A method for realizing multi-fracture fracturing design with in-seam point temporary plugging

Abstract

This invention discloses a design method for multi-fracture fracturing with in-fracture temporary plugging, comprising: simulating the construction parameters and fracture parameters required for the temporary plugging stage using fracturing software; calculating the average dynamic main fracture width; calculating the plugging slug length, plugging agent dosage, and plugging agent particle size; adding a low-density, low-temperature soluble temporary plugging agent at the beginning of the temporary plugging to achieve dynamic main fracture bridging and pressure increase, opening lateral natural microfractures or branch fractures; at the end of the temporary plugging, using low-viscosity fracturing fluid with ultra-low-density small-particle-size proppant to support the natural microfractures; and after the temporary plugging is completed, carrying out main fracturing operations, using large-particle-size proppant for dynamic main fracture filling. This invention is designed for oil wells with high recovery rates in old fractures, achieving orderly filling of secondary and main fractures, thereby improving the effectiveness of multi-fracture fracturing.

Description

Technical Field

[0001] This invention belongs to the field of oilfield production engineering technology, and specifically relates to a design method for realizing fixed-point temporary plugging of multiple fractures in fracture. Background Technology

[0002] The Ordos Basin has poor reservoir properties and low formation temperature, classifying it as a typical "three-low" reservoir. Initially, development was carried out using a "water injection + fracturing" model. However, as development time increased and the recovery rate of old fractures improved, repeated fracturing, which mainly extended the length of old fractures, posed a high risk of water breakthrough, and its effectiveness deteriorated year by year. In-fracture temporary plugging and repeated fracturing, which utilizes the remaining oil in the lateral direction of old fractures, has become one of the main technical means for water control and oil enhancement. Due to the timing of temporary plugging and reliance on experience in designing temporary plugging, the controllability of temporary plugging during field construction is poor, and its effectiveness is insufficient. It also has poor adaptability in some reservoir blocks, urgently requiring a multi-fracture fracturing design method with fixed-point temporary plugging within the fractures. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of conventional temporary plugging scientific design and to provide a design method for multi-fracturing with fixed-point temporary plugging within the fracture.

[0004] This invention is achieved using the following technical solution:

[0005] A method for designing multi-fracturing systems with fixed-point temporary plugging within the fracture zone includes the following steps:

[0006] S1. Determine the location of new fractures in the reservoir and the conditions for pressurization, and use fracturing software to simulate the construction parameters and fracture parameters required for the fixed-point temporary plugging stage;

[0007] S2. Calculate the average dynamic main crack width based on the net pressure value inside the natural micro-cracks in the block.

[0008] S3. Calculate the plugging slug length, plugging agent dosage, and plugging agent particle size by combining the dynamic main fracture width and fracture parameters;

[0009] S4. At the beginning of the temporary plugging, a low-density, low-temperature soluble temporary plugging agent is added to achieve dynamic main crack bridging and pressure increase, thereby opening lateral natural microcracks or branch cracks.

[0010] S5. At the end of the temporary plugging, low-viscosity fracturing fluid is added with ultra-low density small particle size proppant to support the natural micro fractures.

[0011] S6. After the temporary plugging is completed, the main fracturing operation is carried out, and large-diameter proppant is used to dynamically fill the main fracture.

[0012] A further improvement of the present invention is that, in step S1, the location of the new fracture in the reservoir and the pressure increase conditions are clearly defined. The location of the new fracture is determined by geological numerical modeling software, the pressure increase conditions for the new fracture are the natural microfracture initiation pressure, and the fracturing software is the commercial full three-dimensional fracturing software PRACPRO or STIMPLAN.

[0013] A further improvement of the present invention is that, in step S1, the construction parameters and the fracture parameters are the fracturing fluid volume V, injection displacement Q, fracture length L, and fracture height h required before temporary plugging, respectively.

[0014] A further improvement of the present invention is that, in step S2, the net pressure inside the seam is calculated using the following formula:

[0015] P net =o.5(σ H -σ h (1-cos2θ)

[0016] In the formula σ H For the maximum horizontal principal stress in the block, σ h The minimum horizontal principal stress is given by θ, where θ is the angle between the natural microcracks.

[0017] The average dynamic seam width is calculated using the following formula:

[0018]

[0019] In the formula, υ is Poisson's ratio, L is the crack length, and E is Young's modulus.

