recovery ratio.

Description

Technical Field

[0001] The invention belongs to the technical field of oil and gas field development, and particularly relates to an in-situ cross-linking-self-degrading high-strength gel temporary plugging agent, a preparation method and application thereof. Background Art

[0002] Temporary plugging and diversion technology is widely used in shale and tight sandstone mining to enhance the density of fracture networks and increase the production of oil and gas in undeveloped reservoirs. Temporary plugging and diversion technology blocks the initial fractures to avoid ineffective fracturing caused by energy loss during fracturing, and forces the fracturing fluid to divert and open new fractures, thereby restoring the initial fractures to continue production. Traditional mechanical temporary plugging methods are mainly suitable for wellbore plugging, and their scope of application is limited. Chemical temporary plugging methods mainly include solid phase material injection and liquid rubber plug segment plugging. After the temporary plugging and diversion material is injected into the reservoir fracture, an effective temporary plug segment is formed through bridging and in-situ cross-linking, which prompts the fracturing fluid to divert and open new fractures. After the temporary plug segment is degraded, the initial fracture resumes production. Studies have reported that the segment plug structure constructed by fibers and degradable particles has high strength and wide temperature adaptability, but the lack of access to real reservoir fracture information limits its plugging performance. Liquid rubber plug temporary plugging materials are injected into the fractures in a plugging manner and then cross-linked and degraded in situ. Currently, liquid rubber plug temporary plugging materials are mainly used for profile control and water plugging, but the non-degradability of such materials makes them difficult to apply to temporary plugging and diversion processes.

[0003] More and more scholars have begun to study self-degradable liquid plugging agents, "A thermally induced supramolecular gel temporary plugging and diverting fracturing fluid" (CN106190087B), and prepared a thermally responsive temporary plugging and diverting agent. The system is a low-viscosity, flowable liquid at room temperature. As the temperature rises to 60-90°C, the viscosity increases rapidly and loses fluidity. When the temperature continues to rise to 90-150°C, it automatically breaks into small molecules and restores a low-viscosity, flowable state. Although the system achieves thermal phase change, the phase change temperatures required for liquid, solid and liquid are not the same, and it is difficult to heat the formation in actual production. The thermal phase change system still has certain limitations.

[0004] The present invention proposes for the first time an in-situ cross-linked and self-degradable physical and chemical interpenetrating high-strength gel temporary plugging agent, which can achieve self-degradation of liquid plug under constant temperature conditions in the formation without temperature change, and under the action of the physical cross-linked structure, the polymer gel system has both thermal phase change properties and stronger wall adhesion properties. Summary of the invention

[0005] The purpose of the present invention is to provide an in-situ cross-linked and self-degradable high-strength gel temporary plugging agent, which has the advantages of strong toughness, self-degradation, wide applicable temperature, excellent wall adhesion performance and low price, and has broad market application prospects.

[0006] Another object of the present invention is to provide a method for preparing the in-situ cross-linking-self-degrading high-strength gel temporary plugging agent, which has reliable principle, simple operation, cheap and readily available raw materials, controllable preparation process, and shows great prospects for industrial promotion.

[0007] Another object of the present invention is to provide an application of the in-situ cross-linked and self-degradable high-strength gel temporary plugging agent in a reservoir temporary plugging and diversion process, which can achieve self-degradation of the liquid plug under constant formation temperature conditions without temperature changes, and is of great significance for achieving efficient development of oil fields and improving oil and gas recovery rates.

[0008] In order to achieve the above technical objectives, the present invention adopts the following technical solutions.

[0009] The in-situ cross-linking and self-degrading high-strength gel temporary plugging agent is composed of the following substances in parts by weight: 0.33-2.33 parts of polyvinyl alcohol, 0.67-4.67 parts of corn amylopectin, 2.8-7.0 parts of acrylamide, 1.2-3.0 parts of N-vinyl pyrrolidone, 0.05-1.05 parts of a cross-linking agent, 0.001-0.06 parts of an initiator, 0.3-2.10 parts of glycerol, 0.02-0.14 parts of calcium chloride, and the balance is water. The sum of the parts by weight of the above substances is 100 parts.

[0010] Furthermore, the cross-linking agent is polyethylene glycol diacrylate.

[0011] Furthermore, the initiator is tert-butyl perbenzoate.

[0012] Furthermore, the mass ratio of acrylamide to N-vinyl pyrrolidone is 7:3.

