Shale oil horizontal well fracturing sand plugging distinguishing method based on chart

Abstract

According to the shale oil horizontal well fracturing sand plugging judgment method based on the chart, aiming at the problems that the shale oil reservoir multi-scale fracture propping agent migration rule is complex and the like, a propping agent migration model is built based on a double Euler and dense discrete phase model, the fluid-solid coupling effect between propping agent particles and liquid is fully considered, and the shale oil reservoir fracturing sand plugging judgment method is provided. A proppant migration rule under different displacements, viscosities, sand ratios and proppant particle sizes is defined, a horizontal shaft and in-seam sand plugging judgment chart is guided to be established, the safe sand adding range of the horizontal well can be comprehensively predicted by utilizing the chart, optimization of pump injection parameters such as construction displacement, sand ratios and fracturing fluid viscosity is guided, and the construction efficiency is improved. The migration and paving effect of the shale oil complex crack system proppant is improved, the sand blocking risk is reduced, and the overall construction efficiency is improved.

Description

Technical Field

[0001] The present invention belongs to the field of fracturing technology in the field of petroleum development, specifically to the field of proppant placement and migration simulation in wellbores and fractures, and specifically relates to a method for distinguishing fracturing sand plugging in shale oil horizontal wells based on a plate. Background Art

[0002] After ten years of exploration, shale oil has entered the stage of large-scale production. The depth and length of horizontal wells are gradually increasing, and the migration law of proppants in complex fracture systems is more complicated, and the risk of fracturing sand plugging is higher. Therefore, it is urgent to explore the migration law of proppants in wellbores and multi-scale fractures, optimize the overall pumping scheme, improve the effect of proppant laying in fractures, and reduce the risk of sand plugging.

[0003] However, due to the influence of complex fracture systems, the conventional sand plugging identification method based on pressure fitting and net pressure-time double logarithmic curve is less applicable to shale oil. At present, shale oil mainly relies on the horizontal well drilling trajectory, the previous construction conditions of adjacent wells, and the operation experience of on-site technicians to comprehensively predict the risk of sand plugging in horizontal well fracturing. This method has certain defects in accuracy and timeliness. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of the above-mentioned prior art and provide a plate-based method for identifying sand plugging in shale oil horizontal well fracturing, so as to solve the problem in the prior art that conventional mining technology is not obvious in shale reservoirs and it is difficult to avoid sand plugging.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A plate-based method for identifying sand plugging in shale oil horizontal well fracturing, comprising the following steps:

[0007] Step 1, establishing a horizontal wellbore proppant migration model, wherein the horizontal wellbore proppant operation model obtains sand volume concentration through displacement, sand ratio and viscosity;

[0008] Step 2, obtaining the sand volume concentration at multiple positions through the horizontal wellbore proppant migration model, wherein the multiple positions include the wellbore entrance, the middle of the wellbore and the bottom of the wellbore, and obtaining the wellbore sand plugging map through the sand volume concentration at the multiple positions in combination with the first sand plugging judgment standard;

[0009] Step 3, establishing a variable fracture width proppant migration model, wherein the variable fracture width proppant migration model obtains the pressure difference at both ends of the fracture at each moment through displacement, sand ratio and viscosity;

[0010] Step 4, using the variable fracture width proppant migration model, the pressure difference at both ends of the fracture is obtained at each moment, and combined with the second sand plugging judgment standard, a sand plugging chart in the fracture is obtained;

[0011] Step 5, collecting displacement, sand ratio and viscosity, and judging whether sand plugging will occur in the shale oil horizontal well fracturing through the wellbore sand plugging chart and the fracture sand plugging chart. As long as one chart judges that sand plugging will occur, it is determined that the shale oil horizontal well will be sand plugged.

[0012] A further improvement of the present invention is:

[0013] Preferably, in step 2, the first sand plugging judgment standard includes:

[0014] (1) The sand volume concentration at the bottom of the wellbore is greater than 0.4;

[0015] (2) The volume concentration of sand in the middle of the wellbore is greater than the volume concentration of sand at the wellbore entrance.