[0020] A further improvement of this invention is that, in step S3, the plugging length refers to the length of the plugging material accumulated within the joint, calculated using the following formula:

[0021]

[0022] In the formula, μ is the viscosity of the fracturing fluid, and k f The value represents the crack permeability.

[0023] A further improvement of this invention is that, in step S3, the amount of plugging agent refers to the volume of the plugging agent, which is calculated using the following formula:

[0024]

[0025] A further improvement of the present invention is that, in step S3, the particle size d of the plugging agent meets the following requirements:

[0026]

[0027] A further improvement of this invention is that, in step S4, the apparent density of the low-density, low-temperature soluble temporary plugging agent is 1.45-1.55 g / cm³. 3Its bulk density is 1.0-1.1 g / cm³. 3 In water at 20-40℃, it softens into a clump in 10-15 minutes and dissolves completely in 60 minutes.

[0028] A further improvement of this invention is that, in step S5, the viscosity of the low-viscosity fracturing fluid is 3-5 cp, and the apparent density of the ultra-low density small-particle-size proppant is 1.00-1.08 g / cm³. 3 Its bulk density is 0.40-0.50 g / cm³. 3 The particle size is 0.15-0.075 mm.

[0029] A further improvement of the present invention is that, in step S6, the main fracturing operation refers to the use of conventional cross-linked gel to carry proppant to complete the sand filling of the main fracture, the fracturing fluid viscosity of the cross-linked gel is greater than 500cp, and the particle size of the proppant is greater than 0.42mm.

[0030] The present invention has at least the following beneficial technical effects:

[0031] This invention provides a method for designing multi-fracture fracturing with in-fracture temporary plugging. This method determines the fracture size at the optimal location for temporary plugging required by the reservoir, defines the dynamic fracture width for multi-fracture fracturing by combining the reservoir's natural microfractures and stress conditions, and designs the plugging slug and key parameters based on the dynamic fracture width. This ensures graded support for both the temporary plugging multi-fracture fracturing and the main fracturing, and guarantees the conductivity requirements of different fractures, ultimately forming a targeted temporary plugging optimization design method. The overall steps of this method are simple and easy to implement, providing an effective process design approach for improving the effectiveness of in-fracture temporary plugging fracturing. It has significant practical implications for improving the effectiveness of multi-fracture temporary plugging fracturing and can also be applied to similar reservoirs in China.

[0032] This invention utilizes the relationship between net pressure and dynamic fracture width, combined with fracture parameters simulated by full three-dimensional fracturing software, to achieve a fixed-point temporary plugging design.

[0033] This invention uses a low-temperature, fast-dissolving temporary plugging agent to ensure that it does not affect the normal production of the oil well in the later stages.

[0034] This invention employs an ultra-low density, small-particle-size proppant, with a density comparable to water, which allows for long-distance transport of low-viscosity fracturing fluid. The small particle size also facilitates entry into natural micro-fractures, thus achieving effective support for the fracture.

[0035] In this invention, the temporary plugging stage and the main fracturing stage are carried out separately, and the proppant is not mixed in the main fracture, so as to ensure that the main fracture has a high conductivity without losing the conductivity of the branch fractures. Attached Figure Description

[0036] Figure 1 This is a schematic diagram illustrating the implementation of a multi-fracturing design method for achieving fixed-point temporary plugging within the fracture, as described in this invention.

[0037] Explanation of reference numerals in the attached figures:

[0038] 1. Wellbore; 2. Dynamic main fracture; 3. Temporary plugging agent; 4. Natural micro fractures or secondary fractures; 5. Small-diameter proppant; 6. Large-diameter proppant. Detailed Implementation

[0039] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the disclosure to those skilled in the art. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0040] Example 1:

[0041] To overcome the shortcomings of conventional intra-fracturing temporary plugging and repeated fracturing, a design method for multi-fracturing with fixed-point intra-fracturing is provided.

[0042] like Figure 1 As shown, the technical solution adopted in this invention is as follows:

[0043] S1. Determine the location of new fractures in the reservoir and the conditions for pressurization, and use fracturing software to simulate the construction parameters and fracture parameters required for the fixed-point temporary plugging stage;

[0044] S2. Calculate the average dynamic main crack width based on the net pressure value inside the natural micro-cracks in the block.

[0045] S3. Calculate the plugging slug length, plugging agent dosage, and plugging agent particle size by combining the dynamic main fracture width and fracture parameters;

[0046] S4. At the beginning of the temporary plugging, add low-density, low-temperature soluble temporary plugging agent 3 to achieve dynamic main crack 2 bridge plugging pressure increase, and open lateral natural micro cracks or branch cracks 4.

