Method for evaluating non-uniform transformation reserves of tight gas reservoir fractured horizontal well

Abstract

The invention discloses a tight gas reservoir fractured horizontal well non-uniform transformation reserve evaluation method, and relates to the field of oil and gas field development. According to the method, a fractured horizontal well non-uniform transformation concept physical model is established, a rectangular closed reservoir fractured horizontal well non-uniform transformation reservoir unstable seepage mathematical model is established and solved, and a fracture model is coupled to obtain a bottom hole pressure asymptotic solution and a quasi-steady state bottom hole pressure asymptotic solution of the unstable seepage mathematical model; according to the method, actual production data are processed to draw a quasi-steady state productivity index curve and a Blasingame yield decline curve, and an actually measured curve is dragged to be compared with a theoretical curve, so that dynamic reserve calculation and inversion of the width and permeability of each sub-region are realized, namely, the permeability and the transformation range of each section of transformed reservoir are obtained through chart fitting; and the reserve evaluation accuracy is improved.

Description

Technical Field

[0001] The present invention relates to the field of oil and gas field development, and specifically to a method for evaluating the reserves of non-uniformly stimulated fractured horizontal wells in tight gas reservoirs. Background Art

[0002] Due to the tight reservoir in tight gas reservoirs, the gas well production is low. Therefore, large-scale volume fracturing must be adopted to achieve economic development. At the same time, due to the strong heterogeneity of tight reservoirs, there are obvious differences in the stimulation effects of fractures in each section during the large-scale volume fracturing process of horizontal wells, and finally a non-uniformly stimulated area is formed. Material balance and production decline analysis are important methods for dynamic reserve evaluation. Gas well EUR evaluation is based on gas well prediction using the results of dynamic reserve evaluation.

[0003] The dynamic reserve evaluation method based on Blasingame production decline analysis is an important method. For the method of calculating reserves using Blasingame production decline, the accuracy of the coefficient b Dpss calculation is the key to dynamic reserve evaluation. However, b Dpss is directly related to the asymptotic solution of the pseudo-steady bottom-hole pressure and is directly related to the pseudo-steady productivity index J Dpss There is a direct relationship. For simple well types (such as vertical wells, horizontal wells, and fractured vertical wells), it is easy to obtain their pseudo-steady productivity index and calculate the accurate Blasingame production decline theoretical chart. However, for complex-structured wells, it is very difficult to calculate the coefficient b Dpss It is very difficult to calculate, and finally the dynamic reserve evaluation is inaccurate, which affects the gas well EUR prediction. Therefore, it is necessary to establish a non-uniformly stimulated fractured horizontal well reserve evaluation and prediction model and method for tight gas reservoirs.

[0004] The invention patent (CN202310126528.2) discloses a well-controlled dynamic reserve evaluation method and system based on the hole-fracture-hole mode, which is applicable to fault-controlled fracture-cavity type volatile oil reservoirs, including: collecting geological and production data of the well to be evaluated; based on the material balance principle, considering the change of the compressibility coefficient of volatile crude oil with pressure, establishing a differential material balance equation for the double-hole series mode, and based on this, combining geological and production data to obtain a series of reservoir average pressure for calculation and a series of bottom-hole flowing pressure for calculation; establishing a first objective function between the calculated reservoir average pressure and the measured bottom-hole static pressure and a second objective function between the calculated bottom-hole flowing pressure and the measured bottom-hole flowing pressure, and using geological and production data to solve the two objective functions respectively to obtain the dynamic reserves of the reservoir. The present invention provides a basis for single-well dynamic reserve evaluation and recovery degree analysis of fracture-cavity type oil reservoirs. However, this model is not applicable to large-scale volume pressure of horizontal wells and does not consider the influence of non-uniform stimulation.

