A method for optimizing fracturing parameters under variable load

Abstract

This invention provides a method for optimizing fracturing parameters under variable load, belonging to the field of petroleum development technology. The method includes: obtaining geological parameters from the field; establishing a theoretical calculation model to obtain the distribution law of downhole load along the horizontal section during variable load fracturing; establishing a fluid-structure interaction two-dimensional plane strain reservoir model based on the field parameters; obtaining the downhole load distribution law under constant amplitude load conditions; combining theoretical calculation results and numerical simulation results to invert the downhole load distribution during variable load fracturing under actual formation conditions; determining the fracturing initiation situation of multiple perforations; changing the construction conditions, performing multiple inversions, and finally determining the construction parameters that can achieve the preset fracturing effect. This method can effectively alleviate problems such as excessively high formation fracturing pressure and uneven perforation initiation.

Description

Technical Field

[0001] This invention belongs to the field of petroleum development technology, and in particular relates to a method for optimizing fracturing parameters under variable load. Background Technology

[0002] Mahu is the world's largest conglomerate oil reservoir, with reserves exceeding 1 billion tons. However, its extraction faces numerous challenges: deep reservoir burial, well-developed interlayers, low reservoir permeability, complex minerals, strong heterogeneity, poor fracture development, and significant inter-well variations. Since its overall deployment and large-scale development, the average daily oil production of horizontal wells in the main blocks of the Mahu conglomerate reservoir has decreased year by year. Long horizontal wells require increased fracture-controlled reserve development, and fracturing technology urgently needs to be upgraded while controlling costs. Due to the extremely strong heterogeneity of the conglomerate reservoir, conventional fracturing methods require high operating pressures, making formation fracturing difficult; at the same time, there is also significant non-uniform fracturing initiation during perforation, resulting in unsatisfactory fracturing effects.

[0003] Variable load fracturing, which involves periodically changing downhole loads, can effectively alleviate problems such as excessive formation fracturing pressure and uneven perforation initiation. However, it remains largely theoretical, with imperfect practical construction design methods. Therefore, this paper proposes methods for determining and effectively optimizing construction parameters to improve construction design, which is of great significance for the field implementation of variable load fracturing. Summary of the Invention

[0004] To address the problems existing in the prior art, the present invention provides a method for optimizing fracturing parameters under variable load. The technical problem to be solved by the present invention is how to effectively alleviate problems such as excessive formation fracturing pressure and uneven perforation initiation.

[0005] To address the aforementioned technical problems, this invention provides a method for optimizing fracturing parameters under varying loads, comprising the following steps:

[0006] Step S1: Obtain geological parameters from the site;

[0007] Step S2: Establish a theoretical calculation model and calculate the distribution law of downhole load along the horizontal section during the variable load fracturing process based on the set conditions;

[0008] Step S3: Based on the field parameters, establish a fluid-structure interaction two-dimensional plane strain reservoir model;

[0009] Step S4: Based on the established fluid-structure interaction two-dimensional plane strain reservoir model, conduct single-valued simulation to obtain the downhole load distribution law under constant amplitude load conditions;

[0010] Step S5: Combining the calculation results of the theoretical calculation model and the numerical simulation results of the fluid-structure interaction two-dimensional plane strain reservoir model, the downhole load distribution during the variable load fracturing process under actual formation conditions is obtained by inversion.

[0011] Step S6: Based on the comparison between the downhole load distribution and formation conditions during the variable load fracturing process under actual working conditions, determine the multi-cluster perforation initiation situation;

[0012] Step S7: Change the construction conditions, perform multiple inversions, and finally determine the construction parameters that can achieve the preset fracturing effect.

[0013] Furthermore, in step S1, the geological parameters include reservoir geological stress conditions, reservoir rock mechanical properties, vertical depth, and construction parameters.

[0014] Furthermore, step S2 includes the following steps:

[0015] Step H1: Determine the standing wave pressure distribution on the surface of the main fracture under variable load fracturing based on the construction parameters;

[0016] Step H2: Randomly select time t = t1 to perform inversion and obtain the standing wave pressure distribution law;

[0017] Step H3: Obtain the analytical solution σ of the stress distribution on the surface of a semi-infinite body under a normal distributed load based on elasticity mechanics. xa Stress distribution σ on the crack surface under uniformly distributed load conditions xa ′.

