Method for measuring saturation of fracture two-phase flow based on light transmission method and lis model

Abstract

The application provides a kind of fissure two-phase flow saturation measurement method based on light transmission method and LIS model, comprising: establishing the light transmission method detection system comprising uniform backlight illumination system, two-dimensional fissure device and high-precision CCD camera, constructing LIS model library suitable for fissure, obtaining the light intensity value matrix of two-dimensional fissure device filled with water and injected target fluid by light transmission method detection system, as background light intensity and process light intensity respectively;According to the type of two-phase flow system, select the corresponding LIS model and input the background light intensity and process light intensity, and the absolute saturation of each spatial position in the two-phase flow system fissure at the corresponding time is obtained by inversion, based on the saturation result, combined with the geometric parameters of two-dimensional fissure device, the total volume of specified fluid phase in fissure is obtained. By combining the light transmission method detection system with the LIS model suitable for fissure, the accurate solution of the saturation and volume of fluid phase in fissure is solved.

Description

Technical Field

[0001] This invention relates to the field of groundwater pollution monitoring technology, and in particular to a method for measuring the saturation of fractured two-phase flow based on optical transmission method and LIS model. Background Technology

[0002] With the continuous expansion of industrial activities, the problem of organic pollution in groundwater is becoming increasingly serious. In particular, the transport patterns and remediation of non-aqueous liquid pollutants in fractured aquifers have become a hot topic and a challenge in the field of environmental hydrogeology both domestically and internationally. Compared with porous media, fractured media have a complex structure and a high degree of randomness, which makes the study of pollutant transport mechanisms in them extremely challenging.

[0003] In this study, fluid saturation is an indispensable key parameter for quantitatively characterizing the content, distribution, and two-phase transport of pollutants. However, accurately measuring fluid saturation in fractured media remains a technical challenge. Among numerous indoor monitoring methods, optical transmission methods demonstrate great application potential due to their non-destructive, efficient, safe, and low-cost advantages. The core challenge of this technology lies in how to reliably convert easily measurable light intensity information into the required fluid saturation data.

[0004] Currently, the development of light transmission techniques faces significant limitations and gaps. Existing research, such as Niemet et al. (2001), pioneered the establishment of a light transmission system for water / gas two-phase flow and proposed five saturation calculation models, laying the foundation for this method. Subsequent researchers, such as O'Carroll et al. (2007) and Bob et al. (2008), attempted to apply such models to NAPL (Non-Aqueous Phase Liquid) / water two-phase systems, but these attempts suffered from problems such as unverified model parameters, failure to consider the light absorption effect of dyes, or an excessive number of model parameters that were difficult to obtain.

[0005] Crucially, all the aforementioned optical transmission models are designed and developed for porous media. Currently, there is a lack of publicly available literature and technologies specifically applicable to quantitative measurement models of two-phase flow saturation using optical transmission methods for fractured media. For example, Chinese patent application CN103913429A discloses a method for quantitatively measuring fluid saturation in two-phase flow within porous media using optical transmission. This method provides LIS (Light Intensity–Saturation Model) models suitable for gas / water two-phase systems and NAPL / water two-phase systems in porous media, and also provides a two-dimensional porous device suitable for measuring the saturation of porous liquids. The liquid saturation in the pores is measured through the combined action of the two-dimensional porous device and the LIS model suitable for porous media.

[0006] Because fractured media differ fundamentally from porous media in terms of structural scale and fluid transport patterns, directly applying porous media models to fractured media will introduce significant errors, leading to insufficient measurement accuracy. For example, Chinese Patent CN103913429A discloses a method for quantitatively measuring fluid saturation in two-phase flow within porous media using optical transmission, but the combination of a two-dimensional pore device and a LIS model cannot accurately measure liquid saturation in fractures.

[0007] Therefore, a special optical transmission method for measuring fractured media is needed to fill the gap in existing technology, achieve high-precision and high-resolution quantitative inversion of the saturation and volume of two-phase fluids within fractures, and provide a reliable technical tool for scientific research and engineering management in related fields. Summary of the Invention

[0008] This invention proposes a method for measuring the saturation of two-phase flow in fractures based on optical transmission and a LIS model. It innovatively constructs a two-dimensional fracture device specifically for measuring the saturation of two-phase flow in fractures. Based on the specific fracture width within the two-dimensional fracture device, the LIS model, which is only applicable to porous media, is improved and optimized (by setting the fracture width of the two-dimensional fracture device and generalizing a single fracture in the device to a "single pore," that is, reasonably generalizing the LIS model parameter (porosity) applicable to porous media to 1). Under the combined action of the two-dimensional fracture device and the improved LIS model, the liquid phase saturation of the gas / water two-phase system and the NAPL / water two-phase system in the fracture is measured, and the volume within the fracture device is accurately calculated. Furthermore, to further address fluid saturation measurement under complex environments (water phase staining), an innovative LIS model suitable for measuring the liquid phase saturation of the gas / stained water two-phase system in the fracture device is proposed. Experiments have demonstrated that the two-dimensional fracture device and the LIS model suitable for fractured media can accurately determine the saturation of different liquid phase systems, and at the same time accurately measure the volume of different liquid phases within the fracture device, thus broadening the application range of the optical transmission method.

[0009] This invention provides a method for measuring the saturation of fractured two-phase flow based on optical transmission method and LIS model, the specific steps of which include:

[0010] S1. Establish a light transmission detection system comprising a uniform backlight illumination system, a two-dimensional fracture device, and a high-precision CCD camera; wherein, the uniform backlight illumination system is used to provide a uniform and stable surface light source; the two-dimensional fracture device is disposed in the optical path of the uniform backlight illumination system to simulate fractured media and provide a fluid transport channel; the high-precision CCD camera is disposed on the opposite side of the two-dimensional fracture device to receive the light signal transmitted through the two-dimensional fracture device and convert it into a digital image signal;

[0011] S2. Construct a LIS model library suitable for fractures; wherein, the LIS model library suitable for fractures includes WG-A model and WG-B model applied to water / gas two-phase systems; NW-A and NW-B models applied to NAPL / water two-phase systems; and MWG-A modified model and MWG-B modified model applied to dyed water / gas two-phase systems.

