An environment-friendly self-degradable cross-linked gel for plugging a medium-temperature geothermal well and a preparation method thereof
By preparing an environmentally friendly, self-degradable crosslinking gel composed of water, gelling agent, and delayed crosslinking agent, the problem of wellbore instability caused by drilling fluid loss in medium-temperature geothermal wells was solved, achieving effective plugging and protection of the geothermal reservoir.
Patent Information
- Application Number
- CN202610726441.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-05-25
- Publication Date
- 2026-07-28
AI Technical Summary
After drilling fluid loss, existing plugging materials in medium-temperature geothermal wells can easily clog the pores and fractures of geothermal reservoirs, leading to wellbore instability. Furthermore, conventional plugging methods present difficulties in removing cuttings from the well and pose safety risks to the wellbore. There is a lack of effective environmentally friendly, self-degradable cross-linked gel materials.
An environmentally friendly, self-degradable crosslinking gel composed of water, gelling agent, delayed crosslinking agent, crosslinking control agent, reinforcing agent, and stabilizer is used. By controlling the crosslinking time and enhancing the pressure resistance of the gel, it ensures effective leak sealing in a medium-temperature environment and self-degradation within 7 days, thus protecting the thermal reservoir.
It achieves effective and environmentally friendly plugging in medium-temperature geothermal wells, avoids damage to the geothermal reservoir, and completely degrades within 7 days, solving the problem of drilling fluid loss in the exploration and development of medium-temperature geothermal resources.
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Figure CN122465568A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of plugging technology in geological drilling, oil and gas drilling and scientific drilling processes, and particularly to an environmentally friendly self-degradable cross-linked gel for plugging leaks in medium-temperature geothermal wells and its preparation method. Background Technology
[0002] Geothermal energy is a renewable and clean energy source. Geothermal resources are classified into three categories based on temperature: high-temperature (above 150℃), medium-temperature (90~150℃), and low-temperature (25~90℃). During geothermal exploration and development, drilling fluid loss is a prominent issue, often resulting in loss-of-return leakage. Once severe loss-of-return leakage occurs, the inability to establish drilling fluid circulation severely impacts wellbore stability, construction efficiency, and costs. To protect the pores and fractures of geothermal reservoirs and water quality in exploration and reinjection wells, the use of bridging materials and cement slurry for plugging is generally prohibited. Typically, drilling with exposed drilling is the only option, which presents difficulties in removing cuttings and poses wellbore safety risks. Therefore, research on temporary plugging technology is urgently needed to address the problems of existing plugging materials blocking geothermal reservoir pores and fractures, and causing wellbore instability in open-hole sections, providing technical support for the exploration, development, and utilization of geothermal resources.
[0003] Domestic research focuses on temporary plugging technology for oil and gas well reservoirs, but there is limited data on the research and application of temporary plugging technology for geothermal wells. Currently, there are no maturely applied temporary plugging materials for geothermal reservoirs, and research is largely in the exploratory or basic research stage. These materials mainly include self-degradable temporary plugging cement, self-degradable cross-linked gel, and temperature-sensitive shape memory polymers.
[0004] Therefore, there is an urgent need to develop environmentally friendly, self-degradable cross-linked gel temporary plugging technology to meet the special requirements of medium-temperature geothermal exploration wells and reinjection wells that "both plug the leaking layer and degrade without damaging the geothermal reservoir". Summary of the Invention
[0005] To address the issues of drilling fluid loss and the prominent contradiction between "protecting the geothermal reservoir and plugging leaks" in the exploration and development of medium-temperature geothermal resources, this invention provides an environmentally friendly, self-degradable cross-linked gel for plugging leaks in medium-temperature geothermal wells and its preparation method. The environmentally friendly, self-degradable cross-linked gel for plugging leaks in medium-temperature geothermal wells of this invention has a controllable cross-linking time, high pressure resistance, and a stabilization period of up to 7 days, making it suitable for plugging leaks in geothermal wells with temperatures not exceeding 120℃.
