Pressure-bearing plugging material, drilling fluid and application for malignant leakage in fractured formations

Abstract

The present invention particularly relates to a pressure-bearing plugging material, drilling fluid, and application for treating malignant leakage in fractured formations. The plugging material comprises: 20-25 parts by weight of a plugging agent, 2-6 parts by weight of a filling binder, 1-2 parts by weight of an active agent, and 1-2 parts by weight of a dispersant; the plugging agent is selected from at least one of diatomaceous earth, ultrafine calcium carbonate, mica flakes, walnut shell powder, bamboo fiber, and composite mineral fiber SQD-98; the filling binder is selected from at least one of white asphalt, asbestos fiber, and sodium silicate; the active agent is selected from at least one of heavy calcium carbonate and silica fume; and the dispersant is selected from at least one of humates, polycarboxylates, and polyanionic cellulose. The plugging material has a high degree of compatibility with the crack size, is easy to enter the leaking layer, has a long retention time, is compatible with the drilling fluid, and is resistant to shear dilution. The formed plugging layer has a dense structure, strong pressure and high temperature bearing capabilities, and is easy to be acidified and unplugged in the later stage, with minimal damage to the reservoir.

Description

Technical Field

[0001] The invention belongs to the technical field of oilfield chemicals, and in particular relates to a pressure-bearing plugging material for treating malignant leakage in fractured formations, a drilling fluid and applications thereof. Background Art

[0002] During drilling in fractured formations, drilling fluid leakage occurs frequently, in large amounts, and at high rates. Some formations with larger fractures and holes may even experience fluid loss, significantly increasing the cost of plugging a single well and even causing the wellbore to be scrapped, resulting in significant economic losses.

[0003] At present, the plugging technologies at home and abroad, such as "one-bag" plugging technology, curable plugging technology, chemical cross-linking plugging technology, intelligent plugging technology, and cementing sealing technology, still have the following shortcomings: ① The leakage channels such as natural fractures, secondary fractures and induced fractures in the formation are affected by the excitation pressure (or increased drilling fluid density) and expand and close, resulting in poor pressure bearing capacity of the drilling fluid, short retention time of the plugging material, and high frequency of drilling fluid leakage; ② The plugging material has poor matching degree with the fracture size and is not easy to enter the leaking layer. At the same time, the particles themselves have insufficient pressure resistance and low friction resistance between particles. The formed plugging layer is easily destroyed under high temperature and high pressure, resulting in spitting; ③ The plugging material is easily sheared, dispersed and thinned during long-term circulation, which increases the thixotropic properties of the drilling fluid and generates greater pressure excitation; ④ The plugging layer formed in the fracture has poor acid solubility and oil solubility, and is difficult to deblock later, causing irreversible reservoir damage. Summary of the Invention

[0004] To address the above-mentioned issues, the present invention provides a pressure-bearing plugging material, drilling fluid, and application for preventing significant leakage in fractured formations. The pressure-bearing plugging material has a high degree of compatibility with fracture dimensions, easily enters the leaking layer, maintains a long retention time, exhibits excellent compatibility with drilling fluid, and resists shear dilution. The resulting plugging layer has a dense structure, strong pressure and high temperature bearing capabilities, is easily unblocked, and minimizes reservoir damage. This material can be used to prepare an excellent pressure-bearing plugging working fluid, ensuring safe and efficient drilling in fractured formations, shortening drilling cycles, and reducing the cost of completing a single well.

[0005] The first aspect of the present invention provides a pressure-bearing plugging material for severe leakage in fractured formations, which includes the following raw material components, in parts by weight: 20-25 parts by weight of a plugging agent, 2-6 parts by weight of a filling binder, 1-2 parts by weight of an active agent, and 1-2 parts by weight of a dispersant; preferably, it includes the following raw material components: 20 parts by weight of a plugging agent, 4 parts by weight of a filling binder, 1 part by weight of an active agent, and 1 part by weight of a dispersant.

