Oil-based drilling fluid plugging agent and its preparation method

Abstract

This invention relates to an oil-based drilling fluid plugging agent and its preparation method, comprising granular materials made of the following components by weight percentage: asphalt powder: 15-28 wt%; organic clay: 6-16 wt%; rock fiber: 25-40 wt%; nano-SiO2: 5-12 wt%; sepiolite: 8-15 wt%; elastic graphite: 8-18 wt%; and polyurethane (TPU) powder particles: 10-20 wt%. This invention features good compatibility, high efficiency, and excellent plugging effect. It can repair formation defects in the wellbore, prevent wellbore leakage, enhance the retention and plugging effect of oil-based drilling fluid in formation microfractures, improve wellbore stability, and effectively plug and strengthen the wellbore.

Description

Technical Field

[0001] This invention relates to the field of wellbore plugging technology in oil well operations, specifically to an oil-based drilling fluid plugging agent and its preparation method. Background Technology

[0002] Oil-based drilling fluids have strong inhibitory effects on shale and excellent lubrication properties, so they are widely used in the horizontal section of shale formation wells. However, the horizontal section of shale has well-developed bedding and microfractures, making it prone to well leakage and wellbore collapse. The loss of oil-based drilling fluid leads to increased production costs and long recovery time after well collapse, which seriously affects the exploration and development of shale oil and gas wells.

[0003] Oil well plugging agents are typically liquid or powdered. For example, CN116948609A discloses the preparation of a nano-plugging agent and an oil-based drilling fluid. This plugging agent is formed by the reaction of emulsified asphalt, microfibers, ammonium acrylate, and modified nano-silica. While micro / nano liquid plugging agents are used to seal micro-fractured formations, their compatibility with oil-based drilling fluids is poor after addition due to factors such as unreasonable particle size structure and a lack of elastic plugging materials, resulting in ineffective and unstable sealing of the wellbore.

[0004] For example, CN118389130A discloses a shale oil-based drilling fluid filtration reduction and plugging agent and its preparation method. The shale oil-based drilling fluid filtration reduction and plugging agent comprises the following components by weight: 15-25 parts asphalt powder, 10-20 parts modified rubber powder, 10-20 parts organic lignite, 5-10 parts emulsifier, 10-20 parts oil-absorbing resin, 10-20 parts sepiolite, 10-15 parts polyamide wax, 10-20 parts solvent oil, and 10-30 parts water. This shale oil-based drilling fluid filtration reduction and plugging agent has good filtration reduction and shale plugging effects. Through skeleton plugging, flexible filling, and expansion elastic release, it quickly forms a tight sealing layer in sandstone, shale, and microfractured pores. On the one hand, the plugging agent is a powder, which makes it difficult to achieve uniform distribution in formation microfractures. This results in large particles blocking the fractures while small particles leak out with the drilling fluid, creating a problem of "not being able to get in and not being able to stay in." On the other hand, the composition uses modified rubber powder and sepiolite as a skeleton, which are prone to deformation under heat and pressure, and the plugging effect needs to be further improved. Summary of the Invention

[0005] The purpose of this invention is to solve the above-mentioned technical problems and provide an oil-based drilling fluid plugging agent that has good compatibility, high efficiency, good sealing effect, can repair wellbore formation defects, prevent wellbore leakage, enhance the retention and sealing effect of oil-based drilling fluid in formation microfractures, improve wellbore stability, and effectively play the role of sealing and strengthening the wellbore.

[0006] The present invention also provides a method for preparing the above-mentioned oil-based drilling fluid plugging agent with extremely simple process and low cost.

[0007] The oil-based drilling fluid plugging agent of the present invention is characterized in that it comprises granular material made of the following components in mass percentage:

[0008] Asphalt powder: 15-28 wt%;

[0009] Organic clay: 6–16 wt%;

[0010] Rock fiber: 25–40 wt%;

[0011] Nano SiO2: 5–12 wt%;

[0012] Sepiolite: 8-15 wt%;

[0013] Elastic graphite: 8–18 wt%;

[0014] Polyurethane (TPU) powder particles: 10-20 wt%.

[0015] The particle size of the granular material is 0.5 to 3 mm.

[0016] The rock fibers have a diameter of 500–800 nm and a length of 100–200 μm.

