Sand-carrying agent, preparation method thereof and water-based drilling fluid

Abstract

The invention provides a sand-carrying agent, a preparation method thereof and a water-based drilling fluid. The sand-carrying agent is prepared from the following raw materials in parts by mass: 1 to 16000 parts of polyvinyl alcohol, 1 to 1000 parts of chitosan, 1 to 8 parts of cross-linking agent and 10 to 200 parts of water. The invention also provides a preparation method of the sand-carrying agent, which comprises the following steps: dissolving the polyvinyl alcohol and the chitosan in water, and adding the cross-linking agent for reaction to obtain the sand-carrying agent. The invention also provides a water-based drilling fluid prepared from the sand-carrying agent. The sand-carrying agent provided by the invention has relatively high anti-shearing capability, inhibition capability and sand-carrying capability.

Description

Technical Field

[0001] The invention relates to the technical field of oilfield drilling fluid, in particular to a sand carrying agent and a preparation method thereof and a water-based drilling fluid. Background Art

[0002] Drilling fluid is a circulating flushing medium used in the drilling process, which can be divided into water-based drilling fluid, oil-based drilling fluid and gas drilling fluid. Water-based drilling fluid has the advantages of low cost, simple maintenance, wide range of treatment agents, easy performance control, and protection of oil and gas layers. It is a commonly used drilling fluid system in oilfield drilling. In high-angle well sections and horizontal well sections, the static sand suspension and dynamic rock carrying capacity of drilling fluid is a difficult point. Under the premise of certain drilling parameters such as drill bit assembly and wellbore trajectory design, and limited by the rated power of the ground unit, in order to achieve the maximum extension of the horizontal well section, it is necessary to achieve efficient rock carrying under low density, low displacement and low return speed conditions, keep the wellbore clean, reduce the friction torque of the drill bit as much as possible, and reduce the total circulation pressure loss. Rock carrying and sand removal of drilling fluid is one of the indispensable research objects in drilling engineering.

[0003] At present, the commonly used technical means at the drilling site is to pump in heavy slurry, thick slurry, and fiber sand cleaning fluid (less used) for circulating sand lifting. However, this technical means has major drawbacks: ① It has an adverse effect on the performance of the original well slurry. The increase of macromolecular polymers causes the slurry viscosity to increase, especially when used in high-density well slurry. The impact is more serious; ② It induces wellbore instability. When heavy slurry is used in the narrow density window well section, the formation stress is released under the action of external force, causing the wellbore to collapse; ③ The use effect is poor and the purpose of cleaning the wellbore cannot be achieved. When the thick slurry is pumped into the horizontal well section of the open hole, the flow pattern of the sand-carrying fluid in the horizontal section is mostly laminar flow, which cannot achieve the effect of turbulent rock carrying and sand cleaning, or can only move the cuttings to a certain distance and cannot carry them out; ④ Non-degradable fibers block the annulus or drilling tool water hole, and the gaps in the downhole tools or annulus are small and easy to block the gaps or channels.

[0004] Polyvinyl alcohol is a water-soluble polymer, which contains a large number of hydroxyl groups in its molecules, making it easily soluble in water and having excellent film-forming properties, adhesion, miscibility and chemical resistance. Although polyvinyl alcohol can form gel, it has insufficient mechanical strength and poor mechanical properties, and its sand-carrying capacity is not outstanding when used in sand-carrying agents.

[0005] Existing sand-carrying agents have the problems of adversely affecting the performance of the original well slurry, inducing well wall instability, having poor use effects, and being non-degradable. Summary of the invention

[0006] In order to solve the above problems, the present invention aims to provide a sand-carrying agent and a preparation method thereof and a water-based drilling fluid. The sand-carrying agent has good suppression ability and high temperature resistance.

[0007] To achieve the above object, the present invention provides a proppant. By mass, the raw materials of the proppant include: 1-16000 parts of polyvinyl alcohol, 1-1000 parts of chitosan, 1-8 parts of crosslinking agent, and 10-200 parts of water.

