Method for evaluating fracture parameters after fracturing of thin interbedded reservoirs

Abstract

The present application relates to the technical field of oil and gas field development, in particular to a kind of thin interbedded reservoir fracture parameter evaluation method after fracturing. The influence range of the multilayer fracturing well of thin interbedded reservoir is divided into different flow regions in horizontal direction according to the position relationship with the fracturing region, and the corresponding flow equation is established for different flow regions. The influence range of the multilayer fracturing well of thin interbedded reservoir is divided into different interlayer channeling regions in vertical direction according to the interlayer channeling condition between different layer fracturing area and adjacent layer, and the corresponding interlayer channeling flow equation is established for different interlayer channeling regions. The flow equation and interlayer channeling flow equation are solved to obtain the bottom hole pressure model and pressure derivative model of the multilayer fracturing well of thin interbedded reservoir. The bottom hole pressure model and pressure derivative model are fitted with the actual test data, and the fitting parameters are continuously adjusted until the fitting error is satisfied. The adjusted fitting parameters are used as the fracturing effect evaluation parameters of the multilayer fracturing well of thin interbedded reservoir.

Description

Technical Field

[0001] This invention relates to a method for evaluating fracture parameters after fracturing in thin interbedded oil reservoirs, belonging to the field of oil and gas field development technology. Background Technology

[0002] Sandstone reservoirs are widely distributed and diverse in type in my country. Thin-interbedded sandstone reservoirs are a type of sandstone reservoir characterized by their predominance of thin-interbedded sand bodies, small reservoir thickness, and strong interlayer heterogeneity. Preparatory work for the development of thin-interbedded sandstone reservoirs requires fracturing the oil-bearing reservoir portion. During the actual fracturing process, the geological characteristics of thin-interbedded sandstone inevitably lead to several problems that need to be addressed. On the one hand, due to the well-developed thin interbedded layers between the reservoir and interlayers, fracturing can easily penetrate these layers, leading to interlayer channeling. On the other hand, the significant differences in reservoir properties along the vertical direction result in substantial variations in fracture length and conductivity between fracturing layers, increasing the cost of reservoir development. Therefore, accurately assessing the geological characteristics of fractures, i.e., evaluating fracture parameters, is of great significance for exploration and assessment of development value in the early stages of oil and gas exploration and development.

[0003] Currently, mainstream fracturing technologies primarily employ fracture monitoring and well test analysis to evaluate fracture parameters. Fracture monitoring methods are only suitable for acquiring geometric parameters of the fracture, including length, height, and azimuth, and cannot evaluate fracture conductivity and interlayer flow. Well test analysis, on the other hand, mainly evaluates fracturing effectiveness by establishing a pressure analysis mathematical model. Existing well test models use vertical fracture models, and while a few consider interlayer flow in the fracturing zone, none account for flow from the unfracturing zone to the fracturing zone caused by differences in fracture length and conductivity. This leads to inaccurate fracturing evaluation results, consequently affecting the effectiveness of subsequent adjustment and remediation measures.

[0004] In his doctoral dissertation published in December 2015 at Southwest Petroleum University, entitled "Research on Unstable Flow Model and Well Test Analysis Method for Fracturing Wells in Complex Reservoirs," the author established a multi-layer crossflow flow model for fractured wells using planar radial flow. The fracture length xf and conductivity FC of each layer were the same. The model considered the interlayer crossflow in the fractured zone but did not consider the crossflow from the fractured zone to the unfractured zone.

[0005] In the paper titled "Dynamic Characteristics of Elliptical Seepage Pressure in Multi-Layer Fracturing Gas Wells" published in Volume 27, Issue 2 of "Fault-Block Oil and Gas Fields" in March 2020, the authors used an elliptical composite seepage model based on the concept of fracturing SRV to consider the situation of multi-layer fracturing and combined production. However, the model fracturing fractures were infinitely conductive fractures, so it was impossible to obtain the fracture conductivity parameters and did not consider the problem of interlayer flow after fracturing.