[0018] Furthermore, in step H1, the standing wave pressure distribution formula is:

[0019] p s (x,t)=p0+p am sin(2πtf t sin(2πxf) x )

[0020] In the formula, p s (x,t) represents the pressure distribution on the main fracture surface, in MPa; p0 is the average pressure pulse value, in MPa; p am t is the pressure pulse amplitude, MPa; t is the time, s; x is the distance between the pressure analysis point and the main seam opening, m; f t f is the time frequency. x For distance frequency.

[0021] Furthermore, in step H3, the analytical solution is:

[0022]

[0023] In the formula, p(ξ) is the pressure distribution equation; x q y and y are the horizontal and vertical coordinates of the unit cell inside the semi-infinite body, respectively; a and b are the upper and lower limits of integration; ξ is the length of the smallest differential unit.

[0024] Furthermore, in step S4, a fluid-structure interaction two-dimensional plane strain reservoir model is established based on field parameters, and the numerical solution σ of the stress distribution on the fracture surface under uniformly distributed load is calculated. xs ′.

[0025] Furthermore, in step S5, under uniformly distributed load and variable load conditions, the stress difference Δσ is obtained analytically using the formula for calculating the difference in stress distribution on the crack surface. xa The stress difference Δσ obtained from the numerical solution xs Based on Δσ xa and σ xs The stress distribution on the surface of the main fracture during the variable load fracturing process under actual formation conditions is obtained through inversion.

[0026] Furthermore, in step S5, the formula for calculating the difference in stress distribution on the crack surface is:

[0027] Δσ xa =σ xa -σ xa ′

[0028] The variable load fracturing parameter optimization method of the present invention has the following beneficial effects:

[0029] (1) The parameter optimization method is reliable. Based on extensive theoretical research, numerical simulation studies, and field applications, this method has been developed to optimize parameters, and the results are reliable.

[0030] (2) Good economic efficiency. The drawing of this invention can optimize construction parameters, and the desired effect can be achieved simply by changing the construction flow rate, without the need for other construction steps.

[0031] (3) Convenient and quick. The method of the present invention can efficiently optimize construction parameters and determine the optimal construction parameters by inverting the expected effect through calculation. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of a variable load fracturing parameter optimization method according to the present invention.

[0033] Figure 2 This is a schematic diagram of downhole load inversion in a variable load fracturing well according to a variable load fracturing parameter optimization method of the present invention; Figure 2 (a) is a schematic diagram of the numerical solution of stress distribution on the crack surface under uniform load, obtained by establishing a two-dimensional plane strain reservoir model based on field parameters and calculating the stress distribution on the crack surface under uniform load. Figure 2 (b) in the diagram is a schematic diagram of the pressure distribution obtained based on the theoretical calculation model; Figure 2 In the diagram, (c) is a schematic diagram of the stress difference obtained from the analytical solution and the stress difference obtained from the numerical solution; p(x) is the pressure distribution.

[0034] Figure 3 This is a schematic diagram of the fluid-structure interaction two-dimensional plane strain reservoir model established by the variable load fracturing parameter optimization method of the present invention. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0037] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0038] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0039] To better understand the purpose, structure, and function of this invention, the following detailed description of a variable load fracturing parameter optimization method is provided in conjunction with the accompanying drawings.

[0040] Example 1:

[0041] like Figure 1 As shown, the present invention provides a method for optimizing fracturing parameters under varying loads, comprising the following steps:

[0042] Step S1: Obtain geological parameters from the site;

[0043] Step S2: Establish a theoretical calculation model and calculate the distribution law of downhole load along the horizontal section during the variable load fracturing process based on the set conditions;

[0044] Step S3: Based on the field parameters, establish a fluid-structure interaction two-dimensional plane strain reservoir model;

[0045] Step S4: Based on the established fluid-structure interaction two-dimensional plane strain reservoir model, conduct single-valued simulation to obtain the downhole load distribution law under constant amplitude load conditions;

[0046] Step S5: Combining the calculation results of the theoretical calculation model and the numerical simulation results of the fluid-structure interaction two-dimensional plane strain reservoir model, the downhole load distribution during the variable load fracturing process under actual formation conditions is obtained by inversion.

