Oil nozzle discharge prediction method and post-compression flowback regulation oil nozzle selection method

Abstract

The application discloses a kind of oil nozzle discharge prediction method, and the selection method of pressure post flowback regulating oil nozzle, and oil nozzle discharge prediction method includes: respectively establishing gas phase fluid model and liquid phase fluid model of wellhead cross section, and gas phase fluid model and liquid phase fluid model of oil nozzle cross section;According to the gas phase fluid model and liquid phase fluid model, generate the pressure difference model of wellhead cross section and oil nozzle cross section;The pressure difference model is converted into the function of oil nozzle outlet flow rate variable and pressure difference;According to the function of oil nozzle outlet flow rate variable and pressure difference, generate the flow prediction model at oil nozzle outlet;According to the flow prediction model at oil nozzle outlet, determine the flow at oil nozzle outlet.Utilize the scheme of the application, can realize the accurate prediction of liquid amount and gas amount in the process of low permeability reservoir volume fracturing flowback oil nozzle adjustment, provide effective reference data for the selection of oil nozzle.

Description

Technical Field

[0001] This invention relates to the field of oil and gas development in petroleum and natural gas engineering, specifically to a method for predicting nozzle displacement, and also to a method for selecting a post-pressure return flow regulating nozzle. Background Technology

[0002] In oil and gas development, due to the poor reservoir properties of low-permeability reservoirs, fracturing is typically used to increase reservoir conductivity and thus production. The production capacity of post-fracturing oil and gas wells largely depends on this conductivity. During fracturing, proppant and fracturing fluid are injected underground to create fractures. Before production, the fracturing fluid needs to be returned to the surface by adjusting the well-closing time and nozzle size. Improper well-closing time and nozzle size can damage the reservoir and reduce its conductivity.

[0003] In existing technologies, post-pressure flowback regulation mainly requires the installation of nozzles at the wellhead to adjust the gas and liquid volumes. Since the flowback fluid usually contains two phases of gas and liquid, existing calculation methods cannot calculate the accurate gas and liquid volumes under conditions without nozzle size. Under normal conditions, only historical experience of the block can be used, and it is impossible to accurately select the appropriate nozzle size. This results in a large difference between the expected flow rate and the flowback volume after using an inappropriate nozzle, which in turn leads to sand discharge and a decrease in fracture conductivity. Summary of the Invention

[0004] This invention provides a method for predicting nozzle displacement and a method for selecting nozzles for post-fracturing flowback adjustment, so as to achieve accurate prediction of liquid and gas volume during the adjustment of nozzles in low-permeability reservoirs and provide effective reference data for nozzle selection.

[0005] Therefore, the present invention provides the following technical solution:

[0006] A method for predicting fuel injector displacement, the method comprising:

[0007] Gas-phase fluid models and liquid-phase fluid models were established for the wellhead cross-section and the nozzle cross-section, respectively.

[0008] Based on the aforementioned gas phase fluid model and liquid phase fluid model, pressure difference models for the wellhead cross-section and nozzle cross-section are generated;

[0009] The pressure difference model is converted into a function of the nozzle outlet flow rate variable and the pressure difference;

[0010] A flow rate prediction model at the nozzle outlet is generated based on the function of the nozzle outlet velocity variable and the pressure difference.

[0011] The flow rate at the nozzle outlet is determined based on the flow rate prediction model at the nozzle outlet.

[0012] Optionally, establishing the gas-phase fluid model and liquid-phase fluid model for the wellhead cross-section, and the gas-phase fluid model and liquid-phase fluid model for the nozzle cross-section, respectively, includes:

[0013] Establish a physical model of the gas-liquid two-phase flow nozzle wellhead structure;

[0014] Based on the physical model, gas phase fluid model and liquid phase fluid model of wellhead cross section, and gas phase fluid model and liquid phase fluid model of oil nozzle cross section are established respectively.

[0015] Optionally, the oil and gas two-phase fluids in the physical model have the following relationship;

[0016] The flow process of fluid in the wellbore and the flow process of fluid in the nozzle are one-dimensional flows;

[0017] The single-phase flow rate is equal at any location in the wellbore and at any nozzle.

