A characteristic research method based on the dynamic model of cuttings transportation in long horizontal wells

Abstract

The present invention proposes a characteristic research method based on the dynamic model of cuttings transportation in long horizontal wells, and uses the dynamic model of cuttings transportation in long horizontal wells to simulate the dynamic transportation of cuttings, and calculates relevant parameters to study the dynamic transportation characteristics of cuttings. The dynamic model is a two-layer model, which is taken from a microelement section of the wellbore, and the cuttings are divided into a lower cuttings bed and an upper suspended layer in the wellbore; according to the laws of conservation of mass and momentum, and combined with the cuttings stress characteristics of the cuttings bed and the suspended layer, the continuity equation and motion equation of the cuttings bed and the suspended layer are calculated. The present invention establishes a two-layer cuttings transportation dynamic model for long horizontal wells that takes into account the actual wellbore trajectory, fluid pressure drop, and diffusion of suspended layer particles, uses the finite difference method to solve the model, simulates the dynamic transportation of cuttings under different working conditions, and then studies the dynamic transportation characteristics of cuttings, optimizes the relevant parameters of wellbore cleaning, and guides the wellbore cleaning work in actual engineering.

Description

Technical Field

[0001] The invention relates to the technical field of application of long horizontal wells in exploiting oceans, deep formations and unconventional oil and gas reservoirs, and specifically to a characteristic research method based on a dynamic model of long horizontal well cuttings transport. Background Art

[0002] In recent years, long horizontal wells have been widely used in the exploitation of oceans, deep formations and unconventional oil and gas reservoirs because they can effectively increase the oil leakage area, increase the single well production, and improve the development effect of oil and gas reservoirs. However, the problems of wellbore cleaning, hydraulic parameter optimization, and hydraulic extension capacity prediction and improvement in the drilling process of long horizontal wells have become increasingly prominent and have received widespread attention. In the high-angle section of long horizontal wells, the gravity effect of cuttings is prominent, and it is easy to accumulate in the wellbore to form a cuttings bed, which leads to increased friction, stuck drill, drill string wear and other complex downhole situations, which not only directly increases the drilling cost and risk, but also limits the extension capacity of long horizontal wells and delays the drilling schedule. Therefore, the analysis and research of the law and characteristics of cuttings migration in long horizontal wells has important theoretical guiding significance for ensuring the wellbore cleaning and safe and efficient drilling of long horizontal wells. Summary of the invention

[0003] In view of the above problems, the present invention proposes a characteristic research method based on a dynamic model of cuttings transportation in long horizontal wells.

[0004] A method for studying the characteristics of long horizontal well cuttings transport dynamic model is proposed. A two-layer long horizontal well cuttings transport dynamic model is established to simulate the dynamic transport of cuttings. The continuity equation and momentum equation are numerically quantified to calculate parameters and study the dynamic transport characteristics of cuttings. The method includes the following steps:

[0005] Step 1: Calculate the wellbore trajectory curve, input basic parameters to construct the well inclination function, use the pursuit method to solve, and restore the real wellbore trajectory curve;

[0006] Step 2: Generate a discrete network, obtain the well inclination angle based on the wellbore trajectory curve, and estimate the cross-sectional area of ​​the cuttings bed at the initial position at a certain time under relevant parameters and boundary conditions. and the concentration of rock fragments in the suspended layer

[0007] Step 3: Estimate the cross-sectional area of ​​the cuttings bed at the next location at the same time and suspended layer cuttings concentration Combined with the correlation function, we can calculate

[0008] Step 4: and If the difference is small, the relevant parameters are calculated using the calculated suspension layer cuttings concentration. If the error is large, the relevant parameters are re-estimated.

