Shale oil effective transformation volume calculation method based on fracturing flowback data

Abstract

The invention provides a shale oil effective transformation volume calculation method based on fracturing flowback data. The shale oil effective transformation volume calculation method comprises the steps that 1, a material balance equation in an effective transformation volume in the early stage of flowback is established; 2, considering the stress sensitivity of the reservoir, and establishing a flow equation in the effective transformation volume; step 3, establishing an effective transformation volume calculation model after fracturing, establishing a relationship between flow normalized pressure and material balance time, and calculating an effective transformation volume through a slope; and step 4, establishing a method for iteratively solving the effective transformation volume, presetting the effective transformation volume, calculating a new effective transformation volume by utilizing the curve slope of the flow normalized pressure and the material balance time, and outputting a final effective transformation volume value conforming to a preset error. According to the method for calculating the effective transformation volume of the shale oil, the effective transformation volume of the shale oil can be rapidly and accurately calculated by utilizing the flowback initial stage data after fracturing and the oil reservoir parameters, and guidance is provided for efficient development of the shale oil.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas field development, and in particular to a method for calculating the effective transformation volume of shale oil based on fracturing flowback data. Background Art

[0002] Affected by the heterogeneity of the shale reservoir itself, an extremely complex fracture network system is often formed in the reservoir after fracturing. These fracture networks greatly improve the reservoir seepage capacity, increase the oil leakage volume of the oil well, and make the efficient development of shale oil possible. In order to obtain better shale oil and gas development effects, it is necessary to increase the oil leakage volume after volume fracturing. At present, relevant research mainly focuses on the fracturing stimulation volume (SRV), but field monitoring and production dynamic analysis show that most of the stimulation volume does not contribute to the production of shale oil, and the fracturing stimulation volume is different from the effective stimulation volume of shale oil and gas. Therefore, it is necessary to establish a calculation method for the effective stimulation volume of shale oil to provide support for the efficient development of shale oil.

[0003] Currently, there are relatively few methods for calculating effective transformation volume, most of which focus on reservoir transformation volume, including the following methods: production transient analysis method, fracturing construction design inversion method, geological engineering integrated simulation method, etc.

[0004] In the Chinese patent application with application number: CN201910062347.1, a method for calculating the volume of a fracturing reformed oil and gas reservoir is involved, including: obtaining the occurrence time of each defined microseismic event point in the microseismic monitoring data, determining the time position of each occurrence time in the fracturing reform process, based on which, excluding the microseismic event points corresponding to natural fractures and unknown disturbance conditions, forming a primary microseismic event cloud representing the effective fracturing reform volume; tetrahedralizing the primary microseismic event cloud to obtain a microseismic optimized event partitioning model; calculating the volume of each tetrahedron composed of microseismic event points in the microseismic optimized event partitioning model, and further obtaining an estimated result of the volume of the fracturing reformed oil and gas reservoir based on the volume of each tetrahedron. This invention effectively reduces the proportion of invalid volume in the reformed oil and gas reservoir volume, and improves the effectiveness and accuracy of the evaluation of volume fracturing operations, but requires special microseismic monitoring, is costly, and does not consider the flow of fluids in the reformed volume.

[0005] In the Chinese patent application with application number: CN201710006652.X, a method for calculating the volume area of ​​tight reservoir fracturing transformation is involved, which includes the following steps: establishing a non-planar turning extension model of multiple hydraulic fractures in the process of tight reservoir horizontal well fracturing, a formation stress field change model, a reservoir pressure field change model, and a natural fracture destruction criterion, obtaining geological parameters, horizontal well fracturing construction parameters, and total fracturing time, assigning initial values ​​of fracture filtration loss, initial values ​​of fracture half-length, initial values ​​of fracture pressure, initial fracture extension turning angle, initial permeability, and initial values ​​of fracturing time, solving each model, and calculating the coordinate data of the natural fracture destruction point; using the spatial numerical integration method, respectively calculating the volume of the tensile destruction transformation area and the shear destruction transformation area in the reservoir, and defining the spatial union of the two as the overall transformation volume area. This method can realize the accuracy, economy, and rapidity of the evaluation of tight reservoir horizontal well fracturing, and solve the existing laborious, costly, and time-consuming process of calculating the volume area of ​​tight reservoir horizontal well fracturing transformation. This method calculates the volume of the tensile damage transformation zone and the shear damage transformation zone in the reservoir respectively, and defines the spatial union of the two as the overall transformation volume area. However, there is still a certain gap in the applicability of this method to tight oil and shale oil reservoirs.

