Method and system for analyzing wellbore deposition characteristics of alkane blockages

Abstract

The invention discloses a wellbore deposition characteristic analysis method and system for alkane blockages, and belongs to the technical field of oil-gas field development. Influences of factors such as temperature and pressure in a wellbore are comprehensively considered, an alkane blockage characteristic calculation model is established, and the alkane blockages are analyzed under the conditions such as the temperature and the pressure of the wellbore. The analysis of the concentration and particle size distribution condition along with the well depth provides more accurate and reliable technical support for the research of the influence of the alkane blockages on the shaft, and the safety of the gas well production process is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of oil and gas field development, and particularly relates to a method and system for analyzing wellbore deposition characteristics of alkane blockages. Background Art

[0002] During the process of increasing and stabilizing gas well production, heavy alkanes contained in the gas can form alkane blockages in the wellbore string. Furthermore, corrosion inhibitors and various additives introduced into the wellbore fluid degrade at high temperatures, causing the fragmented small organic molecules to aggregate and condense, forming deposits on the wellbore wall. Due to factors such as adhesion and gravity, the gas in the wellbore is unable to remove these deposits, leading to blockages.

[0003] Blockages within wellbores can disrupt normal production, necessitating an urgent investigation into the mechanisms of wellbore blockages to prevent the formation of alkane blockages. Currently, this analysis primarily relies on the development of wellbore blockage prediction models. However, these models primarily focus on predicting concentration distribution and fail to account for the influence of factors such as wellbore temperature and pressure, resulting in low reliability and accuracy. Furthermore, these models are unable to effectively predict the flow state within the wellbore after blockage formation. Summary of the Invention

[0004] In order to solve the problems of low reliability and accuracy of prediction results and single results in existing analysis technologies, the present invention provides a method and system for analyzing the wellbore deposition characteristics of alkane blockages. The present invention comprehensively considers the influence of factors such as temperature and pressure in the wellbore, establishes a calculation model for the characteristics of alkane blockages, and analyzes the concentration and particle size distribution of alkane blockages with well depth under conditions such as wellbore temperature and pressure. This provides more accurate and reliable technical support for the study of the impact of alkane blockages on wellbores, and improves the safety of the gas well production process.

[0005] The present invention is achieved through the following technical solutions:

[0006] A method for analyzing the deposition characteristics of alkane blockages in wellbore, the method comprising:

[0007] Obtain parameters related to the deposition of alkane blockages in the wellbore, and model the distribution of the wellbore temperature and pressure fields based on these parameters;

[0008] According to the distribution of the wellbore temperature field, the change of the viscosity of the alkane blockage is obtained;

[0009] Based on the distribution of wellbore temperature and pressure fields and the change in viscosity of alkane plugging materials, the concentration and particle size distribution of alkane plugging materials with well depth under wellbore temperature and pressure conditions were calculated.

[0010] As a preferred embodiment, the present invention obtains the distribution of the wellbore temperature field and pressure field based on the relevant parameter modeling, specifically including:

[0011] Based on the heat transfer model and related boundary conditions, the distribution of the wellbore temperature field is calculated using the obtained relevant parameters;

[0012] Based on the wellbore multiphase flow theory, the influence of gravity, friction and fluid velocity changes are comprehensively considered, and the distribution of the pressure field in the wellbore is calculated using the obtained relevant parameters.

[0013] As a preferred embodiment, the distribution of the wellbore temperature field of the present invention is analyzed by a heat transfer diffusion model, which is expressed as:

[0014]

[0015] Where, α T is the thermal diffusion rate; t is the time; ε h Turbulent thermal diffusion coefficient; T is the ambient temperature in the wellbore; R is the rate of formation or dissolution of alkane blockages; r, θ, and z are the radial, circumferential, and axial directions of the cylindrical coordinate system, respectively;

[0016] Since the heat generated by the change in the phase behavior of alkane plugging materials can be ignored, the heat diffusion model in the axial direction of the wellbore is:

[0017]

[0018] The temperature of the reservoir fluid entering the wellbore from the reservoir is a constant value, and the boundary conditions at the reservoir location are: the temperature of the plane where the wellbore inlet is located is the reservoir temperature;

[0019] When the reservoir fluid flows out of the wellbore, the temperature at the wellhead is a constant value, and its boundary conditions are: the temperature of the plane where the wellbore outlet is located is the wellhead temperature;

[0020] The temperature gradient at the center of the wellbore is zero, and its boundary conditions are: the rate of change of temperature at the center axis of the wellbore with time is 0;

[0021] The temperature gradient at the wellbore wall is the heat transfer between the wellbore and the formation. Its boundary condition is: the temperature change rate at the wellbore wall in the radial direction is Among them, h o is the convective heat transfer coefficient of the fluid in the wellbore; k c is the thermal conductivity of alkane plugging; T w is the wellbore temperature; T o is the temperature outside the wellbore.