[0012] S3. Obtain the light intensity matrix of the two-dimensional fracture device when it is filled with water using the light transmission detection system, denoted as the background light intensity, with the symbol . I w ;

[0013] S4. Inject the target fluid into the two-dimensional fracture device filled with water phase, and obtain the light intensity matrix at the corresponding time through the optical transmission detection system. This matrix is ​​denoted as the process light intensity, with the symbol . I ;

[0014] S5. Based on the type of two-phase flow system, select the corresponding LIS model for the two-phase flow system, input the background light intensity and the process light intensity into the selected LIS model, and calculate the absolute fluid saturation at each spatial position in the crack of the two-phase flow system at the corresponding time.

[0015] S6. Based on the saturation result, integrate the geometric parameters of the two-dimensional fracture device to obtain the total volume of the specified fluid phase in the fracture.

[0016] Further, the two-dimensional fracture device described in step S1 comprises:

[0017] The structure of the fracture device: The two-dimensional fracture device consists of two parallel sandblasted tempered glass pieces with a rubber pad sandwiched inside, and is fixed by an aluminum frame. The fluid to be tested is injected into the fracture device by a pump. The sandblasting of the tempered glass surface simulates the roughness of a natural fracture, and the thickness of the rubber pad controls the fracture width of the fracture device.

[0018] Hydraulic system of the fracture device: The left and right sides of the device are water-proof boundaries, and the upper and lower ends are constant head boundaries. The water flows vertically from top to bottom. There are three connection holes at the top and bottom, which are connected to form a unified inlet and outlet through a four-way connector. Among them, the left connection hole is connected to the pressure measuring pipe through the extension port of the three-way connector to monitor the inlet and outlet water levels in real time. The middle connection hole is used as a dedicated injection and sampling port for gas or liquid through the extension port of the three-way connector.

[0019] Furthermore, the WG-A model and WG-B model applied to the water / gas two-phase system mentioned in step S2 include:

[0020] The formula for calculating the effective saturation of the WG-A model in a water / gas two-phase system is as follows: The formula for calculating the effective saturation of the WG-B model is: Among them, model parameters , This represents the light intensity value measured when the fracture device contains only residual water. This represents the light intensity value measured when the fissure device is filled with water.

[0021] Furthermore, the NW-A and NW-B models applied to the NAPL / water two-phase system mentioned in step S2 include:

[0022] The formula for calculating the effective saturation of the NW-A model in the NAPL / water two-phase system is as follows: The formula for calculating the effective saturation of the NW-B model is: Among them, model parameters , This represents the light intensity value measured when the slit device is filled with NAPL. This represents the light intensity value measured when the fissure device is filled with water.

[0023] Furthermore, the MWG-A and MWG-B correction models applied to the staining water / air two-phase system described in step S2 include:

[0024] The formula for calculating the effective saturation of the MWG-A modified model in a dyed water / air two-phase system is as follows: The formula for calculating the effective saturation of the MWG-B modified model is as follows: Among them, model parameters , This represents the light intensity value measured when the slit device is filled with gas. This represents the light intensity value measured when the slit device is filled with dyed water.

[0025] Furthermore, the method for calculating light intensity is as follows: ,in, Indicates the intensity of the incident light source. This indicates the medium present within the fracture device. Indicates medium thickness, Medium The light absorption coefficient, Optical geometric parameters representing the difference in light intensity between the emission point and the observation point. It means that light passes through a phase. , Transmittance of the interface; transmittance The calculation formula is ,in, Represents matter i refractive index, Represents matter k The refractive index.

[0026] Furthermore, the water phase color state described in step S3 is either stained or unstained; wherein, the water phase color is determined by the two-phase system to be tested.

[0027] Furthermore, the method for calculating the absolute saturation of the fluid in step S5 is as follows:

[0028] The formula for calculating the absolute saturation of water is: ,in, S w Indicates the effective saturation of the aqueous phase. Indicates the residual saturation of the aqueous phase;

[0029] The formula for calculating the absolute saturation of the non-aqueous phase is: ,in, This indicates the effective saturation of a specified fluid phase X in the fracture device.

[0030] Furthermore, the formula for calculating the total volume of the specified fluid phase within the fracture in step S6 is as follows: Where X represents one of the NAPL or gaseous-fluid phases; Indicates the absolute saturation of the non-aqueous phase. This represents the area per pixel unit. Indicates the spatial location of the fracture device ， The width of the crack, i.e., the actual width of the crack. and These represent the number of pixels in the horizontal and vertical directions of the entire rift device, respectively.

[0031] Furthermore, the formula for calculating the actual width of the crack is as follows: ,in This indicates any spatial location within the fracture device when the medium is pure water. ， The light intensity value on; This indicates any spatial location within the fracture device when the medium is a liquid of a certain solute concentration. ， The light intensity value on the screen; <> represents all spatial locations. ， The upper statistical mean; Indicates the spatial location of the fracture device ， The statistical mean is numerically equal to the average crack width; where the average crack width is... The calculation formula is In the formula, This indicates the mass of the fluid injected into the fracture. This indicates the density of the injected fissure fluid. and These represent the length and width of the fracture device, respectively.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] 1) It achieves high-precision, in-situ inversion of fluid saturation in fractures that cannot be directly measured. The calculated values ​​of the model are in high agreement with the measured values, and the linear correlation coefficient generally reaches above 0.99.

[0034] 2) It has high spatiotemporal resolution, can dynamically depict the fluid migration law in the fracture, can provide pixel-level saturation distribution map, and continuously monitor dynamic processes such as fluid front and path selection.

[0035] 3) The method is robust, the model is universal and the parameters are simple. The same method is applicable to different two-phase systems such as water / air and NAPL / water. It can also be adapted to special conditions such as dyed water by modifying the model. The core model parameters are few and easy to obtain. At the same time, it can further expand the application of NAPL / dyed water two-phase system in pores or cracks.

