A design method for cross-linking particle gradation and a sealing agent for sealing cracks and preventing gas intrusion, and their application.

Abstract

This invention provides a design method for the gradation of bridging particles and a plugging agent for sealing fractures and preventing gas intrusion, and its application, belonging to the field of petrochemical technology. The gradation of the bridging particles in the plugging agent of this invention is obtained through design using Formula I and Formula II. The prepared plugging agent for sealing fractures and preventing gas intrusion, by mass fraction, comprises 50-80% bridging particles and 20-50% plugging material. The plugging agent of this invention can form a high-pressure-bearing plugging layer in sealing fractures, effectively preventing gas from the formation from entering the wellbore and avoiding downhole accidents such as gas intrusion and well kicks.

Description

Technical Field

[0001] This invention belongs to the field of petrochemical technology, specifically relating to a design method for bridging particle gradation and a sealing agent for sealing cracks and preventing gas intrusion, as well as its application. Background Technology

[0002] During drilling in fractured formations containing natural gas, the presence of natural fractures leads to low formation leakage pressure and a high risk of well leakage. Therefore, it is crucial to control the drilling fluid density. When the drilling fluid density in the wellbore cannot balance the formation pressure, natural gas can invade the wellbore, a phenomenon known as gas intrusion. The gas rises rapidly to the wellhead, and if the intrusion is significant, it can cause a well kick or even a blowout. Gas intrusion can typically be controlled by increasing the drilling fluid density, but this can easily cause the dynamic fluid column pressure to exceed the formation leakage pressure, resulting in well leakage and severely impacting the safety and efficiency of drilling operations. Therefore, there is an urgent need to explore efficient methods for preventing gas intrusion.

[0003] Current technologies typically involve adding appropriate types and particle size distributions of plugging materials to drilling fluids to form a dense, pressure-bearing plugging layer on the wellbore surface, potentially slowing gas intrusion into the wellbore. The plugging materials often utilize the synergistic effect of rigid particle bridging, elastic particle filling, and fiber reinforcement to form a network, thereby improving leakage prevention and plugging effectiveness. The particle size distribution of the bridging particles has a significant impact on the pressure-bearing capacity of the plugging layer. Currently, mature bridging plugging criteria for pores or fractures include the 1 / 3 bridging criterion and the D... 90 While existing theories and methods focus on sealing fractures to prevent drilling fluid leakage into the formation, sealing fractures to prevent natural gas intrusion into the wellbore is the opposite process. The effectiveness and applicability of drilling fluids prepared using existing design methods for sealing fractures and preventing gas intrusion are unclear. Current technologies have not yet established a refined design method for sealing agents suitable for drilling fluids to prevent gas intrusion into fractured formations. This results in a lack of theoretical basis for current drilling fluid technology countermeasures against gas intrusion in fractured formations, affecting drilling safety and efficiency in fractured formations containing natural gas. Summary of the Invention

[0004] The purpose of this invention is to provide a design method for the gradation of bridging particles and a plugging agent for sealing fractures and preventing gas intrusion, as well as their applications. By rationally designing the particle size distribution of bridging particles in the plugging agent, the invention can effectively prevent and seal gas intrusion in fractures, and provides higher safety performance and work efficiency when drilling in fractured formations containing natural gas.

[0005] To achieve the objectives of this invention, the following technical solutions are provided:

[0006] A method for designing cross-linked particle gradations includes the following steps:

[0007] The maximum and minimum diameters of the bridging particles are determined according to the size of the crack to be sealed. The maximum diameter of the bridging particles is 0.9 to 1.1 times the maximum opening of the crack to be sealed, and the minimum diameter is 0.4 to 0.6 times the average opening of the crack to be sealed.

[0008] Based on the maximum and minimum diameters of the bridging particles, the particle size grades of the bridging particles are classified using the difference method, wherein the particle size grade is ≥4.

