Sand-carrying agents and their preparation methods and water-based drilling fluids

Abstract

This invention provides a sand-carrying agent, its preparation method, and a water-based drilling fluid. The sand-carrying agent comprises, by weight, 1-16000 parts of polyvinyl alcohol, 1-1000 parts of lignin, 1-8 parts of a crosslinking agent, and 10-270 parts of water. This invention also provides a method for preparing the above-mentioned sand-carrying agent, comprising dissolving polyvinyl alcohol and lignin in water, adding a crosslinking agent, and reacting to obtain the sand-carrying agent. This invention further provides a water-based drilling fluid prepared from the above-mentioned sand-carrying agent. The sand-carrying agent provided by this invention exhibits high temperature resistance, mechanical strength, inhibition ability, and sand-carrying capacity.

Description

Technical Field

[0001] This invention relates to the field of oilfield drilling fluid technology, and in particular to a sand-carrying agent and its preparation method, as well as a water-based drilling fluid. Background Technology

[0002] Drilling fluid is the circulating flushing medium used in the drilling process, and can be divided into water-based drilling fluid, oil-based drilling fluid, and gas drilling fluid. Water-based drilling fluid has advantages such as low cost, simple maintenance, wide range of treatment agents, easy performance control, and protection of oil and gas reservoirs, making it a commonly used drilling fluid system in oilfield drilling. In highly deviated and horizontal well sections, the static sand-carrying and dynamic rock-carrying capacity of drilling fluid is a challenge. Given fixed drilling parameters such as drill string assembly and wellbore trajectory design, and limited by the rated power of the surface rig, to achieve maximum extension in horizontal well sections, it is necessary to achieve efficient rock-carrying under low-density, low-flow-rate, and low-return-velocity conditions, maintain wellbore cleanliness, minimize drill string friction torque, and reduce total circulating pressure loss. Rock-carrying and sand removal by drilling fluid are essential research subjects in drilling engineering.

[0003] Currently, the commonly used technology in drilling sites involves circulating sand-lifting by pumping in heavy mud, thick mud, or fiber-reinforcing sand-removing fluid (less frequently used). However, this technology has significant drawbacks: ① It adversely affects the properties of the original well mud. The increase in macromolecular polymers leads to increased mud viscosity and shear, especially when used in high-density mud; ② It induces wellbore instability. When heavy mud is used in narrow density windows, the formation stress is released under external forces, causing wellbore collapse; ③ The effect is poor, failing to achieve the purpose of cleaning the wellbore. When thick mud is pumped into the open-hole horizontal section, the flow pattern of the sand-carrying fluid in the horizontal section is mostly laminar, failing to achieve the effect of turbulent flow for carrying cuttings and removing sand, or only being able to transport cuttings a certain distance without being able to carry them out; ④ Non-degradable fibers clog the annulus or drill string water holes. The small gap size of downhole tools or annulus makes it easy to clog gaps or channels.

[0004] Polyvinyl alcohol (PVA) is a water-soluble polymer containing a large number of hydroxyl groups, making it readily soluble in water. It exhibits excellent film-forming properties, adhesion, miscibility, and chemical resistance. Although PVA can form gels, its mechanical strength and properties are insufficient, resulting in a less than ideal sand-carrying capacity when used in sand-carrying agents.

[0005] Existing sand-carrying agents have problems such as adversely affecting the performance of the original well mud, inducing wellbore instability, poor performance, and non-degradability. Summary of the Invention

[0006] To address the aforementioned problems, the present invention aims to provide a sand-carrying agent, its preparation method, and a water-based drilling fluid.

[0007] To achieve the above objectives, the present invention provides a sand-carrying agent, wherein the raw materials of the sand-carrying agent, by weight, include: 1-16000 parts of polyvinyl alcohol, 1-1000 parts of lignin, 1-8 parts of crosslinking agent, and 10-270 parts of water.

[0008] In the above-mentioned sand-carrying agent, the polyvinyl alcohol and lignin can crosslink to form a gel sand-carrying agent with high mechanical strength, thereby improving the thickening and inhibiting abilities of the sand-carrying agent.

[0009] In the above-mentioned sand-carrying agent, the polyvinyl alcohol includes one or more of polyvinyl alcohol 1788, polyvinyl alcohol 1799, polyvinyl alcohol 2688, and polyvinyl alcohol 2699.

[0010] In the aforementioned sand-carrying agents, the lignin used in this invention has the advantages of being inexpensive, readily available, and environmentally friendly compared to petroleum-based raw materials, resulting in a low-cost and environmentally friendly sand-carrying agent. Lignin also has good biodegradability and is inexpensive, which can significantly reduce production costs.