[0006] In the Chinese patent application with application number: CN201710811402.3, a method and device for determining the volume of reservoir transformation is involved, wherein the method includes: obtaining the reservoir parameters and fluid parameters of the area where the target well is located; establishing rules based on the gas material balance in the reservoir according to the reservoir parameters and fluid parameters; conducting production tests on the target well and obtaining the volume and first pressure of the cumulative gas production; determining the reservoir transformation volume according to the rules based on the volume and first pressure of the cumulative gas production. Since the scheme establishes rules based on the gas material balance in the reservoir according to the reservoir parameters and fluid parameters, and determines the specific reservoir transformation volume using the above rules, it solves the technical problems of large error and low precision of the determined reservoir transformation volume existing in the existing methods, and achieves the technical effect of accurately and finely determining the reservoir transformation volume. However, this method is mainly applicable to gas reservoirs, not shale oil reservoirs.

[0007] It is difficult to accurately and efficiently calculate the effective transformation volume of shale oil with the existing technology. For this reason, a method for calculating the effective transformation volume of shale oil based on fracturing backflow data is invented. Summary of the invention

[0008] The purpose of the present invention is to provide a method and system for quickly and accurately calculating the effective transformation volume of shale oil by using the initial flowback data after shale oil fracturing and reservoir parameters, so as to provide guidance for the efficient development of shale oil.

[0009] The object of the present invention can be achieved by the following technical measures: a method for calculating the effective transformation volume of shale oil based on fracturing flowback data, the method for calculating the effective transformation volume of shale oil includes:

[0010] Step 1, establishing the material balance equation within the effective transformation volume in the early stage of flowback;

[0011] Step 2, considering the stress sensitivity of the reservoir, establish the flow equation within the effective transformation volume;

[0012] Step 3, establishing a calculation model for the effective transformation volume after fracturing, establishing the relationship between flow normalized pressure and material balance time, and calculating the effective transformation volume through the slope;

[0013] Step 4, establish an iterative method for solving the effective transformation volume. By presetting the effective transformation volume, the new effective transformation volume is calculated using the slope of the curve of flow normalized pressure and material balance time, and the final effective transformation volume value that meets the preset error is output.

[0014] The purpose of the present invention can also be achieved by the following technical measures:

[0015] In step 1, in the early stage of flowback, the pressure wave propagates within the effective transformation volume. The production of shale oil wells comes entirely from the effective transformation volume, and the contribution of reservoirs outside the effective transformation volume to the production can be ignored. According to the principle of material balance, the mass of the inflowing crude oil minus the mass of the outflowing crude oil is equal to the change in the mass of the crude oil in the effective transformation volume, and the material balance equation is established.

[0016] In step 2, the reservoir in the effective transformation volume has been fully transformed, so the fluid flow can be considered to satisfy the Darcy equation. During the production process, the pressure in the effective transformation volume gradually changes. Affected by the stress sensitivity of the reservoir, the permeability and phase permeability curve in the oil leakage volume gradually change, and a flow equation that takes into account the stress sensitivity of the reservoir is established.

[0017] In step 2, the flow equation considering the reservoir stress sensitivity is established as:

[0018]

[0019] μ o is the crude oil viscosity, mPa·s; B o is the volume coefficient of oil, m 3 / m 3 ; is the gradient operator; p f is the pressure in the effective transformation volume, MPa; is the porosity of the effective transformation volume; K f is the permeability of the effective transformation volume, mD; C t is the comprehensive compression coefficient term defined, MPa -1 ; K ro is the relative permeability function, measured from experimental data.

[0020] In step 3, by combining the material balance equation and the flow equation considering reservoir stress sensitivity, taking into account different well types and different boundary conditions, the pressure distribution in the effective transformation volume is further obtained. According to the relationship between the average pressure in the effective transformation volume and the bottom hole flow pressure, the relationship between the flow normalized pressure and the material balance time is obtained.

[0021] In step 3, the relationship between flow normalized pressure and material balance time is:

[0022]

[0023] p f is the pressure in the effective transformation volume, MPa; μ o is the crude oil viscosity, mPa·s; B o is the volume coefficient of oil, m 3 / m 3 ; is the porosity of the effective transformation volume; K f is the permeability of the effective transformation volume, mD; q t is the total liquid flow, m 3 / d;K ro is the relative permeability function; V fi is the initial effective fracture volume.

