Fractured-vuggy reservoir gas-water synergistic displacement flow field visualization experiment device based on fluorescent PIV technology and evaluation method of fracture-vuggy reservoir gas-water synergistic displacement flow field visualization experiment device

Abstract

The invention discloses a fissure-vuggy reservoir gas-water synergistic displacement flow field visualization experiment device based on a fluorescent PIV technology and an evaluation method. The device comprises a transparent fracture-cavity model, an immersion tank, external matching liquid, an injection fluid pump, a double-pulse laser, a sheet light shaping unit, a high-speed camera, a temperature control assembly, an outlet back pressure and output metering assembly and a data acquisition and processing assembly, and is used for acquiring a liquid phase image sequence and calculating a liquid phase velocity field under the gas-water synergistic displacement condition. The method comprises the steps of establishing an optical correction visualization experiment platform, calculating flow state self-adaptive injection parameters, carrying out gas-water cooperative displacement and multi-dimensional data acquisition, carrying out data processing and flow field calculation, and realizing macro-micro cooperative quantitative evaluation based on a vortex oil displacement efficiency index SEIV.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas field development experimental technology and multiphase flow field visualization testing technology, specifically involving a visualization experimental device and evaluation method for gas-water synergistic displacement flow field in fractured-vuggy reservoirs based on fluorescence PIV technology. Background Technology

[0002] Fractured-vuggy carbonate reservoirs commonly feature fractures, caverns, and their interconnected structures. These reservoirs exhibit diverse reservoir types, large scales, and strong heterogeneity. Fluid migration within these reservoirs is simultaneously influenced by gravity, viscosity, interfacial tension, and complex boundary conditions. During water injection, gas injection, and gas-water synergistic displacement, complex flow phenomena such as interfacial migration, gas-liquid differentiation, flow around the reservoir, channeling, and localized eddies frequently occur. These flow behaviors directly affect the swept volume, remaining oil distribution, and ultimate recovery rate. Therefore, establishing experimental characterization methods that can accurately represent the gas-water two-phase flow characteristics within fractured-vuggy reservoirs is crucial for revealing the gas-water synergistic displacement mechanism and optimizing development parameters.

[0003] Current research on the displacement mechanism of fractured-vuggy reservoirs typically employs methods such as visual physical simulation, conventional production parameter monitoring, or numerical simulation analysis. Visual experiments based on transparent models can, to some extent, reflect the fluid transport process within the fractured-vuggy structure; analytical methods based on macroscopic parameters such as pressure, flow rate, production volume, water cut, and recovery rate can reflect the displacement results; and numerical simulation methods can be used to analyze the flow field distribution characteristics under specific operating conditions. However, most of these methods focus on observing macroscopic phenomena, analyzing production responses, or characterizing model calculation results. Direct acquisition of the local flow field structure within the fractured-vuggy medium, the actual velocity distribution of the liquid phase, and the driving effect of eddies remains insufficient, making it difficult to accurately understand the microscopic flow behavior during gas-water synergistic displacement.

[0004] Particle image velocimetry (PIV), a non-contact flow field measurement method, can invert fluid velocity fields by tracking particle image displacement and has been used in some visualized flow experimental studies. However, in transparent models of fracture-vuggy reservoirs, the complex morphology of fracture-vuggy boundaries, with local curved surfaces, sharp corners, thickness variations, and refractive interfaces, makes it easy for laser light to undergo refraction shift and imaging distortion during propagation, resulting in distorted velocity measurement results near the boundary region. Simultaneously, during gas-liquid two-phase displacement, the gas-liquid interface generates strong reflection, scattering, and high-brightness interference. Images acquired using traditional imaging methods often contain both interface optical noise and tracer particle signals, easily leading to an increase in pseudo-vectors in cross-correlation calculations, failure to identify local velocity fields, and distortion of liquid phase flow field information, thus affecting the application effect of PIV in gas-liquid two-phase flow testing in fracture-vuggy reservoirs.