[0009] Step 5: Calculate the cross-sectional area of ​​the cuttings bed using the calculated relevant parameters combined with the momentum equation and the continuity equation

[0010] Step 6: The calculated With estimated If the error is small, then Calculate the height of the cuttings bed like If the boundary conditions are met, the result is output. If the conditions are not met, steps 2 to 5 are repeated to re-estimate. and

[0011] Furthermore, a method for studying the characteristics of the long horizontal well cuttings transport dynamic model is characterized in that the calculation of the borehole trajectory in step 1 uses cubic spline interpolation to calculate the well inclination angle at the node, and the interval [S k-1 , S k ](k=1,2,3,...,N) The calculation formula of the well inclination spline function is:

[0012]

[0013] In the formula, M k-1 =θ n (s k-1 ); k is the measuring point number; L k is the length of the measuring section, L k =s k -s k-1 , the unit is m; s represents the well depth at the interpolation point, the unit is m; N represents the number of measuring points.

[0014] Furthermore, a characteristic research method based on the dynamic model of cuttings transport in long horizontal wells is characterized in that the continuity equation of the cuttings bed and the suspended layer is derived from the law of conservation of mass, and the sum of the flow difference between the two sides of the model cuttings bed and the amount of block falling from the well wall per unit time is equal to the mass of the cuttings bed in the micro-element control volume per unit time, that is:

[0015]

[0016] The continuity equation of the cuttings bed is expressed as:

[0017]

[0018] The continuity equation of the suspended layer is expressed as:

[0019]

[0020] Among them, ρ s , b are the equivalent densities of the suspended layer and the cuttings bed, respectively, in kg / m 3 ; V s 、V b are the migration velocities of solid particles in the suspended layer and the cuttings bed, respectively, in m / s; A s , A b are the cross-sectional areas of the suspended layer and the cuttings bed, respectively, in m 2 ; C b is the volume concentration fraction of cuttings in the cuttings bed; V s is the amount of block loss from the well wall, in m 3 / (m / s).

[0021] Furthermore, a method for studying the characteristics of the long horizontal well cuttings transport dynamic model is provided, wherein the calculation of some relevant parameters in the dynamic model characteristic study method includes:

[0022] Annulus cross-sectional area:

[0023] Shear stress between cuttings bed and wellbore wall:

[0024] Shear stress between the suspended layer and the well wall:

[0025] Shear stress at the interface between the suspended layer and the cuttings bed:

[0026] Equivalent density of cuttings bed: ρ b =ρ p C b +ρ f (1-C b );

[0027] Equivalent density of the suspended layer: ρ s =ρ p C s +ρ f (1-C s );

[0028] In addition, the friction coefficient between the cuttings bed and the wellbore wall is b =0.15, the friction coefficient between the suspension layer and the well wall (turbulence), (laminar flow), interface friction coefficient Fluid Reynolds number Hydraulic diameter of suspended layer d o is the borehole diameter, in meters; di is the outer diameter of the drill pipe, in m; d p is the average diameter of solid particles, in mm; μ e is the effective viscosity of the fluid, in Pa·s; ρ p , K f They are respectively the density of solid particles and the density of drilling fluid, in kg / m3; C s is the volume concentration fraction of rock fragments in the suspension layer, C b is the volume concentration fraction of cuttings in the cuttings bed.

[0029] Furthermore, a characteristic research method based on the dynamic model of cuttings transport in long horizontal wells is characterized in that in the calculation of the boundary conditions, during the drilling process, the cross-sectional area of ​​the cuttings bed is:

[0030]

[0031]

[0032] During the simulation, the wellbore toe pressure is:

[0033]

[0034] Where ROP is the mechanical drilling speed, in m / h; d b is the drill bit diameter, in meters; H is the vertical depth of the wellbore, in meters; Δp f It is the pressure drop along the wellhead to the calculated well section, in Pa.