[0036] 4) The application scope of the model has been expanded, a quantitative model applicable to fractured media has been verified and developed, the porous media model has been successfully applied to fractured media, and a new LIS model has been innovatively established for special conditions.

[0037] 5) It provides quantitative analysis from local to global perspectives, not only providing local saturation but also accurately calculating the total volume of fluid within the entire fracture through integration. Attached Figure Description

[0038] Figure 1 The flowchart illustrates the steps of the method for measuring the saturation of fractured two-phase flow based on optical transmission method and LIS model provided in this embodiment of the invention.

[0039] Figure 2 This is a schematic diagram of the optical transmission detection system device provided in an embodiment of the present invention.

[0040] Figure 3 This is a schematic diagram illustrating the changes in light intensity at different times during the gas injection process of the two-dimensional fracture device, as provided in an embodiment of the present invention.

[0041] Figure 4 A comparison chart of the results of the improved water / gas two-phase LIS model provided in the embodiments of the present invention and experimental data.

[0042] Figure 5A schematic diagram showing the change in light intensity corresponding to the gas saturation in the fractured medium calculated by the improved WG-A model provided in this embodiment of the invention.

[0043] Figure 6 Comparison of light intensity changes caused by gas injection in Examples 2 and 3 of this invention.

[0044] Figure 7 This is a comparison chart of the calculation results and measured data of the improved water / gas two-phase LIS model provided in the embodiments of the present invention.

[0045] Figure 8 A comparison chart of the calculation results and measured data of the MWG-A and MWG-B correction models provided in the embodiments of the present invention.

[0046] Figure 9 The diagram shows the light intensity variation at different times during the TCE injection process of the two-dimensional fracture device, as provided in the embodiments of the present invention.

[0047] Figure 10 A diagram showing the bottom gap width distribution of a two-dimensional crack device provided in an embodiment of the present invention.

[0048] Figure 11 This is a comparison chart of the calculation results and measured data of the NAPL / water two-phase LIS model provided in the embodiments of the present invention.

[0049] Figure 12 The light intensity distribution diagram corresponding to the gas saturation in the fractured medium is obtained by calculating the improved model NW-A provided in the embodiments of the present invention.

[0050] Figure 13 The graph shows the light intensity variation corresponding to the TCE (trichloroethylene) saturation calculated by model NW-B and model NW-A in the embodiments of the present invention. Detailed Implementation

[0051] To enable those skilled in the art to better understand the technical solutions in this specification, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this specification, and not all embodiments. Based on the embodiments in this specification, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this specification.

[0052] Please see Figure 1 , Figure 1 A flowchart illustrating the steps of the fracture two-phase flow saturation measurement method based on optical transmission method and LIS model provided in this embodiment of the invention includes the following steps:

[0053] S1. Establish a light transmission detection system comprising a uniform backlight illumination system, a two-dimensional fracture device, and a high-precision CCD camera; wherein, the uniform backlight illumination system is used to provide a uniform and stable surface light source; the two-dimensional fracture device is disposed in the optical path of the uniform backlight illumination system to simulate fractured media and provide a fluid transport channel; the high-precision CCD camera is disposed on the opposite side of the two-dimensional fracture device to receive the light signal transmitted through the two-dimensional fracture device and convert it into a digital image signal;

[0054] S2. Construct a LIS model library suitable for fractures; wherein, the LIS model library suitable for fractures includes WG-A model and WG-B model applied to water / gas two-phase systems; NW-A and NW-B models applied to NAPL / water two-phase systems; and MWG-A modified model and MWG-B modified model applied to dyed water / gas two-phase systems.

[0055] S3. Obtain the light intensity matrix of the two-dimensional fracture device when it is filled with water using the light transmission detection system, denoted as the background light intensity, with the symbol . I w ;

[0056] S4. Inject the target fluid into the two-dimensional fracture device filled with water phase, and obtain the light intensity matrix at the corresponding time through the optical transmission detection system. This matrix is ​​denoted as the process light intensity, with the symbol . I ;

[0057] S5. Based on the type of two-phase flow system, select the corresponding LIS model for the two-phase flow system, input the background light intensity and process light intensity into the selected LIS model, and calculate the absolute fluid saturation at each spatial location in the two-phase flow system at the corresponding time.

[0058] S6. Based on the saturation result, integrate the geometric parameters of the two-dimensional fracture device to obtain the total volume of the specified fluid phase in the fracture.

[0059] In one specific embodiment of this example, the light transmission detection system includes:

[0060] A schematic diagram of the light transmission detection system is shown below. Figure 2 As shown, the light transmission method detection system includes a uniform backlight illumination system, a two-dimensional slit device, and a high-precision CCD camera; wherein the optical axes of the uniform backlight illumination system, the two-dimensional slit device, and the high-precision CCD camera are kept coaxially aligned; the specific components are as follows:

[0061] Uniform backlighting system, the light box in the system (see attached) Figure 2d) serves as the sole light source, located 12.5 cm to one side of the slit device. It is powered by parallel-distributed LEDs, providing a uniform and stable surface light source. The light source's uniformity is ensured by a diffuser plate. (See Appendix for details on the two-dimensional slit device.) Figure 2 (b) is placed in the optical path of the uniform backlighting system, forming a whole with the wooden dark box, to simulate fractured media and provide a fluid transport channel; a high-precision CCD camera (see appendix) Figure 2 a) is placed in a wooden dark box integrated with the fissure device, 1.8m away from the fissure device, and is connected to a computer (see Appendix). Figure 2 The connection in section e) is used to receive light transmitted through the slit and automatically record the light source intensity using the software Maxim DL (Ottawa, ON); during the experiment, a syringe pump (LSP01-2A, Baoding Lange Constant Flow Pump Co., Ltd.) or a peristaltic pump (see attached) is used. Figure 2 c) (Longer Pump, BT100-1F) injects TCE or gas into the fracture device.

[0062] In one specific embodiment of this example, the absolute saturation calculation process in the fracture device includes:

[0063] Selecting the LIS model corresponding to the liquid phase system: In this embodiment of the invention, different LIS models are proposed for water / gas two-phase systems, NAPL / water two-phase systems, and dyed water / gas two-phase systems. The effective saturation of the liquid phase is calculated through the LIS model.

