Well testing analysis method for tight gas reservoir multi-section fractured horizontal well

Abstract

The invention discloses a well testing analysis method for a tight gas reservoir multi-section fractured horizontal well, belongs to the technical field of oil-gas field development, and aims at solving the problem of well testing analysis for the tight sandstone gas reservoir multi-section fractured horizontal well at present. And when main flow well test interpretation software and a traditional well test model are used for well test analysis, the influence of the communication effect between a fracturing crack and a matrix cannot be considered, and the complex seepage characteristics of the segmented multi-cluster fracturing transformation area cannot be analyzed. According to the technical scheme, the method comprises the steps that a multi-section fractured horizontal well physical model is established, on the basis of tight gas reservoir line convergence solution, the matching effect between fractured fractures and a reservoir matrix is described through numerical discretization of fractured main fractures with unequal half lengths and unequal intervals and the concept of equivalent fractures distributed in the fractured main fractures, and therefore a mathematical model is established for solution; drawing a typical well testing curve; fitting the curve with an actually measured curve based on microseism monitoring and fracturing construction data to obtain well testing analysis parameters; and carrying out sensitivity analysis on the influence parameters.

Description

Technical Field

[0001] The invention belongs to the field of oil and gas field development, and particularly relates to a well testing analysis method for a multi-stage fractured horizontal well in a tight gas reservoir. Background Art

[0002] After long-term exploitation, conventional oil and gas resources on the earth have gradually decreased, and unconventional oil and gas resources have begun to become an important research object. In recent years, the United States, China, Canada and other countries have successively carried out large-scale development of tight gas reservoirs. Tight gas reservoirs usually refer to low-permeability reservoirs that produce dry gas. They have no natural production capacity and need to be developed through large-scale fracturing and transformation technology. my country's tight gas reserves are very rich, distributed in the Tarim Basin, Ordos Basin, Sichuan Basin, Qaidam Basin, Junggar Basin and other regions. Among them, the Sichuan Basin is rich in tight gas resources and has excellent development prospects.

[0003] Typical tight gas reservoirs are dense, have low permeability, small porosity, and poor connectivity, resulting in low production, rapid decline, and low natural production capacity. Therefore, it is difficult to achieve good results in the development of tight gas reservoirs using conventional methods. The use of fracturing horizontal well technology to develop tight gas reservoirs can not only help improve the production capacity of a single well, but also increase the ultimate recovery rate.

[0004] At present, the tight sandstone reservoirs in the Sichuan Basin are difficult to form complex fracture networks after fracturing due to their strong heterogeneity and underdeveloped natural fractures. Therefore, a high-intensity, low-damage multi-fracture fracturing technology suitable for tight sandstone gas reservoirs has been developed. The "multi-cluster perforation within a segment" process has been adopted to achieve the effect of replacing volume fracturing with close-spacing fracturing, which has promoted the development of tight sandstone gas reservoirs.

[0005] Due to the large-scale transformation of the reservoir, the formation characteristics of the near-well area have changed, and the fracturing effect is complex, which means that researchers cannot accurately obtain the parameters required for production layer evaluation and fracturing effect evaluation through traditional seepage models. When solving the seepage model of multi-stage fracturing horizontal wells, traditional models generally assume that the fractures are equally spaced and equal in length, the fracture surface is orthogonal to the horizontal wellbore, the fractures completely penetrate the reservoir, and there is infinite flow in the fractures.

[0006] By sorting out and statistically analyzing the well test curves of multi-stage fractured horizontal wells in tight gas reservoirs, it is found that the well test curves of multi-stage fractured horizontal wells often show radial flow horizontal section characteristics after the transition section. The overall trend of the curve is upward after the horizontal section, showing linear characteristics, which is more complex with the horizontal well seepage curve. This radial flow horizontal section feature cannot be accurately explained from the perspective of fractured horizontal well seepage theory, and is caused by the difference in the matching effect of the main fracture and the matrix in the reservoir.

[0007] At present, mainstream commercial well test software is usually used to interpret the well test of multi-stage fractured horizontal wells in tight gas reservoirs, and the interpretation is carried out according to the conventional multi-fracture horizontal well model and boundary conditions. However, since the 2D or 3D fracture models established by mainstream well test interpretation software for analytical well test and numerical well test cannot consider the influence of the communication effect between fractured fractures and matrix, only conventional multi-limited conductivity fractures or infinite conductivity fracture horizontal well models can be selected for interpretation, which leads to the fitting well test curve showing 1 / 4 slope linear flow or 1 / 2 slope linear flow after the transition section, which is obviously inconsistent with the seepage mechanism and real geological understanding of multi-stage fractured horizontal wells in tight gas reservoirs. The fracture parameters of multi-stage fractured horizontal wells obtained by interpretation often have large errors, resulting in a wrong understanding of the real production capacity of the reservoir when formulating development plans.

