Microfluidic experimental method and system for studying influence of pore structure on shale oil imbibition

Abstract

The application provides a microfluidic experiment method and system for the influence of pore structure on shale oil imbibition, comprising the following steps: a. constructing different types of pore structure micro-nano chip models according to scanning electron microscope pictures; b. establishing a microfluidic visual experiment process to simulate fracturing and elastic development pressure-surge-production processes; c. calculating different pore imbibition efficiencies according to the change of oil saturation in the surge well stage; d. calculating different pore fracturing fluid flowback rates according to the change of water saturation in the elastic development stage; and e. analyzing the influence of pore structure on imbibition and shale oil production performance through the overall recovery degree and flowback rate. The microfluidic experiment method realizes the influence of different pore structures on the imbibition of shale oil pressure-surge-production processes, reveals the flow rules of shale oil and fracturing fluid in different lithofacies, and determines the fracturing fluid flowback rules and imbibition oil production contribution rate.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of data supervision, and in particular to a microfluidic experimental method and system for studying the influence of pore structure on shale oil imbibition. BACKGROUND

[0002] Shale oil resources with abundant reserves have been discovered in Bohai Bay Basin, Songliao Basin, Ordos Basin and Junggar Basin, and efficient development of shale oil is of great significance for ensuring national energy security. The shale oil reservoir in Jiyang has developed micro-nano pores, with a high proportion of inorganic pores and obvious imbibition effect. In addition, the lithofacies are diverse, the pore structure is complex, and the water content varies greatly between wells and between fracturing sections. Therefore, it is necessary to determine the influence of pore structure on imbibition, which is one of the keys to shale oil sweet spot evaluation and working system optimization.

[0003] Domestic and foreign scholars have studied the imbibition mechanism through nuclear magnetic resonance assisted core scale imbibition experiments, and have preliminarily understood the influence of lithofacies, imbibition medium and imbibition pressure difference on imbibition. However, the mechanism of micro-nano pore scale imbibition is still unclear, and there is a lack of experimental and analytical methods for studying the influence of pore structure on imbibition.

[0004] The commonly used methods for studying the mechanism of imbibition include core experiments, micro-visualization experiments and simulations, which still have some defects and shortcomings: (1) the shale pore structure is complex, and the differences in wettability, clay mineral content and micro-pore distribution between different lithofacies will affect the experimental results, so the core experiment results have weak comparability; (2) the core experiment can only compare and evaluate the parameters such as T2 spectrum and flowback rate, and the influence of micro-pore structure on imbibition is unclear; (3) the commonly used micro-visualization model is mainly micron scale, and it is difficult to depict nano-scale pores, so the conceptual model has poor representativeness and cannot reflect the influence of real pore structure; (4) the commonly used microfluidic model has not effectively divided different scale pores, and cannot independently and quantitatively analyze key parameters such as imbibition efficiency of different scale pores. SUMMARY

[0005] In view of the above problems, the present application is proposed to provide a microfluidic experimental method and system for studying the influence of pore structure on shale oil imbibition, which overcomes the above problems or at least partially solves the above problems.

[0006] According to one aspect of the present application, a microfluidic experimental method for studying the influence of pore structure on shale oil imbibition is provided, which comprises:

[0007] Step S1: According to the high-precision scanning electron microscope image of the shale rock sample, a representative position is selected, and a micro-nano chip model of different types and different scales of pore structure is extracted and established;

[0008] Step S2: Establish a microfluidic visualization experiment system, record the fluid distribution in different stages of pore structure in real time through a microscope and a camera;

[0009] Step S3: Open the injection port and the discharge port, inject crude oil into the micro-nano chip model, and after complete saturation, establish high temperature and high pressure conditions and close the inlet and outlet;

[0010] Step S4: Fracturing process simulation, open the injection port to inject fracturing fluid into the model, and observe the flow path of the fracturing fluid;

[0011] Step S5: Well killing process simulation, close the inlet and observe the change of oil and water distribution in different pore structures, and calculate the seepage absorption efficiency of different pores;

[0012] Step S6: Elastic development process simulation, keep the injection port and the discharge port closed, open the flowback port and gradually reduce the outlet pressure, and oil and water begin to flow back. According to the oil and water distribution at different times, calculate the fracturing fluid flowback rate in different pores;

[0013] Step S7: According to the differences in fluid distribution and flowback rate, analyze the influence of pore structure on seepage absorption and shale oil production performance.