[0047] Step S6: Based on the comparison between the downhole load distribution and formation conditions during the variable load fracturing process under actual working conditions, determine the multi-cluster perforation initiation situation;

[0048] Step S7: Change the construction conditions, perform multiple inversions, and finally determine the construction parameters that can achieve the preset fracturing effect.

[0049] Example 2:

[0050] like Figure 1 As shown, the present invention provides a method for optimizing fracturing parameters under varying loads, comprising the following steps:

[0051] Step S1: Obtain geological parameters from the site;

[0052] Step S2: Establish a theoretical calculation model and calculate the distribution law of downhole load along the horizontal section during the variable load fracturing process based on the set conditions;

[0053] Step S3: Based on the field parameters, establish a fluid-structure interaction two-dimensional plane strain reservoir model;

[0054] Step S4: Based on the established fluid-structure interaction two-dimensional plane strain reservoir model, conduct single-valued simulation to obtain the downhole load distribution law under constant amplitude load conditions;

[0055] Step S5: Combining the calculation results of the theoretical calculation model and the numerical simulation results of the fluid-structure interaction two-dimensional plane strain reservoir model, the downhole load distribution during the variable load fracturing process under actual formation conditions is obtained by inversion.

[0056] Step S6: Based on the comparison between the downhole load distribution and formation conditions during the variable load fracturing process under actual working conditions, determine the multi-cluster perforation initiation situation;

[0057] Step S7: Change the construction conditions, perform multiple inversions, and finally determine the construction parameters that can achieve the preset fracturing effect.

[0058] The difference between this embodiment and the first embodiment is that:

[0059] In step S1, the geological parameters include reservoir geological stress conditions, reservoir rock mechanical properties, vertical depth, and construction parameters, etc.

[0060] Step S2 includes the following steps:

[0061] Step H1: Determine the standing wave pressure distribution on the surface of the main fracture under variable load fracturing based on the construction parameters;

[0062] Step H2: Take any time t = t1 and perform the inversion. The pressure distribution at this time is as follows: Figure 2 As shown in (b);

[0063] Step H3: Based on elasticity mechanics, obtain the analytical solution σ for the stress distribution on the surface of a semi-infinite body (i.e., the crack surface) under a normal distributed load. xa Stress distribution σ on the crack surface under uniformly distributed load conditions xa ′;

[0064] In step H1, the standing wave pressure distribution formula is:

[0065] p s (x,t)=p0+p am sin(2πtf t sin(2πxf) x )

[0066] In the formula, p s (x,t) represents the pressure distribution on the main fracture surface, in MPa; p0 is the average pressure pulse value, in MPa; p am t is the pressure pulse amplitude, MPa; t is the time, s; x is the distance between the fracturing analysis point and the main fracture opening, m; f t and f x f is the frequency. t f is the time frequency. x For distance frequency.

[0067] In step H2, the standing wave pressure distribution formula is:

[0068] p s (x,t1)=p0+p am sin(2πt1f t sin(2πxf) x );

[0069] In the formula, t1 represents a certain moment;

[0070] In step H3, the analytical solution is:

[0071]

[0072] In the formula, p(ξ) is the pressure distribution equation; x qy and y are the horizontal and vertical coordinates of the unit cell inside the semi-infinite body, respectively; a and b are the upper and lower limits of integration; ξ is the length of the smallest differential unit.

[0073] In step S4, such as Figure 2 As shown in (a), a two-dimensional plane strain reservoir model of fluid-structure interaction was established based on field parameters, and the numerical solution σ of the stress distribution on the fracture surface under uniformly distributed load was calculated. xs ',like Figure 2 As shown in the dashed line portion (a) in the text;

[0074] In step S5, under uniform load and variable load conditions, the difference in stress distribution on the crack surface is calculated using the formula, such as... Figure 2 As shown in (c), the stress difference Δσ obtained by analytical solution xa The stress difference Δσ obtained from the numerical solution xs The error is low, based on Δσ xa σ xs The stress distribution on the surface of the main fracture during the variable load fracturing process under actual formation conditions is obtained through inversion.

[0075] In step S5, the formula for calculating the difference in stress distribution on the crack surface is:

[0076] Δσ xa =σ xa -σ xa ′

[0077] Example 3:

[0078] This invention provides a method for optimizing variable load fracturing parameters. This method can be used to determine and optimize variable load fracturing construction parameters, providing support for variable load fracturing design and improving reservoir fracturing effect.

