Method for real-time inversion of gas well productivity based on fracturing construction curve

Abstract

Aiming at the vacancy of the prior art, real-time data including construction pressure, displacement, sand concentration and the like in the fracturing construction process are creatively utilized, and the production capacity of a stratum is rapidly evaluated by analyzing a fracturing construction curve. Compared with a traditional method, the method does not need to depend on long-term production data and a complex geologic model, prediction of the gas well productivity and evaluation of the fracturing effect can be completed in a short time through real-time analysis of the fracturing construction curve, efficiency is improved, the defects in the prior art are overcome, rapid and accurate evaluation of the gas well productivity is achieved, and the method is suitable for popularization and application. Therefore, powerful technical support is provided for oil and gas field development and production.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas field development, and in particular to a method for real-time inversion of gas well productivity based on a fracturing construction curve. Background Art

[0002] In recent years, with the continuous development of oil and gas exploration and development technology, fracturing technology has gradually improved and matured. It has now become one of the important construction links for increasing oil and gas well production and has been widely used. During the fracturing construction process, timely evaluation of formation production capacity is the key to judging the fracturing effect so as to timely adjust and optimize the fracturing plan. Accurate prediction results of gas well post-fracturing production capacity will have a significant impact on the optimization design of fracturing construction and post-fracturing economic evaluation.

[0003] For the prediction of gas well production capacity, traditional production capacity prediction methods are mainly based on the analysis of geological engineering data and post-fracturing test data, including well test analysis, production capacity equation fitting and other methods. These methods usually require a large amount of production data and long-term observation, and production capacity prediction and evaluation can only be carried out after the fracturing construction is completed. This not only increases the time cost, but also delays the rapid assessment of the production capacity of the formation. Many evaluation methods rely on complex geological models and detailed geological data, and the acquisition and construction process of geological models and data is cumbersome, and may not accurately reflect the actual formation conditions. Therefore, the current gas well post-fracturing production capacity prediction method has a certain degree of insufficiency and is not suitable for large-scale application in field practice. This patent intends to achieve a rapid and accurate evaluation of gas well production capacity based on fracturing construction curve data, thereby providing strong technical support for oil and gas field development and production. Summary of the invention

[0004] The purpose of the present invention is to innovatively utilize real-time data during the fracturing construction process, including construction pressure, displacement, sand concentration, etc., and quickly evaluate the production capacity of the formation by analyzing the fracturing construction curve. Compared with the traditional method, this method does not need to rely on long-term production data and complex geological models. Through real-time analysis of the fracturing construction curve, the prediction of gas well production capacity and the evaluation of fracturing effect can be completed in a short time, which improves efficiency and overcomes the shortcomings of the prior art.

[0005] The technical solution adopted by the present invention to solve the above technical problems includes the following contents:

[0006] A method for real-time inversion of gas well productivity based on a fracturing operation curve comprises the following steps:

[0007] S1. Obtaining fracturing construction parameters of a fracturing gas well according to a fracturing construction curve;

[0008] S2. Based on real-time displacement injection data and formation parameters, the KGD model is used to estimate the geometric dimensions of the fractures during the fracturing process;

[0009] S3. Establish a fracturing percolation model to analyze the flow states of formation linear flow, fracture linear flow, and dual linear flow, and describe the expansion of fractures and the flow behavior of fluids during fracturing;

[0010] S4. Establish a gas well productivity equation based on the fracturing permeation model, calculate the open flow rate of the gas well, and evaluate the fracturing effect;

[0011] S5. Determine whether the open flow rate of the gas well reaches the target open flow rate of the gas well. If not, determine the displacement of the fracturing fluid for subsequent fracturing, and return to steps S2 and S4 to recalculate;

[0012] Furthermore, the fracturing construction parameters in steps S1 and S2 include bottom hole flowing pressure, fracturing fluid displacement, porosity, permeability, reservoir thickness, original formation pressure, Poisson's ratio, Young's modulus, and fracturing fluid viscosity.

[0013] Furthermore, the method for estimating the geometric dimensions of the cracks during the fracturing process in step S2 is:

[0014] (1) The KGD model is modified to obtain the calculation formula for the length and width of the fracturing crack:

[0015]

[0016] Where: L is the half length of the fracture, m; G is the shear modulus, MPa; Q is the displacement of the fracturing fluid, m 3 / min; v is Poisson's ratio; μ is liquid viscosity, MPa·min; t is injection time, h; W is slit width, m;

[0017] (2) The values ​​of fracturing fluid displacement and injection time are obtained through the fracturing construction curve.