[0024] In step 4, an iterative method for solving the effective transformation volume is established, oil-water flowback data is collected, and the early flow stage is identified according to the oil-water ratio, and the liquid flow rate and flow normalized pressure are calculated. The initial effective transformation volume V is given. fi , calculate the relative permeability and comprehensive compression coefficient, further calculate the material balance time, the relationship between the root flow normalized pressure and the material balance time, and invert the new effective transformation volume V fi,new , until V fi With V fi,new The error of satisfies the given range, and the effective transformation volume is finally calculated.

[0025] Step 4 specifically includes:

[0026] 4.1 Identify the flow phase;

[0027] 4.2 Calculate liquid flow rate and flow normalized pressure;

[0028] 4.3 Calculate relative permeability and comprehensive compressibility;

[0029] 4.4 Calculation of material balance time t a , plot flow normalized pressure RNP-t a Curve, inversion of effective transformation volume.

[0030] In step 4.1, the flowback data of the wells are collected, the oil-water ratio change curve is drawn, the early flow stage is identified, and the relevant parameters of the reservoir are collected.

[0031] In step 4.2, according to the liquid flow rate q t and the definition of flow normalized pressure RNP, calculate the corresponding value.

[0032] In step 4.3, given the preset V fi value, calculate k using experimental data ro (t), the comprehensive compression coefficient is calculated using the following formula:

[0033]

[0034] C t is the total compressibility term, MPa -1 , each term of its expression represents the influence of different driving mechanisms in turn: oil phase expansion, liquid phase expansion, and fracture closure; Indicates the reciprocal of the fracture stiffness determined by the elastic energy or strain energy required to keep the hydraulic fracture open, MPa -1 ; C w , C o is the water and oil compressibility coefficient, MPa -1 ; S oi , S wi are the initial oil and water saturations, dimensionless; B o , B w are the volume coefficients of oil and water, respectively, m 3 / m 3 ; B oi , B wi are the initial oil and water volume coefficients, m 3 / m 3 .

[0035] In step 4.3, the material balance time is calculated by numerical integration method using the following formula:

[0036]

[0037] t a is the material equilibrium time; K ro is the relative permeability function; μ o is the crude oil viscosity, mPa·s; B o is the volume coefficient of oil, m 3 / m 3 ; C t is the defined comprehensive compressibility, MPa -1 ;

[0038] Draw the RNP-ta relationship curve and calculate the effective transformation volume V according to the slope K of the straight line segment on the curve. fi,new , determine and preset the effective transformation volume value V fi Does the error meet the requirements? If so, the effective transformation volume is obtained; if not, the updated value is (V fi,new -V fi ) / 2, return to step 4.3 and continue calculating until the set error requirement is met.

[0039] The method for calculating the effective transformation volume of shale oil based on fracturing flowback data in the present invention solves the problem of accurately and efficiently determining the effective transformation volume of shale oil reservoirs using fracturing flowback data. The effective transformation volume of shale oil can be calculated at the initial stage of shale oil well flowback, providing guidance for the subsequent production plan design, and no additional testing is required, which is low in cost. The present invention is based on the material balance principle within the effective transformation volume, considers the influence of stress sensitivity on the oil-water two-phase seepage capacity, establishes a calculation model of the average pressure and production within the effective transformation volume after volume fracturing of different well types, obtains the relationship between the normalized pressure of the production and the material balance time, solves the effective transformation volume through slope iteration, and provides guidance for the efficient development of shale oil. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 A schematic diagram of flowback data of a well in a specific embodiment of the present invention;

[0041] Figure 2 It is an oil-water ratio curve diagram in a specific embodiment of the present invention;

[0042] Figure 3 It is a diagram of liquid flow calculation results in a specific embodiment of the present invention;

[0043] Figure 4 It is a schematic diagram of the flow normalized pressure calculation result in a specific embodiment of the present invention;

[0044] Figure 5 A diagram showing the calculation results of a relative permeability function in a specific embodiment of the present invention;

[0045] Figure 6 It is a graph showing the calculation result of the comprehensive compression coefficient in a specific embodiment of the present invention;

[0046] Figure 7 It is a graph showing the material balance time calculation result in a specific embodiment of the present invention;

[0047] Figure 8 It is a graph showing the relationship between RNP and ta in a specific embodiment of the present invention;

[0048] Fig. 9It is an iterative calculation flow chart in a specific embodiment of the present invention;

[0049] Fig.10 The present invention is a flowchart of a specific embodiment of the method for calculating the effective transformation volume of shale oil based on fracturing flowback data. DETAILED DESCRIPTION

[0050] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0051] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations and / or combinations thereof.

