Foam scrubbing agent optimization method based on foam friction characteristic analysis

Abstract

The invention relates to the technical field of shale gas well foam scrubbing agent optimization, in particular to a foam scrubbing agent optimization method based on foam friction characteristic analysis. Based on a mechanical equilibrium principle, foam size parameters and elastic mechanical characteristics are comprehensively considered, and an analysis model of the contact distance between the foam and the wall surface is established; the influence of factors such as bubble separation pressure, fluid dynamic film thickness and bubble speed is comprehensively considered, and a foam resistance prediction model is established; based on a single foam and single-layer foam structure model, a shape characteristic and stress analysis model of the three-dimensional foam system is established, and a pressure gradient model is obtained. And obtaining bubble data through an experiment, substituting the bubble data into the pressure gradient model to obtain pressure drop data, and sorting the pressure drop data to screen the foam scrubbing agent. According to the method, the bubbles of the foam scrubbing agent are analyzed more comprehensively by combining the microscopic friction mechanical characteristics of the foam, meanwhile, the friction force of the foam scrubbing agent under different conditions is analyzed, and a pressure gradient model reflecting the actual situation is established.

Description

Technical Field

[0001] The invention relates to the technical field of shale gas well foaming agent optimization, and in particular to a foaming agent optimization method based on foam friction characteristic analysis. Background Art

[0002] Shale gas wells often face the problem of wellbore liquid accumulation. As an important means to solve the problem of wellbore liquid accumulation, foam drainage technology faces the problem of low foam drainage efficiency during actual construction. This is because when the foam flows in the oil pipe, it will be affected by the wall friction or wall slip effect, so that the pressure driving the foam flow at the bottom of the well is consumed by the resistance along the oil pipe, resulting in the inability to carry the wellbore liquid out of the wellbore. Therefore, it is of great significance to carry out the analysis of the friction characteristics of foam flow resistance for the optimization design of foam drainage work.

[0003] The velocity of a simple liquid flowing near a solid smooth wall is usually consistent with the velocity at the boundary. Due to the wall slip effect, velocity mismatch is often observed in complex fluids such as foam. The presence of surfactant molecules makes it difficult to predict the friction characteristics of foam walls. When they are adsorbed on the gas-liquid interface and the wall of the foam flow channel, they will affect the van der Waals or electrostatic surface interaction. The interaction between surface forces and fluid dynamics determines the wall friction. Therefore, surfactants can greatly affect the fluid dynamics behavior of the gas-liquid interface.

[0004] Existing research on foam flow friction is mainly based on indoor wellbore models. By testing the macroscopic wellbore pressure drop performance and analyzing the friction loss along the way, the influence of the microscopic friction mechanical properties of foam is ignored. Summary of the invention

[0005] In view of the above problems, the present invention provides a foam removal agent optimization method based on foam friction characteristic analysis.

[0006] A foaming agent optimization method based on foam friction characteristic analysis, comprising:

[0007] In a container containing a simulated formation water solution, bubbles are generated by a microfluidic device;

[0008] Acquire bubble data through resistivity detection device and high-speed camera;

[0009] Substitute the bubble data into the pressure gradient model obtained by shear stress to obtain the pressure drop data, and sort the pressure drop data to screen the foaming agent.

[0010] Furthermore, the bubble data includes: moving speed, average gas volume fraction and shear force.

[0011] Furthermore, bubbles are generated by a microfluidic device, including: generating nitrogen bubbles at the bottom of the container by the microfluidic device and releasing them, and preparing single bubbles, single-layer bubbles or foam systems by controlling the openings through which the bubbles enter.

[0012] Furthermore, bubble data is obtained through a resistivity detection device and a high-speed camera, including: immersing an inclined transparent plexiglass plate in a container containing a simulated formation water solution, and bubbles flow upward along the plexiglass under the action of buoyancy. The resistivity detection device and the high-speed camera are used to test the bubble movement speed, gas average volume fraction and shear force parameters.

[0013] Furthermore, the pressure gradient model obtained by shear stress includes:

[0014] Based on the principle of mechanical balance, a single bubble and wall contact characteristic analysis model is established to calculate the contact film thickness.

[0015] Calculate the Bond number based on the dimensionless characteristic parameters affected by surface tension;

[0016] According to the contact film thickness and Bond number, the calculation model of friction force under flow conditions and rigid conditions is established, and the friction force is calculated;

[0017] Establish a calculation model for the wall contact area of ​​the foam system and calculate the number of bubbles;

[0018] According to the friction force and the number of bubbles, the shear stress of the wall is obtained through the relationship between the friction force of the foam system in contact with the wall and the shear stress applied to the wall;

[0019] According to the relationship between the wall slip velocity and the wall shear stress, as well as the slip wall boundary conditions, the pressure gradient model can be obtained by integrating the wall shear stress.

