Numerical simulation method for dynamic migration and blockage of mineral particles during CO2 injection

Abstract

The present invention discloses a numerical simulation method for the dynamic migration and blockage of mineral particles during CO2 injection. The method is specifically as follows: based on the inherent physical properties of mineral particles and fluid characteristics, a fluid dynamics model and a mineral particle migration model are established, wherein the mineral particle migration model includes an irregular discrete element collision model based on particle collision theory; mineral particles are allowed to enter pores using the differentiated shedding pattern of regular discrete element mineral particles, and the effects of fluid physical properties, mineral particle parameters, and the CO2 injection process into low-permeability sandstone are calculated and analyzed; the CO2 injection rate and injection pressure are adjusted to obtain the migration patterns of the injected CO2 and its detached weakly cemented irregular mineral particles in the branched pores and the blocking effect of the particles on the pores. The beneficial effect of the present invention is that a method for predicting the clogging efficiency of weakly cemented irregular mineral particles during CO2 geological storage is proposed, thereby guiding the CO2 injection process and achieving more efficient CO2 storage in low-permeability sandstone reservoirs.

Description

Technical Field

[0001] The present invention relates to the field of unconventional oil and gas exploration, and in particular to a method, device and storage device for numerical simulation of dynamic migration and blockage of mineral particles during CO2 injection. Background Art

[0002] Carrying out CO2 geological storage in low-permeability sandstone reservoirs is one of the effective ways to achieve CO2 capture, utilization and storage (CCUS). Its advantages are, on the one hand, reducing CO2 emissions, and on the other hand, increasing the recovery of oil / gas / heat and other resources.

[0003] During the continuous injection of CO2 into the absorption layer, the CO2 injection may be affected by mineral precipitation and shedding, fluid bypass, and particle migration. Existing research on particle migration technology includes the following: when water is injected into coal seams, particle migration can cause changes in coal reservoir permeability; the particle migration mechanism in porous media is related to the characteristics of the porous medium and the suspended particle fluid; and rock pore structure, particle size, and concentration are all important parameters affecting particle migration.

[0004] Previous studies on the mechanisms by which particle migration affects CO2 injection have been comprehensive, but none have addressed the impact of particle morphology on CO2 injection. In actual carbon storage, when supercritical CO2 is injected into low-permeability sandstone reservoirs, the dislodged weakly cemented particles vary in shape, creating more contact points. This alters the forces between particles, between particles and fluid, and between particles and the rock surface, leading to differences in the degree of pore and fracture blockage.

[0005] To solve the above problems, we can carry out simulations of the migration of irregular mineral particles in pores / fractures, adjust the physical properties of the injected fluid such as the CO2 injection rate and injection pressure, and then explore the migration patterns of the injected CO2 and its detached weakly cemented irregular mineral particles in the branched pores and the blocking effect of the particles on the pores, thereby guiding the CO2 injection process and achieving more efficient CO2 storage in low-permeability sandstone reservoirs.

[0006] At the same time, predecessors proposed a method to determine the mass flow rate of supercritical fluid, but did not discuss the influence of parameters such as mineral particle morphology on CO2 injection.

[0007] To simulate the migration of irregular mineral particles in pores / cracks, the technical difficulties are how to use computational fluid dynamics (CFD) technology to solve the CO2 injection process, how to use the discrete element method (DEM) to perform dynamic stress analysis of irregular particle systems, and how to establish an irregular discrete element fluid-solid coupling model. Summary of the Invention

[0008] In order to achieve more efficient CO2 storage in low-permeability sandstone reservoirs, the present invention provides a numerical simulation method for dynamic migration and blockage of mineral particles during CO2 injection, wherein the method specifically includes the following steps:

[0009] S1. Based on the inherent physical properties of mineral particles and fluid characteristics, a fluid dynamics model and a mineral particle transport model are established. The mineral particle transport model includes an irregular discrete element collision model based on particle collision theory.