[0016] Preferably, if any one of the two judgment criteria is met, it is determined that sand plugging will occur.

[0017] Preferably, in step 4, the second sand plugging judgment criterion is that the pressure difference between the two ends of the fracture is greater than 400Pa.

[0018] Preferably, the wellbore sand plugging chart has multiple sand plugging critical lines corresponding to displacement; the seam sand plugging chart has multiple sand plugging critical lines corresponding to viscosity;

[0019] Through two sand plugging critical lines, the process parameters to avoid sand plugging are determined.

[0020] Preferably, in step 1, the horizontal wellbore proppant migration model is obtained based on a dual Euler and dense discrete model, combined with a turbulent state formula and particle size interaction.

[0021] Preferably, the dense discrete model achieves force balance by:

[0022]

[0023]

[0024]

[0025] Where: F D is the particle drag coefficient per unit mass, s -1 ; is the particle collision force per unit mass related to the shear stress tensor, m / s 2 ; The unit is Basset force, m / s 2 ; is the unit virtual mass force, m / s 2 ;μ f is the fluid viscosity, Pa·s; ds is the particle diameter, mm; C Dis the resistance coefficient, dimensionless; Re s is the Reynolds number.

[0026] Preferably, the turbulent state formula is:

[0027]

[0028]

[0029] Where, Πk, Πε interphase turbulence exchange terms, kg / (m·s 3 ), k is the turbulent kinetic energy m 2 / s 2 ; σ k is the turbulent Prandtl number for energy k, dimensionless; σ ε is the ε turbulent Prandtl number, dimensionless; G k,f is the turbulent kinetic energy associated with the velocity gradient, kg / (m·s 3 ); μ t is the fluid shear viscosity, Pa·s; ε is the dissipation rate, m 2 / s 3 ; C1, C2 are empirical constants;

[0030] The particle size interaction is the force on the proppant particles, expressed as:

[0031]

[0032] In the formula, k Θ is the particle temperature diffusion coefficient, kg·m -1 ·s -1 ; Θ s is the particle temperature, m 2 ·s -2 ; γ is the particle energy dissipation rate, kg·m -1 ·s -3 Φ is the interphase energy transfer caused by the change of particle velocity, kg·m -1 ·s -3 .

[0033] Preferably, the variable fracture width proppant migration model is obtained based on dense discrete model simulation, the variable density discrete model is coupled with discrete element method to process the proppant, and the fluid domain is discretized by finite volume method.

[0034] Preferably, in the dense discrete model, dense molecular dynamics theory is used to describe the interaction between particles. The specific formula is:

[0035]

[0036] in

[0037]

[0038]

[0039]

[0040] Φ=-3βθ s (44)

[0041] In the formula, k Θ is the particle temperature diffusion coefficient, kg·m -1 ·s -1 ; Θ s is the particle temperature, m 2 ·s -2 ; γ is the particle energy dissipation rate, kg·m -1 ·s -3 Φ is the interphase energy transfer caused by the change of particle velocity, kg·m -1 ·s -3 Compared with the prior art, the present invention has the following beneficial effects:

[0042] The present invention provides a method for distinguishing sand plugging in shale oil horizontal well fracturing based on a plate, and aims at the problems such as the complex proppant migration law of multi-scale fractures in shale oil reservoirs. A proppant migration model is constructed based on a double Euler and dense discrete phase model, and the fluid-solid coupling effect between proppant particles and liquid is fully considered. The proppant migration law under different displacement, viscosity, sand ratio and proppant particle size is clarified, and a horizontal wellbore and fracture sand plugging discrimination plate is established. The plate can be used to comprehensively predict the safe sand addition range of the horizontal well, guide the optimization of pumping parameters such as construction displacement, sand ratio, and fracturing fluid viscosity, improve the proppant migration and paving effect of complex fracture systems of shale oil, reduce the risk of sand plugging, and improve the overall construction efficiency. The method is used to guide the fracturing construction of J10039_H well and J10812 well, and the operation process is relatively stable and no sand plugging occurs. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 A flow chart of the method of the present invention;

