Variable load fracturing parameter optimization method

Abstract

The invention provides a variable-load fracturing parameter optimization method, which belongs to the technical field of petroleum development and comprises the following steps: acquiring geological parameters on site; a theoretical calculation model is established, and the distribution rule of the underground load along the horizontal section in the variable load fracturing process is obtained; establishing a fluid-structure interaction two-dimensional plane strain reservoir model based on the field parameters; an underground load distribution rule under the constant-amplitude load condition is obtained; in combination with a theoretical calculation result and a numerical simulation result, performing inversion to obtain underground load distribution in the variable load fracturing process under the actual formation condition; the multi-cluster perforation crack initiation condition is judged; and the construction conditions are changed, multiple times of inversion are carried out, and finally the construction parameters capable of achieving the preset fracturing effect are determined. The method can effectively relieve the problems of overhigh formation fracture pressure, uneven perforation crack initiation and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of petroleum development, and in particular relates to a variable load fracturing parameter optimization method. Background Art

[0002] Mahu is the world's largest conglomerate oil reservoir, with reserves of more than 1 billion tons, but its exploitation process also faces many difficulties: deep reservoir burial, well-developed interlayers, low reservoir permeability, complex minerals, strong heterogeneity, undeveloped fractures, and significant differences between wells. Since the overall deployment and large-scale development of the Mahu conglomerate oil reservoir, the average daily oil production of horizontal wells in major blocks has decreased year by year. Long horizontal wells need to improve fracture-controlled reserve development, and fracturing production technology urgently needs to be upgraded under the premise of controlling costs. Due to the extremely strong heterogeneity of the conglomerate reservoir, the construction pressure is high under conventional fracturing methods, and it is difficult to break the formation; at the same time, there is a significant phenomenon of non-uniform fracturing of perforations, and the fracturing effect is not ideal.

[0003] The variable load fracturing method of periodically changing the downhole load can effectively alleviate the problems of excessive formation fracture pressure and uneven perforation fracturing, but it is still mainly in the theoretical stage and the actual construction design method is not perfect. Therefore, it is of great significance to propose the determination and effective optimization method of construction parameters and improve the construction design for the on-site implementation of variable load fracturing. Summary of the invention

[0004] In view of the problems existing in the above-mentioned prior art, the present invention provides a variable load fracturing parameter optimization method. The technical problem to be solved by the present invention is how to effectively alleviate the problems such as excessive formation fracture pressure and uneven perforation initiation.

[0005] In order to solve the above technical problems, the present invention provides a variable load fracturing parameter optimization method, comprising the following steps:

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

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

[0008] Step S3: establishing a fluid-solid coupled two-dimensional plane strain reservoir model based on field parameters;

[0009] Step S4: performing a single numerical simulation based on the established fluid-solid coupling two-dimensional plane strain reservoir model to obtain the downhole load distribution law under the constant amplitude load condition;

[0010] Step S5: combining the calculation results of the theoretical calculation model with the numerical simulation results of the fluid-solid coupling two-dimensional plane strain reservoir model, inverting to obtain the downhole load distribution during the variable load fracturing process under actual formation conditions;

[0011] Step S6: comparing the downhole load distribution and formation conditions during the variable load fracturing process under actual working conditions to determine the multi-cluster perforation fracturing initiation conditions;

[0012] Step S7: Changing the construction conditions, performing multiple inversions, and finally determining 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, the step S2 includes the following steps:

[0015] Step H1: determining the standing wave pressure distribution on the main fracture surface under variable load fracturing according to the construction parameters;

[0016] Step H2: taking any time t=t1 for inversion, and obtaining the standing wave pressure distribution law;

[0017] Step H3: Based on elastic mechanics, we obtain the analytical solution of stress distribution when the surface of a semi-infinite body is subjected to a normal distributed load: xa and the stress distribution of the crack surface under uniform load conditions σ 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) is the pressure distribution on the main crack surface, MPa; p0 is the mean value of the pressure pulse, MPa; p am is the pressure pulse amplitude, MPa; t is the time, s; x is the distance between the pressure analysis point and the main slit, m; f t is the temporal frequency, f x is the distance frequency.

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

[0022]

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

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

[0025] Furthermore, in step S5, under the conditions of uniform load and variable load, the stress difference Δσ obtained by analytical solution is calculated using the difference calculation formula of the stress distribution on the crack surface. xa The stress difference Δσ obtained by numerical solution xs , based on Δσ xa and σ xs ′The stress distribution on the main fracture surface during variable load fracturing under actual formation conditions was obtained by inversion.

[0026] Furthermore, in step S5, the difference calculation formula of the 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. This method is based on a large amount of theoretical research, numerical simulation research and field application to complete the parameter optimization method, and the results are reliable.