[0020] Furthermore, based on the principle of mechanical equilibrium, a single bubble and wall contact characteristic analysis model is established to calculate the contact film thickness, including:

[0021] A contact film is maintained between the contact area and the wall, and the capillary force F on a single bubble is c for:

[0022]

[0023] In the formula, F c is the capillary force; γ is the surface tension; l is the diameter of the contact area between a single bubble and the wall; d is the bubble diameter;

[0024] The normal component of the buoyancy force on the bubble is F b for:

[0025]

[0026] Where ρ is the liquid density, g is the gravitational acceleration, d is the bubble diameter, and α is the wall inclination angle;

[0027] Among them, based on the balance principle between the normal component of buoyancy and capillary force, the diameter l of the contact area between a single bubble and the wall is obtained, which is calculated as follows:

[0028]

[0029] Where α is the wall inclination angle, d is the bubble diameter, and a is the capillary length;

[0030] The van der Waals force acting on the bubble is calculated as follows:

[0031]

[0032] In the formula, F v is the van der Waals force; h is the contact film thickness; d is the bubble diameter; A e is the effective Hammark constant, A e The calculation formula is:

[0033]

[0034] In the formula, A l and A s are the effective Hamark constants for the liquid and solid phases, respectively;

[0035] The electrostatic repulsion force between the plane and the bubble is calculated as follows:

[0036] F e (h)=πdw(h) (6)

[0037] In the formula, F e is the electrostatic repulsion between the foam and the wall, d is the bubble diameter; w(h) is the interaction potential energy between the bubble and the wall at a distance h, and the calculation formula is as follows:

[0038]

[0039] Where c is the electrolyte concentration; h is the contact film thickness; Ψ is the surface point; κ is the reciprocal of the Debye length;

[0040] According to the principle of mechanical equilibrium, the combined force of electrostatic repulsion and van der Waals force is equal to the capillary force, and the contact film thickness h is calculated.

[0041] Furthermore, the Bond number is calculated based on the dimensionless characteristic parameters affected by the surface tension, including:

[0042] The Bond number Bo is calculated as follows:

[0043] Bo=(d / 2a) 2 (8)

[0044] Where d is the bubble diameter; a is the capillary length, and the calculation formula is as follows:

[0045]

[0046] Where γ is the surface tension, ρ is the liquid density, and g is the acceleration due to gravity.

[0047] Furthermore, according to the contact film thickness and Bond number, a calculation model of friction force under flow conditions and rigid conditions is established, and the friction force is calculated, including:

[0048] When the Bond number Bo < 0.01 and the bubble velocity ≠ liquid velocity are satisfied at the same time, the calculation formula of the friction force is as follows:

[0049]

[0050] Where V is the bubble velocity, η is the dynamic viscosity, d is the bubble diameter, and h is the contact film thickness.

[0051] Furthermore, according to the contact film thickness and Bond number, a calculation model of friction force under flow conditions and rigid conditions is established to calculate the friction force, which also includes:

[0052] When the Bond number Bo < 0.01 and the bubble velocity = liquid velocity are satisfied at the same time, the friction force is calculated as follows:

[0053]

[0054] Where η is the dynamic viscosity; d is the foam diameter; h is the contact film thickness.

[0055] Furthermore, according to the contact film thickness and Bond number, a calculation model of friction force under flow conditions and rigid conditions is established to calculate the friction force, which also includes:

[0056] When the Bond number Bo ≥ 0.01, the Bond number Bo < capillary length, and the bubble velocity ≠ liquid velocity are satisfied at the same time, the calculation formula of the friction force is as follows:

[0057]

[0058] Where η is the dynamic viscosity; d is the foam diameter; C(F) is the coefficient related to the drag force, and its calculation formula is as follows:

[0059]

[0060] Furthermore, according to the contact film thickness and Bond number, a calculation model of friction force under flow conditions and rigid conditions is established to calculate the friction force, which also includes:

[0061] When the Bond number Bo ≥ 0.01, the Bond number Bo < capillary length, and the bubble velocity = liquid velocity are satisfied at the same time, the calculation formula of the friction force is as follows:

[0062]

[0063] Where η is the dynamic viscosity; d is the foam diameter; C(F) is the coefficient related to the drag force, and its calculation formula is as follows:

[0064]

[0065] Furthermore, according to the contact film thickness and Bond number, a calculation model of friction force under flow conditions and rigid conditions is established to calculate the friction force, which also includes:

[0066] When the Bond number Bo < 1, the Bond number Bo ≥ the capillary length, and the bubble velocity ≠ the liquid velocity are satisfied at the same time, the calculation formula of the friction force is as follows:

[0067]

[0068] Where γ is the surface tension; α is the wall inclination angle; a is the capillary length; d is the bubble diameter; Ca is a dimensionless number related to the capillary force, which is calculated as follows:

[0069] Ca=ηV / γ(16)

[0070] Where η is the dynamic viscosity; V is the bubble velocity; γ is the surface tension.

