A micro crack plugging agent

Abstract

The present invention relates to a micro-fracture plugging agent, belonging to the technical field of oil and gas reservoir chemicals. The micro-fracture plugging agent of the present invention comprises a biopolymer, calcium carbonate particles, biomass particles and a cross-linking agent. The thermoplastic rubber in the biopolymer has high temperature resistance and viscosity, and the xanthan gum has good salt resistance. The two are used in combination to synergistically plug leaks and improve the suspension stability of the calcium carbonate particles and biomass particles in the liquid phase. The biopolymer contains groups such as carboxyl and hydroxyl groups. After being injected into the formation, it can react with the cross-linking agent to form a stable gel, thereby improving the plugging strength. The calcium carbonate particles and biomass particles serve as fillers. After being injected into the formation, they can bridge the cracks and have good plugging strength. The calcium carbonate particles can be decomposed in acid solution, and acid injection can be used to remove the plugging according to actual needs.

Description

Technical Field

[0001] The invention relates to a micro-fracture plugging agent, belonging to the technical field of oil and gas reservoir chemicals. Background Art

[0002] Gas storage plays a crucial role in natural gas peak-shaving. During the off-season, natural gas can be stored in underground storage and withdrawn during the peak season, thereby ensuring the natural gas supply needed for production and daily life. Due to alternating pressure fluctuations and formation creep during injection and withdrawal, injection and production wells within gas storage facilities are prone to developing microcracks in the cement sheaths of these wells, with crack widths typically below 100 μm. These cracks can lead to upward flow of natural gas. If not promptly sealed, these microcracks can rapidly expand under the pressure differential, severely impacting gas storage production and even rendering the well useless. Downhole tubing in gas storage injection and production wells is typically a stationary string with a packer. When the leakage zone is below the packer, mechanical plugging is impractical, and chemical plugging carries the risk of stratum blockage, making it difficult to plug the leak.

[0003] The micro-fracture plugging in the above-mentioned well conditions requires that the plugging agent be evenly dispersed, have good injectability, and have a small particle size; it must not only have plugging performance, but also de-plugging performance, because when the micro-fractures in the leakage layer are plugged, it is easy to cause the production layer to be contaminated, and the contamination needs to be removed to restore the permeability.

[0004] Nanomaterials, due to their small particle size, can effectively penetrate micro- and nano-scale cracks and pores, making them the preferred material for plugging microcracks. Currently, nanomaterials mainly include organic nano-plugging agents, inorganic nano-plugging agents (nanomaterials such as nano-silica, nano-calcium carbonate, and nano-iron oxide), and organic / inorganic composite plugging agents. Among them, organic nano-plugging agents have low plugging strength, while inorganic nano-plugging agents are prone to agglomeration. There are many reports on the combined application of these two materials. The plugging material studied by Sun Yingsheng, which is a combination of inorganic nanomaterials and organic gelling materials that undergo hydration bonding, does not shrink in volume after curing, has a dense and uniform microstructure, and achieves a plugging rate of 99.9%. The plugging material has a plastic viscosity of less than 40 mPa·s, making it easy to pump, temperature resistant to 120°C, salt resistance of 216,000 mg / L, and compressive strength ≥30 MPa. However, inorganic nanomaterials are prone to agglomeration and cannot be dissolved.

[0005] Chinese patent document CN110591673B discloses a high-strength sealing plugging agent for oil and water well casing leakage, comprising 15-20% fluorene-based epoxy resin, 10-12% epoxy resin, 10-12% alkaline phenolic resin, 20-30% solvent, 4-5% coupling agent, 15-20% filler (nanomaterial), 4-5% degassing agent, and 4-5% cross-linking agent; the degassing agent is a modified calcium-based degassing agent. The preparation method of the modified calcium-based degassing agent includes multiple steps such as reaction-aging-drying-grinding-calcination, and the preparation process is complicated. The nanomaterials in the plugging agent have poor dispersibility and are not environmentally friendly. It is a solidified plugging agent and cannot be dissolved. Summary of the Invention

[0006] The purpose of the present invention is to provide a micro-crack plugging agent, which can solve the problem that the current plugging agents cannot simultaneously meet the requirements of sealing and unblocking when used to plug micro-cracks in gas storage.

[0007] In order to achieve the above objectives, the technical solution adopted by the micro-crack plugging agent of the present invention is:

[0008] A micro-crack plugging agent mainly consists of a biopolymer, calcium carbonate particles, biomass particles and a cross-linking agent; the biopolymer mainly consists of Weinberg gum and xanthan gum, and the mass ratio of the Weinberg gum to the xanthan gum is (2-4):1; the mass ratio of the biopolymer, calcium carbonate particles and biomass particles is (0.3-1.5):(1-5):(1-5).