[0006] In the paper titled "Pressure Transient Analysis for Hydraulically Fractured Wells with Changing Conductivity in Stratified Reservoirs: Case Study in Xinjiang Oilfield," published in ACS OMEGA in July 2022 (pages 30313-30320), the authors established a fracturing and production well model using a three-line flow pattern. This model considered the unequal fracture lengths (xf) of each layer and the non-uniform conductivity of each layer's fractures (the conductivity coefficient FC1 of the near-well section is not equal to the conductivity coefficient FC2 of the far-well section). However, it did not consider the problem of interlayer crossflow after fracturing.

[0007] The Chinese patent authorization announcement document with authorization announcement number CN108894777B discloses a method for determining the reservoir properties and fracture characteristics parameters of multi-layer fracturing and multi-layer synergistic oil and gas reservoirs. It uses a seepage model to obtain the fracture parameters of multi-layer fracturing and then performs production splitting of each layer. However, it does not consider the problem of interlayer flow in the reservoir after fracturing.

[0008] Therefore, the mathematical models currently used for evaluating fracturing parameters in thin interbedded reservoirs are not comprehensive in their consideration of factors. They do not simultaneously take into account the different fracture lengths and conductivity of each layer, as well as the interlayer flow from the unfractured zone to the fractured zone caused by fracturing differences. They are not suitable for analyzing the flow scenarios of multi-layer fracturing and combined production wells in thin interbedded reservoirs, which greatly limits the evaluation of fracturing effects and the formulation of subsequent development adjustment measures for thin interbedded reservoirs. Summary of the Invention

[0009] The purpose of this invention is to provide a method for evaluating fracture parameters after fracturing in thin interbedded reservoirs, in order to solve the problem that the existing mathematical models for evaluating fracturing parameters in thin interbedded reservoirs do not take into account all factors, which severely limits the evaluation of fracturing effects and the formulation of subsequent development and adjustment measures.

[0010] To achieve the above objectives, the present invention includes the following steps: Based on the obtained field pressure test data, considering the influence of fracture length, conductivity, and interlayer crossflow coefficient of each layer, a flow equation for different seepage zones of a multi-layered fractured well in a thin interbedded reservoir is established. According to the condition that the flow rate and pressure are equal at the boundaries of the flow equations of each seepage zone, the flow equations are solved to obtain the bottom hole pressure and pressure derivative models. Then, the bottom hole pressure and pressure derivative models are fitted to the actual test data using the least squares method. The bottom hole pressure and pressure derivative models are corrected by adjusting the fitting parameters until they are within the fitting error range. Finally, the adjusted fitting parameters are used as fracture parameters to explain the fracture length, fracture conductivity, and interlayer crossflow coefficient of each layer.

[0011] The present invention provides a method for evaluating fracture parameters after fracturing in thin interbedded reservoirs, comprising the following steps:

[0012] 1) Divide the synergistic reservoir of the thin interbedded reservoir into different flow regions in the horizontal direction according to its positional relationship with the fracturing area, and establish corresponding flow equations for different flow regions. Divide the synergistic reservoir into different interlayer flow regions in the vertical direction according to the flow between different fracturing zones and adjacent layers, and establish corresponding interlayer flow equations for different interlayer flow regions.

[0013] 2) Solve the flow equation and the interlayer crossflow flow equation to obtain the bottom hole pressure model and pressure derivative model of the multi-layer fracturing well in the thin interlayer reservoir;

[0014] 3) Fit the bottom hole pressure model and pressure derivative model to the actual test data, and continuously adjust the fitting parameters until the fitting error is satisfied. Use the adjusted fitting parameters as the evaluation parameters for the fracturing effect of multi-layered fracturing wells in thin interbedded reservoirs.

[0015] Furthermore, in step 1), based on the seepage of fractured wells and the theory of unsteady well testing, the area where the fractures are located in the horizontal direction of any layer of the syndicated reservoir is divided into the fractured area, the area adjacent to the fractured area in the horizontal direction of any layer of the syndicated reservoir is divided into the near-fractured reservoir area, and the other areas in the horizontal direction of any layer of the syndicated reservoir are divided into the far-fractured reservoir area. The unfractured area of ​​any layer of the syndicated reservoir includes the near-fractured reservoir area and the far-fractured reservoir area.