[0064] The LIS models applied to water / gas two-phase systems include the WG-A model and the WG-B model. The effective saturation calculation formula for the WG-A model is shown in equation (1), and the effective saturation calculation formula for the WG-B model is shown in equation (2).

[0065] (1)

[0066] (2)

[0067] In the formula, model parameters , This represents the light intensity value measured when the slit device is filled with gas or residual water. This represents the light intensity value measured when the fracture device is filled with water.

[0068] The LIS models applied to the NAPL / water two-phase system include the NW-A model and the NW-B model. The effective saturation calculation formula for the NW-A model is shown in equation (3), and the effective saturation calculation formula for the NW-B model is shown in equation (4).

[0069] (3)

[0070] (4)

[0071] In the formula, model parameters , This represents the light intensity value measured when the slit device is filled with NAPL. This represents the light intensity value measured when the fracture device is filled with water.

[0072] The LIS models applied to the staining water / air two-phase system include the MWG-A correction model and the MWG-B correction model. The effective saturation calculation formula for the MWG-A correction model is shown in equation (5), and the effective saturation calculation formula for the MWG-B correction model is shown in equation (6).

[0073] (5)

[0074] (6)

[0075] In the formula, model parameters , This represents the light intensity value measured when the slit device is filled with gas. This represents the light intensity value measured when the slit device is filled with dyed aqueous phase.

[0076] Calculate the corresponding light intensity value in the LIS model parameters. The formula for calculating light intensity is shown in equation (7):

[0077] (7)

[0078] In the formula, Indicates the intensity of the incident light source. This indicates the medium present within the fracture device. Indicates medium thickness, Indicates medium The light absorption coefficient, Optical geometric parameters representing the difference in light intensity between the emission point and the observation point. It means that light passes through a phase. i, k Transmittance of the interface;

[0079] transmittance The calculation formula is shown in equation (8):

[0080] (8)

[0081] In the formula, Represents matter refractive index, Represents matter The refractive index.

[0082] Based on the calculated effective saturation, the absolute saturation of the fluid is further calculated. The formula for calculating the absolute saturation of the aqueous phase is shown in equation (9), and the formula for calculating the absolute saturation of the non-aqueous phase is shown in equation (10).

[0083] (9)

[0084] In the formula, Indicates the residual saturation of the aqueous phase. S w Indicates the effective saturation of the aqueous phase;

[0085] (10)

[0086] In the formula, Indicates a specified substance in a fracture device X Effective saturation.

[0087] In one specific embodiment of this example, the process of calculating the total volume of the fluid phase within the fracture includes:

[0088] Obtain the absolute saturation of the fluid phase in the fracture device .

[0089] Calculate the average crack width: After completing the crack device installation, use a peristaltic pump to pump in a certain amount of deionized water at a rate of 10 mL / min; after saturation, drain the water completely naturally and weigh the volume of the drained water; repeat the above operation multiple times, and take the average of the drainage volumes as the crack volume. This volume is the volume of free water that can flow freely in the crack medium, ignoring the thin film water bound to the crack surface. The crack volume is used to calculate the average crack width, that is, divide the measured volume by the length and width of the crack. The formula for calculating the average crack width is shown in equation (11):

[0090] (11)

[0091] In the formula, M Indicates the mass of the fluid injected into the fracture; ρ This indicates the density of the fluid injected into the fracture. L and w These represent the length and width of the fracture device, respectively.

[0092] The true width of the crack is calculated using the formula (12):

[0093] (12)

[0094] In the formula, This indicates any spatial location within the fracture device when the medium is pure water. ， The light intensity value on; This indicates any spatial location within the fracture device when the medium is a liquid of a certain solute concentration. ， The light intensity value on; Indicates the spatial location of the fracture device ， The width above, i.e., the actual width of the crack; <> represents all spatial locations. ， The upper statistical mean; Indicates the spatial location of the fracture device ， The statistical mean is numerically equal to the average gap width.

[0095] The total volume of the fluid phase within the fracture is calculated using the formula (13):

[0096] (13)

[0097] In the formula, X It represents one of the following fluid phases: water, NAPL, or gaseous fluid. Indicates fluid phase absolute saturation, This represents the area per pixel unit. This represents the actual width of the crack. and These represent the number of pixels in the horizontal and vertical directions of the entire rift device, respectively.

[0098] To further verify the applicability of the LIS model for calculating different liquid phase saturations in fractures, and to verify the accuracy of the liquid phase volume calculation within the fracture device, this invention is validated and analyzed through specific embodiments.

[0099] Example 1

[0100] This embodiment verifies the correctness of the WG-A and WG-B models applied to the fractured water / gas two-phase system by conducting an air injection test on a two-dimensional fracture device and comparing the results with the experimental results. At the same time, the corresponding liquid volume inside the fracture device is calculated.

[0101] Step 1: Experimental Preparation

[0102] Assemble and debug the light transmission method detection device, prepare 5L of distilled water that has been aerated with air for 24 hours, and a high-sensitivity electronic scale.

[0103] Step 2, Light Intensity Measurement

[0104] Before the gas injection fracture device test began, 5L of distilled water, which had been aerated with air for 24 hours, was pumped into the saturated fracture device at a flow rate of 5 mL / min using a peristaltic pump to completely replace the original distilled water and eliminate interference from dissolved gases. At the same time, a high-precision CCD camera was used to record the reference light intensity value of the saturated fracture device in the saturated state. I w ).

[0105] During the gas injection process, air was injected from the gas injection port at the center of the bottom of the fracture device at a rate of 1 mL / min under static water conditions using a syringe pump until all free water in the water-saturated fracture medium was discharged. During this process, the mass of water discharged from the fracture device at different times was measured using a high-sensitivity electronic balance to obtain the measured value of the gas phase volume. Simultaneously, a high-precision CCD camera was used to record the changes in light intensity during the two-dimensional fracture device process at different times (e.g., ...). Figure 3 As shown), where, Figure 3 (a), (b), (c), (d), (e), and (f) in the figure correspond to the light intensity images of the two-dimensional fracture device at different times. The shooting interval of the CCD camera is set to 10 seconds during the gas injection process and adjusted to 10 minutes during the resting process after the injection is completed.