[0022] As a preferred embodiment, the distribution of the pressure field in the wellbore of the present invention is expressed as follows:

[0023]

[0024] Where ΔP is the wellbore pressure drop; g is the acceleration of gravity; ρ is the wellbore fluid density; Δz is the vertical height difference; Δv is the velocity difference; ΔL is the unit length of the wellbore in the iterative calculation section; v is the fluid velocity; f p is the flow friction; D is the hydraulic radius.

[0025] As a preferred embodiment, the flow friction calculation method under laminar flow conditions of the present invention is:

[0026]

[0027] Where N Re is the Reynolds number;

[0028] The flow friction under turbulent conditions is calculated as follows:

[0029]

[0030] Where ε is the relative roughness.

[0031] As a preferred embodiment, the present invention obtains the change in viscosity of the alkane blockage according to the distribution of the wellbore temperature field, specifically including:

[0032] By fitting empirical parameters, the viscosity calculation model of alkane blockages is obtained as follows:

[0033]

[0034] Where, η is the viscosity of the alkane plug; η * is the viscosity of the rare gas; ξ is the viscosity reduction parameter; ρ r is the relative density; a1-a5 are the fitting coefficients;

[0035] The calculation model for the viscosity of the dilute solution of the suspension containing alkane plugging particles is:

[0036]

[0037] Where φ is the volume fraction of alkane plugging particles, which is calculated as follows:

[0038]

[0039] Where μ res is the residual chemical potential; k is the number of blockage particle size groups; T is the ambient temperature in the wellbore; η p is a stacked fraction; a res is the residual Helmholtz free energy.

[0040] As a preferred embodiment, the calculation process of the concentration and particle size distribution with well depth of the present invention specifically includes:

[0041] Based on the theory of sedimentation dynamics, the deposition, precipitation and aggregation of alkane blockages are analyzed;

[0042] The distribution of alkane blockage concentration field in the wellbore is calculated based on the deposition, precipitation and aggregation of alkane blockages and combined with other influencing factors;

[0043] Based on the concentration field distribution of alkane blockages, the particle size distribution of alkane blockages in the wellbore is calculated.

[0044] As a preferred embodiment, the deposition, precipitation, and aggregation analysis process of the alkane blockage of the present invention specifically includes:

[0045] Constructing a model for the precipitation rate of alkane blockages:

[0046]

[0047] Where R is the rate of formation or dissolution of alkane blockages; k p Precipitation rate constant; C is the concentration of alkane plugging material in the solution; C eq is the concentration of alkane plugging material reaching the equilibrium state of deposition; k0 and α p All are coefficients for calculating precipitation rate;

[0048] Based on the empirical model of precipitation concentration, the accumulation rate model of alkane blockages is constructed:

[0049] R d =-k d C nμ

[0050] Where R d is the sediment accumulation rate of alkane blockage; μ is the viscosity of dilute solution; k d and n are empirical parameters.

[0051] As a preferred embodiment, the calculation process of the distribution of the concentration field of alkane blockages in the wellbore of the present invention specifically includes:

[0052] Based on the cylindrical coordinate system, the radial diffusion model of the concentration field is obtained by comprehensively considering the deposition, precipitation aggregation and molecular diffusion of alkane blockages:

[0053]

[0054] Where C is the concentration of alkane plugging material in the solution; v r , v z , v θare radial, axial and circumferential velocities respectively; R is the rate of formation or dissolution of alkane plugs; ε m Turbulent mass diffusion coefficient; D wo is the diffusion coefficient of alkane blockage in solution, and the diffusion coefficient is calculated as follows:

[0055]

[0056] Where, f d is the characteristic parameter of the diffusion coefficient; k b is the Boltzmann constant; T is the ambient temperature in the wellbore; μ is the viscosity of the dilute solution; r k is the particle size of k particles

[0057] According to the alkane blockage precipitation velocity model, the mass transfer model of alkane blockage concentration in the wellbore axial direction is obtained:

[0058]

[0059] Where k p Sedimentation rate constant; C eq The concentration of alkane plugs reaches the equilibrium state of deposition;

[0060] Among them, the initial conditions of the alkane blockage concentration field are: the initial concentration at any point in the wellbore is C0;

[0061] The concentration of alkane blockage at the entrance to the wellbore is a constant value, and the boundary condition at the entrance to the wellbore is: the concentration at the plane where the wellbore entrance is located is C r ;

[0062] The boundary conditions at the center of the wellbore are: the rate of change of concentration at the center axis of the wellbore with time is 0;

[0063] The deposition of alkane plugs at the wellbore wall conforms to the relevant dynamic model, so the boundary condition at the wellbore wall is: the concentration at the wellbore wall changes with time at a rate of Among them, C d is the concentration of alkane blockage deposited on the well wall surface; μ is the viscosity of the dilute solution; k d and n are empirical parameters.

