Design method for realizing in-seam fixed-point temporary plugging multi-seam fracturing

Abstract

The invention discloses a multi-crack fracturing design method for realizing fixed-point temporary plugging in a crack. The method comprises the following steps: simulating construction parameters and crack parameters required in a fixed-point temporary plugging stage by adopting fracturing software; calculating an average dynamic main crack width; calculating the plugging agent slug length, the plugging agent dosage and the plugging agent particle size; at the beginning of temporary plugging, adding a low-density and low-temperature soluble temporary plugging agent to realize dynamic main crack bridge plugging and boosting, and opening lateral natural micro cracks or branch cracks; at the end of temporary plugging, low-viscosity fracturing fluid is adopted, and an ultralow-density small-particle-size proppant is added to support natural micro-cracks; and after temporary plugging is finished, main fracturing construction is carried out, and a large-particle-size proppant is adopted for dynamic main crack filling. According to an oil well with the high recovery degree of old cracks, ordered filling of the secondary cracks and the main cracks is achieved, and the purpose of improving the multi-crack fracturing effectiveness is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of oilfield production engineering, and particularly relates to a design method for realizing temporary plugging of multiple fractures at fixed points within fractures. Background Art

[0002] The reservoir physical properties of the Ordos Basin are poor, and the formation temperature is low. It is a typical "three lows" oil reservoir. In the early stage, the "water injection + fracturing" mode was used for development. As the development time prolonged, the degree of old fracture production increased. Repeated fracturing, which mainly extended the length of old fractures, had a high risk of water breakthrough, and the effect became worse year by year. Temporary plugging and repeated fracturing in the fractures, which was based on the concept of using the lateral residual oil in the old fractures, became one of the main technical means of controlling water and increasing oil production. Due to the timing of temporary plugging and the reliance on experience to design temporary plugging, the controllability of temporary plugging was poor during the on-site construction process, the effectiveness of temporary plugging was insufficient, and the adaptability of some reservoir blocks was poor. There was an urgent need for a design method of temporary plugging and multiple fractures fracturing with fixed points in the fractures. Summary of the invention

[0003] The purpose of the present invention is to overcome the shortcomings of insufficient scientific design of conventional temporary plugging, and to provide a design method for realizing temporary plugging of multiple fractures at fixed points within fractures.

[0004] The present invention is achieved by adopting the following technical solutions:

[0005] A method for realizing temporary plugging of multiple fractures at fixed points within fractures by hydraulic fracturing design comprises the following steps:

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

[0007] S2. Calculate the average dynamic main fracture width based on the net pressure value in the fractures of natural micro-fractures opened in the block;

[0008] S3. Calculate the plugging agent segment length, plugging agent dosage and plugging agent particle size based on the dynamic main crack width and crack parameters;

[0009] S4. Add low-density, low-temperature soluble temporary plugging agent at the beginning of temporary plugging to achieve dynamic main crack bridge plugging and pressure increase, and open lateral natural microcracks or branch cracks;

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

[0011] S6. After the temporary plugging is completed, the main fracturing construction is carried out, and large-size proppant is used for dynamic main fracture filling.

[0012] A further improvement of the present invention is that in step S1, the position of opening a new fracture in the reservoir and the pressure-increasing condition are clearly defined, the position of opening a new fracture is established by geological digital modeling software, the pressure-increasing condition for opening a new fracture is the opening pressure of a natural micro-fracture, and the fracturing software is PRACPRO or STIMPLAN commercial full three-dimensional fracturing software.

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

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

[0015] P net =0.5(σ H -σ h )(1-cos2θ)

[0016] Where σ H is the maximum horizontal principal stress in the block, σ h is the minimum horizontal principal stress, θ is the natural microcrack angle;

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

[0018]

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

[0020] A further improvement of the present invention is that in step S3, the plugging agent segment length refers to the length of the plugging agent accumulated in the seam, which is calculated using the following formula:

[0021]

[0022] Where μ is the viscosity of the fracturing fluid, k f is the fracture permeability.