[0014] Optionally, in the step S1, the pore structure characteristics are combined with the core nuclear magnetic resonance test, a real bright banded pore structure model is extracted based on a high-precision scanning electron microscope image, nanoscale matrix, micrometer-scale intercrystalline seams, and ten-micrometer-scale bedding seam structures are extracted, and the volume and porosity of different pores are calculated by image method.

[0015] Optionally, in the step S1, the bright banded pore structure micro-nano chip model is established, and the model has a hydrophilic wetting characteristic;

[0016] Establish a cryptoband structure model composed of matrix pores and intercrystalline seams and a massive matrix structure model composed of matrix pores, and compare the influence of different scales and different types of pores on seepage absorption.

[0017] Optionally, the bright banded pore structure specifically includes: matrix pores, intercrystalline seams, and bedding seams.

[0018] Optionally, in the step S2, the micro-nano chip experiment system is similar to a conventional water injection and huff and puff system, different fluids are injected by a micro-flow pump, a high-temperature and high-pressure micro-nano chip holder is used as a holder, a microscope and a video recorder are used to observe the flow and distribution of fluids in real time during the experiment.

[0019] Optionally, in the step S3, during the oil saturation process, the injection port pressure is slightly higher than the discharge port by 0.1 MPa, the temperature and pressure are gradually increased, more than 5 PV of oil is injected until complete saturation, the injection port and the discharge port valves are closed, and high temperature and high pressure conditions are established.

[0020] Optionally, in the step S4, the fracturing fluid is injected through the injection port at a constant pressure difference of 1 MPa until pressure balance is reached, the amount of fracturing fluid injected is calculated according to the injection volume, and the flow path of the fracturing fluid is recorded in real time.

[0021] Optionally, in the step S5, the injection port is closed to simulate the fluid distribution change in the blowout prevention stage, the fluid saturation change before and at the end of the blowout prevention is recorded by the image method, and the imbibition efficiency of different scales is evaluated.

[0022] Imbibition efficiency calculation:

[0023]

[0024] Optionally, in the step 6) elastic development stage, the fluid is flowed back from the flowback port, the pressure of the flowback port is reduced to atmospheric pressure, and the fracturing fluid flowback rate in different scales is calculated by the image processing method.

[0025] Fracturing fluid flowback rate calculation:

[0026]

[0027] Optionally, in the step S7, the influence of the pore structure on the flowback rate and production performance is compared and evaluated according to the fluid distribution and fracturing fluid flowback law in different models.

[0028] The application also provides a microfluidic experimental system for the influence of pore structure on shale oil imbibition, which applies the microfluidic experimental method for the influence of pore structure on shale oil imbibition.

[0029] The pore structure micro-nano chip model extraction module is used to select representative positions and extract different types and different scales of pore structure micro-nano chip models according to the high-precision scanning electron microscope pictures of the shale rock sample.

[0030] The microfluidic visualization experimental system establishment module is used to establish a microfluidic visualization experimental system, and the fluid distribution in different stages of the pore structure is recorded in real time through a microscope and a camera.

[0031] The crude oil saturation injection module is used to open the injection port and the flowback port, inject crude oil saturation into the micro-nano chip model, and close the inlet and outlet after complete saturation under high temperature and high pressure conditions.

[0032] The fracturing process simulation module is used for fracturing process simulation, opening the injection port to inject fracturing fluid into the model, and observing the flow path of the fracturing fluid.

[0033] The blowout prevention process simulation module is used for blowout prevention process simulation, closing the inlet to observe the oil-water distribution change in different pore structures, and calculating the imbibition efficiency of different pores.