[0052] The present invention provides a method for calculating the effective transformation volume of shale oil based on fracturing flowback data, comprising: establishing a material balance equation within the effective transformation volume in the early stage of flowback; establishing a flow equation within the effective transformation volume, taking into account the stress sensitivity of the reservoir; establishing a calculation model for the effective transformation volume after fracturing, by simultaneously establishing the material balance equation and the flow equation taking into account the stress sensitivity of the reservoir, taking into account different well types (vertical wells, inclined wells, horizontal wells, etc.) and different boundary conditions, further obtaining the pressure distribution within the effective transformation volume, and obtaining the relationship between the flow normalized pressure (the relationship between the reservoir pressure drop and the liquid flow rate) and the material balance time according to the relationship between the average pressure within the effective transformation volume and the bottom hole flow pressure; establishing a method for iteratively solving the effective transformation volume, by presetting the effective transformation volume, using the established calculation model for the effective transformation volume after fracturing to calculate the new effective transformation volume, and outputting the final effective transformation volume value that meets the preset error.

[0053] The following are several specific embodiments of the present invention.

[0054] Example 1

[0055] In a specific embodiment 1 of the present invention, Fig.10 As shown, the method for calculating the effective transformation volume of shale oil based on fracturing flowback data of the present invention includes:

[0056] Step 101, establishing a material balance equation within the effective transformation volume in the early stage of flowback.

[0057] Establish a material balance equation within the effective transformation volume in the early stage of flowback. In the early stage of flowback, the pressure wave propagates within the effective transformation volume. The production of shale oil wells comes entirely from the effective transformation volume. The contribution of reservoirs outside the effective transformation volume to the production can be ignored. According to the material balance principle, the mass of the inflowing crude oil minus the mass of the outflowing crude oil equals the change in the mass of the crude oil within the effective transformation volume. Establish a material balance equation;

[0058] Step 102, establishing a flow equation within the effective transformation volume, taking into account the stress sensitivity of the reservoir.

[0059] The flow equation within the effective transformation volume is established. The reservoir within the effective transformation volume has been fully transformed, so the fluid flow can be considered to satisfy the Darcy equation. During the production process, the pressure in the effective transformation volume gradually changes. Affected by the stress sensitivity of the reservoir, the permeability and phase permeability curve in the oil leakage volume gradually change. The flow equation considering the stress sensitivity of the reservoir is established.

[0060] Step 103, establish a calculation model for the effective reconstruction volume after fracturing, combine the above-mentioned material balance equation and flow equation, establish the relationship between flow normalized pressure and material balance time, and calculate the effective reconstruction volume through the slope.

[0061] A calculation model for the effective transformation volume after fracturing is established. By combining the material balance equation and the flow equation considering reservoir stress sensitivity, different well types (vertical wells, inclined wells, horizontal wells, etc.) and different boundary conditions are considered to further obtain the pressure distribution in the effective transformation volume. According to the relationship between the average pressure in the effective transformation volume and the bottom hole flowing pressure, the relationship between the flow normalized pressure (the relationship between the reservoir pressure drop and the liquid flow rate) and the material balance time is obtained.

[0062] Step 104, establishing an iterative method for solving the effective transformation volume, by presetting the effective transformation volume, using the established calculation model for the effective transformation volume after fracturing to calculate the new effective transformation volume, and outputting a final effective transformation volume value that meets the preset error.

[0063] Establish an iterative method to solve the effective transformation volume, collect oil-water (gas) flowback data, identify the early flow stage according to the oil-water ratio, calculate the liquid flow rate and flow normalized pressure, and give the initial effective transformation volume V fi , calculate the relative permeability and comprehensive compressibility, further calculate the material balance time, and invert the new effective transformation volume V according to the relationship between flow normalized pressure and material balance time fi,new , until V fi With V fi,new The error of satisfies the given range, and the effective transformation volume is finally calculated.