[0023] A further improvement of the present invention is that in step S3, the amount of plugging agent used 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 the present 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 / cm 3, volume density is 1.0-1.1g / cm 3 , in 20-40℃ clean water, it softens into a mass in 10-15 minutes and completely dissolves in 60 minutes.

[0028] A further improvement of the present 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 proppant is 1.00-1.08 g / cm 3 , volume density is 0.40-0.50g / cm 3 , particle size is 0.15-0.075mm.

[0029] A further improvement of the present invention is that in step S6, the main fracturing construction refers to using 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] The present invention provides a method for realizing the design of temporary plugging of multiple fractures in fractures. The method specifies the fracture size according to the optimal position of temporary plugging required by the reservoir, specifies the dynamic fracture width of temporary plugging of multiple fractures in combination with the natural micro-cracks and stress conditions of the reservoir, designs the plugging agent segment plug and key parameters according to the dynamic fracture width of temporary plugging, ensures the graded support of temporary plugging of multiple fractures and main fractures, ensures the flow conductivity requirements of different fractures, and finally forms a method for optimizing the design of temporary plugging at a fixed point. The steps of the method are simple and easy to implement as a whole, and provide an effective process design idea for improving the effectiveness of temporary plugging of fractures in fractures. It has important practical significance for improving the effectiveness of temporary plugging of multiple fractures, and can also be designed and applied in similar domestic reservoirs.

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

[0033] The present invention uses a low-temperature fast-dissolving temporary plugging agent to ensure that the normal production of the oil well is not affected in the later stage.

[0034] The present invention adopts ultra-low density and small particle size proppant, the density of which is equivalent to that of water, so that low viscosity fracturing fluid can be carried over long distances, and the small particle size makes it easier to enter natural micro-cracks, thereby achieving effective support for branch seams.

[0035] The temporary plugging stage and the main fracturing stage are constructed separately, and the proppant in the main fracture is not mixed, so that the main fracture has a higher conductivity while the conductivity of the branch fracture is not lost. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 The present invention is a schematic diagram of a method for implementing a multi-fracture fracturing design method for achieving temporary plugging of multiple fractures at fixed points within the fracture.

[0037] Description of reference numerals:

[0038] 1. Wellbore, 2. Dynamic main fracture, 3. Temporary plugging agent, 4. Natural micro fracture or branch fracture, 5. Small particle size proppant, 6. Large particle size proppant. DETAILED DESCRIPTION

[0039] Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided in order to enable a more thorough understanding of the present disclosure and to be able to fully convey the scope of the present disclosure to those skilled in the art. It should be noted that, in the absence of conflict, the embodiments of the present invention and the features described in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0040] Embodiment 1:

[0041] In order to overcome the shortcomings of conventional fracture temporary plugging and repeated fracturing, a design method for achieving fixed-point temporary plugging and multiple fracture fracturing in fractures is provided.

[0042] like Figure 1 As shown, the technical solution adopted by the present invention is:

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

[0044] S2. Calculate the average dynamic main fracture width based on the net pressure value in the fractures of natural micro-fractures opened in the block;

[0045] S3. Calculate the plugging agent segment length, plugging agent dosage and plugging agent particle size based on the dynamic main crack width and crack parameters;

[0046] S4, adding a low-density, low-temperature soluble temporary plugging agent 3 at the beginning of temporary plugging to achieve dynamic main fracture 2 bridge plugging and pressure increase, and open lateral natural micro-cracks or branch fractures 4;

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

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

[0049] The method is aimed at the wellbore 1 of the oil well with a high degree of production of old fractures. According to the temporary plugging process at fixed points in the fractures, the relationship between net pressure and fracture width is used to optimize the amount of plugging agent and the particle size of the plugging agent. Ultra-low density and small-particle proppant plugs are used to support natural micro-fractures. Combined with the filling of the main fractures, the secondary fractures and the main fractures are filled in an orderly manner, thereby achieving the purpose of improving the effectiveness of multi-fracture fracturing.