[0008] For conventional well test interpretation of multi-stage fracturing horizontal wells, traditional models are too ideal. Their modeling characteristics are based on the evenly spaced distribution of artificial fractures of equal length, which cannot accurately represent the seepage of gas in the reservoir, resulting in mismatched results when performing pressure and production analysis. This paper analyzes the new horizontal well fracturing technology in recent years. On the basis of meeting the field seepage characteristics, it aims at the communication effect between the main fracture and the reservoir matrix in the tight sandstone reservoir, and provides a method for the study of segmented multi-cluster fracturing technology in tight sandstone gas reservoirs by proposing the concept of equivalent fractures. Summary of the invention

[0009] In order to overcome the defects and deficiencies in the above-mentioned prior art, the present invention provides a well test analysis method for multi-stage fracturing horizontal wells in tight gas reservoirs. Aiming at the problem that the seepage around the volume fracturing cracks in multi-stage fracturing horizontal wells in tight sandstone gas reservoirs presents complex flow, which is different from the seepage model of traditional fracturing horizontal wells, the present invention provides a way of thinking that considers the matching effect of reservoir matrix and fracturing cracks, and establishes a well test method that is more in line with field characteristics. Thus, it is determined that the stress sensitive effect influencing parameters include formation permeability modulus and fracture permeability modulus, the reservoir influencing parameters include formation permeability, original formation pressure, and reservoir thickness, and the fracture influencing parameters include the number of fractures, fracture half-length, and fracture conductivity; based on the influencing factors, a seepage model for multi-stage fracturing horizontal wells in tight sandstone gas reservoirs is established; the seepage model is processed to obtain the relationship between the bottom hole flow pressure and the influencing factors; and the well test analysis is completed according to the relationship between the bottom hole flow pressure and the influencing factors.

[0010] In order to solve the above problems existing in the prior art, the present invention is implemented through the following technical solutions.

[0011] The present invention provides a well testing analysis method for a multi-stage fractured horizontal well in a tight gas reservoir, the method comprising the following steps:

[0012] S1. Based on the relevant data of multi-stage fractured horizontal wells in tight gas reservoirs, a physical model of multi-stage fractured horizontal wells in tight gas reservoirs is established;

[0013] S2. Determine the factors affecting reservoir and fracture parameters of multi-stage fractured horizontal wells in tight gas reservoirs;

[0014] S3, establishing a mathematical model of seepage applicable to multi-stage pressure horizontal wells in tight gas reservoirs based on the influencing factors and the physical model;

[0015] S4, solving the seepage mathematical model established in step S3 to obtain a relationship between the bottom hole flow pressure and the influencing factors;

[0016] S5. Obtaining a measured curve of a multi-stage fractured horizontal well test in a tight gas reservoir based on the collected well test data, and fitting the measured curve with a theoretical curve obtained by solving the seepage mathematical model based on known well test reservoir and fracture parameter initial values;

[0017] S6. According to the fitting result between the measured curve and the theoretical curve, the initial values ​​of the test well reservoir and fracture parameters are dynamically adjusted, and when the fitting result meets the conditions, the seepage mathematical model is solved based on the current test well reservoir and fracture parameters to obtain the pressure transformation parameters.

[0018] Further preferably, in step S1, the relevant data of the multi-stage fracturing horizontal well in the tight gas reservoir includes the reservoir characteristics of the on-site tight gas reservoir, the fracturing construction technology of the multi-stage fracturing horizontal well and the monitoring microseismic data.

[0019] Further preferably, in step S1, the assumptions of the physical model of the multi-stage fractured horizontal well in the tight gas reservoir established include that the tight gas reservoir is infinite in the horizontal direction, and the top and bottom are closed boundaries; the fractured horizontal well is located at any position of the gas reservoir, parallel to the top and bottom boundaries, and after multi-stage fracturing, a total of multiple vertical transverse fractures are formed, and the half-lengths of the main fractures and the main fracture spacing are different; horizontal transverse equivalent fractures are established perpendicular to the main fracture distribution to describe the matching effect between the fracture and the reservoir matrix; the gas well is produced at a constant surface production rate, and the fluid in the formation first flows from the matrix into the fracture at different flow rates, and then flows into the horizontal wellbore along the direction of the hydraulic fracture, and the hydraulic fracture and the horizontal wellbore are both infinitely conductive.

[0020] Further preferably, in step S2, the influencing factors include starting pressure gradient, stress sensitivity effect, reservoir parameters and fracture parameters.

[0021] More preferably, the stress sensitive effect includes formation permeability modulus and fracture permeability modulus.

[0022] More preferably, the reservoir parameters include formation permeability, formation original pressure and reservoir thickness.

[0023] More preferably, the fracture parameters include the number of fractures, the half-length of fractures and the conductivity of fractures.

[0024] Further preferably, in step S3, a dimensionless unstable seepage differential equation of the centerline sink of the tight gas reservoir is established taking into account the stress sensitivity effect and reservoir parameters:

[0025]

[0026] The initial condition is The boundary conditions of fixed production are The infinite outer boundary condition in the horizontal direction is Defining dimensionless variables

[0027] In the above formula, K i is the reservoir permeability, mD; h is the reservoir thickness, m; T is the absolute temperature, K; q sc is the ground production, m 3 / d; m is pseudo pressure, MPa 2 / (mPa·s);m i is the original pseudo-pressure of the reservoir, MPa 2 / (mPa·s);γ m is the permeability modulus defined by pseudo-pressure, mPa·s / MPa 2 ; t is time, h; μ is gas viscosity, mPa·s; φ is gas reservoir porosity, decimal; C t is the comprehensive compression coefficient, MPa -1 ;X f is the crack half-length, m; r is the radial distance, m.

[0028] Further preferably, in step S3, a mathematical model that supplementarily considers fracture parameters is established based on the dimensionless unstable seepage differential equation of the centerline sink of the tight gas reservoir based on stress sensitivity effect and reservoir parameters.