[0018] (3) Calculate and draw a curve showing the relationship between the crack geometry and the fracturing construction time;

[0019] Furthermore, in step S3, a fracturing percolation model is established to analyze the flow states of formation linear flow, fracture linear flow, and bilinear flow, and to describe the expansion of fractures and the flow behavior of fluids during the fracturing process, including the following calculation process:

[0020] Introduce the following dimensionless quantity:

[0021] Dimensionless Time: Dimensionless pressure: Dimensionless bottom hole pressure: Dimensionless fracture pressure: Dimensionless hydraulic diffusivity: Dimensionless fracture reservoir coefficient: Dimensionless wellbore storage coefficient: Dimensionless crack transmission coefficient: Dimensionless length:

[0022] Where: C t is the total compression coefficient, C ft is the total crack compression coefficient, C w is the wellbore storage coefficient

[0023] Note: Since it is an injection well, the injection volume q is a negative number.

[0024] Establish the differential equations for fracture linear flow and formation linear flow:

[0025] The differential equation for linear flow in fracture is:

[0026]

[0027] The differential equation for linear flow in the formation is:

[0028]

[0029] The two differential equations are respectively based on the dimensionless time The Laplace transform of and the related dimensionless quantities can be solved to obtain the double logarithmic pressure formula for different flow states:

[0030] (1) The inversion of fracture linear flow results is:

[0031] In the early stage of fracturing, when the wellbore reservoir effect plays a dominant role:

[0032]

[0033] In the early stage of fracturing, when the wellbore storage effect is not obvious:

[0034]

[0035] (2) The bilinear flow results are inverted to obtain:

[0036] When the wellbore reservoir effect and skin effect are not considered:

[0037]

[0038] (3) The formation linear flow results are inverted to obtain:

[0039] When the wellbore reservoir effect and skin effect are not considered:

[0040]

[0041] Furthermore, in step S4, a gas well productivity equation is established based on the fracturing permeation model, and the calculation of the open flow rate of the gas well includes the following calculation process:

[0042] Introducing dimensionless time and dimensionless bottom hole pressure:

[0043]

[0044]

[0045] Since the linear flow in the mid-term formation is relatively stable, the prediction of the productivity of the fracturing gas well is based on the mid-term formation linear flow without considering the wellbore storage effect and skin effect as the basic analysis condition.

[0046] In isochronous well testing or modified isochronous well testing, it is necessary to conduct a stable point test for delayed well opening. The so-called stability is based on a practical consideration, which is reflected in the measuring point time, and it is considered that the pressure no longer changes significantly at this time. Therefore, the initial point of entering the quasi-steady state becomes the "marking point" for determining the delayed well opening time.

[0047] According to the definition of influence radius, calculate the influence radius r i Formula For radius r = r e constant volume gas reservoir, when r i =r e When , the flow begins to enter the quasi-steady state, and the time at this time is:

[0048]

[0049] Where: t s is the time it takes for a constant volume gas reservoir to reach a quasi-steady state after well opening, h; μ g is the viscosity of the formation natural gas, mPa·s; φ is the porosity of the gas layer, a decimal; k is the effective permeability of the formation, 10 -3 μm 2 (mD); r e is the radius of the gas well supply boundary, m; P R is the measured formation pressure, MPa;

[0050] The values ​​of parameters such as fracturing fluid displacement and sand concentration are obtained from the fracturing construction curve. According to the patent: A method for calculating the dynamic bottom hole pressure of fracturing based on construction data (CN112145167A), the bottom hole flowing pressure of the gas well is calculated, and a curve of the relationship between the bottom hole flowing pressure of the gas well and the fracturing construction time is drawn.

[0051] According to the theory of seepage mechanics, the open-flow rate of a gas well for radial steady Darcy flow of a single-phase gas in a plane can be solved by combining the double logarithmic pressure formula under medium-term formation linear flow, the dimensionless time formula, and the dimensionless bottom hole pressure formula:

[0052]

[0053] Where: q is the gas well production, m 3 / d; k is the gas layer permeability, D; h is the gas layer thickness, m; x f is the half length of the crack, m; t s is the time it takes for a constant volume gas reservoir to reach a quasi-steady state after well opening, h; C t is the total compression coefficient, 1 / MPa; p i is the formation pressure, MPa; p wf is the bottom hole flowing pressure, MPa.