[0006] The plugging agent is selected from at least one of diatomaceous earth, ultrafine calcium carbonate, mica flakes, walnut shell powder, bamboo fiber and composite mineral fiber SQD-98; the filling binder is selected from at least one of white asphalt, asbestos fiber and sodium silicate; the active agent is selected from at least one of heavy calcium carbonate and silica fume; the dispersant is selected from at least one of humate, polycarboxylate and polyanionic cellulose.

[0007] The plugging material of the present invention is designed to address the malignant leakage characteristics of fractured formations. A plugging agent forms a sealing framework within the fractures, while a filling binder fills the internal spaces of the plugging agent particles and the gaps between the particles, thereby tightly sealing the leakage path. The filler active agent plays an orienting and stacking role, enhancing the matching of the plugging material particle size and shape with the leakage path, forming a dense slug and improving the retention and solidification capacity of the plugging material. The dispersant improves the rheological properties and sedimentation stability of the drilling fluid system in the wellbore.

[0008] The plugging agent is composed of diatomaceous earth, ultrafine calcium carbonate, and mica flakes; preferably, the mass ratio of the diatomaceous earth, ultrafine calcium carbonate, and mica flakes is 1-2:1-2:1-2; more preferably, the mass ratio of the diatomaceous earth, ultrafine calcium carbonate, and mica flakes is 2:1:1. The diatomaceous earth, ultrafine calcium carbonate, and mica flakes form a high-water-loss composite plugging agent. While forming a sealing framework in the cracks, the composite plugging agent utilizes the "filtration-aiding" effect of the diatomaceous earth to rapidly lose water due to the pressure differential generated by the drilling fluid column pressure and the formation pressure, thereby effectively plugging the leakage channel.

[0009] The average particle size of the diatomaceous earth is 30-40 μm, the average particle size of the ultrafine calcium carbonate is 13-30 μm, and the diameter of the mica flakes is 840-2000 μm.

[0010] The filling binder comprises white asphalt, asbestos fibers, and sodium silicate. Preferably, the mass ratio of the white asphalt, asbestos fibers, and sodium silicate is 1-4:1-4:1-4; more preferably, the mass ratio of the white asphalt, asbestos fibers, and sodium silicate is 1:2:1. This composite filling binder, composed of white asphalt, asbestos fibers, and sodium silicate, effectively fills the spaces within diatomaceous earth particles and the gaps between particles, thereby effectively sealing leaking pathways.

[0011] The active agent is composed of ground calcium carbonate and silica fume; preferably, the mass ratio of ground calcium carbonate to silica fume is 0.5-1:0.5-1; more preferably, the mass ratio of ground calcium carbonate to silica fume is 1:1. Preferably, the mesh size of the ground calcium carbonate is 300 mesh, and the mesh size of the silica fume is 300 mesh. The acid-soluble composite active agent composed of ground calcium carbonate and silica fume effectively enhances the matching of the plugging material's particle size and shape with the leakage channel, forming a dense plug and improving the retention and curing capacity of the plugging material.

[0012] The dispersant is composed of humate and polycarboxylate. Preferably, the mass ratio of humate to polycarboxylate is 0.5-1:0.5-1; more preferably, the mass ratio of humate to polycarboxylate is 1:1. The composite dispersant composed of humate and polycarboxylate has the effect of effectively improving the rheological properties and sedimentation stability of the drilling fluid system in the wellbore.

[0013] The second aspect of the present invention provides a drilling fluid, which is composed of the aforementioned pressure-bearing plugging material for severe leakage in fractured formations and a base slurry; the base slurry can be conventionally selected from clean water, mud, and common water-based drilling fluid. Preferably, the added amount of the pressure-bearing plugging material for severe leakage in fractured formations is 19-26% of the total weight of the drilling fluid.

[0014] The third aspect of the present invention provides a method for preparing the aforementioned drilling fluid: separately taking a plugging agent, a filling binder, an active agent, a dispersant and a base slurry, stirring and mixing them evenly to obtain the drilling fluid.

[0015] A fourth aspect of the present invention provides the use of the pressure-bearing plugging material or drilling fluid for preventing severe leakage in fractured formations in plugging fractured leakage formations.

