Auxiliary agent for drilling fluid

Abstract

The invention belongs to the technical field of drilling fluid, and particularly belongs to the field of auxiliaries for water-based drilling fluid. The additive for the drilling fluid, which is prepared from the block copolymer or the block copolymer and the free copolymer, is added into the drilling fluid, so that the filtration performance of the drilling fluid can be remarkably improved, and the filtration loss can be reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of drilling fluids, and more specifically, to the field of additives for water-based drilling fluids. Background Art

[0002] Drilling fluid is a circulating flushing graft used in the borehole during the drilling process. Among them, water-based drilling fluid is widely used due to its low cost and small environmental pollution. Additives for drilling fluid are chemical additives used to adjust and optimize the performance of drilling fluid, usually including viscosifiers, filtration loss reducers, lubricants, weighting agents, etc. Among them, the filtration loss reducer is related to the filtration loss performance of the drilling fluid.

[0003] Filtration loss performance is one of the important performances of drilling fluid. Filtration loss of drilling fluid and the formation of filter cake are inevitable during the drilling process. The filter cake can be formed through filtration loss to protect the wellbore. However, if the filtration loss of the drilling fluid is too large, it is easy to cause shale swelling and collapse, resulting in unstable wellbore. In addition, as the filtration loss increases, the filter cake thickens, reducing the wellbore diameter, causing a large torque on the rotating drill string, and causing swabbing and pressure fluctuations during tripping, which is likely to cause differential sticking.

[0004] When the drilling fluid undergoes filtration loss, a filter cake is formed. When the drilling fluid undergoes filtration loss again, it must pass through the already formed filter cake. Therefore, the permeability of the filter cake is an important factor determining the magnitude of the filtration loss. How to form a high-quality filter cake with low permeability to prevent further filtration loss of the drilling fluid is one of the main issues to be considered in the preparation of drilling fluid. At present, an important means to reduce the filtration loss of drilling fluid is to add a filtration loss reducer to the drilling fluid. The filtration loss reducer can reduce the permeability of the filter cake, make the filter cake more dense, and thus reduce the filtration loss of the drilling fluid as much as possible.

[0005] For example, in CN112409541B, modified cellulose is used as a filtration loss reducer. Compared with unmodified cellulose, it has better filtration loss reduction effect and better adsorption stability in high-temperature and high-salt environments. In CN117820572A, a copolymer-type filtration loss reducer is used. Sepiolite is modified with multiple monomers and added to the drilling fluid, which can significantly improve the filtration loss reduction effect of the drilling fluid and also improve the high-temperature and salt tolerance of the drilling fluid.

[0006] In order to continuously enrich the types of filtration loss reducers and provide more choices for drilling fluids, the present invention designs an additive for drilling fluid with simple preparation and excellent filtration loss reduction performance. Summary of the Invention

[0007] The present invention includes an additive for drilling fluid and a drilling fluid using the additive for drilling fluid. The additive for drilling fluid includes a poly(ethylene glycol)-b-poly(lactic acid) block copolymer with a total molecular weight of 4000 - 6000 Daltons.

[0008] Preferably, the molecular weight ratio of the polyethylene glycol segment to the polylactic acid segment is 2:1 - 3:2.

[0009] In addition, the drilling fluid additive may further include polyethylene glycol (or free polyethylene glycol, to distinguish it from the polyethylene glycol segment in the block copolymer), and the molecular weight of the polyethylene glycol is 800 - 1200 Daltons.

[0010] Preferably, the mass ratio of the polyethylene glycol to the block copolymer is 1:9 - 1:10.

[0011] And / or, the drilling fluid may further include a hydrophobic polymer. Such as common polymers like polystyrene, polycaprolactone, polylactic acid, etc. Most preferably, polylactic acid polymer (or free polylactic acid, to distinguish it from the polylactic acid segment in the block copolymer) is used, and the molecular weight of the polylactic acid polymer is 600 - 800 Daltons.

[0012] Preferably, the mass ratio of the polylactic acid to the block copolymer is 1:18 - 1:20.

[0013] Adding the drilling fluid additive to the drilling fluid can obtain a drilling fluid with enhanced filtration loss resistance.

[0014] The drilling fluid has different types according to the additives. The drilling fluid in the present invention can be a conventional oil-based drilling fluid or water-based drilling fluid at the present stage.