[0064] Example 2

[0065] In a specific embodiment 2 of the present invention, the present invention utilizes the material balance equation within the effective transformation volume in the early stage of flowback to jointly establish the flow equation within the effective transformation volume (taking into account the stress sensitivity of the reservoir), establishes the relationship between flow normalized pressure and material balance time, establishes a calculation model for the effective transformation volume after fracturing, calculates the effective transformation volume by the slope, establishes a method for iteratively solving the effective transformation volume, presets the effective transformation volume, and uses the established calculation model for the effective transformation volume after fracturing to calculate the new effective transformation volume, and outputs the final effective transformation volume value that meets the preset error.

[0066] Step 1: Establish the material balance equation within the effective transformation volume in the early stage of flowback, including:

[0067] In the early stage of flowback, the pressure wave propagates within the effective transformation volume. The production of shale oil wells comes entirely from the effective transformation volume. The contribution of reservoirs outside the effective transformation volume to the production can be ignored. According to the material balance principle, the mass of the inflowing crude oil minus the mass of the outflowing crude oil equals the change in the mass of the crude oil in the effective transformation volume. The material balance equation is established:

[0068]

[0069] q o is the oil phase flow rate under ground conditions, m 3 / d;ρ os and ρ oR are the densities at surface conditions and reservoir conditions, kg / m 3 ; V o 、V f 、V w are the volume of oil in the fracture, the volume of the fracture, and the volume of water in the fracture, m 3 . There are the following relations:

[0070] V o (t) = V f (t)-V w (t) (2)

[0071] Isothermal compressibility coefficient of oil C o and Relationship:

[0072]

[0073] is the rate of change of volume with pressure under isothermal conditions, m 3 / MPa; is the rate of change of crude oil density with time.

[0074] Calculation formula 3 yields:

[0075]

[0076] is the rate of change of pressure in the effective reformed fracture volume over time.

[0077] The combined equations 1, 2, and 4 are simplified to:

[0078]

[0079] Define V o 、V w is a function of cumulative oil and water production:

[0080] V o (t)=(O fi -O p )B o (6)

[0081] V w (t)=(W fi -W p )B w (7)

[0082] O p (t), W p (t) are oil and water production, O fi , W fi are the volume of crude oil under initial conditions, B o , B w are the volume coefficients of oil and water, m 3 / m 3 .

[0083] V o 、V w Substituting the definition of into formula 5, we get:

[0084]

[0085] Using the chain rule to expand equation 8 we get:

[0086]

[0087] B oi , B wi are the volume coefficients of formation oil and water under initial conditions, m 3 / m 3 .

[0088] Initial crack volume V fi It can be expressed as:

[0089]

[0090] Assume that in the early flow stage:

[0091] B o ≈B oi ,B w ≈B wi (11)

[0092] Divide both sides of equation 9 by the fracture volume V fi get:

[0093]

[0094] Define a valid compression item,

[0095]

[0096] C t is the total compressibility term, MPa -1 , each term of which represents a different driving mechanism in turn: oil phase expansion, liquid phase expansion, and fracture closure; Indicates the reciprocal of the fracture stiffness determined by the elastic energy or strain energy required to keep the hydraulic fracture open, MPa -1 ; C w , C o is the water and oil compressibility coefficient, MPa -1 ; S oi , S wi are the initial oil and water saturations, dimensionless; B o , B w are the volume coefficients of oil and water, respectively, m 3 / m 3 . B oi , B wi are the initial oil and water volume coefficients, m 3 / m 3 .

[0097] Define the total fluid flow,

[0098] q t =q o B o +q w B w (14)

[0099] q t is the total liquid flow rate under ground conditions, m 3 / d.

[0100] The final fracture material balance equation is:

[0101]

[0102] Step 2: Establish the flow equation within the effective transformation volume, including:

[0103] The flow equation in the effective transformation volume is established. The reservoir in the effective transformation volume has been fully transformed, so the fluid flow can be considered to satisfy the Darcy equation. During the production process, the pressure in the effective transformation volume gradually changes. Affected by the stress sensitivity of the reservoir, the permeability and phase permeability curve in the drainage volume gradually change. The flow equation considering the stress sensitivity of the reservoir is established:

[0104]

[0105] μ o is the crude oil viscosity, mPa·s; is the porosity of the effective transformation volume, is the gradient operator, K ro is the relative permeability function, measured from experimental data.

