Bridging grain composition design method, plugging agent for plugging cracks and preventing gas cut and application of plugging agent

Abstract

The invention provides a bridging grain composition design method, a plugging agent for plugging cracks and preventing gas cut and application of the plugging agent, and belongs to the technical field of petrochemical engineering. The grading of the bridging particles in the plugging agent is designed according to a formula I and a formula II, and the prepared plugging agent for plugging cracks and preventing gas cut comprises the following components in percentage by mass: 50-80% of the bridging particles and 20-50% of a plugging material. The plugging agent disclosed by the invention can form a plugging layer with high pressure-bearing capacity in a plugging crack, effectively prevent gas in a stratum from invading a shaft, and avoid underground accidents such as gas cut and well kick. # imgabs0 #

Description

Technical Field

[0001] The invention belongs to the technical field of petrochemical industry, and in particular relates to a design method of bridging particle grading, a plugging agent for plugging cracks and preventing gas intrusion, and application thereof. Background Art

[0002] During the drilling process of fractured formations containing natural gas, due to the development of natural fractures in the formation, the formation loss pressure is low and the risk of well leakage is high. It is necessary to reasonably control the density of the drilling fluid. When the density of the drilling fluid in the wellbore cannot balance the formation pressure, the natural gas in the formation will invade the wellbore, which is called gas invasion. The gas rises rapidly to the wellhead in the wellbore. If the amount of gas invasion is large, it will further cause well kicks or even blowout accidents. Usually, gas invasion can be controlled by increasing the density of the drilling fluid, but it is easy to cause the pressure of the drilling fluid dynamic column to exceed the formation loss pressure, causing well leakage, which seriously affects the safety and efficiency of the drilling operation. Therefore, it is urgent to explore efficient methods to prevent gas invasion.

[0003] The existing technology usually adds plugging materials of appropriate types and particle size distribution to the drilling fluid to form a dense pressure-bearing plugging layer on the surface of the wellbore, which is expected to slow down the invasion of gas into the wellbore. The plugging materials usually use the synergistic effect of rigid particle bridging, elastic particle filling, and fiber material reinforcement to form a network, which can form a dense pressure-bearing plugging layer, thereby improving the leak prevention and plugging effect. Among them, the particle size distribution of the bridging particles has a great influence on the pressure bearing capacity of the plugging layer. At present, the more mature bridging plugging criteria for pores or cracks include the 1 / 3 bridging criterion, D 90 However, the above theories and methods mainly focus on plugging cracks to prevent drilling fluid from leaking into the formation, while plugging cracks to prevent natural gas in the formation from invading the wellbore is the opposite process. The effect and applicability of drilling fluids prepared by existing design methods in plugging cracks to prevent gas invasion are still unclear. The prior art has not yet established a refined design method for plugging agents suitable for drilling fluids to plug cracks to prevent gas invasion, resulting in a lack of theoretical basis for the current technical countermeasures for drilling fluids against gas invasion in fractured formations, which affects the drilling safety and efficiency of fractured formations containing natural gas. Summary of the invention

[0004] The purpose of the present invention is to provide a design method for bridging particle grading, a plugging agent for plugging cracks and preventing gas invasion, and applications thereof. The present invention reasonably designs the particle size grading of bridging particles in the plugging agent, and the prepared plugging agent and drilling fluid can effectively prevent gas invasion in plugged cracks, and have higher safety performance and work efficiency when used for drilling in fractured formations containing natural gas.

[0005] In order to achieve the purpose of the present invention, the present invention provides the following technical solutions:

[0006] A design method for bridging particle gradation comprises the following steps:

[0007] The maximum diameter and minimum diameter of the bridging particles are determined according to the size of the cracks to be plugged, wherein the maximum diameter of the bridging particles is 0.9 to 1.1 times the maximum opening of the cracks to be plugged, and the minimum diameter is 0.4 to 0.6 times the average opening of the cracks to be plugged;

[0008] According to the maximum diameter and the minimum diameter of the bridging particles, the particle size grade of the bridging particles is divided by the compensation method, and the particle size grade is ≥4;

[0009] The volume percentage of bridging particles of each particle size grade is obtained according to formula I:

[0010]

[0011] In Formula I, is the volume proportion of the bridging particles of the i-th particle size grade relative to all bridging particles, %; D i90 D is the maximum diameter in the i-th particle size range, mm; i10 is the minimum diameter in the i-th particle size range, mm; D L and D s are the maximum and minimum diameters of the bridging particles in all particle size grades, mm; η is the distribution modulus, which is 0.3 or 0.4;

[0012] The mass proportion of each particle size grade of the bridging particles is obtained according to formula II:

[0013]

[0014] In Formula II, C i is the mass proportion of the bridging particles of the i-th particle size grade relative to all bridging particles, %; C m is the mass proportion of the bridging particles with the largest diameter, %; is the volume proportion of bridging particles of the i-th particle size grade relative to all bridging particles, %; is the volume proportion of the bridging particles with the largest diameter, %.