[0029] More preferably, the fracturing crack unit of the bottom hole pressure response of the fracturing horizontal well is numerically discretized; specifically:

[0030] M transverse fractures of different lengths are distributed perpendicular to the horizontal wellbore at different intervals. The half length of the fracture is X if , the coordinates of the intersection of the i-th crack on the y-axis and the y-axis are (0, yi), where i = 1, 2, …, M; the distance between adjacent cracks is Δyi = yi-yi-1; each crack is divided into 2N micro-element segments along the X-axis, then the main crack has a total of 2N+1 endpoints and 2N center points, and each equivalent crack is divided into 2O micro-element segments, then the equivalent crack has a total of 2O+1 endpoints and 2O center points;

[0031] Defining dimensionless variables Yes wD =y Di , x mwD =x mD i; where r w is the wellbore radius, m; X if is the half length of each main crack, m; X xf is the half length of an equivalent crack, m; △f i is the spacing between cracks, m;

[0032] The dimensionless pseudo-pressure response of the discrete unit (i, j) at any point (x, y) in the gas reservoir in the pull-type space is obtained as follows:

[0033]

[0034] Applying the principle of pressure drop superposition, (M×2N×2O) discrete units are placed at any position (x D ,y D The dimensionless pseudo-pressure total response generated at ) is In the formula, (x D ,y D ) is taken as the midpoint of a discrete unit (X Dk,v ,Y Dk,v ),but Where K0 is the Bessel function of the second-order zero-order imaginary quantity, s is the Laplace variable, is the linear density flow corresponding to the discrete unit (i, j), the unit is dimensionless;

[0035] According to the infinite conductivity assumption, the pressure in the horizontal wellbore and the artificial fracture system is equal everywhere, and the dimensionless pseudo-pressure in the horizontal wellbore can be expressed as

[0036] Will In the expression, k and v are taken over all discrete units (k = 1, 2, ..., M; v = 1, 2, ..., 2N), then M × 2N linear equations can be obtained, including M × 2N + 1 unknown quantities. and

[0037] More preferably, the endpoint coordinates of the i-th crack are marked as (x i,1 ,y i,1 ) to (x i,2N+1 ,y i,2N+1 ), whose 2N center points are marked as (X i,1 ,Y i,1 ) to (X i,2N ,Yi,2N );Each center point has an equal length X xf The lateral equivalent fractures are parallel to the horizontal wellbore, that is, the number of equivalent fractures is equal to the number of microelement ends of the main fractures. The number of equivalent fractures can be changed by adjusting the number of microelement ends of the main fractures.

[0038] More preferably, the coordinates of the two endpoints of the jth segment (j=1, 2, ..., 2N) of the ith main crack are expressed as (x i,j ,y i,j ) and (x i,j+1 ,y i,j+1 ), the corresponding center point coordinates are expressed as (X i,j , Y i,j ), whose mathematical expressions are respectively,

[0039] The endpoints of the main crack micro-element segment are expressed as

[0040] The midpoint of the main crack microelement segment is expressed as

[0041] The coordinates of the two endpoints of the equivalent crack segment z of the i-th main crack segment j (j=1, 2, ..., 2N) are expressed as (x i,j,z ,y i,j,z ) and (x i,j+1,z ,y i,j+1,z ), the corresponding center point coordinates are expressed as (X i,j,z , Y i,j,z ); their mathematical expressions are,

[0042] The endpoints of the equivalent crack microelement segment are expressed as

[0043]

[0044] The midpoint of the equivalent crack microelement segment is expressed as

[0045]

[0046] Further preferably, in step S4, the seepage mathematical model established in step S3 is solved, specifically, M×2N+1 equations are closed-formed and solved to obtain the linear density flow and bottom hole pseudo-pressure response in each discrete unit; the superposition principle is utilized to obtain the bottom hole pressure solution considering the wellbore reservoir effect and the skin effect according to the bottom hole pressure solution; and Stehfest numerical inversion is utilized to transform the bottom hole pressure in Laplace space considering the wellbore reservoir effect and the skin effect into the bottom hole pressure in real space.

[0047] More preferably, the flow normalization constraint condition is limited to the total flow into the horizontal wellbore being equal to the sum of the flow rates of the discrete fracture units, and its expression in Laplace space is: That is, (M×2N+1) equations can be closed to solve (M×2N+1) unknown quantities, namely, the linear density flow rate in each discrete unit and the bottom hole pseudo-pressure response

[0048] Further preferably, according to the Duhamel principle, the expression of the pseudo-pressure perturbation solution of the pressure horizontal well considering the influence of wellbore reservoir and skin effect is: Through Stehfest numerical inversion, the dimensionless pseudo-pressure solution of a fractured horizontal well in a uniform medium tight gas reservoir considering the permeability stress sensitivity effect can be obtained as: Defining a dimensionless variable Where C is the well storage coefficient, m 3 / MPa; S is the skin coefficient, the unit is dimensionless.

[0049] Further preferably, in step S5, the pressure and pressure derivative measured curves are obtained based on the collected well test data, and then the actual flow process of the fluid is analyzed based on the characteristics of the measured curves; the pressure and pressure derivative curves are divided into multiple fractured horizontal well seepage flow stages according to the actual flow process of the fluid.

[0050] Further preferably, based on the relationship between the bottom hole flowing pressure and the influencing factors, a typical curve graph under the influence of the starting pressure gradient, stress sensitivity effect and fracturing crack parameters is obtained, and a parameter sensitivity analysis is performed on the typical curve graph to obtain the sensitivity of the influencing factors.