[0009] The microcrack plugging agent of the present invention includes a biopolymer, calcium carbonate particles, biomass particles, and a cross-linking agent. The thermoplastic rubber in the biopolymer has high temperature resistance and viscosity, and the xanthan gum has good salt tolerance. The two are used in combination to synergistically plug leaks and improve the suspension stability of calcium carbonate particles and biomass particles in the liquid phase. The biopolymer contains groups such as carboxyl and hydroxyl groups. After injection into the formation, it can react with the cross-linking agent to form a stable gel, thereby improving the plugging strength. The calcium carbonate particles and biomass particles serve as fillers. After injection into the formation, they can bridge the cracks and have good plugging strength. The calcium carbonate particles can be decomposed in acid solution, and acid injection can be used to unblock the cracks as needed. The biopolymer, calcium carbonate particles, and biomass particles can play a synergistic role to achieve a better plugging effect. The micro-fracture plugging agent of the present invention has good dispersibility in water, does not produce layer burial phenomenon after being injected into the formation, has high plugging strength, and is solvable. It is suitable for plugging micro-fractures in production layers that can be protected by sand filling or bridge plugging, and can also be used for plugging micro-fractures in production layers that cannot be protected, and has great economic, social and environmental benefits.

[0010] In order to ensure that the calcium carbonate particles can enter pores or cracks with a diameter of less than 20 μm, so as to achieve the purpose of sealing microcracks, preferably, the particle size of the calcium carbonate particles and the biomass particles is not greater than 6.5 μm.

[0011] It is understood that the microcracks in the present invention refer to cracks with a width of less than 100 μm.

[0012] In order to reduce costs and play a good plugging effect, preferably, the biomass particles are selected from one or any combination of bagasse, wood chips, and corn grits.

[0013] It can be understood that sugarcane bagasse is the residue left after sugarcane is extracted; wood chips refer to the powder left when wood is processed; and corn grits are the powder formed after corn is ground.

[0014] Preferably, the microcrack plugging agent further comprises a deoxidizer, which can remove oxygen from the system and improve the stability of the plugging agent slurry.

[0015] Preferably, the oxygen scavenger is an inorganic oxygen scavenger and / or an organic oxygen scavenger. Preferably, the inorganic oxygen scavenger is a sulfite and / or a thiosulfate. For example, the sulfite is an alkali metal sulfite; and the thiosulfate is an alkali metal thiosulfate. Alkali metal sulfites and alkali metal thiosulfates as oxygen scavengers have the beneficial effects of good water solubility, low cost, high oxygen removal efficiency, and no interference with the crosslinking reaction.

[0016] Preferably, the crosslinking agent is an organometallic crosslinking agent and / or an aldehyde crosslinking agent. Any organometallic crosslinking agent and / or aldehyde compound suitable for use in plant gums is suitable for use in the present invention. For example, the organometallic crosslinking agent is an organochromium crosslinking agent and / or an organozirconium crosslinking agent; the aldehyde crosslinking agent is a dialdehyde compound having 2 to 8 carbon atoms. For example, the dialdehyde compound is selected from one or any combination of glyoxal, malondialdehyde, and succinaldehyde.

[0017] Further preferably, the crosslinking agent is composed of an organometallic crosslinking agent and an aldehyde crosslinking agent, and the mass ratio of the organometallic crosslinking agent to the aldehyde crosslinking agent is (1-2):(2-4). For example, the mass ratio of the organometallic crosslinking agent to the aldehyde crosslinking agent is (1-1.8):(2-4). Carboxyl groups, hydroxyl groups, and other groups in the biopolymer can undergo crosslinking reactions with trivalent and polyvalent metals to form a gel, and the aldehyde compound can undergo a hydroxyethylation reaction with the biopolymer, further polymerizing and enhancing the gel strength.

[0018] Preferably, the mass ratio of the biopolymer, calcium carbonate particles, biomass particles and cross-linking agent is (0.3-1.5):(1-5):(1-5):(0.3-6).

[0019] Preferably, the mass ratio of the biopolymer, calcium carbonate particles, biomass particles, oxygen scavenger, and cross-linking agent is (0.3-1.5):(1-5):(1-5):(0.01-0.07):(0.3-6). For example, the mass ratio of the biopolymer, calcium carbonate particles, biomass particles, oxygen scavenger, and cross-linking agent is (0.6-1.5):(1-2):(1-2):(0.02-0.07):(3-6).