[0016] Furthermore, in step 1), based on the seepage and unsteady well testing theory of fractured wells, the flow from the fractured area of ​​the adjacent upper layer in the vertical direction of any layer of the syndicated reservoir is defined as the upper fractured area flow, the flow from the unfractured area of ​​the adjacent upper layer is defined as the upper unfractured area flow, the flow from the fractured area of ​​the adjacent lower layer is defined as the lower fractured area flow, and the flow from the unfractured area of ​​the adjacent lower layer is defined as the lower unfractured area flow.

[0017] Furthermore, in step 1), the flow equation and the interlayer crossflow flow equation are obtained based on the principle of mass conservation, combined with the fracture length, conductivity and interlayer crossflow coefficient of the multi-layer fractured well in the thin interlayer reservoir.

[0018] Furthermore, in step 2), based on the condition that the flow rate and pressure are equal at the boundary of each region in any layer of a multi-layered fractured well in a thin interlayered reservoir, the flow equation and the interlayer crossflow flow equation are solved to obtain the bottom hole pressure model and bottom hole pressure derivative model of the multi-layered fractured well in a thin interlayered reservoir.

[0019] Furthermore, in step 3), the parameters include the fracture length, fracture conductivity, and interlayer crossflow coefficient.

[0020] The beneficial effects of this invention are as follows:

[0021] This invention provides a method for evaluating fracture parameters after fracturing in thin-layered reservoirs. After fracturing a thin-layered reservoir, the influence area of ​​the multi-layered fracturing well in the thin-layered reservoir is divided into different flow regions horizontally according to its positional relationship with the fracturing area, and corresponding flow equations are established for each flow region. Vertically, the influence area of ​​the multi-layered fracturing well in the thin-layered reservoir is divided into different interlayer crossflow regions according to the crossflow between different fracturing zones and adjacent layers, and corresponding interlayer crossflow flow equations are established for each interlayer crossflow region. Solving the flow equations and interlayer crossflow flow equations yields the bottomhole pressure model and pressure derivative model of the multi-layered fracturing well in the thin-layered reservoir. The bottomhole pressure model and pressure derivative model are fitted with actual test data, and the fitting parameters are continuously adjusted until the fitting error is satisfied. The adjusted fitting parameters are used as evaluation parameters for the fracturing effect of the multi-layered fracturing well in the thin-layered reservoir. A pressure analysis mathematical model for multi-layer fracturing wells in thin interbedded reservoirs was established. This model integrates the differences in fracture length and conductivity of each layer in multi-layer fracturing, as well as the crossflow problem between different regions. It can effectively determine the different fracture lengths, fracture conductivity, and crossflow degree of each layer after fracturing in thin interbedded reservoirs. It can effectively evaluate the fracture parameters after fracturing in thin interbedded reservoirs, which facilitates the formulation of subsequent exploitation plans. Attached Figure Description

[0022] Figure 1 A flowchart illustrating a method for evaluating fracture parameters after hydraulic fracturing in thin interbedded reservoirs;

[0023] Figure 2 This is a schematic diagram of the planar flow in the j-th layer of the model of this invention;

[0024] Figure 3 This is the intended meaning of interlayer flow in the j-th layer of the model of this invention;

[0025] Figure 4 A flowchart for fitting stress data from example tests;

[0026] Figure 5 The initial fitting effect of pressure and pressure derivative data is tested as an example.

[0027] Figure 6 The final fitting result of the method of this invention is shown in the example.

[0028] Figure 7 The example does not consider the fitting results of the interlayer flow model from the unfractured zone to the fractured zone;

[0029] Figure 8The following diagram illustrates the fracturing effect and parameters using examples.

[0030] Figure 9 Table of basic reservoir and fluid parameters for example wells;

[0031] Figure 10 This is the bottom hole pressure test data for the example well. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0033] Example:

[0034] This invention provides a method for evaluating fracture parameters after fracturing in thin interbedded reservoirs, which can be applied in multiple fields such as geological exploration, oil and gas field development, and engineering construction. By accurately evaluating fracture parameters, the permeability and reservoir properties of the reservoir can be understood, providing a scientific basis and technical support for decision-making and implementation in related fields.