[0034] The elastic development process simulation module is used for elastic development process simulation, keeps the injection port and the discharge port closed, opens the backflow port and gradually reduces the outlet pressure, and oil and water begin to backflow, and the fracturing fluid backflow rate in different pores is calculated according to the oil and water distribution at different times;

[0035] The influence analysis module is used for analyzing the influence of the pore structure on the imbibition and the shale oil production dynamic according to the fluid distribution and the backflow rate difference.

[0036] The microfluidic experimental method and system for analyzing the influence of the pore structure on the shale oil imbibition provided by the application comprises the following steps: a. constructing different types of pore structure micro-nano chip models according to scanning electron microscope pictures; b. establishing a microfluidic visual experiment process to simulate the fracturing and elastic development pressure-bleeding-production process; c. calculating the imbibition efficiency of different pores according to the oil saturation change in the bleeding well stage; d. calculating the fracturing fluid backflow rate of different pores according to the water saturation change in the elastic development stage; and e. analyzing the influence of the pore structure on the imbibition and the shale oil production dynamic through the overall recovery degree and the backflow rate. The microfluidic experimental method realizes the influence of different pore structures on the imbibition of the shale oil pressure-bleeding-production process, reveals the flow law of the shale oil and the fracturing fluid in different lithofacies, and determines the fracturing fluid backflow law and the imbibition oil production contribution rate. The model in the experimental method is representative, the experimental method is reasonable, and the analysis precision is high, which provides a new technical method for studying the micro imbibition mechanism and influence.

[0037] The above description is only a summary of the technical scheme of the application, in order to more clearly understand the technical means of the application, the specific embodiments of the application can be implemented according to the content of the specification, and in order to make the above and other purposes, characteristics and advantages of the application more obvious and easy to understand, the following will specifically describe the embodiments of the application. BRIEF DESCRIPTION OF DRAWINGS

[0038] In order to more clearly illustrate the technical scheme of the embodiments of the application, the following will briefly introduce the drawings needed in the embodiment description. Obviously, the drawings in the following description are only some embodiments of the application, and those skilled in the art can also obtain other drawings according to these drawings without creating any creative labor.

[0039] Figure 1 It is a scanning electron microscope picture of typical bright crystal lamella shale in a specific embodiment of the application;

[0040] Figure 2 It is a micro-nano chip model of different types of pore structures of shale in a specific embodiment of the application;

[0041] Figure 3 It is a research flowchart in a specific embodiment of the application;

[0042] Figure 4 is the real oil-water distribution map at the end of the well shut-in in a specific embodiment of the present application;

[0043] Figure 5 is the real oil-water distribution map at the end of the flowback in a specific embodiment of the present application. DETAILED DESCRIPTION

[0044] Exemplary embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it is understood that the present disclosure can be embodied in various forms without being limited by the embodiments set forth herein. Rather, these embodiments are provided so that the present disclosure will be thorough and complete, and will fully convey the scope of the present disclosure to those skilled in the art.

[0045] The terms "include" and "have" and any variations thereof in the specification, claims and drawings of the present application are intended to cover the non-exclusive inclusion, for example, the inclusion of a series of steps or units.

[0046] The technical solutions of the present application will be described in further detail below in conjunction with the drawings and embodiments.

[0047] Embodiment 1

[0048] In a specific embodiment 1 of the present application, the following steps are specifically included:

[0049] Step 1) According to the high-precision scanning electron microscope picture of the shale rock sample, as shown in FIG. 1, representative positions are selected, and a micrometer chip model of bright crystal lamina pore structure composed of matrix, intercrystalline seam and bedding seam is extracted and established, as shown in FIG. 2, the model as a whole shows hydrophilic wetting; Figure 1 Figure 2 Step 2) Connect the microfluidic visualization experimental system, as shown in FIG. 3, record the fluid distribution in the pore structure at different stages in real time through the microscope and camera;