[0106] Step 3: Establish a calculation model for the effective transformation volume after fracturing, including:

[0107] A calculation model for the effective transformation volume after fracturing is established. By combining the material balance equation and the flow equation considering reservoir stress sensitivity, different well types (vertical wells, inclined wells, horizontal wells, etc.) and different boundary conditions are considered to further obtain the pressure distribution in the effective transformation volume. According to the relationship between the average pressure in the effective transformation volume and the bottom hole flow pressure, the relationship between the flow normalized pressure (the relationship between the reservoir pressure drop and the liquid flow rate) and the material balance time is obtained.

[0108] The control equation is given by equations 15 and 16 as follows:

[0109]

[0110] The well type given in this example is a horizontal well, and the boundary conditions are constant pressure on the inner boundary and closed outer boundary:

[0111]

[0112] It is also the outer boundary of the effective transformation volume.

[0113] Integrate equation 17,

[0114]

[0115] Establishing average reservoir pressure and p wf relationship.

[0116]

[0117] Assume V f is a rectangular parallelepiped infinitesimal element, wf 、h f ,y f are the width, height and length of the microelement respectively, is the porosity of the rectangular parallelepiped element.

[0118]

[0119] Substituting equation 21 into equation 20 yields:

[0120]

[0121] Represents the average pressure distribution of the entire reservoir.

[0122] Solving equations 19 and 22 simultaneously yields:

[0123]

[0124] Define a material balance time function t a Concept:

[0125]

[0126] Relationship between fracture pressure and material equilibrium time:

[0127]

[0128] Integrate the above formula:

[0129]

[0130] P i is the initial reservoir pressure, MPa.

[0131] Define the fracture storage factor:

[0132]

[0133] The combined equations 22-27 eliminate the average reservoir pressure:

[0134]

[0135] In the formula, RNP is the flow normalized pressure function.

[0136] According to Formula 28, the relationship between the flow normalized pressure function RNP of the original fracture pressure and the bottom hole flow pressure and the material balance time MBT can be calculated.

[0137] Step 4: Establish an iterative method for solving the effective transformation volume, including:

[0138] Establish an iterative method to solve the effective transformation volume, collect oil-water (gas) flowback data, identify the early flow stage according to the oil-water ratio, calculate the liquid flow rate and flow normalized pressure, and give the initial effective transformation volume V fi , calculate the relative permeability and comprehensive compressibility, further calculate the material balance time, and invert the new effective transformation volume V according to the relationship between flow normalized pressure and material balance time fi,new Until Vfi and V fi,new The error of satisfies the given range, and the effective transformation volume is finally calculated.

[0139] Further, including:

[0140] 4.1 Identifying the flow phase

[0141] Collect flowback data from wells, such as Figure 1 , draw the oil-water ratio change curve. Figure 2 , identify the early flow stage. In the initial stage of flowback, affected by the wellbore reservoir and skin coefficient, the characteristics of the produced fluid cannot accurately represent the characteristics of the transformed volume; but after the flowback time is too long, the produced fluid not only comes from the transformed volume, but the matrix also begins to supply fluid. Therefore, the time corresponding to the early flow stage should not be too small or too large. The more reasonable range is to select the stage before the slope of the oil-water ratio curve changes significantly. For example Figure 2 In the above figure, after 40 days of production, the slope of the oil-water ratio change curve becomes significantly larger, indicating that the matrix has begun to supply fluid. Therefore, the curve before 40 days should be selected as the early flow stage. Table 1 Reservoir parameters

[0142]

[0143]

[0144] 4.2 Calculation of liquid flow rate and flow normalized pressure

[0145] According to the liquid flow rate q t and the definition of flow normalized pressure RNP, calculate the corresponding value, such as Figure 3 , Figure 4 .

[0146] 4.3 Calculation of relative permeability and comprehensive compressibility

[0147] Given a preset V fi value, calculate k using experimental data ro (t), such as Figure 5 , Figure 5-Figure 8 The results are all the results of the last iteration. Use formula 13 to calculate the comprehensive compression coefficient, as shown in Figure 6 .

[0148] 4.4 Calculation of material balance time t a , draw RNP-t a Curve, inversion of effective transformation volume

[0149] The material balance time is calculated by numerical integration method using Equation 24, as Figure 7 , and draw the RNP-ta relationship curve, such as Figure 8 , Figure 8 The RNP-ta relationship curve diagram in a specific embodiment of the present invention shows the straight line segment inversion result; the effective transformation volume V is calculated using the slope K of the straight line segment. fi,new , determine and preset the effective transformation volume value V fi Does the error meet the requirements? If so, the effective transformation volume is obtained; if not, the updated value is (V fi,new -V fi ) / 2, return to step 4.3 and continue calculating until the set error requirement is met.