[0071] Furthermore, according to the contact film thickness and Bond number, a calculation model of friction force under flow conditions and rigid conditions is established to calculate the friction force, which also includes:

[0072] When the Bond number Bo < 1, the Bond number Bo ≥ capillary length, and the bubble velocity = liquid velocity are satisfied at the same time, the calculation formula of the friction force is as follows:

[0073]

[0074] Where γ is the surface tension; α is the wall inclination angle; a is the capillary length; d is the bubble diameter; Ca is a dimensionless number related to the capillary force, which is calculated as follows:

[0075] Ca=ηV / γ(16)

[0076] Where η is the dynamic viscosity; V is the bubble velocity; γ is the surface tension.

[0077] Furthermore, a calculation model for the wall contact area of ​​the foam system is established to calculate the number of bubbles and the foam osmotic pressure, including:

[0078] The number of bubbles is calculated as follows:

[0079]

[0080] Where Φ is the dimensionless number of bubbles in contact with the wall per unit area, N is the number of bubbles on the wall contact area A; A is the contact area between the foam and the wall; d is the bubble diameter;

[0081] Where A is calculated by the following relationship:

[0082]

[0083] Where H is the foam thickness, is the average volume fraction of the gas phase.

[0084] Furthermore, a calculation model for the wall contact area of ​​the foam system is established to calculate the number of bubbles and the foam osmotic pressure, including:

[0085] The foam osmotic pressure is calculated as follows:

[0086]

[0087] Where, П is the foam osmotic pressure, d is the bubble diameter; F c is the capillary force;

[0088] Among them, F c The calculation is as follows:

[0089]

[0090] In the formula, F c is the capillary force; l is the contact area diameter of the foam system on the wall; P c is the capillary pressure.

[0091] Furthermore, according to the friction force and the number of bubbles, the shear stress of the wall is obtained through the relationship between the friction force of the foam system in contact with the wall and the shear stress applied to the wall, including:

[0092] The friction force of the foam system in contact with the wall is related to the shear stress applied to the wall, and the relationship is:

[0093]

[0094] In the formula, τ w is the shear stress of the wall; F is the friction force; 4Φ / πd 2 is the number of bubbles per unit area on the wall.

[0095] The expression of the shear stress on the wall is:

[0096]

[0097] In the formula, C l is an empirical constant; γ is the surface tension; d is the bubble diameter; П is the osmotic pressure; P c is the capillary pressure; Ca is the capillary number.

[0098] Furthermore, according to the relationship between the wall slip velocity and the wall shear stress, as well as the slip wall boundary conditions, the pressure gradient model can be obtained by integrating the wall shear stress, including:

[0099] The relationship between the wall slip velocity and the wall shear stress is:

[0100]

[0101] In the formula, u silp is the wall slip velocity; τ w is the shear stress on the wall; D is the pipe diameter; β c is the wall slip coefficient, and its calculation formula is:

[0102]

[0103] In the formula, R is a function related to the expansion ratio, σ is the surface tension, μ is the liquid viscosity, D is the pipe diameter, ε is the expansion ratio of the foam, and R is a function related to the expansion ratio, and its expression is:

[0104]

[0105] Where al is the film length of each bubble in contact with the tube wall; ε is the expansion ratio of the foam.

[0106] Furthermore, according to the relationship between the wall slip velocity and the wall shear stress, as well as the slip wall boundary condition, the pressure gradient model can be obtained by integrating the wall shear stress, which also includes:

[0107] Based on the slip wall boundary condition, the pressure gradient model can be obtained by integrating the shear stress on the wall, including:

[0108]

[0109] P is the pressure integral value, P0 is the initial pressure boundary condition, R is a function related to the expansion ratio, Q is the volume flow rate, π is a constant, ε is the expansion ratio of the foam, n and k are the power law viscosity characteristic coefficients, u slip is the wall slip velocity, L is the wall contact length, and x is the length integral value;

[0110] Where Q is the volume flow rate, and its calculation formula is:

[0111]

[0112] R is a function related to the expansion ratio, Q is the volume flow rate, π is a constant, u slip is the wall slip velocity, n and k are the characteristic coefficients of power-law viscosity, P is the pressure integral value, x is the unit length, and dP / dx is the pressure gradient.

[0113] Furthermore, the pressure drop data is sorted and the foaming agent is screened, including:

[0114] Sort the pressure drop data by size and select the foaming agent with the smallest pressure drop data.

[0115] Smaller wellbore pressure drop has better foam drainage and fluid carrying effect.

[0116] The present invention has at least the following beneficial effects:

[0117] The present invention can analyze the friction characteristics of the surfactant on the foam flow process and the wellbore pressure drop characteristics, so as to optimize the appropriate foam drainage treatment agent; and can also use the constructed indoor experimental method to calibrate the prediction results of the friction characteristics of the foam.

[0118] Other features and advantages of the present invention will be described in the following description, and partly become obvious from the description, or be understood by implementing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0119] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0120] Figure 1 The figure is a flow chart of a preferred method according to an embodiment of the present invention. DETAILED DESCRIPTION

[0121] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution 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. Obviously, 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.

[0122] Existing research on foam flow friction is mainly based on indoor wellbore models. By testing the macroscopic wellbore pressure drop performance and analyzing the friction loss along the way, the influence of the microscopic friction mechanical properties of foam is ignored.