[0050] Embodiment 2:

[0051] Based on Example 1, in this example, preferably, the fracturing software described in step S1 is common commercial full three-dimensional fracturing software such as PRACPRO and STIMPLAN that are mature in the market.

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

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

[0054] P net =0.5(σ H -σ h )(1-cos2θ)

[0055] Where σ H is the maximum horizontal principal stress in the block, σ h is the minimum horizontal principal stress, θ is the natural microcrack angle, and the net pressure calculated based on regional tests is 3-5MPa.

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

[0057]

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

[0059] Preferably, the plugging agent segment length in step S3 refers to the length of the plugging agent accumulated in the seam, which is calculated using the following formula:

[0060]

[0061] Where μ is the viscosity of the fracturing fluid, k f is the fracture permeability.

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

[0063]

[0064] Preferably, the particle size d of the plugging agent in step S3 meets the following requirements: In order to improve the temporary plugging and bridging effect, a temporary plugging agent with a combined particle size is used.

[0065] Preferably, the low-density, low-temperature soluble temporary plugging agent in step S4 has an apparent density of 1.45-1.55 g / cm 3 , volume density 1.0-1.1g / cm 3 , in 20-40℃ clean water, it softens into a mass in 10-15 minutes and completely dissolves in 60 minutes.

[0066] Preferably, the viscosity of the low-viscosity fracturing fluid in step S5 is 3-5 cp, and the ultra-low-density small-particle proppant refers to an apparent density of 1.00-1.08 g / cm 3 , volume density is 0.40-0.50g / cm 3 , particle size 0.15-0.075mm.

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

[0068] Example 3

[0069] Based on Example 1 and Example 2, in this well embodiment (oil layer thickness 10m, maximum horizontal principal stress 30MPa, minimum principal stress 25MPa, Poisson's ratio 0.23, Young's modulus 34000MPa, natural microcrack angle 45°, crack permeability 45D, fracturing fluid slick water viscosity 3mpa·s), preferably, the construction parameters and crack parameters described in step S1 are respectively the fracturing fluid volume V required before temporary plugging = 50m 3 、Injection displacement Q=2.0m 3 / min, temporarily plugging the main crack with a length of L=25m and a height of h=17m, etc.

[0070] Preferably, the calculation result of the net pressure in the seam described in step S2 is P net =2.5MPa:

[0071] Preferably, the average dynamic slit width described in step S2 is

[0072] Preferably, the plugging agent segment length in step S3 refers to the length of the plugging agent accumulated in the seam, which is 0.7 m;

[0073]

[0074] Preferably, the plugging agent volume ΔV in step S3 is 0.2 m 3 ;

[0075] Preferably, the particle size d of the plugging agent in step S3 meets the following requirements: In order to improve the temporary plugging and bridging effect, a combined particle size temporary plugging agent of 5.8mm to 10mm is used.

[0076] Preferably, the low-density, low-temperature soluble temporary plugging agent in step S4 has an apparent density of 1.45-1.55 g / cm3 and a volume density of 1.0-1.1 g / cm3. It softens into a mass in 20-40°C clean water in 10-15 minutes and completely dissolves in 60 minutes.

[0077] Preferably, in step S5, the viscosity of the low-viscosity fracturing fluid is 3-5 cp, and the ultra-low density small-particle proppant refers to 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 construction in step S6 refers to using conventional cross-linked guar gum fracturing fluid to carry a proppant of 20 / 40 mesh to complete the sand filling of the main fracture.

[0079] The above examples are merely illustrative of the present invention and do not constitute a limitation on the scope of protection of the present invention. All designs identical or similar to the present invention belong to the scope of protection of the present invention. The reagents and method steps not described in detail in this embodiment are all well-known techniques and commonly used methods in the industry and will not be described one by one here.

