Anti-sloughing and anti-leakage drilling fluid for improving loading capacity of weak stratum and preparation method thereof

Abstract

The invention relates to an anti-sloughing and anti-leakage drilling fluid for improving the pressure-bearing capacity of weak stratums and a preparation method thereof, and the anti-sloughing and anti-leakage drilling fluid comprises the following components: 3%-5% of bentonite, 0.1%-0.3% of sodium carbonate, 0.2%-0.4% of caustic soda, 0.2%-0.4% of calcium oxide, 0.5%-1% of a vinyl monomer multipolymer MAN101 for drilling fluid, 0.5%-1% of a vinyl monomer multipolymer MAN104 for drilling fluid, 0.4%-0.6% of compound ammonium salt, 1%-3% of a filtrate reducer and the balance of water. The concrete is prepared from the following components in percentage by weight: 4 to 8 percent of anti-collapse inhibitor, 2 to 4 percent of superfine calcium carbonate, 1 to 3 percent of emulsified asphalt, 1 to 3 percent of plugging agent QCX, 0.4 to 0.6 percent of liquid lubricant and the balance of water. A compact filter cake can be formed, and the permeability of the filter cake is reduced to 10 <-6 > mD or even 10 <-7 > mD, so that the filter loss of the drilling fluid can be effectively reduced. According to the invention, the transmission of pressure can be retarded, and the pressure breakthrough time is prolonged to 200h, so that the collapse of the well wall can be prevented. And the pressure bearing capacity of the rock can be improved by more than 10 MPa.

Description

Technical Field

[0001] This invention belongs to the field of oilfield chemical additives technology, specifically relating to anti-collapse and anti-leakage drilling fluid for improving the pressure-bearing capacity of weak formations and its preparation method. Background Technology

[0002] Data from drilled exploration wells indicate that coal seams are well-developed in some areas, exhibiting high brittleness and low effective stress for breaking them. This makes them prone to wellbore instability and collapse, as well as complex well leakage issues. Improper operation or drill string collisions can also induce cracks in the coal seam or improve the connectivity of existing cracks, exacerbating well leakage problems.

[0003] Patent CN116004200A discloses an oil-based drilling fluid for improving the pressure-bearing capacity of formations, its preparation method, and its application. The drilling fluid comprises white oil, CaCl2 brine, organic clay, emulsifier, high-temperature and salt-resistant filtration loss reducer, alkalinity regulator, and inorganic micro / nano rigid particles. Based on 80 parts by weight of white oil, the CaCl2 brine comprises 20 parts by weight, the organic clay 4 parts by weight, the emulsifier 3-5 parts by weight, the high-temperature and salt-resistant filtration loss reducer 2-5 parts by weight, the alkalinity regulator 2-4 parts by weight, and the inorganic micro / nano rigid particles 3-9 parts by weight. However, this drilling fluid lacks inhibitors, has poor inhibitory performance, and is not suitable for improving the pressure-bearing capacity of weak formations such as coal seams.

[0004] Patent CN112143469A discloses a drilling fluid for improving the pressure-bearing capacity of formations, its preparation method, and its application. The drilling fluid comprises water, bentonite, low-viscosity anionic cellulose, lignite resin, a high-temperature and salt-resistant filtration loss reducer, a silanol inhibitor, inorganic micro / nano rigid particles, and emulsified asphalt. Based on 100 parts by weight of water, the bentonite comprises 2-9 parts by weight, the low-viscosity anionic cellulose 0.1-1 parts by weight, the lignite resin 1-5 parts by weight, the high-temperature and salt-resistant filtration loss reducer 0.1-2 parts by weight, the silanol inhibitor 0.1-2 parts by weight, the inorganic micro / nano rigid particles 0.5-5 parts by weight, and the emulsified asphalt 1-10 parts by weight. However, this drilling fluid lacks an inhibitor, has poor inhibitory performance, and is not suitable for improving the pressure-bearing capacity of weak formations such as coal seams.

