A new method for evaluating effect of downhole ultrasonic atomization drainage gas recovery

Abstract

This invention relates to a novel method for evaluating the effectiveness of downhole ultrasonic atomization drainage gas production, belonging to the field of gas well drainage and gas production technology. The method includes: calculating the wellbore pressure drop ΔP before the intervention of the downhole ultrasonic atomization drainage gas production process; and calculating the pressure drop ΔP downstream of the nozzle in the pipeline section after the intervention of the downhole ultrasonic atomization drainage gas production process. 1 ; Calculate the local pressure drop ΔP of the gas-liquid two phases through the nozzle. 2 Determine the local pressure drop through the nozzle and the total pressure drop ΔP in the downstream pipe section. 3 Compare the wellbore pressure drop ΔP before and after the intervention under the same conditions. 3 The method for evaluating the effect of downhole ultrasonic atomization drainage gas production overcomes the shortcomings of existing methods, such as inaccuracy and lack of consideration for actual well conditions. It provides a more intuitive evaluation of the application effect of the process and offers a theoretical basis for the design and well selection of downhole ultrasonic atomization drainage gas production processes.

Description

A novel method for evaluating the gas production effect of downhole ultrasonic atomization drainage. Technical Field

[0001] This invention belongs to the field of gas well drainage and gas production technology, specifically relating to a new method for evaluating the effect of downhole ultrasonic atomization drainage and gas production. Background Technology

[0002] Natural gas, as a widely used clean energy source, is increasingly important in the nation's energy strategy. However, the development of my country's major gas fields has entered its mid-to-late stages, leading to frequent problems of liquid accumulation in gas wells, severely impacting normal production. Therefore, timely implementation of drainage and gas production technologies is crucial for stable gas well production. Ultrasonic atomization drainage and gas production utilizes a Laval nozzle to accelerate natural gas to supersonic speeds. On one hand, the high-speed gas shears the liquid entering the nozzle outlet; on the other hand, the reduced pressure or even negative pressure at the nozzle outlet, combined with the high temperature at the wellbore, vaporizes the liquid. Under the combined effect of these two methods, the liquid is atomized, and then the natural gas uses its own kinetic energy to carry the droplets out of the wellhead. Compared with existing drainage and gas production technologies, this technology has advantages such as simple structure, ease of use, and low application cost.

[0003] Existing methods for evaluating the effectiveness of ultrasonic atomization drainage and gas production compare the diameter of the atomized droplets with the maximum droplet diameter calculated by a droplet model under the same conditions. However, in reality, when the diameter of the atomized droplets is much smaller than the calculated result by the droplet model, the liquid-carrying effect of the atomizer in the field is still poor. Furthermore, current methods for measuring the diameter of the atomized droplets have flaws. During experiments, the droplet diameter is measured with the downstream of the atomizer exposed, failing to consider downhole operating conditions, such as the presence of thousands of meters of tubing downstream of the atomizer. Visual experimental results show that the liquid in the tubing downstream of the atomizer should be carried in both droplet and liquid film forms, not just droplets. Therefore, there is currently a lack of a direct and effective method for evaluating the effectiveness of downhole ultrasonic atomization drainage and gas production technology.

[0004] The essence of downhole atomized drainage gas production is to use ultrasonic atomization to continuously carry the existing liquid in the wellbore to the surface, thereby reducing the internal pressure drop and extending the gas well's lifespan. To this end, this invention compares the wellbore pressure drop before and after the implementation of downhole ultrasonic atomized drainage gas production technology, using the reduction in pressure drop as an evaluation index of the atomized drainage gas production effect. This provides a more intuitive evaluation of the technology's application effect from a field application perspective, and proposes a new method for evaluating the effectiveness of downhole ultrasonic atomized drainage gas production. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing downhole ultrasonic atomization drainage gas production effect evaluation methods, which are inaccurate and do not fully consider the actual working conditions of gas wells in the field. A new method for evaluating the effect of downhole ultrasonic atomization drainage gas production is proposed, which can more intuitively evaluate the application effect of the process from the perspective of field application, and provide a theoretical basis for the design of downhole ultrasonic atomization drainage gas production process and well selection.