[0005] The authorized invention patent (CN201610832309.6) provides a method and device for evaluating the recoverable reserves of a single well. The method includes: calculating and obtaining the time period with the strongest correlation between the single-well production of the production well and the ultimate recoverable reserves of the single well according to the existing production of each production well in the same oil and gas reservoir; obtaining a first relational expression based on the percentage of the single-well production of each production well in the time period and the single-well production of the production well; obtaining a second relational expression based on the percentage of the ultimate recoverable reserves of each production well and the ultimate recoverable reserves of the single well; obtaining the production of a new well in the time period, and obtaining the percentage of the new well production corresponding to the new well production according to the new well production and the first relational expression; obtaining the ultimate recoverable reserves of the new well according to the percentage of the new well production and the second relational expression. Using the above method and device can make the evaluated ultimate recoverable reserves of a single well closer to the actual reserves. However, this method does not consider the influence of non-uniform stimulation.

[0006] The invention patent (CN202310199267.7) provides a method for evaluating the dynamic reserves of a shale condensate gas well, which includes: determining the basic geological parameters, PVT cell phase behavior experiment parameters, and PVT basic parameters of the target well; determining the isothermal adsorption experiment parameters of shale condensate gas under reservoir temperature and pressure conditions; determining the completion and wellbore string parameters of the target well; determining the production dynamic data and pressure measurement data of the target well; establishing an oil and gas molar conservation material balance equation for the shale condensate gas reservoir based on the basic geological parameters, PVT cell phase behavior experiment parameters, PVT basic parameters, isothermal adsorption experiment parameters, completion and wellbore string parameters, production dynamic data, and pressure measurement data, and calculating the dynamic reserves of free gas, adsorbed gas, and condensate oil. The present invention does not require complex component model phase equilibrium calculations, is simple to implement, and can evaluate the dynamic reserves of free gas, condensate oil, and adsorbed gas at one time. However, this method does not consider the influence of non-uniform stimulation and does not give an accurate Dpss calculation method, resulting in errors in the evaluation of dynamic reserves. Summary of the Invention

[0007] The purpose of the present invention is to provide a method for evaluating the reserves of a fractured horizontal well with non-uniform stimulation in a tight gas reservoir to solve the technical problems raised in the background art.

[0008] To achieve the above purpose, the present invention provides the following technical solution: A method for evaluating the reserves of a fractured horizontal well with non-uniform stimulation in a tight gas reservoir includes at least the following steps:

[0009] S1: Based on the microseismic detection results, depict the fracture stimulation area of a single stage or single cluster, and establish a conceptual physical model of the non-uniform stimulation of the fractured horizontal well.

[0010] S2: Based on the characterization results of the fracturing transformation area, establish an unsteady seepage mathematical model for a fractured horizontal well with non-uniform transformation in a rectangular closed reservoir. The unsteady seepage mathematical model for a fractured horizontal well with non-uniform transformation in a rectangular closed reservoir describes the reservoir seepage behavior under non-uniform fracturing transformation conditions through mathematical modeling;

[0011] S3: Taking the fracture unit as the basic model, establish a fracture flow seepage mathematical model, which further refines the flow behavior inside the fracture after fracturing;

[0012] S4: Using the principle of pressure drop superposition, couple the unsteady seepage mathematical model for a fractured horizontal well with non-uniform transformation in a rectangular closed reservoir and the fracture flow seepage mathematical model to obtain the bottom-hole pressure solution of the unsteady seepage model and the pseudo-steady state coefficient b Dpss , and calculate the production integral and the production integral derivative curve according to the Blasingame production decline curve calculation principle;

[0013] S5: Process the production data and bottom-hole pressure data of the fractured horizontal well with non-uniform transformation in the reservoir, and draw the production integral, production integral derivative, and pseudo-steady state productivity index curves of the measured data;

[0014] S6: Draw the production integral and production integral derivative of the measured and theoretical calculations in the same double logarithmic coordinate system, and draw the pseudo-steady state productivity index curves of the measured and theoretical calculations in the same rectangular coordinate system;

[0015] S7: Drag the measured curve and the theoretical curve. When the measured curve and the theoretical curve are matched, the curve fitting is completed, and the pseudo-steady state productivity index and the dynamic reserve are calculated, and an evaluation is given.