[0020] For ease of direct use, the microcrack plugging agent preferably also includes water. When the plugging agent contains water, the biopolymer in the plugging agent can improve the suspension stability of the calcium carbonate particles and biomass particles, and impart good salt resistance, temperature resistance, and shear thinning properties to the plugging agent, thereby improving the injectability of the plugging agent.

[0021] The water in the micro-fracture plugging agent of the present invention can be deionized water, tap water, or oilfield injection water. According to the results of the indoor plugging agent slurry suspension stability test, the total mineralization of the water is ≤30×10 4 mg / L.

[0022] Preferably, the mass fraction of the biopolymer in the microcrack plugging agent is 0.3 to 1.5%. For example, the mass fraction of the biopolymer in the microcrack plugging agent is 0.6 to 1.5%. When the mass fraction of the biopolymer in the microcrack plugging agent is 0.3 to 1.5%, the plastic viscosity of the microcrack plugging agent of the present invention is lower than 40 mPa·s, and the concentration resistance is 30×10 4 The salt of 100 mg / L can be suspended stably for more than 5 hours at 110°C, is easy to inject and has no coagulation; the micro-fracture plugging agent of the present invention has a plugging rate of more than 99.5% for 20mD cores and a pressure difference resistance of 10MPa.

[0023] Preferably, the microcrack plugging agent is composed of the following components in mass fraction: 0.6-1.5% biopolymer, 1-2% calcium carbonate particles, 1-2% biomass particles, 0.02-0.07% deoxidizer, 3-6% crosslinking agent, and the balance is water.

[0024] Preferably, the micro-crack plugging agent is used for mineralization ≤15×10 4 mg / L, and sealing of cracks in formations with formation temperature ≤110℃.

[0025] During injection of the microfracture plugging agent of the present invention into the formation, it preferentially enters the lower-pressure leakage zone. Under the action of the pressure differential, the rigid particles in the microfracture plugging agent accumulate and form bridges in the middle of the microfractures. The highly fluid biopolymer enters the front portion and gradually forms a biogel. The plugging agent at the tail of the fracture gradually forms a mixed gel composed of the biogel and rigid particles. The front and tail portions have certain waterproof and acid- and alkali-resistant properties. A small amount of plugging agent entering the production zone can be used to displace a small amount of acid into the formation, thereby preventing damage to the production zone.

[0026] Preferably, the microcrack plugging agent is prepared by a method comprising the following steps:

[0027] (1) mixing the formulated amount of calcium carbonate particles, biomass particles and deoxidizer with a portion of water to obtain a dispersion;

[0028] Mixing a formulated amount of biopolymer and a portion of water to obtain a suspension;

[0029] (2) mixing the suspension and the dispersion to obtain a mixed solution;

[0030] (3) mixing the mixed solution, the cross-linking agent in the formula amount, and the balance water to obtain a micro-crack plugging agent;

[0031] The amount of water used in preparing the dispersion is 25-35% of the total water volume, and the amount of water used in preparing the suspension is 45-55% of the total water volume.

[0032] Preferably, the time for mixing the formulated amount of biopolymer and part of water is 1 to 2 hours.

[0033] Preferably, the method for uniformly mixing the suspension and the dispersion comprises the following steps: adding the suspension to the stirred dispersion, and after the suspension is added, continuing to mix until the system is uniformly dispersed. Experimental results show that when the dispersion is added to the suspension, or when the suspension and the dispersion are added simultaneously, the prepared microcrack plugging agent will agglomerate after being left at 60°C for 5 hours, affecting injectability and performance.

[0034] Preferably, the suspension is added at a rate of 10 to 15 mL / min.

[0035] In order to reduce costs and ensure uniform mixing of the raw materials, preferably, stirring is used to mix the raw materials when preparing the dispersion. Preferably, the stirring speed when preparing the dispersion is not less than 1000 r / min.

[0036] In order to reduce costs and ensure uniform mixing of the raw materials, preferably, stirring is used to mix the suspension. Preferably, the stirring speed during the preparation of the suspension is not less than 1000 r / min. DETAILED DESCRIPTION

[0037] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0038] The microcrack plugging agent of Examples 1-9 is composed of biopolymer, calcium carbonate particles, biomass particles, deoxidizer, crosslinker and water, wherein the biopolymer is composed of Wenlun gum and xanthan gum, the deoxidizer is sodium sulfite and / or sodium thiosulfate, the crosslinker is composed of organic metal crosslinker and aldehyde crosslinker, the organic metal crosslinker is chromium acetate and / or zirconium acetate, and the aldehyde crosslinker is glyoxal.