[0035] like Figure 1 As shown, the method for evaluating fracture parameters after fracturing in a thin interbedded reservoir according to the present invention includes the following steps:

[0036] 1) Divide the influence range of multi-layer fracturing wells in thin interbedded reservoirs into different flow regions in the horizontal direction according to their positional relationship with the fracturing area, and establish corresponding flow equations for different flow regions. Divide the influence range of multi-layer fracturing wells in thin interbedded reservoirs into different interlayer flow regions in the vertical direction according to the flow between different fracturing zones and adjacent layers, and establish corresponding interlayer flow equations for different interlayer flow regions.

[0037] Specifically, in step 1), based on the seepage and unsteady well testing theory of fractured wells, the area in any layer of the multi-layer fractured well in the thin interbedded reservoir that is adjacent to and perpendicular to the fracture in the horizontal direction is divided into the near-fracture reservoir area, and the area that is not adjacent to and parallel to the fracture is divided into the far-fracture reservoir area.

[0038] For the j-th layer of a multi-layered fracturing and combined production well, such as Figure 2 As shown, it can be divided into three linear flow regions in the horizontal direction (on the plane); the j-th layer of the stratified fractured and co-produced reservoir can be divided into three regions: Region I is the fractured region; Region II is the near-fractured reservoir region, where the flow is perpendicular to the fracture direction and is a linear flow in the y-direction; Region III is the far-fractured reservoir region, where the flow is parallel to the fracture direction and is a linear flow in the x-direction.

[0039] Specifically, in step 1), based on the seepage and unsteady well testing theory of fractured wells, any layer of a multi-layered fractured well in a thin interbedded reservoir is vertically divided into an upper fractured zone, an upper unfractured zone, a lower fractured zone, a lower unfractured zone, and the fractured zone of this layer.

[0040] like Figure 3 As shown, there are four directions of interlayer flow in the vertical direction of the fractured well. For the j-th fractured zone, there are four directions of flow: flow in the j-1-th fractured zone, flow in the j-1-th unfractured zone, flow in the j+1-th fractured zone, and flow in the j+1-th unfractured zone.

[0041] Specifically, in step 1), the flow equation and the interlayer crossflow flow equation are obtained based on the principle of mass conservation, combined with the fracture length, conductivity, and interlayer crossflow coefficient of multi-layer fractured wells in thin interlayer reservoirs, as follows:

[0042] 1.1) Establish the flow equation for the fracturing zone. The pressure in the j-th fracturing zone is denoted as P. j,1D The dimensionless distance range of the crack in zone I is 0. <x D <L fDj According to the principle of mass conservation, its dimensionless flow equation in Laplace space is expressed as:

[0043]

[0044] Where, p j,1D The dimensionless pressure of the j-th fracturing zone x D dimensionless distance in the x-direction y D dimensionless distance in the y-direction L fDj Let j be the dimensionless length of the crack in the j-th layer. F cDj Let be the dimensionless conductivity coefficient of the fracture in the j-th layer. q D(j-1,1),(j，1) Dimensionless flow rate from the (j-1)th fracturing zone q (j-1,2),(j，1) The dimensionless flow rate from the unfractured zone of layer j-1 q (j+1,1),(j，1) The dimensionless flow rate from the (j+1)th fracturing zone q (j+1,2),(j，1) The dimensionless flow rate from the (j+1)th fracturing zone

[0045] In Laplace space, the initial condition for dimensionless pressure is:

[0046] p j,1D (u→∞)=0 (2)

[0047] x at the connection between the crack and the wellbore D =0, the flow velocity in the fracture region is constant. Therefore, the inner boundary condition of the near-wellhead fracture region in zone I is:

[0048]

[0049] Where u is a Lapalce space variable; κ j The ratio of the stratigraphic coefficient of the j-th layer

[0050] x at the end of the crack D =L fDj The flow rate along the fracture direction is 0. Therefore, the outer boundary conditions of the fracture region at the far end of the well in Zone I are:

[0051]

[0052] In formulas (1)-(4), k j This represents the permeability of the unfractured zone in the j-th layer, in meters. 2 ;r w Indicates well diameter, in meters (m); p i p represents the original reservoir pressure, in Pa. j,1 Q represents the pressure in the j-th fracturing zone, in Pa; Q represents the well production rate, in m³. 3 / s; μ represents viscosity, in Pa·s; B represents the isothermal volume coefficient, in m³ / s. 3 / m 3 x represents the distance in the x-direction, in meters; y represents the distance in the y-direction, in meters; L fj w represents the fracturing distance of the j-th layer, in meters. fj F represents the width of the crack in the j-th layer, in meters. Cj This represents the conductivity coefficient of the fracture in the j-th layer, in meters. 3 ; q represents the flow rate, in m³ / s. 3 / s;h j This represents the thickness of the j-th layer, in meters (m).