[0035] Furthermore, a characteristic research method based on the dynamic model of cuttings transport in long horizontal wells is characterized in that the calculation of the suspended layer cuttings volume concentration includes the integration of the particle settling velocity and the particle obstructed deposition velocity, as well as the suspended layer volume concentration, and the average suspended layer cuttings volume concentration is:

[0036] C s =C b (I0-I i ) / A s

[0037]

[0038]

[0039] Where α is the contact angle between the cuttings bed and the wellbore wall; β is the contact angle between the cuttings bed and the drill pipe; h is the height of the cuttings bed, in m; e is the eccentricity, in m; ε p is the diffusion coefficient, in m 2 / s;v h is the hindered settling velocity, in m / s.

[0040] Furthermore, a characteristic research method based on the dynamic model of cuttings transport in long horizontal wells is characterized in that the motion equations of the cuttings bed and the suspended layer are derived from the momentum conservation theorem, and the sum of the momentum time change rate in the cuttings bed in the micro-element control volume and the momentum flow rate flowing out of the cuttings bed in the micro-element control volume is equal to the resultant force on the cuttings bed in the micro-element control volume, that is:

[0041]

[0042] The equation of motion for the cuttings bed is expressed as:

[0043]

[0044] The equation of motion of the suspended layer is expressed as:

[0045]

[0046] p is pressure; τ s , τ b , τ i They are the shear stress between the suspended layer and the wellbore wall, the shear stress between the cuttings bed and the wellbore wall, and the shear stress at the interface between the suspended layer and the cuttings bed; S s , S b , S i They are the wetted perimeter of the suspended layer, the wetted perimeter of the cuttings bed, and the wetted perimeter of the interface between the suspended layer and the cuttings bed, in m; F is the hydrodynamic friction between the cuttings bed and the wellbore wall per unit length, in N / m; θ is the well inclination angle; g is the gravitational acceleration, in m 2 / s.

[0047] Furthermore, a characteristic research method based on the long horizontal well cuttings transport dynamic model is characterized in that the partial differential equation of the discrete network model is: Its integral over the unit grid integration area L is: The curve integral along the boundary L is: Numericalization of the continuity equation,

[0048] The difference equation of the continuity equation of the cuttings bed is:

[0049]

[0050] The difference equation of the continuity equation of the suspended layer is:

[0051]

[0052] Momentum equation numericalization,

[0053] The difference equation of the momentum equation for the cuttings bed is:

[0054]

[0055] The difference equation of the momentum equation of the suspended layer is:

[0056]

[0057] p is pressure; τ s , τ b , τ i They are the shear stress between the suspended layer and the wellbore wall, the shear stress between the cuttings bed and the wellbore wall, and the shear stress at the interface between the suspended layer and the cuttings bed; S s , S b , S i They are the wetted perimeter of the suspended layer, the wetted perimeter of the cuttings bed, and the wetted perimeter of the interface between the suspended layer and the cuttings bed, in m; F is the hydrodynamic friction between the cuttings bed and the wellbore wall per unit length, in N / m; θ is the well inclination angle; g is the gravitational acceleration, in m 2 / s.

[0058] The beneficial effects of the present invention are as follows: a dynamic model of two-layer cuttings transport in a long horizontal well is established, which takes into account the actual wellbore trajectory, fluid pressure drop and diffusion of suspended layer particles. The finite difference method is used to solve the model, and the dynamic transport of cuttings under different working conditions is simulated. Then, the dynamic transport characteristics of cuttings are studied, and the relevant parameters of wellbore cleaning are optimized, thereby guiding the wellbore cleaning work in actual engineering. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 It is a flow chart of a characteristic research method based on a long horizontal well cuttings transport dynamic model proposed by the present invention.

[0060] Figure 2 This is a diagram of the dynamic model of cuttings transportation in long horizontal wells in a characteristic research method based on the dynamic model of cuttings transportation in long horizontal wells proposed by the present invention.

[0061] Figure 3 This is a schematic diagram of grid division and discrete unit area in a characteristic research method based on a long horizontal well cuttings transport dynamic model proposed in the present invention. DETAILED DESCRIPTION

[0062] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, specific embodiments of the present invention are now described with reference to the accompanying drawings.