[0016] Furthermore, the unsteady seepage mathematical model for a fractured horizontal well with non-uniform transformation in a rectangular closed reservoir can be abbreviated as the unsteady seepage model for a rectangular heterogeneous reservoir;

[0017] Solve the solution of the unsteady seepage model for a rectangular heterogeneous reservoir based on methods such as Laplace integral transformation. The solution of the unsteady seepage model for a rectangular heterogeneous reservoir includes at least the following steps:

[0018]

[0019] Among them, the expression forms of relevant parameters are:

[0020]

[0021] β n = nπ / x eD

[0022] y Dl = y wD +yD

[0023] y D2 = y wD -y D

[0024]

[0025]

[0026] By simplifying the solution of the unsteady seepage model of a rectangular heterogeneous reservoir, the asymptotic solution of the bottom-hole pressure at the pseudo-steady flow stage in real space is obtained through analytical inversion. The specific solution includes at least the following steps:

[0027]

[0028] Where: M kref is the mobility ratio between region k and the reference region, x eD is the dimensionless rectangular boundary width, y eD is the dimensionless rectangular boundary length, ΔL D is the dimensionless fracture discrete element length, x mD is the midpoint of the dimensionless fracture discrete element in the x direction, x D is the dimensionless calculation point in the x direction, y wD is the midpoint of the dimensionless fracture discrete element in the y direction, y D is the dimensionless calculation point in the y direction, s is the Laplace integral variable, and n is the accumulation variable.

[0029] Furthermore, by solving the mathematical model of fracture flow seepage, the pressure difference between the inlet and outlet ends of the fracture element and the pressure difference between the inlet end of the fracture element and the midpoint of the fracture element are obtained;

[0030] The pressure difference between the inlet and outlet ends of the fracture element is:

[0031]

[0032] The pressure difference between the inlet end of the fracture element and the midpoint of the fracture element;

[0033]

[0034] Where: is the dimensionless pseudo-pressure at the outlet end of the fracture in the Laplace space of the kth region, is the dimensionless pseudo-pressure at the inlet end of the fracture in the Laplace space of the kth region, x inD is the dimensionless coordinate at the inlet end of the fracture element, x ou tD is the dimensionless coordinate at the outlet end of the fracture element, is the dimensionless surface flow rate in the Laplace space, is the dimensionless inflow rate at the Laplace space, C FD is the dimensionless fracture conductivity.

[0035] Further, the S7 at least includes the following steps:

[0036] Judge whether the pseudo-steady flow stage is reached according to the measured data of the pseudo-steady productivity index curve;

[0037] When the pseudo-steady state stage is reached, calculate the pseudo-steady coefficient b Dpss ;

[0038] If not, predict the pseudo-steady coefficient b according to the trend of the measured curve Dpss ;

[0039] According to the calculated pseudo-steady coefficient b Dpss , draw the Blasingame production decline curve to realize the dynamic reserve evaluation.

[0040] Compared with the prior art, the beneficial effects of the present invention are:

[0041] The present invention establishes a conceptual physical model of non-uniform stimulation of a fractured horizontal well, establishes and solves a mathematical model of unsteady seepage in a rectangular closed reservoir with non-uniform stimulation of a fractured horizontal well, couples the fracture model to obtain the asymptotic solution of the bottom hole pressure and the asymptotic solution of the pseudo-steady bottom hole pressure of the unsteady seepage mathematical model, processes the actual production data to draw the pseudo-steady productivity index curve and the Blasingame production decline curve, and compares the measured curve with the theoretical curve to realize the calculation of dynamic reserves and the inversion of the width and permeability of each sub-region, that is, the permeability of each stimulated reservoir and the size of the stimulation range are obtained through curve fitting, improving the accuracy of reserve evaluation. Description of the Drawings

[0042] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

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

[0044] Figure 2 is the unstructured grid meshing diagram of the present invention;

[0045] Figure 3 is the double logarithmic diagnostic diagram of the bottom hole pressure and pressure derivative curve of the present invention;

[0046] Figure 4It is the linear analysis diagram of the pressure derivative curve of the present invention;

[0047] Figure 5 It is the automatic fitting result diagram of the double logarithmic curve of the present invention;

[0048] Figure 6 It is the productivity index curve and material balance curve diagram of the present invention;

[0049] Figure 7 It is the schematic diagram of the Blasingame production decline curve of the present invention. Detailed implementation manners

[0050] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments.