[0053] 1.2) Establish the flow equation for the unfractured zone.

[0054] 1.2.1) Establish the flow equation for the near-fracture reservoir region. The pressure in region II of layer j is denoted as P. j,2D The dimensionless distance range is 0. <x D <L fDj 0 <y D For values ​​<∞, the dimensionless flow equation in Laplace space can be written as:

[0055]

[0056] Where, ω j The ratio of the storage coefficient of the j-th layer

[0057] Initially, the pressure at all points is the same as the original formation pressure of the reservoir. Therefore, the initial conditions for the governing equations of Zone II are:

[0058] p j,2D (u→∞)=0 (6)

[0059] Where, p j,2D The dimensionless pressure of the j-th unfractured zone II

[0060] x at the junction of the fracture distal segment and the reservoir D =L fDj The pressures are equal. Therefore, the inner boundary conditions of the governing equations for region II are:

[0061] p j,1D =p j,2D ,(0 <x D <L fDj ,y D =0) (7)

[0062] At infinity along the vertical direction of the crack y D As the reservoir pressure approaches infinity, the original formation pressure equals the initial formation pressure. Therefore, the outer boundary conditions for the governing equations in Zone II are:

[0063] p j,2D (y D →∞)=0 (8)

[0064] In formulas (5)-(8), p j,2 h represents the pressure in the unfractured zone II of layer j, in Pa. j This represents the thickness of the j-th layer, in meters (m). c represents the porosity of the unfractured zone in the j-th layer, in %; tj This represents the compressibility coefficient of the j-th unfractured zone, in MPa. -1 .

[0065] 1.2.2) The pressure in region III of layer j is denoted as p. j,3D The dimensionless distance range is L fDj <x D <∞,0 <y D For values ​​<∞, the dimensionless flow equation in Laplace space can be written as:

[0066]

[0067] Where p j,3DThe dimensionless pressure of the j-th unfractured zone III

[0068] Initially, the pressure at each point is the same as the original formation pressure of the reservoir. Therefore, the initial conditions for the governing equations of Zone III are:

[0069] p j,3D (u→∞)=0 (10)

[0070] x at the distal segment of the crack D =L fDj The pressure in region II is equal to the pressure in region III. Therefore, the boundary conditions within the governing equations for region III are:

[0071] p j,3D =p j,2D ,(x D =L fDj (11)

[0072] x at infinity along the direction of the crack D As the reservoir pressure approaches infinity, the original formation pressure equals the initial formation pressure. Therefore, the external boundary conditions for the governing equations in Zone III are:

[0073] p j,3D (x D →∞)=0 (12)

[0074] In formulas (5) to (12): p j,3 This represents the pressure in the unfractured zone III of layer j, in Pa.

[0075] 1.2.3) Establish the interlayer crossflow equation. For any region m in the j-th layer (hereinafter denoted by (j,m), where j represents the layer number and m=1 represents the fracturing zone), as follows: Figure 3 The flow is shown to originate from four directions, including the upper (j-1) fracturing zone (j-1, 1), the unfracturing zone (j-1, 2), and the lower (j+1) fracturing zone (j+1, 1) and the unfracturing zone (j+1, 2), with dimensionless flow rates as follows:

[0076]

[0077] In formula (13): λ jn (n=1,2,3,4) represents the crossflow coefficients corresponding to different regions of the j-th layer.

[0078] 2) Solve the flow equations to obtain the bottom hole pressure model and pressure derivative model of the multi-layered fracturing well in the thin interbedded reservoir;

[0079] Specifically, based on the condition that the flow rate and pressure are equal at the boundary of each region in any layer of a multi-layered fractured well in a thin interlayered reservoir, the flow equation and the interlayer crossflow flow equation are solved to obtain the bottom hole pressure model and bottom hole pressure derivative model of the multi-layered fractured well in a thin interlayered reservoir.