[0054] Since the gas layer permeability k substituted into the calculation process is the result of lithology analysis and cannot accurately represent the entire gas layer, the calculation method of the inversion gas well production capacity has a certain error. The following formula is established to correct the gas layer permeability according to the relevant data of the formation linear flow after the pump is stopped during the fracturing construction based on the fracturing construction curve, and calculate the corrected gas well open flow.

[0055]

[0056] Furthermore, judging whether the open flow rate of the gas well reaches the target open flow rate of the gas well in step S5 comprises the following steps:

[0057] (1) According to steps S2 to S4, the open-flow rate that can be achieved by the gas well as the fracturing operation proceeds is calculated.

[0058] (2) The calculation results are displayed in the form of a curve, and the fracturing scheme is optimized by adjusting the fracturing displacement and fracturing construction time according to the target open flow rate of the gas well.

[0059] The beneficial effects of the present invention are:

[0060] The present invention calculates and draws a curve of the relationship between the geometric size of the fracturing crack and the fracturing construction time through the fracturing construction curve, calculates the open flow rate of the fracturing gas well by analyzing the flow state of the fluid in the formation and the crack, and draws a curve of the relationship between the open flow rate of the gas well and the fracturing construction time. The gas well production capacity can be predicted and the fracturing effect can be evaluated in real time during the fracturing construction process, thereby providing a basis for timely optimizing and adjusting the fracturing construction plan according to the target production of the gas well. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 It is the technical roadmap of the present invention.

[0062] Figure 2 It is the fracturing construction curve of AX well.

[0063] Figure 3It is a representation of a linearly extending crack—the KGD model.

[0064] Figure 4 It is a fracturing percolation model.

[0065] Figure 5 This is the curve of the change of fracture geometry size in AX well with fracturing construction time.

[0066] Figure 6 This is the relationship curve between the open flow rate of AX well and the fracturing construction time.

[0067] Figure 7 This is the relationship curve between the bottom flow pressure of Well AX and the fracturing construction time.

[0068] Figure 8 This is the relationship curve between the open-flow rate of well AX and the fracturing construction time (the arrow points to the current maximum open-flow rate).

[0069] Fig. 9 This is the relationship curve between the unimpeded flow rate of the AX well and the fracturing construction time (fracturing continues at the maximum displacement).

[0070] Fig.10 This is the relationship curve between the unobstructed flow rate of the AX well and the fracturing construction time (increasing the displacement and continuing fracturing). DETAILED DESCRIPTION

[0071] The present invention is described in detail below in conjunction with embodiments. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0072] A method for real-time inversion of gas well productivity based on a fracturing operation curve comprises the following steps:

[0073] S1. Obtaining fracturing construction parameters of a fracturing gas well according to a fracturing construction curve;

[0074] S2. Based on real-time displacement injection data and formation parameters, the KGD model is used to estimate the geometric dimensions of the fractures during the fracturing process;

[0075] S3. Establish a fracturing percolation model to analyze the flow states of formation linear flow, fracture linear flow, and dual linear flow, and describe the expansion of fractures and the flow behavior of fluids during fracturing;

[0076] S4. Establish a gas well productivity equation based on the fracturing permeation model, calculate the open flow rate of the gas well, and correct the open flow rate of the gas well according to the permeability to evaluate the fracturing effect;

[0077] S5. Determine whether the open flow rate of the gas well reaches the target open flow rate of the gas well. If not, determine the displacement of the fracturing fluid for subsequent fracturing, and return to steps S2 and S4 to recalculate;

[0078] The overall process of the present invention is shown in Figure 1 .

[0079] The fracturing construction parameters in step S1 include bottom hole flow pressure, fracturing fluid displacement, porosity, permeability, reservoir thickness, original formation pressure, Poisson's ratio, Young's modulus, and fracturing fluid viscosity.