[0064] As a preferred embodiment, the calculation process of the particle size distribution of the wellbore of the present invention specifically includes:

[0065] Obtain the concentration change of alkane blockage particles, expressed as:

[0066]

[0067] Where C k is the concentration of plugging particles of size k; Ci , C j are the concentrations of particles i and j respectively; K ij is the coefficient related to the collision and aggregation between particles i and j;

[0068]

[0069] Where, T is the ambient temperature in the wellbore; β is the collision rate; k b is the Boltzmann constant; μ is the viscosity of the dilute solution;

[0070] Obtain the classification of particle size distribution and calculate the concentration of each particle size;

[0071] Based on the principle of conservation of mass, the concentration of alkane blockages can be obtained by summing the concentrations of all particle sizes.

[0072] As a preferred embodiment, the method of the present invention further comprises:

[0073] Based on the Poiseuille equation and the modified wall theory, an analytical model for the effect of alkane blockages on the axial velocity of fluids in the wellbore is established, which is used to analyze the mechanism of the influence of alkane blockage deposition on the longitudinal velocity of fluids in the wellbore. The present invention also establishes an analytical model for the effect of alkane blockages on the axial velocity of fluids in the wellbore based on the Poiseuille equation and the modified wall theory, which realizes the analysis of the mechanism of the influence of alkane blockage deposition on the axial velocity of fluids in the wellbore, providing more comprehensive data support for the impact of alkane blockages on the wellbore.

[0074] As a preferred embodiment, the present invention establishes an analytical model for the effect of alkane blockages on the axial velocity of fluid in the wellbore based on the Poiseuille equation and the modified wall theory, specifically including:

[0075] Based on the Poiseuille equation, the calculation model of the axial velocity distribution in the wellbore under laminar flow conditions is obtained:

[0076]

[0077] Where r is the radial distance; r w is the radius of the wellbore or capillary; L is the flow distance; ΔP is the pressure drop; R is the rate of formation or dissolution of alkane blockages; μ is the viscosity of the dilute solution;

[0078] Based on the modified wall theory, the calculation model of the wellbore axial velocity distribution under turbulent conditions is obtained:

[0079]

[0080] Where V z + is the dimensionless flow velocity; τ w is the dimensionless shear stress, and:

[0081]

[0082]

[0083] Where r + is a dimensionless distance, expressed as:

[0084]

[0085] Where, v μ is the kinematic viscosity.

[0086] On the other hand, the present invention also provides a system for analyzing the deposition characteristics of alkane blockages in wellbore, the system comprising:

[0087] The temperature and pressure distribution module is used to obtain parameters related to the deposition of alkane blockages in the wellbore and to model the distribution of the wellbore temperature and pressure fields based on the relevant parameters;

[0088] The viscosity change module obtains the viscosity change of alkane blockages based on the distribution of the wellbore temperature field;

[0089] The sedimentation characteristics calculation module calculates the concentration and particle size distribution of alkane blockages with well depth under wellbore temperature and pressure conditions based on the distribution of wellbore temperature and pressure fields and the change in viscosity of alkane blockages.

[0090] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0091] The present invention comprehensively considers influencing factors such as temperature and pressure in the wellbore, establishes a calculation model for the deposition characteristics of alkane blockages, and can obtain more accurate and reliable concentration and particle size distribution of alkane blockages with well depth, thereby providing more accurate and reliable data and technical support for the study of blockage mechanisms in the wellbore and improving the safety of the gas well production process.

[0092] In addition, based on the Poiseuille equation and the modified wall theory, the present invention establishes an analytical model for the influence of alkane blockages on the axial flow velocity of the fluid in the wellbore, and analyzes the influence of alkane blockage deposition on the axial flow velocity of the fluid in the wellbore, thereby providing more comprehensive data and technical support for the study of the blockage mechanism in the wellbore, and further ensuring the safety of the gas well production process. BRIEF DESCRIPTION OF THE DRAWINGS

[0093] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, constitute a part of this application, and do not constitute a limitation of the embodiments of the present invention. In the drawings:

[0094] Figure 1 Flowchart of a method according to an embodiment of the present invention.

[0095] Figure 2 2 is a system principle block diagram of an embodiment of the present invention.

[0096] Figure 3 This is the temperature and pressure distribution of the wellbore in an embodiment of the present invention.

[0097] Figure 4 The figure shows the distribution of the viscosity of the alkane plugging material with the well depth according to the embodiment of the present invention.

[0098] Figure 5 The figure shows the distribution of alkane blockage concentration with well depth in an embodiment of the present invention.

[0099] Figure 6 The figure shows the distribution of particle size of alkane blockages with well depth in an embodiment of the present invention. DETAILED DESCRIPTION

[0100] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with examples and drawings. The exemplary embodiments of the present invention and their descriptions are only used to explain the present invention and are not intended to limit the present invention.