[0080] Given the dimensionless pressure p in the unfractured zone II of layer j. j,2D In x D =L fDj The flow rate caused by the gradient change at a certain point and the dimensionless pressure p in the unfractured zone III of layer j j,3D Since the flow rates caused by gradient changes are equal, the dimensionless pressure solution for region III of layer j can be obtained as follows:

[0081]

[0082] in:

[0083]

[0084] Given the dimensionless pressure p in the unfractured zone I of layer j. j,1D The gradient in y D =w fDj The flow rate caused by the change at point j and the dimensionless pressure p in the unfractured zone II of layer j j,2D The gradient changes result in equal flow rates, thus the dimensionless pressure solution for region II is obtained as follows:

[0085]

[0086] In formula (16), coefficient A j for:

[0087]

[0088] The dimensionless pressure solution for region I is:

[0089] p j,1D =C j1 +C j2 (18)

[0090] Differentiating the pressure in region II and substituting it into the governing equations for pressure in region I, we obtain the dimensionless pressure solution for region I by simultaneously solving the boundary conditions:

[0091]

[0092] In equation (19), the coefficient B j for:

[0093]

[0094] Solving formula (20) yields the unknown coefficient C. j1 Cj2 :

[0095]

[0096] In formula (21):

[0097]

[0098] Substituting equation (21) into equation (18) yields the fracture pressure at each layer. In Laplace space, the dimensionless fracture pressure p at the j-th layer of the fracture skin is considered. j,1D With dimensionless bottom hole pressure p wfD The relationship is:

[0099]

[0100] In formula (23), S j This represents the skin coefficient of each layer of cracks.

[0101] In real-space logarithmic coordinates, the dimensionless bottom-hole pressure derivative is:

[0102]

[0103] In equation (24): dimensionless time parameter Where: t represents time, and the unit is seconds.

[0104] 3) Fit the bottom hole pressure model and pressure derivative model to the actual test data, and continuously adjust the fitting parameters until the fitting error is satisfied. Use the adjusted fitting parameters as the evaluation parameters for the fracturing effect of multi-layered fracturing wells in thin interbedded reservoirs.

[0105] Specifically, in step 3, the parameters for evaluating the fracturing effect include the fracture length, fracture conductivity, and interlayer flow coefficient.

[0106] Specifically, the derivative of pressure is calculated from the measured pressure value using an interpolation method.

[0107] like Figure 4 As shown, the specific steps for fitting the model and obtaining the fracturing effect evaluation parameters of the crack are as follows:

[0108] ① Input field data and adjacent well interpretation data (including: number of fracturing layers j, original formation pressure p) i Initial reservoir permeability k j Porosity reservoir thickness h j , wellbore radius r w Crack width w fj Overall compression coefficient c tj Given an initial value M0;

[0109] ② The bottom hole pressure curve is obtained by using the initial bottom hole pressure model to calculate the data from step ①, and the predicted bottom hole pressure data sequence is obtained.

[0110] ③ Use the least squares method to calculate the error between the predicted pressure data series and the measured pressure data series;

[0111] ④ The general standard for error is 10. -3 Within this range, determine whether the error meets the requirements: if it does, stop; if not, proceed to step ①.

[0112] ⑤ Output the adjusted fitting parameters and use the adjusted fitting parameters, such as fracture length, fracture conductivity, and interlayer flow coefficient, as evaluation parameters for fracturing effect.

[0113] The following uses a sandstone thin interbedded reservoir well A in a certain area as an example to provide a detailed explanation of the evaluation method of fracture parameters after fracturing in a thin interbedded reservoir according to the present invention, combined with examples.

[0114] Well A in a sandstone thin interbedded oil reservoir has two main producing layers. The upper layer has a permeability of 12.6 mD, a thickness of 3 m, and a porosity of 15.2%, while the lower layer has a permeability of 35.3 mD, a thickness of 6 m, and a porosity of 17.3%. The wellbore radius r is... w =0.1m. Other physical properties are as follows: Figure 9 As shown.