[0123] The present invention is based on the principle of mechanical equilibrium, comprehensively considers the foam size parameters and elastic mechanical properties, and establishes an analysis model of the contact distance between the foam and the wall; comprehensively considers the influence of factors such as bubble separation pressure, fluid dynamics film thickness and bubble speed, and establishes a foam resistance prediction model; based on a single foam and a single-layer foam structure model, the shape characteristics and force analysis model of the three-dimensional foam system are derived; based on microscopic image processing means, an indoor simulation evaluation method for foam friction characteristics is established; based on a volume equilibrium power-law viscosity model, the characteristic parameters related to foam flow friction resistance are comprehensively considered, and a pressure gradient model of foam carrying liquid is established.

[0124] like Figure 1 As shown, the present invention provides a foaming agent optimization method based on foam friction characteristics analysis, the method comprising:

[0125] S101, generating bubbles in a container containing a simulated formation water solution by using a microfluidic device;

[0126] S102, obtaining bubble data through a resistivity detection device and a high-speed camera;

[0127] S103, substituting the bubble data into the pressure gradient model obtained by shear stress to obtain pressure drop data, and sorting the pressure drop data to select the foaming agent.

[0128] When implementing it, it is implemented through the following steps:

[0129] 1. Taking into account the influence of factors such as capillary force, van der Waals and electrostatic repulsion, an analytical model for the contact characteristics between a single bubble and the wall is established based on the principle of mechanical equilibrium.

[0130] For horizontal wells, the bubble is pressed against the tubing wall by the buoyancy component perpendicular to the plane. Its shape is no longer spherical, but flattened on a circular contact area with a diameter of l. Assuming that the contact wall is wetted so that a contact film is retained between the contact area and the wall, the capillary force on a single bubble is:

[0131]

[0132] In the formula, F c is the capillary force; γ is the surface tension; l is the diameter of the contact area between a single bubble and the wall; d is the bubble diameter.

[0133] The normal component of the buoyancy force on the bubble is:

[0134]

[0135] Where, ρ is the liquid density, g is the gravitational acceleration, d is the bubble diameter, and α is the wall inclination angle;

[0136] Based on the balance principle between the normal component of buoyancy and capillary force, the diameter of the contact area between a single bubble and the wall can be obtained.

[0137]

[0138] In the formula, α is the wall inclination angle, d is the bubble diameter, and a is the capillary length, which are changed to am;

[0139] The thickness of the contact film is determined by the balance between capillary forces and long-range forces, which tend to push the bubble away from the plane due to van der Waals and electrostatic repulsion. Assuming the distance between the bubble and the wall is h, the van der Waals force acting on the bubble is calculated as follows:

[0140]

[0141] In the formula, F v is the van der Waals force; h is the contact film thickness; d is the bubble diameter; A e is the effective Hammark constant, which is calculated as follows:

[0142]

[0143] In the formula, A l and A s are the effective Hamark constants for the liquid and solid phases, respectively. The effective van der Waals interaction is repulsive. Since charged surfactant molecules are adsorbed on the solid surface or liquid-air interface, there is an additional electrostatic repulsion between the plane and the bubble, which is calculated as:

[0144] F e (h)=πdw(h) (6)

[0145] Where Fe is the electrostatic repulsion between the foam and the wall, d is the bubble diameter; w(h) is the interaction potential energy between two planes separated by a distance h, and the specific calculation formula is:

[0146]

[0147] Where c is the electrolyte concentration; h is the contact film thickness; Ψ is the surface point; κ is the reciprocal of the Debye length.

[0148] According to the principle of mechanical equilibrium, the combined force of electrostatic repulsion and van der Waals force is equal to the capillary force, and the contact film thickness can be calculated.

[0149] 2. Based on the dimensionless characteristic parameters affected by surface tension, the Bond number is calculated and the boundary conditions for the solution are determined.

[0150] The Bond number is defined as:

[0151] Bo=(d / 2a) 2 (8)

[0152] Where d is the bubble diameter; a is the capillary length, and the calculation formula is:

[0153]

[0154] Where γ is the surface tension, ρ is the liquid density, and g is the acceleration due to gravity.

[0155] 3. Based on the assumption that separation pressure is dominant, the calculation model of friction force under flow conditions and rigid conditions can be obtained.

[0156] Under this condition, the Bond number is much less than 1.

[0157] ① Flow conditions

[0158] The presence of surfactants has a strong influence on the stress boundary conditions and, in turn, the flow profile of the foam. In the mobile case, the interface is tangentially stress-free, as in a pure liquid, and the bubble then performs a sliding motion along the plane, which can be achieved by high surfactant concentrations well above the critical micelle concentration.

[0159] Assuming that the thickness of the contact film is fixed and much smaller than the bubble diameter, the friction force under this condition is calculated as:

[0160]

[0161] Where V is the bubble velocity, η is the dynamic viscosity, d is the bubble diameter, and h is the contact film thickness.