[0016] The beneficial effects of the present invention are:

[0017] The present invention prepares a pressure-bearing plugging material by compounding a plugging agent, a filling binder, an active agent and a dispersant composed of specific raw materials and supplementing them with an appropriate weight ratio: 1) under a pressure of 8MPa, the HTHP (150°C) water loss can reach 206.6mL within 2 minutes, and a dense slug can be quickly formed in the leakage channel to temporarily block the leakage channel, which can effectively increase the retention time of the plugging material, thereby preventing the fluid in the wellbore from flowing into the leakage formation gap; 2) the formed particle size gradation has a high degree of matching with the development of the fracture, and the particle size of the drilling fluid system is mainly in the range of 0 to 4537μm (D50=394μm, D90=2010μm m), the particle size composition distribution has a multi-peak structure, the upper limit of the sealed crack width reaches 4.0 mm, the pressure bearing capacity of the sealing layer can reach 8 MPa, and the upper limit of temperature resistance can reach 150°C; 3) the formula has good compatibility. Its viscosity modulus can still be restored before and after aging and after repeated shearing at high and low rates, indicating that the pressure-bearing plugging material has excellent shear dilution resistance. In addition, after the pressure-bearing plugging material is added, the apparent viscosity of the drilling fluid before and after aging changes slightly, indicating good compatibility; 4) the plugging layer formed by this formula has an acid solubility of 85.8%. After dissolution in white oil at 150°C, the total solubility rate increases to 98.7%, that is, the residue is less than 2.0%, which can effectively reduce damage to the reservoir. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a particle size distribution test diagram of the drilling fluid of the present invention;

[0019] Figure 2a The HTHP plugging test results of the drilling fluid of the present invention at a crack width of 0.2 mm are shown;

[0020] Figure 2b The HTHP plugging test results of the drilling fluid of the present invention at a crack width of 0.5 mm;

[0021] Figure 2c The HTHP plugging test results of the drilling fluid of the present invention at a crack width of 1.0 mm are shown;

[0022] Figure 2d The HTHP plugging test results of the drilling fluid of the present invention at a crack width of 2.0 mm are shown;

[0023] Figure 2e The HTHP plugging test results of the drilling fluid of the present invention at a seam width of 3.0 mm are shown;

[0024] Figure 2f The HTHP plugging test results of the drilling fluid of the present invention at a seam width of 4.0 mm are shown;

[0025] Figure 3 This is a curve diagram of the elastic modulus change of the drilling fluid of the present invention under alternating strain. DETAILED DESCRIPTION

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0027] In the following examples, all raw materials were purchased from the market, and the raw material parameters are as follows:

[0028] Diatomaceous earth, appearance: white solid powder; average particle size: 30-40μm; specific surface area: ≤1000m 2 / g; loose density: ≤3.12g / cm 3 ; Suspension: 97-99%;

[0029] Ultrafine calcium carbonate, appearance: white solid powder; composed of 425 mesh ultrafine calcium carbonate and 1000 mesh ultrafine calcium carbonate in a mass ratio of 1:2; particle size: 13-30μm;

[0030] Mica flakes, appearance: gray solid material; morphology: pseudo-hexagonal plate-like and short columnar; diameter: 840-2000μm; loose density: ≤3.44g / cm 3 ; Mineral density: 2.7-2.85g / cm3;

[0031] White asphalt, appearance: white or slightly yellow granules or powder; pH value: 7-10; water-soluble matter content: ≥40%; oil-soluble matter content: ≥40%; fluorescence level: ≤5;

[0032] Asbestos fiber, appearance: white; mesh: 100 mesh; particle size: 1-3mm; hardness: 2-2.5; mass: 600g / cm;

[0033] Sodium silicate, Appearance: Colorless or translucent liquid; Relative density: 2.614g / cm 3 ;Solubility: soluble in water;

[0034] Silica fume: Appearance: gray powder; Density: 2.78-2.91; pH: 6; Thermal expansion coefficient: 6.5-10.6; Mohs hardness: 5.0; Mesh size: 300 mesh;