[0063] A method for studying the characteristics of cuttings transport dynamics based on a long horizontal well cuttings transport dynamics model is used to simulate the dynamic transport of cuttings, digitize the continuity equation and momentum equation, calculate the parameters, and study the dynamic transport characteristics of cuttings. Figure 1 As shown, the following steps are included:

[0064] Step 1: Calculate the wellbore trajectory curve, input basic parameters to construct the well inclination function, use the pursuit method to solve, and restore the real wellbore trajectory curve;

[0065] Step 2: Generate a discrete network, obtain the well inclination angle based on the wellbore trajectory curve, and estimate the cross-sectional area of ​​the cuttings bed at the initial position at a certain time under relevant parameters and boundary conditions. and the concentration of rock fragments in the suspended layer

[0066] Step 3: Estimate the cross-sectional area of ​​the cuttings bed at the next location at the same time and suspended layer cuttings concentration Combined with the correlation function, we can calculate

[0067] Step 4: and If the difference is small, the relevant parameters are calculated using the calculated suspension layer cuttings concentration. If the error is large, the relevant parameters are re-estimated.

[0068] Step 5: Calculate the cross-sectional area of ​​the cuttings bed using the calculated relevant parameters combined with the momentum equation and the continuity equation

[0069] Step 6: The calculated With estimated If the error is small, then Calculate the height of the cuttings bed like If the boundary conditions are met, the result is output. If the conditions are not met, steps 2 to 5 are repeated to re-estimate. and

[0070] The dynamic model of cuttings transport in long horizontal wells is a two-layer model, such as Figure 2 As shown in the figure, a microelement section of the wellbore is taken to divide the cuttings into a lower cuttings bed and an upper suspended layer in the wellbore; according to the laws of conservation of mass and momentum, and combined with the cuttings stress characteristics of the cuttings bed and the suspended layer, the continuity equation and motion equation of the cuttings bed and the suspended layer are calculated.

[0071] Derivation of the continuity equation:

[0072] (1) Mass flow rate of cuttings bed flowing in from surface A: ρ b v b A b ;

[0073] (2) Mass flow rate out of the cuttings bed on surface B:

[0074] (3) Amount of well wall falling off:

[0075] (4) The mass of the cuttings bed in the micro-element control volume at time T: ρ b A b dx;

[0076] (5) The mass of the cuttings bed in the micro-element control volume at time T+dt:

[0077] From the law of conservation of mass, we know that: (1)-(2)+(3)=(5)-(4), that is:

[0078]

[0079] Therefore, the continuity equation of the cuttings bed can be expressed as:

[0080]

[0081] Similarly, the continuity equation of the suspended layer can be expressed as:

[0082]

[0083] Among them, ρ s , b are the equivalent densities of the suspended layer and the cuttings bed, in kg / m3; V s 、V b are the migration velocities of solid particles in the suspended layer and the cuttings bed, respectively, in m / s; A s , A b are the cross-sectional areas of the suspended layer and the cuttings bed, respectively, in m 2 ; C b is the volume concentration fraction of cuttings in the cuttings bed; V s is the amount of block loss from the well wall, in m 3 / (m / s).

[0084] Derivation of the momentum equation:

[0085] (8) The time rate of change of momentum in the cuttings bed in the micro-element control volume:

[0086] (9) Momentum flow rate flowing out of the cuttings bed in the micro-element control volume:

[0087] (10) Resultant force on the cuttings bed in the micro-element control volume:

[0088] From the law of conservation of momentum, we know that: (8)+(9)=(10), that is:

[0089]

[0090] Therefore, the equation of motion for the cuttings bed can be expressed as:

[0091]

[0092] Similarly, the motion equation of the suspension layer can be expressed as:

[0093]

[0094] p is pressure; τ s , τ b , τ i They are the shear stress between the suspended layer and the wellbore wall, the shear stress between the cuttings bed and the wellbore wall, and the shear stress at the interface between the suspended layer and the cuttings bed; S s , S b , S i They are the wetted perimeter of the suspended layer, the wetted perimeter of the cuttings bed, and the wetted perimeter of the interface between the suspended layer and the cuttings bed, in m; F is the hydrodynamic friction between the cuttings bed and the wellbore wall per unit length, in N / m; θ is the well inclination angle; g is the gravitational acceleration, in m 2 / s.