[0005] Furthermore, existing experimental designs typically employ fixed injection rates, empirical settings, or single similarity criteria to determine injection parameters, making it difficult to simultaneously account for the differences in dominant force mechanisms between fractured and cavernous regions. For fractured-cavernous reservoirs, fractures are smaller and interfacial forces have a significant impact, while caverns are larger and gravity differentiation is more pronounced, resulting in inconsistent flow control mechanisms across different regions. The lack of experimental parameter design methods that address the differences in fracture-cavern scale and the coupling effects of multiple factors can easily lead to deviations between experimental conditions and actual flow characteristics, thereby affecting the representativeness and comparability of experimental results.

[0006] On the other hand, existing methods for evaluating displacement effects mainly rely on macroscopic indicators such as cumulative oil production, water cut, recovery rate, and pressure difference. While these methods can reflect the overall development effect, they struggle to establish a direct link between the evolution characteristics of the internal flow field and the remaining oil mobilization process. In particular, they are difficult to quantitatively characterize the contribution of flow phenomena such as local eddies, entrainment, and interface disturbances to the oil displacement effect. Therefore, current technology lacks an experimental device and evaluation method that can accurately measure the liquid phase flow field, effectively suppress optical interference at the gas-liquid interface, adapt to complex boundary conditions, and couple internal flow field information with the displacement effect during gas-water synergistic displacement in fractured-vuggy reservoirs.

[0007] The purpose of this invention is to overcome the problems in existing technologies, such as the difficulty in accurately measuring the liquid phase flow field in gas-water synergistic displacement experiments in fractured-vuggy reservoirs, the easy generation of optical distortion in complex boundary regions, severe gas-liquid interface interference, and the lack of quantitative evaluation indicators for the displacement effect. This invention provides a visualization experimental device and evaluation method for the gas-water synergistic displacement flow field in fractured-vuggy reservoirs based on fluorescence PIV technology. Summary of the Invention

[0008] The purpose of this invention is to overcome the problems in existing technologies, such as the difficulty in accurately measuring the liquid phase flow field in gas-water synergistic displacement experiments in fractured-vuggy reservoirs, the easy generation of optical distortion in complex boundary regions, severe gas-liquid interface interference, and the lack of quantitative evaluation indicators for the displacement effect. This invention provides a visualization experimental device and evaluation method for the gas-water synergistic displacement flow field in fractured-vuggy reservoirs based on fluorescence PIV technology.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: A visualization experimental device for gas-water synergistic displacement flow field in fractured-vuggy reservoirs based on fluorescent PIV technology includes a transparent fractured-vuggy model, an immersion tank and an external matching fluid, an injection fluid pump, a dual-pulse laser, a sheet beam shaping unit, a high-speed camera, a temperature control component, an outlet backpressure and production metering component, and a data acquisition and processing component. The transparent fractured-vuggy model is entirely immersed in the immersion tank and the external matching fluid; fluorescent tracer particles are added to the liquid phase fluid, but not to the gas phase fluid; the laser emitted by the dual-pulse laser is shaped into a sheet beam by the sheet beam shaping unit and then illuminates the internal measurement plane of the transparent fractured-vuggy model; the high-speed camera is used to acquire liquid phase image sequences; and the data acquisition and processing component is used to calculate the liquid phase velocity field based on the image sequences.

[0010] Preferably, the transparent slit model material, the liquid fluid, and the external matching liquid satisfy a preset refractive index matching relationship to reduce imaging distortion at the model boundary and improve the measurability of the liquid flow field near the boundary of the complex slit.

[0011] This invention also provides a visualization evaluation method for the gas-water synergistic displacement flow field of fractured-vuggy reservoirs based on the above-mentioned experimental device, including: establishing an optically corrected visualization experimental platform; calculating flow-adaptive injection parameters; carrying out gas-water synergistic displacement and multi-dimensional data acquisition; performing data processing and flow field calculation; and achieving macro-micro synergistic quantitative evaluation based on the eddy current oil displacement efficiency index SEIV.