[0035] Heavy calcium carbonate: Appearance: white solid powder; Mesh size: 300 mesh; Bulk density: 1.7g / cm 3 ; Apparent density is 1.8g / cm 3 ;

[0036] Sodium humate: Appearance: bright color; Density: 1.4g / cm 3 ;Mesh number: 80-120 mesh;

[0037] Sodium polycarboxylate: Appearance: colorless, transparent liquid; Viscosity: 350-500 MPa·s; pH: 7-8; Active ingredient: 40%;

[0038] In the following examples, the plugging agent is composed of diatomaceous earth, ultrafine calcium carbonate and mica flakes in a mass ratio of 2:1:1; the filling binder is composed of white asphalt, asbestos fiber and sodium silicate in a mass ratio of 1:2:1; the activator is composed of heavy calcium carbonate and silica fume in a mass ratio of 1:1; the dispersant is composed of sodium humate and sodium polycarboxylate in a mass ratio of 1:1; and the base slurry is taken from the on-site water-based drilling fluid.

[0039] Example 1

[0040] A drilling fluid, the formula and preparation method are as follows:

[0041] Formula: 20 parts by weight of plugging agent, 2 parts by weight of filling binder, 1.5 parts by weight of active agent, 1 part by weight of dispersant, and 100 parts by weight of base slurry;

[0042] Preparation method: Step 1: Take the base slurry into a high-stirring cup, turn on the agitator, adjust the speed to 4000r / min for stirring; Step 2: Add the plugging agent to the high-stirring cup and continue stirring for 15 minutes; Step 3: Add the filling binder to the high-stirring cup and continue stirring for 15 minutes; Step 4: Add the active agent to the high-stirring cup and continue stirring for 20 minutes; Step 5: Add the dispersant to the high-stirring cup, adjust the speed to 6000r / min, and stir for 30 minutes.

[0043] Example 2

[0044] A drilling fluid, the formula and preparation method are as follows:

[0045] Formula: 22.5 parts by weight of plugging agent, 4 parts by weight of filling binder, 1 part by weight of active agent, 1 part by weight of dispersant, and 100 parts by weight of clean water;

[0046] Preparation method: Step 1: Pour clean water into a high-stirring cup, turn on the agitator, adjust the speed to 6000r / min for stirring; Step 2: Add a plugging agent to the high-stirring cup and continue stirring for 15 minutes; Step 3: Add a filling binder to the high-stirring cup and continue stirring for 15 minutes; Step 4: Add an active agent to the high-stirring cup and continue stirring for 20 minutes; Step 5: Add a dispersant to the high-stirring cup, adjust the speed to 8000r / min, and stir for 30 minutes.

[0047] Example 3

[0048] A drilling fluid, the formula and preparation method are as follows:

[0049] Formula: 25 parts by weight of plugging agent, 4 parts by weight of filling binder, 2 parts by weight of active agent, 1 part by weight of dispersant, and 100 parts by weight of base slurry;

[0050] Preparation method: Step 1: Take the base slurry into a high-stirring cup, turn on the agitator, adjust the speed to 5000r / min for stirring; Step 2: Add the plugging agent to the high-stirring cup and continue stirring for 15 minutes; Step 3: Add the filling binder to the high-stirring cup and continue stirring for 15 minutes; Step 4: Add the active agent to the high-stirring cup and continue stirring for 20 minutes; Step 5: Add the dispersant to the high-stirring cup, adjust the speed to 7000r / min, and stir for 30 minutes.

[0051] Example 4

[0052] A drilling fluid, the formula and preparation method are as follows:

[0053] Formula: 20 parts by weight of plugging agent, 5 parts by weight of filling binder, 1 part by weight of active agent, 2 parts by weight of dispersant, 100 parts by weight of base slurry;

[0054] Preparation method: Step 1: Take the base slurry into a high-stirring cup, turn on the agitator, adjust the speed to 5000r / min for stirring; Step 2: Add the plugging agent to the high-stirring cup and continue stirring for 15 minutes; Step 3: Add the filling binder to the high-stirring cup and continue stirring for 15 minutes; Step 4: Add the active agent to the high-stirring cup and continue stirring for 20 minutes; Step 5: Add the dispersant to the high-stirring cup, adjust the speed to 7000r / min, and stir for 30 minutes.

