A design method for plugging system in ultra-deep fractured formations based on force chain network structure

Abstract

The present invention discloses a design method for ultra-deep fractured formation plugging system based on force chain network structure, which belongs to the technical field of drilling and completion fluid loss control. The method comprises: respectively determining the critical state of each ultra-deep fractured formation well leakage control particle system, for a single ultra-deep fractured formation well leakage control particle system, obtaining the change process of the network density of the particle contact network in the fracture plugging layer with the loading pressure through a loading experiment, and taking the maximum value point of the network density before the shear failure of the plugging layer as the critical state; evaluating the fracture plugging layer force chain network of each ultra-deep fractured formation well leakage control particle system under the critical state condition according to the descending priority order of the Y-direction density of the force chain network, the average shear strength of the force chain network and the L3-type force ring structure density of the particle contact network, and determining its stability. The present invention can quickly and accurately compare the pressure bearing capacity of the formula, which can save time and reduce costs.

Description

Technical Field

[0001] The invention belongs to the technical field of drilling and completion fluid leakage control, and specifically relates to a design method for an ultra-deep fractured formation plugging system based on a force chain network structure. Background Art

[0002] With the exhaustion of conventional oil and gas and the continuous increase in proven reserves of deep and ultra-deep oil and gas, it has become inevitable to advance into the depths of the earth. However, due to the harsh formation conditions, the development of fractures in deep formations leads to a large loss of drilling fluid. Therefore, higher requirements are further put forward for deep well leakage control. The pressure bearing capacity of the plugging formula is the key to the control of working fluid loss and efficient drilling, which directly determines the success of the bridge plugging and the cost of subsequent drilling construction.

[0003] At present, the bridging plugging technology in the drilling process mainly forms a bridge section in a certain size of cracks by adding granular materials to the drilling and completion fluid, and then fills the subsequent cracks in turn, and finally forms a densely packed plugging layer to prevent the drilling fluid from leaking into the formation. However, the on-site plugging operation lacks underground vision, and it is impossible to know the plugging structure of different formulas and their pressure bearing capacity. The plugging experiment takes too long and is not conducive to on-site implementation.

[0004] In this regard, CN114550852A discloses a method for optimizing plugging granular materials based on force chain structural parameters, which optimizes rigid granular materials in accordance with the number of force chain network structures, the average shear strength of the force chain, and the priority of the force chain ratio, and selects a formula with a large number of force chain network structures, a strong average shear strength of the force chain, and a high force chain ratio. However, it was later discovered that there was a situation where the force chain ratio was larger but the pressure bearing capacity was insufficient, that is, judging the pressure bearing capacity of the formula according to the current force chain ratio had accuracy defects, and the method for obtaining the average shear strength of the force chain was difficult, complicated to operate, and had limitations. Summary of the invention

[0005] To solve at least one of the above problems, the present invention aims to provide a method for designing a plugging system for ultra-deep fractured formations based on a force chain network structure.

[0006] The present invention is achieved through the following technical solutions:

[0007] A method for designing a plugging system for ultra-deep fractured formations based on a force chain network structure comprises the following steps:

[0008] S1. Configure multiple ultra-deep fractured formation well loss control particle systems and determine the critical state of each ultra-deep fractured formation well loss control particle system respectively. For a single ultra-deep fractured formation well loss control particle system, obtain the change process of the network density of the particle contact network in the fracture plugging layer with the loading pressure through loading experiments, and take the maximum value point of the network density before the shear failure of the plugging layer as the critical state;

[0009] In this step, there are many specific methods for configuring multiple ultra-deep fractured formation lost circulation control particle systems. The configuration can be based on field experience, or a lost circulation control particle system that is in use or has been used in the field can be used.