[0115] (1) Well shut-in test pressure data

[0116] Due to low production during the trial production of Well A, fracturing was subsequently employed to stimulate the reservoir. Fracturing was performed simultaneously on both the upper and lower layers. After stimulation, pressure data was tested by shutting the well in; the pressure gauge was placed at the bottom of the well, and the data is as follows: Figure 10 As shown in columns 1 and 2, the derivative of the test pressure is calculated based on the three-point interpolation method (25), as follows: Figure 10 As shown in column 3.

[0117]

[0118] (2) Establish flow equations for different seepage zones in multi-layered fractured wells

[0119] Based on the theory of seepage in fractured wells and unsteady well testing, for the j-th layer of a two-layer fractured well A, according to the principle of mass conservation, flow equations are established based on formulas (26) to (33) for three linear flow regions in the plane and two crossflow directions in the vertical direction.

[0120] Planar seepage (Cracked zone I):

[0121] upper layer:

[0122] Lower layer:

[0123] Planar seepage (Zone II, near the fracture zone):

[0124] upper layer:

[0125] Lower layer:

[0126] Planar seepage (Zone III, far-fracture zone):

[0127] upper layer:

[0128] Lower layer:

[0129] Interlayer flow zone:

[0130] q D(1,1),(2,1) =λ1(p 1,1D -p 2,1D (32)

[0131] q D(1,2),(2,1) =λ2(p 1,2D -p 2,1D (33)

[0132] (3) Solve the bottom hole pressure and pressure derivative model

[0133] Based on the condition that the flow rate and pressure are equal at the boundary of each zone in the j-th layer, the established flow equation is solved using formulas (34) to (39) to obtain the bottom hole pressure P of well A. wfD and pressure derivative P' wfD Model.

[0134] Dimensionless pressure solution for the far-fracture region:

[0135]

[0136] Dimensionless pressure solution near the fracture zone:

[0137]

[0138] Dimensionless pressure solution for fractured zone:

[0139] p j,1D =C j1 +C j2 (36)

[0140]

[0141] Bottom hole pressure model:

[0142] pwfD =f(M,t D ), M = (L f1 ,L f2 ,F c1 ,F c2 ,λ1,λ2) (38)

[0143] Pressure derivative model:

[0144]

[0145] (4) Model fitting to obtain fracturing effect evaluation parameters

[0146] The test pressure of well A was fitted using a fracturing and combined production model, with j=2 fracturing layers and W width of each fracture layer. f1 =W f2 =5cm, fitting accuracy e is set to 10 -3 Set the initial crack length L f1o =L f2o =100, initial fracture conductivity F c1o =F c2o =500, initial interlayer crossflow coefficient λ 1o =λ 2o =10 -5 That is, the initial fitting parameters M0 = (100, 100, 500, 500, 10) -5 10 -5 The initial fitting results are as follows: Figure 5 As shown, the fitting error is 7.52 × 10⁻⁶. 2 .

[0147] The computer automatically adjusts and fits the data based on mine experience, setting the fitting precision value to 10. -3 The final fitting result is as follows Figure 6 As shown, the fitting error is 3.68 × 10⁻⁶. -4 The fitting results of the seepage model for multi-layered syngas fracturing wells established by Wang Xiaolu of Southwest Petroleum University are as follows: Figure 7 As shown, the fitting error is 9.42 × 10⁻⁶. -4 Its pressure derivative fit is poor, and the values ​​of the fracturing parameters explained by the fit show abnormalities.

[0148] The final fitting parameters are M = (61.8, 90.2, 318, 496, 3.8 × 10⁻⁶). -7 6.1×10 -6 The evaluation result is: the length L of the upper layer pressure crack. f1 The depth is 61.8m, and the conductivity F of the upper layer is... C1 The value is 318 mD·m; the length of the lower layer pressure fracture is L. f2The depth is 90.2m, and the conductivity F of the lower layer is... C2 The coefficient of flow from the upper fracturing zone to the lower fracturing zone is 496 mD·m; the cross-flow coefficient λ1 is 3.8 × 10⁻⁶ mD·m. -7 The cross-flow coefficient λ2 from the unfractured upper zone to the fractured lower zone is 6.1 × 10⁻⁶. -6 The results showed that the fracturing effect in the upper layer was worse than that in the lower layer, and there was obvious crossflow between layers in the fracturing zone. The fracturing effect is illustrated in the diagram below. Figure 8 As shown.