[0055] Example 5

[0056] A drilling fluid, the formula and preparation method are as follows:

[0057] Formula: 25 parts by weight of plugging agent, 6 parts by weight of filling binder, 2 parts by weight of active agent, 2 parts by weight of dispersant, 100 parts by weight of base slurry;

[0058] Preparation method: Step 1: Take the base slurry into a high-stirring cup, turn on the agitator, adjust the speed to 5000r / min for stirring; Step 2: Add the plugging agent to the high-stirring cup and continue stirring for 15 minutes; Step 3: Add the filling binder to the high-stirring cup and continue stirring for 15 minutes; Step 4: Add the active agent to the high-stirring cup and continue stirring for 20 minutes; Step 5: Add the dispersant to the high-stirring cup, adjust the speed to 7000r / min, and stir for 30 minutes.

[0059] Example 6

[0060] A drilling fluid, the formula and preparation method are as follows:

[0061] Formula: 20 parts by weight of plugging agent, 4 parts by weight of filling binder, 1 part by weight of active agent, 1 part by weight of dispersant, and 100 parts by weight of base slurry;

[0062] Preparation method: Step 1: Take the base slurry into a high-stirring cup, turn on the agitator, adjust the speed to 5000r / min for stirring; Step 2: Add the plugging agent to the high-stirring cup and continue stirring for 15 minutes; Step 3: Add the filling binder to the high-stirring cup and continue stirring for 15 minutes; Step 4: Add the active agent to the high-stirring cup and continue stirring for 20 minutes; Step 5: Add the dispersant to the high-stirring cup, adjust the speed to 7000r / min, and stir for 30 minutes.

[0063] Test example

[0064] 1. Formula screening test research

[0065] 1. Screening of plugging agents:

[0066] Taking the cumulative leakage at 6 MPa pressure through a 4.0 mm seam as the evaluation indicator, a seven-factor, two-level orthogonal table L8 (27) was used to evaluate the plugging capacity of the plugging materials added to the drilling fluid on site. See Tables 1 and 2.

[0067] Among them, the 4mm seam plate plugging performance evaluation under 6MPa pressure uses the DL plugging material evaluation device to evaluate the plugging performance of the plugging material used. The specific steps are as follows:

[0068] ① Prepare the plugging slurry, heat it at 150℃ for 16 hours, and stir it on an electric mixer for 30 minutes;

[0069] ②Pour the slurry into the DL leak plugging instrument and install the gas source manifold;

[0070] ③ Increase the pressure at a rate of 0.069 MPa per second to the target pressure, or until the plug is broken and the drilling fluid in the instrument container flows out. Record the volume of drilling fluid that flows out and the maximum pressure reached. If the plug is successful, maintain the pressure for 10 minutes and record the final drilling fluid volume.

[0071] Acid solubility test of plugging materials:

[0072] The acid solubility test of the plugging material was used to evaluate its acid solubility. The main experimental instruments were a mixer and a drying oven. The test was conducted in accordance with the petroleum industry standard SYT / 5061-93 "Limestone Powder for Drilling Fluids." The specific steps are as follows:

[0073] ① Weigh 2 g of the sample dried at 105±3℃ for 2 h (accurate to 0.01 g), place it in a 200 mL beaker, add 30 mL of the 15% concentration mixed acid solution (mainly composed of hydrochloric acid and hydrofluoric acid) on site respectively, cover it, and after stopping the reaction, transfer it to a Buchner funnel for suction filtration, and wash with distilled water until there is no chloride ion (check with 1% (m / m) silver nitrate solution).

[0074] ② Place the Buchner funnel in a drying oven at 150±3℃ and dry it for 2 hours. Take it out and place it in a desiccator. After cooling to room temperature, weigh it.