[0106] Step 3: Saturation Calculation

[0107] Based on the above formulas (1), (2), (7), (8), (9), and (10), calculate the absolute saturation of the liquid phase in the fractured water / gas two-phase system.

[0108] Step 4: Calculation of liquid phase volume in the fractured water / gas two-phase system

[0109] Based on the obtained absolute saturation, the liquid phase volume in the fractured water / gas two-phase system was calculated using equations (11), (12), and (13) above. In the experiment, a 1 mm thick rubber pad was used to control the fracture width on a scale of approximately 1 mm. The calculation results of the fracture volume and average fracture width are shown in Table 1.

[0110] Table 1. Statistics on volume and gap width of the fractured water / gas two-phase system

[0111]

[0112] Validation and analysis of LIS model for fractured water / gas two-phase system

[0113] ① Generalization and Rationality Analysis: During the water / gas two-phase system experiment, it was found that the gas injected into the fracture device mainly migrated upward rapidly in the form of bubbles (see...). Figure 3(c), (d), and (e) in the diagram ultimately resulted in a continuous gas distribution at the top of the fracture device, but a continuous lateral migration path failed to form. Simultaneously, during the gas injection process, abrupt changes in light intensity were detected at local pixels (see [link to diagram]). Figure 3 (e) and (f) in the text) This phenomenon may be related to the gravitational migration or vaporization of the water film on the fracture surface. When applying the water / gas two-phase LIS model, to simplify the model, only the light intensity change caused by rapid displacement of the water / gas phases is considered (see [reference]). Figure 3 In (d) of the equation, the phenomenon of sudden changes in light intensity is not considered. Based on this condition, the statistical mean of the model parameter C1 for the fractured medium, calculated from experimental data, is 0.9434. Simultaneously, based on the principle of light transmission, the fractured medium is generalized to a porous medium with a pore number k=1. The theoretical value of C1 calculated based on this physical generalization is 0.9602, which is close to the experimental statistical mean, verifying the rationality of the generalization method.

[0114] ② Model rationality analysis: The calculation results of WG-A and WG-B in the water / air LIS model were compared with the measured values ​​of the drainage. The comparison between the calculated values ​​and the measured values ​​of the water / air LIS model is shown in Table 2, and the comparison relationship is shown in [the table below]. Figure 4 ,in, Figure 4 (a) in the figure is a comparison chart of the predicted and measured values ​​of the WG-A model with the experimental data. Figure 4 (b) in the figure is a comparison of the predicted and measured values ​​of the WG-B model with the experimental data.

[0115] Table 2. Calculated and measured values ​​of the water / air two-phase system using the LIS model.

[0116]

[0117] From Table 2 and Figure 4 As can be seen, the predicted values ​​of both WG-A and WG-B models are in high agreement with the measured values, and the linear correlation coefficients are both as high as 0.9992, further demonstrating the rationality of ignoring the influence of sudden changes in light intensity. Throughout the time series, the model calculation results are slightly lower than the measured values. This error may be due to the fact that the calculation of parameter C1 did not fully consider the slow drainage process of the water film on the fracture surface over time, and the difference between the volume measured by the drainage method and the artificial gas injection displacement method.

[0118] In addition, the image of gas saturation light intensity distribution in the fractured medium calculated based on the WG-A model (see...) Figure 5 ) and measured light intensity image (see Figure 3 By comparing, we found Figure 5 and Figure 3The overall pattern of light intensity changes is consistent, indicating that the gas saturation distribution in the fractured medium calculated based on the water / gas LIS model can effectively reflect the actual light intensity changes in the medium, and the abrupt change in light intensity has no significant impact on the model calculation results. By calculating the difference in saturation obtained from models WG-B and WG-A, it was found that its order of magnitude is 10. -3 This further demonstrates that there is no essential difference between the two water / gas two-phase system LIS models in fractured media applications.

[0119] The above experiments verified that the improved water / air LIS model is suitable for accurate calculation of fracture saturation.

[0120] Example 2

[0121] This embodiment involves changing the color of the aqueous phase and conducting an air injection test on a two-dimensional fracture device. The aqueous phase is an aqueous solution stained with RWT (Rhodamine WT). The effective saturation is calculated using the MWG-A and MWG-B corrected models of the stained water / air two-phase system, while the corresponding liquid phase volume within the fracture device is also calculated.

[0122] Step 1: Experimental Preparation

[0123] Assemble and debug the light transmission method detection device, prepare 5L of distilled water that has been aerated with air for 24 hours and dyed with RWT, and a high-sensitivity electronic scale.

[0124] Step 2, Light Intensity Measurement

[0125] Before the gas injection fracture device test began, 5L of distilled water, which had been aerated with air for 24 hours and dyed with RWT, was pumped into the saturated fracture device at a flow rate of 5 mL / min using a peristaltic pump to completely replace the original dyed water and eliminate interference from dissolved gases. At the same time, a high-precision CCD camera was used to record the reference light intensity value of the saturated fracture device in the saturated state. I w ).

[0126] During the gas injection process, air was injected from the gas injection port at the center of the bottom of the fracture device at a rate of 1 mL / min under static water conditions using a syringe pump until all the dyed free water in the water-saturated fracture medium was discharged. During this process, the mass of water discharged from the fracture device at different times was weighed using a high-sensitivity electronic balance to obtain the measured value of the gas phase volume. At the same time, the light intensity changes of the two-dimensional fracture device at different times were recorded using a high-precision CCD camera. The shooting interval of the CCD camera was set to 10 seconds during the gas injection process and adjusted to 10 minutes during the static period after the injection was completed.

[0127] Step 3: Saturation Calculation

[0128] Based on the above formulas (5), (6), (7), (8), (9), and (10), calculate the absolute saturation of the liquid phase in the dyeing water / air two-phase system.