[0009] The volume percentage of bridging particles for each particle size class is obtained according to Equation I:

[0010]

[0011] In formula I, Let D be the volume percentage of the crosslinking particles at the i-th particle size level relative to all crosslinking particles, in %; i90 D represents the maximum diameter within the i-th particle size range, in mm. i10 D is the minimum diameter within the i-th particle size range, in mm; L and D s , respectively, represent the maximum and minimum diameters of bridging particles within all particle size classes, in mm; η is the distribution modulus, which is 0.3 or 0.4;

[0012] The mass percentage of each particle size class of the bridging particles is obtained according to Formula II:

[0013]

[0014] In Equation II, C i C represents the mass percentage of the crosslinking particles at the i-th particle size level relative to all crosslinking particles, in %; m The percentage of the mass of the bridging particles with the largest diameter, in %. Let be the volume percentage of the bridging particles at the i-th particle size level relative to all bridging particles, in %; The percentage of the volume of the largest diameter bridging particle, %.

[0015] The present invention also provides a sealing agent for sealing cracks and preventing gas intrusion, comprising, by mass fraction, 50-80% bridging particles and 20-50% sealing material; the gradation of the bridging particles is obtained by the design method described in the above technical solution.

[0016] Preferably, the bridging particles comprise calcium carbonate and / or hydroxyapatite.

[0017] Preferably, the sealing material includes bridging materials, elastic materials, and fibers.

[0018] Preferably, the bridging material includes walnut shells and / or olive shells.

[0019] Preferably, the elastic material comprises graphite and / or rubber.

[0020] Preferably, the mass ratio of the bridging material, the elastic material, and the fiber is 0–15:0–10:0–1.

[0021] The present invention also provides the application of the sealing agent for sealing cracks and preventing gas intrusion described in the above technical solution in drilling fluid.

[0022] Preferably, the mass of the sealing agent used to seal the fractures and prevent gas intrusion accounts for 10-16% of the total mass of the drilling fluid.

[0023] This invention provides a design method for the gradation of bridging particles. Using this method, a sealing agent for sealing fractures and preventing gas intrusion is prepared from bridging particles. By mass fraction, it comprises 50-80% bridging particles and 20-50% sealing material. The sealing agent provided by this invention, when applied to drilling fluids, can form a high-pressure-bearing sealing layer in the fracture, effectively preventing gas from the formation from entering the wellbore and avoiding downhole accidents such as gas intrusion and well kicks. Detailed Implementation

[0024] This invention provides a method for designing cross-linked particle gradation, comprising the following steps:

[0025] The maximum and minimum diameters of the bridging particles are determined according to the size of the crack to be sealed. The maximum diameter of the bridging particles is 0.9 to 1.1 times the maximum opening of the crack to be sealed, and the minimum diameter is 0.4 to 0.6 times the average opening of the crack to be sealed.

[0026] Based on the maximum and minimum diameters of the bridging particles, the particle size grades of the bridging particles are classified using the difference method, wherein the particle size grade is ≥4.

[0027] The volume percentage of bridging particles for each particle size class is obtained according to Equation I:

[0028]

[0029] In formula I, Let D be the volume percentage of the crosslinking particles at the i-th particle size level relative to all crosslinking particles, in %; i90 D represents the maximum diameter within the i-th particle size range, in mm. i10 D is the minimum diameter within the i-th particle size range, in mm; L and D s , respectively, represent the maximum and minimum diameters of bridging particles within all particle size classes, in mm; η is the distribution modulus, which is 0.3 or 0.4;

[0030] The mass percentage of each particle size class of the bridging particles is obtained according to Formula II:

[0031]

[0032] In Equation II, C i C represents the mass percentage of the crosslinking particles at the i-th particle size level relative to all crosslinking particles, in %; m The percentage of the mass of the bridging particles with the largest diameter, in %. Let be the volume percentage of the bridging particles at the i-th particle size level relative to all bridging particles, in %; The percentage of the volume of the largest diameter bridging particle, %.