[0012] Preferably, during the determination of injection parameters, the Bond number is calculated based on fluid density difference, interfacial tension, liquid phase viscosity, gravitational acceleration, and geometric characteristic scale, and the injection parameters are determined in combination with capillary number and Froude number; during the evaluation process, the SEIV is correlated with the dynamic changes in water cut and recovery rate to characterize the degree of utilization of remaining oil during gas-water synergistic displacement.

[0013] Compared with existing technologies, the present invention has at least the following beneficial effects: by immersing the transparent fractured-vuggy model entirely in the external matching liquid and maintaining the refractive index matching state between the model material, the liquid phase fluid, and the external matching liquid, optical distortion in complex boundary regions can be reduced, and the measurability of the liquid phase flow field can be improved; by adding fluorescent tracer particles to the liquid phase but not to the gas phase, the interference of gas-liquid interface reflection and scattering on liquid phase velocity measurement can be reduced; by removing gas phase region interference from the liquid phase image before performing PIV cross-correlation calculation, the reliability of the liquid phase velocity field and eddy field calculation results can be improved; by coupling the internal flow field information with indicators such as water cut and recovery rate, a quantitative evaluation of the gas-water synergistic displacement effect of fractured-vuggy reservoirs can be achieved. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the experimental apparatus of the present invention.

[0015] Figure 2 This is a schematic diagram of the transparent slit model structure.

[0016] Figure 3 This is an overall flowchart of the method of the present invention.

[0017] Figure 4 The diagram shows the local liquid phase velocity field and eddy field of the transparent slit model.

[0018] The annotations in the attached figures are explained as follows: 1. Transparent slit model; 2. Inlet; 3. Outlet; 4. Immersion tank and external matching liquid; 5. Injection fluid pump; 6. Gas phase intermediate container; 7. Liquid phase intermediate container; 8. Inlet pressure sensor; 9. Dual-pulse laser; 10. Sheet light shaping unit; 11. High-speed camera; 12. Temperature control component; 13. Gas-liquid separator; 14. Gas flow meter; 15. Outlet pressure sensor; 16. Production fluid pump. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0020] Example 1: An experimental device for visualizing the gas-water synergistic displacement flow field in fractured-vuggy reservoirs based on fluorescence PIV technology like Figure 1 As shown, this embodiment provides a visualization experimental device for gas-water synergistic displacement flow field in fractured-vuggy reservoirs based on fluorescence PIV technology, including a transparent fractured-vuggy model 1, an immersion tank and external matching liquid 4, an injection fluid pump 5, a dual-pulse laser 9, a sheet light shaping unit 10, a high-speed camera 11, a temperature control component 12, a gas-liquid separator 13, a gas flow meter 14, an outlet pressure sensor 15, and a produced fluid pump 16.

[0021] The transparent fracture-cavity model 1 has an inlet 2 and an outlet 3, used to characterize the fracture-cavity combination reservoir space structure of fracture-cavity type reservoirs. Preferably, as shown in the figure... Figure 2 As shown, the transparent slit model 1 is made of transparent material and can adopt a modular structure to simulate different combinations of slit shapes, scale parameters, and connectivity relationships. The transparent slit model 1 forms a visualized flow channel for fluid flow, enabling flow field observation and analysis during the gas-water co-displacement process.

[0022] The immersion tank and external matching liquid 4 are used to contain the transparent slit model 1 and provide an external refractive index matching environment. The transparent slit model 1 is completely immersed in the immersion tank and external matching liquid 4 to reduce the refractive offset and imaging distortion when the laser passes through the model boundary, and to improve the measurability of the liquid flow field near the boundary of the complex slit.

[0023] The injection fluid pump 5 is connected to the inlet 2 of the transparent slit model 1 and is used to inject gaseous and liquid fluids into the transparent slit model 1. Preferably, the injection fluid pump 5 includes a gaseous intermediate container 6, a liquid intermediate container 7, and an inlet pressure sensor 8. The gaseous intermediate container 6 is used to temporarily store or stabilize the gaseous fluid, the liquid intermediate container 7 is used to temporarily store the liquid fluid, and the inlet pressure sensor 8 is used to monitor the pressure change at the injection end in order to obtain inlet pressure data during the experiment.