[0075] Calculation: Acid insoluble matter = (m3–m2) / m1×100%

[0076] Where: m3——mass of filter paper and residue, g;

[0077] m2——filter paper mass, g;

[0078] m1——sample mass, g.

[0079] Table 1 Orthogonal experimental design table

[0080]

[0081] Table 2 Orthogonal experiment results

[0082]

[0083] Through range (Rj) analysis, comprehensive consideration of the impact on leakage and plugging removal properties (acid solubility), diatomaceous earth, ultrafine calcium carbonate and flaky mica flakes were selected to form the formula of high-water-loss composite plugging agent, and the addition ratio was 2:1:1.

[0084] Using the cumulative leakage at 6 MPa pressure in a 4.0 mm seam as the evaluation indicator, 22.5% of a plugging material combination (diatomaceous earth: ultrafine calcium carbonate: flaky mica = 2:1:1) was added to the on-site drilling fluid to evaluate its plugging capacity. (See Table 3.)

[0085] Table 3 Performance evaluation test results

[0086]

[0087] It was determined that diatomaceous earth, ultrafine calcium carbonate and flaky mica flakes were selected to form the formula of high water loss composite plugging agent, and the addition ratio was 2:1:1.

[0088] 2. Screening of filling binders, see Table 4.

[0089] Table 4 Results of the filling binder screening test

[0090]

[0091] Base slurry: On-site drilling fluid + 20.0% plugging agent (diatomaceous earth: ultrafine calcium carbonate: flaky mica flakes = 2:1:1)

[0092] The optimal ratio of white asphalt particles, asbestos fibers and sodium silicate as filling binders was determined to be 1:2:1. Under 6MPa conditions, the filtration loss of the 4.0mm seam plate was reduced to 208.2mL.

[0093] 3. Screening of active agents, see Table 5.

[0094] Table 5 Active agent screening test results

[0095]

[0096] Base slurry: On-site drilling fluid + 20.0% plugging agent (diatomaceous earth: ultrafine calcium carbonate: flaky mica = 2:1:1) + 4.0% filling binder (white asphalt granules: asbestos fiber: sodium silicate = 1:2:1)

[0097] It was determined that the optimal composition of the active agent was silica fume powder and heavy calcium carbonate in a 1:1 ratio. Under 8MPa conditions, the filtration loss of the 4.0mm seam plate was reduced to 238.8mL, which can further improve the pressure bearing capacity of the plugging slurry.

[0098] 4. Dispersant screening, see Table 6.

[0099] Table 6 Dispersant screening test results

[0100]

[0101] Base slurry: on-site drilling fluid + 20.0% plugging agent (diatomaceous earth: ultrafine calcium carbonate: flaky mica = 2:1:1) + 4.0% filling binder (white asphalt granules: asbestos fiber: sodium silicate = 1:2:1) + 1.0% activator (silica fume: heavy calcium carbonate = 1:1); aging conditions: 150℃×16h.

[0102] After adding 0.5% sodium humate and 0.5% sodium polycarboxylate to the base mud, the apparent viscosity and plastic viscosity of the base mud decreased by 3-5 mPa·s, while the dynamic shear force remained stable. However, the dynamic-to-plastic ratio increased significantly, indicating enhanced rock-carrying properties of the drilling fluid. Furthermore, at 8 MPa, the fluid loss of a 4.0 mm seam plate was further reduced to 234.8 mL, demonstrating enhanced plugging capability.

[0103] 2. Performance Testing

[0104] 1. Particle size distribution test

[0105] With reference to the determination standard of 3.3.2 particle size distribution in the "Indoor test method of bridging plugging materials for drilling fluids SY / T 5840-2007" of the petroleum industry, the particle size distribution of the drilling fluid prepared in Example 6 was measured. The experimental results are as follows: Figure 1 The particle size of the drilling fluid prepared by the present invention is mainly in the range of 0 to 4537 μm (D50=394 μm, D90=2010 μm), and the particle size composition distribution has a multi-peak structure, which is conducive to plugging cracks of varying sizes and improving the plugging effect.