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

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

[0017] Preferably, the blocking material comprises a bridging material, an elastic material and fibers.

[0018] Preferably, the bridging material comprises 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 use of the plugging agent for plugging cracks and preventing gas intrusion described in the above technical solution in drilling fluid.

[0022] Preferably, the mass of the plugging agent for plugging cracks to prevent gas intrusion accounts for 10-16% of the total mass of the drilling fluid.

[0023] The present invention provides a design method for grading of bridging particles, and a plugging agent for plugging cracks and preventing gas intrusion prepared by the bridging particles is obtained by the design method, which comprises 50-80% of bridging particles and 20-50% of plugging materials by mass fraction. The plugging agent provided by the present invention is applied to drilling fluid, and can form a plugging layer with high pressure bearing capacity in plugging cracks, effectively preventing gas in the formation from invading the wellbore, and avoiding underground accidents such as gas intrusion and well kick. DETAILED DESCRIPTION

[0024] The present invention provides a design method for bridging particle gradation, comprising the following steps:

[0025] The maximum diameter and minimum diameter of the bridging particles are determined according to the size of the cracks to be plugged, wherein the maximum diameter of the bridging particles is 0.9 to 1.1 times the maximum opening of the cracks to be plugged, and the minimum diameter is 0.4 to 0.6 times the average opening of the cracks to be plugged;

[0026] According to the maximum diameter and the minimum diameter of the bridging particles, the particle size grade of the bridging particles is divided by the compensation method, and the particle size grade is ≥4;

[0027] The volume percentage of bridging particles of each particle size grade is obtained according to formula I:

[0028]

[0029] In Formula I, is the volume proportion of the bridging particles of the i-th particle size grade relative to all bridging particles, %; D i90 D is the maximum diameter in the i-th particle size range, mm; i10 is the minimum diameter in the i-th particle size range, mm; D L and D s are the maximum and minimum diameters of the bridging particles in all particle size grades, mm; η is the distribution modulus, which is 0.3 or 0.4;

[0030] The mass proportion of each particle size grade of the bridging particles is obtained according to formula II:

[0031]

[0032] In Formula II, C i is the mass proportion of the bridging particles of the i-th particle size grade relative to all bridging particles, %; C m is the mass proportion of the bridging particles with the largest diameter, %; is the volume proportion of bridging particles of the i-th particle size grade relative to all bridging particles, %; is the volume proportion of the bridging particles with the largest diameter, %.

[0033] In the present invention, the particle size grades of the bridging particles are divided by arithmetic difference method according to the maximum diameter and the minimum diameter of the bridging particles, and the particle size grade is ≥4, and in a specific embodiment, it can be 4 or 6.

[0034] In the present invention, there is no special limitation on the maximum opening and average opening of the cracks to be sealed. In a specific embodiment, it can be 1-5 mm; the average opening can be 0.75-4.5 mm; the maximum diameter of the bridging particles is 0.9-1.1 times the maximum opening of the cracks to be sealed, and the minimum diameter is 0.4-0.6 times the average opening of the cracks to be sealed.

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

[0036] Assume that there are n components of plugging materials in the plugging slurry formula, 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 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 enlarging or reducing the boundary value of the particle size of some materials in the system, the particle system that originally exists in the form of discrete distribution or cross distribution can be transformed into a continuous distribution system.

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

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

[0041] In the present invention, the plugging agent for sealing cracks and preventing gas intrusion includes 50-80% bridging particles, and in a specific embodiment, it can be 53.5%, 55%, 60%, 70% or 75; the bridging particles include calcium carbonate and / or hydroxyapatite, and in a specific embodiment, it can be calcium carbonate.

[0042] In the present invention, the plugging agent for sealing cracks and preventing gas intrusion includes 20-50% of plugging materials; the plugging materials include bridging materials, elastic materials and fibers; the bridging materials include walnut shells and / or olive shells; the present invention has no special restrictions on the parameters of the bridging material. Preferably, the elastic material includes graphite and / or rubber; the present invention has no special restrictions on the type of the fiber, and in a specific embodiment it can be polyester fiber and / or polypropylene fiber.

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

[0044] The present invention has no special limitation on the preparation method of the plugging agent for plugging cracks and preventing gas intrusion, and conventional mixing can be used.

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

[0046] In the present invention, the mass of the plugging agent for plugging cracks to prevent gas intrusion accounts for 10-16% of the total mass of the drilling fluid. In a specific embodiment of the present invention, it can be 11%, 13% or 15%.