[0150] Fig. 9 The flowchart of iterative calculation is shown in Figure 1. First, collect the oil-water (gas) return data ( Figure 1 ), and identify the early flow area based on the oil-water ratio ( Figure 2 ), calculate the liquid flow rate ( Figure 3 ) and flow normalized pressure ( Figure 4 ), given the initial effective transformation volume V fi , calculate the relative permeability ( Figure 5 ) and comprehensive compression factor ( Figure 6 ), and further calculate the material balance time ( Figure 7 ), according to the relationship between flow normalized pressure and material balance time ( Figure 8 ), find the slope of the straight line segment, and invert the new effective transformation volume V fi,new , until V fi With V fi,new The error of satisfies the given range, and the effective transformation volume is finally calculated.

[0151]

[0152] Where K is the slope.

[0153] The final calculation shows that the effective transformation volume of the well is 59.4*10 4 m 3 The effective transformation volume of the well obtained by geological and engineering integrated simulation is 56.3*10 4 m 3, the error between the two is only 5.5%, which fully confirms the accuracy of this method. The present invention mainly uses the early flowback data of the oil well after fracturing. This data can be obtained very conveniently on site without the need for additional testing, and the solution process is very simple, and the calculation can be completed in just a few minutes; but the integrated simulation of geology and engineering requires the use of reservoir geostress field data, pore permeability data, oil, gas and water production dynamic data and fracturing construction data, etc., and it is also necessary to perform multiple historical fittings on the model, which is a very large workload, and it often takes several months to interpret a well. Therefore, the method provided by the present invention can accurately and efficiently calculate the effective transformation volume of shale oil.

[0154] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the system disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0155] The principles and implementation methods of the present invention are described in this article using specific examples. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

[0156] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions recorded in the aforementioned embodiments or replace some of the technical features therein with equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

[0157] Except for the technical features described in the specification, all other technical features are known technologies to those skilled in the art.

Claims

1. A method for calculating the effective transformation volume of shale oil based on fracturing flowback data, characterized in that: The calculation method of the effective transformation volume of shale oil includes: Step 1, establishing the material balance equation within the effective transformation volume in the early stage of flowback; Step 2, considering the stress sensitivity of the reservoir, establish the flow equation within the effective transformation volume; Step 3, establishing a calculation model for the effective transformation volume after fracturing, establishing the relationship between flow normalized pressure and material balance time, and calculating the effective transformation volume through the slope; Step 4, establish an iterative method for solving the effective transformation volume. By presetting the effective transformation volume, the new effective transformation volume is calculated using the slope of the curve of flow normalized pressure and material balance time, and the final effective transformation volume value that meets the preset error is output.

2. The method for calculating the effective transformation volume of shale oil based on fracturing flowback data according to claim 1, characterized in that: In step 1, in the early stage of flowback, the pressure wave propagates within the effective transformation volume. The production of shale oil wells comes entirely from the effective transformation volume, and the contribution of reservoirs outside the effective transformation volume to the production can be ignored. According to the principle of material balance, the mass of the inflowing crude oil minus the mass of the outflowing crude oil is equal to the change in the mass of the crude oil in the effective transformation volume, and the material balance equation is established.

3. The method for calculating the effective transformation volume of shale oil based on fracturing flowback data according to claim 1, characterized in that: In step 2, the reservoir in the effective transformation volume has been fully transformed, so the fluid flow can be considered to satisfy the Darcy equation. During the production process, the pressure in the effective transformation volume gradually changes. Affected by the stress sensitivity of the reservoir, the permeability and phase permeability curve in the oil leakage volume gradually change, and a flow equation considering the stress sensitivity of the reservoir is established.

4. The method for calculating the effective transformation volume of shale oil based on fracturing flowback data according to claim 3 is characterized in that: In step 2, the flow equation considering the reservoir stress sensitivity is established as: In the formula, μ o is the crude oil viscosity, mPa·s; B o is the volume coefficient of oil, m 3 / m 3 ; ▽ is the gradient operator; p f is the pressure in the effective transformation volume, is the porosity within the effective transformation volume; K f is the permeability within the effective transformation volume, mD; C t is the comprehensive compression coefficient term defined, MPa -1 ; K ro is the relative permeability function, measured from experimental data.