[0162] ② Rigidity conditions

[0163] In the rigid case, the interface can withstand tangential shear stress and exhibit incompressible rigid characteristics, but can deform. When the liquid velocity at the interface is equal to the bubble velocity, the bubble slides with a no-slip boundary condition. If the interface velocity is equal to the wall velocity, the bubble rolls.

[0164] Under rigid conditions, the friction force calculation formula is:

[0165]

[0166] Where η is the dynamic viscosity; d is the foam diameter; h is the contact film thickness.

[0167] 4. Based on the assumption that fluid dynamics dominates, a calculation model for friction under flow conditions and rigid conditions can be obtained.

[0168] ① For tiny bubbles, the Bond number is much smaller than the capillary length, and the bubble remains quasi-spherical. The contact film thickness is determined by the balance between the buoyancy component perpendicular to the wall and the fluid dynamic lift. The contact film thickness increases with velocity or is equivalent to resistance, and the friction resistance under flow conditions can be obtained:

[0169]

[0170] The friction force expression under rigid conditions is:

[0171]

[0172] Where η is the dynamic viscosity; d is the foam diameter; C(F) is the coefficient related to the drag force, and its calculation formula is as follows:

[0173]

[0174] Where ρ is the liquid density; g is the acceleration due to gravity; a is the capillary length; d is the bubble diameter; and F is the friction force.

[0175] ② When the bubble diameter is large, greater than the capillary length and less than 1, the problem is similar to the movement of small bubbles in a capillary filled with liquid. The calculation formula for friction under the moving interface condition is:

[0176]

[0177] In the formula, γ is the surface tension; α is the wall inclination angle; a m is the capillary length; d is the bubble diameter; Ca is the dimensionless number related to the capillary force, and its expression is:

[0178] Ca=ηV / γ(16)

[0179] Where η is the dynamic viscosity; V is the bubble velocity; γ is the surface tension.

[0180] In the case of a rigid interface with rolling bubble motion, the formula has a smaller exponent than the moving case:

[0181]

[0182] 5. Based on the single bubble model, the mechanical balance between long-range force and capillary force is comprehensively considered, and a calculation model for the wall contact area of ​​the foam system can be obtained.

[0183] The foam system exerts an upward force on the wall, which is caused by the sum of the buoyancy forces of all the bubbles below the plate. Assume that the average volume fraction of the gas phase is The contact area between the foam and the wall is A, and the buoyancy calculation formula is:

[0184]

[0185] H is the thickness of the foam, and the component of this force acting on the wall per unit area is equal to the osmotic pressure on the bubble. Therefore, similar to the case of a single bubble, the bubble flattens in an area of ​​diameter l and is kept apart from the contact film, and the steady-state thickness of the contact film is determined by the balance between long-range forces and capillary forces:

[0186]

[0187] In the formula, F c is the capillary force; l is the contact area diameter of the foam system on the wall; P c is the capillary pressure.

[0188] Capillary pressure is the pressure difference between the gas phase and the liquid phase. Therefore, the normal force per unit area exerted by the layer of bubbles in contact with the wall is related to the osmotic pressure as follows:

[0189]

[0190] Where, П is the foam osmotic pressure, d is the bubble diameter; F c is the capillary force; Φ is the dimensionless number of bubbles in contact with the wall per unit area, and its calculation formula is as follows:

[0191]

[0192] Where N is the number of bubbles on the wall contact area A; A is the contact area between the foam and the wall; d is the bubble diameter.

[0193] From the above relationship, the relationship between the size of the contact membrane and the osmotic pressure and capillary pressure can be derived:

[0194]

[0195] 6. Based on the contact model between the foam system and the wall, a calculation model for the friction force acting on the foam system is obtained.

[0196] The friction force of the foam system in contact with the wall is related to the shear stress applied to the wall, and the relationship is:

[0197]

[0198] In the formula, τ w is the shear stress of the wall; F is the friction force; 4Φ / πd 2 is the number of bubbles per unit area on the wall.

[0199] The expression of the shear stress on the wall is:

[0200]

[0201] In the formula, C l is an empirical constant; γ is the surface tension; d is the bubble diameter; П is the osmotic pressure; P c is the capillary pressure; Ca is the capillary number.

[0202] 7. Based on microscopic image processing, an indoor simulation evaluation method for foam friction characteristics is established.

[0203] A transparent plexiglass plate is used to simulate the wall of the wellbore. The plate can simulate an inclination angle of 0-90°. The inclined plexiglass plate is immersed in a container containing a simulated formation water solution, and nitrogen bubbles are generated by a microfluidic device. Bubbles are generated and released at the bottom of the container. By controlling the openings through which the bubbles enter, single bubbles, single-layer bubbles or foam systems are prepared. Under the action of buoyancy, the bubbles flow upward along the wall. The movement of the bubbles is observed using a high-speed camera placed above the plane. The resistivity detection device and the high-speed camera are used to test the movement speed of the bubbles, the average volume fraction of the gas, the shear force and other parameters.