[0005] Patent CN104046338A discloses a drilling fluid for preventing collapse and leakage, and its construction method. It is suitable for Mesozoic Triassic formations with low pressure resistance, repeated blockages, and difficult plugging. The drilling fluid consists of polyanionic cellulose, a drilling fluid salt-resistant filtration reducer, water-dispersible emulsified asphalt powder, ultrafine calcium carbonate, sodium formate, sodium hydroxide, potassium chloride, and water. However, the drilling fluid contains relatively few types of plugging agents and does not include plugging agents with a particle size exceeding 1 mm, making it unsuitable for formations with large fracture widths. Summary of the Invention

[0006] Based on the problems existing in the prior art, the objectives of this invention are: first, to provide a drilling fluid that improves the pressure-bearing capacity of weak formations; second, to provide a method for preparing the drilling fluid that improves the pressure-bearing capacity of weak formations; and third, to provide the application of the drilling fluid that improves the pressure-bearing capacity of weak formations.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A drilling fluid for preventing collapse and leakage in order to improve the pressure-bearing capacity of weak formations, comprising the following components by mass percentage:

[0009]

[0010]

[0011] As a further optimization of the present invention, the anti-collapse and anti-leakage drilling fluid also includes a weighting agent, the amount of which is determined according to the density of the drilling fluid.

[0012] As a further preferred embodiment of the present invention, the weighting agent includes one or more of iron ore powder, activated iron ore powder, manganese ore powder, calcium carbonate, barium carbonate, and galena powder.

[0013] As a further preferred embodiment of the present invention, the compounded ammonium salt is prepared by mixing hydrolyzed polyacrylonitrile ammonium salt NH4-HPAN and polyacrylamide PAM in a 1:1 ratio with drilling fluid.

[0014] In another preferred embodiment of the present invention, the filtration loss reducer is HY-2 for drilling fluid; the anti-collapse inhibitor is KCl; and the liquid lubricant is HLG.

[0015] As a further preferred embodiment of the present invention, the particle size of the ultrafine calcium carbonate is 0.075 to 0.15 mm.

[0016] The plugging agent QCX is calcium carbonate with a particle size of 0.5 to 1.5 mm.

[0017] As a preferred embodiment of the present invention, the anti-collapse and anti-leakage drilling fluid comprises the following components by mass percentage: 4% bentonite, 0.2% soda ash, 0.3% caustic soda, 0.3% calcium oxide, 0.5% drilling fluid vinyl monomer multi-component copolymer MAN101, 0.5% drilling fluid vinyl monomer multi-component copolymer MAN104, 0.5% compound ammonium salt, 1.5% drilling fluid filtration loss reducer HY-2, 5% anti-collapse inhibitor KCl, 3% ultrafine calcium carbonate, 2% emulsified asphalt, 1.5% plugging agent QCX, 0.5% liquid lubricant, and a certain amount of barite.

[0018] This invention further protects a method for preparing a drilling fluid that improves the pressure-bearing capacity of weak formations, comprising the following steps:

[0019] S1. Preparation of base slurry

[0020] Add 3%–5% bentonite, 0.1%–0.3% soda ash, 0.2%–0.4% caustic soda, and 0.2%–0.4% calcium oxide to a certain amount of water, stir evenly, and the base slurry is prepared.

[0021] S2. Preparation of anti-collapse and anti-leakage drilling fluid

[0022] The following materials are added to the base slurry by weight percentage: 0.5%–1% of drilling fluid vinyl monomer multi-component copolymer MAN101, 0.5%–1% of drilling fluid vinyl monomer multi-component copolymer MAN104, 0.4%–0.6% of compound ammonium salt, 1%–3% of drilling fluid filtration reducer, 4%–8% of anti-collapse inhibitor, 2%–4% of ultrafine calcium carbonate, 1%–3% of emulsified asphalt, 1%–3% of plugging agent QCX, 0.4%–0.6% of liquid lubricant, and a certain amount of barite. The mixture is stirred evenly to obtain an anti-collapse and anti-leakage drilling fluid that can improve the pressure-bearing capacity of weak formations.