[0015] When selecting a water-based drilling fluid, the drilling fluid additive may include water, bentonite, sodium chloride, potassium chloride, weighting agent. At the same time, to improve the filtration loss reduction property, the drilling fluid additive in the present invention with a mass content less than or equal to 5% is added.

[0016] Beneficial effects

[0017] 1. The present invention selects a PEG-PLA block copolymer as an additive for the filtration loss reducer and adds it to the drilling fluid. This block copolymer can adsorb on the surface of the filter cake and / or formation voids by using the hydrophobic segment, while the hydrophilic segment can be compatible with the water phase in the drilling fluid (microscopic swelling) to form a dynamic "anchoring - stretching structure". It can effectively fill the voids and cracks from micrometers to nanometers; at the beginning of the formation of the filter cake, a part of the block copolymer is doped in the filter cake. In a high-temperature environment, the aqueous components in the environment will swell the PEG segment, causing it to undergo microscopic expansion, further filling the voids of the filter cake, etc., to avoid further filtration loss caused by the loose filter cake. As the temperature increases, the swelling degree of the PEG segment further increases, which can ensure better filtration loss resistance in a high-temperature environment.

[0018] 2. However, when the molecular weight of the PEG-PLA block copolymer is too large, the water solubility of the block copolymer deteriorates. During the experimental verification process, the filtration loss resistance of the block copolymer with too small a molecular weight is not good. At present, when selecting block copolymers, hydrophobic segments or hydrophilic segments are usually selected as the main segments, accounting for a relatively high proportion. However, it is found in the experimental process that when the proportion of PEG or PLA segments is too high, it is difficult to exhibit excellent filtration loss resistance. Therefore, it is particularly important to select a block copolymer with an appropriate molecular weight and an appropriate segment ratio. In the actual experimental process, it is found that when the molecular weight is maintained at 4000-6000 Daltons and the PEG segment is slightly higher than the PLA segment (PEG:PLA = 2:1-3:2), the best filtration loss resistance effect can be achieved.

[0019] 3. To further improve the water solubility (or water dispersion stability) of the block copolymer, free polyethylene glycol is added simultaneously. The free polyethylene glycol can attract the polyethylene glycol segments in the block copolymer to improve the stability and uniformity of the block copolymer dispersed in water. At the same time, as the free polyethylene glycol and the polyethylene glycol segments in the block copolymer can entangle with each other to form a local microscopic intertwined network, based on swelling effects, etc., the compactness of the filter cake can be significantly reduced, thus avoiding further filtration loss. The present invention has explored the optimal addition amount and molecular weight of polyethylene glycol through experiments.

[0020] 4. During the experimental process, it is found that adding a small amount of low molecular weight polylactic acid polymer can significantly reduce the filtration loss performance, especially that the formed filter cake is thinner. Selecting other types of low molecular weight hydrophobic polymers can also reduce the filtration loss performance to a certain extent. The reason may be that the polylactic acid polymer first forms a uniform filter cake at the beginning of the filter cake formation. The polylactic acid polymer has certain surface activity and can reduce the tension between the drilling fluid and the bottom rock surface to a certain extent, which is beneficial to the formation of a uniform filter cake in the water-based drilling fluid. In the drilling fluid, polylactic acid will attract and entangle with the polylactic acid segments, and the increased hydrophobic segments are more conducive to preventing the approach and aggregation of clay particles. Only a thinner filter cake can be formed at the beginning of the filter cake formation. At the same time, the addition of polylactic acid can also improve the filter cake strength.

[0021] 5. In the drilling fluid, due to the presence of hydrophilic and hydrophobic groups, the steric hindrance near the block copolymer is relatively high, which can prevent the aggregation of bentonite or weighting agents in the drilling fluid and maintain the uniform dispersion of the system while reducing the precipitation of free water. Description of the Drawings

[0022] Figure 1 : Data graphs of Examples 2, 6, 10, 14 and Comparative Example 13

[0023] Figure 2 : Scanning electron micrograph of the surface of the filter cake after Test 1 (room temperature filtration loss measurement) of the drilling fluid additive in Example 14 Detailed implementation mode

[0024] Example 1

[0025] The auxiliary agent for drilling fluid includes polyethylene glycol-b-polylactic acid with a total molecular weight of 4000 Daltons, and the molecular weight ratio of the polyethylene glycol block to the polylactic acid block is 2:1.