[0010] Obtaining the network density of the particle contact network includes the following steps:

[0011] S11, obtaining the force chain network of the crack sealing layer;

[0012] In this step, the force chain network acquisition method includes but is not limited to photoelastic force chain characterization experiments and computer simulations;

[0013] S12, obtaining contact information of particle materials in the force chain network of the crack sealing layer, and generating a particle contact network;

[0014] S13, calculating the network density of the particle contact network, wherein the network density is calculated as follows:

[0015]

[0016] Where ρ is the network density; M is the number of edges actually connected in the particle contact network; N is the number of network nodes (number of particles);

[0017] S2. Evaluate the fracture plugging layer force chain network of each ultra-deep fractured formation well leakage control particle system under critical state conditions in descending order of priority of the density of the strong force chain network in the Y direction, the average shear strength of the strong force chain network, and the density of the L3 type force ring structure of the particle contact network, and determine its stability, that is, its pressure bearing capacity. The greater the density of the strong force chain network in the Y direction, the better the stability; the greater the average shear strength of the strong force chain network, the more stable it is; the greater the density of the L3 type force ring structure of the particle contact network, the more stable it is, and select the ultra-deep fractured formation well leakage control particle system with strong stability; the Y direction is the direction perpendicular to the fracture wall; the strong force chain is composed of a collection of particles whose contact force is greater than the average contact force;

[0018] Among them, the calculation formula for the density of the strong chain network in the Y direction is:

[0019]

[0020] Where, δ is the density of the force chain network in the Y direction; N(x1, x2) is the number of force chains with an angle with the Y axis in the range of x1, x2;

[0021] When the plugging layer balances the pressure difference between the wellbore and the formation, the stress is transmitted through the contact between the particles, and the unevenness of the particle surface causes the non-uniformity of the particle contact size and direction, resulting in the high anisotropy of the force chain network. The properties of the entire network are determined by the strong force chain network. With the increase of shear deformation, the contact force in the strong force chain network is significantly enhanced, which dominates and causes the macroscopic shear strength and anisotropic structure of the particle system to form. There is a positive correlation between the anisotropic characteristics of the strong force chain network and the macroscopic shear strength, so the greater the strong force chain density in the Y direction orthogonal to the pressure difference direction, the stronger the pressure-bearing stability. Therefore, the present invention adopts the Y-direction density of the strong force chain network to determine the pressure-bearing stability.

[0022] The average shear strength of the strong chain network is the product of the average contact force of the strong chain particles and the average friction coefficient of the strong chain particle surface. The friction between particles in the blocking layer is the force that prevents their relative movement due to mutual contact and extrusion, which affects the stability and fluidity of the particle system by preventing the relative movement of particles. Therefore, the friction between particles is actually the specific manifestation of the shear force between particles on the contact surface. When there is shear force between particles, due to the irregularity and interaction of the particle surface, friction will be generated on the contact surface to prevent the relative movement of the particles. Among them, the contact force level in the strong chain network is significantly stronger than that of other particles. Therefore, the relationship between the friction and shear force between particles in the strong chain network can be used to judge shear failure in the particle system.

[0023] L 3 The density of the force ring structure is the ratio of the number of closed triplets to the number of all triplets, where all triplets include closed triplets and open triplets.

[0024] L 3 The density of the force ring structure is a topological network formed by effective contact connections within the particle system. In the process of gradual compaction of the particle system, a force ring structure will gradually form. The most stable force ring structure is a triangle, which can provide good lateral support for the force chain. At the same time, the number of triangles is proportional to the evolution of the force chain, which plays an important role in maintaining the stability of the force chain and the pressure-bearing capacity of the sealing layer.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] At present, the screening and evaluation of plugging formulas are all based on indoor pressure leakage experiments to compare the pressure bearing capacity of the formulas, which is time-consuming and has a certain degree of randomness. The present invention can more accurately evaluate the pressure bearing performance of the plugging formula by comparing the Y-direction density of the strength chain of the particle sealing layer in the critical state, the shear strength of the strength chain and the clustering coefficient. This will undoubtedly save time, reduce costs and improve accuracy for screening formulas through a large number of complicated pressure leakage experiments with a certain degree of randomness.