[0013] The preparation method of the in-situ cross-linking-self-degrading high-strength gel temporary plugging agent comprises the following steps: First, a certain amount of polyvinyl alcohol (PVA) was weighed and dissolved in an appropriate amount of water. The corn amylopectin was dispersed in the polyvinyl alcohol solution. Glycerol and CaCl were added at the same time. 2 , after being mixed uniformly at room temperature, it is placed in a constant temperature environment of 90°C for 30 minutes to obtain a pre-gelatinized solution; Secondly, a certain mass of monomers acrylamide (AM) and N-vinyl pyrrolidone (NVP) are weighed and dissolved in water to prepare a base liquid of a certain concentration, and a crosslinking agent and an initiator are added to the base liquid to obtain a monomer solution; Finally, the pre-gelatinized solution and the monomer solution are mixed evenly at room temperature to obtain a reaction solution of the gel temporary plugging agent.

[0014] The application of the in-situ cross-linked and self-degradable high-strength gel temporary plugging agent in the reservoir temporary plugging and diversion process is as follows: first, a pre-fluid is injected, then a prepared gel temporary plugging agent reaction solution is injected according to the requirements of the oil and gas reservoir, and finally a displacement fluid is injected; after the gel temporary plugging agent reaction solution enters a formation environment with a temperature of 100-150° C., it is in-situ polymerized and cross-linked in the cracks for 20-200 minutes to form a high-strength gel temporary plugging agent, and then a subsequent fracturing process is immediately carried out; after the construction is completed, the gel temporary plugging agent is spontaneously degraded into a low-viscosity degradation fluid in a high-temperature environment of 100-150° C. after 12-90 hours, and is returned to the ground with the fracturing fluid.

[0015] The present invention forms a gel temporary plugging agent with a physical and chemical interpenetrating structure through a physical cross-linking network constructed by polyvinyl alcohol and starch and a chemical cross-linking network constructed by acrylamide and N-vinyl pyrrolidone. At the beginning, starch and polyvinyl alcohol are mixed to form an initial physical cross-linking network (pre-gelatinized solution), and then acrylamide and N-vinyl pyrrolidone react in the physical network formed by starch and polyvinyl alcohol under high temperature conditions in the formation to form a chemical cross-linking network, and the chemical cross-linking network grows in the starch network and permeates each other, and finally a uniform high-strength cross-linking network with interpenetrating physical and chemical structures can be obtained.

[0016] The glycerol and CaCl 2 It is mainly used to provide plasticization for physical cross-linking, thereby ensuring the fluidity of physical cross-linking.

[0017] The reaction process of the physical and chemical interpenetrating network formation is as follows:

[0018] Compared with the prior art, the present invention has the following beneficial effects: (1) The gel temporary plugging agent of the present invention uses acrylamide monomers, N-vinyl pyrrolidone, polyvinyl alcohol and starch as reaction materials, and adds a chemical crosslinking agent. The obtained physicochemical interpenetrating crosslinked gel temporary plugging agent can effectively dissipate energy when subjected to external forces, further improving the strength and toughness of the gel temporary plugging agent; (2) The raw materials for preparing the temporary gel plugging agent of the present invention include an unstable cross-linking agent, which contains an ester group. When the temporary gel plugging agent is heated, the ester group is hydrolyzed, and the gel is automatically broken and degraded, without the need for additional gel breaking means. The degradation time of the temporary gel plugging agent can be controlled by adjusting the amount of the unstable cross-linking agent in the system; (3) The initiator used in the gel temporary plugging agent system of the present invention is a high-temperature initiator, which can only have strong initiation activity under higher temperature conditions, so that the system can be applied to high-temperature reservoirs; (4) The gel temporary plugging agent forms a gel structure with high-temperature thixotropy under the mixed action of polyvinyl alcohol, starch, glycerol and calcium chloride, so that it can reduce filtration loss while ensuring effective migration; (5) After the physical cross-linking of polyvinyl alcohol and starch is introduced into the gel temporary plugging agent, more hydrogen bond donors can be provided for the gel temporary plugging agent, thereby enhancing the adhesion strength between the gel and the rock interface and effectively improving the plugging performance of the gel. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Microscopic morphology of the gel temporary plugging agent under different cross-linking conditions.

[0020] (a) Pure chemical cross-linked gel (b) Physical and chemical interpenetrating cross-linked gel Figure 2 This is a graph showing the change in elastic modulus of chemically cross-linked gel and physicochemically interpenetrating cross-linked gel. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0022] 1. Preparation of in-situ cross-linked self-degradable high-strength gel temporary plugging agent

[0023] Example 1 Dissolve 0.33g PVA in 50g water, weigh 0.67g corn amylopectin and disperse it in the PVA solution, and add 0.3g glycerol and 0.02g CaCl 2 , mix at 200r / min at room temperature, and then place in a constant temperature environment of 90℃ for pre-gelatinization for 30min to obtain a pre-gelatinized solution. Take 5.6gAM and 2.4gNVP and add them to 20g water, then add 0.2g cross-linking agent and 0.004g initiator to obtain a base liquid, add the base liquid to the pre-gelatinized solution, add clean water to 100g, mix at 200r / min at room temperature, and prepare an in-situ cross-linking-self-degradable high-strength gel temporary plugging agent reaction solution.