[0023] This invention further protects the application of the aforementioned anti-collapse and anti-leakage drilling fluid, which enhances the pressure-bearing capacity of weak formations, in oil and gas extraction or drilling.

[0024] By adopting the above technical solution, the present invention has the following beneficial effects:

[0025] 1. This invention can form a dense filter cake, reducing the permeability of the filter cake to 10%. -6 mD even 10 -7 Therefore, it can effectively reduce the filtration loss of drilling fluid.

[0026] 2. This invention can slow down the transmission of pressure and extend the time for pressure breakthrough to 200 hours, thus preventing wellbore collapse.

[0027] 3. This invention can increase the pressure-bearing capacity of rocks by more than 10 MPa.

[0028] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described in detail below. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other design solutions and drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 A schematic diagram showing the experimental results of wellbore reinforcement using asphalt-based plugging agents;

[0031] Figure 2 A schematic diagram of the wellbore reinforcement experiment results using rigid particulate plugging agent;

[0032] Figure 3 A schematic diagram showing the experimental results of wellbore strengthening with emulsified paraffin and polyethylene glycol;

[0033] Figure 4 Schematic diagram of wellbore strengthening experiment results for compound plugging agent;

[0034] Figure 5 This is a schematic diagram illustrating the effect of drilling fluid on rock wettability.

[0035] Figure 5 In the middle section, a is a dry rock sample; b is a rock sample after displacement by the base slurry; and c is a rock sample after displacement by drilling fluid with added emulsified bitumen.

[0036] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described in detail below. Detailed Implementation

[0037] The invention can be further understood in conjunction with the following detailed description of preferred embodiments and included examples. Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. If any definition of a specific term disclosed in the prior art differs from any definition provided herein, the definition provided herein shall prevail.

[0038] It should be noted that the implementation conditions used in the examples can be further adjusted according to the specific experimental environment, and the implementation conditions not specified are usually those in conventional experiments. Unless otherwise specified, the preparation methods mentioned in this invention are all conventional methods; unless otherwise specified, all chemical reagents and chemicals mentioned in the following examples are commercially available.

[0039] In a typical embodiment of this application, a drilling fluid for preventing collapse and leakage, which improves the pressure-bearing capacity of weak formations, is provided, comprising the following components by mass percentage:

[0040]

[0041]

[0042] As a further improvement to the above-mentioned technical solution of the present invention, the anti-collapse and anti-leakage drilling fluid also includes a weighting agent, the amount of which is determined according to the density of the drilling fluid.

[0043] As a further optimization of the present invention, the weighting agent includes one or more of iron ore powder, activated iron ore powder, manganese ore powder, calcium carbonate, barium carbonate, and galena powder.

[0044] As a further optimization of the present invention, the compound ammonium salt is prepared by mixing hydrolyzed polyacrylonitrile ammonium salt NH4-HPAN and polyacrylamide PAM in a 1:1 ratio with drilling fluid. The filtration loss reducer is drilling fluid filtration loss reducer HY-2; the anti-collapse inhibitor is KCl; and the liquid lubricant is liquid lubricant HLG. The plugging agent QCX is calcium carbonate with a particle size of 0.5-1.5 mm.

[0045] Based on the above embodiments, the present invention makes the following improvements: the particle size of the ultrafine calcium carbonate is preferably 0.075 to 0.15 mm.

[0046] As a preferred embodiment of the present invention, the anti-collapse and anti-leakage drilling fluid comprises the following components by mass percentage: 4% bentonite, 0.2% soda ash, 0.3% caustic soda, 0.3% calcium oxide, 0.5% drilling fluid vinyl monomer multi-component copolymer MAN101, 0.5% drilling fluid vinyl monomer multi-component copolymer MAN104, 0.5% compound ammonium salt, 1.5% drilling fluid filtration loss reducer HY-2, 5% anti-collapse inhibitor KCl, 3% ultrafine calcium carbonate, 2% emulsified asphalt, 1.5% plugging agent QCX, 0.5% liquid lubricant, and a certain amount of barite.