[0018] The density of the gas and liquid phases remains unchanged when the two-phase fluid passes through the nozzle.

[0019] The gas content is the same across different cross-sections;

[0020] The pressure is the same at all points on the same cross-section;

[0021] For the same cross-section, the flow velocity of fluids in the same phase is the same;

[0022] The two-phase fluids have the same velocity ratio as the surface pipeline and the nozzle.

[0023] Optionally, both the gas phase fluid model and the liquid phase fluid model are represented by the Bernoulli equation.

[0024] Optionally, generating the pressure difference models for the wellhead cross-section and the nozzle cross-section based on the gas-phase fluid model and the liquid-phase fluid model includes:

[0025] Based on the gas phase fluid model and the liquid phase fluid model, the formula for calculating the pressure difference between the wellhead cross section and the nozzle cross section is determined;

[0026] A fluid continuity equation is established based on the aforementioned fluid continuity.

[0027] The pressure difference models of the wellhead cross section and the nozzle cross section are generated using the fluid continuity equation and the pressure difference calculation formula.

[0028] Optionally, converting the pressure difference model into a function of the nozzle outlet flow rate variable and the pressure difference includes:

[0029] Determine the slip ratio parameter between the two phases, which is used to characterize the slip between the two phases;

[0030] Based on the slip ratio parameter, the pressure difference model is converted into a function of the nozzle outlet flow velocity variable and the pressure difference.

[0031] Optionally, generating the flow rate prediction model at the nozzle outlet based on the function of the nozzle outlet flow rate variable and the pressure difference includes:

[0032] Determine the relationship between cross-sectional gas content, volumetric gas content, and slip velocity ratio;

[0033] A flow prediction model for the nozzle outlet is generated based on the aforementioned relationship and the function of the nozzle outlet flow velocity variable and pressure difference.

[0034] Optionally, the flow prediction model at the nozzle outlet includes: a two-phase fluid total volume flow prediction model at the nozzle outlet, a liquid flow prediction model at the nozzle outlet, and a gas flow prediction model at the nozzle outlet.

[0035] Optionally, the method further includes:

[0036] The relationship between nozzle outlet velocity and pressure is determined based on the function of the nozzle outlet velocity variable and the pressure difference.

[0037] Based on the relationship between the nozzle outlet velocity and pressure and the two-phase fluid total volume flow rate prediction model, a model for the total volume flow rate of the two-phase fluid at the nozzle outlet is established.

[0038] Based on the relationship between the nozzle outlet velocity and pressure and the liquid flow prediction model, a volumetric flow rate model for the liquid at the nozzle outlet is established.

[0039] Based on the total volumetric flow rate model of the two-phase fluid at the nozzle outlet and the volumetric flow rate model of the liquid at the nozzle outlet, a volumetric flow rate model of the gas at the nozzle outlet is established.

[0040] The gas flow prediction model is modified based on the volumetric flow rate model of the gas at the nozzle outlet.

[0041] A method for selecting a post-pressure return flow regulating nozzle, the method comprising:

[0042] The flow rate at the nozzle outlet under the pressure return regulation is predicted using the nozzle displacement prediction method described above.

[0043] Determine the nozzle parameters based on the flow rate at the nozzle outlet;

[0044] Select the appropriate nozzle based on the nozzle parameters.

[0045] The present invention provides a method for predicting nozzle discharge under gas-liquid two-phase conditions. It establishes gas-phase and liquid-phase fluid models for the wellhead cross-section and the nozzle cross-section, respectively. These models are used to generate pressure difference models for the wellhead and nozzle cross-sections. The pressure difference models are then converted into outlet velocity variable functions. Based on these outlet velocity variable functions, a flow rate prediction model for the nozzle outlet is generated. This enables accurate calculation of gas and liquid volumes under different nozzles, gas-liquid ratios, and pressure conditions. Furthermore, it allows for accurate calculation of gas and liquid volumes before adjusting the return nozzle, preventing reservoir damage caused by improper nozzle selection.