[0101] Example 1:

[0102] The existing technology mainly focuses on predicting the concentration distribution of alkane blockages, without considering the influence of factors such as wellbore temperature and pressure. At the same time, it is also impossible to effectively predict the flow state in the wellbore after the blockage is formed. Based on this, this embodiment proposes a method for analyzing the wellbore deposition characteristics of alkane blockages. The method comprehensively considers the influence of factors such as temperature and pressure in the wellbore, establishes a method for calculating the characteristics of alkane blockages, and obtains an analytical model for the deposition, precipitation and aggregation of alkane blockages based on the deposition dynamics theory. Finally, based on the Poiseuille equation and the modified wall theory, an analytical model for the influence of alkane blockages on the axial flow velocity of the fluid in the wellbore is established. This can obtain the concentration and particle size distribution of alkane blockages with well depth under wellbore temperature and pressure conditions during gas well production, as well as the influence mechanism of alkane blockage deposition on the longitudinal flow velocity of the fluid in the wellbore, thereby achieving effective and reliable analysis of the influence of alkane blockages on the wellbore, providing effective technical support for preventing the formation of alkane blockages, and ensuring stable production of gas wells.

[0103] Specific as Figure 1 As shown, the method proposed in this embodiment specifically includes the following steps:

[0104] Step 1: Obtain parameters related to the deposition of alkane blockages in the wellbore, and model the distribution of the wellbore temperature field and pressure field based on the relevant parameters.

[0105] Step 2: Obtain the change in viscosity of the alkane blockage based on the distribution of the wellbore temperature field.

[0106] Step 3: Based on the distribution of the temperature field and pressure field of the wellbore and the change in the viscosity of the alkane blockage, the concentration and particle size distribution of the alkane blockage with the well depth under the wellbore temperature and pressure conditions are calculated.

[0107] In an optional implementation manner, step 1 specifically includes the following steps:

[0108] Step 11, based on the heat transfer model and relevant boundary conditions, calculate the distribution of the wellbore temperature field using the obtained relevant parameters, specifically including:

[0109] The heat transfer diffusion model can be expressed as:

[0110]

[0111] Where, α T is the thermal diffusion rate; t is the time; ε h Turbulent thermal diffusion coefficient; T is the ambient temperature in the wellbore; R is the rate of formation or dissolution of alkane blockages; r, θ, and z are the radial, circumferential, and axial directions of the cylindrical coordinate system, respectively.

[0112] Since the heat generated by the change in the phase behavior of alkane plugging materials can be ignored, the heat diffusion model in the axial direction of the wellbore is:

[0113]

[0114] The temperature of the reservoir fluid entering the wellbore from the reservoir is a constant value, and the boundary conditions at the reservoir position are:

[0115] T=T f ,t,z=0,r(3)

[0116] Formula (3) indicates that at the boundary of the wellbore (z = 0), at the time when t is an arbitrary value and r is an arbitrary value, that is, the temperature of the plane at the wellbore entrance is T f Among them, T f is the reservoir temperature.

[0117] When the reservoir fluid flows out of the wellbore, the temperature at the wellhead is a constant value, and its boundary conditions are:

[0118] T=T out ,t,z=H,r(4)

[0119] Formula (4) indicates that at the boundary of the wellbore (z = H), at the time when t is an arbitrary value and r is an arbitrary value, the temperature of the plane at the wellbore outlet is Tout Among them, T out is the wellhead temperature.

[0120] The temperature gradient at the center of the wellbore is zero, and the boundary conditions are:

[0121]

[0122] Formula (5) indicates that the temperature change rate with time at the center of the wellbore (r=0) at the time when t is an arbitrary value and z is an arbitrary value, that is, at the position of the wellbore central axis is 0.

[0123] The temperature gradient at the wellbore wall is the heat transfer between the wellbore and the formation, and its boundary conditions are:

[0124]

[0125] Formula (6) shows that the wellbore wall (r = r w ), at any time t and any position z, i.e., the radial temperature change rate at the wellbore wall is Among them, h o is the convective heat transfer coefficient of the fluid in the wellbore; k c is the thermal conductivity of alkane plugging; T w is the wellbore temperature; T o is the temperature outside the wellbore; r w is the wellbore radius.

[0126] Step 12, based on the wellbore multiphase flow theory, comprehensively considering the effects of gravity, friction, and fluid velocity changes, and using the acquired relevant parameters to calculate the distribution of the pressure field in the wellbore, specifically including:

[0127]

[0128] Where ΔP is the wellbore pressure drop; g is the acceleration of gravity; ρ is the wellbore fluid density; Δz is the vertical height difference; Δv is the velocity difference; ΔL is the unit length of the wellbore in the iterative calculation section; v is the fluid velocity; f p is the flow friction; D is the hydraulic radius.

[0129] The flow friction coefficient under laminar flow conditions is calculated as follows:

[0130]

[0131] Where N Re is the Reynolds number.

[0132] The flow friction coefficient under turbulent conditions is calculated as follows:

[0133]

[0134] Where ε is the relative roughness.

[0135] In an optional embodiment, step 1 further includes: based on wellbore multiphase flow theory, comprehensively considering the effects of gravity, friction, and fluid velocity changes, and using the acquired relevant parameters to calculate the distribution of the velocity field in the wellbore, specifically including:

[0136] Based on the Poiseuille equation, the calculation model of the axial velocity distribution in the wellbore under laminar flow conditions can be obtained as follows:

[0137]

[0138] Where r is the radial distance; r w is the radius of the wellbore or capillary; L is the flow distance; ΔP is the pressure drop; R is the rate of formation or dissolution of alkane blockages; and μ is the viscosity of the dilute solution.