[0017] The nano-SiO2 particles have a diameter of 300–800 nm;

[0018] The sepiolite is sepiolite fiber with a diameter of 15-30 μm and a length of 1-2 mm.

[0019] The elastic graphite particles have a particle size of 5–40 μm.

[0020] The polyurethane (TPU) powder has a particle size of 300–500 μm.

[0021] The rock fiber is made from basalt and granite as raw materials, which are crushed, melted at high temperature, alloyed and drawn into wires, and then cut.

[0022] The preparation method of the rock fiber is as follows: basalt and granite are mixed and crushed into fine particles of 40-80 mesh in a mechanical pulverizer at a mass ratio of 7:3. Then, the particles are put into a basalt furnace and melted and mixed evenly at a temperature of 1600℃. The fibers are then drawn at high speed through an alloy wire drawing stencil to form fibers. The fibers are then surface-impregnated with polyether-modified organosilicon SF309, dried, and then processed by a cutting machine to obtain the final product.

[0023] The preparation method of the above-mentioned oil-based drilling fluid plugging agent is characterized by comprising the following steps:

[0024] S1. Add asphalt powder into the reactor and maintain the stirring speed of the reactor at 100 r / min. Then, heat the reactor to 120°C and add organic clay, sepiolite, and polyurethane (TPU) in sequence, and stir for 1 hour.

[0025] S2, rock fiber, elastic graphite and nano SiO2 are added sequentially to S1, and stirred for 3 hours;

[0026] S3 is made by extruding S2 through a twin-screw extruder to granulate it, then crushing and sieving it to produce granular material.

[0027] The granular material has a particle size of 0.5–3 mm;

[0028] To address the problems existing in the background technology, the inventors made the following improvements:

[0029] 1) Specially added rock fibers, made from mineral rocks, have high compatibility with the formation in terms of physical properties. As a rigid bridging material, these particles can stably bridge at the throats and narrow fractures of leakage channels, and are not easily deformed by heat and pressure, which helps to form a sealing layer skeleton. On the other hand, due to their nanometer-scale diameter (500-800nm) and micrometer-scale length, they are particularly suitable for micrometer-scale pores and fractures. Furthermore, rock fibers have low agglomeration and can be stably and uniformly dispersed in the oil phase environment. They have good compatibility with oil-based drilling fluids and can also form a stable fit with formation fractures. Compared with other fiber materials, they have a better sealing effect on micropores and microfractures. Here, considering that the length of rigid material particles has a direct impact on the bridging effect, the preferred length of rock fibers should be 100-200μm. Rock fibers of this length can better build a bridging network in the fracture, achieving the purpose of step-by-step filling and sealing within the fracture. If the length is too long, it will bridge at the fracture entrance, and if it is too short, it will not be able to form a network structure.

[0030] Furthermore, the inventors preferentially use basalt and granite as raw materials for rock fibers. Basalt possesses properties such as compressive and flexural strength, heat absorption and storage, and wear resistance, while granite enhances wear resistance and corrosion resistance. The resulting rock fibers exhibit good toughness and strength, significantly improving formation pressure resistance and meeting the requirements of high-temperature, high-pressure, and strongly alkaline downhole environments. Considering the requirements of the drawing process and the physical strength properties of the rock fibers, the mass ratio of basalt to granite is 7:3. Excessive basalt content reduces fiber strength, while insufficient content increases the difficulty of fiber preparation. In the preparation step, polyether-modified organosilicon SF309 is used to surface-wet the drawn fibers, which improves the fiber's dispersion in drilling fluid and further enhances compatibility.

[0031] 2) Elastic graphite and polyurethane (TPU) powder are used as elastic filler materials. On one hand, this utilizes materials with different particle sizes (elastic graphite particles with a diameter of 5–40 μm, and TPU powder particles with a diameter of 300–500 μm) to achieve graded filling. On the other hand, elastic graphite possesses unique flexibility and resilience, while TPU powder has good hardness. The combination of the two complements each other, balancing the needs for elasticity and hardness. It can penetrate into fissures under a certain degree of external force and then restore its original shape, exhibiting good hardness and low stiffness, allowing it to withstand significant deformation without cracking. This allows it to fill fissures and pores in the lost circulation formation according to their morphology. Meanwhile, asphalt, in addition to its carrier function, also has good elastic deformation and good retention in the oil phase environment, playing a repairing role on the wellbore. Its preferred addition amount is 15–28 wt%. Too much will lead to uneven distribution of the plugging material, while too little will fail to act as a carrier, reducing the sealing effect.