[0006] In a first aspect, the present invention provides an environmentally friendly, self-degradable crosslinking gel for plugging leaks in medium-temperature geothermal wells. The raw materials used to prepare the environmentally friendly, self-degradable crosslinking gel for plugging leaks in medium-temperature geothermal wells are composed of the following components in parts by weight: 100 parts water, 1.2-1.5 parts gelling agent, 1.5-2.5 parts delayed crosslinking agent, 0.1-0.3 parts crosslinking control agent, 1-3 parts reinforcing agent, and 0.5-1.5 parts stabilizer; The raw materials for the delayed crosslinking agent include wood flour, diatomaceous earth, zirconate crosslinking agent, and thermosensitive material.
[0007] Furthermore, the gelling agent is composed of any two of hydroxypropyl guar gum, carboxymethyl hydroxypropyl guar gum, and high-viscosity polyanionic cellulose.
[0008] In this invention, any two raw materials in the above-mentioned gelling agent can be compounded in any proportion. For example, the mass ratio of hydroxypropyl guar gum to high-viscosity anionic cellulose is (3~6):1; the mass ratio of carboxymethyl hydroxypropyl guar gum to high-viscosity anionic cellulose is (4~6):1.
[0009] Furthermore, the temperature-sensitive material is one of hot melt adhesive and hydrogenated petroleum resin.
[0010] Furthermore, the softening point of the temperature-sensitive material is 95~120℃.
[0011] Furthermore, the crosslinking control agent is one of citric acid and sodium citrate. The function of the crosslinking control agent is to control the crosslinking time between the delayed crosslinking agent and the gelling agent.
[0012] Furthermore, the reinforcing agent comprises diatomaceous earth and elm wood powder, and its function is to enhance the strength of the gel. Preferably, the mass ratio of diatomaceous earth to elm wood powder is 1:(0.25~2).
[0013] Furthermore, the stabilizer is either sodium metabisulfite or a phosphite. The stabilizer's function is to improve the thermal stability of the gel.
[0014] Further, the delayed crosslinking agent comprises a mixture of wood flour, diatomaceous earth and zirconate crosslinking agent in a mass ratio of (0.4~0.6):(0.4~0.6):1, and the mass ratio of the mixture to the temperature-sensitive material is (0.8~1):1.
[0015] Furthermore, the environmentally friendly self-degradable cross-linking gel for plugging medium-temperature geothermal wells has an applicable temperature of 95~120℃ and a cross-linking time of 11~85min.
[0016] Furthermore, the environmentally friendly self-degradable cross-linked gel used for plugging leaks in medium-temperature geothermal wells has a pressure resistance of ≥7MPa and a stabilization period of ≤7 days.
[0017] In this invention, the stabilization period refers to the time during which the environmentally friendly, self-degradable cross-linked gel used for plugging medium-temperature geothermal wells maintains a certain shape and strength at a temperature of 95~120℃.
[0018] Furthermore, the biodegradability (BOD5 / COD) of the gel breaking solution of the environmentally friendly self-degradable cross-linked gel for plugging medium-temperature geothermal wells is ≥5%, and the biotoxicity (EC5 / COD) of the gel breaking solution of the environmentally friendly self-degradable cross-linked gel for plugging medium-temperature geothermal wells is ≥5%. 50 ≥30,000 mg / L.
[0019] Understandably, there is currently no direct method to evaluate the environmental performance of environmentally friendly self-degradable cross-linked gels used for plugging leaks in medium-temperature geothermal wells. Therefore, the only method is to use the degraded gel solution after degradation as a test sample to measure the ratio of five-day biochemical oxygen demand (BOD5) to chemical oxygen demand (COD) and the median effective concentration (EC5). 50 For example, the preparation method of the debonding fluid of the environmentally friendly self-degradable cross-linked gel for plugging medium-temperature geothermal wells includes the following steps: the environmentally friendly self-degradable cross-linked gel for plugging medium-temperature geothermal wells decomposes at 95~120℃ to form a fluid, which is the debonding fluid.
[0020] Secondly, the present invention also provides a method for preparing the above-mentioned environmentally friendly self-degradable crosslinking gel for plugging leaks in medium-temperature geothermal wells, comprising the following steps: (1) Mix water and gelling agent, hydrate at 20~25℃ for 30~60min to obtain gelling agent dispersion; (2) Add reinforcing agent, crosslinking control agent and stabilizer to the gelling agent dispersion, stir and mix evenly to obtain gel base liquid; (3) The gel base liquid obtained in step (2) is mixed with a delayed crosslinking agent to obtain a gel solution, and then the crosslinking reaction is carried out at 95~120℃ for 11~85 minutes to obtain an environmentally friendly self-degradable crosslinking gel for plugging leaks in medium-temperature geothermal wells.