[0095] In addition, in this embodiment, the calculation of the wellbore trajectory is also required, and the well inclination angle at the node is calculated by using cubic spline interpolation, and the interval [S k-1 , S k ](k=1,2,3,...,N) The inclination function expression is:

[0096]

[0097] In the formula, M k-1 =θ n (s k-1 ); k is the measuring point number; L k is the length of the measuring section, L k =s k -s k-1 , the unit is m; s represents the well depth at the interpolation point, the unit is m; N represents the number of measuring points.

[0098] In this embodiment, the establishment of a dynamic model of cuttings transport in a long horizontal well also requires the calculation of the suspended layer cuttings volume concentration, which includes the particle settling velocity and the particle obstructed deposition velocity, as well as the integration of the suspended layer volume concentration. The average suspended layer cuttings volume concentration is:

[0099] C s =C b (I0-I i ) / A s

[0100]

[0101]

[0102] Where α is the contact angle between the cuttings bed and the wellbore wall; β is the contact angle between the cuttings bed and the drill pipe; h is the height of the cuttings bed, in m; e is the eccentricity, in m; ε p is the diffusion coefficient, in m 2 / s;v h is the hindered settling velocity, in m / s.

[0103] In this embodiment, the calculation of the auxiliary parameters includes:

[0104] Annulus cross-sectional area:

[0105] Shear stress between cuttings bed and wellbore wall:

[0106] Shear stress between the suspended layer and the well wall:

[0107] Shear stress at the interface between the suspended layer and the cuttings bed:

[0108] Equivalent density of cuttings bed: ρ b =ρ p C b +ρ f (1-C b );

[0109] Equivalent density of the suspended layer: ρ s =ρ p C s +ρ f (1-C s );

[0110] In addition, the friction coefficient between the cuttings bed and the wellbore wall is b =0.15, the friction coefficient between the suspension layer and the well wall (turbulence), (laminar flow), interface friction coefficient Fluid Reynolds number Hydraulic diameter of suspended layer Among them, d o is the borehole diameter, in meters; d i is the outer diameter of the drill pipe, in m; d p is the average diameter of solid particles, in mm; μ e is the effective viscosity of the fluid, in Pa·s; ρ p , K f They are respectively the density of solid particles and the density of drilling fluid, in kg / m3; C s is the volume concentration fraction of rock fragments in the suspension layer, C s is the volume concentration fraction of cuttings in the cuttings bed.

[0111] Furthermore, this embodiment includes the calculation of boundary conditions. During the drilling process, the cross-sectional area of ​​the cuttings bed is:

[0112]

[0113]

[0114] During the flushing process, drilling is stopped and a large amount of drilling fluid is used to flush the cuttings bed in the wellbore, assuming that the height of the cuttings bed is consistent throughout the well section.

[0115] In the simulation, the wellbore toe pressure is:

[0116]

[0117] Where ROP is the mechanical drilling speed, m / h; d b is the drill bit diameter, in meters; H is the vertical depth of the wellbore, in meters; Δp f It is the pressure drop along the wellhead to the calculated well section, in Pa.