[0139] Based on the modified wall theory, the calculation model of the axial velocity distribution in the wellbore under turbulent conditions is:

[0140]

[0141] Where V z + is the dimensionless flow velocity; τ w is the dimensionless shear stress, and the specific calculation model is as follows:

[0142]

[0143]

[0144] Where r + is a dimensionless distance, and its specific calculation model is:

[0145]

[0146] Where, v μ is the kinematic viscosity.

[0147] This embodiment establishes an analytical model for the effect of alkane blockages on the axial velocity of fluid in a wellbore based on the Poiseuille equation and the modified wall theory, and is used to analyze the mechanism of the effect of alkane blockage deposition on the longitudinal velocity of fluid in a wellbore.

[0148] In an optional embodiment, step 2 is to calculate the viscosity of the alkane plug based on a viscosity-density correlation model, specifically including:

[0149] By fitting empirical parameters, the viscosity calculation model of alkane blockages is obtained as follows:

[0150]

[0151] Where, η is the viscosity of the alkane plug; η * is the viscosity of the rare gas; ξ is the viscosity reduction parameter; ρ r is the relative density; a1-a5 are the fitting coefficients.

[0152] The calculation model for the viscosity of the dilute solution of the suspension containing alkane plugging particles is:

[0153]

[0154] Where φ is the volume fraction of alkane plugging particles, which is calculated as follows:

[0155]

[0156] Where μ res is the residual chemical potential; k is the number of blockage particle size groups; T is the ambient temperature in the wellbore; η p is a stacked fraction; a res is the residual Helmholtz free energy.

[0157] In an optional implementation manner, step 3 specifically includes the following steps:

[0158] Step 31, based on the theory of deposition kinetics, performs deposition, precipitation, and aggregation analysis of alkane blockages, specifically including:

[0159] Construct a kinetic model for the precipitation of alkane blockages in solution, including the first-order function expression of the rate of formation or dissolution of alkane blockages:

[0160] R=-k p (CC eq ) (18)

[0161] Where k p Precipitation rate constant; C is the concentration of alkane plugging material in the solution; C eq It is the concentration at which alkane plugs reach a deposition equilibrium state.

[0162] The calculation model of the precipitation rate constant is as follows:

[0163]

[0164] Where k0 and α p are all precipitation rate calculation coefficients.

[0165] Therefore, the final expression for the deposition rate of alkane plugs is:

[0166]

[0167] Based on the empirical model of precipitation concentration, the accumulation rate of alkane blockages is calculated as follows:

[0168] R d =-k d C nμ (twenty one)

[0169] Where R d is the sediment accumulation rate of alkane blockage; μ is the viscosity of dilute solution; k d and n are empirical parameters.

[0170] Step 32, based on the deposition, precipitation, and aggregation of the alkane blockages and in combination with other influencing factors, calculates the distribution of the alkane blockage concentration field in the wellbore, specifically including:

[0171] Based on the cylindrical coordinate system, considering the influence of factors such as the deposition, precipitation aggregation and molecular diffusion of alkane blockages, the radial diffusion model of the concentration field can be obtained as follows:

[0172]

[0173] Where, v r , v z , v θ are radial, axial and circumferential velocities respectively; ε m Turbulent mass diffusion coefficient; D wo is the diffusion coefficient of alkane blockage in solution, and its specific calculation model is:

[0174]

[0175] Where, f d is the characteristic parameter of the diffusion coefficient; k b is the Boltzmann constant; T is the ambient temperature in the wellbore; μ is the viscosity of the dilute solution; r k is the particle size of k particles.

[0176] Substituting model (18) into model (22), the mass transfer model of alkane plugging concentration in the wellbore axial direction can be obtained as follows:

[0177]

[0178] The initial conditions of the alkane blockage concentration field are:

[0179] C=C0,t=0,z,r(25)

[0180] Formula (25) indicates that at the initial moment t=0, at a position where z and r are arbitrary values, that is, at any point in the wellbore, the initial concentration is C0, where C0 is the initial concentration of the blockage in the wellbore.

[0181] The concentration of alkane blockage at the entrance to the wellbore is a constant, so the boundary condition at this location is:

[0182] C=C r ,t,z=0,r(26)

[0183] Formula (26) indicates that at the boundary of the wellbore (z = 0), at the time when t is an arbitrary value and r is an arbitrary value, that is, the concentration of the plane at the wellbore entrance is C r , where C r It is the blockage concentration at the plane where the wellbore entrance is located.

[0184] When the concentration change of alkane plugging in the center of the wellbore can be ignored, then:

[0185]

[0186] Formula (27) indicates that at the center of the wellbore (r=0), at the time when t is an arbitrary value and at the position where z is an arbitrary value, that is, at the central axis of the wellbore, the rate of change of concentration with time is 0.