[0021] Further, in step (2) above, at 20~25℃, a reinforcing agent, a crosslinking control agent and a stabilizer are added to the gelling agent dispersion and stirred until uniform to obtain a gel base liquid.
[0022] Furthermore, in step (3) above, the gel base liquid obtained in step (2) is mixed with a delayed crosslinking agent at 20~25°C to obtain a gel solution.
[0023] Furthermore, the method for preparing the delayed crosslinking agent includes the following steps: (3-1) The wood flour, the diatomaceous earth, and the zirconate crosslinking agent are stirred and mixed evenly to obtain component I; (3-2) Add the temperature-sensitive material to the reaction vessel and heat it to 20-30°C above the softening point of the temperature-sensitive material. After the temperature-sensitive material has completely melted, add component I and stir evenly to obtain component II. (3-3) Pour the component II in the reaction vessel into a container filled with water, cool it, dry it in a forced-air drying oven at 60~75°C, and then pulverize it with a high-speed universal pulverizer to obtain a delayed crosslinking agent.
[0024] Further, in step (3-1) above, the wood flour, the diatomaceous earth and the zirconate crosslinking agent are stirred and mixed evenly at 20~25℃ to obtain component I.
[0025] Furthermore, in step (3-3) above, when component II in the reaction vessel is poured into a container containing water, there are no special requirements for the volume of water; it is sufficient to allow component II to cool down.
[0026] The advantages of this invention compared to the prior art are as follows: (1) The present invention selects materials with good environmental performance or harmless to the environment as components of the self-degradable cross-linked gel for plugging medium-temperature geothermal wells, which will not pollute geothermal water or the environment.
[0027] (2) By using a delayed crosslinking agent and a crosslinking control agent to regulate the crosslinking reaction rate between zirconium ions and hydroxyl groups on molecular chains such as hydroxypropyl guar gum, the crosslinking time of the gel in the temperature range of 95~120℃ is controlled within 11~85min, so as to meet the requirements of plugging and pumping operations of medium-temperature geothermal wells and ensure that the self-degradable crosslinking gel used for plugging medium-temperature geothermal wells has not been fully crosslinked when it enters the leakage channel.
[0028] (3) Self-degradable cross-linked gel for plugging leaks in medium-temperature geothermal wells can degrade itself, causing little damage to the geothermal reservoir, and can solve the prominent contradiction between "protecting the geothermal reservoir and plugging leaks" in the exploration and development of medium-temperature geothermal resources. Attached Figure Description
[0029] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention. In the drawings: Figure 1 This is a photograph of the environmentally friendly, self-degradable crosslinked gel for plugging medium-temperature geothermal wells prepared in Example 3.
[0030] Figures 2-5 These are photos of the environmentally friendly, self-degradable crosslinking gel for plugging medium-temperature geothermal wells prepared in Example 3, aged at 120°C for 3 days, 5 days, 7 days, and 10 days. Detailed Implementation
[0031] The present invention will be further described below with reference to specific embodiments, so that those skilled in the art can better understand and implement the present invention, but the embodiments are not intended to limit the present invention.
[0032] All materials used in the examples are commercially available. For example, hydroxypropyl guar gum and carboxymethyl hydroxypropyl guar gum can be sourced from products of companies such as Kunshan Jingkun Oilfield Chemical Technology Development Co., Ltd. and Beijing Guarrun Technology Co., Ltd.; high-viscosity polyanionic cellulose can be sourced from products of companies such as Xuzhou Liyuan Cellulose Technology Co., Ltd. and Dongzheng Chemical Group; zirconate crosslinking agents can be sourced from products of companies such as Tianchang Green Chemical Additives Factory and Guangzhou Jianyi Chemical Import & Export Co., Ltd.; wood flour and elm flour can be sourced from products of Lingshou County Heshun Mineral Products Processing Plant; diatomaceous earth can be sourced from products of companies such as Lingshou County Jushi Mineral Products Processing Plant and Lingshou County Huixin New Materials Co., Ltd.; hot melt adhesives can be sourced from products of Wuhan Jiyesheng Chemical Co., Ltd.; hydrogenated petroleum resins can be sourced from products of companies such as Henghe Materials Technology Co., Ltd. and Puyang Hengtai Petrochemical Co., Ltd.; citric acid and sodium citrate can be sourced from products of Daziran Biotechnology Group Co., Ltd.; sodium metabisulfite can be sourced from products of Tangshan Huizhong Chemical Co., Ltd.; and phosphites can be sourced from products of Changhe Chemical New Materials (Jiangsu) Co., Ltd.; high-speed universal pulverizers are commercially available products, and the model can be referenced from the FW100 high-speed pulverizer of Tianjin Test Instrument Co., Ltd.