[0024] The dual-pulse laser 9, the sheet light shaping unit 10, and the high-speed camera 11 together constitute the optical measurement section. The laser emitted by the dual-pulse laser 9 is shaped into a laser sheet light by the sheet light shaping unit 10 and then illuminates the measurement plane inside the transparent slit model 1. The high-speed camera 11 is used to acquire image sequences of fluorescent tracer particles within the measurement plane to obtain motion information of the liquid phase flow field.

[0025] The temperature control component 12 is used to control the temperature of the experimental environment where the transparent slit model 1, the immersion tank, and the external matching liquid 4 are located, so as to maintain the refractive index matching state between the transparent slit model material, the liquid phase fluid, and the external matching liquid, and improve the stability and repeatability of the experimental conditions.

[0026] The gas-liquid separator 13, gas flow meter 14, outlet pressure sensor 15, and produced fluid pump 16 together constitute the outlet back pressure and production metering section. The gas-liquid separator 13 is used to separate the produced fluid into gas and liquid components, the gas flow meter 14 is used to measure the produced gas flow rate, the outlet pressure sensor 15 is used to monitor changes in outlet pressure, and the produced fluid pump 16 is used to transport the produced fluid to subsequent collection or processing units. During the experiment, image data, pressure data, flow data, and production metering data can be synchronously recorded and analyzed by an external data acquisition and processing terminal.

[0027] In this embodiment, the refractive index of the transparent slit model material is denoted as . The refractive index of a liquid fluid is denoted as The refractive index of the external matching liquid in the immersion tank and external matching liquid 4 is denoted as . Preferably, to reduce the refraction shift and imaging distortion when the laser passes through the model boundary, the following relationship is satisfied: ; ; ; Preferably, fluorescent tracer particles are added to the liquid phase fluid, but not to the gas phase fluid. The fluorescent tracer particles are preferably fluorescent microspheres dispersed in the liquid phase fluid, with their particle size and concentration selected according to the PIV velocimetry requirements to ensure image signal quality and velocity field solution accuracy.

[0028] Example 2: A Visual Evaluation Method for Gas-Water Synergistic Displacement Flow Field in Fractured-Void Reservoirs Based on Fluorescent PIV Technology Based on the experimental setup described in Example 1, this example provides a visualization evaluation method for the gas-water synergistic displacement flow field of fractured-vuggy reservoirs based on fluorescence PIV technology. Figure 3 As shown, the method includes the following steps: S1. Establish an optical correction visualization experimental platform.

[0029] In this step, a transparent slit model 1 is first prepared and placed in an immersion tank and an external matching liquid 4 to construct a visualization experimental platform. Subsequently, the refractive indices of the transparent slit model material, the liquid phase fluid, and the external matching liquid are matched to reduce image distortion caused by boundary refraction. Simultaneously, the experimental environment is light-shielded, and a temperature control component 12 is used to maintain a constant experimental temperature to ensure stable refractive index matching.

[0030] S2. Perform flow-adaptive injection parameter calculation.

[0031] In this step, the feature scales of the transparent slit model 1 are extracted, and based on the fluid density difference... interfacial tension Liquid phase viscosity Gravitational acceleration and geometric feature scale Calculate the Bond number Its expression is: ; Injection rate calculation and injection parameter control are performed based on the results of the main flow mechanism judgment. Preferably, when At that time, in capillary numbers The dominant control parameter is: ; when At that time, according to Froude's number The dominant control parameter is: ; when At that time, combined capillary number With Froude Determine the injection parameters, where, This refers to the feature injection speed.

[0032] S3. Conduct gas-water synergistic displacement and collect multi-dimensional data.

[0033] In this step, gaseous and liquid phase fluids are injected into the transparent slit model 1 via injection pump 5 to conduct a gas-liquid synergistic displacement experiment. During the experiment, PIV images are acquired using a dual-pulse laser 9, a sheet light shaping unit 10, and a high-speed camera 11. Simultaneously, the metering data of the produced fluid, including gas flow rate, liquid output, and outlet pressure, are recorded using a gas-liquid separator 13, a gas flow meter 14, an outlet pressure sensor 15, and an output fluid pump 16.