[0008] In the above proppant, the polyvinyl alcohol and chitosan can crosslink to form a gel proppant with high mechanical strength, which can not only improve the water solubility of chitosan, but also enhance the thickening ability and inhibition ability of the proppant, so as to carry out static sand suspension and dynamic rock carrying.

[0009] In the above proppant, the polyvinyl alcohol includes one or a combination of more than two of polyvinyl alcohol 1788, polyvinyl alcohol 1799, polyvinyl alcohol 2688, and polyvinyl alcohol 2699.

[0010] In the above proppant, the chitosan adopted in the present invention has the characteristics of being cheap, easily available, and environmentally friendly compared with petroleum-based raw materials. The prepared proppant has low cost and is environmentally friendly. Chitosan also has good biodegradability and low price, which can greatly reduce the production cost.

[0011] In the above proppant, the chitosan can adopt different functionalized chitosans. Specifically, the chitosan can include deacetylated chitin; one or a combination of more than two of poly(D-glucosamine) and poly(D-glucosamine).

[0012] In the above proppant, by controlling the deacetylation degree of chitosan, the solubility of chitosan in different pH environments can be regulated, and then the thickening ability of the proppant can be controlled. In some specific embodiments, the deacetylation degree of the chitosan is 80%-95%.

[0013] In the above proppant, the viscosity of the chitosan can be 50-800 mPa·s.

[0014] The crosslinking agent adopted in the present invention can make the gel formed by crosslinking polyvinyl alcohol and chitosan have the characteristics of high crosslinking density and high crosslinking strength. In the above proppant, the crosslinking agent can specifically include an organic boron crosslinking agent.

[0015] In the above proppant, the preparation method of the organic boron crosslinking agent includes: mixing a boron source, a solvent and an alkali, and heating in a water bath until the borax is completely dissolved; then adding mannitol and reacting to obtain the organic boron crosslinking agent.

[0016] The organic boron crosslinking agent prepared by the above method is a high-temperature delayed organic boron crosslinking agent, which can greatly extend the crosslinking time of the fracturing fluid in a high-temperature environment (such as 80°C-120°C).

[0017] In the above preparation method of the organic boron crosslinking agent, the temperature of the water bath is 50-65°C, such as specific values of 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, etc. and ranges with any two of the above specific values as endpoints.

[0018] In the above preparation method of the organic boron crosslinking agent, the temperature of the reaction is 70-80°C, such as specific values of 70°C, 71°C, 72°C, 73°C, 74°C, 75°C, 76°C, 77°C, 78°C, 79°C, 80°C, etc. and ranges with any two of the above specific values as endpoints. The reaction time is 4h-5h.

[0019] In the above preparation method of the organic boron crosslinking agent, the mass ratio of the boron source to the mannitol can be 1:1-3:1, such as specific values of 1:1, 1.5:1, 2:1, 2.5:1, 3:1, etc. and ranges with any two of the above specific values as endpoints.

[0020] In the above preparation method of the organic boron crosslinking agent, the boron source includes borax.

[0021] In the above preparation method of the organic boron crosslinking agent, the solvent includes water and glycerol. In some specific embodiments, the volume ratio of water to glycerol can be 3:1.

[0022] In the above preparation method of the organic boron crosslinking agent, the base can include sodium hydroxide.

[0023] In the above preparation method of the organic boron crosslinking agent, the pH value of the obtained organic boron crosslinking agent after the reaction can be 8-9. The dosage of the base during the preparation process can be adjusted accordingly according to the pH value of the organic boron crosslinking agent.

[0024] In the above proppant, the mass ratio of the polyvinyl alcohol to the chitosan can be 1-16000:1-1000, and can be further controlled to 200:10-100:50, such as 190:10.