[0047] This invention further provides a method for preparing a drilling fluid that improves the pressure-bearing capacity of weak formations, comprising the following steps:

[0048] S1. Preparation of base slurry

[0049] Add 3%–5% bentonite, 0.1%–0.3% soda ash, 0.2%–0.4% caustic soda, and 0.2%–0.4% calcium oxide to a certain amount of water, stir evenly, and the base slurry is prepared.

[0050] S2. Preparation of anti-collapse and anti-leakage drilling fluid

[0051] The following materials are added to the base slurry by weight percentage: 0.5%–1% of drilling fluid vinyl monomer multi-component copolymer MAN101, 0.5%–1% of drilling fluid vinyl monomer multi-component copolymer MAN104, 0.4%–0.6% of compound ammonium salt, 1%–3% of drilling fluid filtration reducer, 4%–8% of anti-collapse inhibitor, 2%–4% of ultrafine calcium carbonate, 1%–3% of emulsified asphalt, 1%–3% of plugging agent QCX, 0.4%–0.6% of liquid lubricant, and a certain amount of barite. The mixture is stirred evenly to obtain an anti-collapse and anti-leakage drilling fluid that can improve the pressure-bearing capacity of weak formations.

[0052] This invention further protects the application of the aforementioned anti-collapse and anti-leakage drilling fluid, which enhances the pressure-bearing capacity of weak formations, in oil and gas extraction or drilling.

[0053] The present invention will be further described below with reference to embodiments:

[0054] First, the effects of different types of plugging agents on improving the formation's bearing capacity were examined:

[0055] (1) Asphalt-based sealing agents

[0056] Asphalt-based plugging agents are easily displaced into formation microfractures under differential pressure, forming a plugging zone. Due to the hydrophobic properties of asphalt, it reduces the intrusion of water phase from drilling fluid into the formation rock, thus maintaining wellbore stability. Sulfonated asphalt, oxidized asphalt, and emulsified asphalt were added to the base slurry at concentrations of 3% for drilling fluid-enhanced wellbore experiments. The changes in core pore pressure over time are shown below. Figure 1As shown, with pressurization reaching approximately 600 s, the core pressure begins to increase. Initially, the pressure rises slowly, then increases linearly and rapidly. Once the pressure reaches the core fracturing pressure, the core is fractured, and the pore pressure decreases sharply. The core corresponding to the base slurry was fractured at 924 s, while the core with added bitumen required a longer fracturing time. The fracturing times for drilling fluids containing oxidized bitumen, sulfonated bitumen, and emulsified bitumen were 1029 s, 1282 s, and 1150 s, respectively, demonstrating the ability of bitumen to delay formation rock fracturing. The rock fracturing pressure corresponding to the base slurry was 12.98 MPa, while the rock fracturing pressures for drilling fluids containing oxidized bitumen, sulfonated bitumen, and emulsified bitumen were 13.6 MPa, 14.23 MPa, and 15.51 MPa, respectively. These correspond to increases in formation bearing capacity of 0.62 MPa, 1.25 MPa, and 2.53 MPa, respectively, showing a significant effect in improving formation bearing capacity. Based on the increase in formation bearing capacity, it can be concluded that emulsified asphalt has the best wellbore strengthening effect among asphalt-based plugging agents.

[0057] (2) Rigid particulate plugging agent

[0058] Rigid particulate plugging materials are squeezed into the pores of the wellbore rock under the pressure difference between the drilling fluid column pressure and the formation pore pressure, forming a plugging layer with a certain strength. This slows down the intrusion of the drilling fluid liquid phase and improves the wellbore's pressure-bearing capacity. Three concentrations of ultrafine silica, ultrafine calcium carbonate, nano silica, and nano calcium carbonate were added to the base slurry, respectively. Drilling fluid wellbore strengthening experiments were then conducted, and the results are as follows... Figure 2 As shown in the figure, the wellbore pressure curve of drilling fluid with added rigid granular materials exhibits a similar trend to that of the base slurry before fracturing, i.e., it first increases slowly and then increases linearly until the rock is fractured, at which point the corresponding pressure curve shows a sharp decrease. Specifically, the rock fracturing pressures of drilling fluids with added ultrafine silica, ultrafine calcium carbonate, nano silica, and nano calcium carbonate are 18.79 MPa, 19.76 MPa, 16.25 MPa, and 15.43 MPa, respectively. Compared with the base slurry, they increase the formation bearing capacity by 5.81 MPa, 6.78 MPa, 3.27 MPa, and 2.45 MPa, respectively, with ultrafine calcium carbonate showing the best effect in improving rock bearing capacity. Unlike the base slurry, the wellbore pressure of drilling fluid with added rigid granular materials shows a sawtooth pattern after core fracturing, indicating that the corresponding core still has a certain bearing capacity. This is because after fracturing, the rigid granular materials enter the sealing layer formed by the fracture and have bearing capacity.