[0034] S4. Perform data processing and flow field calculation.

[0035] In this step, the acquired liquid phase images are first preprocessed, including background subtraction, image enhancement, and removal of abnormal light spots. Then, gas phase regions in the images are identified and a gas phase mask is generated to eliminate reflection and scattering interference from the gas-liquid interface. Finally, PIV cross-correlation calculations are performed on the processed liquid phase images at adjacent time points to obtain the liquid phase velocity field, and the vorticity field and related flow field parameters are further calculated based on the liquid phase velocity field. Figure 4 As shown, the local liquid phase velocity field and vorticity field results of the transparent slit model can be obtained.

[0036] S5. Conduct a coordinated quantitative evaluation of macro and micro levels.

[0037] In this step, representative parameters are extracted from the velocity field, eddy field, and production dynamics, and parameter correlation analysis is conducted to achieve a macro- and micro-level synergistic evaluation of the gas-water co-displacement process. Preferably, the eddy current displacement efficiency index is calculated based on the liquid phase velocity field, eddy field, injection pressure, and injection flow rate. Its expression is: ; in, For the observation area, For position At the moment vorticity. For fluid density, For position At the moment fluid velocity vector modulus, To inject pressure, To inject traffic.

[0038] Furthermore, Curve of change over time and moisture content and recovery rate The dynamic change curves were correlated to characterize the degree of utilization of remaining oil during gas-water synergistic displacement. Among these, the recovery rate... Calculate using the following formula: ; Moisture content Calculate using the following formula: ; in, To accumulate oil production volume, This represents the oil phase volume in the original model. This represents the cumulative water production volume.

[0039] when When the changes in oil recovery rate or water cut show a corresponding relationship, it can be considered that local eddies and entrainment have a promoting effect on the utilization of remaining oil.

Claims

1. A visualization experimental device for gas-water synergistic displacement flow field in fractured-vuggy reservoirs based on fluorescence PIV technology, characterized in that, It includes a transparent slit model, an immersion tank and external matching liquid, an injection fluid pump, a dual-pulse laser, a sheet light shaping unit, a high-speed camera, a temperature control component, an outlet back pressure and output metering component, and a data acquisition and processing component. The transparent fracture-cavity model has an inlet and an outlet, used to characterize the fracture-cavity combination reservoir space structure of fracture-cavity reservoirs. The transparent fracture-cavity model is completely immersed in the immersion tank and the external matching liquid. The injection fluid pump is connected to the inlet of the transparent fracture-cavity model and is used to inject gaseous and liquid phase fluids into the transparent fracture-cavity model for gas-drive, water-drive, or gas-water synergistic displacement experiments. The laser emitted by the dual-pulse laser is formed into a laser sheet beam by the sheet beam shaping unit and illuminates the internal measurement plane of the transparent fracture-cavity model. The high-speed camera is used to acquire image sequences of the liquid phase flow field inside the transparent fracture-cavity model. Fluorescent tracer particles are added to the liquid phase fluid, but no fluorescent tracer particles are added to the gaseous phase fluid. The temperature control component is used to control the temperature of the transparent slit model, the liquid fluid, and the external matching liquid to maintain the refractive index matching state between the transparent slit model material, the liquid fluid, and the external matching liquid; The outlet back pressure and output metering component is connected to the outlet of the transparent slit model to control the outlet pressure and to separate, monitor, and transport the output fluid. The data acquisition and processing component is connected to the injection fluid pump, the dual-pulse laser, the high-speed camera, the temperature control component, and the outlet back pressure and output metering component to simultaneously acquire image data, pressure data, flow data, and output data, and to calculate the liquid phase velocity field based on the image sequence.