[0050] Step 3) Open the injection port and the discharge port, the injection port pressure is slightly higher than the discharge port by 0.1 MPa, inject more than 5 PV until there is no bubble in the model, confirm complete oil saturation, gradually increase the temperature and pressure to 70℃, 30 MPa, then establish the closed inlet and outlet; Figure 3

[0051] Step 4) Fracturing process simulation, open the injection port, inject fracturing fluid into the model at a pressure difference of 1 MPa, until the pressure is balanced, and record the fracturing fluid flow path in real time;

[0052] Step 5) Well shut-in process simulation, close the inlet, record the oil-water distribution changes in different pore structures, as shown in FIG. 6;

[0053] Step 5) Well shut-in process simulation, close the inlet, record the oil-water distribution changes in different pore structures, as shown in FIG. 6; Figure 4 ​​The different pore imbibition efficiencies are calculated, as shown in Table 1.

[0054] Table 1 Imbibition efficiency of different pores in the well soaking stage

[0055]

[0056]

[0057] Step 6) Elastic development process simulation, keep the injection port and the discharge port closed, open the flowback port and reduce the outlet pressure to atmospheric pressure, record the change of oil-water distribution in different pore structures, such as Figure 5 The fracturing fluid flowback rates in different pores after flowback are calculated, as shown in Table 2 fracturing fluid flowback rates of different pores in the flowback stage.

[0058] Table 2

[0059]

[0060] Step 7) According to the fluid distribution and flowback rate difference, it is found that a large amount of fracturing fluid is retained in the intercrystalline fissures and matrix pores, and the bedding fissures greatly reduce the fracturing fluid flowback rate in the matrix pores and intercrystalline fissures.

[0061] Example 2:

[0062] In one embodiment 2 of the present application, based on example 1, according to the characteristics of the cryptocrystalline layer pore structure of shale, a cryptocrystalline layer pore structure model is established to analyze the influence of pore structure on imbibition. It specifically includes the following steps:

[0063] Step 1) According to the high-precision scanning electron microscope picture of the shale sample and the cryptocrystalline layer pore structure model, after extracting the structure of the bedding fissure, a cryptocrystalline layer structure model composed of matrix pores and intercrystalline fissures is established, as shown in Figure 2

[0064] Step 2) Connect the microfluidic visualization experimental system, as shown in Figure 3 Real-time record fluid distribution in different stages of pore structure through microscope and camera;

[0065] Step 3) Open the injection port and the discharge port, the injection port pressure is slightly higher than the discharge port 0.1MPa, inject more than 5PV until there is no bubble in the model, confirm complete oil saturation, gradually increase the temperature and pressure to 70℃, 30MPa, then establish the closed inlet and outlet;

[0066] Step 4) Fracturing process simulation, open the injection port, inject fracturing fluid into the model at a pressure difference of 1MPa, until the pressure is balanced, and record the fracturing fluid flow path in real time;

[0067] ​Step 5) soak process simulation, close the inlet, record the oil-water distribution changes in different pore structures, as shown in Figure 4 , calculate the different pore percolation efficiency, see Table 1;

[0068] Step 6) elastic development process simulation, keep the injection inlet and outlet closed, open the flowback port and reduce the outlet pressure to atmospheric pressure, record the oil-water distribution changes in different pore structures, as shown in Figure 5 , calculate the fracturing fluid flowback rate in different pores after flowback, see Table 2;

[0069] Step 7) according to the fluid distribution and flowback rate difference, it is found that the fracturing fluid is retained in both intercrystalline cracks and matrix pores, but the overall fracturing fluid flowback rate is significantly higher than that of the bright band.