[0051] Compared with the prior art, the beneficial technical effects brought by the present invention are as follows:

[0052] 1. The implementation of the present invention determines the input and output of the inversion parameters through the collected geological data, well test data, fracturing construction data, etc. Secondly, the pressure and pressure derivative curves are obtained according to the well test data, and then the actual flow process is analyzed according to the characteristic line segments shown on the curve. The flow type of the well test data is divided according to the actual flow process, and a suitable model is selected for well test fitting. The fitting parameters are coupled with pressure and production using production dynamic data to test the reliability of the results. Finally, the fracturing transformation parameters are determined, evaluated and applied.

[0053] 2. The present invention considers the stress sensitivity effect and the influence of matrix and reservoir fracturing crack factors to obtain the relationship between bottom hole flow pressure and influencing factors, filling the gap in the current well test analysis of tight gas multi-stage volume fracturing horizontal wells. At the same time, according to the typical curve diagram drawn according to the obtained relationship between the bottom hole flow pressure and the influencing factors, the parameter sensitivity analysis can be realized, and the influence of each parameter on the shape of the well test analysis interpretation curve can be further understood, thereby improving the pertinence and efficiency of the fitting work. Aiming at the special seepage characteristics of tight gas multi-stage volume fracturing horizontal wells, the well test analysis method of the present invention is more in line with the seepage theory and actual geological conditions of low permeability gas reservoirs, and the analysis parameters are more accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 It is a flow chart of the well testing analysis method of the multi-stage fractured horizontal well in a tight gas reservoir of the present invention;

[0055] Figure 2 This is a schematic diagram of microseismic monitoring;

[0056] Figure 3 Schematic diagram of the crack discrete mathematical model established to consider the equivalent crack;

[0057] Figure 4 This is a typical curve diagram of the well test model without considering the equivalent fracture;

[0058] Figure 5 This is a typical curve of the well test model considering equivalent fractures;

[0059] Figure 6 This is the well test curve of the horizontal well with tight gas fracturing measured on site;

[0060] Figure 7 The well test curves of horizontal wells with tight gas fracturing due to different fracture half-lengths;

[0061] Figure 8 The well test curves of horizontal wells with tight gas fracturing are shown below:

[0062] Fig. 9 This is a well test curve diagram of the effect of different fracture spacing on tight gas fracturing horizontal wells. DETAILED DESCRIPTION

[0063] The technical solution of the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0064] Example 1

[0065] As a preferred embodiment of the present invention, refer to the attached specification Figure 1 As shown, this embodiment discloses a well testing analysis method for a multi-stage fractured horizontal well in a tight gas reservoir, the method comprising the following steps:

[0066] S1. Based on the relevant data of multi-stage fractured horizontal wells in tight gas reservoirs, a physical model of multi-stage fractured horizontal wells in tight gas reservoirs is established;

[0067] S2. Determine the factors affecting reservoir and fracture parameters of multi-stage fractured horizontal wells in tight gas reservoirs;

[0068] S3, establishing a mathematical model of seepage applicable to multi-stage pressure horizontal wells in tight gas reservoirs based on the influencing factors and the physical model;

[0069] S4, solving the seepage mathematical model established in step S3 to obtain a relationship between the bottom hole flow pressure and the influencing factors;

[0070] S5. Obtaining a measured curve of a multi-stage fractured horizontal well test in a tight gas reservoir based on the collected well test data, and fitting the measured curve with a theoretical curve obtained by solving the seepage mathematical model based on known well test reservoir and fracture parameter initial values;

[0071] S6. According to the fitting result between the measured curve and the theoretical curve, the initial values ​​of the test well reservoir and fracture parameters are dynamically adjusted, and when the fitting result meets the conditions, the seepage mathematical model is solved based on the current test well reservoir and fracture parameters to obtain the pressure transformation parameters.

[0072] In this embodiment, the relevant data of the multi-stage fracturing horizontal well in the tight gas reservoir include but are not limited to: reservoir characteristics of the on-site tight gas reservoir, fracturing construction technology of the multi-stage fracturing horizontal well and monitoring microseismic data.

[0073] In this embodiment, the assumptions of the physical model of the multi-stage fractured horizontal well in the tight gas reservoir include that the tight gas reservoir is infinite in the horizontal direction, and the top and bottom are closed boundaries; the fractured horizontal well is located at any position of the gas reservoir, parallel to the top and bottom boundaries, and after multi-stage fracturing, a total of multiple vertical transverse fractures are formed, and the half-lengths of the main fractures and the main fracture spacing are different; horizontal transverse equivalent fractures are established perpendicular to the main fracture distribution to describe the matching effect between the fracture and the reservoir matrix; the gas well is produced at a constant surface rate, and the fluid in the formation first flows from the matrix into the fracture at different flow rates, and then flows into the horizontal wellbore along the direction of the hydraulic fracture, and both the hydraulic fracture and the horizontal wellbore have infinite conductivity.

[0074] Example 2

[0075] As another preferred embodiment of the present invention, this embodiment is a further detailed elaboration and supplement to the technical solution of the present invention based on the above-mentioned embodiment 1. In this embodiment, the factors affecting the reservoir and fracture parameters of the multi-stage fractured horizontal well in the imaged tight gas reservoir include the starting pressure gradient, the stress sensitivity effect, the reservoir parameters and the fracture parameters, wherein the stress sensitivity effect includes the formation permeability modulus and the fracture permeability modulus. The reservoir parameters include the formation permeability, the original formation pressure and the reservoir thickness. The fracture parameters include the number of fractures, the fracture half-length and the fracture conductivity.

[0076] Furthermore, a mathematical seepage model applicable to multi-stage pressure horizontal wells in tight gas reservoirs is established based on the influencing factors and the physical model.