[0046] Furthermore, considering the impact of different gas states on the accuracy of gas flow rate calculation, a volumetric flow rate model of the gas at the nozzle inlet is established, and this volumetric flow rate model is used to correct the gas flow rate prediction model, making the corrected gas flow rate prediction model more accurate.

[0047] The method for selecting a flowback regulating nozzle provided by this invention uses the above-mentioned nozzle flow rate prediction method to predict the flow rate at the nozzle outlet under flowback regulation, determines the nozzle parameters based on the flow rate at the nozzle outlet, and selects the nozzle based on the determined nozzle parameters, which can make the nozzle better adapt to the fracturing flowback requirements of the current low-permeability reservoir. Attached Figure Description

[0048] Figure 1 This is a flowchart of a nozzle displacement prediction method provided by the present invention;

[0049] Figure 2 This is a schematic diagram of the physical model of the gas-liquid two-phase flow oil nozzle wellhead structure;

[0050] Figure 3 This is a flowchart of a gas flow prediction model in the method of this invention;

[0051] Figure 4 This is a comparison chart of the actual flowback volume and the simulated flowback volume during the fracturing fluid flowback stage of a certain well.

[0052] Figure 5 This is a flowchart of a method for selecting a post-pressure return flow regulating nozzle provided by the present invention. Detailed Implementation

[0053] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly described below. Obviously, the drawings described below are merely some embodiments of the present invention, and those skilled in the art can obtain other drawings based on these drawings without creative effort.

[0054] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. The embodiments cannot be described in detail here, but the embodiments of the present invention are not limited to the following embodiments.

[0055] To address the problem in existing technologies that cannot accurately calculate the gas and liquid volumes after nozzle replacement during post-pressure return flow, leading to improper nozzle selection and affecting reservoir flowability, this invention provides a nozzle discharge prediction method and a post-pressure return flow adjustment nozzle selection method. A gas-liquid two-phase nozzle flow model is established to achieve accurate calculation of gas and liquid volumes under different nozzles, different gas-liquid ratios, and different pressure conditions.

[0056] like Figure 1 The diagram shown is a flowchart of a nozzle displacement prediction method provided by the present invention, which includes the following steps:

[0057] Step 101: Establish gas phase fluid model and liquid phase fluid model for the wellhead cross section, and gas phase fluid model and liquid phase fluid model for the nozzle cross section, respectively.

[0058] The following is combined with Figure 2 The schematic diagram of the physical model of the gas-liquid two-phase flow nozzle wellhead structure illustrates the principle of establishing the above models.

[0059] based on Figure 2 The physical model shown satisfies the following oil-gas two-phase fluid relationship:

[0060] The flow process of fluid in the wellbore and the flow process of fluid in the nozzle are one-dimensional flows;

[0061] The single-phase flow rate is equal at any location in the wellbore and at any nozzle.

[0062] The density of the gas and liquid phases remains unchanged when the two-phase fluid passes through the nozzle.

[0063] The gas content is the same across different cross-sections;

[0064] The pressure is the same at all points on the same cross-section;

[0065] For the same cross-section, the flow velocity of fluids in the same phase is the same;

[0066] The two-phase fluids pass through surface pipelines and nozzles at the same velocity ratio;

[0067] Both gaseous and liquid single-phase fluids satisfy the conditions of Bernoulli's equation.

[0068] In this embodiment of the invention, the gas phase fluid model and the liquid phase fluid model can be represented by the Bernoulli equation.

[0069] Bernoulli's equation, also known as the steady flow energy equation, is the dynamic equation for steady flow of an ideal fluid. It means that in a fluid flow where viscous losses are neglected, the sum of pressure potential energy, kinetic energy, and potential energy at any two points on a streamline remains constant.

[0070] Bernoulli's principle is stated as:

[0071]

[0072] In the formula, P is the pressure at a certain measuring point in the fluid, v is the velocity of the fluid at that measuring point, ρ is the fluid density, g is the gravitational acceleration, h is the height of the measuring point, and C is a constant.