[0044] Figure 2 Wellbore critical safety sand addition (displacement-sand ratio-viscosity) chart;

[0045] Figure 3 Proppant migration under different sand ratio conditions in Well J10039_H;

[0046] Figure 4 Proppant migration and sand plugging prediction chart in fractures;

[0047] Among them, (a) shows different viscosities; (b) shows different viscosities and particle sizes

[0048] Figure 5 is the pressure difference between the inlet and outlet at different injection times in the variable width fracture;

[0049] Figure 6 J10039_H Well construction status;

[0050] Figure 7 Construction status of J10812 well. DETAILED DESCRIPTION

[0051] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments:

[0052] On the one hand, the present invention provides a method for distinguishing sand plugging in shale oil horizontal well fracturing; a proppant migration model is established based on the dual Euler and dense discrete phase models, the fluid-solid coupling between proppant particles and liquid is fully considered, the proppant migration law under different displacement, viscosity, sand ratio and proppant particle size is clarified, and a horizontal wellbore and fracture sand plugging distinction chart is established to guide the optimization of fracturing parameters. Figure 1 , the specific implementation method is as follows:

[0053] Step 1: Establish a horizontal wellbore proppant migration model. Based on the dual Euler and dense discrete phase models, and considering the interaction between turbulence and actual particle size, a horizontal wellbore proppant migration model is established. The specific process is as follows:

[0054] (1) The mass conservation and momentum conservation equations are established as follows:

[0055] Mass Conservation Equation

[0056]

[0057]

[0058] Where α is the volume fraction of the solid and liquid phases, dimensionless; ρ is the phase density, kg / m 3 ; is the linear velocity, m / s; subscript f is the liquid phase, s is the particle phase; t is the time, s.

[0059] Momentum conservation equation:

[0060]

[0061]

[0062] in,

[0063]

[0064]

[0065] Where: is the vector differential operator; τ is the shear stress tensor, kg / (m·s 2 ); g is the acceleration due to gravity, g = -9.81 m / s 2 ; The momentum exchange coefficient between the β phases is the velocity, kg / (m 3 ·s). μ is shear viscosity, Pa·s; λ is mass viscosity, Pa·s; is the unit tensor and has no dimension.

[0066] (2) Using the dense discrete phase model and particle dynamics model, it is necessary to consider the momentum conversion between phases and achieve force balance through the following equation:

[0067]

[0068]

[0069]

[0070] Where: F D is the particle drag coefficient per unit mass, s -1 ; is the particle collision force per unit mass related to the shear stress tensor, m / s 2 ; The unit is Basset force, m / s 2 ; is the unit virtual mass force, m / s 2 ;μ f is the fluid viscosity, Pa·s; ds is the particle diameter, mm; C D is the resistance coefficient, dimensionless; Re s is the Reynolds number.

[0071] (3) The dense discrete phase model uses the dense molecular dynamics theory to describe the interaction between particles, and the expression is:

[0072]

[0073] In the formula, k Θ is the particle temperature diffusion coefficient, kg·m -1 ·s -1 ; Θ s is the particle temperature, m 2 ·s -2 ; γ is the particle energy dissipation rate, kg·m -1 ·s -3 Φ is the interphase energy transfer caused by the change of particle velocity, kg·m -1 ·s -3 .

[0074] (4) The Gidaspow drag force model is used in the dense discrete phase model to describe the momentum exchange coefficient between proppant particles:

[0075]

[0076]

[0077] in,

[0078]

[0079]

[0080] Where: d s is the particle size of proppant particles, mm; C D is the drag force coefficient and is dimensionless.