[0059] (3) Other sealing agents

[0060] Adding emulsified paraffin to drilling fluid can improve filter cake quality, forming a low-permeability barrier zone on the wellbore rock, preventing the drilling fluid from penetrating deep into the formation, thereby improving the formation's pressure-bearing capacity. The anti-collapse mechanism of polyols is that they disperse in water when the temperature is below their cloud point. When the temperature is above the cloud point of the polyol, phase separation occurs, preventing the drilling fluid liquid phase from invading the formation, thus stabilizing the wellbore. The wellbore strengthening effect was evaluated by adding 3% emulsified paraffin and polyethylene glycol to the base slurry, and the results are as follows: Figure 3 As shown in the figure, the wellbore pressure curves of drilling fluids with added emulsified paraffin and polyethylene glycol are similar to those of the base mud, decreasing sharply after reaching the fracturing pressure, and exhibiting lower pressure-bearing capacity after rock fracturing. Specifically, the rock fracturing pressure of drilling fluids with added emulsified paraffin is 14.44 MPa, while that of drilling fluids with added polyethylene glycol is 13.86 MPa. The corresponding increases in formation pressure-bearing capacity are 1.46 MPa and 0.88 MPa, respectively. Compared to the latter, emulsified paraffin is more effective in improving formation pressure-bearing capacity.

[0061] (4) Experiment on strengthening of intact core wellbore with compound plugging agent

[0062] Binary compound formulations were selected from asphalt-based plugging agents, rigid particle plugging agents, and other plugging agents with good wellbore strengthening effects. 3% ultrafine calcium carbonate + 3% emulsified asphalt, 3% emulsified asphalt + 3% emulsified paraffin, and 3% ultrafine calcium carbonate + 3% emulsified paraffin were added to the base slurry, respectively. The effects on improving formation bearing capacity were investigated, and the results are as follows: Figure 4 As shown in the figure, compared with single-agent drilling fluids, the wellbore strengthening effect of compound plugging agents is significantly improved. The drilling fluid containing ultrafine calcium carbonate and emulsified asphalt corresponds to a rock fracturing pressure of 23.71 MPa, which is 10.73 MPa higher than that of the base slurry, demonstrating a good effect on improving the formation's bearing capacity. The drilling fluid containing ultrafine calcium carbonate and emulsified paraffin corresponds to a rock fracturing pressure of 20.76 MPa, which is 7.78 MPa higher than that of the base slurry. The drilling fluid containing emulsified asphalt and emulsified paraffin shows a lower improvement in rock bearing capacity, with a corresponding rock fracturing pressure of 17.33 MPa.

[0063] To further investigate the mechanism by which drilling fluid containing ultrafine calcium carbonate and emulsified asphalt enhances formation bearing capacity, the contact angles of dry core samples and the rock after displacement by the drilling fluid and base slurry were tested. The results are as follows: Figure 5As shown, the contact angle of the dry rock sample was 14.25°. After displacement with the base fluid, its hydrophilicity slightly increased, and the contact angle decreased to 12.58°. After displacement with drilling fluid containing emulsified bitumen, the contact angle of the rock increased to 24.35°, and its hydrophobicity was enhanced. This indicates that emulsified bitumen can change the wettability of the rock, enhance its hydrophobicity, slow down the intrusion of the drilling fluid water phase, reduce drilling fluid loss, and improve the formation's bearing capacity.