[0051] Embodiment 1:

[0052] Refer to Figure 1 , a method for evaluating the reserves of a fractured horizontal well with non-uniform stimulation in a tight gas reservoir, at least including the following steps:

[0053] S1: Based on the microseismic detection results, depict the fracture stimulation area of a single stage or a single cluster, and establish a conceptual physical model of the fractured horizontal well with non-uniform stimulation according to the size and width of the stimulation section depiction area (refer to Figure 2 );

[0054] S2: Based on the results of the stimulation area depiction, establish a mathematical model of unsteady seepage in a fractured horizontal well with non-uniform stimulation in a rectangular closed reservoir. The mathematical model of unsteady seepage in a fractured horizontal well with non-uniform stimulation in a rectangular closed reservoir describes the seepage behavior of the reservoir under non-uniform stimulation conditions through mathematical modeling;

[0055] The mathematical model of unsteady seepage in a fractured horizontal well with non-uniform stimulation in a rectangular closed reservoir can be simply referred to as the unsteady seepage model of a rectangular heterogeneous reservoir;

[0056] Based on methods such as Laplace integral transform, solve the solution of the unsteady seepage model of a rectangular heterogeneous reservoir. The solution of the unsteady seepage model of a rectangular heterogeneous reservoir at least includes the following steps:

[0057]

[0058] Among them, the expression forms of relevant parameters are:

[0059]

[0060] β n = nπ / x eD

[0061] y Dl = y wD + y D

[0062] y D2 = y wD - y D

[0063]

[0064]

[0065] By simplifying the solution of the unstable seepage model of a rectangular heterogeneous reservoir, the asymptotic solution of the bottom-hole pressure in the real-space pseudo-steady flow stage is obtained through analytical inversion. The specific solution includes at least the following steps:

[0066]

[0067] Where: M kref is the mobility ratio between region k and the reference region, x eD is the dimensionless rectangular boundary width, y eD is the dimensionless rectangular boundary length, ΔL D is the dimensionless fracture discrete element length, x mD is the midpoint of the dimensionless fracture discrete element in the x direction, x D is the dimensionless calculation point in the x direction, y wD is the midpoint of the dimensionless fracture discrete element in the y direction, y D is the dimensionless calculation point in the y direction, s is the Laplace integral variable, and n is the accumulation variable.

[0068] S3: Taking the fracture element as the basic model, a mathematical model of fracture flow seepage is established, and the mathematical model of fracture flow seepage further refines the flow behavior inside the fracture after fracturing;

[0069] Solving the mathematical model of fracture flow seepage yields the pressure difference between the inlet and outlet ends of the fracture element and the pressure difference between the inlet end of the fracture element and the midpoint of the fracture element;

[0070] The pressure difference between the inlet and outlet ends of the fracture element is:

[0071]

[0072] The pressure difference between the inlet end of the fracture element and the midpoint of the fracture element;

[0073]

[0074] Where: is the dimensionless pseudo-pressure at the outlet end of the fracture in the Laplace space of the kth region, is the dimensionless pseudo-pressure at the fracture inflow end in the Laplace space of the k-th region, x inD is the dimensionless coordinate at the fracture element inflow end, x ou tD is the dimensionless coordinate at the fracture element outflow end, is the dimensionless surface flow rate in the Laplace space, is the dimensionless inflow end flow rate in the Laplace space, C FD is the dimensionless fracture conductivity.