[0081] (5) In the particle dynamics model, the particle shear viscosity includes collision viscosity, dynamic viscosity, and resistance viscosity, and the equations corresponding to the transient phase, dilute phase, and dense phase are as follows:

[0082] μ s =μ s,kin +μ s,col +μ s,fri (15)

[0083]

[0084]

[0085]

[0086] Specifically, Johnson's viscoelastic model is used to calculate the friction viscosity, and Lun's method is used to correct the radial distribution coefficient in the mass viscosity:

[0087]

[0088]

[0089]

[0090] Specifically, the particle pressure is calculated by analogy with the pressure of dense gas molecular dynamics, and the equation is as follows:

[0091] P s =α s ρ s θ s +2α s 2 ρ s θ s g 0(1+e) (23)

[0092] (6) Considering the turbulence effect as described in step 1, since the fluid pumping speed is relatively high during shale reservoir fracturing, the proppant and fracturing fluid flow in the complex fractures is in a turbulent state. The following equation is used to deal with the turbulence problem:

[0093]

[0094]

[0095] Where, Πk, Πε interphase turbulence exchange terms, kg / (m·s 3 ), k is the turbulent kinetic energy m 2 / s 2 ; σ k is the turbulent Prandtl number for energy k, dimensionless; σ ε is the ε turbulent Prandtl number, dimensionless; G k,f is the turbulent kinetic energy associated with the velocity gradient, kg / (m·s 3 ); μ t is the fluid shear viscosity, Pa·s; ε is the dissipation rate, m 2 / s 3 ; C1, C2 are empirical constants.

[0096] (7) In step 1, the proppant particles are subjected to forces. During the proppant migration process, the axial velocity is greater than the radial and circumferential velocities, and the radial and circumferential forces are smaller. This model ignores some forces acting perpendicular to the relative motion direction of the particles, and mainly considers the gravity, drag force, particle collision force, virtual force, and Basset force parallel to the particle motion direction that determine the particle acceleration. The formula is as follows:

[0097]

[0098]

[0099]

[0100]

[0101]

[0102] Where, d S is the particle diameter, mm; C S A is the drag force coefficient between the two phases, dimensionless; P is the particle surface area, mm 2 ; V S is the volume of proppant particles, mm 3 ; v, ρ are the velocity and density of the phase, m / s, kg / m3 .

[0103] Step 2: Establish a wellbore sand plugging chart. Based on the calculation results of the previous step, draw a horizontal wellbore sand plugging identification chart under different displacement and viscosity parameter combinations. The specific process is as follows:

[0104] Collect data of different displacement, sand ratio, and viscosity, and output the sand volume concentration at different locations based on the model in step 1. The different locations include the bottom of the wellbore, the middle of the wellbore, and the wellbore entrance; set the first sand plugging judgment standard as follows:

[0105] (1) The volume concentration of sand at the bottom of the wellbore is greater than 0.4;

[0106] (2) The volume concentration in the middle of the wellbore is greater than the volume concentration of sand at the wellbore entrance.

[0107] A chart is established with sand ratio as the horizontal axis and viscosity as the vertical axis; different displacements, sand ratios, and viscosities are collected, and based on the model of step 1, the sand volume concentration at different positions is output. If any one of the above-mentioned first sand plugging judgment criteria is met, sand plugging is likely to occur, and it is determined that sand plugging will occur, and the points corresponding to the sand ratio and viscosity are plotted in the generated chart, and multiple boundary points where sand plugging will occur at different sand ratios and viscosities under the same displacement are obtained, and a sand plugging fitting curve under the displacement is generated; further, sand plugging fitting curves under multiple displacements are obtained, and the part under each curve is the area where sand plugging will occur under the displacement.

[0108] Step 3: Establish a variable fracture width proppant migration model. The proppant migration model in the variable fracture width is simulated based on the dense discrete phase model, the variable density discrete model is coupled with the discrete element method to process the proppant, and the fluid domain is discretized by the finite volume method; the input of the variable fracture width proppant migration model is the displacement, sand ratio and viscosity, and the output is the pressure difference at both ends of the fracture at each moment.