[0077] As an example, the dimensionless unstable seepage differential equation of the centerline sink in a tight gas reservoir considering stress sensitivity effects and reservoir parameters is established:

[0078]

[0079] The initial condition is The boundary conditions of fixed production are The infinite outer boundary condition in the horizontal direction is Defining dimensionless variables

[0080] In the above formula, K i is the reservoir permeability, mD; h is the reservoir thickness, m; T is the absolute temperature, K; q sc is the ground production, m 3 / d; m is pseudo pressure, MPa 2 / (mPa·s);m i is the original pseudo-pressure of the reservoir, MPa 2 / (mPa·s);γ m is the permeability modulus defined by pseudo-pressure, mPa·s / MPa 2 ; t is time, h; μ is gas viscosity, mPa·s; φ is gas reservoir porosity, decimal; C t is the comprehensive compression coefficient, MPa -1 ;X f is the crack half-length, m; r is the radial distance, m.

[0081] Example 3

[0082] As another preferred embodiment of the present invention, this embodiment is a further detailed description and supplement to the technical solution of the present invention based on the above-mentioned embodiment 1 or embodiment 2. In this embodiment, based on the dimensionless unstable seepage differential equation of the centerline sink of a tight gas reservoir based on stress sensitivity effect and reservoir parameters, a mathematical model that supplements the consideration of fracture parameters is established.

[0083] The key point is how to consider the pressure response characteristics of different sections of the fractured horizontal well. Specifically, the fracture unit of the bottom hole pressure response of the fractured horizontal well is numerically discretized: M transverse fractures of unequal lengths are distributed perpendicular to the horizontal wellbore at unequal intervals, and the half-length of the fracture is X. if , the coordinates of the intersection of the i-th crack on the y-axis and the y-axis are (0,yi), where i=1,2,…,M; the distance between adjacent cracks is Δyi=yi-yi-1; each crack is divided into 2N micro-element segments along the X-axis, then the main crack has a total of 2N+1 endpoints and 2N center points, and each equivalent crack is divided into 2O micro-element segments, then the equivalent crack has a total of 2O+1 endpoints and 2O center points.

[0084] As an example, the endpoint coordinates of the i-th crack are marked as (x i,1 ,y i,1 ) to (x i,2N+1 ,y i,2N+1 ), whose 2N center points are marked as (X i,1 ,Y i,1 ) to (X i,2N ,Y i,2N );Each center point has an equal length X xf The lateral equivalent fractures are parallel to the horizontal wellbore, that is, the number of equivalent fractures is equal to the number of microelement ends of the main fractures. The number of equivalent fractures can be changed by adjusting the number of microelement ends of the main fractures.

[0085] Specifically, the coordinates of the two endpoints of the jth segment (j=1, 2, ..., 2N) of the ith main crack are expressed as (x i,j ,y i,j ) and (x i,j+1 ,y i,j+1 ), the corresponding center point coordinates are expressed as (X i,j , Y i,j ), whose mathematical expressions are respectively,

[0086] The endpoints of the main crack micro-element segment are expressed as

[0087] The midpoint of the main crack microelement segment is expressed as

[0088] The coordinates of the two endpoints of the equivalent crack segment z of the i-th main crack segment j (j=1, 2, ..., 2N) are expressed as (xi,j,z ,y i,j,z ) and (x i,j+1,z ,y i,j+1,z ), the corresponding center point coordinates are expressed as (X i,j,z , Y i,j,z ); their mathematical expressions are,

[0089] The endpoints of the equivalent crack microelement segment are expressed as

[0090]

[0091] The midpoint of the equivalent crack microelement segment is expressed as

[0092]

[0093] The process of establishing a mathematical model for seepage in multi-stage pressure horizontal wells in tight gas reservoirs based on fracture parameters is as follows:

[0094] Defining dimensionless variables Yes wD =y Di , x mwD =x mD i; where r w is the wellbore radius, m; X if is the half length of each main crack, m; X xf is the half length of an equivalent crack, m; △f i is the spacing between cracks, m;

[0095] The dimensionless pseudo-pressure response of the discrete unit (i, j) at any point (x, y) in the gas reservoir in the pull-type space is obtained as follows:

[0096]

[0097] Applying the principle of pressure drop superposition, (M×2N×2O) discrete units are placed at any position (x D ,y D The dimensionless pseudo-pressure total response generated at ) is In the formula, (x D ,y D ) is taken as the midpoint of a discrete unit (X Dk,v ,Y Dk,v ),but Where K0 is the Bessel function of the second-order zero-order imaginary quantity, s is the Laplace variable, is the linear density flow corresponding to the discrete unit (i, j), the unit is dimensionless;

[0098] According to the infinite conductivity assumption, the pressure in the horizontal wellbore and the artificial fracture system is equal everywhere, and the dimensionless pseudo-pressure in the horizontal wellbore can be expressed as

[0099] Will In the expression, k and v are taken over all discrete units (k = 1, 2, ..., M; v = 1, 2, ..., 2N), then M × 2N linear equations can be obtained, including M × 2N + 1 unknown quantities. and

[0100] Example 4

[0101] As another preferred embodiment of the present invention, this embodiment is a further detailed supplement and elaboration of the technical solution of the present invention based on the above-mentioned embodiment 1, embodiment 2 or embodiment 3. In this embodiment, the mathematical model of seepage established in step S3 is solved, specifically, M×2N+1 equations are closed-formed to obtain the linear density flow rate and bottom hole pseudo-pressure response in each discrete unit; the bottom hole pressure solution considering the wellbore reservoir effect and the skin effect is obtained according to the bottom hole pressure solution by using the superposition principle; the bottom hole pressure considering the wellbore reservoir effect and the skin effect in Laplace space is transformed into the bottom hole pressure in real space by using Stehfest numerical inversion.