[0073] correspond Figure 2 The physical model shown indicates that the gas-liquid two-phase flow can be approximated as two single-phase fluids flowing separately, with each phase flowing at a uniform velocity in stages. Figure 2 The model shown is suitable for analyzing flow patterns such as laminar flow, wave flow, and annular flow with low mass flow rates.

[0074] Based on the above theory, Bernoulli equations for gas-liquid two-phase fluids at cross sections a-a1 and b-b1 are established respectively.

[0075] Bernoulli's equation for gaseous fluids is:

[0076]

[0077] Bernoulli's equation for liquid fluids is:

[0078]

[0079] In the formula:

[0080] z3 is the position head at section a-a1 (i.e., the position height of the calculation point from the reference plane), in meters; z4 is the position head at section b-b1, in meters.

[0081] β is the gas content, which is dimensionless;

[0082] λ is the friction coefficient, which is dimensionless;

[0083] p3 and p4 are the fluid pressures at sections a-a1 and b-b1, respectively;

[0084] v 3g v 4g v represents the flow velocity of the gas phase fluid at sections a-a1 and b-b1, respectively, in m / s; 3l v 4l The values ​​are the flow velocities of the liquid phase fluid at sections a-a1 and b-b1, respectively, in m / s.

[0085] ρg ρ l These are the fluid densities of the gas phase fluid and the liquid phase fluid, respectively.

[0086] The method for solving the friction coefficient λ requires consideration of the fluid Reynolds number R. e The Reynolds number is a dimensionless number used to characterize fluid flow. It can be used to distinguish between laminar and turbulent flow, and also to determine the resistance experienced by an object moving through a fluid.

[0087] Rayleigh number R e The calculation formula is as follows:

[0088] Assuming full-pipe flow, to determine the flow regime, first calculate the Reynolds number R. e :

[0089]

[0090] In the formula, Re is the Reynolds number, which is dimensionless; v is the fluid velocity at a certain measuring point, in m / s; ρ is the fluid density, in kg / m³. 3 μ is the viscosity coefficient of the fluid, in mPa·s; d is a characteristic length, in meters. For example, if the fluid flows through a circular pipe, then d is the equivalent diameter of the pipe.

[0091] If R e If the value is ≤2000, the flow pattern is laminar, and the friction coefficient is:

[0092]

[0093] If R e If the value is greater than 2000, the flow pattern is turbulent, which can be divided into three cases, i.e., three regions:

[0094] if but

[0095]

[0096] if but

[0097]

[0098] if but

[0099]

[0100] in,

[0101] In the formula, δ represents the laminar sublayer. l represents the length in meters (m); Δ represents the absolute roughness, which can be found in a table. For general oil pipelines, the roughness is 0.14–0.15 mm.

[0102] In addition, the partitioning results can be verified by the following method: when δ≥Δ, it is a hydraulically smooth pipe; when δ<Δ, it is a hydraulically rough pipe.

[0103] Step 102: Generate the pressure difference models of the wellhead cross-section and the nozzle cross-section based on the gas phase fluid model and the liquid phase fluid model.

[0104] Specifically, based on the gas phase fluid model and the liquid phase fluid model, the pressure difference calculation formula for the wellhead cross section and the nozzle cross section is determined; the fluid continuity equation is established based on the fluid continuity; and then the pressure difference model for the wellhead cross section and the nozzle cross section is generated using the fluid continuity equation and the pressure difference calculation formula.

[0105] Reference Figure 2 The fluid continuity equation is as follows:

[0106] v 3g A3 = v 4g A4 (8)

[0107] v 3l A3 = v 4l A4 (9)

[0108]

[0109]

[0110] In the formula, d and D are the diameters of the nozzle at the front and rear positions, respectively, in meters; A3 and A4 are the cross-sectional areas at sections a-a1 and b-b1, respectively.

[0111] Based on the above formulas (1) and (2), the formulas for calculating the pressure difference between the wellhead cross section and the nozzle cross section can be obtained:

[0112]

[0113] Substituting the continuity equation into (12) yields:

[0114]

[0115] The above equation (13) is the pressure difference model.