[0010] S2. Using the particle collision form of irregular discrete element flow in the fluid dynamics physical model, the mineral particles are allowed to enter the pores using the differentiated shedding mode of regular discrete element mineral particles. The effects of fluid physical properties, mineral particle parameters, and the CO2 injection process on low-permeability sandstone are calculated and analyzed.

[0011] S3. Adjust the CO2 injection rate and injection pressure to obtain the migration law of the injected CO2 and its detached weakly cemented irregular mineral particles in the branch pores and the blocking effect of the particles on the pores.

[0012] The beneficial effects provided by the present invention are:

[0013] (1) When CO2 is continuously injected into the absorption layer, weakly cemented sandstone particles will fall off and may form particle accumulation. The discrete element fluid-solid coupling blockage model based on polymorphic mineral particles established in the present invention can reveal the quantitative relationship between CO2 physical properties, weakly cemented irregular particle parameters and injection blockage on this basis.

[0014] (2) The construction of the fluid dynamics model takes into account mineral particle parameters such as multi-level particle size, irregular morphology, rotation, and differentiated shedding patterns, as well as fluid physical properties such as CO2 injection rate and injection pressure, which is more consistent with the actual situation.

[0015] (3) Calculate and analyze the effects of fluid properties such as CO2 injection rate and injection pressure, as well as mineral particle concentration, rotation, density, gravity, shape, shedding pattern, size, migration velocity, and their effects on the CO2 injection process into low-permeability sandstone. This allows for dynamic prediction and visualization of the transient accumulation of weakly cemented irregular mineral particles in sandstone pores. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a flow chart of the method of the present invention;

[0017] Figure 2 This is a schematic diagram of the collision model of irregular mineral particles;

[0018] Figure 3 This is a schematic diagram of the model of collision, rotation and accumulation of irregular mineral particles;

[0019] Figure 4 It is a schematic diagram of the grid structure and grid plane;

[0020] Figure 5 is the schematic diagram of the SEM experiment after injection and the CT scan of the experimental sandstone;

[0021] Figure 6 This is the influence of mineral particle size and mineral particle velocity on micro-nano pore blockage under CO2 injection conditions. DETAILED DESCRIPTION

[0022] In order to make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0023] Please refer to Figure 1 , Figure 1 It is a flow chart of the method of the present invention.

[0024] The present invention provides a numerical simulation method for the dynamic migration and blockage of mineral particles during CO2 injection, which specifically adopts a fluid dynamics and irregular discrete element coupling method, including a fluid dynamics model and a mineral particle migration model established based on the Wiener-Stokes equations, wherein the mineral particle migration model includes an irregular discrete element collision model established based on particle collision theory.

[0025] Specifically, the method includes the following steps:

[0026] S1. Based on the inherent physical properties of mineral particles and fluid characteristics, a fluid dynamics model and a mineral particle transport model are established. The mineral particle transport model includes an irregular discrete element collision model based on particle collision theory.

[0027] S2. Using the particle collision form of irregular discrete element flow in the fluid dynamics physical model, the mineral particles are allowed to enter the pores using the differentiated shedding mode of regular discrete element mineral particles. The effects of fluid physical properties, mineral particle parameters, and the CO2 injection process on low-permeability sandstone are calculated and analyzed.

[0028] Please refer to Figure 2 , Figure 2 Figure 2 is a schematic diagram of the irregular mineral particle collision model. Step S2 employs a particle collision model based on an irregular discrete element flow model of a fluid dynamics model. Because mineral particles are irregular in shape, their collision model is more complex than that of circular particle collisions. The direction of motion of irregular particles after collision is also more difficult to capture. Furthermore, the forces acting on irregular particles remain unchanged, primarily including fluid resistance, pressure, gravity, and other non-contact forces.