[0006] To achieve the above objectives, the present invention provides a novel method for evaluating the effectiveness of downhole ultrasonic atomization drainage and gas production, comprising the following steps:

[0007] Step 1: Calculate the wellbore pressure drop ΔP before the intervention of the downhole ultrasonic atomization drainage and gas production process;

[0008] Step 2: Calculate the pressure drop ΔP1 in the downstream pipe section of the nozzle after the intervention of the downhole ultrasonic atomization drainage gas production process;

[0009] Step 3: Calculate the local pressure drop ΔP2 of the gas-liquid two phases passing through the downhole atomizing nozzle;

[0010] Step 4: Determine the local pressure drop through the nozzle and the total pressure drop ΔP3 in the downstream pipe section;

[0011] Step 5: Compare the wellbore pressure drop ΔP before the intervention of the downhole ultrasonic atomization drainage gas production process with the wellbore pressure drop ΔP3 after the intervention of the downhole ultrasonic atomization drainage gas production process under the same conditions to determine the reduction in wellbore pressure drop after the intervention of the process.

[0012] Beneficial effects:

[0013] The present invention has the following beneficial effects:

[0014] This invention presents a novel method for evaluating the effectiveness of downhole ultrasonic atomization drainage and gas production. It analyzes the essence of downhole atomization drainage and gas production, comparing the wellbore lift pressure drop before and after the intervention. The reduction in wellbore lift pressure drop after the intervention is used as the evaluation index for the effectiveness of atomization drainage and gas production, which is more consistent with actual conditions. Therefore, this method can more intuitively evaluate the application effect of this technology from a field application perspective, providing a new approach for accurately evaluating the effectiveness of downhole ultrasonic atomization drainage and gas production. Attached Figure Description

[0015] Figure 1 is a schematic diagram of wellbore pressure drop before the intervention of downhole ultrasonic atomization drainage and gas production technology.

[0016] Figure 2 is a schematic diagram of wellbore pressure drop after the intervention of downhole ultrasonic atomization drainage and gas production technology.

[0017] Figure 3 is a schematic diagram of the pressure drop of the gas-liquid two phases through the downhole atomizing nozzle. Detailed Implementation

[0018] To make the objectives, calculation processes, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of the invention.

[0019] Step 1: Calculate the wellbore pressure drop ΔP before the intervention of the downhole ultrasonic atomization drainage gas production process. Its expression is:

[0020]

[0021] Among them G m =A(V) SL ρ L +V SG ρ G (2)

[0022] In the formula, G m f is the mass flow rate of the gas-liquid mixture, in kg / s. m D is the two-phase friction coefficient; D is the inner diameter of the tubing, in meters; A is the cross-sectional area of ​​the tubing, in meters. 2 .

[0023] The key to calculating the pressure gradient in equation (1) is to calculate the ρ of the gas-liquid mixture. m and the gas-liquid two-phase friction coefficient f m .

[0024] First, calculate the liquid holdup H. L Then calculate the ρ of the gas-liquid mixture. m The liquid holdup can be expressed as H. L The plate analysis method yields the following results. When determining the liquid holdup using the plate method, four dimensionless quantities need to be calculated: liquid velocity number, gas velocity number, pipe diameter number, and liquid viscosity number. Their expressions are as follows:

[0025]

[0026]

[0027]

[0028]

[0029] In the formula, μ L The viscosity of the liquid phase is expressed in Pa·s and μ. g ρ represents the gas phase viscosity, Pa·s.

[0030] Then calculate N under average pressure and temperature conditions. Lv Ngv N D and N L According to N L Determine the intermediate process parameter CN by referring to the experimental data chart. L The value is then used to calculate the retention coefficient Φ, which is expressed as:

[0031]

[0032] In the formula, P sc Standard atmospheric pressure; The average pressure in the calculated section of the wellbore is expressed in Pa.

[0033] Then, based on the Φ value, find H from the liquid holdup coefficient chart. L / Φ, then calculate Φ s The expression is:

[0034]

[0035] Then based on Φ and Φ s The intermediate process parameter Φ is obtained from the relationship diagram, and then based on H... L / Φ value is used to calculate liquid holdup H L .

[0036] Then the density ρ of the mixture m The expression is:

[0037] ρ m =ρ L H L +ρ g (1-H L (9)

[0038] Its two-phase friction coefficient f m The calculation expression is:

[0039]

[0040] In the formula, e is the absolute roughness of the pipe wall, in meters (m); N Rem It is the two-phase Reynolds number.