[0116] Step 103: Convert the pressure difference model into a function of the nozzle outlet flow rate variable and the pressure difference.

[0117] Specifically, the slip ratio parameter between the two phases is determined, and the slip ratio parameter is used to characterize the slip between the two phases; based on the slip ratio parameter, the pressure difference model is converted into a function of the nozzle outlet flow velocity variable and the pressure difference.

[0118] Continue to refer to Figure 2 The expression for the slip ratio s is:

[0119]

[0120] In the formula, s is the slip ratio, which is dimensionless.

[0121] Substituting the above slip ratio into equation (13), and expressing the model pressure difference in terms of the outlet flow velocity variable, we can obtain the function of the nozzle outlet flow velocity variable and the pressure difference:

[0122]

[0123]

[0124] In the formula, Δp is the pressure difference between sections a-a1 and b-b1, and B is the intermediate equation for calculation.

[0125] Step 104: Generate a flow prediction model at the nozzle outlet based on the function of the nozzle outlet flow velocity variable and the pressure difference.

[0126] Specifically, the relationship between cross-sectional gas content, volumetric gas content, and slip ratio can be determined, and a flow prediction model at the nozzle outlet can be generated based on the relationship and the function of the nozzle outlet velocity variable and pressure difference.

[0127] Continue to refer to Figure 2 The calculation methods for cross-sectional gas content, volumetric gas content, and slip velocity ratio are as follows:

[0128]

[0129] In the formula, s is the sliding speed ratio, which is dimensionless; α is the cross-sectional gas content, which is dimensionless; and β is the volumetric gas content, which is dimensionless.

[0130] Substitute the above relationship (17) into the function (15) of the nozzle outlet flow velocity variable and pressure difference to generate a flow prediction model at the nozzle outlet.

[0131] In this embodiment of the invention, the flow prediction model at the nozzle outlet may include the following three models: a two-phase fluid total volume flow prediction model at the nozzle outlet, a liquid flow prediction model at the nozzle outlet, and a gas flow prediction model at the nozzle outlet, which are represented as follows:

[0132] The prediction model for the total volumetric flow rate of the two-phase fluid at the nozzle outlet is as follows:

[0133] Q 4total =A4αv 4g +A4(1-α)v 4l (18)

[0134] The liquid flow prediction model at the nozzle outlet is as follows:

[0135] Q 4l =A4(1-α)v 4l (19)

[0136] The gas flow prediction model at the nozzle outlet is as follows:

[0137] Q 4g =A4αv 4g (20)

[0138] In the formula: Q 4total The total volumetric flow rate of the two-phase fluid, in cubic meters per second (m³). 3 / s;Q 4l The total volumetric flow rate of the liquid, in cubic meters (m³). 3 / s;Q 4g The total volumetric flow rate of the gas, in cubic meters per second (m³). 3 / s.

[0139] Step 105: Determine the flow rate at the nozzle outlet based on the flow rate prediction model at the nozzle outlet.

[0140] The present invention provides a method for predicting nozzle discharge under gas-liquid two-phase conditions. It establishes gas-phase and liquid-phase fluid models for the wellhead cross-section and the nozzle cross-section, respectively. These models are used to generate pressure difference models for the wellhead and nozzle cross-sections. The pressure difference models are then converted into outlet velocity variable functions. Based on these outlet velocity variable functions, a flow rate prediction model for the nozzle outlet is generated. This enables accurate calculation of gas and liquid volumes under different nozzles, gas-liquid ratios, and pressure conditions. Furthermore, it allows for accurate calculation of gas and liquid volumes before adjusting the return nozzle, preventing reservoir damage caused by improper nozzle selection.

[0141] Considering the impact of different gas states on the accuracy of gas flow rate calculation, in another non-limiting embodiment of the method of the present invention, a volumetric flow rate model of the gas at the nozzle inlet can be established, and the gas flow rate prediction model can be corrected using the volumetric flow rate model, so that the corrected gas flow rate prediction model is more accurate.