[0070] Example 3

[0071] In one embodiment of the present application, on the basis of Example 1 and Example 2, a blocky matrix pore structure model is established according to the pore structure characteristics of blocky matrix shale, and the influence of pore structure on percolation is analyzed. It specifically includes the following steps:

[0072] Step 1) according to the high-precision scanning electron microscope picture of shale rock sample and the bright band pore structure model, a blocky matrix pore structure model with only matrix pores is established, as shown in Figure 2 ;

[0073] Step 2) connect the microfluidic visualization experiment system, as shown in Figure 3 , record the fluid distribution in different stages of pore structure in real time through a microscope and a camera;

[0074] Step 3) open the injection inlet and outlet, the injection inlet pressure is slightly higher than the outlet by 0.1 MPa, inject more than 5 PV until there is no bubble in the model, confirm complete oil saturation, gradually increase the temperature and pressure to 70℃, 30MPa, and then establish the closed inlet and outlet;

[0075] Step 4) fracturing process simulation, open the injection inlet, inject fracturing fluid into the model at a pressure difference of 1 MPa until the pressure is balanced, and record the fracturing fluid flow path in real time;

[0076] Step 5) soak process simulation, close the inlet, record the oil-water distribution changes in different pore structures, as shown in Figure 4 , calculate the different pore percolation efficiency, see Table 1;

[0077] Step 6) elastic development process simulation, keep the injection inlet and outlet closed, open the flowback port and reduce the outlet pressure to atmospheric pressure, record the oil-water distribution changes in different pore structures, as shown in Figure 5 , calculate the fracturing fluid flowback rate in different pores after flowback, see Table 2;

[0078] Step 7) According to the fluid distribution and the difference in flowback rate, it is found that the amount of fracturing fluid retained in the matrix pores is small, and the overall flowback rate of the fracturing fluid is relatively highest.

[0079] Beneficial effects: The microfluidic experimental method of the present application realizes the influence of different pore structures on the imbibition effect of the shale oil pressure-maturation-recovery process, reveals the flow law of shale oil and fracturing fluid in different lithofacies, and determines the fracturing fluid flowback law and the imbibition oil production contribution rate. The experimental method of the present application has strong model representation, reasonable experimental method and high analysis precision, and provides a new technical method for studying the microcosmic imbibition mechanism and influence.

[0080] The above specific embodiments further illustrate the purpose, technical solutions and beneficial effects of the present application. It should be understood that the above is only a specific embodiment of the present application and is not used to limit the protection scope of the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A microfluidic experimental method for the effect of pore structure on the imbibition of shale oil, characterized in that, The microfluidic experiment method comprises: Step S1: According to the high-precision scanning electron microscope picture of the shale rock sample, a representative position is selected, and a micro-nano chip model of different types and different scales of pore structures is extracted and established; Step S2: A microfluidic visualization experiment system is established, and the fluid distribution in the pore structure at different stages is recorded in real time through a microscope and a camera; Step S3: Open the injection port and the discharge port, inject crude oil into the micro-nano chip model, completely saturate after completely saturating, and then close the inlet and outlet under high temperature and high pressure conditions; Step S4: Fracturing process simulation, open the injection port to inject fracturing fluid into the model, and observe the flow path of the fracturing fluid; Step S5: Simulation of the well killing process, close the inlet and observe the oil-water distribution change in different pore structures, and calculate the seepage absorption efficiency of different pores; Step S6: Simulation of the elastic development process, keep the injection port and the discharge port closed, open the flowback port and gradually reduce the outlet pressure, and the oil and water begin to flow back, and the fracturing fluid flowback rate in different pores is calculated according to the oil and water distribution at different times; Step S7: According to the fluid distribution and the difference in the flowback rate, the influence of the pore structure on the seepage absorption and the shale oil production performance is analyzed.

2. The microfluidic experimental method for investigating the influence of pore structure on the imbibition of shale oil according to claim 1, characterized in that, In step S1, the pore structure characteristics of the core nuclear magnetic resonance test are combined, the real lamellar porosity structure model is extracted based on the high-precision scanning electron microscope image, the nanoscale matrix, the micrometer intercrystalline seam and the ten-micrometer layering seam structure are extracted respectively, and the volume and porosity of different pores are calculated respectively by the image method.

3. The microfluidic experimental method for investigating the influence of pore structure on the imbibition of shale oil according to claim 1, characterized in that, In step S1, the lamellar porosity structure micro-nano chip model is established, and the model has a hydrophilic wetting characteristic; The cryptocrystalline layer structure model composed of matrix pores and intercrystalline seams and the massive matrix structure model composed of matrix pores are established, and the influence of different scales and different types of pores on the seepage absorption is compared.