[0075] S4: Using the principle of pressure drop superposition, couple the unstable seepage mathematical model of the fractured horizontal well with non-uniform reservoir transformation in a rectangular closed reservoir and the seepage mathematical model of fracture flow to obtain the bottom hole pressure solution of the unstable seepage model and the pseudo-steady state coefficient b Dpss , According to the calculation principle of the Blasingame production decline curve, calculate the production integral and the production integral derivative curve;

[0076] That is, the coupling of the discrete fracture and the heterogeneous reservoir interface, the asymptotic solution of the bottom hole pressure in the real space pseudo-steady state flow stage and the fracture model (see Figure 3 ), Calculate the steady state coefficient b Dpss and the pseudo-steady state index J Dpss , According to the obtained steady state coefficient b Dpss Calculate the Blasingame production decline curve, and analyze the influence of parameters such as the width of different intermediate regions on the pseudo-steady state productivity index and the Blasingame production decline curve (see Figure 4 and Figure 5 );

[0077] S5: Process the production data and bottom hole pressure data of the fractured horizontal well with non-uniform reservoir transformation, and draw the production integral, production integral derivative and pseudo-steady state productivity index curves of the measured data;

[0078] S6: Draw the production integral and production integral derivative of the measured and theoretical calculations in the same double logarithmic coordinate system, and draw the pseudo-steady state productivity index curves of the measured and theoretical calculations in the same rectangular coordinate system;

[0079] S7: Drag the measured curve and the theoretical curve, and when the measured curve and the theoretical curve are matched, the curve fitting is completed, calculate the pseudo-steady state productivity index and the dynamic reserves, and give an evaluation.

[0080] Judge whether the pseudo-steady state flow stage is reached according to the pseudo-steady state productivity index curve of the measured data;

[0081] When the pseudo-steady state stage is reached, calculate the pseudo-steady state coefficient b Dpss ;

[0082] If not, predict the pseudo-steady state coefficient b according to the trend of the measured curveDpss ;

[0083] Based on the calculated pseudo-steady state coefficient b Dpss , draw the Blasingame decline curve to achieve dynamic reserve evaluation.

[0084] Drag the measured curve and the theoretical curve. When the measured curve matches the theoretical curve, the curve fitting is completed. During the dragging process of the measured curve, the proportion of the rectangular boundary and the width of the heterogeneous reservoir remains unchanged. According to the actual size of the outer boundary of the gas reservoir, adjust the width of the heterogeneous reservoir proportionally, and assign values to each sub-region according to the average permeability to calculate the reservoir permeability.

[0085] Example 2:

[0086] This example takes a certain tight gas reservoir as an example;

[0087] The total depth of the completed well is 2892 m, the original formation pressure is 23.25 MPa, the reservoir temperature is 83.71 °C, the reservoir porosity is 0.058, the horizontal section length is 1003 m, a total of 8 fracturing stages are carried out, the gas compressibility factor is 0.95, the relative density of natural gas is 0.65, draw the productivity index curve and the material balance curve (see Figure 6 ), and at the same time draw the double logarithmic Blasingame decline curve. According to the material balance curve and the productivity index curve of the measured curve, calculate the dimensionless pseudo-steady state productivity coefficient b Dpss , according to the calculated b Dpss calculate the theoretical Blasingame decline curve, drag the measured curve to match the theoretical curve, and obtain the dynamic reserve of 1.17×10 8 m 3 , the permeabilities of the four sub-regions are 0.15 mD, 0.05 mD, 0.35 mD, and 0.75 mD respectively, and the dimensionless fracture conductivity is 45 (see Figure 7 ).

[0088] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present invention. Any reference signs in the claims should not be regarded as limiting the claimed rights.