5. The method for calculating the effective transformation volume of shale oil based on fracturing flowback data according to claim 1, characterized in that: In step 3, by combining the material balance equation and the flow equation considering reservoir stress sensitivity, taking into account different well types and different boundary conditions, the pressure distribution in the effective transformation volume is further obtained. According to the relationship between the average pressure in the effective transformation volume and the bottom hole flow pressure, the relationship between the flow normalized pressure and the material balance time is obtained.

6. The method for calculating the effective transformation volume of shale oil based on fracturing flowback data according to claim 3, characterized in that: In step 3, the relationship between the flow normalized pressure, i.e., the reservoir pressure drop and the liquid flow rate, and the material balance time is: In the formula, p f is the pressure in the effective transformation volume, MPa; μ o is the crude oil viscosity, mPa·s; B o is the volume coefficient of oil, m 3 / m 3 ; is the porosity of the effective transformation volume; K f is the permeability of the effective transformed volume, mD; q t is the total liquid flow, m 3 / d;K ro is the relative permeability function; V fi is the initial effective fracture volume.

7. The method for calculating the effective transformation volume of shale oil based on fracturing flowback data according to claim 1, characterized in that: In step 4, an iterative method for solving the effective transformation volume is established, oil-water flowback data is collected, and the early flow stage is identified according to the oil-water ratio, and the liquid flow rate and flow normalized pressure are calculated. The initial effective transformation volume V is given. fi , calculate the relative permeability and comprehensive compressibility, further calculate the material balance time, and invert the new effective transformation volume V according to the slope of the curve of flow normalized pressure and material balance time fi,new , until V fi With V fi,new The error of satisfies the given range, and the effective transformation volume is finally calculated.

8. The method for calculating the effective transformation volume of shale oil based on fracturing flowback data according to claim 7, characterized in that: Step 4 specifically includes: 4.1 Identify the flow phase; 4.2 Calculate liquid flow rate and flow normalized pressure; 4.3 Calculate relative permeability and comprehensive compressibility; 4.4 Calculation of material balance time t a , draw RNP-t a Curve, inversion of effective transformation volume.

9. The method for calculating the effective transformation volume of shale oil based on fracturing flowback data according to claim 8, characterized in that: In step 4.1, the flowback data of the wells are collected, the oil-water ratio change curve is drawn, the early flow stage is identified, and the relevant parameters of the reservoir are collected.

10. The method for calculating the effective transformation volume of shale oil based on fracturing flowback data according to claim 8, characterized in that: In step 4.2, according to the liquid flow rate q t and the definition of flow normalized pressure RNP, calculate the corresponding value.

11. The method for calculating the effective transformation volume of shale oil based on fracturing flowback data according to claim 8, characterized in that: In step 4.3, given the preset V fi value, calculate k using experimental data ro (t), the comprehensive compression coefficient is calculated using the following formula: In the formula, C t is the total compressibility term, MPa -1 , each term of its expression represents the influence of different driving mechanisms in turn: oil phase expansion, liquid phase expansion, and fracture closure; Indicates the reciprocal of the fracture stiffness determined by the elastic energy or strain energy required to keep the hydraulic fracture open, MPa -1 ; C w , C o is the water and oil compressibility coefficient, MPa -1 ; S oi , S wi are the initial oil and water saturations, dimensionless; B o , B w are the volume coefficients of oil and water, respectively, m 3 / m 3 ; B oi , B wi are the initial oil and water volume coefficients, m 3 / m 3 .

12. The method for calculating the effective transformation volume of shale oil based on fracturing flowback data according to claim 8, characterized in that: In step 4.3, the material balance time is calculated by numerical integration method using the following formula: Where, t a is the material equilibrium time; K ro is the relative permeability function; μ o is the crude oil viscosity, mPa·s; B o is the volume coefficient of oil, m 3 / m 3 ; C t is the defined comprehensive compressibility, MPa -1 ; Draw the RNP-ta relationship curve and calculate the effective transformation volume V according to the slope K of the straight line segment on the curve. fi,new , determine and preset the effective transformation volume value V fi Does the error meet the requirements? If so, the effective transformation volume is obtained; if not, the updated value is (V fi,new -V fi ) / 2, return to step 4.3 and continue calculating until the set error requirement is met.

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