[0142] like Figure 3 The diagram shown is a flowchart of a gas flow prediction model in the method of this invention, including the following steps:

[0143] Step 301: Determine the relationship between nozzle outlet flow rate and pressure based on the function of outlet flow rate variable and pressure difference.

[0144] According to the above formula (15), the relationship between the flow rate and pressure at the nozzle outlet can be obtained.

[0145] Step 302: Based on the relationship between the nozzle outlet velocity and pressure and the two-phase fluid total volume flow rate prediction model, establish the two-phase fluid total volume flow rate model at the nozzle outlet.

[0146] Substituting the velocity-pressure relationship at the nozzle outlet into the outlet flow rate expression (18), we obtain the total volumetric flow rate model of the two-phase fluid at the nozzle outlet, namely:

[0147]

[0148] Step 303: Based on the relationship between the nozzle outlet velocity and pressure and the liquid flow prediction model, establish a volumetric flow rate model for the liquid at the nozzle outlet.

[0149] Substituting the relationship between flow velocity and pressure at the nozzle outlet into the outlet flow rate expression (19), we obtain the volumetric flow rate model of the liquid at the nozzle outlet, namely:

[0150]

[0151] Step 304: Based on the total volumetric flow rate model of the two-phase fluid at the nozzle outlet and the volumetric flow rate model of the liquid at the nozzle outlet, establish the volumetric flow rate model of the gas at the nozzle outlet.

[0152] Step 305: Correct the gas flow prediction model based on the volumetric flow rate model of the gas at the nozzle outlet.

[0153] Treating the liquid phase as a Newtonian fluid, and since the inlet and outlet liquid volumes are equal, Q in equations (21) and (22) above... 4total With Q 4l The difference is the gas flow rate at the nozzle inlet. If we want to solve for the actual gas flow rate at the nozzle outlet, the equation needs to be corrected according to the gas state equation.

[0154] The gas state equations at sections a-a1 and b-b1 in the above physical model are:

[0155] p3V3=ZnRT3 (23)

[0156] p4V4=ZnRT4 (24)

[0157] ∫p3Q 3g dt=ZnRT3 (25)

[0158] ∫p4Q4g dt=ZnRT4 (26)

[0159] In the formula: Z is the gas deviation factor; n is the number of moles; R is a constant; T3 and T4 are the temperatures at sections a-a1 and b-b1, respectively, in K.

[0160] According to equations (25) and (26), the corrected actual outlet gas flow rate is:

[0161]

[0162]

[0163]

[0164] Equation (29) above is the modified gas flow prediction model at the nozzle outlet.

[0165] Compared to conventional nozzle flow calculation methods, the present invention can accurately calculate the gas and liquid volumes under different gas contents, different nozzle sizes, and different pressure conditions, and achieves effective prediction of gas and gas discharge volumes under different nozzle sizes during the backflow process.

[0166] The model was validated using data from a real fracturing and flowback well in a low-permeability block, LX1. The well's pipeline geometry, fluid properties, and reservoir properties are shown in Table 1.

[0167] Table 1

[0168]

[0169] Fracturing operations commenced on April 28, 2022, and fracturing fluid flowback began four days after well shut-in. A comparison of the actual flowback volume with the simulated flowback volume during the flowback phase of this well is shown below. Figure 4 .

[0170] During two-phase fluid flowback, the fluid pressure decreases, and the fluid's phase parameters change accordingly, often resulting in bubbly and slug flow patterns in the pipeline. When the fluid pressure decreases at various nodes in the wellbore, the gas volume increases. At this point, the gas is located at the center of the pipeline, while the liquid is at the pipe wall, causing fluctuations in the gas content and consequently, fluctuations in the outlet liquid volume. Figure 4 As can be seen, the simulated production rate crosses the actual production rate line, indicating that the simulated discharge rate in this stage is close to the actual cumulative discharge rate; the simulated average discharge rate in this stage is 28.31 m³. 3 / d, the actual average backflow rate is 29.32m³. 3 / d, with an error of approximately 3.4%. During gas-liquid two-phase flow, this accuracy fully meets the requirements for field measurements (error within 5%). Therefore, even with unstable gas flow, the calculation results remain highly accurate and can be used to predict wellhead flowback volume, gas volume, and total flow rate.