[0106] 2. Plugging performance evaluation

[0107] The plugging performance of the drilling fluid prepared in Example 6 was evaluated using a high-temperature, high-pressure plugging tester. The specific steps are as follows: ① Prepare the drilling fluid and stir it on an electric mixer for 30 minutes; ② Select crack templates of different widths (0.2 mm, 0.5 mm, 1.0 mm, 2.0 mm, 3.0 mm, and 4.0 mm), place the templates in a test cup, and assemble the test assembly; ③ Inject 2000 mL of drilling fluid into the test container; ④ Pre-pressurize the test container with a pressure of 2.0 MPa and set the temperature to 150°C; ⑤ Uniformly pressurize the container at a pressure of 0.5 to 1.0 MPa each time. After pressurization, stabilize the pressure at each pressure point for 10 minutes before starting a timer and recording the leakage; ⑥ Pressurize to 8.0 MPa and stabilize the pressure for 60 minutes.

[0108] The experimental results are shown in Figure 2. The drilling fluid of the present invention is compatible with plugging cracks with a wide width and can withstand pressure to plug cracks with a width of 0.2 mm to 4.0 mm. The upper limit of the pressure bearing capacity of the plugging layer can reach 8 MPa, and the temperature resistance of the plugging material is greater than 150°C, with good overall performance. Specifically, for a 4.00 mm seam plate under a pressure of 8 MPa, the HTHP water loss can reach 206.6 mL within 2 minutes, indicating that the drilling fluid can quickly lose water in the leakage channel, forming a dense plug, which can effectively solve the problem of malignant leakage in fractured formations and ensure safe and efficient drilling in formations prone to leakage.

[0109] 3. Acid and oil solubility evaluation

[0110] With reference to the petroleum industry standard SYT / 5061-93, "Limestone Powder for Drilling Fluids," acid and oil solubility tests were conducted on the drilling fluid from Example 6. The test results, shown in Table 7, demonstrate excellent acid solubility, reaching over 85% in 15% hydrochloric acid. Upon dissolution in 150°C white oil, the solubility rose to 98.2%, resulting in less than 2.0% residue. This demonstrates ease of blockage removal in later stages, effectively minimizing reservoir damage.

[0111] Table 7 Acid and oil soluble test results of plugging materials

[0112]

[0113] 4. Rheological properties evaluation

[0114] With reference to the national standard GB / T 16783.1-2014 "Field Testing of Drilling Fluids in the Petroleum and Natural Gas Industry - Part 1: Water-Based Drilling Fluids," the rheological properties of the drilling fluid from Example 6 were evaluated. The test results are shown in Table 8. The plugging material had little effect on the viscosity and fluid loss of the drilling fluid. The apparent viscosity increased slightly, while the fluid loss remained essentially stable.

[0115] Table 8 Rheological properties evaluation

[0116]

[0117]

[0118] Aging conditions: 150℃×16h. High temperature and high pressure filtration test: 150℃×3.5MPa, 30min.

[0119] 5. Lubrication performance evaluation

[0120] With reference to the petroleum industry standard SY / T6094-94 "Evaluation Procedure for Lubricants for Drilling Fluids", the lubrication performance of the drilling fluid of Example 6 was tested using an extreme pressure lubricity tester. The test results are shown in Table 9. The pressure-bearing plugging material of the present invention has little effect on the lubricity of the base slurry and has strong compatibility.

[0121] Table 9 Lubrication performance evaluation

[0122]

[0123] 6. Evaluation of shear thinning resistance

[0124] The change of viscous modulus under alternating strain was measured according to the HAKKE rheometer test procedure. The test results are as follows: Figure 3 As shown in the figure, the viscosity modulus of the drilling fluid in Example 6 can be recovered after repeated shearing at high and low rates before and after aging, indicating that the drilling fluid has excellent anti-shear thinning performance, which can ensure pumpability and retention and plugging capabilities during on-site construction, while reducing the leakage of drilling fluid during the later drilling process.

[0125] The present invention also carried out the above-mentioned performance tests on the remaining embodiments, and the test results were substantially the same, which will not be described in detail due to space limitations.