[0064] Based on the results of the plugging agent selection, optimization experiments were carried out to minimize the amount of treatment agent added, while ensuring the rheological properties, filtration and wall-building properties, and plugging properties of the drilling fluid. The drilling fluid formulation optimization experiments are shown in Table 1.

[0065] Table 1 Drilling fluid formulation optimization experiment

[0066]

[0067]

[0068]

[0069] Table 8-14 above are comparative examples.

[0070] The base slurry in the table above is prepared from 3%–5% bentonite, 0.1%–0.3% soda ash, 0.2%–0.4% caustic soda, 0.2%–0.4% calcium oxide, and a certain amount of water. The preparation steps of the base slurry are common knowledge and will not be repeated here.

[0071] The table above lists the manufacturers and product models of the polymer filtration loss reducer Redu1. For example, the polymer filtration loss reducer Redu1 may be purchased from Tianjin Xiong Guan Technology Development Co., Ltd., and the model is Redu1.

[0072] From the table above and appendix Figure 1-5 The specific components of the drilling fluid with good filtration, wall-building, and anti-collapse / sealing properties are as follows: 3%–5% bentonite + 0.1%–0.3% soda ash + 0.2%–0.4% caustic soda + 0.2%–0.4% calcium oxide + 0.5%–1% MAN101 (a vinyl monomer multi-component copolymer for drilling fluid) + 0.5%–1% MAN104 (a vinyl monomer multi-component copolymer for drilling fluid) + 0.4%–0.6% compound ammonium salt + 1%–3% filtration reducer + 4%–8% anti-collapse inhibitor + 2%–4% ultrafine calcium carbonate + 1%–3% emulsified asphalt + 1%–3% QCX (a plugging agent) + 0.4%–0.6% liquid lubricant + barite (the amount of barite is determined according to the density of the drilling fluid).

[0073] As shown in Table 1, the present invention can form a dense filter cake and reduce the permeability of the filter cake to 10%. -6 mD even 10 -7 Therefore, this invention can effectively reduce the filtration loss of drilling fluid.

[0074] This invention can slow down the transmission of pressure and extend the time for pressure breakthrough to 200 hours, thus preventing wellbore collapse.

[0075] Depend on Figure 1 It can be seen that the rock fracturing pressure corresponding to the base grout is 12.98 MPa, from Figure 4 It is known that the drilling fluid containing ultrafine calcium carbonate and emulsified asphalt has a fracture pressure of 23.71 MPa, which is 10.73 MPa higher than that of the original fluid. Therefore, this invention can increase the pressure-bearing capacity of rocks by more than 10 MPa.

[0076] After research, a preferred composition for a drilling fluid designed to improve the pressure-bearing capacity of weak formations and prevent collapse and leakage was finally formed, based on the following formula: 4% bentonite + 0.2% soda ash + 0.3% caustic soda + 0.3% calcium oxide (CaO) + 0.5% drilling fluid vinyl monomer multi-component copolymer MAN101 + 0.5% drilling fluid vinyl monomer multi-component copolymer MAN104 + 0.5% compound ammonium salt + 1.5% drilling fluid filtration loss reducer HY-2 + 5% KCl + 3% ultrafine calcium carbonate + 2% emulsified asphalt + 1.5% plugging agent QCX + 0.5% liquid lubricant + barite. The functions of drilling fluid vinyl monomer multi-component copolymer MAN101 and drilling fluid filtration loss reducer HY-2 are to reduce drilling fluid filtration loss, while KCl enhances the drilling fluid's inhibition performance. Ultrafine calcium carbonate and emulsified asphalt serve two main functions: first, they form a dense filter cake, reducing drilling fluid filtrate seepage and simultaneously slowing pressure transmission to the formation near the wellbore, thus preventing wellbore collapse; second, they effectively seal micro-fractures, improving formation pressure-bearing capacity and preventing further fracture expansion that could induce well leakage, thereby preventing leakage. The plugging agent QCX also exhibits some leakage prevention effect.