[0102] Specifically, the flow normalization constraint condition is that the total flow into the horizontal wellbore is equal to the sum of the flow rates of each fracture discrete unit, and its expression in Laplace space is: That is, (M×2N+1) equations can be closed to solve (M×2N+1) unknown quantities, namely, the linear density flow rate in each discrete unit and the bottom hole pseudo-pressure response

[0103] According to Duhamel's principle, the expression of the pseudo-pressure perturbation solution of a pressure horizontal well considering the influence of wellbore reservoir and skin effect is: Through Stehfest numerical inversion, the dimensionless pseudo-pressure solution of a fractured horizontal well in a uniform medium tight gas reservoir considering the permeability stress sensitivity effect can be obtained as: Defining a dimensionless variable Where C is the well storage coefficient, m 3 / MPa; S is the skin coefficient, the unit is dimensionless.

[0104] In step S5, the measured pressure and pressure derivative curves are obtained based on the collected well test data, and then the actual flow process of the fluid is analyzed based on the characteristics of the measured curves; the pressure and pressure derivative curves are divided into multiple fracturing horizontal well seepage flow stages according to the actual flow process of the fluid. According to the relationship between the bottom hole flow pressure and the influencing factors, a typical curve under the influence of the starting pressure gradient, stress sensitivity effect and fracturing crack parameters is obtained, and a parameter sensitivity analysis is performed on the typical curve to obtain the sensitivity of the influencing factors.

[0105] Example 5

[0106] As another preferred embodiment of the present invention, this embodiment is based on the above-mentioned embodiment 1, embodiment 2, embodiment 3 or embodiment 4, and further elaborates and supplements the technical solution of the present invention. In this embodiment, the well test analysis is completed according to the relationship between the bottom hole flow pressure and the influencing factors, including: according to the relationship between the bottom hole flow pressure and the influencing factors, a typical curve diagram under the influence of stress sensitivity effect and reservoir / crack parameters is obtained. Among them, the well test analysis is performed based on the microseismic data of the fractured horizontal well, and the microseismic monitoring diagram is as follows Figure 2 , Figure 3 is a schematic diagram of the fracture discrete mathematical model established by considering equivalent fractures. The typical curve of the well test model without considering equivalent fractures is as follows: Figure 4 The typical curve of the well test model considering equivalent fracture is as follows: Figure 5 , compared with the field measured tight gas fracturing horizontal well test curve Figure 6 Comparative analysis shows that this method of model building is more in line with the actual situation; Figure 5 The typical curves of dimensionless pseudo-pressure and its derivative in fractured horizontal wells in tight gas reservoirs can be divided into six flow stages: 1-pure wellbore storage effect stage; 2-transition flow stage after wellbore storage; 3-early fracture linear flow stage; 4-mid-term fracture pseudo-radial flow stage; 5-system linear flow stage; 6-late system pseudo-radial flow stage.

[0107] like Figures 7 to 9 As shown, further, completing the well test analysis based on the relationship between the bottom hole flowing pressure and the influencing factors also includes: performing parameter sensitivity analysis on the typical curve diagram to obtain the sensitivity of the influencing factors; including taking the fracture half-length as 10m, 50m, and 100m respectively, Figure 7 It can be seen that the pressure curve does not change significantly when the combination of fractures with different half-lengths is changed, indicating that the total controlled area of ​​the fractures is the same due to the equal total length of the fractures; the larger the overall dimensionless fracture half-length, the longer the duration of the linear flow stage and the shorter the early radial flow stage; the fracture conductivity is 1mD, 10mD, and 100mD respectively, Figure 8It can be seen that permeability mainly affects the transition stage and the linear flow stage. The greater the fracture conductivity, the stronger the fracture gas transport capacity, the earlier the flow in the fracture ends, and the more the production pressure difference decreases. The fracture spacing is 10m, 100m, and 450m respectively. Fig. 9 It can be seen that the larger the crack spacing is, the longer the early radial flow stage lasts and the later the overall elliptical flow stage appears. When the spacing is small, the early radial flow stage may be masked.

[0108] Typical well test analysis, obtaining measured curves of multi-stage fractured horizontal well test in tight oil reservoirs based on collected well test data, and fitting the measured curves with the theoretical curves obtained by solving the mathematical model, including: obtaining measured pressure and pressure derivative curves based on the collected well test data, and then analyzing the actual flow process of the fluid based on the characteristics of the measured curves; dividing the pressure and pressure derivative curves into seepage flow stages of the multi-stage fractured horizontal well according to the actual flow process of the fluid.

[0109] Characteristic curve sensitivity analysis, completing the well test analysis based on the relationship between the bottom hole flow pressure and the influencing factors also includes: obtaining the typical curve graph under the influence of the starting pressure gradient, the stress sensitivity effect and the fracturing crack parameters according to the relationship between the bottom hole flow pressure and the influencing factors, performing parameter sensitivity analysis on the typical curve graph, and obtaining the sensitivity of the influencing factors.

[0110] Parameter fitting analysis, completing the well test analysis according to the relationship between the bottom hole flowing pressure and the influencing factors also includes: obtaining well test data of multi-stage fractured horizontal wells in tight gas reservoirs; obtaining an actual parameter curve graph based on the well test data; fitting the actual parameter curve graph with the typical curve graph to obtain well test analysis parameters.