[0080] The method for estimating the geometric dimensions of the cracks during the fracturing process in step S2 is:

[0081] (1) The KGD model is modified to obtain the calculation formula for the length and width of the fracturing crack:

[0082]

[0083] Where: L is the half length of the crack, m; G is the shear modulus, MPa; Q is the displacement, m 3 / min; v is Poisson's ratio; μ is liquid viscosity, MPa·min; t is injection time, h; W is slit width, m;

[0084] (2) Obtaining the values ​​of fracturing fluid displacement and injection time through the fracturing operation curve;

[0085] (3) Calculate and draw a curve showing the relationship between the crack geometry and the fracturing construction time;

[0086] The description of the expansion of the cracks and the flow behavior of the fluid during the fracturing process in step S3 includes the following derivation process:

[0087] Establish the differential equations for fracture linear flow and formation linear flow:

[0088] The differential equation for linear flow in fracture is:

[0089]

[0090] The differential equation for linear flow in the formation is:

[0091]

[0092] The two differential equations are respectively based on the dimensionless time The Laplace transform of and the related dimensionless quantities can be solved to obtain the double logarithmic pressure formula for different flow states:

[0093] (1) The inversion of fracture linear flow results is:

[0094] In the early stage of fracturing, when the wellbore reservoir effect plays a dominant role:

[0095]

[0096] In the early stage of fracturing, when the wellbore storage effect is not obvious:

[0097]

[0098] (2) The bilinear flow results are inverted to obtain:

[0099] When the wellbore reservoir effect and skin effect are not considered:

[0100]

[0101] (3) The formation linear flow results are inverted to obtain:

[0102] When the wellbore reservoir effect and skin effect are not considered:

[0103]

[0104] In step S4, the gas well productivity equation is established, and the calculation of the open flow rate of the gas well includes the following calculation process:

[0105] Introducing dimensionless time and dimensionless bottom hole pressure:

[0106]

[0107] In isochronous well testing or modified isochronous well testing, it is necessary to conduct a stable point test for delayed well opening. The so-called stability is based on a practical consideration, which is reflected in the measuring point time, and it is considered that the pressure no longer changes significantly at this time. Therefore, the initial point of entering the quasi-steady state becomes the "marking point" for determining the delayed well opening time.

[0108] According to the definition of influence radius, calculate the influence radius r i Formula For radius r = r e constant volume gas reservoir, when r i =r e When , the flow begins to enter the quasi-steady state, and the time at this time is:

[0109]

[0110] Where: t s is the time it takes for a constant volume gas reservoir to reach a quasi-steady state after well opening, h; μ g is the viscosity of the formation natural gas, mPa·s; φ is the porosity of the gas layer, a decimal; k is the effective permeability of the formation, 10 -3 μm 2 (mD); r e is the radius of the gas well supply boundary, m; P R is the measured formation pressure, MPa;

[0111] Since the linear flow in the mid-term formation is relatively stable, the prediction of the production capacity of the fracturing gas well is based on the basic analysis condition of not considering the wellbore storage effect and the skin effect under the linear flow in the mid-term formation. According to the seepage mechanics theory, the open-flow rate of the gas well with radial stable Darcy flow in the plane of single-phase gas can be solved by the double logarithmic pressure formula under the linear flow in the mid-term formation, the dimensionless time formula, and the dimensionless bottom hole pressure formula:

[0112]

[0113] Where: q is the gas well production, m 3 / d; k is the gas layer permeability, D; h is the gas layer thickness, m; x f is the half length of the crack, m; t s is the time it takes for a constant volume gas reservoir to reach a quasi-steady state after well opening, h; C t is the total compression coefficient, 1 / MPa; p i is the formation pressure, MPa; p wf is the bottom hole flowing pressure, MPa.

[0114] Since the gas layer permeability k substituted into the calculation process is the result of lithology analysis and cannot accurately represent the entire gas layer, the calculation method of the inversion gas well production capacity has a certain error. The following formula is established to correct the gas layer permeability according to the relevant data of the formation linear flow after the pump is stopped during the fracturing construction based on the fracturing construction curve, and calculate the corrected gas well open flow.

[0115]

[0116] In step S5, judging whether the open flow rate of the gas well reaches the target open flow rate of the gas well includes the following steps:

[0117] (1) According to steps S2 to S4, the open-flow rate that can be achieved by the gas well as the fracturing operation proceeds is calculated.

[0118] (2) The calculation results are displayed in the form of a curve, and the fracturing scheme is optimized by adjusting the fracturing displacement and fracturing construction time according to the target open flow rate of the gas well.