[0118] In this embodiment, the discrete network model partial differential equation is: Its integral over the unit grid integration area L is: Integration area L Figure 3 As shown, the curve integral along the boundary L is:

[0119] Numericalization of the continuity equation,

[0120] The difference equation of the continuity equation of the cuttings bed is:

[0121]

[0122] The difference equation of the continuity equation of the suspended layer is:

[0123]

[0124] Momentum equation numericalization,

[0125] The difference equation of the momentum equation for the cuttings bed is:

[0126]

[0127] The difference equation of the momentum equation of the suspended layer is:

[0128]

[0129] p is pressure; τ s , τ b , τ i They are the shear stress between the suspended layer and the wellbore wall, the shear stress between the cuttings bed and the wellbore wall, and the shear stress at the interface between the suspended layer and the cuttings bed; S s , S b , S i They are the wetted perimeter of the suspended layer, the wetted perimeter of the cuttings bed, and the wetted perimeter of the interface between the suspended layer and the cuttings bed, in m; F is the hydrodynamic friction between the cuttings bed and the wellbore wall per unit length, in N / m; θ is the well inclination angle; g is the gravitational acceleration, in m 2 / s.

[0130] By using a characteristic research method based on a dynamic model of cuttings transport in a long horizontal well proposed by the present invention, a graph of the cuttings bed height change over time at the bottom of the well and a graph of the cuttings bed height change at each position at the same time are made, and the dynamic movement of cuttings under different working conditions is judged by observing the images. In one embodiment, a characteristic study of the dynamic movement of cuttings during drilling is conducted, and it can be found that: cuttings are gradually deposited with the accumulation of time, the height of the cuttings bed increases, the circulation area of ​​the drilling fluid decreases, the annular return velocity increases, the rock carrying capacity of the drilling fluid increases, and the cuttings transport rate gradually balances with the cuttings deposition rate. Therefore, the height of the cuttings bed at each position will first increase and gradually stabilize with time; in addition, the greater the well inclination angle, the greater the gravity component of the cuttings acting on the well wall, the easier it is for the cuttings to accumulate, and the higher the cuttings bed height. The greater the displacement, the lower the cuttings bed height, and the shorter the time it takes for the cuttings bed height to stabilize; the greater the drilling fluid density, the lower the cuttings bed height, and the shorter the time it takes for the cuttings bed height to stabilize; the slower the mechanical speed, the lower the cuttings bed height, and the shorter the time it takes for the cuttings bed height to stabilize; the smaller the wellbore size, the lower the cuttings bed height, and the shorter the time it takes for the cuttings bed height to stabilize.

[0131] In another embodiment, the dynamic migration characteristics of cuttings during the well washing process are studied, and it can be found that: the cuttings bed is gradually eroded, the height of the cuttings bed decreases, the flow area of ​​the drilling fluid increases, the annular return speed decreases, the rock carrying capacity of the drilling fluid decreases, and the cuttings migration rate gradually balances with the cuttings deposition rate, so the height of the cuttings bed at each position will first decrease and gradually stabilize over time; in addition, the smaller the well inclination angle, the smaller the component force of the drilling fluid acting on the cuttings bed, the smaller the erosion effect, and the higher the residual height of the cuttings bed. The larger the displacement during the process, the more severe the erosion, the lower the residual height of the cuttings bed, and the longer the time it takes for the cuttings bed height to reach stability; the greater the density of the drilling fluid, the more severe the erosion, the lower the residual height of the cuttings bed, and the shorter the time it takes for the cuttings bed height to reach stability; the smaller the wellbore size, the more severe the erosion, the lower the residual height of the cuttings bed, and the shorter the time it takes for the cuttings bed height to reach stability.

[0132] The present invention proposes a method for studying the characteristics of the long horizontal well cuttings transport dynamic model, establishes a two-layer long horizontal well cuttings transport dynamic model that takes into account the actual wellbore trajectory, fluid pressure drop, and suspension layer particle diffusion, solves the model using the finite difference method, and simulates the dynamic migration of cuttings under drilling and well washing conditions to study the dynamic migration characteristics of cuttings. The research method proposed in the present invention considers the complete wellbore trajectory, conducts a systematic study on the dynamic migration of cuttings in the wellbore trajectory, and effectively guides the optimization of engineering parameters.