[0047] To further illustrate the present invention, a design method for bridging particle grading, a plugging agent for plugging cracks and preventing gas intrusion, and applications thereof provided by the present invention are described in detail below in conjunction with embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0048] Example 1

[0049] Calcium carbonate, graphite and polyester fiber are weighed in a mass ratio of 60:10:1, and mixed to obtain a plugging agent for plugging cracks and preventing gas intrusion; wherein, the maximum diameter of calcium carbonate is 1 times the maximum opening of the formation crack, and the minimum diameter is 0.5 times the average opening of the crack; its particle size grading is designed according to formula I and formula II, and the distribution modulus η is 0.3. Through calculation, for 1×0.5mm cracks, 4 particle size grades are designed, and the particle size ratio of calcium carbonate is 15-30 mesh, 80-200 mesh, 400-600 mesh, and 800-1000 mesh, and the mass ratio is 19:27:38:16;

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

[0051] Example 2

[0052] Calcium carbonate, graphite, walnut shell and polyester fiber are weighed in a mass ratio of 53.5:15:10:1, and mixed to obtain a plugging agent; wherein, the maximum diameter of calcium carbonate is 0.9 times the maximum opening of the formation fracture, and the minimum diameter is 0.4 times the average opening of the fracture. Its particle size grading is designed according to formula I, and the distribution modulus η is 0.4. Through calculation, for 1×0.5mm fractures, 4 particle size grades are designed, and the particle size ratio of calcium carbonate is 15-20 mesh, 50-200 mesh, 200-400 mesh, 600-800 mesh, and the mass ratio is 21:31:35:13;

[0053] The particle size ratio for 2×1mm crack opening is 10-20 mesh, 50-100 mesh, 200-400 mesh, and 400-800 mesh, and the mass ratio is 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 plugging agent; wherein the maximum diameter of calcium carbonate is 0.9 times the maximum opening of the formation fracture, and the minimum diameter is 0.6 times the average opening of the fracture; its particle size grading is designed according to formula I and formula II, and the distribution modulus η is 0.4. Through calculation, for 1×0.5mm cracks, 4 particle size grades are designed, and the particle size ratio of calcium carbonate is 18-30 mesh, 50-100 mesh, 200-500 mesh, and 500-800 mesh, with a mass ratio of 17:31:32:20;

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

[0057] Example 4

[0058] Hydroxyapatite, olive shell, rubber and polypropylene fiber are weighed in a mass ratio of 50:9:8:1 and mixed to obtain a plugging agent; wherein the maximum diameter of calcium carbonate is 1.1 times the maximum opening of the formation fracture, and the minimum diameter is 0.4 times the average opening of the fracture; its particle size grading is designed according to formula I and formula II, and the distribution modulus η is 0.4. Through calculation, for 1×0.5mm fractures, 4 particle size grades are designed, and the particle size ratio of calcium carbonate is 14-20 mesh, 50-100 mesh, 200-400 mesh, and 400-800 mesh, with a mass ratio of 26:31:33:10;

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

[0060] Example 5

[0061] Calcium carbonate, graphite, walnut shell and polypropylene fiber are weighed in a mass ratio of 55:13:9:1, and mixed to obtain a plugging agent; wherein, the maximum diameter of calcium carbonate is 0.9 times the maximum opening of the formation fracture, and the minimum diameter is 0.4 times the average opening of the fracture; its particle size grading is designed according to formula I and formula II, and the distribution modulus η is 0.4. Through calculation, for 1×0.5mm cracks, 4 particle size grades are designed, and the particle size ratio of calcium carbonate is 18-30 mesh, 50-100 mesh, 200-400 mesh, 400-800 mesh, and the mass ratio is 14:29:38:19;

[0062] The particle size ratio for 2×1mm crack opening is 10-30 mesh, 50-100 mesh, 100-200 mesh, and 200-400 mesh, and the mass ratio is 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 shell, nut shell powder and polypropylene fiber are weighed in a mass ratio of 50:20:10:1 and mixed to obtain a plugging agent; wherein, the maximum diameter of the calcium carbonate is 0.9 times the maximum opening of the formation fracture, and the minimum diameter is 0.6 times the average opening of the fracture. The particle size gradation is designed according to the 1 / 3 criterion currently used in the petroleum industry, and the distribution modulus η is 0.4.