[0039] The particle sizes of the calcium carbonate particles in the microcrack plugging agents of Examples 1-9 are 2000 mesh, 5000 mesh, 2000 mesh, 3000 mesh, 3000 mesh, 6000 mesh, 8000 mesh, 2000 mesh, and 5000 mesh, respectively; the biomass particles in the microcrack plugging agents of Examples 1-9 are all sugarcane bagasse, and the particle sizes are 2000 mesh, 5000 mesh, 2000 mesh, 3000 mesh, 3000 mesh, 2000 mesh, 3000 mesh, 2000 mesh, and 2000 mesh, respectively.

[0040] The mass fractions of vinca gum and xanthan gum in the biopolymer, the mass fractions of calcium carbonate particles and biomass particles, the mass fractions of sodium sulfite and / or sodium thiosulfate in the scavenger, the mass fractions of organic chromium crosslinker and / or organic zirconium crosslinker and glyoxal in the crosslinker, and the mass fractions of water in each embodiment are shown in Table 1.

[0041] Table 1 Mass fractions of each raw material in the microcrack plugging agent of each embodiment

[0042]

[0043] The microcrack plugging agents of Examples 1-9 are prepared by a method comprising the following steps:

[0044] (1) At a speed of 2000 r / min, the formulated amount of calcium carbonate particles, biomass particles and deoxidizer are added to a portion of water (the amount of water is 30% of the total water volume) and stirred evenly to obtain a dispersion; at a speed of 1000 r / min, the formulated amount of biopolymer is added to a portion of water (the amount of water is 50% of the total water volume) and stirred for 2 hours to obtain a suspension;

[0045] (2) slowly adding the suspension (at a rate of 15 mL / min) to the dispersion in a stirring state, stirring thoroughly to obtain a mixed solution;

[0046] (3) Add the formulated amount of cross-linking agent to the mixed solution, then add the remaining amount of water, and stir for 0.5 hours to obtain a micro-crack plugging agent.

[0047] Comparative Example 1

[0048] The only difference between the plugging agent of this comparative example and the plugging agent of Example 1 is that the mass fraction of xanthan gum in the plugging agent of this comparative example is 15 parts, and the mass fraction of Wenlun rubber is 0 parts.

[0049] Comparative Example 2

[0050] The only difference between the plugging agent of this comparative example and the plugging agent of Example 1 is that the mass fraction of xanthan gum in the plugging agent of this comparative example is 0 parts, and the mass fraction of Wenlun rubber is 15 parts.

[0051] Comparative Example 3

[0052] The only difference between the plugging agent of this comparative example and the plugging agent of Example 1 is that the mass fraction of chromium acetate in the plugging agent of this comparative example is 0 parts, and the mass fraction of glyoxal is 56 parts.

[0053] Comparative Example 4

[0054] The only difference between the plugging agent of this comparative example and the plugging agent of Example 1 is that the mass fraction of chromium acetate in the plugging agent of this comparative example is 56 parts, and the mass fraction of glyoxal is 0 parts.

[0055] Comparative Example 5

[0056] The only difference between the plugging agent of this comparative example and the plugging agent of Example 1 is that the mass fraction of calcium carbonate particles in the plugging agent of this comparative example is 20 parts, and the mass fraction of bagasse is 0 parts.

[0057] Comparative Example 6

[0058] The only difference between the plugging agent of this comparative example and the plugging agent of Example 1 is that the mass fraction of calcium carbonate particles in the plugging agent of this comparative example is 0 parts, and the mass fraction of bagasse is 20 parts.