4. The microfluidic experimental method for investigating the influence of pore structure on shale oil imbibition according to claim 3, characterized in that, The lamellar porosity structure specifically comprises: matrix pores, intercrystalline seams and layering seams.

5. The microfluidic experimental method for investigating the influence of pore structure on shale oil imbibition according to claim 1, characterized in that, In step S2, the micro-nano chip experiment system is similar to the conventional water injection and huff and puff system, different fluids are injected by a micro-flow pump, a high-temperature and high-pressure micro-nano chip holder is used as a holder, and a microscope and a video recorder are used to observe the flow and distribution of the fluid in the experiment process in real time.

6. The microfluidic experimental method for investigating the influence of pore structure on shale oil imbibition according to claim 1, wherein, In step S3, during the oil saturation process, the pressure of the injection port is slightly higher than that of the discharge port by 0.1 MPa, the temperature and pressure are gradually increased, more than 5 PV of oil is injected until complete saturation, the injection port and the discharge port valve are closed, and the high temperature and high pressure conditions are established.

7. The microfluidic experimental method for investigating the influence of pore structure on shale oil imbibition according to claim 1, characterized in that, In step S4, the fracturing fluid is injected through the injection port at a constant pressure difference of 1 MPa until the pressure is balanced, the amount of the injected fracturing fluid is calculated according to the injection volume, and the flow path of the fracturing fluid is recorded in real time.

8. The microfluidic experimental method for investigating the influence of pore structure on shale oil imbibition according to claim 1, characterized in that, In step S5, the injection port is closed to simulate the fluid distribution change in the well killing stage, the fluid saturation change before and after the well killing is recorded by the image method, and the seepage absorption efficiency of different scales is evaluated; Seepage absorption efficiency calculation:

9. The microfluidic experimental method for investigating the influence of pore structure on shale oil imbibition according to claim 1, characterized in that, In step 6), the fluid flows back from the flowback port, the flowback port pressure is reduced to atmospheric pressure, and the fracturing fluid flowback rate in different scales is calculated by image processing; Fracturing fluid flowback rate calculation:

10. The microfluidic experimental method for investigating the influence of pore structure on shale oil imbibition according to claim 1, characterized in that, In step S7, according to the fluid distribution and the fracturing fluid flowback law in different models, the influence of the pore structure on the flowback rate and the production performance is compared and evaluated.

11. A microfluidic experimental system for the effect of pore structure on shale oil imbibition, applying the microfluidic experimental method for the effect of pore structure on shale oil imbibition according to any one of claims 1-10, characterized in that, The experiment system comprises: The pore structure micro-nano chip model extraction module is used for selecting representative positions and extracting and establishing different types and different scales of pore structure micro-nano chip models according to high-precision scanning electron microscope pictures of shale rock samples; The micro-fluidic visualization experiment system establishment module is used for establishing a micro-fluidic visualization experiment system, and recording fluid distribution in different stages of pore structure in real time through a microscope and a camera; The crude oil saturation injection module is used for opening an injection port and a discharge port, injecting crude oil saturation into the micro-nano chip model, and closing the injection port and the discharge port after complete saturation and establishment of high-temperature and high-pressure conditions; The fracturing process simulation module is used for fracturing process simulation, opening an injection port, injecting fracturing fluid into the model, and observing a fracturing fluid flow path; The well killing process simulation module is used for well killing process simulation, closing the injection port, observing oil-water distribution changes in different pore structures, and calculating different pore imbibition efficiencies; The elastic development process simulation module is used for elastic development process simulation, keeping the injection port and the discharge port closed, opening a flowback port and gradually reducing outlet pressure, starting oil-water flowback, and calculating fracturing fluid flowback rates in different pores according to oil-water distribution at different times; The influence analysis module is used for analyzing influences of pore structures on imbibition and shale oil production dynamics according to fluid distribution and flowback rate differences.

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