[0027] Compared with the optimization method of plugging granular materials based on force chain structural parameters disclosed in CN114550852A, the increase in the number of strong chains and the proportion of strong chains is a passive process, similar to the greater the pressure bearing capacity of the formula, the better, and the evaluation method has no obvious advantages. The present invention replaces the proportion of strong chains with the density of the strong chain in the Y direction, and the difficulty of obtaining it in operation is not increased, and it is more scientific. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is the particle contact network diagram;

[0029] Figure 2 is the network density evolution diagram;

[0030] Figure 3 This is the network structure diagram of the strong chain;

[0031] Figure 4 5mm, 8mm, 10mm particles <G 2 >-FN fitting curve plot. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. The described embodiments are 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 creative work are within the scope of protection of the present invention.

[0033] Example 1

[0034] In this embodiment, LCC-D2 (10-20 mesh, D90 is 1 mm), LCC-D4 (20-30 mesh, D90 is 0.8 mm) and LCC-D8 (30-40 mesh, D90 is 0.5 mm) are used as granular materials. The above four materials are from Chengdu Dedao Industrial Co., Ltd., and the above materials are prepared into four formulas according to the mass ratios of 10:6:1, 6:3:1, 5:10:5 and 6:6:4 for screening. The specific parameters of each formula are shown in Table 1.

[0035] Table 1 Composition of rigid plugging materials in alternative plugging formulas

[0036] serial number Rigid plugging materials and their mass addition Recipe 1 10% LCC-D2 (10-20 mesh) + 6% LCC-D4 (20-30 mesh) + 1% LCC-D8 (30-40 mesh) Recipe 2 6% LCC-D2 (10-20 mesh) + 3% LCC-D4 (20-30 mesh) + 1% LCC-D4 (30-40 mesh) Recipe 3 5% LCC-D2 (10-20 mesh) + 10% LCC-D4 (20-30 mesh) + 5% LCC-D4 (30-40 mesh) Recipe 4 6% LCC-D2 (10-20 mesh) + 6% LCC-D4 (20-30 mesh) + 2% LCC-D4 (30-40 mesh)

[0037] The whole screening process will be described in detail below. To facilitate recording of the experimental process, the photoelastic experiment in this embodiment uses the prepared photoelastic particles of 1 mm, 0.8 mm and 0.5 mm for simulation. These sizes correspond to 10 times of D90 in LCC-D2, LCC-D4 and LCC-D8, i.e., the photoelastic particles with a magnification of 10 are used for the experiment. The specific screening process includes the following steps:

[0038] S1. Determine the critical state of each ultra-deep fractured formation loss control particle system respectively. For a single ultra-deep fractured formation loss control particle system, obtain the change process of the network density of the particle contact network in the fracture plugging layer with the loading pressure through loading experiments, and take the maximum value point of the network density before the shear failure of the plugging layer as the critical state.

[0039] The loading device used in this embodiment is a microscopic contact pressurizing device for drilling completion plugging materials disclosed in CN202021285127.X. It is placed in a circularly polarized light field formed by a polarizer and a 1 / 4 wave plate, and the force chain network structure formed by the photoelastic particles in a similar stress environment to the formation fracture can be observed. During the loading experiment, the formula is added to the microscopic contact pressurizing device of the plugging material, and the paving method selects a stable single-layer paving. The hydraulic pump pushes the pressure plate to squeeze the seam plate to simulate the crack closure stress. The shear load is applied to the plugging layer through the horizontal pressure plate to simulate the pressure difference between the wellbore and the formation. The pressure gradient is 0.5MPa. During the experiment, each increase of 0.5Mpa is called a loading process. After each loading process is completed, it is paused, and a high-definition camera is used to record the force chain evolution image (0°-45°-45°-0°) and the plugging layer particle structure image (90°-45°-45°-0°). Among them, there are four angles in brackets, and these degrees correspond to the angles of the analyzer, the second 1 / 4 wave plate, the first 1 / 4 wave plate and the polarizer from left to right.