[0011] In the aforementioned sand-carrying agent, the lignin is alkali-treated lignin, which can be called alkali lignin. In alkali-modified lignin, the lignin monomers break down into small flakes, and the methoxy groups in the lignin molecular structure are removed, dissolving into alkali lignin. Alkali lignin has high reactivity, low molecular weight, and good hydrophobicity. The molecular weight of alkali-treated lignin is 1000-2000 g / mol.

[0012] In the above-mentioned sand-carrying agent, the alkali treatment method includes: mixing lignin with an alkali solution, reacting, filtering, adjusting the pH value to 2-3, and obtaining a solution of the lignin.

[0013] In the above-described alkaline treatment method, the pH value of the alkaline solution is 10-13.

[0014] In the above-described alkali treatment method, the reaction temperature can be 90-120℃, for example, specific values ​​such as 90℃, 100℃, 110℃, 120℃, etc., and a range with any two of the above specific values ​​as endpoints. The reaction time can be 20-30 hours, for example, 24 hours.

[0015] In the above-mentioned sand-carrying agent, the above-mentioned alkali treatment method may specifically include: mixing lignin with an alkaline solution to fully dissolve the lignin in an alkaline solution with a pH of 10-13 to form a mixed solution, reacting, filtering the mixed solution to remove insoluble impurities, then adjusting the pH of the filtrate to 2-3, centrifuging (the speed can be 8000 rpm), washing the centrifuged precipitate three times with deionized water, and drying to obtain the lignin.

[0016] In the aforementioned sand-carrying agent, the mechanical properties of the sand-carrying agent can be adjusted by controlling the proportion of lignin added, thereby achieving effective control of shear resistance. In some specific embodiments, the mass ratio of polyvinyl alcohol to lignin is generally 1-16000:1-1000, and can be further controlled to 300-2000:12-220.

[0017] In the aforementioned sand-carrying agent, the crosslinking agent may include glutaraldehyde crosslinking agent. By using crosslinking agents such as glutaraldehyde, the gel formed by crosslinking lignin and polyvinyl alcohol can have the characteristics of high crosslinking density and high crosslinking strength.

[0018] In the above-mentioned sand-carrying agent, the mass ratio of the crosslinking agent to the polyvinyl alcohol can be 1-8:300-2000.

[0019] In the above-mentioned sand-carrying agent, the mass ratio of water to polyvinyl alcohol is generally 10-270:1-16000, and can be further controlled to 20-270:300-2000 or 10-200:300-2000.

[0020] In some specific embodiments, the raw materials of the sand-carrying agent may include, by weight: 300-2000 parts of polyvinyl alcohol, 12-220 parts of lignin, 1-8 parts of crosslinking agent, and 20-270 parts of water.

[0021] The sand-carrying agent obtained by the present invention can be used as a lignin-modified polyvinyl alcohol sand-carrying agent.

[0022] The present invention also provides a method for preparing the above-mentioned sand-carrying agent, the method comprising: dissolving polyvinyl alcohol and lignin in water, adding a crosslinking agent to react, and obtaining the sand-carrying agent.

[0023] In the above preparation method, the reaction temperature can be controlled at 70-90℃, specifically 70℃, 75℃, 80℃, 85℃, 90℃, etc., or a range with any two of the above specific values ​​as endpoints.

[0024] In the above preparation method, the reaction time can be controlled to be 30 min-40 min, specifically 30 min, 31 min, 32 min, 33 min, 34 min, 35 min, 36 min, 37 min, 38 min, 39 min, 40 min, etc., and a range with any two of the above specific values ​​as endpoints.

[0025] In the above preparation method, the polyvinyl alcohol and lignin are dissolved in water to form a mixed solution, and the mixed solution can be heated to 80-90℃ to promote the dissolution of lignin.

[0026] The preparation method provided by this invention uses simple and widely available raw materials, is easy to operate, has mild reaction conditions, and produces products with excellent performance, making it easy to scale up production and promote its application.

[0027] The present invention also provides a water-based drilling fluid made from the aforementioned proppant-carrying agent. The water-based drilling fluid made using the aforementioned proppant-carrying agent can maintain high viscosity and mechanical strength even in high-temperature drilling environments, and has high shear resistance and inhibition capabilities.

[0028] The beneficial effects of this invention are as follows:

[0029] 1. The sand-carrying agent provided by the present invention is obtained by cross-linking and polymerization of lignin and polyvinyl alcohol, which can effectively improve the mechanical properties, shear resistance and inhibition ability of the sand-carrying agent.

[0030] 2. Conventional polyvinyl alcohol (PVA) sand-carrying agents often experience a significant decrease in viscosity or even degradation in high-temperature drilling environments, resulting in a substantial reduction in sand-carrying capacity. The sand-carrying agent provided by this invention can withstand high-temperature drilling environments and maintains viscosity and mechanical properties higher than PVA at 80°C, thereby improving the sand-carrying capacity of the sand-carrying agent at high temperatures.