[0047] S5. At the end of the temporary plugging, low-viscosity fracturing fluid is added with ultra-low density small particle size proppant 5 to support the natural micro fractures.

[0048] S6. After the temporary plugging is completed, the main fracturing operation is carried out, and large-diameter proppant 6 is used for dynamic filling of the main fracture.

[0049] This method targets wellbore 1 in oil wells with high recovery rates due to old fractures. Based on the fixed-point temporary plugging process within the fracture, it optimizes the amount and particle size of plugging agent by utilizing the relationship between net pressure and fracture width. It also uses ultra-low density, small-particle-size proppant slugs to support natural micro fractures. Combined with main fracture filling, it achieves orderly filling of secondary and main fractures, thereby improving the effectiveness of multi-fracture fracturing.

[0050] Example 2:

[0051] Based on Example 1, in this example, preferably, the fracturing software mentioned in step S1 is a common, commercially available, fully three-dimensional fracturing software such as PRACPRO and STIMPLAN.

[0052] Preferably, the construction parameters and crack parameters mentioned in step S1 are the fracturing fluid volume V, injection displacement Q, crack length L, and crack height h required before temporary plugging.

[0053] Preferably, the net pressure within the seam mentioned in step S2 is calculated using the following formula:

[0054] P net =0.5(σ H -σ h (1-cos2θ)

[0055] In the formula σ H For the maximum horizontal principal stress in the block, σ h The minimum horizontal principal stress is given, θ is the angle between natural microcracks, and the net pressure is calculated to be 3-5 MPa based on regional testing.

[0056] Preferably, the average dynamic seam width mentioned in step S2 is calculated using the following formula:

[0057]

[0058] In the formula, υ is Poisson's ratio, L is crack length, E is Young's modulus, and the average dynamic crack width is 10-15 mm.

[0059] Preferably, the plugging length mentioned in step S3 refers to the length of the plugging material accumulated in the joint, which is calculated using the following formula:

[0060]

[0061] In the formula, μ is the viscosity of the fracturing fluid, and k f The value represents the crack permeability.

[0062] Preferably, the amount of plugging agent used in step S3 refers to the volume of the plugging agent, calculated using the following formula:

[0063]

[0064] Preferably, the particle size d of the plugging agent mentioned in step S3 meets the following requirements: To improve the effect of temporary plugging and bridging, a combination of particle size temporary plugging agents is used.

[0065] Preferably, the low-density, low-temperature soluble temporary plugging agent in step S4 refers to an apparent density of 1.45-1.55 g / cm³. 3 Bulk density 1.0-1.1 g / cm³ 3 In water at 20-40℃, it softens into a clump in 10-15 minutes and dissolves completely in 60 minutes.

[0066] Preferably, in step S5, the low-viscosity fracturing fluid has a viscosity of 3-5 cp, and the ultra-low density small-particle-size proppant has an apparent density of 1.00-1.08 g / cm³. 3 Its bulk density is 0.40-0.50 g / cm³. 3 Particle size: 0.15-0.075 mm.

[0067] Preferably, the main fracturing operation described in step S6 refers to the use of conventional cross-linked guar gum fracturing fluid to carry 20 / 40 mesh proppant to complete the sand filling of the main fracture.

[0068] Example 3

[0069] Based on Examples 1 and 2, in this well example (oil layer thickness 10m, maximum horizontal principal stress 30MPa, minimum principal stress 25MPa, Poisson's ratio 0.23, Young's modulus 34000MPa, natural microfracture angle 45°, fracture permeability 45D, fracturing fluid slickwater viscosity 3mpa·s), preferably, the construction parameters and fracture parameters mentioned in step S1 are as follows: fracturing fluid volume V = 50m³ required before temporary plugging. 3 Injection displacement Q = 2.0 m³ 3 / min, temporary plugging of the main crack length L=25m and crack height h=17m, etc.

[0070] Preferably, the net pressure calculation result within the joint in step S2 is P. net =2.5MPa:

[0071] Preferably, the average dynamic seam width mentioned in step S2

[0072] Preferably, the plugging length mentioned in step S3 refers to the length of the plugging material accumulated in the joint being 0.7m;

[0073]

[0074] Preferably, the volume of the plugging agent used in step S3 is ΔV = 0.2 m³. 3 ;

[0075] Preferably, the particle size d of the plugging agent mentioned in step S3 meets the following requirements: To improve the effect of temporary plugging and bridging, a combination of temporary plugging agents with particle sizes of 5.8 mm to 10 mm was used.