[0204] 8. Based on the relationship between foam sliding velocity and shear stress, a calculation model for the characteristic parameters related to foam friction is obtained.

[0205] The relationship between the wall slip velocity and the wall shear stress is:

[0206]

[0207] In the formula, u silp is the wall slip velocity; τ w is the shear stress on the wall; D is the pipe diameter; β c is the wall slip coefficient, and its calculation formula is:

[0208]

[0209] In the formula, R is a function related to the expansion ratio, σ is the surface tension, μ is the liquid viscosity, D is the pipe diameter, ε is the expansion ratio of the foam, and R is a function related to the expansion ratio, and its expression is:

[0210]

[0211] Where a is the film length of each bubble in contact with the tube wall; ε is the expansion ratio of the foam.

[0212] 9. Based on the volume equilibrium power law viscosity model, the foam pipe flow equation is derived, and the pressure gradient model representing the foam-liquid friction and resistance loss is obtained.

[0213] The slip boundary condition means that the velocity of the fluid on the solid wall (on the boundary) is different from the velocity of the solid wall, that is, a slip velocity is generated.

[0214] Based on the slip wall boundary condition, the calculation equation of the pressure gradient model can be obtained by integrating the shear stress on the wall:

[0215]

[0216] P is the pressure integral value, P0 is the initial pressure boundary condition, R is a function related to the expansion ratio, Q is the volume flow rate, π is a constant, ε is the expansion ratio of the foam, n and k are the power law viscosity characteristic coefficients, u slip is the wall slip velocity, L is the wall contact length, and x is the length integral value

[0217] Where Q is the volume flow rate, and its calculation formula is:

[0218]

[0219] R is a function related to the expansion ratio, Q is the volume flow rate, π is a constant, u slip is the wall slip velocity, n and k are the power law viscosity characteristic coefficients, P is the pressure integral value, x is the unit length, dP / dx is the pressure gradient

[0220] In order to enable those skilled in the art to better understand the present invention, the principle of the present invention is described as follows in conjunction with the accompanying drawings:

[0221] Assuming that nonionic polyoxyethylene ether, cationic organic amine derivative salts and zwitterionic betaine foaming agents are used to simulate foaming under the same test concentration conditions, the basic parameters of the foaming agent performance simulation are shown in Table 1. The wall friction force is obtained through indoor simulation experiments and prediction model calculations, and is substituted into the pressure gradient model to calculate the pressure gradient reduction effect of the three surfactants. The calculation results of the wellbore pressure drop of different surfactants are shown in Table 2.

[0222] Table 1

[0223]

[0224]

[0225] Table 2

[0226] Surfactants <![CDATA[Pressure drop per unit length / kPa·m -1 > Polyoxyethylene ether 84 Organic amine derivative salts 102 Betaines 57

[0227] It can be seen from Table 2 that at the same usage concentration, the zwitterionic surfactant betaine has a smaller wellbore pressure drop, so it has a better foaming and liquid carrying effect.

[0228] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0229] ① It can predict the friction force of foam flow in the wellbore, and thus deduce the flow friction resistance of foam in the wellbore;

[0230] ② The relationship function between surfactant and foam flow friction can be used to guide the optimization design and optimization evaluation of surfactants;

[0231] ③ It helps to predict the pressure distribution gradient in the wellbore under foam flow conditions, so as to evaluate the effect of foam drainage.

[0232] Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent substitutions for some of the technical features therein; and these modifications or substitutions do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A foaming agent optimization method based on foam friction characteristics analysis, characterized in that: include: In a container containing a simulated formation water solution, bubbles are generated by a microfluidic device; Acquire bubble data through resistivity detection device and high-speed camera; Substitute the bubble data into the pressure gradient model obtained by shear stress to obtain the pressure drop data, and sort the pressure drop data to screen the foaming agent.

2. A foaming agent optimization method based on foam friction characteristics analysis according to claim 1, characterized in that: The bubble data include: moving speed, average gas volume fraction and shear force.

3. The foaming agent optimization method based on foam friction characteristic analysis according to claim 1, characterized in that: Generating bubbles by a microfluidic device comprises: generating and releasing nitrogen bubbles at the bottom of a container by a microfluidic device, and preparing a single bubble, a single-layer bubble or a foam system by controlling the opening through which the bubbles enter.

4. A foaming agent optimization method based on foam friction characteristics analysis according to claim 3, characterized in that: The bubble data is obtained by using a resistivity detection device and a high-speed camera, including: immersing an inclined transparent organic glass plate in a container containing a simulated formation water solution, and the bubbles flow upward along the organic glass under the action of buoyancy. The movement speed of the bubbles, the average volume fraction of the gas and the shear force parameters are tested by using a resistivity detection device and a high-speed camera.