[0109] Step 3.1, Model Assumptions

[0110] Based on the theoretical research of variable density discrete phase model and discrete element and the solid-liquid two-phase flow characteristics of actual fracturing operation, that is, taking into full account the collision friction of particles, turbulence effect, the force between continuous phase liquid and discrete phase particles, and the coupling between particles and fracture wall, the following basic assumptions are given:

[0111] (1) The dense discrete phase particle phase is transformed into a pseudo-plastic fluid phase and satisfies the characteristics of macroscopic physical quantities;

[0112] (2) The flow of fluid in complex fracture flow fields is a non-steady flow based on pressure;

[0113] (3) The geometric model does not deform or get damaged during proppant migration, settling, and collision;

[0114] (4) The proppant particles are regarded as rigid spheres with fixed sphericity. When collisions and frictions occur between particles or between particles and the wall of the flow field, mass loss is not considered, but mass exchange with the fluid phase is considered.

[0115] (5) The temperature change of the flow field in the fracture does not affect the viscosity and sand carrying performance of the fluid;

[0116] (6) The particle size of the proppant particles is uniform.

[0117] Step 3.2 Calculate the fluid dynamics equations

[0118] The flow of fracturing fluid and proppant in the fracture is liquid-solid two-phase flow. Conventional discrete phase models use Lagrangian methods according to Newton's laws to track particles. However, discrete phase models can only consider situations where particle concentrations are low and volume fractions are small. Since the volume fraction of proppant is relatively high during hydraulic fracturing, a dense two-phase flow method must be used to solve the volume fraction problem. Therefore, the present invention uses a variable density discrete phase model and a discrete element coupling method to establish a three-dimensional non-steady-state complex fracture network proppant migration mass conservation equation and momentum conservation equation.

[0119] (1) Mass conservation equation:

[0120]

[0121]

[0122] Where α is the volume fraction of the solid and liquid phases, dimensionless; ρ is the phase density, kg / m 3 ; is the linear velocity, m / s; subscript f is the liquid phase, s is the particle phase; t is the time, s.

[0123] (2) Momentum conservation equation:

[0124]

[0125]

[0126] in

[0127]

[0128]

[0129] Where: is the vector differential operator; τ is the shear stress tensor, kg / (m·s 2 ); g is the acceleration due to gravity, g = -9.81 m / s 2 ; The momentum exchange coefficient between the β phases is the velocity, kg / (m 3·s). μ is shear viscosity, Pa·s; λ is mass viscosity, Pa·s; is the unit tensor and has no dimension.

[0130] When using the variable density discrete phase and particle dynamics model, although the flow trajectory of the particles can be tracked, the momentum conversion between phases needs to be considered. The Newton momentum equation is used to describe each proppant particle or proppant cluster in the flow field, and the force balance is achieved through the following equation:

[0131]

[0132]

[0133]

[0134] Where: F D is the particle drag coefficient per unit mass, s -1 ; is the particle collision force per unit mass related to the shear stress tensor, m / s 2 ; The unit is Basset force, m / s 2 ; is the unit virtual mass force, m / s 2 ;μ f is the fluid viscosity, Pa·s; ds is the particle diameter, mm; C D is the resistance coefficient, dimensionless; Re s is the Reynolds number.

[0135] Considering the high sand content in actual fracturing construction, the collision and friction between particles may change the momentum and energy exchange between the solid and liquid phases. The model uses dense molecular dynamics theory to describe the interaction between particles, thereby calculating parameters such as particle pressure, shear viscosity term, mass viscosity, etc. The expression is:

[0136]

[0137] in

[0138]

[0139]

[0140]

[0141] Φ=-3βθ s (44)

[0142] In the formula, k Θ is the particle temperature diffusion coefficient, kg·m -1 ·s-1 ; Θ s is the particle temperature, m 2 ·s -2 ; γ is the particle energy dissipation rate, kg·m -1 ·s -3 Φ is the interphase energy transfer caused by the change of particle velocity, kg·m -1 ·s -3 .