[0187] The deposition of alkane plugs at the wellbore wall conforms to the relevant kinetic model, which is expressed as:

[0188]

[0189] Formula (28) indicates that at the center of the wellbore (r = 0), at the time when t is an arbitrary value and z is an arbitrary value, that is, the rate of change of the concentration at the wellbore wall with time is Among them, C d It is the concentration of alkane blockages deposited on the well wall surface.

[0190] Step 33, based on the concentration field distribution of the alkane blockage, calculates its particle size distribution, specifically including:

[0191] First, obtain the concentration change of alkane blockage particles, which is expressed as:

[0192]

[0193] Where C k is the concentration of plugging particles of size k; C i , C j are the concentrations of particles i and j respectively; K ij is the coefficient related to the collision and aggregation between particles i and j, and its specific expression is as follows:

[0194]

[0195] Where T is the ambient temperature in the wellbore; β is the collision rate.

[0196] The particle size distribution of alkanes is shown in Table 1:

[0197] Table 1

[0198] type Particle size / μm 1 0.01 2 0.02 3 0.04 4 0.08 5 0.16 6 0.32 7 0.64 8 1.28 9 2.56 10 5.12 11 10.24 12 20.48

[0199] According to the particle size distribution shown in Table 1 (i.e., the particle size is exponentially distributed and the particle size distribution is divided into 12 levels), the concentration calculation method for each particle size can be obtained as follows:

[0200]

[0201]

[0202]

[0203] Where, K is the coefficient related to particle collision and aggregation, which can be obtained through experiments; C i is the concentration of particle i.

[0204] Based on the principle of mass conservation, the sum of all particle size concentrations is the value in the alkane blockage concentration field, and the expression is:

[0205]

[0206] It should be noted that the concentration field calculation process is only an illustrative explanation based on the particle size distribution classification shown in Table 1, and is not limited to this. That is, in another preferred embodiment, the concentration value in the alkane blockage concentration field is obtained by summing the concentrations of all particle sizes using Formulas (31) to (33).

[0207] The analysis method proposed in this embodiment can not only obtain the characteristics of the blockage within a preset time period, that is, the concentration and particle size distribution of alkane blockages with well depth under the wellbore temperature and pressure conditions, but also analyze the impact of alkane blockage deposition on the longitudinal flow velocity of the fluid in the wellbore, providing more accurate and reliable technical and data support for studying the impact of alkane blockages on the wellbore.

[0208] This embodiment also proposes a system for analyzing the characteristics of alkane blockage wellbore deposition. Figure 2 As shown, the system includes a temperature and pressure field distribution module, a viscosity change module, and a deposition characteristic calculation module.

[0209] Among them, the temperature and pressure field distribution module obtains the relevant parameters of alkane blockage deposition in the wellbore, and models the distribution of the temperature field and pressure field of the wellbore based on the relevant parameters.

[0210] The viscosity change module obtains the change of the viscosity of the alkane blockage according to the distribution of the temperature field of the wellbore.

[0211] The sedimentation characteristic calculation module calculates the concentration and particle size distribution of alkane blockages with wellbore depth under wellbore temperature and pressure conditions based on the distribution of the wellbore temperature and pressure fields and the change in the viscosity of the alkane blockages.

[0212] Example 2:

[0213] This embodiment uses the analysis method and system proposed in the above embodiment to analyze the wellbore deposition characteristics of a certain alkane blockage, which specifically includes the following process:

[0214] First, the parameters related to the wellbore deposition of the alkane blockage are obtained, as shown in Table 2:

[0215] Table 2

[0216] Parameter name Numerical Well depth / m 4500 Oil pipe diameter / cm 3.5 <![CDATA[Geothermal gradient / K·m -1 > 0.025 Formation pressure / MPa 36 Wellhead pressure / MPa 9 <![CDATA[Thermal conductivity / W·m -1 ·K -1 > 45 <![CDATA[Thermal conductivity / m 2 ·s -1 > <![CDATA[1×10 -6 ]]> Diffusion coefficient / dimensionless 170 Collision rate / dimensionless 0.5 <![CDATA[Thermal diffusion rate / cm 3 ·g -1 > 800 <![CDATA[Deposition rate coefficient of alkane blockages / s -1 > <![CDATA[6×10 -4 ]]> Maximum deposition concentration of alkane plugging materials / % 50

[0217] Then, according to the parameters shown in Table 2, the distribution of the wellbore temperature field and pressure field is calculated, as shown in Figure 3 shown.

[0218] Then, based on the obtained wellbore temperature field and pressure field, the viscosity change of the alkane plugging material is calculated, such as Figure 4 shown.

[0219] Finally, based on the changes in temperature and pressure fields and the viscosity of alkane plugging materials, the concentration and particle size distribution of alkane plugging materials in the wellbore with the depth of the well were calculated, as shown in the following example: Figure 5-6 shown.

[0220] Those skilled in the art will appreciate that the embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, the present application can adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application can adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) that contain computer-usable program code.

[0221] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the steps in the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0222] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0223] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 The steps for the function specified in one or more boxes.