[0029] The method uses discrete element particles to be randomly released into pores, where the pores are set as branched pores to ensure that the particles have sufficient collisions in the pores. The particle size and concentration can be changed. In the pores / fractures, the particles are stacked and cross-linked. The pressure, velocity, displacement, fluid velocity and migration process of each irregular mineral particle can be monitored and recorded in real time in the model (see Figure 3 , Figure 3 (Schematic diagram of the model of collision, rotation and accumulation of irregular mineral particles).

[0030] S3. Adjust the CO2 injection rate and injection pressure to obtain the migration law of the injected CO2 and its detached weakly cemented irregular mineral particles in the branch pores and the blocking effect of the particles on the pores.

[0031] As a more detailed description, steps S1 to S3 are as follows:

[0032] Step (1): Considering the inherent physical properties of mineral particles such as gravity and rotation of mineral particles and fluid properties, the model of steps (2) to (4) is established based on the inherent physical properties of mineral particles and fluid properties;

[0033] Step (2): Establish a fluid dynamics physical model based on the following theory;

[0034] The CO2 fluid flow is described based on the conservation of mass and momentum according to the Wiener-Stokes equations:

[0035]

[0036] Where ρ is the CO2 density, kg / m 3 ; is the CO2 injection rate, m / s; p is the static pressure, Pa; is the stress tensor; is the external force, N;

[0037] Step (3): Establish a mineral particle transport model based on the following theory;

[0038] The mineral particle migration model is based on the following equation. The stress state of the mineral particles under CO2 injection is:

[0039]

[0040] Where, is the mineral particle velocity, m / s; F D is the acceleration force (force / unit mass), N; is the drag force per unit mass, N; ρ s is the density of weakly cemented mineral particles, kg / m 3 ;

[0041] In the mineral particle transport model, the contact force of the irregular discrete unit is composed of linear elastic force and damping force. The energy dissipation in the linear spring damper model is viscous in nature. The normal damping coefficient C l It can be determined by matching the viscous energy dissipation with the inelastic collision energy dissipation, which in turn is determined by the coefficient of restitution;

[0042]

[0043] Among them, F l is the force at the contact point, N; K l is the contact stiffness, C l is the damping coefficient; s l is the contact normal overlap area, m2; is the time derivative of the contact normal overlap area; ζ is the damping ratio; m is the mass of the irregular discrete unit, kg;

[0044] The rotational force on the particle needs to be considered. In three-dimensional space, the force on the particle in the z direction can be described by the forces in the x and y directions:

[0045]

[0046]

[0047] Where ω is the angular velocity of weak cementation rotation, rad / s; u s,y and u y is the velocity of mineral particles and fluid in the Cartesian y direction, m / s; u s,x and u x is the velocity of mineral particles and fluid in the Cartesian x direction, m / s;

[0048] The rotation diameter of irregular mineral particles needs to be divided into different types according to the shape of the collision medium;

[0049]

[0050] Among them, D roll is the rolling diameter of irregular mineral particles, m; D s1 and D s2 is the rotation diameter of the contacting mineral particles, m; D sw is the rotation diameter of the mineral grain in contact with the boundary, m;

[0051] Step (4): The mineral particle transport model includes the irregular sandstone particle collision model;

[0052] The collision of circular particles is based on the traditional particle collision model, but the collision mode of irregular particles is different from the traditional particle collision model. The collision of irregular mineral particles adopts the optimized linear adhesion model of irregular shapes, and its adhesion force model is:

[0053]

[0054] Among them, F la is the normal adhesive contact force, N; δ a is the adhesion distance, m; r a is the ratio of adhesion stiffness to contact load stiffness;

[0055] Momentum exchange is the calculation of momentum transfer from continuous phase to discrete phase through the momentum change of irregular mineral particles.

[0056]

[0057] Where c is the friction coefficient; Δt is the time step; is the discrete unit mass flow rate, m3 / s;

[0058] Step (5): Using a particle collision method based on an irregular discrete element flow model of a fluid dynamics model, discrete element particles are randomly released into pores, where the pores are set as branched pores to ensure that the particles have sufficient collisions in the pores.