[0077] The above description is merely a preferred embodiment of the present invention and is illustrative in nature, not intended to limit the scope of the invention. Various modifications and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit of the invention should fall within the protection scope defined by the claims.

Claims

1. A drilling fluid for preventing collapse and leakage in order to improve the pressure-bearing capacity of weak formations, characterized in that, By mass percentage, it includes the following components: The remainder is water.

2. The anti-collapse and anti-leakage drilling fluid for improving the pressure-bearing capacity of weak formations as described in claim 1, characterized in that: The anti-collapse and anti-leakage drilling fluid also includes a weighting agent, the amount of which is determined according to the density of the drilling fluid.

3. The anti-collapse and anti-leakage drilling fluid for improving the pressure-bearing capacity of weak formations as described in claim 2, characterized in that: The weighting agent includes one or more of the following: iron ore powder, activated iron ore powder, manganese ore powder, calcium carbonate, barium carbonate, and galena powder.

4. The anti-collapse and anti-leakage drilling fluid for improving the pressure-bearing capacity of weak formations as described in claim 1, characterized in that: The compound ammonium salt is prepared by mixing hydrolyzed polyacrylonitrile ammonium salt NH4-HPAN and polyacrylamide PAM in a 1:1 ratio with drilling fluid.

5. The anti-collapse and anti-leakage drilling fluid for improving the pressure-bearing capacity of weak formations as described in claim 1 or 2, characterized in that: The fluid loss reducer is drilling fluid fluid reducer HY-2; The anti-collapse inhibitor is KCl; The liquid lubricant is HLG.

6. The anti-collapse and anti-leakage drilling fluid for improving the pressure-bearing capacity of weak formations as described in claim 1, characterized in that: The particle size of the ultrafine calcium carbonate is 0.075–0.15 mm.

7. The anti-collapse and anti-leakage drilling fluid for improving the pressure-bearing capacity of weak formations as described in claim 1, characterized in that: The plugging agent QCX is calcium carbonate with a particle size of 0.5 to 1.5 mm.

8. The anti-collapse and anti-leakage drilling fluid for improving the pressure-bearing capacity of weak formations as described in claim 5, characterized in that, The anti-collapse and anti-leakage drilling fluid comprises the following components by mass percentage: 4% bentonite, 0.2% soda ash, 0.3% caustic soda, 0.3% calcium oxide, 0.5% drilling fluid vinyl monomer multi-component copolymer MAN101, 0.5% drilling fluid vinyl monomer multi-component copolymer MAN104, 0.5% compound ammonium salt, 1.5% drilling fluid filtration loss reducer HY-2, 5% anti-collapse inhibitor KCl, 3% ultrafine calcium carbonate, 2% emulsified asphalt, 1.5% plugging agent QCX, 0.5% liquid lubricant, and a certain amount of barite.

9. A method for preparing a drilling fluid for preventing collapse and leakage in order to improve the pressure-bearing capacity of weak formations, characterized in that, Includes the following steps: S1. Preparation of base slurry Add 3%–5% bentonite, 0.1%–0.3% soda ash, 0.2%–0.4% caustic soda, and 0.2%–0.4% calcium oxide to a certain amount of water, stir evenly, and the base slurry is prepared. S2. Preparation of anti-collapse and anti-leakage drilling fluid The following materials are added to the base slurry by weight percentage: 0.5%–1% of drilling fluid vinyl monomer multi-component copolymer MAN101, 0.5%–1% of drilling fluid vinyl monomer multi-component copolymer MAN104, 0.4%–0.6% of compound ammonium salt, 1%–3% of drilling fluid filtration reducer, 4%–8% of anti-collapse inhibitor, 2%–4% of ultrafine calcium carbonate, 1%–3% of emulsified asphalt, 1%–3% of plugging agent QCX, 0.4%–0.6% of liquid lubricant, and a certain amount of barite. The mixture is stirred evenly to obtain an anti-collapse and anti-leakage drilling fluid that can improve the pressure-bearing capacity of weak formations.

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