[0032] 3) Adding sepiolite fiber utilizes its excellent adsorption and sealing properties to effectively improve the formation's pressure-bearing capacity after sealing. Further control the sepiolite fiber diameter to 15-30μm and length to 1-2mm. Sepiolite fibers of this size have good flowability and sealing performance. Control the addition amount to 8-15wt%. Too much will affect the rheological properties of the drilling fluid, while too little will reduce the sealing effect on fractures. Adding organic clay can improve the compatibility with oil-based drilling fluids.

[0033] 4) Conventional powder or liquid-based plugging materials, when introduced into fractures by drilling fluid, exhibit poor sealing performance because nano- and micron-sized particles enter and are quickly lost, while millimeter-sized particles cannot penetrate, failing to form bridging and gradual filling within the fracture. This invention, however, uses asphalt particles as a carrier to create 0.5–3 mm granular plugging materials. Based on the different properties of the raw materials, these particles are graded in nano, micro, and millimeter sizes. Employing a "plugging capsule" mechanism, the plugging capsules are transported to the fracture opening or portal. Under the influence of high formation temperature and wellbore pressure, the asphalt releases rigid and elastic plugging materials of varying particle sizes, rapidly aggregating to form a bridge. Subsequent nano- and micron-sized materials gradually fill this bridge, significantly improving the stability and sealing effect of the plugging layer, and effectively increasing the bridging rate and success rate.

[0034] The plugging agent of this invention has good compatibility, high plugging efficiency and good effect. It can repair formation defects in the wellbore, prevent wellbore leakage, enhance the retention and plugging effect of oil-based drilling fluid in formation microfractures, improve wellbore stability, and effectively play the role of plugging and strengthening the wellbore. Detailed Implementation

[0035] Example of rock fiber preparation:

[0036] Basalt and granite are mixed and pulverized into 40-80 mesh fine particles in a mechanical pulverizer at a mass ratio of 7:3. The particles are then fed into a basalt furnace and melted and mixed evenly at 1600℃. The mixture is then drawn into fibers at high speed through an alloy wire drawing stencil. The fibers are then surface-impregnated with polyether-modified organosilicon SF309 for 10 minutes, dried at 200℃ for 30 minutes, and finally processed by a cutting machine to obtain rock fibers with a diameter of 500-800 nm and a length of 100-200 μm.

[0037] Ingredients list:

[0038]

[0039] Example of sealing agent preparation process:

[0040] S1. Add asphalt powder into the reactor and maintain the stirring speed of the reactor at 100 r / min. Then, heat the reactor to 120℃ and add organic clay, sepiolite fiber (diameter 15-30 μm, length 1-2 mm), and polyurethane (TPU) powder particles (particle size 300-500 μm) in sequence. Stir for 1 hour.

[0041] S2, rock fiber, elastic graphite (particle size 5-40 μm), and nano-SiO2 (particle size 300-800 nm) are added sequentially to S1, and stirred for 3 hours;

[0042] S3 is made by extruding and granulating S2 through a twin-screw extruder, then crushing and sieving to produce granular material with a particle size of 0.5 to 3 mm.

[0043] Comparative Example 1:

[0044] In Example 1, the only difference is that polyurethane powder particles are not added and the amount of elastic graphite added is increased to 22 wt%.

[0045] Comparative Example 2:

[0046] In Example 1, the rock fiber was replaced with modified plant fiber, but otherwise the same as in Example 1.

[0047] Comparative Example 3:

[0048] Except for replacing the asphalt powder with modified paraffin, all components are physically mixed to obtain a powdered material, and the rest is the same as in the example.

[0049] Performance Indicators and Comparative Experiments

[0050] The base slurry of the oil-based drilling fluid is: 0# diesel oil + 3.0~5.0wt% emulsifier + 2.0wt% wetting agent + 1.5wt% emulsifying viscosity improver and shearing agent + 25wt% brine + 3.0wt% organic clay + 2.0wt% CaO + 6wt% filtration loss reducer, with a density of 1.10g / cm3 and an oil-water ratio of 80:20.