[0224] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of 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 method for analyzing the deposition characteristics of alkane blockages in wellbore, characterized in that: The method includes: Obtain the relevant parameters of alkane blockage deposition in the wellbore, and model the distribution of the wellbore temperature field and pressure field based on the relevant parameters; According to the distribution of the wellbore temperature field, the change of the viscosity of the alkane plugging material is obtained; Based on the distribution of wellbore temperature and pressure fields and the change in viscosity of alkane plugging materials, the concentration and particle size distribution of alkane plugging materials with well depth under wellbore temperature and pressure conditions are calculated.

2. A method for analyzing the deposition characteristics of alkane blockages in wellbore according to claim 1, characterized in that: The distribution of wellbore temperature and pressure fields is obtained by modeling based on relevant parameters, including: Based on the heat transfer model and related boundary conditions, the distribution of the wellbore temperature field is calculated using the obtained related parameters; Based on the wellbore multiphase flow theory, the influence of gravity, friction and fluid velocity changes are comprehensively considered, and the distribution of the pressure field in the wellbore is calculated using the obtained relevant parameters.

3. A method for analyzing the deposition characteristics of alkane plugging in wellbore according to claim 2, characterized in that: The distribution of the wellbore temperature field is analyzed by the heat transfer diffusion model, which is expressed as: In the formula, α T is the thermal diffusion rate; t is the time; ε h Turbulent thermal diffusion coefficient; T is the ambient temperature in the wellbore; R is the rate of formation or dissolution of alkane plugging; r, θ, z are the radial, circumferential and axial directions of the cylindrical coordinate system, respectively; Since the heat generated by the change in the phase behavior of alkane plugging materials can be ignored, the heat diffusion model in the axial direction of the wellbore is: The temperature of the reservoir fluid entering the wellbore from the reservoir is a constant value, and the boundary conditions at the reservoir location are: the temperature of the plane where the wellbore entrance is located is the reservoir temperature; When the reservoir fluid flows out of the wellbore, the temperature at the wellhead is a constant value, and its boundary conditions are: the temperature of the plane where the wellbore outlet is located is the wellhead temperature; The temperature gradient at the center of the wellbore is zero, and its boundary conditions are: the rate of change of temperature with time at the center axis of the wellbore is 0; The temperature gradient at the wellbore wall is the heat transfer between the wellbore and the formation, and its boundary condition is: the temperature at the wellbore wall surface changes in the radial direction at a rate of Among them, h o is the convective heat transfer coefficient of the fluid in the wellbore; k c is the thermal conductivity of alkane plugging; T w is the temperature in the wellbore; T o is the temperature outside the wellbore.

4. A method for analyzing the deposition characteristics of alkane plugging in wellbore according to claim 2, characterized in that: The distribution of the pressure field in the wellbore is expressed as: Where ΔP is the wellbore pressure drop; g is the gravitational acceleration; ρ is the wellbore fluid density; Δz is the vertical height difference; Δv is the velocity difference; ΔL is the wellbore unit length of the iterative calculation section; v is the fluid velocity; f p is the flow friction; D is the hydraulic radius.

5. A method for analyzing the deposition characteristics of alkane plugging in wellbore according to claim 4, characterized in that: The flow friction under laminar flow conditions is calculated as: Where N Re is the Reynolds number; The flow friction under turbulent conditions is calculated as: Where ε is the relative roughness.

6. The method for analyzing the deposition characteristics of alkane plugging in a wellbore according to claim 1, characterized in that: According to the distribution of the wellbore temperature field, the change of the viscosity of the alkane plugging material is obtained, including: By fitting empirical parameters, the viscosity calculation model of alkane plugging is obtained as follows: Where, η is the viscosity of the alkane plug; η * is the viscosity of the rare gas; ξ is the viscosity reduction parameter; ρ r is the relative density; a1-a5 are the fitting coefficients; The calculation model of the dilute solution viscosity of the suspension containing alkane plugging particles is: Where φ is the volume fraction of alkane plugging particles, which is calculated as follows: In the formula, μ res is the residual chemical potential; k is the number of blockage particle size groups; T is the ambient temperature in the wellbore; η p is the stacked fraction; a res is the residual Helmholtz free energy.

7. The method for analyzing the deposition characteristics of alkane plugging in a wellbore according to claim 1, characterized in that: The calculation process of concentration and particle size distribution with well depth specifically includes: Based on the theory of sedimentation kinetics, the deposition, precipitation and aggregation of alkane blockages are analyzed; According to the deposition, precipitation and aggregation of alkane plugging materials and combined with other influencing factors, the distribution of the concentration field of alkane plugging materials in the wellbore is calculated; Based on the concentration field distribution of alkane blockages, the distribution of particle sizes of alkane blockages in the wellbore is calculated.