[0031] 3. The sand-carrying agent provided by this invention has good degradation ability, which can avoid the problem of sand-carrying agent clogging the drill bit or the channel. Attached Figure Description

[0032] Figure 1 The results show the test results of the storage modulus and loss modulus of the sand-carrying agent in Comparative Example 1.

[0033] Figure 2 The results are the test results of the storage modulus and loss modulus of the sand-carrying agent in Example 1.

[0034] Figure 3 The graph shows the relationship between the viscosity of the sand-carrying agent and the angular frequency in Comparative Example 1.

[0035] Figure 4 The graph shows the relationship between the viscosity of the sand-carrying agent and temperature in Comparative Example 1.

[0036] Figure 5 The graph shows the relationship between the viscosity of the sand-carrying agent and the angular frequency in Example 1.

[0037] Figure 6 This is a graph showing the relationship between the viscosity of the sand-carrying agent and temperature in Example 1.

[0038] Figure 7 The graph shows the relationship between the viscosity and angular frequency of the sand-carrying agent in Example 1 after heating for 3 hours.

[0039] Figure 8 The graph shows the relationship between the viscosity and angular frequency of the sand-carrying agent in Example 1 after heating for 120 hours. Detailed Implementation

[0040] In order to provide a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail below, but it should not be construed as limiting the scope of implementation of the present invention.

[0041] Example 1

[0042] This embodiment provides a sand-carrying agent, the preparation method of which includes:

[0043] (1) Alkali treatment of lignin: 10g of lignin was added to a 2mol / L NaOH aqueous solution and reacted at 100°C for 24 hours to fully dissolve the lignin. The solution was filtered to remove insoluble impurities. The pH value was further adjusted to 2 by adding salt solution to the filtrate, centrifuged at 8000rpm, and the precipitate was washed three times with deionized water and dried in a vacuum oven to obtain lignin.

[0044] (2) By mass, 2000 parts of polyvinyl alcohol 1799, 80 parts of lignin obtained in step (1) and 100 parts of water are stirred at 90°C for 3 hours until completely dissolved. Then, 8 parts of glutaraldehyde crosslinking agent are added, and the crosslinking reaction is carried out at 80°C for 30 minutes. After cooling, a sand-carrying agent is obtained. This sand-carrying agent is a lignin-modified polyvinyl alcohol sand-carrying agent.

[0045] Example 2

[0046] This embodiment provides a sand-carrying agent, the preparation method of which includes:

[0047] (1) Alkali treatment of lignin: 10g of lignin was added to a 2mol / L NaOH aqueous solution and reacted at 100°C for 24 hours to fully dissolve the lignin. The solution was filtered to remove insoluble impurities. The pH value was further adjusted to 2 by adding salt solution to the filtrate, centrifuged at 8000rpm, and the precipitate was washed three times with deionized water and dried in a vacuum oven to obtain lignin.

[0048] (2) By mass, 1799 1000 parts of polyvinyl alcohol, 220 parts of lignin obtained in step (1) and 270 parts of water are stirred at 90°C for 3 hours until completely dissolved. Then, 8 parts of glutaraldehyde crosslinking agent are added, and the crosslinking reaction is carried out at 80°C for 30 minutes. After cooling, a sand-carrying agent is obtained. This sand-carrying agent is a lignin-modified polyvinyl alcohol sand-carrying agent.

[0049] Example 3

[0050] This embodiment provides a sand-carrying agent, the preparation method of which includes:

[0051] (1) Alkali treatment of lignin: 10g of lignin was added to a 2mol / L NaOH aqueous solution and reacted at 100°C for 24 hours to fully dissolve the lignin. The solution was filtered to remove insoluble impurities. The pH value was further adjusted to 2 by adding salt solution to the filtrate, centrifuged at 8000rpm, and the precipitate was washed three times with deionized water and dried in a vacuum oven to obtain lignin.

[0052] (2) By mass, 300 parts of polyvinyl alcohol, 12 parts of lignin and 20 parts of water are stirred at 90°C for 3 hours until completely dissolved. Then, 1 part of glutaraldehyde crosslinking agent is added, and the crosslinking reaction is carried out at 80°C for 30 minutes. After cooling, a sand-carrying agent is obtained. This sand-carrying agent is a lignin-modified polyvinyl alcohol sand-carrying agent.

[0053] Comparative Example 1

[0054] This comparative example provides a sand-carrying agent, the preparation method of which includes:

[0055] By weight, 2000 parts of polyvinyl alcohol (1799) and 100 parts of water are stirred at 90°C for 3 hours until completely dissolved. Then, 8 parts of glutaraldehyde crosslinking agent are added, and the mixture is stirred at 80°C for 1-2 minutes. After cooling, a sand-carrying agent is obtained, which is a polyvinyl alcohol sand-carrying agent.