[0149] This invention provides a method for evaluating fracture parameters after fracturing in thin interbedded reservoirs. By combining the differences in fracture length and conductivity of each layer in multi-layer fracturing and the problem of crossflow between different regions, it can effectively determine the different fracture lengths, fracture conductivity, and interlayer crossflow of each layer after fracturing in thin interbedded reservoirs. This invention proposes and applies a relatively accurate method for evaluating fracture parameters after fracturing in thin interbedded reservoirs, laying a good foundation for a more accurate evaluation of the fracturing effect of thin interbedded reservoirs and the formulation of subsequent development adjustment measures during oilfield gas development.

[0150] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. The scope of patent protection of the present invention shall be determined by the claims. Similarly, any equivalent structural changes made based on the description and drawings of the present invention shall also be included within the scope of protection of the present invention.

Claims

1. A method for evaluating fracture parameters after fracturing in thin interbedded oil reservoirs, characterized in that, Includes the following steps: 1) Divide the synergistic reservoir of the thin interbedded oil reservoir into different flow regions in the horizontal direction according to its positional relationship with the fracturing area, and establish corresponding flow equations for different flow regions. Divide the synergistic reservoir into different interlayer flow regions in the vertical direction according to the flow between different fracturing zones and adjacent layers, and establish corresponding interlayer flow equations for different interlayer flow regions. 2) Solve the flow equation and the interlayer crossflow flow equation to obtain the bottom hole pressure model and pressure derivative model of the multi-layer fracturing well in the thin interlayer reservoir; 3) Fit the bottom hole pressure model and pressure derivative model to the actual test data, and continuously adjust the fitting parameters until the fitting error is satisfied. Use the adjusted fitting parameters as the evaluation parameters for the fracturing effect of the multi-layered fracturing well in the thin interbedded reservoir.

2. The method for evaluating fracture parameters after fracturing in thin interbedded reservoirs according to claim 1, characterized in that, In step 1), based on the seepage and unsteady well testing theory of fractured wells, the area where the fractures are located in the horizontal direction of any layer of the syndicated reservoir is divided into the fractured area, the area in the horizontal direction of any layer of the syndicated reservoir adjacent to the fractured area is divided into the near-fractured reservoir area, and the other areas in the horizontal direction of any layer of the syndicated reservoir are divided into the far-fractured reservoir area. The unfractured area of ​​any layer of the syndicated reservoir includes the near-fractured reservoir area and the far-fractured reservoir area.

3. The method for evaluating fracture parameters after fracturing in thin interbedded reservoirs according to claim 2, characterized in that, In step 1), based on the seepage and unsteady well testing theory of fractured wells, the flow from the fractured area of ​​the upper adjacent layer in the vertical direction of any layer of the syndicated reservoir is defined as upper fractured area flow, the flow from the unfractured area of ​​the upper adjacent layer is defined as upper unfractured area flow, the flow from the fractured area of ​​the lower adjacent layer is defined as lower fractured area flow, and the flow from the unfractured area of ​​the lower adjacent layer is defined as lower unfractured area flow.

4. The method for evaluating fracture parameters after fracturing in thin interbedded reservoirs according to claim 1, characterized in that, The flow equations and interlayer crossflow flow equations mentioned in step 1) are obtained based on the principle of mass conservation, combined with the fracture length, conductivity and interlayer crossflow coefficient of the multi-layer fractured well in the thin interlayer reservoir.

5. The method for evaluating fracture parameters after fracturing in thin interbedded reservoirs according to claim 1, characterized in that, In step 2), based on the condition that the flow rate and pressure are equal at the boundary of each region of any layer in the multi-layer fracturing well of the thin interlayer reservoir, the flow equation and the interlayer crossflow flow equation are solved to obtain the bottom hole pressure model and bottom hole pressure derivative model of the multi-layer fracturing well of the thin interlayer reservoir.

6. The method for evaluating fracture parameters after fracturing in thin interbedded reservoirs according to claim 4, characterized in that, In step 3), the parameters include the fracture length, fracture conductivity, and interlayer crossflow coefficient.

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