[0171] Figure 4 The simulated production exhibits a concave decreasing trend, which is consistent with the reservoir fluid seepage law and the production decreasing law of Arps (Advanced Regional Prediction System).

[0172] Accordingly, the present invention also provides a method for selecting a post-pressure return flow regulating nozzle, which uses the above-mentioned nozzle discharge prediction method to predict the flow rate at the nozzle outlet under post-pressure return flow regulation, and selects a suitable nozzle based on the prediction result.

[0173] like Figure 5 The diagram shown is a flowchart of a method for selecting a post-pressure return flow regulating nozzle provided by the present invention, which includes the following steps:

[0174] Step 501: Predict the flow rate at the outlet of the oil nozzle after pressure return adjustment.

[0175] The method for predicting the flow rate at the nozzle outlet can be found in the descriptions of the previous embodiments, and will not be repeated here.

[0176] Step 502: Determine the nozzle parameters based on the flow rate at the nozzle outlet.

[0177] The parameters of the nozzle may include, but are not limited to, the nozzle material, diameter, structure, and other parameters.

[0178] Step 503: Select the oil nozzle according to the oil nozzle parameters.

[0179] The method for selecting a flowback regulating nozzle provided by this invention uses the above-mentioned nozzle flow rate prediction method to predict the flow rate at the nozzle outlet under flowback regulation, determines the nozzle parameters based on the flow rate at the nozzle outlet, and selects the nozzle based on the determined nozzle parameters, which can make the nozzle better adapt to the fracturing flowback requirements of the current low-permeability reservoir.

[0180] It should be noted that the terms "comprising" and "having" and any variations thereof in the specification, claims and accompanying drawings of this invention are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to such processes, methods, products or devices.

[0181] The various embodiments in this specification are described in a progressive manner. Similar or identical parts between embodiments can be referred to interchangeably. Each embodiment focuses on its differences from other embodiments. Furthermore, the system embodiments described above are merely illustrative. The modules and units described as separate components may or may not be physically separate; that is, they may be located on a single network unit or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs. Those skilled in the art can understand and implement this without any creative effort.

[0182] The embodiments of the present invention have been described in detail above. Specific implementation methods have been used to illustrate the present invention. The descriptions of the embodiments above are only for the purpose of helping to understand the methods and systems of the present invention, and are merely some, not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention, and the content of this specification should not be construed as a limitation of the present invention. Therefore, any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for predicting fuel injector displacement, characterized in that, The method includes: Gas-phase fluid models and liquid-phase fluid models were established for the wellhead cross-section and the nozzle cross-section, respectively. Based on the aforementioned gas-phase fluid model and liquid-phase fluid model, pressure difference models for the wellhead cross-section and nozzle cross-section are generated; the pressure difference model is: in, and These are the fluid pressures at sections a-a1 and b-b1, respectively. β is the volumetric gas content; , These are the fluid densities of the gas phase fluid and the liquid phase fluid, respectively. The coefficient of friction; d and D are the diameters of the nozzle at the front and rear positions, respectively, in meters (m). Converting the pressure difference model into a function of the nozzle outlet flow velocity variable and the pressure difference specifically includes: determining the slip ratio parameter between the two phases, the slip ratio parameter being used to characterize the slip between the two phases; and converting the pressure difference model into a function of the nozzle outlet flow velocity variable and the pressure difference based on the slip ratio parameter. slip ratio The expression is: In the pressure difference model and the slip ratio expression, , The velocity of the gas phase fluid at sections a-a1 and b-b1 are respectively, in m / s; , The values ​​are the flow velocities of the liquid phase fluid at sections a-a1 and b-b1, respectively, in m / s. Substituting the above slip ratio into the differential pressure model expression, and representing the differential pressure in the model using the outlet flow rate variable, we obtain a function of the nozzle outlet flow rate variable and the differential pressure. A flow rate prediction model for the nozzle outlet is generated based on the function of the nozzle outlet velocity variable and the pressure difference; cross-sectional gas holdup. Volumetric gas content β and sliding speed ratio The calculation method is as follows: Substituting the above relationship into the function of the nozzle outlet flow velocity variable and pressure difference, a flow prediction model at the nozzle outlet is generated. The flow rate at the nozzle outlet is determined based on the flow rate prediction model at the nozzle outlet.