[0111] Finally, it should be noted that the above embodiments are only used to illustrate rather than limit the technical solutions of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the present invention can still be modified or replaced by equivalents. Any modification or partial replacement that does not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A well testing analysis method for multi-stage fractured horizontal wells in tight gas reservoirs, characterized by: The method comprises the following steps, S1. Based on the relevant data of multi-stage fractured horizontal wells in tight gas reservoirs, a physical model of multi-stage fractured horizontal wells in tight gas reservoirs is established; S2. Determine the factors affecting reservoir and fracture parameters of multi-stage fractured horizontal wells in tight gas reservoirs; S3, establishing a mathematical model of seepage applicable to multi-stage pressure horizontal wells in tight gas reservoirs based on the influencing factors and the physical model; S4, solving the seepage mathematical model established in step S3 to obtain a relationship between the bottom hole flow pressure and the influencing factors; S5. Obtaining a measured curve of a multi-stage fractured horizontal well test in a tight gas reservoir based on the collected well test data, and fitting the measured curve with a theoretical curve obtained by solving the seepage mathematical model based on known well test reservoir and fracture parameter initial values; S6. According to the fitting result between the measured curve and the theoretical curve, the initial values ​​of the test well reservoir and fracture parameters are dynamically adjusted, and when the fitting result meets the conditions, the seepage mathematical model is solved based on the current test well reservoir and fracture parameters to obtain the pressure transformation parameters.

2. A well testing analysis method for a multi-stage fractured horizontal well in a tight gas reservoir as claimed in claim 1, characterized in that: In step S1, the relevant data of the multi-stage fracturing horizontal well in the tight gas reservoir include the reservoir characteristics of the on-site tight gas reservoir, the fracturing construction technology of the multi-stage fracturing horizontal well and the monitoring microseismic data.

3. A well testing analysis method for a multi-stage fractured horizontal well in a tight gas reservoir as claimed in claim 1, characterized in that: In step S1, the assumptions of the physical model of multi-stage fractured horizontal wells in tight gas reservoirs include that the tight gas reservoir is infinite in horizontal direction, and the top and bottom are closed boundaries; the fractured horizontal well is located at any position of the gas reservoir, parallel to the top and bottom boundaries, and after multi-stage fracturing, a total of multiple vertical transverse fractures are formed, and the half-lengths and main fracture spacings of each main fracture are different; horizontal transverse equivalent fractures are established perpendicular to the main fracture distribution to describe the matching effect between the fractures and the reservoir matrix; the gas well is produced at a constant surface rate, and the fluid in the formation first flows from the matrix into the fracture at different flow rates, and then flows into the horizontal wellbore along the direction of the hydraulic fracture, and both the hydraulic fracture and the horizontal wellbore have infinite conductivity.

4. A well testing analysis method for a multi-stage fractured horizontal well in a tight gas reservoir as claimed in claim 1, characterized in that: In step S2, the influencing factors include starting pressure gradient, stress sensitivity effect, reservoir parameters and fracture parameters.

5. A well testing analysis method for a multi-stage fractured horizontal well in a tight gas reservoir as claimed in claim 4, characterized in that: The stress sensitive effects include formation permeability modulus and fracture permeability modulus.

6. A well testing analysis method for a multi-stage fractured horizontal well in a tight gas reservoir as claimed in claim 4, characterized in that: The reservoir parameters include formation permeability, formation original pressure and reservoir thickness.

7. A well testing analysis method for a multi-stage fractured horizontal well in a tight gas reservoir as claimed in claim 4, characterized in that: The fracture parameters include the number of fractures, the half-length of fractures and the conductivity of fractures.

8. A well testing analysis method for a multi-stage fractured horizontal well in a tight gas reservoir according to any one of claims 1 to 7, characterized in that: In step S3, the dimensionless unstable seepage differential equation of the centerline sink of the tight gas reservoir is established considering the stress sensitivity effect and reservoir parameters: The initial condition is The boundary conditions of fixed production are The infinite outer boundary condition in the horizontal direction is Defining dimensionless variables In the above formula, K i is the reservoir permeability, mD; h is the reservoir thickness, m; T is the absolute temperature, K; q sc is the ground production, m 3 / d; m is pseudo pressure, MPa 2 / (mPa·s);m i is the original pseudo-pressure of the reservoir, MPa 2 / (mPa·s);γ m is the permeability modulus defined by pseudo-pressure, mPa·s / MPa 2 ; t is time, h; μ is gas viscosity, mPa·s; φ is gas reservoir porosity, decimal; C t is the comprehensive compression coefficient, MPa -1 ;X f is the crack half-length, m; r is the radial distance, m.

9. A well testing analysis method for a multi-stage fractured horizontal well in a tight gas reservoir according to any one of claim 8, characterized in that: In step S3, a mathematical model that supplements the consideration of fracture parameters is established based on the dimensionless unstable seepage differential equation of the centerline sink of a tight gas reservoir based on stress sensitivity effects and reservoir parameters.