5. The foaming agent optimization method based on foam friction characteristic analysis according to claim 1, characterized in that: Pressure gradient models derived from shear stress include: Based on the principle of mechanical balance, a single bubble and wall contact characteristic analysis model is established to calculate the contact film thickness. Calculate the Bond number based on the dimensionless characteristic parameters affected by surface tension; According to the contact film thickness and Bond number, the calculation model of friction force under flow conditions and rigid conditions is established, and the friction force is calculated; Establish a calculation model for the wall contact area of ​​the foam system and calculate the number of bubbles; According to the friction force and the number of bubbles, the shear stress of the wall is obtained through the relationship between the friction force of the foam system in contact with the wall and the shear stress applied to the wall; According to the relationship between the wall slip velocity and the wall shear stress, as well as the slip wall boundary conditions, the pressure gradient model can be obtained by integrating the wall shear stress.

6. A foaming agent optimization method based on foam friction characteristic analysis according to claim 5, characterized in that: Based on the principle of mechanical balance, a single bubble and wall contact characteristic analysis model is established to calculate the contact film thickness, including: A contact film is maintained between the contact area and the wall, and the capillary force F on a single bubble is c for: In the formula, F c is the capillary force; γ is the surface tension; l is the diameter of the contact area between a single bubble and the wall; d is the bubble diameter; The normal component of the buoyancy force on the bubble is F b for: Where ρ is the liquid density, g is the gravitational acceleration, d is the bubble diameter, and α is the wall inclination angle; Among them, based on the balance principle between the normal component of buoyancy and capillary force, the diameter l of the contact area between a single bubble and the wall is obtained, which is calculated as follows: Where α is the wall inclination angle, d is the bubble diameter, and a is the capillary length; The van der Waals force acting on the bubble is calculated as follows: In the formula, F v is the van der Waals force; h is the contact film thickness; d is the bubble diameter; A e is the effective Hammark constant, A e The calculation formula is: In the formula, A l and A s are the effective Hamark constants for the liquid and solid phases, respectively; The electrostatic repulsion force between the plane and the bubble is calculated as follows: F e (h)=πdw(h)(6) In the formula, F e is the electrostatic repulsion between the foam and the wall, d is the bubble diameter; w(h) is the interaction potential energy between the bubble and the wall at a distance h, and the calculation formula is as follows: Where c is the electrolyte concentration; h is the contact film thickness; Ψ is the surface point; κ is the reciprocal of the Debye length; According to the principle of mechanical equilibrium, the combined force of electrostatic repulsion and van der Waals force is equal to the capillary force, and the contact film thickness h is calculated.

7. The foaming agent optimization method based on foam friction characteristic analysis according to claim 5, characterized in that: Calculate the Bond number based on dimensionless characteristic parameters affected by surface tension, including: The Bond number Bo is calculated as follows: <h2 style=";text-align:left;direction:ltr">Bo = (d / 2a)<h2 style=";text-align:left;direction:ltr"> 2 <h2 style=";text-align:left;direction:ltr"> (8) Where d is the bubble diameter; a is the capillary length, and the calculation formula is as follows: Where γ is the surface tension, ρ is the liquid density, and g is the acceleration due to gravity.

8. The foam-removing agent optimization method based on foam friction characteristic analysis according to claim 5, characterized in that: According to the contact film thickness and Bond number, the calculation model of friction force under flow conditions and rigid conditions is established, and the friction force is calculated, including: When the Bond number Bo < 0.01 and the bubble velocity ≠ liquid velocity are satisfied at the same time, the calculation formula of the friction force is as follows: Where V is the bubble velocity, η is the dynamic viscosity, d is the bubble diameter, and h is the contact film thickness.

9. The foam-removing agent optimization method based on foam friction characteristic analysis according to claim 5, characterized in that: According to the contact film thickness and Bond number, the calculation model of friction force under flow conditions and rigid conditions is established to calculate the friction force, including: When the Bond number Bo < 0.01 and the bubble velocity = liquid velocity are satisfied at the same time, the friction force is calculated as follows: Where η is the dynamic viscosity; d is the foam diameter; h is the contact film thickness.

10. The foaming agent optimization method based on foam friction characteristic analysis according to claim 5, characterized in that: According to the contact film thickness and Bond number, the calculation model of friction force under flow conditions and rigid conditions is established to calculate the friction force, including: When the Bond number Bo ≥ 0.01, the Bond number Bo < capillary length, and the bubble velocity ≠ liquid velocity are satisfied at the same time, the calculation formula of the friction force is as follows: Where η is the dynamic viscosity; d is the foam diameter; C(F) is the coefficient related to the drag force, and its calculation formula is as follows:

11. The foaming agent optimization method based on foam friction characteristic analysis according to claim 5, characterized in that: According to the contact film thickness and Bond number, the calculation model of friction force under flow conditions and rigid conditions is established to calculate the friction force, including: When the Bond number Bo ≥ 0.01, the Bond number Bo < capillary length, and the bubble velocity = liquid velocity are satisfied at the same time, the calculation formula of the friction force is as follows: Where η is the dynamic viscosity; d is the foam diameter; C(F) is the coefficient related to the drag force, and its calculation formula is as follows:

12. The foaming agent optimization method based on foam friction characteristic analysis according to claim 5, characterized in that: According to the contact film thickness and Bond number, the calculation model of friction force under flow conditions and rigid conditions is established to calculate the friction force, including: When the Bond number Bo < 1, the Bond number Bo ≥ the capillary length, and the bubble velocity ≠ the liquid velocity are satisfied at the same time, the calculation formula of the friction force is as follows: Where γ is the surface tension; α is the wall inclination angle; a is the capillary length; d is the bubble diameter; Ca is a dimensionless number related to the capillary force, which is calculated as follows: Ca=ηV / γ(16) Where η is the dynamic viscosity; V is the bubble velocity; γ is the surface tension.

