Fracturing flow-back oil nozzle real-time optimization method considering fluctuating pressure

Abstract

The invention provides an innovative real-time oil nozzle size calculation method, and the method particularly considers the influence of fluctuation pressure on proppant backflow. Firstly, basic parameters of a target reservoir of a fractured well are collected, then the crack width after hydraulic cracks are closed is accurately calculated, the critical flow demand of liquid drainage is derived, and then fluctuation pressure caused by oil nozzle opening and closing operation and the critical flow velocity started by proppant particles are calculated. And dynamically determining the bottom hole pressure, the critical flow velocity and the flow rate of liquid drainage under the given wellhead oil pressure by utilizing the fluctuation pressure and combining the wellhead oil pressure, the critical flow velocity and the tubular column friction loss, so as to ensure the real-time and accurate calculation. The proper oil nozzle diameter is calculated by monitoring the wellhead oil pressure and the critical flow in real time, the dependence on parameters such as the filtration coefficient and the crack height which are difficult to obtain is simplified, and the calculation and operation convenience and reliability are improved. The method can traverse wellhead oil pressure data, perform repeated calculation, adjust and output the diameter of the matched oil nozzle in real time, realize dynamic optimization of the size of the oil nozzle, and guarantee stability and high efficiency of rapid liquid drainage after fracturing.

Description

Technical Field

[0001] The invention relates to a real-time optimization method for a fracturing flowback oil nozzle taking into account fluctuating pressure, and belongs to the field of hydraulic fracturing production enhancement and transformation in oil and gas field development. Technical Background

[0002] In the field of oil and gas extraction, hydraulic fracturing technology has become a landmark technology for the development of low-permeability and unconventional oil and gas reservoirs, greatly improving the commercial development of shale and tight oil and gas. Hydraulic fracturing technology injects high-pressure liquid containing proppant into the bottom of the wellbore to increase the fracture pressure of the formation, prompting the formation of complex cracks in the rock, thereby providing more flow channels for oil and gas, and significantly improving the permeability of the reservoir. However, after the completion of hydraulic fracturing, fracturing backflow operations must be performed to remove the residual fracturing fluid in the well and realize the return of oil and gas from the wellhead. The backflow process depends critically on the nozzle model and adjustment strategy installed at the wellhead. The size of the nozzle opening directly controls the flow rate and pressure of the fluid from the bottom of the well to the ground. Improper nozzle adjustment system will cause backflow and sand control of the proppant layer, which will not only affect the production but also cause damage to the downhole equipment. Therefore, a reasonable nozzle adjustment optimization design method is of great significance to ensure the effect of fracturing development.

[0003] In the traditional nozzle adjustment process, most of the efforts are based on on-site experience, and the replacement of nozzles can easily cause fluctuating pressure at the bottom of the well. Appropriate pressure fluctuations can help remove residual fluids filled in the fractures, reduce fluid retention, and thus improve oil and gas production efficiency. However, frequent adjustment of the nozzle will cause excessive fluctuating pressure, which will produce water hammer, causing instability of the proppant filling layer in the fracture, damaging the fracture conductivity, and even destroying the proppant filling layer to cause sand production problems. For this reason, it is necessary to establish a fracturing flowback method that takes into account the fluctuating pressure at the bottom of the well, that is, to achieve the fluctuation of wellhead pressure by accurately adjusting the nozzle opening, optimize the flowback efficiency, and increase oil and gas production. Since the fluctuating pressure at the wellhead is sudden, real-time and fine-tuning the nozzle opening plays a decisive role in alleviating the impact of fluctuating pressure and optimizing the flowback effect. The advantages of real-time nozzle adjustment also include: direct analysis of factors affecting downhole flow characteristics, including flow rate, pressure, and proppant delivery; real-time monitoring and adjustment can adapt to changes in the downhole environment, such as crack closure, proppant sedimentation, etc., to ensure smooth flowback; avoid crack damage or overload of surface facilities caused by excessive pressure fluctuations. Therefore, inventing a system that can monitor downhole conditions in real time and automatically adjust the nozzle opening according to data feedback is of vital importance to improving flowback efficiency and ensuring operational safety. Based on these factors, the present invention accurately determines the critical flow rate of the liquid flow at which the proppant flows back, providing a scientific basis for controlling proppant loss. Furthermore, the present invention takes the perspective of the system integrity from reservoir fractures to tubing and then to the nozzle, and combines the coordinated constraint relationship between flow and pressure in the system to innovatively propose a method for calculating the nozzle size in real time considering fluctuating pressure, so as to effectively control the backflow of proppant after hydraulic fracturing. This method can not only effectively prevent the wear and damage to the production process caused by proppant backflow, but also avoid the fluctuation pressure damage caused by water hammer or reduce the degree of damage caused by water hammer. It also realizes the efficient and rapid discharge of fracturing working fluid, thereby significantly reducing the negative impact on the reservoir and ultimately improving the production increase effect and overall efficiency of hydraulic fracturing operations.