[0026] Example 2

[0027] Compared with Example 1, the difference lies in that the polyethylene glycol-b-polylactic acid has a total molecular weight of 5000 Daltons.

[0028] Example 3

[0029] Compared with Example 1, the difference lies in that the polyethylene glycol-b-polylactic acid has a total molecular weight of 6000 Daltons.

[0030] Comparative Example 1

[0031] Compared with Example 1, the difference lies in that the polyethylene glycol-b-polylactic acid has a total molecular weight of 3000 Daltons.

[0032] Comparative Example 2

[0033] Compared with Example 1, the difference lies in that the polyethylene glycol-b-polylactic acid has a total molecular weight of 7000 Daltons.

[0034] Example 4

[0035] Compared with Example 2, the difference lies in that the molecular weight ratio of the polyethylene glycol block to the polylactic acid block is 3:2.

[0036] Comparative Example 3

[0037] Compared with Example 2, the difference lies in that the molecular weight ratio of the polyethylene glycol block to the polylactic acid block is 3:1.

[0038] Comparative Example 4

[0039] Compared with Example 2, the difference lies in that the molecular weight ratio of the polyethylene glycol block to the polylactic acid block is 1:1.

[0040] Example 5

[0041] Compared with Example 2, the difference lies in that it further includes free polyethylene glycol with a molecular weight of 800. The mass ratio of free polyethylene glycol to the block copolymer is 1:9.

[0042] Example 6

[0043] Compared with Example 2, the difference lies in that it further includes free polyethylene glycol with a molecular weight of 1000. The mass ratio of free polyethylene glycol to the block copolymer is 1:9.

[0044] Example 7

[0045] Compared with Example 2, the difference is that it further includes free polyethylene glycol with a molecular weight of 1200. The mass ratio of free polyethylene glycol to the block copolymer is 1:9.

[0046] Comparative Example 5

[0047] Compared with Example 2, the difference is that it further includes free polyethylene glycol with a molecular weight of 600. The mass ratio of free polyethylene glycol to the block copolymer is 1:9.

[0048] Comparative Example 6

[0049] Compared with Example 2, the difference is that it further includes free polyethylene glycol with a molecular weight of 1400. The mass ratio of free polyethylene glycol to the block copolymer is 1:9.

[0050] Example 8

[0051] Compared with Example 6, the difference is that the mass ratio of free polyethylene glycol to the block copolymer is 1:10

[0052] Comparative Example 7

[0053] Compared with Example 6, the difference is that the mass ratio of free polyethylene glycol to the block copolymer is 1:8

[0054] Comparative Example 8

[0055] Compared with Example 6, the difference is that the mass ratio of free polyethylene glycol to the block copolymer is 1:11

[0056] Example 9

[0057] Compared with Example 2, the difference is that it further includes free polylactic acid with a molecular weight of 600. The mass ratio of free polylactic acid to the block copolymer is 1:19

[0058] Example 10

[0059] Compared with Example 2, the difference is that it further includes free polylactic acid with a molecular weight of 700. The mass ratio of free polylactic acid to the block copolymer is 1:19

[0060] Example 11

[0061] Compared with Example 2, the difference is that it further includes free polylactic acid with a molecular weight of 800. The mass ratio of free polylactic acid to the block copolymer is 1:19

[0062] Comparative Example 9

[0063] Compared with Example 2, the difference is that it further includes free polylactic acid with a molecular weight of 500. The mass ratio of free polylactic acid to the block copolymer is 1:19

[0064] Comparative Example 10

[0065] Compared with Example 2, the difference is that it further includes free polylactic acid with a molecular weight of 900. The mass ratio of free polylactic acid to block copolymer is 1:19

[0066] Example 12

[0067] Compared with Example 10, the difference is that the mass ratio of free polylactic acid to block copolymer is 1:18

[0068] Example 13

[0069] Compared with Example 10, the difference is that the mass ratio of free polylactic acid to block copolymer is 1:20

[0070] Comparative Example 11

[0071] Compared with Example 10, the difference is that the mass ratio of free polylactic acid to block copolymer is 1:17

[0072] Comparative Example 12

[0073] Compared with Example 10, the difference is that the mass ratio of free polylactic acid to block copolymer is 1:21

[0074] Example 14

[0075] Compared with Example 2, it further includes free polyethylene glycol with a molecular weight of 1000; the mass ratio of free polyethylene glycol to block copolymer is 1:9. It also includes free polylactic acid with a molecular weight of 700; the mass ratio of free polylactic acid to block copolymer is 1:19

[0076] Comparative Example 13

[0077] This comparative example can be used as a reference example, and a common commercially available carboxymethyl cellulose filtrate reducer is used as an additive for drilling fluid.