2. The experimental apparatus according to claim 1, characterized in that, The refractive index of the material of the transparent slit model is... The refractive index of the liquid fluid is The refractive index of the external matching liquid is And satisfy: ； ； 。 3. The experimental apparatus according to claim 1, characterized in that, The transparent slit model adopts a modular structure, including an upper cover plate, an intermediate flow channel layer, and a lower base plate. The intermediate flow channel layer is a replaceable flow channel layer, used to construct internal flow channels with different slit combinations, scale parameters, and connectivity relationships. The fluorescent tracer particles in the liquid phase fluid are fluorescent microspheres.

4. The experimental apparatus according to claim 1, characterized in that, The injection fluid pump includes a gas phase intermediate container, a liquid phase intermediate container, and an inlet pressure sensor. The gas phase intermediate container is used to temporarily store or stabilize the gas phase fluid, the liquid phase intermediate container is used to temporarily store the liquid phase fluid, and the inlet pressure sensor is used to monitor changes in the injection end pressure.

5. The experimental apparatus according to claim 1, characterized in that, The outlet back pressure and output metering assembly includes a gas-liquid separator, a gas flow meter, an outlet pressure sensor, and a produced fluid pump. The gas-liquid separator is used to separate the produced fluid into gas and liquid components. The gas flow meter is used to measure the flow rate of the produced gas. The outlet pressure sensor is used to monitor changes in outlet pressure. The produced fluid pump is used to transport the produced fluid to a subsequent collection or processing unit.

6. A method for visually evaluating the gas-water synergistic displacement flow field in a fractured-vuggy reservoir based on the experimental apparatus described in any one of claims 1 to 5, characterized in that, The experiment includes the following steps: S1. Establish an optical correction visualization experimental platform, place the transparent slit model in an immersion tank and an external matching liquid, and perform refractive index matching on the transparent slit model material, liquid phase fluid, and external matching liquid, while controlling the experimental environment temperature; S2. Extract the characteristic scale of the transparent slit model, perform flow-adaptive injection parameter calculation, and determine the injection parameters based on the dominant flow mechanism; S3. Inject gaseous and liquid phase fluids into the transparent slit model, conduct gas-water synergistic displacement experiments, and simultaneously collect PIV image data and output measurement data. S4. Preprocess the acquired images to generate a vapor phase mask and remove its interference. Perform PIV cross-correlation calculation on the processed images to obtain the liquid phase velocity field and eddy field. S5. Calculate the eddy current oil displacement efficiency index based on the liquid phase velocity field, eddy field, injection pressure and injection flow rate, and perform macro-micro synergistic quantitative evaluation in combination with water cut and recovery rate.

7. The evaluation method according to claim 6, characterized in that, In step S2, based on the fluid density difference interfacial tension Liquid phase viscosity Gravitational acceleration and geometric feature scale Calculate the Bond number Its expression is: ； when At that time, in capillary numbers The dominant control parameter is: ； when At that time, according to Froude's number The dominant control parameter is: ； when At that time, combined capillary number With Froude Determine the injection parameters; where, This refers to the feature injection speed.

8. The evaluation method according to claim 6, characterized in that, The image preprocessing in step S4 includes background subtraction, image enhancement, and abnormal spot removal; the gas phase mask is generated by identifying gas phase regions in the image; the PIV cross-correlation calculation is performed using a multi-step iterative cross-correlation method, and the obtained vector field is subjected to pseudo-vector elimination and smoothing to obtain the liquid phase velocity field; the vorticity field is calculated from the liquid phase velocity field.

9. The evaluation method according to claim 6, characterized in that, The eddy current oil displacement efficiency index in step S5 Calculate using the following formula: ； in, For the observation area, For position At the moment vorticity. For fluid density, For position At the moment fluid velocity vector modulus, To inject pressure, To inject traffic.

10. The evaluation method according to claim 9, characterized in that, In step S5, the aforementioned Curve of change over time and moisture content and recovery rate The dynamic change curves were correlated to characterize the degree of utilization of remaining oil during gas-water synergistic displacement; among them, the recovery rate Calculate using the following formula: ； Moisture content Calculate using the following formula: ； in, To accumulate oil production volume, This represents the oil phase volume in the original model. This represents the cumulative water production volume.

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