[0143] If the change of particle temperature is ignored, and the temperature change caused by convection and phase diffusion is ignored, equation (40) can be simplified to:

[0144]

[0145] According to the particle kinematics theory, using the Gidaspow drag force model, the momentum exchange coefficient between proppant particles satisfies the following formula:

[0146]

[0147]

[0148] in:

[0149]

[0150]

[0151] Where: d s is the particle size of proppant particles, mm; C D is the drag force coefficient and is dimensionless.

[0152] In the particle dynamics model, particle shear viscosity includes collision viscosity, dynamic viscosity, and resistance phase viscosity. These three viscosities correspond to the transient phase, dilute phase, and dense phase, respectively. The corresponding equations are as follows:

[0153] μ s =μ s,kin +μ s,col +μ s,fri (50)

[0154]

[0155]

[0156]

[0157] Among them, Johnson's viscoelastic model is used to calculate the friction viscosity:

[0158]

[0159] The mass viscosity represents the resistance to particle deformation, and the radial distribution coefficient represents the probability of collision between particles. These two coefficients are calculated using Lun's method:

[0160]

[0161]

[0162] The particle pressure is calculated by analogy with the pressure of dense gas molecular dynamics. The equation contains dynamic and collision terms, and the relationship is as follows:

[0163] P s =α s ρ s θ s +2α s 2 ρ s θ s g 0 (1+e) (57)

[0164] (3) Turbulence equation

[0165] Since the fluid pumping speed is relatively high during shale reservoir fracturing, the flow of proppant and fracturing fluid in complex fractures is turbulent. The realizable k~ε turbulence model is used to deal with turbulent problems.

[0166] Turbulent kinetic energy equation:

[0167]

[0168] Dissipation rate ε equation

[0169]

[0170] In the formula, Π k , Π ε Interphase turbulence exchange term, kg / (m·s 3 ), k is the turbulent kinetic energy m 2 / s 2 ; σ k is the turbulent Prandtl number for energy k, dimensionless; σ ε is the ε turbulent Prandtl number, dimensionless; G k,f is the turbulent kinetic energy associated with the velocity gradient, kg / (m·s 3 ); μ t is the fluid shear viscosity, Pa·s; ε is the dissipation rate, m 2 / s 3 ; C1 and C2 are empirical constants with values ​​of 1.44 and 1.92 respectively.

[0171] Step 3.3 Proppant particle force equation

[0172] Due to the large-volume and large-liquid construction of clear water fracturing in shale reservoirs, the stress state of particles in solid-liquid two-phase flow is relatively complex. Many previous studies have simplified the stress, considering only the effects of gravity, resistance, and Stokes force. However, proppant particles are subject to the combined effects of multiple external forces during movement, and the forces can be divided into two categories according to the direction of the forces: forces parallel and perpendicular to the direction of relative movement of the particles. The forces on the particles will cause the proppant particles to undergo varying degrees of velocity changes as the state of motion changes. During the migration of the proppant, the axial velocity is greater than the radial and circumferential velocities, and the radial and circumferential forces are smaller. The model of the present invention ignores some of the forces acting perpendicular to the direction of relative movement of the particles, and focuses on the forces parallel to the direction of particle movement that determine the acceleration of the particles, including gravity, drag force, particle collision force, virtual force, and the influence of Basset force on particle flow.

[0173] gravity:

[0174]

[0175] Drag force:

[0176]

[0177] Particle collision force:

[0178]

[0179] Virtual force:

[0180]

[0181] Basset force:

[0182]

[0183] Among them, d S is the particle diameter, mm; C S A is the drag force coefficient between the two phases, dimensionless; P is the particle surface area, mm 2 ; V S is the volume of proppant particles, mm 3 ; v, ρ are the velocity and density of the phase, m / s, kg / m 3 .