Claims

1. A method for realizing temporary plugging of multiple fractures at fixed points within fractures, characterized in that: The following steps are involved: S1. Identify the location of new fractures in the reservoir and the conditions for increasing pressure, and use fracturing software to simulate the construction parameters and fracture parameters required for the temporary plugging stage at the fixed point; S2. Calculate the average dynamic main fracture width based on the net pressure value in the fractures of natural micro-fractures opened in the block; S3. Calculate the plugging agent segment length, plugging agent dosage and plugging agent particle size based on the dynamic main crack width and crack parameters; S4. Add low-density, low-temperature soluble temporary plugging agent at the beginning of temporary plugging to achieve dynamic main crack bridge plugging and pressure increase, and open lateral natural microcracks or branch cracks; S5: At the end of temporary plugging, low-viscosity fracturing fluid is added with ultra-low-density small-size proppant to support natural micro-fractures; S6. After the temporary plugging is completed, the main fracturing construction is carried out, and large-size proppant is used for dynamic main fracture filling.

2. A method for realizing temporary plugging of multiple fractures by fixed-point fracturing according to claim 1, characterized in that: In step S1, the position of opening new fractures in the reservoir and the pressure-increasing conditions are determined. The position of opening new fractures is determined by geological digital modeling software. The pressure-increasing condition for opening new fractures is the opening pressure of natural micro-fractures. The fracturing software is PRACPRO or STIMPLAN commercial full three-dimensional fracturing software.

3. A method for realizing temporary plugging of multiple fractures by fixed-point fracturing according to claim 1, characterized in that: In step S1, the construction parameters and the fracture parameters are respectively the fracturing fluid volume V, the injection displacement Q, the fracture length L and the fracture height h required before temporary plugging.

4. A method for realizing temporary plugging of multiple fractures by fixed-point fracturing according to claim 3, characterized in that: In step S2, the net pressure in the seam is calculated using the following formula: P net =0.5(σ H -s h (1-cos2θ) Where σ H is the maximum horizontal principal stress in the block, σ h is the minimum horizontal principal stress, θ is the natural microcrack angle; The average dynamic seam width is calculated using the following formula: Where υ is Poisson's ratio, L is the crack length, and E is Young's modulus.

5. A method for realizing temporary plugging of multiple fractures by fixed-point fracturing according to claim 4, characterized in that: In step S3, the plugging agent segment length refers to the length of the plugging agent accumulated in the seam, which is calculated using the following formula: Where μ is the viscosity of the fracturing fluid, k f is the fracture permeability.

6. A method for realizing temporary plugging of multiple fractures by fixed-point fracturing according to claim 5, characterized in that: In step S3, the amount of plugging agent used refers to the volume of the plugging agent, which is calculated using the following formula:

7. A method for realizing temporary plugging of multiple fractures by fixed-point fracturing according to claim 4, characterized in that: In step S3, the particle size d of the plugging agent meets the following requirements:

8. The method for realizing temporary plugging of multiple fractures at fixed points in fractures according to claim 1, characterized in that: In step S4, the apparent density of the low-density, low-temperature soluble temporary plugging agent is 1.45-1.55 g / cm 3 , volume density is 1.0-1.1g / cm 3 , in 20-40℃ clean water, it softens into a mass in 10-15 minutes and completely dissolves in 60 minutes.

9. A method for realizing temporary plugging of multiple fractures by fixed-point fracturing according to claim 1, characterized in 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 proppant is 1.00-1.08 g / cm 3 , volume density is 0.40-0.50g / cm 3 , particle size is 0.15-0.075mm.

10. A method for realizing temporary plugging of multiple fractures by fixed-point fracturing according to claim 1, characterized in that: In step S6, the main fracturing construction refers to using 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.

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