[0041] The two-phase Reynolds number N Rem The expression is:

[0042]

[0043] Step 2: Calculate the pressure drop ΔP1 downstream of the nozzle after the intervention of the downhole ultrasonic atomizing drainage gas production process. In actual gas wells, after installing the downhole atomizing nozzle, the downstream pipe section is several kilometers long. Compared with a bare pipe, under certain operating conditions, the unit pressure drop of the straight pipe section downstream of the atomizing nozzle is less than that of an empty pipe. The calculation expression is as follows:

[0044]

[0045] In the formula, The average density of the oil-gas-water mixture, in kg / m³ 3 g is the acceleration due to gravity, 9.8 m / s². 2 λ is the resistance coefficient of the oil-gas-water mixture in the vertical pipe; Qo is the oil production rate, m 3 / s;G t For a production of 1m 3 Total mass of oil, gas, and water in surface degassed crude oil, kg / m³ 3 D is the pipe diameter, in meters (m).

[0046] Step 3: Calculate the local pressure drop ΔP2 of the gas-liquid two-phase flow through the downhole atomizing nozzle. As shown in Figure 3, the nozzle flow can be simplified into two control volumes: the first control volume starts at position ① and ends at position ②, representing the contraction section; the second control volume starts at position ② and ends at position ③, representing the divergence section. After the fluid passes through the contraction section, the pressure recovers to some extent when it flows through the divergence section.

[0047] First, calculate the pressure drop of the first control volume, using the following expression:

[0048]

[0049]

[0050] In the formula, v is the specific volume of the fluid, and m 3 / kg; G is the mass flux of the mixture, kg / (s·m 2 Pa; A1 is the flow area of ​​the upstream pipe section of the nozzle, m. 2 A c A is the effective flow area of ​​the nozzle throat. c =A1C c σ, m 2 C c σ is the contraction coefficient; σ is the ratio of the flow areas, σ = A c / A1.

[0051] For the second control body, the pressure calculation expression is:

[0052]

[0053] In the formula, A3 is the flow area of ​​the downstream pipe section of the nozzle, in meters. 2 A2 is the flow area of ​​the nozzle throat, in meters. 2 Pa; MF is momentum flux, Pa; subscripts G and L represent the gas phase and liquid phase, respectively.

[0054] Step 4: Determine the local pressure drop through the nozzle and the total pressure drop ΔP3 of the downstream pipe section. In actual gas wells, the straight pipe section downstream of the atomizing nozzle can reach several kilometers in length. In this case, the local pressure drop through the atomizing nozzle accounts for a significantly smaller proportion of the total pressure drop. The total pressure drop after introducing the atomizing nozzle is smaller than that of empty pipe, thus reducing the flow pressure drop in the wellbore. The expression for calculating the total pressure drop is:

[0055] △P3=△P1+△P2(16)

[0056] In the formula, △P1 is the pressure drop of the downstream pipe section of the nozzle after the intervention of the downhole ultrasonic atomization drainage and gas production process, and △P2 is the local pressure drop of the gas and liquid phases through the downhole atomization nozzle.

[0057] Step 5: Compare the wellbore pressure drop ΔP before the intervention of the downhole ultrasonic atomization drainage and gas production process with the wellbore pressure drop ΔP3 after the intervention under the same conditions to determine the reduction in wellbore pressure drop after the intervention. If ΔP3 > ΔP, it indicates poor atomization fluid carrying effect, and its use is not recommended; if ΔP3 < ΔP, it indicates effective atomization fluid carrying effect, and its use is recommended. The effectiveness can be reflected by the reduction in pressure drop.

Claims

1. A novel method for evaluating the gas production effect of downhole ultrasonic atomization drainage, characterized in that, The method includes the following calculation steps: Step 1: Calculate the wellbore pressure drop ΔP before the intervention of the downhole ultrasonic atomization drainage and gas production process; Step 2: Calculate the pressure drop ΔP1 downstream of the nozzle after the intervention of the downhole ultrasonic atomization drainage and gas production process; Step 3: Calculate the local pressure drop ΔP2 of the gas-liquid two phases passing through the downhole atomizing nozzle; Step 4: Determine the local pressure drop through the nozzle and the total pressure drop ΔP3 downstream of the nozzle; Step 5: Compare the wellbore pressure drop ΔP before the intervention of the downhole ultrasonic atomization drainage and gas production process with the wellbore pressure drop ΔP3 after the intervention of the downhole ultrasonic atomization drainage and gas production process under the same conditions to determine the reduction in wellbore pressure drop after the intervention. If ΔP3 > ΔP, it indicates poor atomization liquid carrying effect, and its use is not recommended; if ΔP3 < ΔP, it indicates effective atomization liquid carrying effect, and its use is recommended. The effect can be reflected by the reduction in pressure drop.

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