[0024] The reaction solution was placed in a simulated reservoir environment at 100°C for 90 minutes to form a gel. After forming a gel, the temporary plugging agent was placed in a simulated reservoir environment at 100°C and completely degraded into a low-viscosity liquid within 5 hours.

[0025] Example 2 Dissolve 1.00 g PVA in 50 g water, weigh 2.00 g corn amylopectin and disperse it in the PVA solution, and add 0.9 g glycerol and 0.06 g CaCl 2, mix at 200r / min at room temperature, and then place in a constant temperature environment of 90℃ for pre-gelatinization for 30min to obtain a pre-gelatinized solution. Take 5.6gAM and 2.4gNVP and add them to 20g water, then add 0.2g cross-linking agent and 0.004g initiator to obtain a base liquid, add the base liquid to the pre-gelatinized solution, add clean water to 100g, mix at 200r / min at room temperature, and prepare an in-situ cross-linking-self-degradable high-strength gel temporary plugging agent reaction solution.

[0026] The reaction solution was placed in a simulated reservoir environment at 100°C for 52 minutes to form a gel. When placed in a simulated reservoir environment at 100°C, the gel temporary plugging agent could be completely degraded into liquid within 11 hours.

[0027] Example 3 1.67g PVA was dissolved in 50g water, 3.33g corn amylopectin was weighed and dispersed in the PVA solution, and 1.5g glycerol and 0.1g CaCl were added. 2 , mix at 200r / min at room temperature, and then place it in a constant temperature environment of 90℃ for pre-gelatinization for 30min to obtain a pre-gelatinized solution. Take 5.6gAM and 2.4gNVP and add them to 20g water, then add 0.25g cross-linking agent and 0.002g initiator to obtain a base liquid, add the base liquid to the pre-gelatinized solution, add clean water to 100g, mix at 200r / min at room temperature, and prepare an in-situ cross-linking-self-degradable high-strength gel temporary plugging agent reaction solution.

[0028] The reaction solution was placed in a simulated reservoir environment at 120°C for 23 minutes to form a gel. The gel temporary plugging agent after being placed in a simulated reservoir environment at 120°C can be completely degraded into liquid within 6 hours.

[0029] Example 4 Dissolve 2.33g PVA in 50g water, weigh 4.67g corn amylopectin and disperse it in the PVA solution, and add 2.1g glycerol and 0.14g CaCl 2 , mix at 200r / min at room temperature, and then place in a constant temperature environment of 90℃ for pre-gelatinization for 30min to obtain a pre-gelatinized solution. Take 5.6gAM and 2.4gNVP and add them to 20g water, then add 0.95g cross-linking agent and 0.001g initiator to obtain a base liquid, add the base liquid to the pre-gelatinized solution, add clean water to 100g, mix at 200r / min at room temperature, and prepare an in-situ cross-linking-self-degradable high-strength gel temporary plugging agent reaction solution.

[0030] The reaction solution was placed in a simulated reservoir environment at 150°C for 20 minutes to form a gel. The gel temporary plugging agent after being placed in a simulated reservoir environment at 150°C can be completely degraded into liquid within 10 hours.

[0031] Example 5 Dissolve 1.67g PVA in 50g water, weigh 3.33g corn amylopectin and disperse it in the PVA solution, and add 1.5g glycerol and 0.1g CaCl 2 , mix at 200r / min at room temperature, and then place in a constant temperature environment of 90℃ for pre-gelatinization for 30min to obtain a pre-gelatinized solution. Take 2.8gAM and 1.2gNVP and add them to 20g water, then add 0.65g cross-linking agent and 0.06g initiator to obtain a base liquid, add the base liquid to the pre-gelatinized solution, add clean water to 100g, mix at 200r / min at room temperature, and prepare an in-situ cross-linking-self-degradable high-strength gel temporary plugging agent reaction solution.

[0032] The reaction solution was placed in a simulated reservoir environment at 100°C for 25 minutes to form a gel. The gel temporary plugging agent was placed in a simulated reservoir environment at 100°C and completely degraded into liquid within 37 hours.

[0033] 2. Performance test of in-situ cross-linking-self-degradable high-strength gel temporary plugging agent Comparative Example 1 5.6 g AM and 2.4 g NVP were added to 50 g water, and then 0.25 g cross-linking agent and 0.002 g initiator were added to obtain a base solution, and clean water was added to 100 g to obtain a chemical cross-linking gel reaction solution.