8. A method for analyzing the deposition characteristics of alkane plugging in wellbore according to claim 7, characterized in that: The analysis process of the deposition, precipitation and aggregation of alkane blockages specifically includes: Constructing a model for the precipitation rate of alkane plugs: Where R is the rate of formation or dissolution of alkane plugging; k p The precipitation rate constant; C is the concentration of alkane plugging in the solution; C eq is the concentration of alkane plugging material reaching the deposition equilibrium state; k0 and α p All are coefficients for calculating sedimentation rate; Based on the empirical model of precipitation concentration, the aggregation velocity model of alkane blockages is constructed: R d =-k d C nμ In the formula, R d is the sediment accumulation rate of alkane plugging; μ is the viscosity of dilute solution; k d and n are empirical parameters.

9. A method for analyzing the deposition characteristics of alkane plugging in wellbore according to claim 7, characterized in that: The calculation process of the distribution of the concentration field of alkane blockages in the wellbore specifically includes: Based on the cylindrical coordinate system, the radial diffusion model of the concentration field is obtained by comprehensively considering the deposition, precipitation aggregation and molecular diffusion of alkane blockages: Where, C is the concentration of alkane plugging in the solution; v r , v z , v θ are radial, axial and circumferential velocities respectively; R is the speed of formation or dissolution of alkane plugging; ε m Turbulent mass diffusion coefficient; D wo is the diffusion coefficient of alkane plugging in the solution, and the diffusion coefficient is calculated as follows: In the formula, f d is the characteristic parameter of the diffusion coefficient; k b is the Boltzmann constant; T is the ambient temperature in the wellbore; μ is the viscosity of the dilute solution; r k is the particle size of k particles According to the alkane blockage precipitation velocity model, the mass transfer model of alkane blockage concentration in the wellbore axial direction is obtained: In the formula, k p Sedimentation rate constant; C eq The concentration of alkane plugging material reaches the deposition equilibrium state; Among them, the initial conditions of the concentration field of alkane plugging materials are: the initial concentration at any point in the wellbore is C0; The concentration of alkane plugging material at the entrance to the wellbore is a constant value, and the boundary condition at the entrance to the wellbore is: the concentration of the plane where the wellbore entrance is located is C r ; The boundary conditions at the center of the wellbore are: the rate of change of concentration with time at the center axis of the wellbore is 0; The deposition of alkane plugging at the wellbore wall conforms to the relevant dynamic model, so the boundary condition at the wellbore wall is: the concentration at the wellbore wall changes with time at a rate of Among them, C d is the concentration of alkane plugging material deposited on the well wall surface; μ is the viscosity of the dilute solution; k d and n are empirical parameters.

10. The method for analyzing the deposition characteristics of alkane plugging in a wellbore according to claim 7, characterized in that: The calculation process of the particle size distribution of the wellbore specifically includes: Obtain the change in the concentration of alkane blockage particles, expressed as: In the formula, C k is the concentration of plugging particles with size k; C i , C j are the concentrations of particles i and j respectively; K ij is the coefficient related to the collision and aggregation between particles i and j; Where T is the ambient temperature in the wellbore; β is the collision rate; k b is the Boltzmann constant; μ is the viscosity of the dilute solution; Obtain the classification of particle size distribution and calculate the concentration of each particle size; Based on the principle of mass conservation, the concentration of alkane blockages can be obtained by summing up the concentrations of all particle sizes.

11. The method for analyzing the deposition characteristics of alkane plugging in wellbore according to claim 1, characterized in that: Also includes: Based on the Poiseuille equation and modified wall theory, an analytical model for the effect of alkane plugging on the axial velocity of fluid in the wellbore is established to analyze the mechanism of the effect of alkane plugging deposition on the longitudinal velocity of fluid in the wellbore.

12. The method for analyzing the deposition characteristics of alkane plugging in a wellbore according to claim 1, characterized in that: Based on the Poiseuille equation and modified wall theory, an analytical model for the effect of alkane plugging on the axial velocity of fluid in the wellbore is established, including: Based on the Poiseuille equation, the calculation model of the axial velocity distribution in the wellbore under laminar flow conditions is obtained: Where r is the radial distance; w is the radius of the wellbore or capillary; L is the flow distance; ΔP is the pressure drop; R is the speed of formation or dissolution of alkane plugging; μ is the viscosity of the dilute solution; Based on the modified wall theory, the calculation model of the axial velocity distribution of the wellbore under turbulent conditions is obtained: Where V z + is the dimensionless flow velocity; τ w is the dimensionless shear stress, and: In the formula, r + is a dimensionless distance, expressed as: In the formula, v μ is the kinematic viscosity.

13. A system for analyzing the deposition characteristics of alkane plugging materials in wellbore, characterized in that: The system includes: The temperature and pressure distribution module is used to obtain the relevant parameters of the deposition of alkane blockages in the wellbore, and to obtain the distribution of the wellbore temperature field and pressure field based on the relevant parameters; The viscosity change module obtains the viscosity change of alkane plugging materials according to the distribution of the wellbore temperature field; The sedimentation characteristic calculation module calculates the concentration and particle size distribution of alkane plugging materials with well depth under the wellbore temperature and pressure conditions based on the distribution of wellbore temperature and pressure fields and the change of viscosity of alkane plugging materials.

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