[0059] Step (6): In response to the accumulation and cross-linking of mineral particles in pores / fractures, the parameters and migration process of each irregular mineral particle in the model are monitored and recorded in real time. The migration direction of fluids and mineral particles entering the channel is random. The fluid flow mode is laminar, and the mineral particle tracking mode is transient tracking. The effects of fluid physical factors such as CO2 injection rate and injection pressure, mineral particle parameters, and the CO2 injection process on low-permeability sandstone are calculated and analyzed.

[0060] Step (7): By adjusting the surface CO2 injection rate and injection pressure and other injection fluid physical properties, the migration patterns of the injected CO2 and its detached weakly cemented irregular mineral particles in the branched pores and the blocking effect of the particles on the pores are explored. This will guide the CO2 injection process and achieve more efficient CO2 storage in low-permeability sandstone reservoirs.

[0061] It should be noted that in order to determine the migration path of supercritical CO2 and the size range of the detached sandstone particles, the present invention carries out supercritical CO2 injection physical simulation, selects the supercritical CO2 flow cross-section image in the sandstone sample through scanning electron microscope experimental analysis, and determines the migration path of supercritical CO2 based on the CT scan slices of the CO2 flow cross-section, and determines the size range of the detached sandstone particles based on the SEM results.

[0062] It should be noted that the present invention is based on the numerical simulation of irregular mineral particle migration under CO2 injection conditions, and calculates the influence of irregular sandstone particle shape and concentration, the influence of mineral particle density and fluid physical properties under CO2 injection conditions, the influence of mineral particle size and mineral particle velocity under CO2 injection conditions, the influence of sandstone particle rotation and fluid density under CO2 injection conditions, and the influence of mineral particle shedding pattern under CO2 injection conditions.

[0063] It should be noted that during the migration process, mineral particles do not move in a straight line, but rotate, collide and move randomly within the pores.

[0064] Taking into account the inherent physical properties of mineral particles such as mineral particle gravity and mineral particle rotation and fluid characteristics, the mineral particle concentration, density, velocity and shape are set to 5 types, and the mineral particle shedding mode is set to 5 types, and the above parameters can be adjusted and increased.

[0065] It should be noted that by establishing a fluid dynamics physical model, a mineral particle migration model, and a sandstone particle collision model, it is possible to simulate the migration of irregular mineral particles in pores / fractures, adjust the physical properties of the injected fluid such as the CO2 injection rate and injection pressure, and then explore the migration laws of the injected CO2 and its detached weakly cemented irregular mineral particles in the branched pores and the blocking effect of the particles on the pores, thereby guiding the CO2 injection process and achieving more efficient CO2 storage in low-permeability sandstone reservoirs.

[0066] It should be noted that the particle collision form using the irregular discrete element flow form based on the fluid dynamics model has a motion law that conforms to Newton's second law.

[0067] It should be noted that this method utilizes random release of irregular discrete elements into pores, where the pores are configured as branched pores to ensure sufficient particle collisions within the pores. Particle size and concentration can be varied. The release locations of the irregular discrete elements are based on the inlet surface, and the release method uses a differentiated shedding pattern. Therefore, the movement and direction of particles after entering the pores are random.

[0068] It should be noted that, in view of the stacking and cross-linking between mineral particles in pores / fractures, the real-time pressure, velocity, displacement, fluid velocity and migration process of each irregular mineral particle in the model are monitored and recorded.

[0069] It should be noted that in terms of pore model, physical parameters and grid characteristics, different grid fineness and accuracy are set and fluid calculation and monitoring are carried out (see Figure 4 , Figure 4(This is a schematic diagram of the grid structure and grid plane). At the same time, the channel is set to branch hole mode, and the grid is calculated independently to ensure that the calculation time and calculation accuracy are within the optimal range. Without considering the influence of temperature, the direction of gravity is the negative direction of y, which is -9.81m / s 2 , set the fluid injection mode to be divided into laminar mode and turbulent mode.