[0056] Test case

[0057] This test case provides the performance test results of the above embodiments and comparative examples.

[0058] 1. Viscoelasticity test

[0059] Using a Discovery HR-2 rheometer (USA), frequency scanning was employed to measure the relationship between the storage modulus, loss modulus, and shear rate of polyvinyl alcohol (PVA) sand-carrying agent and lignin-modified PVA sand-carrying agent. The relationship between the storage modulus, loss modulus, and angular frequency of the PVA sand-carrying agent in Comparative Example 1 was obtained as follows: Figure 1 As shown, the data obtained for the lignin-modified polyvinyl alcohol sand-carrying agent in Example 1 are as follows: Figure 2 As shown. Figure 1 , Figure 2 The comparison shows that lignin modification can significantly improve the storage modulus and loss modulus of the sand-carrying agent, giving it higher mechanical strength. The sand and gravel in the sand-carrying agent sample of Example 1 require a longer settling time, resulting in better sand-carrying performance.

[0060] 2. Viscosity test

[0061] Using a Discovery HR-2 rheometer (USA) in temperature ramp mode, the relationship between the viscosity of the sample and shear rate and temperature was measured. The relationship between the viscosity of the polyvinyl alcohol carrying agent and angular frequency and temperature was obtained as follows: Figure 3 , Figure 4 As shown, the data obtained for the lignin-modified polyvinyl alcohol in Example 1 are as follows: Figure 5 , Figure 6 As shown. Figure 5 The complex viscosity corresponding to a mid-angular frequency of 100 rad / s is 77 Pa·s.

[0062] Figures 3 to 6 It can be seen that although the shear-thinning agent with added lignin becomes thinner, when the shear rate is in the range of 0.1 to 100 / s, the viscosity of the lignin-modified sand-carrying agent is much greater than that of the sand-carrying agent without added lignin, and the lignin-modified sand-carrying agent has stronger shear resistance.

[0063] from Figures 3 to 6 It can be seen that the sand-carrying agent of Example 1 has a higher viscosity than that of the sand-carrying agent of Comparative Example 1 in an environment with higher angular frequency and higher temperature. This indicates that the sand-carrying agent of Example 1 has better temperature resistance and can maintain a high viscosity level and mechanical properties even when the temperature rises. The sand-carrying capacity of the sand-carrying agent is significantly improved.

[0064] Figure 7 , Figure 8 The graph shows the relationship between the viscosity and angular frequency of the sand-carrying agent in Example 1 after heating for 3 hours and 120 hours. Figure 7 The complex viscosity corresponding to a mid-angular frequency of 100 rad / s is 72 Pa·s; Figure 8 The complex viscosity corresponding to a mid-angular frequency of 100 rad / s is 23 Pa·s. From Figure 7 , Figure 8 It can be seen that the sand-carrying agent has good degradation ability.

[0065] The above results demonstrate that the sand-carrying agent provided by this invention, through cross-linking polymerization of lignin and polyvinyl alcohol, can effectively improve the mechanical properties, shear resistance, and inhibition capacity of the sand-carrying agent. This sand-carrying agent can withstand high-temperature drilling environments, maintaining viscosity and mechanical properties higher than polyvinyl alcohol at 80°C, and possesses good degradation ability, thus avoiding the problem of sand-carrying agents clogging drill strings or boreholes.

Claims

1. A sand-carrying agent, wherein the raw materials of the sand-carrying agent comprise, by weight: Polyvinyl alcohol 300-2000 parts, lignin 12-220 parts, crosslinking agent 1-8 parts, water 20-270 parts; The crosslinking agent includes glutaraldehyde crosslinking agent; The lignin is alkali-treated lignin, and the alkali treatment method includes: mixing lignin with an alkali solution, reacting, filtering, adjusting the pH value to 2-3, and obtaining a solution of the lignin. The molecular weight of the alkali-treated lignin is 1000-2000 g / mol.

2. The sand-carrying agent according to claim 1, wherein, The polyvinyl alcohol includes one or more of polyvinyl alcohol 1788, polyvinyl alcohol 1799, polyvinyl alcohol 2688, and polyvinyl alcohol 2699.

3. The sand-carrying agent according to claim 1, wherein, The pH value of the alkaline solution is 10-13.

4. A method for preparing the sand-carrying agent according to any one of claims 1-3, the method comprising: Polyvinyl alcohol and lignin are dissolved in water, and a crosslinking agent is added to react and obtain the sand-carrying agent.

5. The preparation method according to claim 4, wherein, The reaction temperature is 70-90℃, and the reaction time is 30-40 minutes.

6. A water-based drilling fluid, which is made from the sand-carrying agent according to any one of claims 1-3.

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