[0003] In response to existing problems, we deeply explored the complex mechanism of solid-phase particle activation under the influence of fluctuating pressure in proppant-filled fractures, combined the material balance principle and fluid dynamics theory, and constructed a mathematical model of critical reflux of proppant flowback that comprehensively considers multiple factors. This model can not only analyze the critical flow rate of proppant particle activation, but also introduce the fluctuating pressure calculation equation, realize the whole process correlation between wellhead oil pressure and nozzle diameter, and provide important theoretical support for on-site fracturing engineers to adjust the flowback strategy. Summary of the invention

[0004] In order to avoid the damage caused by the fluctuating pressure of water hammer or reduce the degree of damage caused by water hammer, the present invention is committed to developing a new method for calculating the real-time nozzle size of hydraulic fracturing proppant return in response to the fluctuating pressure factor. The core of this method is to effectively prevent the proppant from escaping from the cracks during the drainage stage after the fracturing operation, thereby preventing the crack width from shrinking and ensuring that the conductivity of the fracturing propped cracks is not damaged. At the same time, by reducing the wear of the proppant particles on the downhole tubing and the ground transmission pipeline, the service life of these key components is significantly improved. This series of improvements aims to significantly optimize the hydraulic sand fracturing transformation effect of low permeability reservoirs and effectively reduce the overall operating cost.

[0005] The present invention provides a technical solution to solve the above technical problems: a real-time nozzle size calculation method for hydraulic fracturing proppant return considering fluctuating pressure, comprising the following steps:

[0006] Step S10: Collect and organize basic parameter information of the target reservoir in the fracturing well;

[0007] Step S20: Calculating the crack width after the hydraulic crack is closed;

[0008] Step S30: evaluating the fluctuating pressure generated by the opening and closing of the nozzle;

[0009] Step S40: determining the critical flow rate required for proppant particles to start propping up the fracture filling layer;

[0010] Step S50: iteratively calculating the bottom hole pressure using the wellhead oil pressure, critical flow velocity and pipe string friction data, and then determining the bottom hole pressure, drainage critical flow velocity and drainage critical flow rate under specific wellhead oil pressure conditions;

[0011] Step S60: Calculating the nozzle diameter based on the wellhead oil pressure and critical flow data actually monitored;

[0012] Step S70: By traversing the wellhead oil pressure values ​​monitored in real time, steps S40 to S60 are repeated to calculate the nozzle diameter required under different circumstances.

[0013] A further technical solution is that the basic parameters of the target reservoir of the fracturing well include well depth, production layer thickness, closure pressure, fracturing return fluid density, fracturing return fluid viscosity, proppant particle density, proppant particle size, proppant filling porosity and real-time pressure monitoring data of the ground pressure gauge.

[0014] A further technical solution is that the calculation formula in step S20 is:

[0015]

[0016] Where: w p is the width of the support crack, mm; Cp is the proppant laying concentration, kg / m 2 ρ p is the proppant particle density, kg / m 3 .

[0017] A further technical solution is that the calculation formula in step S30 is:

[0018]

[0019] Where: Δp is the fluctuating pressure, MPa; L is the length of the pipeline, m; v0 is the average flow velocity in the pipeline before water hammer, m / s; T z is the valve closing time, s; a0 is the propagation speed of sound waves in water, the water temperature is about 10℃, the pressure is 0.1~2.5MPa, a0=1435m / s; E0 is the elastic modulus of water, E0=2.04×10 5 N / cm 3 ; E is the elastic modulus of the tube wall, N / cm 2 ; d is the pipe diameter, mm; δ is the pipe wall thickness, mm.

[0020] A further technical solution is that the specific process of step S40 is:

[0021] Step S41: Calculate the bottom hole pressure p under a given wellhead oil pressure b ;

[0022] Step S42: according to the bottom hole pressure p b Calculate the critical velocity of proppant particles to start in the closed fracture state;

[0023] Step S43, check the flow morphology according to the Rayleigh number of the proppant particles, and determine the final critical velocity. A further technical solution is that the calculation formula in step S41 is:

[0024] p b =p t +p h +Δp st +Δp

[0025] Where: Δp st is the friction resistance along the pipe string, MPa; p t is the given wellhead oil pressure, MPa; p b is the bottom hole pressure at a given wellhead oil pressure, MPa; p h is the static liquid column pressure, MPa, and Δp is the wellhead fluctuation pressure, MPa.