[0051] 1) Compatibility performance test

[0052] Take 1000 mL of base slurry, add 5% of the sealing agent sample, stir with a high-speed mixer at 11000 r / min for 5 min, hot roll at 180℃ for 16 hours, cool to room temperature, and stir at 4000 r / min for 6 min. Measure the performance of the base slurry and the comparative example after adding the sample. The test conditions for the base slurry and the example after adding the sample should be completely consistent.

[0053]

[0054] As shown in Table 1, the rheological properties and electrical stability of the oil-based drilling fluid did not change significantly after incorporating the plugging agent of this invention. However, the fluid loss under medium pressure and high temperature and high pressure was significantly reduced. This indicates that the plugging agents in Examples 1-5 of this invention have good compatibility with the drilling fluid and exhibit good plugging effects. The compatibility and plugging effects of Comparative Examples 1 and 3 also meet the requirements. The dynamic-plastic ratio of Comparative Example 2 increased significantly, mainly because the modified plant fiber increased the viscosity of the oil-based drilling fluid, affecting its rheological properties.

[0055] 2) Blocking strength test

[0056] Add 10wt% of the sealing agent sample to the base slurry, take 4000mL and stir at 300r / min for 5min. Use a QD-1 type sealing tester to simulate leakage and pressure test under crack width of 0.5-9mm and nitrogen pressure of 12MPa, and record parameters such as leakage amount and pressure strength for 30min.

[0057]

[0058] As shown in Table 2, the addition of the plugging agent of this invention allows the oil-based drilling fluid to effectively seal cracks ranging from 0.5 to 9 mm, achieving a plugging effect. Comparative Example 1, lacking high-strength elastic particle support, suffers from reduced pressure resistance, resulting in significant filtration loss. Comparative Example 2 exhibits poor plugging performance under high pressure due to insufficient strength of the bridging particles. Comparative Example 3 suffers from poor overall retention of the plugging material, leading to unsatisfactory plugging results.

Claims

1. An oil-based drilling fluid plugging agent, characterized in that, Granular materials comprising the following components by weight percentage: Asphalt powder: 15-28 wt%; Organic clay: 6–16 wt%; Rock fiber: 25–40 wt%; Nano SiO2: 5–12 wt%; Sepiolite: 8-15 wt%; Elastic graphite: 8–18 wt%; Polyurethane (TPU) powder particles: 10-20 wt%; The rock fibers have a diameter of 500–800 nm and a length of 100–200 μm; the nano-SiO2 particles have a diameter of 300–800 nm; the sepiolite is sepiolite fiber with a diameter of 15–30 μm and a length of 1–2 mm; the elastic graphite particles have a diameter of 5–40 μm; the polyurethane (TPU) powder particles have a diameter of 300–500 μm; and the granular material has a particle size of 0.5–3 mm. The rock fiber is made by crushing, high-temperature melting, alloy drawing, and cutting basalt and granite in a mass ratio of 7:

3.

2. The oil-based drilling fluid plugging agent as described in claim 1, characterized in that, The preparation method of the rock fiber is as follows: basalt and granite are mixed and crushed into fine particles of 40-80 mesh in a mechanical pulverizer at a mass ratio of 7:

3. Then, the particles are put into a basalt furnace and melted and mixed evenly at a temperature of 1600℃. The fibers are then drawn at high speed through an alloy wire drawing stencil to form fibers. The fibers are then surface-impregnated with polyether-modified organosilicon SF309, dried, and then processed by a cutting machine to obtain the final product.

3. A method for preparing the oil-based drilling fluid plugging agent according to claim 1 or 2, characterized in that, Includes the following steps: S1. Add asphalt powder into the reactor and maintain the stirring speed of the reactor at 100 r / min. Then, heat the reactor to 120°C and add organic clay, sepiolite, and polyurethane (TPU) in sequence, and stir for 1 hour. S2, rock fiber, elastic graphite and nano SiO2 are added sequentially to S1, and stirred for 3 hours; S2 is extruded and granulated using a twin-screw extruder, then crushed and sieved to produce granular material.

4. The preparation method of the oil-based drilling fluid plugging agent as described in claim 3, characterized in that, The particle size of the granular material is 0.5–3 mm.

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