[0119] In a specific embodiment, the target single well is the AX well. In order to timely evaluate the fracturing effect according to the target production of the gas well and provide a basis for optimizing and adjusting the fracturing construction plan, it is necessary to invert the open flow rate of the gas well during the fracturing construction process to evaluate the fracturing effect and optimize the fracturing plan.

[0120] S1. Obtaining reservoir parameters and fracturing parameters of the target well;

[0121] The reservoir temperature is 144.8℃; the formation pressure is 120.47MPa; the effective thickness is 59.5m; the fracturing fluid viscosity is 160.8mpa·s; the average relative density of natural gas is 0.6559; the porosity is 6%; the Young's modulus E=6.2×10 4 MPa; Poisson's ratio ν = 0.25; fracturing fluid viscosity μ = 2.68 × 10 -9 MPa·min.

[0122] The HTP model is used for iterative calculation to obtain the deviation factor Z as 1.80. The calculated natural gas volume coefficient is 0.002153.

[0123] The viscosity of the formation natural gas is calculated using Lee's relationship as μ g It is 0.05189mPa·s.

[0124] The gas layer permeability k is taken as 0.1×10 -3 μm 2 ; Gas layer thickness h is 59.5m; Porosity φ is 6%; Bottom hole pressure p wf Take 0.1MPa.

[0125] For the gas layer, since the rock compression coefficient is much smaller than the gas compression coefficient, the rock compression coefficient is ignored, so C t ≈C g , take C t =8×10 -3 1 / MPa.

[0126] Select a single well control area of ​​2km 2 , other parameters are taken as above, and it can be calculated that the time for this gas reservoir to reach the pseudo-steady state after well opening is t s =164.5266s.

[0127] S2. Estimation of fracture geometry during fracturing using the KGD model

[0128] The values ​​of fracturing fluid displacement and injection time are obtained through the fracturing operation curve. The fracturing operation curve of AX gas well is shown in Figure 2 , and based on formation parameters such as Poisson's ratio and shear modulus, the KGD model is used to estimate the length and width of the fracture:

[0129]

[0130]

[0131] Where: L is the half length of the crack, m; G is the shear modulus, MPa; Q is the displacement, m 3 / min; v is Poisson's ratio; μ is liquid viscosity, MPa·min; t is injection time, h; W is slit width, m.

[0132] The relationship between the length and width of the fracturing crack and the fracturing time is plotted as follows: Figure 4 shown.

[0133] S3. Establish a fracturing percolation model to analyze the flow states of formation linear flow, fracture linear flow, and bilinear flow, and describe the expansion of fractures and the flow behavior of fluids during fracturing.

[0134] Since the mid-term formation linear flow is relatively stable, the prediction of the productivity of the fracturing gas well is based on the mid-term formation linear flow without considering the wellbore storage effect and the skin effect as the basic analysis condition. The double logarithmic pressure formula of the formation linear flow is introduced:

[0135]

[0136] S4. Establish a gas well productivity equation based on the fracturing permeation model, calculate the open flow rate of the gas well, and evaluate the fracturing effect;

[0137] According to the theory of seepage mechanics, the open-flow rate of a gas well for radial steady Darcy flow of a single-phase gas in a plane can be calculated by equation (3.4.21) and the dimensionless quantity The combined solution is:

[0138]

[0139] Substitute the parameters in S1 to calculate and draw the relationship curve between the open flow rate of the gas well and the fracturing construction time, such as Figure 6 shown.

[0140] Since the gas layer permeability k substituted into the calculation process is the result of lithology analysis and cannot accurately represent the entire gas layer, the calculation method of the inversion gas well production capacity has a certain error. The relevant data of the formation linear flow after the pump is stopped during the fracturing construction can be analyzed according to the fracturing construction curve:

[0141]

[0142] Where q is the displacement of fracturing fluid before stopping the pump, m 3 / d; k is the gas layer permeability, μm 2 ; h is the thickness of the air layer, m; p wf1 is the bottom hole flow pressure when the pump is stopped, MPa; p wf2 is the bottom hole pressure after the pump is stopped, MPa; B is the fracturing fluid volume coefficient, which is 1; μ is the fracturing fluid viscosity, mPa·s; x f is the half length of the crack when the pump is stopped, m; t is the time difference between the selected point after the pump is stopped and the time when the pump is stopped, h; C tis the total compression coefficient, 1 / MPa, taken as 4×10 -4 ; φ is the porosity of the gas layer, a decimal.