[0026] A further technical solution is that the calculation formula in step S42 is:

[0027]

[0028] Where: k, τ are dimensionless reference coefficients; p c is the reservoir closure pressure, MPa; p b is the bottom hole pressure at a given wellhead oil pressure, MPa; R ep is the Reynolds number; d s Diameter of a single proppant, mm; ρ s is the density of the proppant, kg / m 3 ; ρ is the density of fracturing fluid, kg / m 3 ; ε is the adhesion coefficient, ε = 2.56 dyn / cm; δ = 0.213 × 10 -4 cm, is the film parameter between particles; v c is the critical velocity for proppant particle activation, m / s.

[0029] A further technical solution is that the specific process of step S50 is:

[0030] Step S51, calculating the critical flow rate and critical flow rate of the fracturing string according to the crack width and the critical flow rate of the proppant particles to start the fracturing string;

[0031] Step S52, calculating the friction resistance along the pipe string in the drainage system;

[0032] Step S53: Substitute the friction resistance along the pipe obtained in step S52 into step S40, and repeat steps S40-S50 for iterative calculation until the friction resistance along the pipe obtained in step S52 is satisfied. Given the accuracy requirement, determine the bottom hole pressure, critical discharge flow rate and critical discharge flow rate under a given wellhead oil pressure.

[0033] A further technical solution is that the calculation formula in step S51 is:

[0034] q=2(0.785w p h e v lin )

[0035] v=q / (πD 2 / 4)

[0036] Where: q is the critical flow rate of discharge, m 3 / s;h e is the effective thickness of the reservoir, m; D is the diameter of the pipe string after compression, mm.

[0037] A further technical solution is that the calculation formula in step S52 is:

[0038]

[0039]

[0040]

[0041]

[0042] Where: Δp b is the friction resistance along the pipe string, MPa; η is the roughness of the pipe wall; d1 is the inner diameter of the pipe, mm; λ is the friction coefficient along the flow, dimensionless; f is the resistance reduction rate of the return fluid, dimensionless.

[0043] A further technical solution is that the calculation formula of the nozzle diameter is:

[0044]

[0045] Where: p ch is the nozzle pressure, MPa; d2 is the nozzle diameter, mm.

[0046] The present invention has the following beneficial effects: the present invention avoids the damage caused by the fluctuating pressure caused by water hammer or reduces the degree of damage caused by water hammer, and the calculation method has the characteristics of simplicity, reliability, and operability; it can also effectively avoid the abrasion of the production process by the support reflux, realize the rapid discharge of the working fluid after pressure to reduce the damage to the reservoir, thereby effectively improving the hydraulic fracturing production increase effect. Figure 1 Technical flow chart for real-time optimization of fracturing flowback nozzles considering fluctuating pressure Figure 2 The results of the analysis of the net pressure change in the fracture caused by the fluctuating pressure during the flowback process under different conditions Figure 3 The bottom hole pressure calculation results under the condition of limiting the fluctuating pressure Figure 4 This is the nozzle working system table without considering the fluctuating stress Figure 5 Table of optimized working system for nozzle considering fluctuating stress Figure 6 This is the result diagram of the nozzle optimization of the actual fracturing return well on site.

Claims

1. A method for calculating the real-time nozzle size of hydraulic fracturing proppant return considering fluctuating pressure, comprising the following steps: step S10: Collect and organize basic parameter information of the target reservoir in the fracturing well; Step S20: Calculating the crack width after the hydraulic crack is closed; Step S30: evaluating the fluctuating pressure generated by the opening and closing of the nozzle; Step S40: determining the critical flow rate required for proppant particles to start propping up the fracture filling layer; Step S50: iteratively calculating the bottom hole pressure using the wellhead oil pressure, critical flow velocity and pipe string friction data, and then determining the bottom hole pressure, drainage critical flow velocity and drainage critical flow rate under specific wellhead oil pressure conditions; Step S60: Calculating the nozzle diameter based on the wellhead oil pressure and critical flow data actually monitored; Step S70: By traversing the wellhead oil pressure values ​​monitored in real time, steps S40 to S60 are repeated to calculate the nozzle diameter required in different situations.