[0033] In the following examples and comparative examples, the room temperature is 25°C.
[0034] Example 1 This invention provides an environmentally friendly, self-degradable crosslinking gel for plugging leaks in medium-temperature geothermal wells. The raw materials for preparing this gel include: 100g water, 1g hydroxypropyl guar gum, 0.2g high-viscosity anionic cellulose, 1.5g delayed crosslinking agent, 0.12g citric acid, 1g diatomaceous earth, 1g elm wood powder, and 0.5g sodium metabisulfite. The delayed crosslinking agent comprises wood powder, diatomaceous earth, zirconate crosslinking agent, and a hot melt adhesive with a softening point of 95°C. The delayed crosslinking agent is a mixture of the wood powder, diatomaceous earth, and zirconate crosslinking agent in a mass ratio of 0.5:0.4:1, and the mass ratio of the mixture to the temperature-sensitive material is 0.83:1.
[0035] The preparation method of the environmentally friendly self-degradable crosslinking gel for plugging medium-temperature geothermal wells in this embodiment of the invention is as follows: S1. The delayed crosslinking agent is prepared according to the method for preparing the delayed crosslinking agent of the present invention. The specific preparation process is as follows: S11. At room temperature, add 5g of wood flour, 4g of diatomaceous earth and 10g of zirconate crosslinking agent to a beaker, stir with a glass rod to mix evenly, and obtain component I. S12. Add 23g of hot melt adhesive to the reaction vessel, heat to 120℃, and after the hot melt adhesive has completely melted, add component I and stir evenly with a glass rod to obtain component II. S13. Pour component II from the reaction vessel into a container filled with water, cool it, and then dry it in a forced-air drying oven at 65°C for 120 minutes. Finally, use a high-speed universal pulverizer to pulverize it at 24,000 rpm for 3 minutes to obtain the delayed crosslinking agent.
[0036] S2. Add 1g of hydroxypropyl guar gum and 0.2g of high-viscosity anionic cellulose to 100g of water, stir evenly with a glass rod, and hydrate at 25℃ for 30min to obtain a gelling agent dispersion. Then, at room temperature, add 1g of diatomaceous earth, 1g of elm wood powder, 0.12g of citric acid, and 0.5g of sodium metabisulfite to the gelling agent dispersion in sequence, and stir evenly with a glass rod to obtain a gel base solution. Finally, at room temperature, add 1.5g of the delayed crosslinking agent prepared in step S1 to the gel base solution, stir evenly to obtain a gel solution, put it into an aging tank, and place it in a 95℃ roller heating furnace for crosslinking reaction for 11min to obtain an environmentally friendly self-degradable crosslinking gel for plugging leaks in medium-temperature geothermal wells.
[0037] Example 2 This invention provides an environmentally friendly, self-degradable crosslinking gel for plugging leaks in medium-temperature geothermal wells. The raw materials used to prepare this gel include: 100g water, 1.2g carboxymethyl hydroxypropyl guar gum, 0.3g high-viscosity anionic cellulose, 2.5g delayed crosslinking agent, 0.2g sodium citrate, 2g diatomaceous earth, 0.5g elm wood powder, and 1g phosphite. The delayed crosslinking agent comprises wood powder, diatomaceous earth, zirconate crosslinking agent, and hydrogenated petroleum resin with a softening point of 105℃. The delayed crosslinking agent is a mixture of wood powder, diatomaceous earth, and zirconate crosslinking agent in a mass ratio of 0.6:0.4:1, and the mass ratio of the mixture to the temperature-sensitive material is 1:1.