[0129] Step 4: Calculation of liquid phase volume in the fracture

[0130] Based on the obtained absolute saturation, the liquid phase volume in the water / gas two-phase system with fissure staining was calculated using formulas (11), (12), and (13). In the experiment, a 1 mm thick rubber pad was used to control the fissure width on a scale of 1 mm. The calculation results of fissure volume and average fissure width are shown in Table 3.

[0131] Table 3. Statistics on the volume and gap width of the stained water / gas two-phase system in the crack.

[0132]

[0133] Example 3

[0134] Step 1: Experimental Preparation

[0135] Assemble and debug the light transmission method detection device, prepare 5L of colorless distilled water that has been aerated with air for 24 hours, and a high-sensitivity electronic scale.

[0136] Step 2, Light Intensity Measurement

[0137] Before the gas injection fracture device test began, 5L of colorless distilled water, which had been aerated with air for 24 hours, was pumped into the saturated fracture device at a flow rate of 5 mL / min using a peristaltic pump to completely replace the original water and eliminate interference from dissolved gases. At the same time, a high-precision CCD camera was used to record the reference light intensity value of the saturated fracture device in the saturated state. I w ).

[0138] During the gas injection process, air was injected from the gas injection port at the center of the bottom of the fracture device at a rate of 1 mL / min under static water conditions using a syringe pump until all the dyed free water in the water-saturated fracture medium was discharged. During this process, the mass of water discharged from the fracture device at different times was weighed using a high-sensitivity electronic balance to obtain the measured value of the gas phase volume. At the same time, the light intensity changes of the two-dimensional fracture device at different times were recorded using a high-precision CCD camera. The shooting interval of the CCD camera was set to 10 seconds during the gas injection process and adjusted to 10 minutes during the static period after the injection was completed.

[0139] Step 3: Saturation Calculation

[0140] Based on the above formulas (1), (2), (7), (8), (9), and (10), calculate the absolute saturation of the liquid phase in the water / gas two-phase system.

[0141] Step 4: Calculation of liquid phase volume in the fracture

[0142] Based on the obtained absolute saturation, the liquid phase volume in the fractured water / gas two-phase system was calculated using formulas (11), (12), and (13). In the experiment, a 1 mm thick rubber pad was used to control the fracture width on a scale of approximately 1 mm. The calculation results of the fracture volume and average fracture width are shown in Table 4.

[0143] Table 4. Statistics on volume and gap width of fractured water / gas two-phase systems

[0144]

[0145] Comparing Examples 2 and 3, the changes in the liquid phase after staining in the crack were observed, and the influence of aqueous phase staining on the calculation of liquid saturation was analyzed. The correctness of the MWG-A and MWG-B corrected models applied to the water / gas two-phase system for crack staining was verified through the experimental phenomena and results of Examples 2 and 3.

[0146] Figure 6 The graph shows the changes in light intensity caused by injecting approximately 32 mL of gas in Examples 2 and 3. Figure 6 (a) in the figure is a graph showing the change in light intensity caused by gas injection in Example 2. Figure 6 (b) in the diagram shows the change in light intensity caused by gas injection in Example 3. Figure 6 As can be seen, RWT staining significantly increased the light intensity difference between the aqueous and gas phases. Unlike conventional gas injection experiments, after injecting gas into the stained water and displacing the water in the fractures, the light intensity value in the gas-bearing region actually increased compared to the water-saturated condition. Figure 6 (a) in the figure shows the change in light intensity when gas is injected into colorless water. It can be seen that the gas accumulates in the upper region of the fracture device. The light intensity in this region is slightly lower than that in the lower water-saturated region, with a difference of about 1000 to 2000. Figure 6 Figure (b) shows the light intensity change when gas is injected into the stained water. The light intensity in the gas-filled area is significantly higher than that in the saturated water area, with a difference of 15,000–16,000. This difference in light intensity is caused by the stained water absorbing some light energy, resulting in a decrease in transmitted light intensity. Simultaneously, air itself is colorless, and its absorption of light is negligible, thus contributing to the light intensity difference. The above analysis results indicate that the light intensity contrast between the water and gas phases is significantly improved after RWT staining.

[0147] Example 3: A separate apparatus was used to conduct another gas injection test on the water / gas two-phase system. The saturation calculation model remained the improved WG-A and WG-B models. During the test, the statistical mean of the measured parameter C1 was 0.9682. The model calculation results were compared with the measured values ​​as follows: Figure 7 As shown. Figure 7The results show that the predicted values ​​of the two models, WG-A and WG-B, are very close to the measured values, with a high degree of linear correlation. Furthermore, the calculation results of WG-A and WG-B are almost completely consistent, with the numerical difference only reflected in the second decimal place. The scatter plots almost overlap, further verifying the reliability of the improved water / gas two-phase LIS model.

[0148] Examples 2 and 3 used the same experimental setup. During the experiment, the statistical mean of the measured parameter C3 was 2.1327, significantly different from parameter C1 in Example 1. This indicates that directly using the improved WG-A and WG-B models from Examples 1 or 3 for related calculations will produce substantial errors. This example, based on the principle of light transmission, considers the absorption of light by the dyeing water and ignores gas absorption, further optimizing the improved water / gas two-phase LIS model to obtain the MWG-A and MWG-B corrected models. The corrected models were applied to the dyeing water / gas two-phase system, and the results are as follows... Figure 8 As shown, the calculation results of the MWG-A and MWG-B corrected models are in high agreement with the measured values ​​(R² is 0.9974 for both), and the difference between the two models remains very small. This verifies the correctness of the MWG-A and MWG-B corrected models applied to the crack-stained water / gas two-phase system.

[0149] Example 4

[0150] This embodiment verifies the correctness of the NW-A and NW-B models applied to the fractured NAPL / water two-phase system by conducting a trichloroethylene (a typical NAPL) injection test and comparing the results with actual measurements.

[0151] Step 1: Experimental Preparation

[0152] Assemble and debug the light transmission method detection device, prepare 5L of distilled water that has been aerated with air for 24 hours, a high-sensitivity electronic balance, and trichloroethylene (TCE) stained with Oil Red O.