[0133] In addition, it should be noted that the shapes and names of the parts and components of the specific embodiments described in this specification may be different, and the above content described in this specification is only an example of the structure of the present invention. Any equivalent changes or simple changes made based on the structure, features and principles described in the patent concept of the present invention are not used to limit the protection scope of the present invention. Any changes and modifications made by any technician familiar with the technology without departing from the concept and scope of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for studying the characteristics of long horizontal well cuttings transport dynamic model is established. A two-layer long horizontal well cuttings transport dynamic model is established to simulate the dynamic transport of cuttings. The continuity equation and momentum equation are numerically quantified to calculate parameters and study the dynamic transport characteristics of cuttings. The method includes the following steps: Step 1: Calculate the wellbore trajectory curve, input basic parameters to construct the well inclination function, use the pursuit method to solve, and restore the real wellbore trajectory curve; Step 2: Generate a discrete network, obtain the well inclination angle based on the wellbore trajectory curve, and estimate the cross-sectional area of ​​the cuttings bed at the initial position at a certain time under relevant parameters and boundary conditions. and the concentration of rock fragments in the suspended layer Step 3: Estimate the cross-sectional area of ​​the cuttings bed at the next location at the same time and suspended layer cuttings concentration Combined with the correlation function, we can calculate Step 4: and If the difference is small, the relevant parameters are calculated using the calculated suspension layer cuttings concentration. If the error is large, the relevant parameters are re-estimated. Step 5: Calculate the cross-sectional area of ​​the cuttings bed using the calculated relevant parameters combined with the momentum equation and the continuity equation Step 6: The calculated With estimated If the error is small, then Calculate the height of the cuttings bed like If the boundary conditions are met, the result is output. If the conditions are not met, steps 2 to 5 are repeated to re-estimate. and 2. A method for studying characteristics of a long horizontal well cuttings transport dynamic model based on claim 1, characterized in that: In the calculation of the wellbore trajectory in step 1, cubic spline interpolation is used to calculate the well inclination angle at the node, and the interval [S k-1 , S k ](k=1,2,3,...,N) The calculation formula of the well inclination spline function is: In the formula, k is the measuring point number; L k is the length of the measuring section, L k =s k -s k-1 , the unit is m; s represents the well depth at the interpolation point, the unit is m; N represents the number of measuring points.

3. A method for studying characteristics of a long horizontal well cuttings transport dynamic model based on claim 1, characterized in that: The continuity equations of the cuttings bed and the suspended layer are derived from the law of conservation of mass. The sum of the flow difference between the two sides of the model cuttings bed and the amount of block falling from the well wall per unit time is equal to the mass of the cuttings bed in the micro-element control volume per unit time, that is: The continuity equation of the cuttings bed is expressed as: The continuity equation of the suspended layer is expressed as: Among them, ρ s , b are the equivalent densities of the suspended layer and the cuttings bed, respectively, in kg / m 3 ; V s 、V b are the migration velocities of solid particles in the suspended layer and the cuttings bed, respectively, in m / s; A s , A b are the cross-sectional areas of the suspended layer and the cuttings bed, respectively, in m 2 ; C b is the volume concentration fraction of cuttings in the cuttings bed; V s is the amount of block loss from the well wall, in m 3 / (m / s).

4. A method for studying characteristics of a long horizontal well cuttings transport dynamic model based on claim 1, characterized in that: The calculation of some relevant parameters in the dynamic model characteristic research method includes: Annulus cross-sectional area: Shear stress between cuttings bed and wellbore wall: Shear stress between the suspended layer and the well wall: Shear stress at the interface between the suspended layer and the cuttings bed: Equivalent density of cuttings bed: ρ b =ρ p C b +ρ f (1-D b ); Equivalent density of the suspended layer: ρ s =ρ p C s +ρ f (1-C s ); In addition, the friction coefficient between the cuttings bed and the wellbore wall is b =0.15, the friction coefficient between the suspension layer and the well wall (turbulence), (laminar flow), interface friction coefficient Fluid Reynolds number Hydraulic diameter of suspended layer d o is the borehole diameter, in meters; d i is the outer diameter of the drill pipe, in m; d p is the average diameter of solid particles, in mm; μ e is the effective viscosity of the fluid, in Pa·s; ρ p , K f They are respectively the density of solid particles and the density of drilling fluid, in kg / m3; C s is the volume concentration fraction of rock fragments in the suspension layer, C b is the volume concentration fraction of cuttings in the cuttings bed.