[0033] In this invention, the particle size of the bridging particles is divided into equal arithmetic grades based on the maximum and minimum diameters of the bridging particles. The particle size grade is ≥4, and in a specific embodiment, it can be 4 or 6.

[0034] In this invention, there is no special limitation on the maximum and average opening of the crack to be sealed. In specific embodiments, they can be 1 to 5 mm; the average opening can be 0.75 to 4.5 mm; the maximum diameter of the bridging particles is 0.9 to 1.1 times the maximum opening of the crack to be sealed, and the minimum diameter is 0.4 to 0.6 times the average opening of the crack to be sealed.

[0035] In this invention, the difference compensation method design method includes:

[0036] Assume that the sealing slurry formulation contains n components, and the particle size distribution ranges of each component are: [x1,x2],[x3,x4],[x5,x6],…[x… n-1 ,x n ], where x1 and x n These are the maximum and minimum particle sizes in the system, respectively.

[0037] The components are divided into a continuous distribution system using the difference compensation method:

[0038] By appropriately increasing or decreasing the boundary values ​​of some material particle sizes in the system, the original discrete or cross-distributed particle system can be transformed into a continuous distribution system.

[0039] The present invention also provides a sealing agent for sealing cracks and preventing gas intrusion, comprising, by mass fraction, 50-80% bridging particles and 20-50% sealing material; the gradation of the bridging particles is obtained by the design method described in the above technical solution.

[0040] In this invention, unless otherwise specified, all raw materials used in the preparation are commercially available products well known to those skilled in the art.

[0041] In this invention, the sealing agent for sealing cracks and preventing gas intrusion comprises 50-80% bridging particles, which in specific embodiments can be 53.5%, 55%, 60%, 70%, or 75%; the bridging particles comprise calcium carbonate and / or hydroxyapatite, which in specific embodiments can be calcium carbonate.

[0042] In this invention, the sealing agent for sealing cracks and preventing gas intrusion comprises 20-50% sealing material; the sealing material comprises bridging material, elastic material, and fiber; the bridging material comprises walnut shell and / or olive shell; this invention does not specifically limit the parameters of the bridging material. Preferably, the elastic material comprises graphite and / or rubber; this invention does not specifically limit the type of fiber, and in specific embodiments it may be polyester fiber and / or polypropylene fiber.

[0043] In this invention, the mass ratio of the bridging material, elastic material and fiber is 0-15:0-10:0-1. In specific embodiments, it can be 9:3:0.5, 10:5:0.8 or 13:8:1.

[0044] The present invention does not have any special limitations on the preparation method of the sealing agent for sealing cracks and preventing gas intrusion; conventional mixing is sufficient.

[0045] The present invention also provides the application of the sealing agent for sealing cracks and preventing gas intrusion described in the above technical solution in drilling fluid.

[0046] In this invention, the mass of the sealing agent used to seal the fracture and prevent gas intrusion accounts for 10-16% of the total mass of the drilling fluid. In specific embodiments of this invention, it can be 11%, 13%, or 15%.

[0047] To further illustrate the present invention, the following detailed description, in conjunction with embodiments, of a design method for cross-linking particle gradation and a sealing agent for sealing cracks and preventing gas intrusion, and their applications, is provided by the present invention. However, these descriptions should not be construed as limiting the scope of protection of the present invention.

[0048] Example 1

[0049] Calcium carbonate, graphite, and polyester fiber were weighed in a mass ratio of 60:10:1 and mixed to obtain a sealing agent for sealing fractures and preventing gas intrusion. The maximum diameter of the calcium carbonate was one time the maximum aperture of the formation fracture, and the minimum diameter was 0.5 times the average fracture aperture. Its particle size distribution was designed according to Formulas I and II, with a distribution modulus η of 0.3. Calculations showed that for a 1×0.5mm fracture, four particle size grades were designed, with the calcium carbonate particle size distribution being 15-30 mesh, 80-200 mesh, 400-600 mesh, and 800-1000 mesh in a mass ratio of 19:27:38:16.