[0153] Step 2, Light Intensity Measurement

[0154] Before the TCE injection fracture device test began, 5L of distilled water, which had been aerated with air for 24 hours, was pumped into the saturated fracture device at a flow rate of 5 mL / min using a peristaltic pump to completely replace the original distilled water and eliminate interference from dissolved gases. At the same time, a high-precision CCD camera was used to record the reference light intensity value of the saturated fracture device in the saturated state. I w ).

[0155] During the TCE injection process, under static water conditions, TCE was injected from the central injection port at the top of the fracture device using a syringe pump at a rate of 0.5 mL / min, discharging some of the free water within the water-saturated fracture medium. During this process, the mass of water discharged from the fracture device at different times was measured using a high-sensitivity electronic balance to obtain the measured value of the TCE volume. Simultaneously, a high-precision CCD camera was used to record the changes in light intensity during the two-dimensional fracture device process at different times (e.g., ...). Figure 9 As shown), where, Figure 9 (a), (b), (c), and (d) in the image correspond to the light intensity images of the two-dimensional fracture device during the TCE injection process at different times. The shooting interval of the CCD camera is set to 10 seconds during the gas injection process and adjusted to 10 minutes during the resting process after the injection is completed.

[0156] Step 3: Saturation Calculation

[0157] Based on the above formulas (3), (4), (7), (8), (9), and (10), calculate the absolute saturation of the liquid phase in the NAPL / water two-phase system in the fracture.

[0158] Step 4: Calculation of liquid phase volume in the NAPL / water two-phase system

[0159] Based on the obtained absolute saturation, the liquid phase volume in the fractured NAPL / water two-phase system was calculated using formulas (11), (12), and (13). In the experiment, a 1 mm thick rubber pad was used to control the fracture width on a scale of approximately 1 mm. The calculation results of the fracture volume and average fracture width are shown in Table 5.

[0160] Table 5. Statistics on volume and gap width of fractured NAPL / water two-phase system

[0161]

[0162] Validation and analysis of the LIS model for the NAPL / water two-phase system

[0163] ① Analysis of light intensity changes

[0164] CCD images of the TCE injection process, such as Figure 9 As shown. Figure 9 (a) shows that TCE mainly migrates downwards after forming droplets at the injection point; Figure 9 (b) in the diagram illustrates that some of the TCE in the early stages accumulates at the bottom of the unit as a continuous contamination pool, and preferentially accumulates on the left side; Figure 9 (c) in the figure illustrates that as TCE is continuously injected, the water at the bottom of the fracture device that was not displaced in time is further displaced by the subsequent TCE as the contaminated pool rises. Figure 9(d) in the figure shows the change in light intensity after injecting 20 mL of TCE, indicating that some water was still trapped inside the contaminated pool during the displacement process and could not be discharged. This is combined with the distribution diagram of the gap width at the bottom of the device. Figure 10 As can be seen, the gap width on the left side of the bottom of the device is slightly larger than that on the right side, and the TCE preferentially migrates in the area with the larger gap width. The change in light intensity is consistent with the gap width distribution, that is, the light intensity value increases with the increase of the gap width, which is consistent with the light transmission method principle that the change in light intensity is positively correlated with the volume of TCE.

[0165] The TCE-saturated region at the bottom of the fracture device (depth approximately 1.39 cm to 8.38 cm) was selected, and the statistical mean of the measured parameter C2 of the NAPL / water two-phase system was calculated to be 0.7057. The generalized models NW-A and NW-B were applied to this experiment (the generalization process is described in Example 1). Table 6 compares the predicted results of the improved NW-A and NW-B models with the measured values. A comparison of the NAPL / water two-phase LIS model results with the experimental data is shown in Table 6. Figure 11 .

[0166] Table 6 Calculated and measured values ​​of NAPL / water two-phase LIS model

[0167]

[0168] From Table 6 and Figure 11 As can be seen from this, the improved NW-A model (see appendix) Figure 11 (a) in the middle and the NW-B model (see appendix) Figure 11 The results in (b) show only a slight difference in the second decimal place; the NW-A value is slightly larger than the NW-B value, and the predicted values ​​are in high agreement with the measured values ​​(NW-A correlation coefficient 0.9971, NW-B 0.9970). The TCE saturation distribution obtained based on the NW-A model is as follows: Figure 12 As shown, the gas saturation distribution within the fractured medium calculated based on the NW-A model (see...) Figure 12 ) and measured light intensity image (see Figure 9 By comparing, we found Figure 12 and Figure 9 The overall shape of the light intensity change is consistent, which indicates that the gas saturation distribution in the fractured medium calculated based on the NAPL / water two-phase LIS model can effectively reflect the light intensity change in the medium during the actual process.

[0169] The difference in saturation obtained by calculating the model NW-B and NW-A (see...) Figure 13 ), and its magnitude was found to be 10. -2 This further demonstrates that the two NAPL / water two-phase system LIS models show little difference in fractured media applications.

[0170] Accuracy Analysis of Volume Calculation in Cracks

[0171] The accuracy of volume calculation in fractures was analyzed using Examples 1-4. Accurate measurement of fracture volume depends on the reliability of the saturation calculation model and the accuracy of the true fracture width in the fracture device. Examples 2-4 of this invention used the same experimental setup. The analysis of Examples 1-4 has sufficiently verified the accuracy of the LIS models for different liquid phase systems proposed in this invention. The true fracture width is crucial for accurately determining the volume; therefore, the reliability of the true fracture width was analyzed to further determine the reliability of the volume measurement.

[0172] The actual crack width was calculated using the formulas (11) and (12) above. Tables 1, 3, 4, and 5 show the calculation results of the crack volume and average crack width for each of Examples 1-4. From the data in Tables 1, 3, 4, and 5, it can be seen that in each example, the total crack volume was obtained by injecting deionized water into the crack medium. The average crack width obtained by reverse calculation according to the formula fluctuated between 993 and 1086. The average crack width basically matched the designed crack width (the crack width was controlled by a 1mm thick rubber pad in the experiment), indicating that the average crack width obtained by the drainage method was accurate. At the same time, the average crack volume calculated in Examples 2 and 3 was 76.74 mL and 73.48 mL, respectively, further illustrating the accuracy of the actual crack width calculation.