2. According to the method for calculating the real-time nozzle size of hydraulic fracturing proppant reflux considering fluctuating pressure according to claim 1, a further technical solution is that the calculation formula in step S20 is: Where: w p is the width of the support crack, mm; C p is the proppant laying concentration, kg / m 2 ρ p is the proppant particle density, kg / m 3 .

3. According to the method for calculating the real-time nozzle size of hydraulic fracturing proppant reflux considering fluctuating pressure in claim 1, a further technical solution is that the calculation formula in step S30 is: Where: Δp is the fluctuating pressure, MPa; L is the length of the pipeline, m; v0 is the average flow velocity in the pipeline before water hammer, m / s; T z is the valve closing time, s; a0 is the propagation speed of sound waves in water, the water temperature is about 10℃, the pressure is 0.1~2.5MPa, a0=1435m / s; E0 is the elastic modulus of water, E0=2.04×10 5 N / cm 3 ; E is the elastic modulus of the tube wall, N / cm 2 ; d is the pipe diameter, mm; δ is the pipe wall thickness, mm.

4. According to the method for calculating the real-time nozzle size of hydraulic fracturing proppant reflux considering fluctuating pressure according to claim 1, a further technical solution is that the specific process of step S40 is: Step S41: Calculate the bottom hole pressure p under a given wellhead oil pressure b ; Step S42: according to the bottom hole pressure p b Calculate the critical velocity of proppant particles to start in the closed fracture state; Step S43: Check the flow morphology according to the Rayleigh number of the proppant particles and determine the final critical velocity.

5. According to the method for calculating the real-time nozzle size of hydraulic fracturing proppant reflux considering fluctuating pressure of claim 1, a further technical solution is that the calculation formula in step S41 is: p b =p t +p h +Δp st +Δp Where: Δp st is the friction resistance along the pipe string, MPa; p t is the given wellhead oil pressure, MPa; p b is the bottom hole pressure at a given wellhead oil pressure, MPa; p h is the static liquid column pressure, MPa, and Δp is the wellhead fluctuation pressure, MPa.

6. According to the method for calculating the real-time nozzle size of hydraulic fracturing proppant reflux considering fluctuating pressure in claim 1, a further technical solution is that the calculation formula in step S42 is: Where: k, τ are dimensionless reference coefficients; p c is the reservoir closure pressure, MPa; p b is the bottom hole pressure at a given wellhead oil pressure, MPa; R ep is the Reynolds number; d s Diameter of a single proppant, mm; ρ s is the density of the proppant, kg / m 3 ; ρ is the density of fracturing fluid, kg / m 3 ; ε is the adhesion coefficient, ε=2.56dyn / cm; δ=0.213×10 -4 cm, is the film parameter between particles; v lin is the critical velocity for proppant particle activation, m / s.

7. According to the method for calculating the real-time nozzle size of hydraulic fracturing proppant reflux considering fluctuating pressure of claim 1, a further technical solution is that the specific process of step S50 is: Step S51, calculating the critical flow rate and critical flow rate of the fracturing string according to the crack width and the critical flow rate of the proppant particles to start the fracturing string; Step S52, calculating the friction resistance along the pipe string in the drainage system; Step S53: Substitute the friction resistance along the pipe obtained in step S52 into step S40, and repeat steps S40-S50 for iterative calculation until the friction resistance along the pipe obtained in step S52 is satisfied. Given the accuracy requirement, determine the bottom hole pressure, critical discharge flow rate and critical discharge flow rate under a given wellhead oil pressure.

8. According to the method for calculating the real-time nozzle size of hydraulic fracturing proppant reflux considering fluctuating pressure in claim 1, a further technical solution is that the calculation formula in step S51 is: q=2(0.785w p h e v lin ) v=q / (πD 2 / 4) Where: q is the critical flow rate of discharge, m 3 / s;h e is the effective thickness of the reservoir, m; D is the diameter of the pipe string after compression, mm.

9. According to the method for calculating the real-time nozzle size of hydraulic fracturing proppant reflux considering fluctuating pressure in claim 1, a further technical solution is that the calculation formula in step S52 is: Where: Δp b is the friction resistance along the pipe string, MPa; η is the roughness of the pipe wall; d1 is the inner diameter of the pipe, mm; λ is the friction coefficient along the flow, dimensionless; f is the resistance reduction rate of the return fluid, dimensionless. A further technical solution is that the calculation formula of the nozzle diameter is: Where: p ch is the nozzle pressure, MPa; d2 is the nozzle diameter, mm.

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