[0050] For 2×1mm cracks, the particle size distribution is 8-20 mesh, 50-100 mesh, 200-400 mesh, and 500-800 mesh in a mass ratio of 17:27:40:16.

[0051] Example 2

[0052] Calcium carbonate, graphite, walnut shells, and polyester fiber were weighed according to a mass ratio of 53.5:15:10:1 and mixed to obtain a sealing agent. The maximum diameter of the calcium carbonate was 0.9 times the maximum aperture of the formation fracture, and the minimum diameter was 0.4 times the average fracture aperture. Its particle size distribution was designed according to Formula I, with a distribution modulus η of 0.4. Calculations showed that for a 1×0.5mm fracture, four particle size grades were designed, with the calcium carbonate particle size distribution being 15-20 mesh, 50-200 mesh, 200-400 mesh, and 600-800 mesh in a mass ratio of 21:31:35:13.

[0053] For a crack opening of 2×1mm, the particle size distribution is 10-20 mesh, 50-100 mesh, 200-400 mesh, and 400-800 mesh in a mass ratio of 19:28:33:20.

[0054] Example 3

[0055] Calcium carbonate, walnut shells, and polypropylene fibers were weighed in a mass ratio of 70:10:1 and mixed to obtain a sealing agent. The maximum diameter of the calcium carbonate was 0.9 times the maximum aperture of the formation fracture, and the minimum diameter was 0.6 times the average fracture aperture. Its particle size distribution was designed according to Formulas I and II, with a distribution modulus η of 0.4. Calculations showed that for a 1×0.5mm fracture, four particle size grades were designed, with the calcium carbonate particle size distribution being 18-30 mesh, 50-100 mesh, 200-500 mesh, and 500-800 mesh in a mass ratio of 17:31:32:20.

[0056] For a crack opening of 2×1mm, the particle size distribution is 10-20 mesh, 50-100 mesh, 100-200 mesh, and 200-600 mesh in a mass ratio of 13:29:32:26.

[0057] Example 4

[0058] Hydroxyapatite, olive shell, rubber, and polypropylene fiber were weighed in a mass ratio of 50:9:8:1 and mixed to obtain the sealing agent. The maximum diameter of calcium carbonate was 1.1 times the maximum aperture of the formation fracture, and the minimum diameter was 0.4 times the average fracture aperture. The particle size distribution was designed according to Formulas I and II, with a distribution modulus η of 0.4. Calculations showed that for a 1×0.5 mm fracture, four particle size grades were designed, with calcium carbonate particle size distributions of 14-20 mesh, 50-100 mesh, 200-400 mesh, and 400-800 mesh in a mass ratio of 26:31:33:10.

[0059] For a crack opening of 2×1mm, the particle size distribution is 8-10 mesh, 20-100 mesh, 100-300 mesh, and 300-600 mesh in a mass ratio of 19:31:36:14.

[0060] Example 5

[0061] Calcium carbonate, graphite, walnut shells, and polypropylene fibers were weighed in a mass ratio of 55:13:9:1 and mixed to obtain a sealing agent. The maximum diameter of the calcium carbonate was 0.9 times the maximum aperture of the formation fracture, and the minimum diameter was 0.4 times the average fracture aperture. Its particle size distribution was designed according to Formulas I and II, with a distribution modulus η of 0.4. Calculations showed that for a 1×0.5mm fracture, four particle size grades were designed, with the calcium carbonate particle size distribution being 18-30 mesh, 50-100 mesh, 200-400 mesh, and 400-800 mesh in a mass ratio of 14:29:38:19.

[0062] For a crack opening of 2×1mm, the particle size distribution is 10-30 mesh, 50-100 mesh, 100-200 mesh, and 200-400 mesh in a mass ratio of 9:36:39:16.