[0038] The preparation method of the environmentally friendly self-degradable crosslinking gel for plugging medium-temperature geothermal wells in this embodiment of the invention is as follows: S1. The delayed crosslinking agent is prepared according to the method for preparing the delayed crosslinking agent of the present invention. The specific preparation process is as follows: S11. At room temperature, add 6g of wood flour, 4g of diatomaceous earth and 10g of zirconate crosslinking agent to a beaker, and stir with a glass rod to mix evenly to obtain component I. S12. Add 20g of hydrogenated petroleum resin to the reaction vessel, heat to 130℃, and after the hydrogenated petroleum resin has completely melted, add component I and stir evenly with a glass rod to obtain component II. S13. Pour component II from the reaction vessel into a container filled with water, cool it, and then dry it in a forced-air drying oven at 70°C for 120 minutes. Finally, use a high-speed universal pulverizer to pulverize it at 24,000 rpm for 3 minutes to obtain the delayed crosslinking agent.
[0039] S2. Add 1.2g of carboxymethyl hydroxypropyl guar gum and 0.3g of high-viscosity anionic cellulose to 100g of water, stir evenly with a glass rod, and hydrate at 25℃ for 60min to obtain a gelling agent dispersion. Then, add 2g of diatomaceous earth, 0.5g of elm wood powder, 0.2g of sodium citrate, and 1g of phosphite to the gelling agent dispersion in sequence, and stir evenly with a glass rod to obtain a gel base solution. Finally, add 2.5g of the delayed crosslinking agent prepared in step S1 to the gel base solution at room temperature, stir evenly to obtain a gel solution, put it into an aging tank, and place it in a roller heating furnace at 105℃ for a crosslinking reaction for 35min to obtain an environmentally friendly self-degradable crosslinking gel for plugging leaks in medium-temperature geothermal wells.
[0040] Example 3 This invention provides an environmentally friendly, self-degradable crosslinking gel for plugging leaks in medium-temperature geothermal wells. The raw materials for preparing this gel include: 100g water, 1g hydroxypropyl guar gum, 0.3g high-viscosity anionic cellulose, 2g delayed crosslinking agent, 0.5g citric acid, 1g diatomaceous earth, 2g elm wood powder, and 1.5g phosphite. The delayed crosslinking agent comprises wood powder, diatomaceous earth, zirconate crosslinking agent, and hydrogenated petroleum resin with a softening point of 120°C. The delayed crosslinking agent is a mixture of wood powder, diatomaceous earth, and zirconate crosslinking agent in a mass ratio of 0.4:0.6:1, and the mass ratio of the mixture to the temperature-sensitive material is 1:1.
[0041] The preparation method of the environmentally friendly self-degradable crosslinking gel for plugging medium-temperature geothermal wells in this embodiment of the invention is as follows: S1. The delayed crosslinking agent is prepared according to the method for preparing the delayed crosslinking agent of the present invention. The specific preparation process is as follows: S11. At room temperature, add 4g of wood flour, 6g of diatomaceous earth and 10g of zirconate crosslinking agent to a beaker, and stir with a glass rod to mix evenly to obtain component I. S12. Add 20g of hydrogenated petroleum resin to the reaction vessel, heat to 145℃, and after the hydrogenated petroleum resin has completely melted, add component I and stir evenly with a glass rod to obtain component II. S13. Pour component II from the reaction vessel into a container filled with water, cool it, and then dry it in a forced-air drying oven at 75°C for 120 minutes. Finally, use a high-speed universal pulverizer to pulverize it at 24,000 rpm for 3 minutes to obtain the delayed crosslinking agent.
[0042] S2. Add 1g of hydroxypropyl guar gum and 0.3g of high-viscosity polyanionic cellulose to 100g of water, stir evenly with a glass rod, and hydrate at 25℃ for 60min to obtain a gelling agent dispersion. Then, add 1g of diatomaceous earth, 2g of elm wood powder, 0.5g of citric acid, and 1.5g of phosphite to the gelling agent dispersion in sequence, and stir evenly with a glass rod to obtain a gel base solution. Finally, add 2g of the delayed crosslinking agent prepared in step S1 to the gel base solution at room temperature, stir evenly to obtain a gel solution, put it into an aging tank, and place it in a 120℃ roller heating furnace for crosslinking reaction for 85min to obtain an environmentally friendly self-degradable crosslinking gel for plugging leaks in medium-temperature geothermal wells.