[0025] In the above proppant, the mass ratio of the polyvinyl alcohol to the crosslinking agent can be 1-16000:1-8, such as 190:1-200:1.

[0026] In the above proppant, the mass ratio of the polyvinyl alcohol to the water can be 1-16000:10-200, such as 190:10-200:10.

[0027] The present invention also provides a preparation method of the above proppant, which includes: mixing polyvinyl alcohol, chitosan and water to obtain a mixed solution; adding a crosslinking agent to the mixed solution and reacting to obtain the proppant.

[0028] In the above method for preparing the proppant, the temperature of the reaction can be controlled at 70 - 90°C, specifically it can be specific values such as 70°C, 75°C, 80°C, 85°C, 90°C, etc. and ranges with any two of the above specific values as endpoints.

[0029] In the above method for preparing the proppant, the reaction time is 3 - 5 min.

[0030] In the above method for preparing the proppant, the temperature for mixing to form the mixed solution can be 70 - 80°C, and the mixing time can be 3 h - 5 h.

[0031] The present invention also provides an aqueous drilling fluid which is prepared from the above proppant.

[0032] The beneficial effects of the present invention include:

[0033] 1. The proppant provided by the present invention is prepared by blending and cross - linking chitosan and polyvinyl alcohol, which can effectively improve the mechanical properties, shear resistance and inhibition ability of the proppant.

[0034] 2. Conventional polyvinyl alcohol proppants will show a significant decrease in viscosity or even degradation in high - temperature drilling environments, resulting in a greatly reduced proppant - carrying capacity. The proppant provided by the present invention can withstand high - temperature drilling environments, can maintain a viscosity and mechanical properties higher than those of polyvinyl alcohol at 80°C, and improve the proppant - carrying capacity at high temperatures.

[0035] 3. The proppant provided by the present invention has good degradation ability, which can avoid the problem of the proppant blocking the drill tool or the pore channel. Description of the Drawings

[0036] Figure 1 It is a graph showing the relationship between the storage modulus, loss modulus and angular frequency of the proppant in Comparative Example 1.

[0037] Figure 2 It is a graph showing the relationship between the storage modulus, loss modulus and angular frequency of the proppant in Example 1.

[0038] Figure 3 It is a graph showing the relationship between the viscosity and angular frequency of the proppant in Comparative Example 1.

[0039] Figure 4 It is a graph showing the relationship between the viscosity and angular frequency of the proppant in Example 1.

[0040] Figure 5 It is a graph showing the relationship between the viscosity and temperature of the proppant in Comparative Example 1.

[0041] Figure 6 It is a graph showing the relationship between the viscosity and temperature of the proppant in Comparative Example 1 after heating for 3 h.

[0042] Figure 7 The relationship diagram of the viscosity and temperature of the proppant in Comparative Example 1 after heating for 16 h.

[0043] Figure 8 The relationship diagram of the viscosity and temperature of the proppant in Example 1.

[0044] Figure 9 The relationship diagram of the viscosity and temperature of the proppant in Example 1 after heating for 3 h.

[0045] Figure 10 The relationship diagram of the viscosity and temperature of the proppant in Example 1 after heating for 16 h. Detailed implementation manners

[0046] For a clearer understanding of the technical features, objectives, and beneficial effects of the present invention, the technical solutions of the present invention are described in detail below, but it should not be construed as a limitation on the scope of implementation of the present invention.

[0047] The chitosan used in the following experiments has a molecular weight of 161.16, a viscosity of 50 - 800 mPa·s, and a deacetylation degree of 80% - 95%.

[0048] Example 1

[0049] This example provides a proppant, and the preparation method of the proppant includes:

[0050] (1) Prepare an organic boron crosslinking agent: Weigh 20% of borax, 10% of mannitol, 68% of a mixed solvent formed by water and glycerol with a volume ratio of 3:1, and 2% of NaOH by mass percentage.