[0184] Step 4: Establish a sand plugging chart in the fracture. Based on the calculation results of the previous step, draw a sand plugging identification chart for the fracture under different combinations of sand ratios, critical fracture widths, proppant particle sizes and other parameters; obtain the pressure difference at both ends of the fracture at different times through the variable fracture width proppant migration model, and distinguish sand plugging by the difference in pressure difference at both ends of the fracture. Preferably, when the difference is greater than 400 Pascals, sand plugging is identified, and finally a sand plugging prediction chart is obtained.

[0185] Step 5: Collect displacement, sand ratio and viscosity, and judge whether sand plugging will occur in shale oil horizontal well fracturing through wellbore sand plugging chart and fracture sand plugging chart. As long as sand plugging is judged to occur in one chart, it is determined that sand plugging will occur in the shale oil horizontal well.

[0186] Furthermore, the wellbore sand plugging chart and the fracture sand plugging chart are used for comprehensive prediction to determine the safe parameter range, guide the optimization of fracturing process parameters, and avoid the occurrence of sand plugging.

[0187] The present invention constructs a proppant migration model based on the dual Euler and dense discrete phase models, considers the fluid-solid coupling effect between proppant particles and liquid, establishes a horizontal wellbore and sand plugging discrimination chart in the fracture, and guides the optimization of fracturing parameters.

[0188] Example 1

[0189] The following is a further analysis in conjunction with specific embodiments.

[0190] Step 1: Establish a horizontal wellbore proppant migration model.

[0191] Step 2: Based on different viscosities, sand ratios and displacements, combined with the horizontal wellbore proppant migration model established in step 1, the sand volume concentration at different positions is output, and according to the sand plugging judgment criteria, the critical sand plugging chart under different displacements is constructed as shown in the figure. Figure 2 shown.

[0192] Step 3: Establish a variable fracture width proppant migration model to analyze the corresponding relationship between the sand plugging position and the fracture pressure at different injection times. Taking Well J10039_H as an example, set the injection rate to 0.25m / s and the sand-carrying fluid viscosity to 5mPa.s to simulate the proppant migration law under different sand ratio conditions. Figure 3 shown.

[0193] Step 4: Based on the calculation results of the previous step, draw a fracture sand plugging discrimination chart under different combinations of sand ratios, critical fracture widths, proppant particle sizes, etc. Figure 4 As shown, see Figure 5 To judge by the inlet and outlet pressure, the point where the pressure difference suddenly rises is the part blocked by sand.

[0194] Step 5, optimize the fracturing process parameters. Use the wellbore sand plugging chart and the seam sand plugging chart to make a comprehensive prediction, determine the safe parameter range, and guide the optimization of the fracturing process parameters. The method is used to guide the optimization of the fracturing parameters of the J10039_H well and the J10812 well. The construction conditions of each section after construction are as follows. Figure 6 , Figure 7 The fracturing operation process was relatively smooth and no sand plugging occurred.

[0195] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A plate-based method for identifying sand plugging in shale oil horizontal well fracturing, characterized in that: The following steps are included: Step 1, establishing a horizontal wellbore proppant migration model, wherein the horizontal wellbore proppant operation model obtains sand volume concentration through displacement, sand ratio and viscosity; Step 2, obtaining the sand volume concentration at multiple positions through the horizontal wellbore proppant migration model, wherein the multiple positions include the wellbore entrance, the middle of the wellbore and the bottom of the wellbore, and obtaining the wellbore sand plugging map through the sand volume concentration at the multiple positions in combination with the first sand plugging judgment standard; Step 3, establishing a variable fracture width proppant migration model, wherein the variable fracture width proppant migration model obtains the pressure difference at both ends of the fracture at each moment through displacement, sand ratio and viscosity; Step 4, using the variable fracture width proppant migration model, the pressure difference at both ends of the fracture is obtained at each moment, and combined with the second sand plugging judgment standard, a fracture sand plugging map is obtained; Step 5, collecting displacement, sand ratio and viscosity, and judging whether sand plugging will occur in the shale oil horizontal well fracturing through the wellbore sand plugging chart and the fracture sand plugging chart. As long as one chart judges that sand plugging will occur, it is determined that the shale oil horizontal well will be sand plugged.