[0043] Comparative Example 1 Comparative Example 1 provides an environmentally friendly, self-degradable crosslinking gel for plugging leaks in medium-temperature geothermal wells. The difference between this gel and the environmentally friendly, self-degradable crosslinking gel for plugging leaks in medium-temperature geothermal wells in Example 1 is that a zirconate ester crosslinking agent is used to replace the delayed crosslinking agent.
[0044] Comparative Example 2 Comparative Example 2 provides an environmentally friendly, self-degradable crosslinking gel for plugging leaks in medium-temperature geothermal wells. Compared with the environmentally friendly, self-degradable crosslinking gel for plugging leaks in medium-temperature geothermal wells in Example 1, the difference is that the delayed crosslinking agent is 1g, while the quality and type of other raw materials remain unchanged.
[0045] Comparative Example 3 Comparative Example 3 provides an environmentally friendly, self-degradable crosslinking gel for plugging leaks in medium-temperature geothermal wells. Compared with the environmentally friendly, self-degradable crosslinking gel for plugging leaks in medium-temperature geothermal wells in Example 1, the difference is that the amount of citric acid added is 0g, while the quality and type of other raw materials remain unchanged.
[0046] Comparative Example 4 Comparative Example 4 provides an environmentally friendly, self-degradable crosslinking gel for plugging leaks in medium-temperature geothermal wells. The raw materials used to prepare this gel include: 100g water, 1g hydroxypropyl guar gum, 0.2g high-viscosity anionic cellulose, 1.5g delayed crosslinking agent, 1g diatomaceous earth, 1g elm wood powder, and 0.5g sodium metabisulfite. The delayed crosslinking agent comprises wood powder, diatomaceous earth, zirconate crosslinking agent, and hot melt adhesive with a softening point of 95°C. The delayed crosslinking agent consists of a mixture of wood powder, diatomaceous earth, and zirconate crosslinking agent in a mass ratio of 0.5:0.4:1, and the mass ratio of this mixture to the temperature-sensitive material is 0.68:1. The preparation method of the environmentally friendly, self-degradable crosslinking gel for plugging leaks in medium-temperature geothermal wells in Comparative Example 4 is the same as that in Example 1.
[0047] Comparative Example 5 Comparative Example 5 provides an environmentally friendly, self-degradable crosslinking gel for sealing leaks in medium-temperature geothermal wells. Compared with the environmentally friendly, self-degradable crosslinking gel for sealing leaks in medium-temperature geothermal wells in Example 1, the difference is that the amount of diatomaceous earth added in the raw materials used to prepare the environmentally friendly, self-degradable crosslinking gel for sealing leaks in medium-temperature geothermal wells is 2g, the amount of elm wood powder added is 0g, and the quality and type of other raw materials remain unchanged.
[0048] Comparative Example 6 Comparative Example 6 provides an environmentally friendly, self-degradable crosslinking gel for plugging leaks in medium-temperature geothermal wells. Compared with the environmentally friendly, self-degradable crosslinking gel for plugging leaks in medium-temperature geothermal wells in Example 1, the difference is that the amount of hydroxypropyl guar gum added is 2g, the amount of high-viscosity anionic cellulose added is 0g, and the quality and type of other raw materials remain unchanged.
[0049] The performance testing method for environmentally friendly, self-degradable cross-linking gel used for plugging leaks in medium-temperature geothermal wells is as follows: (a) Determination of crosslinking time of environmentally friendly self-degradable crosslinking gel for plugging medium-temperature geothermal wells: 200 mL of the gel solutions prepared in Examples 1-3 and Comparative Examples 1-6 were poured into the aging tank, and then 0.2 MPa nitrogen gas was introduced into the tank. After sealing and tightening the lid, the tank was placed in a high-temperature roller heating furnace and allowed to stand at 95~120℃ for a certain period of time. Then, the aging tank was removed, cooled, and the pressure was released before opening the tank to observe whether the gel solution inside had crosslinked (it was a flowing liquid before being placed in the aging tank; if crosslinked, it would form an adjustable gel). The crosslinking time is defined as when the crosslinked gel in the tank can be picked up and stuck. The test results are shown in Table 1.