[0079] In step S1, the main fracture of the target well is 100m long, 0.1m high, and 0.1m wide. The rock tensile strength is 2MPa, the average injection pressure is 10MPa, the injection pressure amplitude is 8MPa, the pressure pulse frequency is 25Hz, and the initial water pressure is 20MPa.

[0080] In step S2, a theoretical calculation model is established to calculate the stress distribution σ on the crack surface during the variable load fracturing process under ideal conditions. xa and stress distribution σ under uniformly distributed load conditions xa ′;

[0081] In step S3, such as Figure 3 As shown, a fluid-structure coupled two-dimensional plane strain reservoir model is established based on geological conditions;

[0082] In step S4, a numerical simulation is performed based on the established reservoir model to obtain the stress distribution σ on the fracture surface under uniformly distributed load conditions.xs ′ ;

[0083] In step S5, the stress distribution on the surface of the main fracture during the actual formation condition variable load fracturing process is obtained by combining the above calculation results.

[0084] In step S6, the downhole load distribution and formation strength are compared to determine the fracturing situation of multiple perforations;

[0085] In step S7, the construction parameters are changed and inversion is performed multiple times to finally determine the construction parameters that can achieve the ideal fracturing effect.

[0086] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the scope of protection of the present invention.

Claims

1. A method for optimizing fracturing parameters under variable load, characterized in that, Includes the following steps: Step S1: Obtain geological parameters from the site; the geological parameters include reservoir geological stress conditions, reservoir rock mechanical properties, vertical depth, and construction parameters; Step S2: Establish a theoretical calculation model and calculate the distribution law of downhole load along the horizontal section during variable load fracturing based on the set conditions; Step S2 includes the following steps: Step H1: Determine the standing wave pressure distribution on the surface of the main fracture under variable load fracturing based on the construction parameters; Step H2: Randomly select a time Inversion is performed to obtain the distribution law of standing wave pressure; Step H3: Obtain the analytical solution of stress distribution on the surface of a semi-infinite body under a normal distributed load based on elasticity mechanics. Stress distribution on the crack surface under uniformly distributed load conditions Step S3: Based on the field parameters, establish a fluid-structure interaction two-dimensional plane strain reservoir model; Step S4: Based on the established fluid-structure interaction two-dimensional plane strain reservoir model, conduct single-valued simulation to obtain the downhole load distribution law under constant amplitude load conditions; In step S4, a fluid-structure interaction two-dimensional plane strain reservoir model is established based on field parameters, and the numerical solution of the stress distribution on the fracture surface under uniformly distributed load is calculated. ; Step S5: Combining the calculation results of the theoretical calculation model and the numerical simulation results of the fluid-structure interaction two-dimensional plane strain reservoir model, the downhole load distribution during the variable load fracturing process under actual formation conditions is obtained by inversion. In step S5, under uniformly distributed load and variable load conditions, the stress difference is obtained analytically using the formula for calculating the difference in stress distribution on the crack surface. Stress difference obtained from numerical solution ,based on and The stress distribution on the surface of the main fracture during the variable load fracturing process under actual formation conditions was obtained through inversion. Step S6: Based on the comparison between the downhole load distribution and formation conditions during the variable load fracturing process under actual working conditions, determine the multi-cluster perforation initiation situation; Step S7: Change the construction conditions, perform multiple inversions, and finally determine the construction parameters that can achieve the preset fracturing effect.

2. The method for optimizing fracturing parameters under varying loads according to claim 1, characterized in that, In step H1, the standing wave pressure distribution formula is: In the formula, Pressure distribution on the main seam surface, MPa; The average pressure pulse value is expressed in MPa. The amplitude of the pressure pulse is expressed in MPa. t represents time, in seconds; x represents the distance between the pressure analysis point and the main joint opening, in meters. For time frequency, For distance frequency.

3. The method for optimizing fracturing parameters under varying loads according to claim 2, characterized in that, In step H3, the analytical solution is: In the formula, The pressure distribution equation is as follows; y and y' are the x and y coordinates of a unit cell inside the semi-infinite body, respectively; a and b are the upper and lower limits of integration; is the length of the smallest differential unit.

4. The method for optimizing fracturing parameters under varying loads according to claim 1, characterized in that, In step S5, the formula for calculating the difference in stress distribution on the crack surface is: 。

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