[0040] In this embodiment, it is necessary to calculate the network density of the particle contact network at the end of each loading stage, wherein each calculation of the network density of the particle contact network includes the following steps:

[0041] S11. Use photoelastic force chain characterization experiment to obtain the force chain network of the crack sealing layer;

[0042] S12. Acquire contact information of granular materials in the force chain network of the crack sealing layer and generate a granular contact network.

[0043] The generation of complex networks requires the construction of an adjacency matrix that can express the contact relationship between particles, which requires recording the information of particles that contact each other.

[0044] Digital image processing technology is used to identify the edge of particles and extract position information from the collected images of the particle structure of the plugging layer. The specific operation method is to convert the bright field photoelastic image into a binary image and then perform morphological processing. First, the shadows in the particles are removed by filling (the shadows are scratches and uneven color blocks of the device on the original image. If they are not removed, the black in the particles will be enlarged when the image is corroded, affecting the subsequent particle identification). After corrosion and expansion, a binary image with incomplete particle information removed is obtained. The edge of the particle is detected by the Roberts operator. Finally, the Matlab built-in function imfindcircles is used to extract the circular information in the image including the particle radius and the coordinates of the center of the circle through the Hough transform method.

[0045] And the following formula is used to determine whether there is contact between particles:

[0046]

[0047] Among them, x i ,y i is the coordinate of the particle center, r i is the particle radius, and △ is the error between camera acquisition and image detection.

[0048] If there is contact, the centers of the circles connecting the particles form a particle contact network. The particle contact network formed at a certain moment in this example is as follows: Figure 1 shown.

[0049] The adjacency matrix is ​​generated by saving the serial number information of interconnected particles. The specific method is as follows: according to the number of particles n, an n-order matrix with a diagonal of 0 is established, and all edges are traversed to assign the edges with particle contact to 1 and otherwise to 0, thereby generating an adjacency matrix.

[0050] S13, calculating the network density of the particle contact network, wherein the network density is calculated as follows:

[0051]

[0052] Among them, ρ is the network density; M is the number of edges actually connected in the particle contact network; N is the number of network nodes (number of particles).

[0053] In this embodiment, the network density evolution process of the four formulations under different pressures is as follows Figure 2 As shown by Figure 2It can be seen that as the horizontal load of the plugging layer gradually increases, the network density also gradually increases, because the number of contacts between particles is increasing. When the limit state is reached, the slope of the network density curve will gradually decrease, and the maximum value before shear failure is the critical state of the particle plugging layer. From the calculation results, it can be seen that the critical state of formula 1 is at 0.0864, ​​the loading process is 10, the critical state of formula 2 is at 0.1012, the loading process is 11, the critical state of formula 4 is at 0.7677, the loading process is 8, and the critical state of formula 3 is at 0.0472, the loading process is 13.

[0054] S2. Evaluate the fracture plugging layer force chain network of each ultra-deep fractured formation well leakage control particle system under the corresponding critical state conditions according to the descending priority order of the density of the force chain network in the Y direction, the average shear strength of the force chain network, and the density of the L3 type force ring structure of the particle contact network, and determine its stability, that is, its pressure bearing capacity. Among them, the greater the density of the force chain network in the Y direction, the better the stability; the greater the average shear strength of the force chain network, the more stable it is; the greater the density of the L3 type force ring structure of the particle contact network, the more stable it is. Select the ultra-deep fractured formation well leakage control particle system with strong stability; the Y direction is the direction perpendicular to the fracture wall;

[0055] S21. Calculate the density of the strong chain network in the Y direction under the critical state;

[0056] The distribution of the force chain network direction mainly observes the proportion of the force chains in the vertical seam direction to all the force chains. The ratio of the force chains in the direction [315°, 45°]∪[135°, 225°] to all the force chains is taken, that is, the density of the force chain network in the Y direction in this embodiment, and the calculation formula is:

[0057]

[0058] Where, δ is the density of the force chain network in the Y direction; N(x1, x2) is the number of force chains with an angle with the Y axis in the range of x1, x2;

[0059] After calculation, the density of the strong chain network in the Y direction of formula 3 under the critical state is 0.25, the density of the strong chain network in the Y direction of formula 4 under the critical state is 0.35, the density of the strong chain network in the Y direction of formula 1 under the critical state is 0.35, and the density of the strong chain network in the Y direction of formula 2 under the critical state is 0.35. According to the relationship between the sizes of the strong chain densities in the y direction, formula 3 is excluded. The density of the strong chain network in the Y direction of formulas 1, 2 and 4 is equal, and further judgment is needed.

[0060] S22. Calculate the average shear strength of the force chain network under critical conditions;

[0061] The average shear strength of the force chain network is defined as the average product of the average contact force of the force chain particles and the average friction coefficient on the surface of the force chain particles after the plugging layer particle system reaches the critical state and before shear failure.

[0062] To obtain the average shear strength of the force chain network in the plugging layer, it is necessary to identify and extract the force chain network. First, the extracted particle edges are covered in the force chain evolution image (0°-45°-45°-0°), and the internal force chain evolution image of the particle edge is calculated for each particle. <G 2 > size, combined with the team's current research results "Mesoscopic mechanical mechanism of structural instability of crack plugging layer based on force chain network representation", <G 2 >As the threshold of the strong force chain of the particle system, and establishes the particle contact force and <G 2 >, so we can calculate the <G 2 >Get the contact force of each particle. When the contact force F between particles is greater than the average contact force F a (i.e., a single particle <G 2 >Larger than particle system <G 2 >), the particles are considered to be in a strong chain, and the strong chain network structure is extracted as follows: Figure 3 shown.

[0063] The average shear strength of the force chain network is the peak value of the product of the average contact force of the force chain particles and the average friction coefficient of the particle surface. <G 2 > and <G 2 >-F N Fit the curve to obtain Figure 4 , where the method for obtaining the particle friction coefficient in the strong chain network is to place the particle material in the loading device according to the number ( Figure 1 ) The friction coefficient of all particles is measured. After the strong chain network is identified and extracted, the friction coefficient of the particles in the strong chain network is searched according to the particle number and the average value is taken. The average friction coefficient measurement results of the particles of the three formulations are 0.24, 0.24 and 0.27 respectively. The contact area between particles is extracted by digital imaging technology. The specific operation is similar to the above process and will not be repeated here. The average contact area between particles in the strong chain network is 4.7mm 2 , 5mm 2 and 6.4mm 2 .

[0064] The average shear strength of the strong chain network under the critical state of Formula 4 is 40.8MPa, the average shear strength of the strong chain network under the critical state of Formula 1 is 45.3MPa, and the average shear strength of the strong chain network under the critical state of Formula 2 is 45.3MPa. The three groups of formulas exclude Formula 4 from the average shear strength of the strong chain network, but the average shear strength of the strong chain network of the formulas with particle size ratio 1 and particle size ratio 2 are equal, which needs further judgment.

[0065] S23, calculate L at critical state 3 Density of force ring structure

[0066] L 3 The density of the force ring structure is the ratio of the number of closed triplets to the number of all triplets, where all triplets include closed triplets and open triplets;

[0067] After the particle edges are identified and extracted, the particles that are in contact with each other are connected to form a contact network. At this time, the particle shape, surface contact properties and contact force are ignored. The particles in contact are represented as an edge, and the center of mass of the particles is represented as a node. Different complex networks indicate different contact states between particles. The particles are numbered according to their relative positions and saved in the form of particle pairs. The particle contact network is input into Matlab to calculate L 3 Density of the force ring structure.

[0068] L of recipe 1 3 The structural density of the force ring is 0.32.