[0078] Performance Test

[0079] Configuration of fresh water base slurry: 200 mL of tap water + 10 g of bentonite, stirred at a speed of 800 r / min for 20 min, then transferred to a high-speed agitator cup and stirred at a speed of 12000 r / min for 15 min, and left to stand and cure at room temperature for 24 h to obtain fresh water base slurry.

[0080] Test 1: Add the drilling fluid additives in the examples and comparative examples to the base mud to obtain the test fluid. The mass fraction of the drilling fluid additive in the configured test fluid is 1%, that is, there is one mass part of the drilling fluid additive in the test fluid. Stir at a speed of 2000 r / min for 2 h, and evaluate the normal temperature filtration loss performance of the water-based drilling fluid according to GB / T 16783.1-2014.

[0081] Test 2: Stir the test fluid in Test 1 at a speed of 2000 r / min for 2 h, and evaluate the high temperature and high pressure (150 °C) filtration loss performance of the water-based drilling fluid according to GB / T 16783.1-2014.

[0082] The specific test performance is shown in Table 1:

[0083] Table 1 Test performance of different examples and comparative examples

[0084]

[0085]

[0086] From the comparison of the above data, it can be known that in the present invention, adding a suitable PEG-b-PLA block copolymer can improve the anti-filtration loss performance, and adding free polyethylene glycol and / or polylactic acid additionally can further improve the anti-filtration loss performance.

[0087] It can be seen in Figure 1 that adding the poly(ethylene glycol)-block-poly(lactic acid) copolymer can reduce the filtration loss. At the same time, the addition of free polyethylene glycol or free polylactic acid has a similar effect in reducing the normal temperature filtration loss, but the addition of free polylactic acid shows a more beneficial effect in reducing the high temperature filtration loss. And adding free polyethylene glycol and free polylactic acid simultaneously can further improve the anti-filtration loss amount.

[0088] In addition, the addition amount of free polyethylene glycol should be kept within a certain numerical range. Too low or too high addition amount may cause an unexpected increase in the high temperature filtration loss. At the same time, the addition amount of free polylactic acid should also be kept within a certain numerical range. Too little amount of free polylactic acid may lead to an insignificant reduction in the high temperature filtration loss, and too much amount will cause an insignificant reduction in the normal temperature filtration loss.

[0089] Select the filter cake after the normal temperature filtration loss test of Example 14 for scanning electron microscopy analysis. It can be seen that the surface is almost completely dense, which is also the reason for the low filtration loss. The initial filtration loss part quickly forms a dense and complete filter cake, thus avoiding further filtration loss, which is also the reason for the low filtration loss.

Claims

1. A drilling fluid additive, characterized in that: The block copolymer comprises a polyethylene glycol having a total molecular weight of 4000-6000 Daltons. b -Polylactic acid.

2. The drilling fluid additive according to claim 1, characterized in that: The molecular weight ratio of the polyethylene glycol segment to the polylactic acid segment in the block copolymer is 2:1-3:

2.

3. The drilling fluid additive according to claim 2, characterized in that: Also included is polyethylene glycol, which has a molecular weight of 800-1200 Daltons.

4. The drilling fluid additive according to claim 3, characterized in that: The mass ratio of polyethylene glycol to block copolymer is 1:9-1:

10.

5. The drilling fluid additive according to any one of claims 1 to 4, characterized in that: Also included are hydrophobic polymers.

6. The drilling fluid additive according to claim 5, characterized in that: The hydrophobic polymer is polylactic acid, and the molecular weight of polylactic acid is 600-800 Daltons.

7. The drilling fluid additive according to claim 6, characterized in that: The mass ratio of polylactic acid to block copolymer is 1:18-1:

20.

8. A drilling fluid, characterized in that: The drilling fluid comprises the drilling fluid additive according to any one of claims 1 to 7.

9. The drilling fluid according to claim 8, wherein the drilling fluid is a water-based drilling fluid.

10. The drilling fluid according to any one of claims 8-9, wherein the mass content of the drilling fluid additive is less than or equal to 5%.

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