[0126] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the scope of protection of the present invention.

Claims

1. A pressure-bearing plugging material for preventing severe leakage in fractured formations, characterized in that: By weight, it includes the following raw material components: 20-25 parts by weight of plugging agent, 2-6 parts by weight of filling binder, 1-2 parts by weight of active agent, and 1-2 parts by weight of dispersant; The plugging agent is composed of diatomaceous earth, ultrafine calcium carbonate and mica flakes in a mass ratio of 2:1:1; The filling binder is selected from at least one of white asphalt, asbestos fiber and sodium silicate; The active agent is selected from at least one of heavy calcium carbonate and silica fume; The dispersant is selected from at least one of humate, polycarboxylate and polyanionic cellulose.

2. The pressure-bearing plugging material for preventing severe leakage in fractured formations according to claim 1, characterized in that: By weight, it includes the following raw material components: 20 parts by weight of plugging agent, 4 parts by weight of filling binder, 1 part by weight of active agent, and 1 part by weight of dispersant.

3. The pressure-bearing plugging material for severe leakage in fractured formations according to any one of claims 1-2, characterized in that: The average particle size of the diatomaceous earth is 30-40 μm, the average particle size of the ultrafine calcium carbonate is 13-30 μm, and the diameter of the mica flakes is 840-2000 μm.

4. The pressure-bearing plugging material for preventing severe leakage in fractured formations according to claim 1, characterized in that: The filling binder consists of white asphalt, asbestos fiber and sodium silicate.

5. The pressure-bearing plugging material for preventing severe leakage in fractured formations according to claim 4, characterized in that: The mass ratio of the white asphalt, asbestos fiber and sodium silicate is 1-4:1-4:1-4.

6. The pressure-bearing plugging material for preventing severe leakage in fractured formations according to claim 5, characterized in that: The mass ratio of the white asphalt, asbestos fiber and sodium silicate is 1:2:

1.

7. The pressure-bearing plugging material for preventing severe leakage in fractured formations according to claim 1, characterized in that: The active agent consists of heavy calcium carbonate and silica fume powder.

8. The pressure-bearing plugging material for preventing severe leakage in fractured formations according to claim 7, characterized in that: The mass ratio of the heavy calcium carbonate to the silica fume is 0.5-1:0.5-1.

9. The pressure-bearing plugging material for preventing severe leakage in fractured formations according to claim 8, characterized in that: The mass ratio of the heavy calcium carbonate to the silica fume is 1:

1.

10. The pressure-bearing plugging material for preventing severe leakage in fractured formations according to claim 7, characterized in that: The mesh number of the heavy calcium carbonate is 300 mesh, and the mesh number of the silica fume is 300 mesh.

11. The pressure-bearing plugging material for preventing severe leakage in fractured formations according to claim 1, characterized in that: The dispersant consists of humate and polycarboxylate.

12. The pressure-bearing plugging material for preventing severe leakage in fractured formations according to claim 11, characterized in that: The mass ratio of the humate to the polycarboxylate is 0.5-1:0.5-1.

13. The pressure-bearing plugging material for preventing severe leakage in fractured formations according to claim 12, characterized in that: The mass ratio of the humate to the polycarboxylate is 1:

1.

14. A drilling fluid, characterized in that: The invention is composed of the pressure-bearing plugging material for preventing severe leakage in fractured formations as claimed in any one of claims 1 to 13 and base slurry.

15. The drilling fluid according to claim 14, characterized in that: The added amount of the pressure-bearing plugging material for severe leakage in fractured formations is 19-26% of the total weight of the drilling fluid.

16. A method for preparing the drilling fluid according to any one of claims 14-15, characterized in that: The preparation method comprises the following steps: respectively taking a plugging agent, a filling binder, an active agent, a dispersant and a base slurry, stirring and mixing them evenly to obtain the product.

17. Use of the pressure-bearing plugging material for severe leakage in fractured formations according to any one of claims 1 to 13 or the drilling fluid according to any one of claims 14 to 15 in plugging fractured leakage formations.

Images