[0076] Preferably, the low-density, low-temperature soluble temporary plugging agent in step S4 refers to an apparent density of 1.45-1.55 g / cm3 and a bulk density of 1.0-1.1 g / cm3, which softens into a clump in water at 20-40℃ for 10-15 minutes and dissolves completely in 60 minutes.

[0077] Preferably, in step S5, the low-viscosity fracturing fluid has a viscosity of 3-5 cp, and the ultra-low density small particle size proppant has an apparent density of 1.00-1.08 g / cm3, a bulk density of 0.40-0.50 g / cm3, and a particle size of 0.15-0.075 mm.

[0078] Preferably, the main fracturing operation described in step S6 refers to the use of conventional cross-linked guar gum fracturing fluid to carry 20 / 40 mesh proppant to complete the sand filling of the main fracture.

[0079] The examples above are merely illustrative of the present invention and do not constitute a limitation on the scope of protection of the present invention. All designs that are the same as or similar to the present invention fall within the scope of protection of the present invention. Reagents and method steps not described in detail in this embodiment are well-known technologies and common methods in the industry, and will not be described in detail here.

Claims

1. A method for designing multi-fracturing systems with fixed-point temporary plugging within the fracture, characterized in that, The method comprises the following steps: S1, determining the position of opening new fractures and the pressure boosting condition of the reservoir, and using fracturing software to simulate the operation parameters and fracture parameters required in the point temporary plugging stage; the operation parameters and fracture parameters are respectively the fracturing fluid volume V, injection displacement Q, fracture length L and fracture height h required before temporary plugging; S2, calculating the average dynamic main fracture width according to the net fracture pressure value of opening natural micro-fractures in the block; the net fracture pressure is calculated by using the following formula: wherein is the maximum horizontal principal stress of the block, is the minimum horizontal principal stress, is the natural microfracture angle; The average dynamic fracture width is calculated by using the following formula: wherein is the Poisson's ratio, is the crack length, is the Young's modulus; S3, combining the dynamic main fracture width and the fracture parameters to calculate the length of the plugging agent slug, the amount of the plugging agent and the particle size of the plugging agent; the length of the plugging agent slug refers to the length of the plugging agent accumulated in the fracture, which is calculated by using the following formula: wherein is the viscosity of the fracturing fluid, is the fracture permeability; The amount of the plugging agent refers to the volume of the plugging agent, which is calculated by using the following formula: The particle size d of the plugging agent meets the following requirements: S4, adding low-density and low-temperature soluble temporary plugging agent at the beginning of temporary plugging to realize dynamic main fracture bridging and pressure boosting, and to open lateral natural micro-fractures or branch fractures; S5, using low-viscosity fracturing fluid to add ultra-low-density small-particle-size proppant to support natural micro-fractures at the end of temporary plugging; S6, after the temporary plugging is completed, main fracturing operation is carried out, and large-particle-size proppant is used to fill the dynamic main fractures.

2. The method of claim 1, wherein, In step S1, the position of opening new fractures and the pressure boosting condition of the reservoir are determined, the position of opening new fractures is determined by using geological numerical modeling software, and the pressure boosting condition of opening new fractures is the opening pressure of natural micro-fractures; the fracturing software is PRACPRO or STIMPLAN commercialized full three-dimensional fracturing software.

3. The method of claim 1, wherein, In step S4, the low-density, low-temperature soluble temporary plugging agent has a specific density of 1.45-1.55 g / cm 3 , a bulk density of 1.0-1.1 g / cm 3 , and is softened into a ball in 10-15 min and completely dissolved in 60 min in clear water at 20-40℃.

4. The method of claim 1, wherein, In step S5, the viscosity of the low-viscosity fracturing fluid is 3-5 cp, the apparent density of the ultra-low-density small-diameter proppant is 1.00-1.08 g / cm 3 , the bulk density is 0.40-0.50 g / cm 3 , and the particle size is 0.15-0.075 mm.

5. The method of claim 1, wherein, In step S6, the main fracturing operation refers to the sand filling of the main fractures by using conventional crosslinked gel carrying proppant, the viscosity of the crosslinked gel fracturing fluid is greater than 500 cp, and the particle size of the proppant is greater than 0.42 mm.

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