[0063] Comparative Example 1

[0064] The plugging agent was prepared according to the preparation method described in Example 1, except that the particle size distribution of calcium carbonate was designed according to the 2 / 3 bridging criterion.

[0065] Comparative Example 2

[0066] The plugging agent was prepared according to the preparation method described in Example 2, except that the particle size distribution of calcium carbonate was designed according to the D90 criterion.

[0067] Comparative Example 3

[0068] Calcium carbonate, walnut shells, fruit shell powder, and polypropylene fiber were weighed in a mass ratio of 50:20:10:1 and mixed to obtain a sealing agent. The maximum diameter of the calcium carbonate was 0.9 times the maximum aperture of the formation fracture, and the minimum diameter was 0.6 times the average aperture of the fracture. The particle size distribution was designed according to the 1 / 3 rule currently used in the petroleum industry, and the distribution modulus η was 0.4.

[0069] Test case

[0070] The sealing agents provided in Examples 1-5 and Comparative Examples 1-3 were tested for their effectiveness in preventing gas intrusion into fractures. The specific steps of the sealing experiment were as follows: The long fracture sealing simulation experimental device developed by China University of Petroleum (East China) was used to evaluate its effectiveness in preventing gas intrusion into fractures. The experiment was carried out in wedge-shaped fracture modules with a length of 1m and fracture openings of 1×0.5mm and 2×1mm, respectively. 400mL of deionized water, 1% xanthan gum, 1% polymer filtration reducer and 0.5% starch filtration reducer were mixed to form a drilling fluid-based slurry. The sealing agents provided in Examples 1-5 and Comparative Examples 1-3 of this invention were stirred evenly with the drilling fluid-based slurry and then tested. The concentration of the sealing agent in the drilling fluid-based slurry is shown in Table 1. The breakthrough pressure and breakthrough time of the sealing layer formed during forward plugging in long fractures were tested. Then, the plugging experiment was repeated, and the pressure was increased to slightly below the breakthrough pressure and stabilized for 5 minutes. The air pump was then connected to the tail of the clamp for pressurization, and the gas breakthrough pressure was recorded. The breakthrough pressure at this time is the pressure-bearing capacity of the sealing layer formed by the drilling fluid in the fracture to resist gas intrusion. The test results are shown in Table 1.

[0071] Table 1. Test results of the sealing and pressure-bearing capacity of the sealing agents in Examples 1-5 and Comparative Examples 1-3 for cracks of different apertures.

[0072]

[0073]

[0074] As shown in Table 1, the drilling fluids provided in Examples 1-5 of this invention can form effective plugging layers in fractures of different apertures, exhibiting significant pressure-bearing and plugging effects against reverse gas intrusion. Example 1 demonstrated a pressure-bearing capacity exceeding 2 MPa for both fracture apertures. In contrast, Comparative Example 1, using the same plugging agent type and concentration as Example 1, employed the traditional 2 / 3 bridging criterion for rigid bridging particle size distribution design, resulting in pressure-bearing capacities of only 1.6 MPa and 1.51 MPa for the two fracture types. Therefore, the comparison demonstrates that the plugging agent design method provided by this invention ensures superior particle size distribution, improves the pressure-bearing and plugging effect of the fracture plugging layer against gas intrusion, and increases the pressure-bearing capacity by more than 35% compared to plugging agents designed using the 2 / 3 criterion.

[0075] Example 2 achieved pressure-bearing capacities of 3.15 MPa and 2.91 MPa for sealing two cracks, respectively, demonstrating excellent pressure-bearing performance. In contrast, Comparative Example 2, using the same type and concentration of sealing agent as Example 2, employed the traditional D90 criterion for rigid cross-linking particle size distribution design, achieving pressure-bearing capacities of 2.49 MPa and 2.32 MPa for two types of cracks. The pressure-bearing capacity of Example 2 is more than 25% higher than that of the sealing agent designed according to the D90 criterion.