2. A plate-based method for distinguishing sand plugging in shale oil horizontal well fracturing according to claim 1, characterized in that: In step 2, the first sand plugging judgment standard includes: (1) The sand volume concentration at the bottom of the wellbore is greater than 0.4; (2) The volume concentration of sand in the middle of the wellbore is greater than the volume concentration of sand at the wellbore entrance.

3. A plate-based method for distinguishing sand plugging in shale oil horizontal well fracturing according to claim 2, characterized in that: If any one of the two judgment criteria is met, it is determined that sand plugging will occur.

4. The plate-based method for distinguishing sand plugging in shale oil horizontal well fracturing according to claim 1, characterized in that: In step 4, the second sand plugging judgment standard is that the pressure difference between the two ends of the fracture is greater than 400Pa.

5. The plate-based method for distinguishing sand plugging in shale oil horizontal well fracturing according to claim 1, characterized in that: The wellbore sand plugging chart has multiple sand plugging critical lines corresponding to displacement; the seam sand plugging chart has multiple sand plugging critical lines corresponding to viscosity; Through two sand plugging critical lines, the process parameters to avoid sand plugging are determined.

6. The plate-based method for distinguishing sand plugging in shale oil horizontal well fracturing according to claim 1, characterized in that: In step 1, the horizontal wellbore proppant migration model is obtained based on the dual Euler and dense discrete models, combined with the turbulent state formula and particle size interaction.

7. A plate-based method for distinguishing sand plugging in shale oil horizontal well fracturing according to claim 6, characterized in that: The dense discrete model achieves force balance by: Where: F D is the particle drag coefficient per unit mass, s -1 ; is the particle collision force per unit mass related to the shear stress tensor, m / s 2 ; The unit is Basset force, m / s 2 ; is the unit virtual mass force, m / s 2 ;μ f is the fluid viscosity, Pa·s; ds is the particle diameter, mm; C D is the resistance coefficient, dimensionless; Re s is the Reynolds number.

8. A plate-based method for distinguishing sand plugging in shale oil horizontal well fracturing according to claim 7, characterized in that: The turbulent state formula is: In the formula, Π k , Π ε Interphase turbulence exchange term, kg / (m·s 3 ), k is the turbulent kinetic energy m 2 / s 2 ; σ k is the turbulent Prandtl number for energy k, dimensionless; σ ε is the ε turbulent Prandtl number, dimensionless; G k,f is the turbulent kinetic energy associated with the velocity gradient, kg / (m·s 3 ); μ t is the fluid shear viscosity, Pa·s; ε is the dissipation rate, m 2 / s 3 ; C1, C2 are empirical constants; The particle size interaction is the force on the proppant particles, expressed as: In the formula, k Θ is the particle temperature diffusion coefficient, kg·m -1 ·s -1 ; Θ s is the particle temperature, m 2 ·s -2 ; γ is the particle energy dissipation rate, kg·m -1 ·s -3 Φ is the interphase energy transfer caused by the change of particle velocity, kg·m -1 ·s -3 .

9. The plate-based method for distinguishing sand plugging in shale oil horizontal well fracturing according to claim 1, characterized in that: The variable fracture width proppant migration model is obtained based on the simulation of dense discrete model, the variable density discrete model is coupled with discrete element method to process the proppant, and the fluid domain is discretized by finite volume method.

10. A plate-based method for distinguishing sand plugging in shale oil horizontal well fracturing according to claim 9, characterized in that: In the dense discrete model, the dense molecular dynamics theory is used to describe the interaction between particles. The specific formula is: in Φ=-3βθ s (44) In the formula, k Θ is the particle temperature diffusion coefficient, kg·m -1 ·s -1 ; Θ s is the particle temperature, m 2 ·s -2 ; γ is the particle energy dissipation rate, kg·m -1 ·s -3 Φ is the interphase energy transfer caused by the change of particle velocity, kg·m -1 ·s -3 .

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