Claims

1. A method for evaluating reserves of non-uniform reconstruction of fractured horizontal wells in tight gas reservoirs, characterized by: At least the following steps are included: S1: Based on the microseismic detection results, the regional characterization of the fracture stimulation of a single segment or a single cluster is carried out, and the conceptual physical model of the heterogeneous stimulation of fractured horizontal wells is established; S2: Based on the characterization results of the fracturing transformation area, a mathematical model of unstable seepage flow in the rectangular closed reservoir fracturing horizontal well non-uniform transformation reservoir is established. The mathematical model of unstable seepage flow in the rectangular closed reservoir fracturing horizontal well non-uniform transformation reservoir is used to describe the reservoir seepage behavior under non-uniform fracturing transformation conditions through mathematical modeling; S3: Taking the fracture unit as the basic model, a fracture flow and seepage mathematical model is established, wherein the fracture flow and seepage mathematical model further refines the flow behavior inside the fracture after fracturing; S4: Using the principle of pressure drop superposition, the unstable seepage mathematical model of rectangular closed reservoir fractured horizontal well non-uniform transformation reservoir is coupled with the fracture flow seepage mathematical model to obtain the bottom hole pressure solution and pseudo-steady-state coefficient b of the unstable seepage model Dpss , according to the Blasingame yield decline curve calculation principle, calculate the yield integral and yield integral derivative curve; S5: Processing the production data of the non-uniformly transformed reservoir and the bottom hole pressure data of the fractured horizontal well, and drawing the production integral of the measured data, the production integral derivative and the pseudo-steady-state production index curve; S6: Plot the measured and theoretically calculated production integrals and production integral derivatives in the same double logarithmic coordinate system, and plot the measured and theoretically calculated quasi-steady-state capacity index curves in the same rectangular coordinate system; S7: Drag the measured curve and the theoretical curve. When the measured curve and the theoretical curve are matched, the curve fitting is completed, and the quasi-steady-state production capacity index and dynamic reserves are calculated, and an evaluation is given.

2. The method for evaluating reserves of non-uniform reconstruction of fractured horizontal wells in tight gas reservoirs according to claim 1, characterized in that: The rectangular closed reservoir fracture horizontal well non-uniform reform reservoir unstable seepage mathematical model can be referred to as rectangular non-homogeneous reservoir unstable seepage model; Based on Laplace integral transformation and other methods, the solution of the unstable seepage model of rectangular heterogeneous reservoir is obtained. The solution of the unstable seepage model of rectangular heterogeneous reservoir is at least The following steps are involved: The relevant parameters are expressed as follows: β n =nπ / x eD and Dl =and wD +y D and D2 =and wD -and D By simplifying the unstable seepage model solution of rectangular heterogeneous reservoir, the asymptotic solution of bottom hole pressure in the pseudo-steady flow stage in real space is obtained by analytical inversion. The specific solution is at least The following steps are involved: Where: m kref is the flow rate ratio between region k and reference region, x eD is the dimensionless rectangle border width, y eD is the dimensionless rectangular boundary length, ΔL D is the dimensionless crack discrete unit length, x mD is the midpoint of the dimensionless crack discrete unit in the x direction, D is the dimensionless calculation point in the x direction, y wD is the midpoint of the dimensionless crack discrete unit in the y direction, y D is the dimensionless calculation point in the y direction, s is the Laplace integral variable, and n is the cumulative variable.

3. The method for evaluating reserves of non-uniform reconstruction of fractured horizontal wells in tight gas reservoirs according to claim 2, characterized in that: The mathematical model of fracture flow and seepage is solved to obtain the pressure difference between the inflow end and the outflow end of the fracture unit and the pressure difference between the inflow end and the midpoint of the fracture unit; The pressure difference between the inflow and outflow ends of the fracture unit is: The pressure difference between the inflow end of the fracture unit and the midpoint of the fracture unit; in: is the dimensionless pseudo-pressure at the outflow end of the crack in the kth region Laplace space, is the dimensionless pseudo-pressure at the inflow end of the crack in the kth region Laplace space, x inD is the dimensionless coordinate of the inflow end of the fracture unit, x ou tD is the dimensionless coordinate of the outflow end of the fracture unit, is the dimensionless surface flow in Laplace space, is the dimensionless inflow flow in Laplace space, C FD is the dimensionless fracture conductivity.

4. The method for evaluating reserves of non-uniform reconstruction of fractured horizontal wells in tight gas reservoirs according to claim 3, characterized in that: The S7 at least comprises the following steps: Determine whether the quasi-steady-state flow stage has been reached based on the quasi-steady-state capacity index curve of the measured data; When the quasi-steady state stage is reached, the quasi-steady state coefficient b is calculated. Dpss ; If it is not reached, the pseudo-steady-state coefficient b is predicted based on the trend of the measured curve. Dpss ; According to the calculated pseudo-steady-state coefficient b Dpss , draw the Blasingame production decline curve to realize dynamic reserve evaluation.

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