[0051] Mix borax, the mixed solvent of water and glycerol with a volume ratio of 3:1, and sodium hydroxide evenly according to the specified ratio, pour them into a 250 ml three-necked flask equipped with a condensing reflux device, and stir in a water bath at 50°C - 65°C until completely dissolved; then add mannitol, raise the temperature to 70°C and react for 4 h - 5 h to obtain an organic boron crosslinking agent. This organic boron crosslinking agent is a high-temperature delayed organic boron crosslinking agent; the pH value of the organic boron crosslinking agent is 8 - 9, with stable performance and can be miscible with water in any ratio.

[0052] (2) Mix 190 parts of polyvinyl alcohol 2488, 10 parts of chitosan, and 10 parts of water by mass, stir and heat at 70°C for 3 h until a completely dissolved mixed solution is formed; add 1 part of the organic boron crosslinking agent in step (1) to the mixed solution, react for 1 - 2 min, and cool to obtain a proppant, which is a chitosan-modified polyvinyl alcohol proppant.

[0053] Comparative Example 1

[0054] This comparative example provides a proppant, and the preparation method of the proppant includes:

[0055] (1) Prepare an organic boron crosslinking agent: By mass percentage, weigh 20% of borax, 10% of mannitol, 68% of a mixed solvent formed by water and glycerol with a volume ratio of 3:1, and 2% of NaOH.

[0056] Mix borax, water and glycerol with a volume ratio of 3:1, and sodium hydroxide evenly according to the formulated ratio, then pour them into a 250 ml three-necked flask equipped with a condenser reflux device, and stir at 50 °C - 65 °C in a water bath until completely dissolved; then add mannitol, heat up to 70 °C and react for 4 h - 5 h to obtain the organic boron crosslinking agent. This organic boron crosslinking agent is a high-temperature delayed organic boron crosslinking agent; the pH value of the organic boron crosslinking agent is 8 - 9, with stable performance and can be miscible with water in any ratio.

[0057] (2) By mass, mix 200 parts of polyvinyl alcohol 2488 and 10 parts of water, stir and heat at 70 °C for 3 h until a completely dissolved mixed solution is formed; add 1 part of the organic boron crosslinking agent obtained in step (1) to the mixed solution, react for 1 - 2 min, and cool to obtain the proppant, and this proppant is a polyvinyl alcohol proppant.

[0058] Test example

[0059] This test example provides the performance test results of the above examples and comparative examples.

[0060] 1. Viscoelasticity test

[0061] Use a Discovery HR-2 rheometer from the United States to measure the relationship between the storage modulus, loss modulus and shear rate of the proppant samples in Example 1 and Comparative Example 1 by frequency scanning. The relationship between the storage modulus, loss modulus and angular frequency of the polyvinyl alcohol proppant in Comparative Example 1 is as Figure 1 shown, and the data of the chitosan-modified polyvinyl alcohol proppant in Example 1 are as Figure 2 shown. By comparing Figure 1 and Figure 2 it can be seen that adding chitosan can greatly improve the storage modulus and loss modulus of the proppant, making it have higher mechanical strength. The sand needs a longer time to settle in the proppant sample of Example 1, and it has better sand-carrying performance.

[0062] 2. Viscosity test

[0063] Use a Discovery HR-2 rheometer from the United States to measure the relationship between the viscosity of the sample and the shear rate and temperature in the temperature ramp mode. The relationship between the viscosity and angular frequency of the polyvinyl alcohol proppant in Comparative Example 1 is as Figure 3As shown, the relationship between the viscosity and angular frequency of the chitosan-modified polyvinyl alcohol proppant in Example 1 was measured as follows Figure 4 shown

[0064] From Figure 3 and Figure 4 it can be seen that the viscosity of the proppant in Example 1 is higher than that of the proppant in Comparative Example 1 in an environment with a higher angular frequency, indicating that the proppant in Example 1 has better shear resistance, and the viscosity and sand-carrying capacity of the proppant have been significantly improved