13. The foaming agent optimization method based on foam friction characteristic analysis according to claim 5, characterized in that: According to the contact film thickness and Bond number, the calculation model of friction force under flow conditions and rigid conditions is established to calculate the friction force, including: When the Bond number Bo < 1, the Bond number Bo ≥ capillary length, and the bubble velocity = liquid velocity are satisfied at the same time, the calculation formula of the friction force is as follows: Where γ is the surface tension; α is the wall inclination angle; a is the capillary length; d is the bubble diameter; Ca is a dimensionless number related to the capillary force, which is calculated as follows: Ca=ηV / γ(16) Where η is the dynamic viscosity; V is the bubble velocity; γ is the surface tension.

14. The foaming agent optimization method based on foam friction characteristic analysis according to claim 5, characterized in that: A calculation model for the wall contact area of ​​the foam system is established to calculate the number of bubbles and the foam osmotic pressure, including: The number of bubbles is calculated as follows: Where Φ is the dimensionless number of bubbles in contact with the wall per unit area, N is the number of bubbles on the wall contact area A; A is the contact area between the foam and the wall; d is the bubble diameter; Where A is calculated by the following relationship: Where H is the foam thickness, is the average volume fraction of the gas phase.

15. The foaming agent optimization method based on foam friction characteristic analysis according to claim 14, characterized in that: A calculation model for the wall contact area of ​​the foam system is established to calculate the number of bubbles and the foam osmotic pressure, including: The foam osmotic pressure is calculated as follows: Where, П is the foam osmotic pressure, d is the bubble diameter; F c is the capillary force; where F c The calculation is as follows: In the formula, F c is the capillary force; l is the contact area diameter of the foam system on the wall; P c is the capillary pressure.

16. The foaming agent optimization method based on foam friction characteristic analysis according to claim 5, characterized in that: According to the friction and the number of bubbles, the shear stress of the wall is obtained through the relationship between the friction of the foam system in contact with the wall and the shear stress applied to the wall, including: The friction force of the foam system in contact with the wall is related to the shear stress applied to the wall, and the relationship is: In the formula, τ w is the shear stress of the wall; F is the friction force; 4Φ / πd 2 is the number of bubbles per unit area on the wall; The expression of the shear stress on the wall is: In the formula, C l is an empirical constant; γ is the surface tension; d is the bubble diameter; П is the osmotic pressure; P c is the capillary pressure; Ca is the capillary number.

17. The foaming agent optimization method based on foam friction characteristic analysis according to claim 5, characterized in that: According to the relationship between the wall slip velocity and the wall shear stress, as well as the slip wall boundary conditions, the pressure gradient model can be obtained by integrating the wall shear stress, including: The relationship between the wall slip velocity and the wall shear stress is: In the formula, u silp is the wall slip velocity; τ w is the shear stress on the wall; D is the pipe diameter; β c is the wall slip coefficient, and its calculation formula is: In the formula, R is a function related to the expansion ratio, σ is the surface tension, μ is the liquid viscosity, D is the pipe diameter, ε is the expansion ratio of the foam, and R is a function related to the expansion ratio, and its expression is: Where al is the film length of each bubble in contact with the tube wall; ε is the expansion ratio of the foam.

18. The foaming agent optimization method based on foam friction characteristic analysis according to claim 5, characterized in that: According to the relationship between the wall slip velocity and the wall shear stress, as well as the slip wall boundary conditions, the pressure gradient model can be obtained by integrating the wall shear stress, which also includes: Based on the slip wall boundary condition, the pressure gradient model can be obtained by integrating the shear stress on the wall, including: P is the pressure integral value, P0 is the initial pressure boundary condition, R is a function related to the expansion ratio, Q is the volume flow rate, π is a constant, ε is the expansion ratio of the foam, n and k are the power law viscosity characteristic coefficients, u slip is the wall slip velocity, L is the wall contact length, and x is the length integral value; Where Q is the volume flow rate, and its calculation formula is: R is a function related to the expansion ratio, Q is the volume flow rate, π is a constant, u slip is the wall slip velocity, n and k are the characteristic coefficients of power-law viscosity, P is the pressure integral value, x is the unit length, and dP / dx is the pressure gradient.

19. The foaming agent optimization method based on foam friction characteristic analysis according to claim 1, characterized in that: Sort the pressure drop data by size to filter the foaming agents, including: Sort the pressure drop data by size and select the foaming agent with the smallest pressure drop data.

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