[0030] (2) Good economy: The plate of the present invention can optimize the construction parameters, and the desired effect can be achieved by only changing the construction displacement, without other construction steps.

[0031] (3) Convenient and fast. The method of the present invention can be used to efficiently optimize construction parameters, and the optimal construction parameters can be determined by calculation based on the expected effect. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0033] Figure 2 It is a schematic diagram of variable load fracturing downhole load inversion of a variable load fracturing parameter optimization method of the present invention; Figure 2 (a) is a schematic diagram of the numerical solution of the stress distribution on the fracture surface under uniform load obtained by establishing a fluid-solid coupled two-dimensional plane strain reservoir model based on field parameters; Figure 2 (b) is a schematic diagram of pressure distribution based on the theoretical calculation model; Figure 2 (c) is a schematic diagram of the stress difference obtained by analytical solution and the stress difference obtained by numerical solution; p(x) is the pressure distribution.

[0034] Figure 3 It is a schematic diagram of establishing a fluid-solid coupling two-dimensional plane strain reservoir model in a variable load fracturing parameter optimization method of the present invention. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0036] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0038] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected or indirectly connected through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0039] In order to better understand the purpose, structure and function of the present invention, a variable load fracturing parameter optimization method of the present invention is further described in detail below with reference to the accompanying drawings.

[0040] Embodiment 1:

[0041] like Figure 1 As shown, the present invention provides a variable load fracturing parameter optimization method, comprising the following steps:

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

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

[0044] Step S3: establishing a fluid-solid coupled two-dimensional plane strain reservoir model based on field parameters;

[0045] Step S4: performing a single numerical simulation based on the established fluid-solid coupling two-dimensional plane strain reservoir model to obtain the downhole load distribution law under the constant amplitude load condition;

[0046] Step S5: combining the calculation results of the theoretical calculation model with the numerical simulation results of the fluid-solid coupling two-dimensional plane strain reservoir model, inverting to obtain the downhole load distribution during the variable load fracturing process under actual formation conditions;

[0047] Step S6: comparing the downhole load distribution and formation conditions during the variable load fracturing process under actual working conditions to determine the multi-cluster perforation fracturing initiation conditions;

[0048] Step S7: Changing the construction conditions, performing multiple inversions, and finally determining the construction parameters that can achieve the preset fracturing effect.

[0049] Embodiment 2:

[0050] like Figure 1 As shown, the present invention provides a variable load fracturing parameter optimization method, comprising the following steps:

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

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

[0053] Step S3: establishing a fluid-solid coupled two-dimensional plane strain reservoir model based on field parameters;

[0054] Step S4: performing a single numerical simulation based on the established fluid-solid coupling two-dimensional plane strain reservoir model to obtain the downhole load distribution law under the constant amplitude load condition;

[0055] Step S5: combining the calculation results of the theoretical calculation model with the numerical simulation results of the fluid-solid coupling two-dimensional plane strain reservoir model, inverting to obtain the downhole load distribution during the variable load fracturing process under actual formation conditions;

[0056] Step S6: comparing the downhole load distribution and formation conditions during the variable load fracturing process under actual working conditions to determine the multi-cluster perforation fracturing initiation conditions;

[0057] Step S7: Changing the construction conditions, performing multiple inversions, and finally determining 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;

[0060] The step S2 includes the following steps:

[0061] Step H1: determining the standing wave pressure distribution on the main fracture surface under variable load fracturing according to the construction parameters;

[0062] Step H2: Take any time t=t1 for inversion. The pressure distribution at this time is as follows: Figure 2 (b)

[0063] Step H3: Based on elastic mechanics, the analytical solution of stress distribution when the semi-infinite surface (i.e., the crack surface) is subjected to normal distribution load is obtained: xa and the stress distribution of the crack surface under uniform load conditions σ 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) is the pressure distribution on the main crack surface, MPa; p0 is the mean value of the pressure pulse, MPa; p am is the pressure pulse amplitude, MPa; t is the time, s; x is the distance between the fracturing analysis point and the main fracture, m; f t and f x is the frequency, f t is the temporal frequency, f x is the 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 is a certain moment;

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

[0071]

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

[0073] In step S4, Figure 2 As shown in (a), a two-dimensional plane strain reservoir model of fluid-solid coupling is established based on field parameters, and the numerical solution σ of the stress distribution on the fracture surface under uniform load is calculated. xs ',like Figure 2 (a) The dotted line shows:

[0074] In step S5, under the conditions of uniform load and variable load, the difference calculation formula of the stress distribution on the crack surface is used, such as Figure 2 (c) shows the stress difference Δσ obtained by analytical solution. xa The stress difference Δσ obtained by numerical solution xs The error is low, based on Δσ xa , σ xs ′The stress distribution on the main fracture surface during variable load fracturing under actual formation conditions was obtained by inversion.