[0069] Formula 2 L 3 The density of the force ring structure is 0.25.

[0070] From the results, it can be seen that the density of the L3 force ring structure of Formula 2 is smaller than that of Formula 1. When the number of large particles increases, it makes a great contribution to the stability of the particle contact structure. Formula 1 is the best choice.

[0071] In addition, in order to verify the invention, the density of the Y direction of the strong chain network in the critical state, the average shear strength of the strong chain network and L 3 In order to verify the accuracy of the pressure bearing capacity determined by the density of the force ring structure, this example carried out an indoor plugging test on the above four formulas. In the pressure plugging verification experiment, 2% GT-HS (medium coarse) + 3% GT-HS (fine) + 1% GT-HS (coarse) fiber materials were uniformly added, and the drilling fluid was a water-based drilling fluid. The experiment determined that the pressure bearing capacity of formula 3 was 5.8MPa, the pressure bearing capacity of formula 4 was 9.8MPa, the pressure bearing capacity of formula 2 was 10MPa, and the pressure bearing capacity of formula 1 was 15MPa. The formula screened by this method has a higher pressure bearing capacity.

[0072] Comparative Example 1

[0073] The implementation process of this comparative example is the same as that of the above embodiment. Two formulas are configured with a plugging formula mass ratio of 5:10:5 (Formula 3) and 6:6:2 (Formula 4). The changes in the proportion of strong chains (the proportion of strong chains to all force chains) and the density of the strong chain network in the Y direction during loading are calculated respectively. The specific results are shown in Table 2.

[0074] Table 2 Statistics of the proportion of strong chains and the density of the strong chain network in the Y direction during loading

[0075]

[0076] It can be seen from the above table that at different loading stages, the size relationship of the proportion of strong chains in the two formulas is different, and the density of the strong chain network in the Y direction of the two is also different.

[0077] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the embodiments of the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for designing a plugging system for ultra-deep fractured formations based on a force chain network structure, characterized in that: The following steps are involved: S1. Configure multiple ultra-deep fractured formation well loss control particle systems and determine the critical state of each ultra-deep fractured formation well loss control particle system respectively. For a single ultra-deep fractured formation well loss control particle system, obtain the change process of the network density of the particle contact network in the fracture plugging layer with the loading pressure through loading experiments, and take the maximum value point of the network density before the shear failure of the plugging layer as the critical state; The network density is calculated as follows: Where ρ is the network density; M is the number of edges actually connected in the particle contact network; N is the number of network nodes; S2. Evaluate the fracture plugging layer force chain network of each ultra-deep fractured formation well leakage control particle system under critical state conditions in descending order of priority of the force chain network density in the Y direction, the average shear strength of the force chain network, and the density of the L3 type force ring structure of the particle contact network, and determine its stability. The greater the density of the force chain network in the Y direction, the better the stability; the greater the average shear strength of the force chain network, the more stable it is; the greater the density of the L3 type force ring structure of the particle contact network, the more stable it is. Select the ultra-deep fractured formation well leakage control particle system with strong stability; the Y direction is the direction perpendicular to the fracture wall; Among them, the calculation formula of the Y-direction density of the strong chain network is: Where, δ is the density of the strong chain network in the Y direction; N(x1, x2) is the number of strong chains with an angle with the Y direction in the range of x1, x2; The average shear strength of the strength chain network is the product of the average contact force of the strength chain particles and the average friction coefficient of the surface of the strength chain particles; The L3-type force ring structure density is the ratio of the number of closed triplets to the number of all triplets, wherein all triplets include closed triplets and open triplets.

2. The method for designing a plugging system for ultra-deep fractured formations based on a force chain network structure according to claim 1, characterized in that: Obtaining the network density of the particle contact network includes the following steps: S11, obtaining the force chain network of the crack sealing layer; S12, obtaining contact information of particle materials in the force chain network of the crack sealing layer, and generating a particle contact network; S13. Calculate the network density of the particle contact network.

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