[0143] The relationship curve between bottom hole flow pressure and fracturing time is drawn through downhole data, and two research nodes are set, such as Figure 7 shown.

[0144] The values ​​of other parameters are consistent with the above fracturing percolation model, and can be calculated as follows:

[0145] k=0.065mD

[0146] When the gas layer permeability k is 0.065mD, the corrected gas well open flow curve can be calculated as follows: Figure 8 shown.

[0147] S5. Determine whether the open flow rate of the gas well reaches the target open flow rate of the gas well. If not, determine the displacement of the fracturing fluid for subsequent fracturing, and return to steps S2 and S4 to recalculate;

[0148] Assume that the target unimpeded flow rate of Bozi 1201 well when the pump is stopped is 700×10 4 m 3 / d, the current maximum unimpeded flow rate is Figure 8 As shown, it is 263×10 4 m 3 / d, if the standard is not met, the maximum displacement is used to continue fracturing, and the displacement Q is 4.75m 3 / min, substituting the target open-flow rate into the formula, it can be calculated that if the target open-flow rate is to be achieved, the length of the fracturing crack needs to reach 482.1336m. Figure 4 The crack length when the pump is stopped is 181.0430 m, and 301.0906 m is required to be added. Then the target crack length x f Substituting the displacement Q into the fracture geometry calculation formula, we can get that the time required to reach the target fracture length at the maximum displacement after the first pump stop is 11.27h. Draw the relationship curve between the unimpeded flow rate and the fracturing construction time when the fracturing is continued at the maximum displacement, as shown in Fig. 9 shown.

[0149] Depend on Fig. 9 It can be seen that the Bozi 1201 well has a 4.75m 3 / min fracturing fluid flow rate and continue fracturing for 11.27 hours to reach the target unobstructed flow rate. However, due to the long fracturing time, the fracturing construction plan can be adjusted, such as using a larger fracturing fluid flow rate for subsequent fracturing work. Change the fracturing fluid flow rate to 6m 3 / min, the relationship curve between the unimpeded flow rate and the fracturing construction time after changing the fracturing construction plan can be drawn, such as Fig.10 shown.

[0150] Depend on Fig.10 It can be seen that if the fracturing construction plan is adjusted after the first pump stop, the 6m 3 If fracturing is continued at a rate of fracturing fluid of / min, the target unobstructed flow rate can be reached after fracturing for 6.38 hours.

[0151] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technician familiar with this profession can make some changes or modify the technical contents disclosed above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A method for real-time inversion of gas well productivity based on fracturing construction curve, characterized in that: The following steps are included in sequence: S1. Obtaining fracturing construction parameters of a fracturing gas well according to a fracturing construction curve; S2. Based on real-time displacement injection data and formation parameters, the KGD model is used to estimate the geometric dimensions of the fractures during the fracturing process; S3. Establish a fracturing percolation model to analyze the flow states of formation linear flow, fracture linear flow, and dual linear flow, and describe the expansion of fractures and the flow behavior of fluids during fracturing; S4. Based on the fracturing permeation model, obtain the gas well productivity equation, calculate the open flow rate of the gas well, and correct the open flow rate of the gas well according to the permeability to evaluate the fracturing effect; S5. Determine whether the open flow rate of the gas well has reached the target open flow rate of the gas well. If not, determine the displacement of the fracturing fluid for subsequent fracturing, and return to steps S2 and S4 to recalculate.

2. The method for real-time inversion of gas well productivity based on fracturing construction curve according to claim 1, characterized in that: The fracturing parameters and formation parameters in steps S1 and S2 include bottom hole flow pressure, fracturing fluid displacement, porosity, permeability, reservoir thickness, original formation pressure, Poisson's ratio, Young's modulus, and fracturing fluid viscosity.

3. The method for real-time inversion of gas well productivity based on fracturing construction curve according to claim 1, characterized in that: The method for estimating the geometric dimensions of the cracks during the fracturing process in step S2 is: (1) The KGD model is modified to obtain the calculation formula for the length and width of the fracturing crack: Where: L is the half length of the crack, m; G is the shear modulus, MPa; Q is the displacement, m 3 / min; v is Poisson's ratio; μ is liquid viscosity, MPa·min; t is injection time, h; W is slit width, m; (2) Obtaining the values ​​of each parameter in the formula through the fracturing operation curve and gas well reservoir parameters; (3) Calculate and draw a curve showing the relationship between the crack geometry and the fracturing construction time.