[0065] 3. Degradability test

[0066] The degradability test includes the following steps

[0067] (1) Take a small amount of the prepared crosslinked proppant fluid sample and place it in a three-necked flask, heat it at 120 °C, and take samples at 3 hours and 16 hours respectively

[0068] (2) Use a rheometer to test the relationship between the viscosity η of the initial sample, the viscosity η' of the sample at 3 hours of heating, and the viscosity η'' of the sample at 16 hours of heating and temperature

[0069] The relationship between the viscosity η of the initial sample of the polyvinyl alcohol proppant in Comparative Example 1, the viscosity η' of the sample at 3 hours of heating, and the viscosity η'' of the sample at 16 hours of heating and temperature is as follows Figure 5 、 Figure 6 、 Figure 7 shown. From Figures 5 to 7 it can be seen that the degradation rate of the proppant sample in Comparative Example 1 is 12.5% when heated at 120 °C for 3 h, and the degradation rate is 95.5% when heated at 120 °C for 16 h

[0070] The relationship between the viscosity v of the initial sample of the chitosan-modified polyvinyl alcohol proppant fluid in Example 1, the viscosity η' of the sample at 3 hours of heating, and the viscosity η'' of the sample at 16 hours of heating and temperature is as follows Figure 8 、 Figure 9 、 Figure 10 shown. From Figures 8 to 10 it can be seen that the degradation rate of the proppant sample in Example 1 is 30.5% when heated at 120 °C for 3 h, and the degradation rate is 95.2% when heated at 120 °C for 16 h

[0071] The above results show that the proppants in Example 1 and Comparative Example 1 are both degradable, especially the proppant in Example 1 has excellent degradability. And the overall viscosity of the chitosan-modified polyvinyl alcohol proppant fluid in Example 1 is higher, so that it can have sufficient sand-carrying capacity in the downhole high-temperature environment, and the high degradation rate at high temperature for a long time makes it not pollute the downhole

Claims

1. A proppant, by mass, the raw materials of the proppant include: 1 - 16,000 parts of polyvinyl alcohol, 1 - 1,000 parts of chitosan, 1 - 8 parts of crosslinking agent, 10 - 200 parts of water.

2. The proppant according to claim 1, wherein, The polyvinyl alcohol includes one or a combination of two or more of polyvinyl alcohol 1788, polyvinyl alcohol 1799, polyvinyl alcohol 2688, and polyvinyl alcohol 2699.

3. The proppant according to claim 1, wherein, The deacetylation degree of the chitosan is 80% - 95%; The viscosity of the chitosan is 50 - 800 mPa·s.

4. The proppant according to claim 1, wherein, The crosslinking agent includes an organic boron crosslinking agent.

5. The proppant according to claim 4, wherein The preparation method of the organic boron crosslinking agent includes: mixing a boron source, a solvent, and an alkali, and water-bathing until the borax is completely dissolved; then adding mannitol and reacting to obtain the organic boron crosslinking agent.

6. The proppant according to claim 5, wherein, The temperature of the reaction is 70 - 80 °C, and the time of the reaction is 4 - 5 h.

7. The proppant according to claim 5, wherein The mass ratio of the boron source to the mannitol is 1:1 - 3:

1.

8. The proppant according to claim 5, wherein The boron source includes borax.

9. The proppant according to claim 1, wherein The mass ratio of the polyvinyl alcohol to the chitosan is 200:10 - 100:

50.

10. The preparation method of the proppant according to any one of claims 1 - 9, which includes: Mixing polyvinyl alcohol, chitosan, and water to obtain a mixed solution; Adding a crosslinking agent to the mixed solution and reacting to obtain the proppant.

11. The preparation method according to claim 10, wherein, The temperature of the reaction is 70 - 90 °C, and the time of the reaction is 3 - 5 min.

12. An aqueous drilling fluid, which is prepared from the proppant according to any one of claims 1 - 9.

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