[0050] (b) Determination of the pressure-bearing capacity of environmentally friendly self-degradable cross-linked gel for plugging leaks in medium-temperature geothermal wells: A GGS71-B high-temperature and high-pressure filtration analyzer was used as the gel plugging test instrument. A filter screen (0.60 mm aperture) was placed at the bottom of the filtration analyzer vessel, and 100 g of 6-10 mesh or 10-20 mesh quartz sand particles were added and gently shaken to mix. Then, 300 mL of the gel solutions prepared in Examples 1-3 and Comparative Examples 1-6 were poured into the vessel, the lid was tightened, and the instrument was started to heat up to 95-120℃ and maintained at a constant temperature for 5 hours. Finally, the pressure was applied to the set pressure to start the test, and the gel volume after 30 minutes of filtration was recorded. The smaller the filtrate volume, the better the plugging effect of the developed environmentally friendly self-degradable cross-linked gel under the test pressure. The higher the test pressure and the smaller the filtrate volume, the stronger the pressure-bearing capacity of the developed environmentally friendly self-degradable cross-linked gel for plugging leaks. The test results are shown in Table 1.
[0051] (c) Stability period determination of environmentally friendly self-degradable crosslinking gel for plugging medium-temperature geothermal wells: 300 mL of the gel solutions prepared in Examples 1-3 and Comparative Examples 1-6 were poured into the aging tank, respectively. After capping and tightening, the tank was placed in a high-temperature roller heating furnace and continuously rolled for aging at 120°C. Then, the aging tank was removed and cooled, and the state of the gel and the volume of water separation were recorded at different aging times. The test results are shown in Table 1.
[0052] (d) Environmental Performance Testing of Environmentally Friendly Self-Degradable Crosslinked Gel for Positive Gas Flow in Medium-Temperature Geothermal Wells: Currently, there is no direct method to evaluate the environmental performance of crosslinked gels; only the degraded gel solution can be used as the test sample. 300 mL of the gel solutions prepared in Examples 1-3 and Comparative Examples 1-6 were poured into an aging tank, capped, and placed in a high-temperature roller furnace. The tank was continuously rolled and aged at 120°C for over 7 days until the crosslinked gel was completely degraded. The aging tank was then removed and cooled, and the degraded gel solution was used as the test solution. The environmental performance of the degraded gel, including biodegradability and biotoxicity, was tested according to standards such as the Technical Specification for Environmental Performance Evaluation of Drilling Fluids (SY / T 7467-2020) and the Technical Requirements for Environmental Protection of Water-Soluble Oilfield Chemicals (SY / T 6787-2010). The test results are shown in Table 1.
[0053] Table 1. Performance test results of environmentally friendly self-degradable crosslinking gel for plugging leaks in medium-temperature geothermal wells. Table 1 shows that the environmentally friendly self-degradable crosslinking gels for plugging medium-temperature geothermal wells prepared in Examples 1-3 have the characteristics of adjustable crosslinking time, strong plugging pressure resistance, and good environmental performance. Furthermore, they are self-degradable and maintain stability for up to 7 days at 120℃. For example, under plugging conditions of 7MPa pressure and different mesh sizes of quartz sand, the volume of the environmentally friendly self-degradable crosslinking gels from Examples 1-3 after filtration for 30 minutes is ≤26mL. The environmentally friendly self-degradable crosslinking gels for plugging medium-temperature geothermal wells in Comparative Examples 2 and 4 have weaker plugging pressure resistance; based on the gel volume after filtration for 30 minutes, the maximum plugging pressure resistance does not exceed 5MPa. Although the environmentally friendly self-degradable crosslinking gels for plugging medium-temperature geothermal wells in Comparative Examples 1, 3, and 6 can achieve a plugging pressure resistance of 7MPa, their rapid crosslinking reaction at 95℃ results in a short crosslinking time, leading to gel formation before reaching the target plugging location, resulting in incomplete sealing. Moreover, the stabilization period of Comparative Example 6 is also shortened to 2 days.