[0059] Experimental example

[0060] In order to evaluate the physical properties of different plugging agents and their effect on microcracks, the rheological properties, suspension stability, plugging performance and solvability of each plugging agent were tested. The rheological test method is as follows: the viscosity of each plugging agent at different rotation speeds was measured using a ZNN-D6 rotational viscometer, and then the plastic viscosity was calculated. The test and calculation results are shown in Table 2. The suspension stability test method is as follows: the plugging agents were prepared according to the preparation methods of the plugging agents of Examples 1-9 and Comparative Examples 1-6, except that the mass fraction of the cross-linking agent used in the preparation of each plugging agent was 0, and the water used in the preparation had a mineralization of 30×10 4mg / L of simulated water, and then the prepared plugging agents were left to stand at different temperatures for 5 hours to observe whether stratification, water extraction, or precipitation occurred. If not, the test result was stable. If stratification, water extraction, or precipitation occurred, the test result was unstable. The test results are shown in Table 2. The plugging performance is expressed as the plugging rate, which is measured using a core flooding test device. The test method is based on 6.7 in the standard Q / SH CG0141-2021 (China Petrochemical Corporation Enterprise Standard). First, a sand-filled pipe with a permeability of about 20 mD is filled with clean quartz sand. The plugging agent is then placed in an intermediate container and injected into the sand-filled pipe using a horizontal flow pump. The injection PV number is 2.5. The sand-filled pipe is then placed in an oven and cured at 110°C for 24 hours. The permeability of the sand-filled pipe after the plugging agent is injected is tested, and the breakthrough pressure is then tested. The test results are shown in Table 3. The test method for solvability is as follows: the plugging agent is allowed to stand at formation temperature (110°C) to form a gel, and then the gel is added to hydrochloric acid and soaked to observe whether the gel becomes loose or precipitated. If the above phenomena occur, the test result is solvable. If no loosening or precipitating occurs, the test result is unsolvable. The test results are shown in Table 3.

[0061] Table 2 Rheological and suspension stability test results of each plugging agent

[0062]

[0063]

[0064] Table 3 Test results of the plugging performance and solvability of each plugging agent

[0065]

[0066]

[0067] As shown in Table 2, the plastic viscosity of the plugging agents of Examples 1-9 is no more than 40 mPa·s, making them easy to pump. After standing for 5 hours at 60-110°C, the plugging agents of Examples 1-9 (without a cross-linking agent) show no stratification, water separation, or precipitation, indicating that the plugging agents of Examples 1-9 (without a cross-linking agent) have excellent suspension stability, ensuring safe injection during construction and preventing solid particles from settling and blocking the wellbore at the bottom of the well. As shown in Table 3, the plugging rate of the plugging agents of Examples 1-9 exceeds 99.5%, and the breakthrough pressure is no less than 10 MPa, indicating that the plugging agents of Examples 1-9 have good plugging ability, can meet the plugging needs of micro-cracks in injection and production wells of on-site gas storage reservoirs, and are also solvable.

[0068] After replacing the chromium acetate in Examples 1-9 with chromium lactate, the performance (rheology, suspension stability, plugging performance and solvability) remained unchanged.

[0069] After replacing the bagasse in Example 1 with sawdust or corn grits with a particle size of no more than 6.5 μm, when the rheological properties, suspension stability, blocking performance and solvability were tested according to the above test methods, the test results were close to the corresponding test results of Example 1.

Claims

1. A micro crack plugging agent, characterized in that: The invention mainly consists of biopolymer, calcium carbonate particles, biomass particles and a crosslinking agent; the biopolymer mainly consists of Weinberg gum and xanthan gum, and the mass ratio of the Weinberg gum to the xanthan gum is (2-4):1; the particle sizes of the calcium carbonate particles and the biomass particles are both no greater than 6.5 μm; the mass ratio of the biopolymer, calcium carbonate particles, biomass particles and the crosslinking agent is (0.3-1.5):(1-5):(1-5):(0.3-6); the crosslinking agent consists of an organic metal crosslinking agent and an aldehyde crosslinking agent, and the mass ratio of the organic metal crosslinking agent to the aldehyde crosslinking agent is (1-2):(2-4).

2. The microcrack plugging agent according to claim 1, characterized in that The biomass particles are selected from one or any combination of bagasse, wood chips, and corn grits.

3. The micro-crack plugging agent according to claim 1, characterized in that The micro-crack plugging agent further comprises a deoxidizer; the deoxidizer is an inorganic deoxidizer and / or an organic deoxidizer; the inorganic deoxidizer is sulfite and / or thiosulfate.

4. The micro-crack plugging agent according to claim 3, characterized in that: The sulfite is an alkali metal sulfite; and the thiosulfate is an alkali metal thiosulfate.

5. The micro-crack plugging agent according to claim 3, characterized in that: The mass ratio of the biopolymer, calcium carbonate particles, biomass particles, oxygen scavenger and cross-linking agent is (0.6-1.5):(1-2):(1-2):(0.02-0.07):(3-6).

6. The micro-crack plugging agent according to claim 1, characterized in that: The aldehyde cross-linking agent is a dialdehyde compound, and the dialdehyde compound is selected from one or any combination of glyoxal, malondialdehyde and succinaldehyde.

7. The micro-crack plugging agent according to claim 1, characterized in that: The plugging agent also includes water; the mass fraction of the biopolymer in the plugging agent is 0.6-1.5%.

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