10. A well testing analysis method for a multi-stage fractured horizontal well in a tight gas reservoir according to any one of claim 9, characterized in that: The fracturing fracture unit of the bottom hole pressure response of the fracturing horizontal well is numerically discretized; specifically: M transverse fractures of different lengths are distributed perpendicular to the horizontal wellbore at different intervals. The half length of the fracture is X if , the coordinates of the intersection of the i-th crack on the y-axis and the y-axis are (0, yi), where i = 1, 2, …, M; the distance between adjacent cracks is Δyi = yi-yi-1; each crack is divided into 2N micro-element segments along the X-axis, then the main crack has a total of 2N+1 endpoints and 2N center points, and each equivalent crack is divided into 2O micro-element segments, then the equivalent crack has a total of 2O+1 endpoints and 2O center points; Defining dimensionless variables Yes wD =y Di , x mwD =x mDi ; where r w is the wellbore radius, m; X if is the half length of each main crack, m; X xf is the half length of an equivalent crack, m; △f i is the spacing between cracks, m; The dimensionless pseudo-pressure response of the discrete unit (i, j) at any point (x, y) in the gas reservoir in the pull-type space is obtained as follows: Applying the principle of pressure drop superposition, (M×2N×2O) discrete units are placed at any position (x D ,y D The dimensionless total pseudo-pressure response generated at ) is In the formula, (x D ,y D ) is taken as the midpoint of a discrete unit (X Dk,v ,Y Dk,v ),but Where K0 is the Bessel function of the second-order zero-order imaginary quantity, s is the Laplace variable, is the linear density flow corresponding to the discrete unit (i, j), the unit is dimensionless; According to the infinite conductivity assumption, the pressure in the horizontal wellbore and the artificial fracture system is equal everywhere, and the dimensionless pseudo-pressure in the horizontal wellbore can be expressed as Will In the expression, k and v are taken over all discrete units (k = 1, 2, ..., M; v = 1, 2, ..., 2N), then M × 2N linear equations can be obtained, including M × 2N + 1 unknown quantities. and 11. A well testing analysis method for a multi-stage fractured horizontal well in a tight gas reservoir as claimed in claim 10, characterized in that: The coordinates of the endpoints of the i-th crack are marked as (x i,1 ,y i,1 ) to (x i,2N+1 ,y i,2N+1 ), whose 2N center points are marked as (X i,1 ,Y i,1 ) to (X i,2N ,Y i,2N );Each center point has an equal length X xf The lateral equivalent fractures are parallel to the horizontal wellbore, that is, the number of equivalent fractures is equal to the number of microelement ends of the main fractures. The number of equivalent fractures can be changed by adjusting the number of microelement ends of the main fractures.

12. A well testing analysis method for a multi-stage fractured horizontal well in a tight gas reservoir according to claim 11, characterized in that: The coordinates of the two endpoints of the jth segment of the ith main crack (j = 1, 2, ..., 2N) are expressed as (x i,j ,y i,j ) and (x i,j+1 ,y i,j+1 ), the corresponding center point coordinates are expressed as (X i,j , Y i,j ), whose mathematical expressions are respectively, The endpoints of the main crack micro-element segment are expressed as The midpoint of the main crack microelement segment is expressed as The coordinates of the two endpoints of the equivalent crack segment z of the i-th main crack segment j (j=1, 2, ..., 2N) are expressed as (x i,j,z ,y i,j,z ) and (x i,j+1,z ,y i,j+1,z ), the corresponding center point coordinates are expressed as (X i,j,z , Y i,j,z ); their mathematical expressions are, The endpoints of the equivalent crack microelement segment are expressed as The midpoint of the equivalent crack microelement segment is expressed as 13. A well testing analysis method for a multi-stage fractured horizontal well in a tight gas reservoir as claimed in claim 10, characterized in that: In step S4, the seepage mathematical model established in step S3 is solved, specifically, M×2N+1 equations are closed-formed and solved to obtain the linear density flow and bottom hole pseudo-pressure response in each discrete unit; the bottom hole pressure solution considering the wellbore reservoir effect and the skin effect is obtained according to the bottom hole pressure solution by using the superposition principle; and the bottom hole pressure considering the wellbore reservoir effect and the skin effect in Laplace space is transformed into the bottom hole pressure in real space by using Stehfest numerical inversion.

14. A well testing analysis method for a multi-stage fractured horizontal well in a tight gas reservoir as claimed in claim 13, characterized in that: The flow normalization constraint condition is that the total flow into the horizontal wellbore is equal to the sum of the flow rates of each fracture discrete unit. Its expression in Laplace space is: That is, (M×2N+1) equations can be closed to solve (M×2N+1) unknown quantities, namely, the linear density flow rate in each discrete unit and the bottom hole pseudo pressure response 15. A well testing analysis method for multi-stage fractured horizontal wells in tight gas reservoirs according to claim 13, characterized in that: According to the Duhamel principle, the expression of the pseudo-pressure perturbation solution of a pressure horizontal well considering the influence of wellbore reservoir and skin effect is: Through Stehfest numerical inversion, the dimensionless pseudo-pressure solution of a fractured horizontal well in a uniform medium tight gas reservoir considering the permeability stress sensitivity effect can be obtained as: Defining a dimensionless variable Where C is the well storage coefficient, m 3 / MPa; S is the skin coefficient, the unit is dimensionless.

16. A well testing analysis method for a multi-stage fractured horizontal well in a tight gas reservoir according to any one of claims 1 to 7, characterized in that: In step S5, the pressure and pressure derivative measured curves are obtained based on the collected well test data, and then the actual flow process of the fluid is analyzed based on the characteristics of the measured curves; the pressure and pressure derivative curves are divided into multi-stage fractured horizontal well seepage flow stages according to the actual flow process of the fluid.

17. A well testing analysis method for a multi-stage fractured horizontal well in a tight gas reservoir according to any one of claims 1 to 7, characterized in that: According to the relationship between the bottom hole flowing pressure and the influencing factors, a typical curve graph under the influence of the starting pressure gradient, stress sensitivity effect and fracturing crack parameters is obtained, and a parameter sensitivity analysis is performed on the typical curve graph to obtain the sensitivity of the influencing factors.

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