[0069] Test Case

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

[0071] Table 1 Test results of the plugging pressure bearing capacity of plugging agents of Examples 1 to 5 and Comparative Examples 1 to 3 for cracks with different openings

[0072]

[0073]

[0074] It can be seen from the results in Table 1 that the drilling fluids provided in Examples 1 to 5 of the present invention can form effective plugging layers in cracks of different openings, and have obvious plugging and pressure-bearing effects against reverse gas invasion. The pressure-bearing capacity of Example 1 for plugging cracks of two openings is above 2MPa, while Comparative Example 1, which has the same plugging agent type and concentration as Example 1, adopts the traditional 2 / 3 bridging criterion to design the particle size grading of rigid bridging particles, and the pressure-bearing capacity for the two types of cracks is only 1.6MPa and 1.51MPa. Therefore, by comparison, it can be seen that the design method of the plugging agent provided by the present invention can ensure a better particle size grading, improve the pressure-bearing plugging effect of the crack plugging layer against gas invasion, and the pressure-bearing capacity is increased by more than 35% compared with the plugging agent designed under the guidance of the 2 / 3 criterion.

[0075] The bearing capacity of Example 2 for plugging two cracks is 3.15MPa and 2.91MPa respectively, and the bearing capacity is excellent. Comparative Example 2, which has the same plugging agent type and concentration as Example 2, adopts the traditional D90 criterion to design the particle size grading of rigid bridging particles, and the bearing capacity for the two cracks is 2.49MPa and 2.32MPa. The bearing capacity of Example 2 is more than 25% higher than that of the plugging agent designed under the guidance of the D90 criterion.

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

[0077] Examples 4 and 5 have excellent pressure-bearing plugging capabilities, and the maximum pressure-bearing capacity of Example 5 for two types of cracks can reach 3.27MPa and 3.08MPa. Comparative Example 3 is a plugging agent used in the eastern Bohai gas field to prevent drilling fluid leakage. It has been confirmed in field applications that it has a good effect of plugging cracks to prevent drilling fluid leakage, but its plugging pressure-bearing capacity for gas invasion in two types of cracks is 2.37MPa and 2.14MPa respectively; and among the embodiments provided by the present invention, the best Example 5 is compared with Comparative Example 3, and the pressure-bearing plugging capacity for the two types of cracks is increased by 38% and 43.9% respectively, which effectively improves the effect of drilling fluid plugging cracks to prevent gas invasion, and confirms the excellent effect of plugging cracks and preventing gas invasion provided by the plugging agent design method provided by the present invention.

[0078] Although the above embodiment describes the present invention in detail, it is only a part of the embodiments of the present invention, not all of the embodiments. People can also obtain other embodiments based on this embodiment without creativity, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A design method for bridging particle gradation, characterized in that: The following steps are involved: The maximum diameter and minimum diameter of the bridging particles are determined according to the size of the cracks to be plugged, wherein the maximum diameter of the bridging particles is 0.9 to 1.1 times the maximum opening of the cracks to be plugged, and the minimum diameter is 0.4 to 0.6 times the average opening of the cracks to be plugged; According to the maximum diameter and the minimum diameter of the bridging particles, the particle size grade of the bridging particles is divided by the compensation method, and the particle size grade is ≥4; The volume percentage of bridging particles of each particle size grade is obtained according to formula I: In Formula I, is the volume proportion of bridging particles of the i-th particle size grade relative to all bridging particles, %; D i90 D is the maximum diameter in the i-th particle size range, mm; i10 is the minimum diameter in the i-th particle size range, mm; D L and D s are the maximum and minimum diameters of the bridging particles in all particle size grades, mm; η is the distribution modulus, which is 0.3 or 0.4; The mass proportion of each particle size grade of the bridging particles is obtained according to formula II: In Formula II, C i is the mass proportion of the bridging particles of the i-th particle size grade relative to all bridging particles, %; C m is the mass proportion of the bridging particles with the largest diameter, %; is the volume proportion of bridging particles of the i-th particle size grade relative to all bridging particles, %; is the volume proportion of the bridging particles with the largest diameter, %.

2. A plugging agent for plugging cracks to prevent gas intrusion, characterized in that: Calculated by mass fraction, it comprises 50-80% of bridging particles and 20-50% of plugging materials; the gradation of the bridging particles is obtained by the design method described in claim 1.

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

4. The plugging agent for plugging cracks and preventing gas intrusion according to claim 2, characterized in that: The blocking material includes a bridging material, an elastic material and fibers.

5. The plugging agent for plugging cracks and preventing gas intrusion according to claim 4, characterized in that: The bridging material comprises walnut shells and / or olive shells.

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

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

8. Use of the plugging agent for plugging cracks and preventing gas intrusion according to any one of claims 2 to 7 in drilling fluid.

9. The use according to claim 8, characterized in that: The mass of the plugging agent for plugging cracks and preventing gas invasion accounts for 10-16% of the total mass of the drilling fluid.

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