[0173] The accuracy of the saturation calculation model and the true width of the fracture is verified, demonstrating that the method provided by this invention can be effectively applied to the calculation of the saturation of different liquid phases in the fracture and the accurate solution of their volume.

[0174] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A method for measuring the saturation of fractured two-phase flow based on optical transmission method and LIS model, characterized in that, The fractured medium is generalized as a porous medium with a pore number of 1, and the following steps are performed based on the generalization: S1. Establish a light transmission detection system comprising a uniform backlight illumination system, a two-dimensional fracture device, and a high-precision CCD camera; wherein, the uniform backlight illumination system is used to provide a uniform and stable surface light source; the two-dimensional fracture device is disposed in the optical path of the uniform backlight illumination system to simulate fractured media and provide a fluid transport channel; the high-precision CCD camera is disposed on the opposite side of the two-dimensional fracture device to receive the light signal transmitted through the two-dimensional fracture device and convert it into a digital image signal; S2. Based on the generalization, construct a LIS model library suitable for fractures; wherein, the LIS model library suitable for fractures includes WG-A model and WG-B model applied to water / gas two-phase systems; NW-A and NW-B models applied to NAPL / water two-phase systems; and MWG-A modified model and MWG-B modified model applied to stained water / gas two-phase systems. S3. Obtain the light intensity matrix of the two-dimensional fracture device when it is filled with water using the light transmission detection system, denoted as the background light intensity, with the symbol . I w ; S4. Inject the target fluid into the two-dimensional fracture device filled with water phase, and obtain the light intensity matrix at the corresponding time through the optical transmission detection system. This matrix is ​​denoted as the process light intensity, with the symbol . I ; S5. Based on the type of two-phase flow system, select the corresponding LIS model for the two-phase flow system, input the background light intensity and the process light intensity into the selected LIS model, and calculate the absolute fluid saturation at each spatial position in the crack of the two-phase flow system at the corresponding time. S6. Based on the saturation result, integrate the geometric parameters of the two-dimensional fracture device to obtain the total volume of the specified fluid phase in the fracture. The formula for calculating the total volume of the specified fluid phase within the fracture is as follows: Where X represents one of the NAPL or gaseous-fluid phases; Indicates the absolute saturation of the non-aqueous phase. This represents the area per pixel unit. Indicates the spatial location of the fracture device , The width of the crack, i.e., the actual width of the crack. and These represent the number of pixels in the horizontal and vertical directions of the entire rift device, respectively.

2. The method according to claim 1, characterized in that, The two-dimensional fracture device described in step S1 comprises: The structure of the fracture device: The two-dimensional fracture device consists of two parallel sandblasted tempered glass pieces with a rubber pad sandwiched inside, and is fixed by an aluminum frame. The fluid to be tested is injected into the fracture device by a pump. The sandblasting of the tempered glass surface simulates the roughness of a natural fracture, and the thickness of the rubber pad controls the fracture width of the fracture device. Hydraulic system of the fracture device: The left and right sides of the device are water-proof boundaries, and the upper and lower ends are constant head boundaries. The water flows vertically from top to bottom. There are three connection holes at the top and bottom, which are connected to form a unified inlet and outlet through a four-way connector. Among them, the left connection hole is connected to the pressure measuring pipe through the extension port of the three-way connector to monitor the inlet and outlet water levels in real time. The middle connection hole is used as a dedicated injection and sampling port for gas or liquid through the extension port of the three-way connector.

3. The method according to claim 1, characterized in that, The WG-A and WG-B models applied to the water / gas two-phase system mentioned in step S2 include: The formula for calculating the effective saturation of the WG-A model in a water / gas two-phase system is as follows: The formula for calculating the effective saturation of the WG-B model is: Among them, model parameters , This represents the light intensity value measured when the fracture device contains only residual water. This represents the light intensity value measured when the fissure device is filled with water.

4. The method according to claim 1, characterized in that, The NW-A and NW-B models applied to the NAPL / water two-phase system mentioned in step S2 include: The formula for calculating the effective saturation of the NW-A model in the NAPL / water two-phase system is as follows: The formula for calculating the effective saturation of the NW-B model is: Among them, model parameters , This represents the light intensity value measured when the slit device is filled with NAPL. This represents the light intensity value measured when the fissure device is filled with water.

5. The method according to claim 1, characterized in that, The MWG-A and MWG-B corrected models applied to the staining water / air two-phase system mentioned in step S2 include: The formula for calculating the effective saturation of the MWG-A modified model in a dyed water / air two-phase system is as follows: The formula for calculating the effective saturation of the MWG-B modified model is as follows: Among them, model parameters , This represents the light intensity value measured when the slit device is filled with gas. This represents the light intensity value measured when the slit device is filled with dyed water.

6. The method according to claim 1, characterized in that, The water phase color state described in step S3 is either stained or unstained; wherein, the water phase color is determined by the two-phase system to be tested.

7. The method according to claim 1, characterized in that, The method for calculating the absolute saturation of the fluid in step S5 is as follows: The formula for calculating the absolute saturation of water is: ,in, S w Indicates the effective saturation of the aqueous phase. Indicates the residual saturation of the aqueous phase; The formula for calculating the absolute saturation of the non-aqueous phase is: ,in, This indicates the effective saturation of a specified fluid phase X in the fracture device.

8. The method according to claim 1, characterized in that, The formula for calculating the actual width of the crack is: ,in This indicates any spatial location within the fracture device when the medium is pure water. ， The light intensity value on; This indicates any spatial location within the fracture device when the medium is a liquid of a certain solute concentration. ， The light intensity value on the screen; <> represents all spatial locations. ， The upper statistical mean; Indicates the spatial location of the fracture device ， The statistical mean is numerically equal to the average crack width; where the average crack width is... The calculation formula is In the formula, This indicates the mass of the fluid injected into the fracture. This indicates the density of the injected fissure fluid. and These represent the length and width of the fracture device, respectively.

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