[0054] Figure 1 This is a photograph of the environmentally friendly, self-degradable crosslinked gel for plugging medium-temperature geothermal wells prepared in Example 3. Figures 2-5These are photographs of the environmentally friendly self-degradable crosslinking gel for plugging medium-temperature geothermal wells prepared in Example 3, aged at 120°C for 3 days, 5 days, 7 days, and 10 days. This shows that the environmentally friendly self-degradable crosslinking gel for plugging medium-temperature geothermal wells prepared in Example 3 will gradually self-degrade until it completely breaks down at a high temperature of 120°C. The stability period of the environmentally friendly self-degradable crosslinking gel for plugging medium-temperature geothermal wells prepared in this way can reach 7 days at a high temperature of 120°C.
[0055] The above-described embodiments are merely preferred embodiments provided to fully illustrate the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the claims.
Claims
1. An environmentally friendly, self-degradable cross-linking gel for plugging leaks in medium-temperature geothermal wells, characterized in that, The raw material used to prepare the environmentally friendly, self-degradable crosslinking gel for plugging leaks in medium-temperature geothermal wells consists of the following components in parts by weight: 100 parts water, 1.2-1.5 parts gelling agent, 1.5-2.5 parts delayed crosslinking agent, 0.1-0.3 parts crosslinking control agent, 1-3 parts reinforcing agent, and 0.5-1.5 parts stabilizer; The raw materials for the delayed crosslinking agent include wood flour, diatomaceous earth, zirconate crosslinking agent, and thermosensitive material.
2. The environmentally friendly self-degradable crosslinking gel for plugging leaks in medium-temperature geothermal wells according to claim 1, characterized in that, The gelling agent is a compound of any two of hydroxypropyl guar gum, carboxymethyl hydroxypropyl guar gum, and high-viscosity polyanionic cellulose.
3. The environmentally friendly self-degradable crosslinking gel for plugging leaks in medium-temperature geothermal wells according to claim 1, characterized in that, The temperature-sensitive material is one of hot melt adhesive and hydrogenated petroleum resin, and the softening point of the temperature-sensitive material is 95~120℃.
4. The environmentally friendly self-degradable crosslinking gel for plugging leaks in medium-temperature geothermal wells according to claim 1, characterized in that, The crosslinking control agent is one of citric acid and sodium citrate.
5. The environmentally friendly self-degradable crosslinking gel for plugging leaks in medium-temperature geothermal wells according to claim 1, characterized in that, The reinforcing agent comprises diatomaceous earth and elm powder, wherein the mass ratio of diatomaceous earth to elm powder is 1:(0.25~2).
6. The environmentally friendly self-degradable crosslinking gel for plugging leaks in medium-temperature geothermal wells according to claim 1, characterized in that, The stabilizer is either sodium metabisulfite or a phosphite.
7. The environmentally friendly self-degradable crosslinking gel for plugging leaks in medium-temperature geothermal wells according to claim 1, characterized in that, The delayed crosslinking agent comprises a mixture of wood flour, diatomaceous earth and zirconate crosslinking agent in a mass ratio of (0.4~0.6):(0.4~0.6):1, and the mass ratio of the mixture to the temperature-sensitive material is (0.8~1):
1.
8. A method for preparing an environmentally friendly, self-degradable cross-linked gel for plugging leaks in medium-temperature geothermal wells as described in any one of claims 1-7, characterized in that, Includes the following steps: (1) Mix the water and the gelling agent, and hydrate at 20~25℃ for 30~60 min to obtain a gelling agent dispersion; (2) Add the reinforcing agent, the crosslinking control agent and the stabilizer to the gelling agent dispersion, stir and mix evenly to obtain a gel base solution; (3) The gel base liquid obtained in step (2) is mixed with the delayed crosslinking agent to obtain a gel solution, and then the crosslinking reaction is carried out at 95~120℃ for 11~85min to obtain an environmentally friendly self-degradable crosslinking gel for plugging leaks in medium-temperature geothermal wells.
9. The preparation method according to claim 8, characterized in that, The method for preparing the delayed crosslinking agent includes the following steps: (1) The wood flour, the diatomaceous earth and the zirconate crosslinking agent are stirred and mixed evenly to obtain component I; (2) Add the temperature-sensitive material to the reaction vessel and heat it to 20-30°C above the softening point of the temperature-sensitive material. After the temperature-sensitive material has completely melted, add component I and stir evenly to obtain component II. (3) Pour the component II in the reaction vessel into a container filled with water, cool it, dry it in a forced-air drying oven at 60~75℃, and then pulverize it with a high-speed universal pulverizer to obtain the delayed crosslinking agent.