5. A method for studying characteristics of a long horizontal well cuttings transport dynamic model based on claim 1, characterized in that: In the calculation of the boundary conditions, during the drilling process, the cross-sectional area of ​​the cuttings bed is: During the simulation, the wellbore toe pressure is: Where ROP is the mechanical drilling speed, in m / h; d b is the drill bit diameter, in meters; H is the vertical depth of the wellbore, in meters; Δp f It is the pressure drop along the wellhead to the calculated well section, in Pa.

6. A method for studying characteristics of a long horizontal well cuttings transport dynamic model based on claim 1, characterized in that: The calculation of the suspended layer rock cuttings volume concentration includes the integration of the particle settling velocity and the particle obstructed deposition velocity, as well as the suspended layer volume concentration. The average suspended layer rock cuttings volume concentration is: C s =C b (I o -I i ) / A s Where α is the contact angle between the cuttings bed and the wellbore wall; β is the contact angle between the cuttings bed and the drill pipe; h is the height of the cuttings bed, in meters; e is the eccentricity, in m; ε p is the diffusion coefficient, in m 2 / s;v h is the hindered settling velocity, in m / s.

7. A method for studying characteristics of a long horizontal well cuttings transport dynamic model based on claim 1, characterized in that: The motion equations of the cuttings bed and the suspended layer are derived from the momentum conservation theorem. The sum of the momentum time change rate in the cuttings bed in the micro-element control volume and the momentum flow rate flowing out of the cuttings bed in the micro-element control volume is equal to the resultant force on the cuttings bed in the micro-element control volume, that is: The equation of motion for the cuttings bed is expressed as: The equation of motion of the suspended layer is expressed as: p is pressure; τ s , τ b , τ i They are the shear stress between the suspended layer and the wellbore wall, the shear stress between the cuttings bed and the wellbore wall, and the shear stress at the interface between the suspended layer and the cuttings bed; S s , S b , S i are the wetted perimeter of the suspended layer, the wetted perimeter of the cuttings bed, and the wetted perimeter of the interface between the suspended layer and the cuttings bed, in m; F is the hydrodynamic friction between the cuttings bed and the wellbore wall per unit length, in N / m; θ is the well inclination angle; g is the gravitational acceleration, unit is m 2 / s.

8. A method for studying characteristics of a long horizontal well cuttings transport dynamic model based on claim 1, characterized in that: The partial differential equation of the discrete network model is: Its integral over the unit grid integration area L is: The curve integral along the boundary L is: Numericalization of the continuity equation, The difference equation of the continuity equation of the cuttings bed is: The difference equation of the continuity equation of the suspended layer is: Momentum equation numericalization, The difference equation of the momentum equation for the cuttings bed is: The difference equation of the momentum equation of the suspended layer is: p is pressure; τ s , τ b , τ i They are the shear stress between the suspended layer and the wellbore wall, the shear stress between the cuttings bed and the wellbore wall, and the shear stress at the interface between the suspended layer and the cuttings bed; S s , S b , S i are the wetted perimeter of the suspended layer, the wetted perimeter of the cuttings bed, and the wetted perimeter of the interface between the suspended layer and the cuttings bed, in m; F is the hydrodynamic friction between the cuttings bed and the wellbore wall per unit length, in N / m; θ is the well inclination angle; g is the gravitational acceleration, unit is m 2 / s.

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