[0070] It should be noted that the calculation and analysis of fluid physical properties such as CO2 injection rate and injection pressure, as well as mineral particle concentration, rotation, density, gravity, shape, shedding pattern, size, migration velocity and their effects on the process of CO2 injection into low-permeability sandstone are necessary.

[0071] As an example, the physical parameters of irregular mineral particles and fluid are shown in Table 1:

[0072] Table 1 Basic parameters of irregular mineral particles and fluids

[0073]

[0074] During migration, over time, large particles form a large grid structure within the pores, and smaller mineral particles gradually fill the gaps between the larger particles, affecting subsequent CO2 injection. Changes in mineral particle size, concentration, and velocity alter both their migration patterns and blockage within pores and fractures. Mineral particles vary in shape and size, and even within the same shape, particles exhibit a size gradient, ensuring the randomness of the simulation state and the reliability of the results.

[0075] In order to determine the migration path of supercritical CO2 and the size range of the exfoliated sandstone particles, a TAW-2000 indoor CO2 injection simulation test machine was used to inject CO2 into the standard core of the Yanchang Formation sandstone. A physical simulation of supercritical CO2 injection was carried out, and CO2 overflowed the surface of the sandstone sample after the injection test. Through scanning electron microscopy experimental analysis, a cross-section image of supercritical CO2 in the sandstone sample was selected. Based on the CT scanning slice of the CO2 cross-section, the migration path of supercritical CO2 was determined. The cross-section of supercritical CO2 in the sample was selected for scanning electron microscopy observation experiment. It can be observed that some weakly cemented mineral particles or mineral particles will migrate with CO2. They may be traces of weakly cemented mineral particles or mineral particle migration. Scratches often appear near relatively large pores. The scratches are caused by the migration of sandstone particles, so the particle size of the detached material is larger than the maximum diameter of the scratches. Based on the SEM results, the maximum diameter of the scratches is 1-2μm, and the particle size of the detached sandstone particles is larger than 1-2μm (see Figure 5 , Figure 5 is a schematic diagram of the SEM experiment after injection and a CT scan of the experimental sandstone);

[0076] Based on the migration path of supercritical CO2 and the determination of the particle size range of detached sandstone particles, numerical simulation of irregular mineral particle migration under CO2 injection conditions was carried out. The influence of irregular sandstone particle shape and concentration, the influence of mineral particle density and fluid physical properties under CO2 injection conditions, the influence of mineral particle size and mineral particle velocity under CO2 injection conditions, the influence of sandstone particle rotation and fluid density under CO2 injection conditions, and the influence of mineral particle detachment mode under CO2 injection conditions were calculated.

[0077] Under CO2 injection conditions, different sizes of detached mineral particles will also have different effects on the blockage of sandstone pores / cracks. The average size of the mineral particles is set to 1 / 2, 1 / 3 and 1 / 5 of the pore diameter. When the total amount of injected CO2 and the mass of detached mineral particles are consistent, the continuous injection effect of CO2 is worst when the average size of the mineral particles is 1 / 3 of the pore diameter. The blockage of the mineral particles with an average size of 1 / 3 of the pore diameter is increased by 10.51% compared with that with an average size of 1 / 5 of the pore diameter. In terms of CO2 injection rate, assuming that the shedding rate of mineral particles is consistent, the injection rate is positively correlated with the stacking efficiency. In addition, in the actual injection process, under higher speed impact, the number of detached mineral particles will also be higher. Therefore, an increase in injection rate will lead to higher stacking efficiency. The blockage improvement ratio of the CO2 injection rate of 0.3m / s is 19.89% relative to the CO2 injection rate of 0.1m / s (see Figure 6 , Figure 6 This is the influence of mineral particle size and mineral particle velocity on micro-nano pore blockage under CO2 injection conditions).