4. The method for real-time inversion of gas well productivity based on fracturing construction curve according to claim 1, characterized in that: The step S3 includes the following calculation process: Establish the differential equations for fracture linear flow and formation linear flow: The differential equation for linear flow in fracture is: The differential equation for linear flow in the formation is: The two differential equations are respectively based on the dimensionless time The Laplace transform of and the related dimensionless quantities can be solved to obtain the double logarithmic pressure formula for different flow states: (1) The inversion of fracture linear flow results is: In the early stage of fracturing, when the wellbore reservoir effect plays a dominant role: In the early stage of fracturing, when the wellbore storage effect is not obvious: (2) The bilinear flow results are inverted to obtain: When the wellbore reservoir effect and skin effect are not considered: (3) The formation linear flow results are inverted to obtain: When the wellbore reservoir effect and skin effect are not considered: The subsequent analysis is based on the mid-term formation linear flow without considering the wellbore reservoir effect and skin effect.

5. The method for real-time inversion of gas well productivity based on fracturing construction curve according to claim 1, characterized in that: In step S4, a gas well productivity equation is established based on the fracturing permeation model, and the calculation of the open flow rate of the gas well includes the following calculation process: Introducing dimensionless time and dimensionless bottom hole pressure: According to the definition of influence radius, calculate the influence radius r i Formula For radius r = r e constant volume gas reservoir, when r i =r e When , the flow begins to enter the quasi-steady state, and the time at this time is: Where: t s is the time it takes for a constant volume gas reservoir to reach a quasi-steady state after well opening, h; μ g is the viscosity of the natural gas in the formation, mPa·s; φ is the porosity of the gas formation, a decimal; k is the effective permeability of the formation, 10 -3 μm 2 (mD); r e is the radius of the gas well supply boundary, m; P R is the measured formation pressure, MPa; Since the linear flow in the mid-term formation is relatively stable, the prediction of the production capacity of the fracturing gas well is based on the basic analysis condition that the wellbore storage effect and the skin effect are not considered under the linear flow in the mid-term formation. According to the seepage mechanics theory, the open-flow rate of the gas well with radial stable Darcy flow in the plane of single-phase gas can be solved by the double logarithmic pressure formula, dimensionless time formula and dimensionless bottom hole pressure formula under the linear flow in the mid-term formation: Where: q is the gas well production, m3 / d; k is the gas layer permeability, D; h is the gas layer thickness, m; x f is the half length of the crack, m; t s is the time it takes for a constant volume gas reservoir to reach a quasi-steady state after well opening, h; C t is the total compression coefficient, 1 / MPa; p i is the formation pressure, MPa; p wf is the bottom hole flowing pressure, MPa; The gas layer permeability k substituted into the calculation process is the result of lithology analysis, which cannot accurately represent the entire gas layer. Therefore, the calculation method of the inversion gas well production capacity has a certain error. The relevant data of the formation linear flow after the pump is stopped during the fracturing construction can be analyzed according to the fracturing construction curve: Where q is the displacement of fracturing fluid before stopping the pump, m 3 / d; k is the gas layer permeability, μm 2 ; h is the thickness of the air layer, m; p wf1 is the bottom hole flow pressure when the pump is stopped, MPa; p wf2 is the bottom hole pressure after the pump is stopped, MPa; B is the fracturing fluid volume coefficient, which is 1; μ is the fracturing fluid viscosity, mPa·s; x f is the half length of the crack when the pump is stopped, m; t is the time difference between the selected point after the pump is stopped and the time when the pump is stopped, h; C t is the total compression coefficient, 1 / MPa, taken as 4×10 -4 ; φ is the porosity of the gas layer, a decimal.

6. The method for real-time inversion of gas well productivity based on fracturing construction curve according to claim 1, characterized in that: Determining whether the open flow rate of the gas well reaches the target open flow rate of the gas well in step S5 comprises the following steps: (1) calculating the open-flow rate that can be achieved by the gas well as the fracturing operation proceeds according to steps S2 to S4; (2) The calculation results are displayed in the form of a curve, and the fracturing scheme is optimized by adjusting the fracturing displacement and fracturing construction time according to the target open flow rate of the gas well.

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