[0034] The chemical crosslinking gel reaction solution of Comparative Example 1 and the physical and chemical interpenetrating crosslinking gel reaction solution of Example 3 were placed in a simulated reservoir environment at 120°C to form gels, and gel temporary plugging agents under different crosslinking conditions were prepared. The microscopic morphology is shown in FIG. Figure 1 (a) Figure 1 (b).

[0035] Figure 2 It shows that the maximum elastic modulus of pure chemical cross-linked gel is 415.25Pa, while the elastic modulus of physicochemical interpenetrating cross-linked gel can reach up to 2637.8Pa, which is 6.3 times that of pure chemical cross-linked gel.

[0036] Comparative Example 2 The cross-linking agent polyethylene glycol diacrylate in Example 4 was replaced by N,N-methylenebisacrylamide of equal mass, and the other components, amounts and reaction conditions were consistent with those in Example 4. The obtained gel temporary plugging agent was not completely degraded into liquid after aging at 150° C. for 3 days.

[0037] The temporary plugging agent formulas of Example 1-Example 5 were used as research objects, and were recorded as 1#-5# to investigate their plugging capabilities. Standard cores were prepared by wire cutting using shale outcrop cores. The plugging performance test method is as follows: First, the shale fracture core was placed in a clamp, the confining pressure was set to 6.0MPa, the back pressure was 1.0MPa, and the temperature was set to 120°C. First, 7wt% KCl brine was injected at a rate of 0.5mL / min, and then the gel temporary plugging agent reaction solution was injected at a rate of 0.5mL / min. The injection pressure was maintained at 1MPa, the confining pressure was constant at 6.0MPa, and the back pressure was 1.0MPa. After reacting for 1h at an ambient temperature of 120°C, the core was taken out after depressurization, placed in reverse, and 7wt% KCl brine was injected at a rate of 1mL / min for displacement. The confining pressure was constant at 6.0MPa and the back pressure was 1.0MPa. The displacement pressure change trend was recorded, and the breakthrough pressure was when the pressure dropped suddenly.

[0038]

[0039] The results show that the plugging strength of the gel temporary plugging agent prepared by the present invention is significantly higher than that of the pure chemical cross-linked gel temporary plugging agent. This is attributed to the fact that the shale surface contains a large number of silanol groups, hydroxyl groups and amide groups to form metal coordination bonds and hydrogen bonding forces, and the doped physical cross-linking provides more hydrogen bond donors for the gel, further enhancing the adhesion strength of the gel-rock interface and improving the plugging performance of the gel.

[0040] In actual use, the system components can be appropriately adjusted according to the well conditions, well type, formation water quality, etc.

[0041] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. In-situ cross-linking-self-degrading high-strength gel temporary plugging agent, composed of the following substances in parts by weight: 0.33-2.33 parts of polyvinyl alcohol, 0.67-4.67 parts of corn amylopectin, 2.8-7.0 parts of acrylamide, 1.2-3.0 parts of N-vinyl pyrrolidone, 0.05-1.05 parts of a cross-linking agent, 0.001-0.06 parts of an initiator, 0.3-2.1 parts of glycerol, 0.02-0.14 parts of calcium chloride, and the balance being water. The sum of the weight parts of the above substances is 100 parts.

2. The in-situ cross-linked and self-degradable high-strength gel temporary plugging agent according to claim 1, characterized in that: The cross-linking agent is polyethylene glycol diacrylate.

3. The in-situ cross-linked and self-degradable high-strength gel temporary plugging agent according to claim 1, characterized in that: The initiator is tert-butyl perbenzoate.

4. The in-situ cross-linked and self-degradable high-strength gel temporary plugging agent according to claim 1, characterized in that: The mass ratio of acrylamide to N-vinyl pyrrolidone is 7:

3.

5. The method for preparing the in-situ cross-linked self-degradable high-strength gel temporary plugging agent according to claim 1, 2, 3 or 4, comprising the following steps: First, a certain amount of polyvinyl alcohol was weighed and dissolved in an appropriate amount of water, corn amylopectin was dispersed in the polyvinyl alcohol solution, glycerol and CaCl2 were added at the same time, and after being mixed evenly at room temperature, the mixture was placed in a constant temperature environment of 90°C for 30 minutes to obtain a pre-gelatinized solution; Secondly, a certain amount of monomers acrylamide and N-vinyl pyrrolidone are weighed and dissolved in water to prepare a base liquid, and a crosslinking agent and an initiator are added to the base liquid to obtain a monomer solution; Finally, the pre-gelatinized solution and the monomer solution are mixed evenly at room temperature to obtain a reaction solution of the gel temporary plugging agent.

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