[0075] In step S5, the difference calculation formula of the stress distribution on the crack surface is:

[0076] Δσ xa =σ xa -σ xa '

[0077] Embodiment 3:

[0078] The present invention provides a variable load fracturing parameter optimization method, which can be used to determine and optimize variable load fracturing construction parameters, provide support for variable load fracturing design, and improve reservoir fracturing effect.

[0079] In step S1, the main fracture length of the target well is collected as 100m, the height is 0.1m, the fracture width is 0.1m, the rock tensile strength is 2MPa, the injection pressure average 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 fracture surface during variable load fracturing under ideal conditions. xa and stress distribution under uniform load conditions σ xa ′;

[0081] In step S3, Figure 3 As shown, a fluid-solid coupling two-dimensional plane strain reservoir model is established according to geological conditions;

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

[0083] In step S5, the stress distribution on the main fracture surface during variable load fracturing under actual formation conditions is obtained by inversion based on the above calculation results;

[0084] In step S6, the downhole load distribution and the formation strength are compared to determine the multi-cluster perforation fracturing situation;

[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 only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention are included in the protection scope of the present invention.

Claims

1. A variable load fracturing parameter optimization method, characterized in that: The following steps are involved: Step S1: Obtain geological parameters from the site; Step S2: Establishing a theoretical calculation model, and calculating the distribution law of the downhole load along the horizontal section during the variable load fracturing process based on the set conditions; Step S3: establishing a fluid-solid coupled two-dimensional plane strain reservoir model based on field parameters; Step S4: performing a single numerical simulation based on the established fluid-solid coupling two-dimensional plane strain reservoir model to obtain the downhole load distribution law under the constant amplitude load condition; Step S5: combining the calculation results of the theoretical calculation model with the numerical simulation results of the fluid-solid coupling two-dimensional plane strain reservoir model, inverting to obtain the downhole load distribution during the variable load fracturing process under actual formation conditions; Step S6: comparing the downhole load distribution and formation conditions during the variable load fracturing process under actual working conditions to determine the multi-cluster perforation fracturing initiation conditions; Step S7: Changing the construction conditions, performing multiple inversions, and finally determining the construction parameters that can achieve the preset fracturing effect.

2. The variable load fracturing parameter optimization method according to claim 1, characterized in that: In step S1, the geological parameters include reservoir geological stress conditions, reservoir rock mechanical properties, vertical depth and construction parameters.

3. The variable load fracturing parameter optimization method according to claim 2, characterized in that: The step S2 includes the following steps: Step H1: determining the standing wave pressure distribution on the main fracture surface under variable load fracturing according to the construction parameters; Step H2: taking any time t=t1 for inversion, and obtaining the standing wave pressure distribution law; Step H3: Based on elastic mechanics, we obtain the analytical solution of stress distribution when the surface of a semi-infinite body is subjected to a normal distributed load: xa and the stress distribution of the crack surface under uniform load conditions σ xa ′ .

4. The variable load fracturing parameter optimization method according to claim 3, characterized in that: In step H1, the standing wave pressure distribution formula is: p s (x,t)=p0+p am sin(2πtf t )sin(2πxf x ) In the formula, p s (x, t) is the pressure distribution on the main crack surface, MPa; p0 is the mean value of the pressure pulse, MPa; p am is the pressure pulse amplitude, MPa; t is time, s; x is the distance between the pressure analysis point and the main seam, m; f t is the temporal frequency, f x is the distance frequency.

5. The variable load fracturing parameter optimization method according to claim 4, characterized in that: In step H3, the analytical solution is: Where p(ξ) is the pressure distribution equation; x q and y are the horizontal and vertical coordinates of the unit cell inside the semi-infinite body; a and b are the upper and lower limits of integration; ξ is the length of the minimum differential unit.

6. The variable load fracturing parameter optimization method according to claim 5, characterized in that: In step S4, a fluid-solid coupling two-dimensional plane strain reservoir model is established based on the field parameters, and the numerical solution σ of the stress distribution on the fracture surface under the uniformly distributed load is calculated. xs ′.

7. The variable load fracturing parameter optimization method according to claim 6, characterized in that: In step S5, under the conditions of uniform load and variable load, the stress difference Δσ is obtained by analytical solution using the difference calculation formula of the stress distribution on the crack surface. xa The stress difference Δσ obtained by numerical solution xs , based on Δσ xa and σ xs ′The stress distribution on the main fracture surface during variable load fracturing under actual formation conditions was obtained by inversion.

8. The variable load fracturing parameter optimization method according to claim 6, characterized in that: In step S5, the difference calculation formula of the stress distribution on the crack surface is: Board xa =s xa -s xa ′。

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