[0076] Example 3 is similar to Example 1, but the sealing agent lacks elastic material and does not reach the optimal state of the present invention. However, the sealing pressure resistance for the two types of cracks can still reach 2.64 MPa and 2.49 MPa.

[0077] Examples 4 and 5 exhibit excellent pressure-bearing and plugging capabilities. Example 5 achieves maximum pressure-bearing capabilities of 3.27 MPa and 3.08 MPa for the two types of fractures. Comparative Example 3 is a plugging agent used in the eastern Bohai gas field to prevent drilling fluid loss. It has been proven in field applications to have good sealing effects against fractures and drilling fluid loss, but its pressure-bearing capabilities against gas intrusion in the two types of fractures are 2.37 MPa and 2.14 MPa, respectively. In contrast, Example 5, the most effective example provided by this invention, shows a 38% and 43.9% increase in pressure-bearing and plugging capabilities against the two types of fractures compared to Comparative Example 3. This effectively improves the sealing effect of drilling fluid against gas intrusion and confirms the excellent effect of the plugging agent design method provided by this invention in sealing fractures and preventing gas intrusion.

[0078] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for designing cross-linked particle gradation, characterized in that, Includes the following steps: The maximum and minimum diameters of the bridging particles are determined according to the size of the crack to be sealed. The maximum diameter of the bridging particles is 0.9 to 1.1 times the maximum opening of the crack to be sealed, and the minimum diameter is 0.4 to 0.6 times the average opening of the crack to be sealed. Based on the maximum and minimum diameters of the bridging particles, the particle size grades of the bridging particles are classified using the difference method, wherein the particle size grade is ≥4. The volume percentage of bridging particles for each particle size class is obtained according to Equation I: In formula I, Let be the volume percentage of the bridging particles at the i-th particle size level relative to all bridging particles, in %; D i90 D represents the maximum diameter within the i-th particle size range, in mm. i10 D is the minimum diameter within the i-th particle size range, in mm; L and D s , respectively, represent the maximum and minimum diameters of bridging particles within all particle size classes, in mm; η is the distribution modulus, which is 0.3 or 0.4; The mass percentage of each particle size class of the bridging particles is obtained according to Formula II: In Equation II, C i C represents the mass percentage of the crosslinking particles at the i-th particle size level relative to all crosslinking particles, in %; m The percentage of the mass of the bridging particles with the largest diameter, in %. Let be the volume percentage of the bridging particles at the i-th particle size level relative to all bridging particles, in %; The percentage of the volume of the largest diameter bridging particle, %.

2. A sealing agent for sealing cracks and preventing gas intrusion, characterized in that, The material comprises 50-80% bridging particles and 20-50% sealing material by mass fraction; the gradation of the bridging particles is obtained by the design method described in claim 1.

3. The sealing agent for sealing cracks and preventing gas intrusion according to claim 2, characterized in that, The bridging particles include calcium carbonate and / or hydroxyapatite.

4. The sealing agent for sealing cracks and preventing gas intrusion according to claim 2, characterized in that, The sealing material includes bridging materials, elastic materials, and fibers.

5. The sealing agent for sealing cracks and preventing gas intrusion according to claim 4, characterized in that, The bridging materials include walnut shells and / or olive shells.

6. The sealing agent for sealing cracks and preventing gas intrusion according to claim 4, characterized in that, The elastic material includes graphite and / or rubber.

7. The sealing agent for sealing cracks and preventing gas intrusion according to any one of claims 4 to 6, characterized in that, The mass ratio of the bridging material, elastic material, and fiber is 0–15:0–10:0–1.

8. The application of the sealing agent for sealing fractures and preventing gas intrusion as described in any one of claims 2 to 7 in drilling fluid.

9. The application according to claim 8, characterized in that, The plugging agent used to seal the fractures and prevent gas intrusion accounts for 10-16% of the total mass of the drilling fluid.

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