[0078] The beneficial effects of the present invention are:

[0079] (1) When CO2 is continuously injected into the absorption layer, weakly cemented sandstone particles will fall off and may form particle accumulation. The discrete element fluid-solid coupling blockage model based on polymorphic mineral particles established in the present invention can reveal the quantitative relationship between CO2 physical properties, weakly cemented irregular particle parameters and injection blockage on this basis.

[0080] (2) The construction of the fluid dynamics model takes into account mineral particle parameters such as multi-level particle size, irregular morphology, rotation, and differentiated shedding patterns, as well as fluid physical properties such as CO2 injection rate and injection pressure, which is more consistent with the actual situation.

[0081] (3) Calculate and analyze the effects of fluid properties such as CO2 injection rate and injection pressure, as well as mineral particle concentration, rotation, density, gravity, shape, shedding pattern, size, migration velocity, and their effects on the CO2 injection process into low-permeability sandstone. This allows for dynamic prediction and visualization of the transient accumulation of weakly cemented irregular mineral particles in sandstone pores.

[0082] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A numerical simulation method for dynamic migration and blockage of mineral particles during CO2 injection, characterized by: The following steps are involved: S1. Based on the inherent physical properties of mineral particles and fluid characteristics, a fluid dynamics model and a mineral particle transport model are established. The mineral particle transport model includes an irregular discrete element collision model based on particle collision theory. S2. Using the particle collision form of irregular discrete element flow in the fluid dynamics physical model, the mineral particles are allowed to enter the pores using the differentiated shedding mode of regular discrete element mineral particles. The effects of fluid physical properties, mineral particle parameters, and the CO2 injection process on low-permeability sandstone are calculated and analyzed. S3. Adjust the CO2 injection rate and injection pressure to obtain the migration pattern of the injected CO2 and its detached weakly cemented irregular mineral particles in the branched pores and the blocking effect of the particles on the pores; The fluid dynamics physical model is described as follows based on the conservation of mass and momentum of the Wiener-Stokes equations: in, is the CO2 density, kg / m 3 ; is the CO2 injection rate, m / s; p is the static pressure, Pa; is the stress tensor; is the external force, N; The mineral particle migration model is as follows: the collision of round particles in the sandstone particle collision model is based on the traditional particle collision model, and the collision of irregular particles adopts the optimized linear adhesion model of irregular shapes, and its adhesion force model is: in, F la is the normal adhesive contact force, N; is the adhesion distance, m; r a is the ratio of adhesion stiffness to contact load stiffness; The mineral particle transport model is as follows: In the above formula, is the mineral particle velocity, m / s; F D is the acceleration force, N; is the drag force per unit mass, N; is the density of weakly cemented mineral particles, kg / m 3 .

2. The method for numerically simulating dynamic migration and blockage of mineral particles during CO2 injection according to claim 1, characterized in that: In step S2, when the mineral particles enter the pores, their migration direction is random, the fluid flow mode is laminar flow, and the mineral particle tracking mode is transient tracking.

3. The method for numerically simulating dynamic migration and blockage of mineral particles during CO2 injection according to claim 1, characterized in that: In step S2, during the migration of mineral particles into the pores, the concentration, density, speed and shape of the mineral particles are set to multiple types, and the mineral particle shedding mode is also set to multiple types, taking into account the inherent physical properties of the mineral particle gravity and the rotation of the mineral particles and the fluid characteristics.

4. The method for numerically simulating dynamic migration and blockage of mineral particles during CO2 injection according to claim 1, characterized in that: In step S2, the pores are set as random branch pores.

5. The method for numerically simulating dynamic migration and blockage of mineral particles during CO2 injection according to claim 1, characterized in that: In step S2, grids of different fineness and precision are set to perform fluid calculation and monitoring; the monitoring process is visualized.

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