2. The method for predicting nozzle displacement according to claim 1, characterized in that, The establishment of gas-phase fluid models and liquid-phase fluid models for the wellhead cross-section and the nozzle cross-section includes: Establish a physical model of the gas-liquid two-phase flow nozzle wellhead structure; Based on the physical model, gas phase fluid model and liquid phase fluid model of wellhead cross section, and gas phase fluid model and liquid phase fluid model of oil nozzle cross section are established respectively.

3. The method for predicting nozzle displacement according to claim 2, characterized in that, The two-phase fluid of oil and gas in the physical model has the following relationship; The flow process of fluid in the wellbore and the flow process of fluid in the nozzle are one-dimensional flows; The single-phase flow rate is equal at any location in the wellbore and at any nozzle. The density of the gas and liquid phases remains unchanged when the two-phase fluid passes through the nozzle. The gas content is the same for sections with different cross-sections; The pressure is the same at all points on the same cross-section; For the same cross-section, the flow velocity of fluids in the same phase is the same; The two-phase fluids have the same velocity ratio as the surface pipeline and the nozzle.

4. The method for predicting nozzle displacement according to claim 1, characterized in that, Both the gas phase fluid model and the liquid phase fluid model are represented using Bernoulli's equation.

5. The method for predicting nozzle displacement according to claim 1, characterized in that, The generation of the pressure difference models for the wellhead cross-section and the nozzle cross-section based on the gas phase fluid model and the liquid phase fluid model includes: Based on the gas phase fluid model and the liquid phase fluid model, the formula for calculating the pressure difference between the wellhead cross section and the nozzle cross section is determined; Establish fluid continuity equations based on fluid continuity; The pressure difference models of the wellhead cross section and the nozzle cross section are generated using the fluid continuity equation and the pressure difference calculation formula.

6. The method for predicting nozzle displacement according to claim 1, characterized in that, The step of generating the flow prediction model at the nozzle outlet based on the function of the nozzle outlet velocity variable and the pressure difference includes: Determine the relationship between cross-sectional gas content, volumetric gas content, and slip velocity ratio; A flow prediction model for the nozzle outlet is generated based on the aforementioned relationship and the function of the nozzle outlet flow velocity variable and pressure difference.

7. The method for predicting nozzle displacement according to claim 6, characterized in that, The flow prediction model at the nozzle outlet includes: a two-phase fluid total volume flow prediction model at the nozzle outlet, a liquid flow prediction model at the nozzle outlet, and a gas flow prediction model at the nozzle outlet.

8. The method for predicting nozzle displacement according to claim 7, characterized in that, The method further includes: The relationship between nozzle outlet velocity and pressure is determined based on the function of the nozzle outlet velocity variable and the pressure difference. Based on the relationship between the nozzle outlet velocity and pressure and the two-phase fluid total volume flow rate prediction model, a model for the total volume flow rate of the two-phase fluid at the nozzle outlet is established. Based on the relationship between the nozzle outlet velocity and pressure and the liquid flow prediction model, a volumetric flow rate model for the liquid at the nozzle outlet is established. Based on the total volumetric flow rate model of the two-phase fluid at the nozzle outlet and the volumetric flow rate model of the liquid at the nozzle outlet, a volumetric flow rate model of the gas at the nozzle outlet is established. The gas flow prediction model is corrected based on the volumetric flow rate model of the gas at the nozzle outlet.

9. A method for selecting a post-pressure return flow regulating nozzle, characterized in that, The method includes: The flow rate at the nozzle outlet under post-pressure backflow regulation is predicted using the nozzle displacement prediction method according to any one of claims 1 to 5. Determine the nozzle parameters based on the flow rate at the nozzle outlet; Select the nozzle based on the nozzle parameters.

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