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

Abstract

The invention provides a microfluidic experiment method and system for the influence of pore structures on shale oil imbibition. The method 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 visualization experiment process, and simulating a fracturing and elastic development pressing-closing-production process; c, different pore imbibition efficiencies are calculated according to the oil saturation change in the well closing stage; d, calculating the flowback rates of fracturing fluids with different pores according to the change of the water saturation in the elastic development stage; and e, analyzing the influence of the pore structure on imbibition and shale oil production dynamics according to the total recovery percentage and the flowback rate. According to the microfluidic experimental method disclosed by the invention, the influence of different pore structures on the imbibition effect of shale oil in the fracturing-stuffy-mining process is realized, the flow rules of shale oil and fracturing fluid in different rock phases are revealed, and the flowback rule of the fracturing fluid and the imbibition oil production contribution rate are clarified.

Description

Technical Field

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

[0002] Rich shale oil resources have been discovered in the Bohai Bay Basin, Songliao Basin, Ordos Basin, and Junggar Basin. The efficient development of shale oil is of great significance to ensuring national energy security. Jiyang shale oil reservoirs have developed micro-nano pores, a high proportion of inorganic pores, and obvious imbibition. At the same time, the lithofacies are diverse, the pore structure is complex, and the water content varies greatly between wells and between fracturing sections. Clarifying the impact of pore structure on imbibition is one of the keys to evaluating shale oil sweet spots and optimizing work systems.

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

[0004] Commonly used methods for studying the mechanism of imbibition include core experiments and microscopic visualization experiments and simulations, but they still have certain defects and shortcomings: (1) The pore structure of shale is complex. In addition to the differences in pore structure, differences in wettability, clay mineral content, microscopic pore distribution, etc. between different lithofacies will affect the experimental results, and the core experimental results are not comparable; (2) Core experiments can only refer to parameters such as T2 spectrum and return flow rate for comparative evaluation, and the impact of microscopic pore structure on imbibition is unclear; (3) Commonly used microscopic visualization models are mainly based on the micrometer scale, and nanoscale pores are difficult to characterize. The conceptual model is poorly representative and difficult to reflect the impact of the real pore structure; (4) Commonly used microfluidic models have not yet effectively divided pores of different scales, and cannot independently and quantitatively analyze key parameters such as the imbibition efficiency of pores of different scales. Summary of the invention

[0005] In view of the above problems, the present invention is proposed to provide a microfluidic experimental method and system for 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 invention, a microfluidic experimental method for the effect of pore structure on shale oil imbibition is provided, the microfluidic experimental method comprising:

[0007] Step S1: Select representative positions based on high-precision scanning electron microscope images of shale samples, extract and establish micro-nano chip models of pore structures of different types and scales;

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

[0009] Step S3: opening the injection port and the discharge port, injecting crude oil into the micro-nano chip model to saturate it, and after complete saturation, establishing high temperature and high pressure conditions, closing the inlet and outlet;

[0010] Step S4: simulating the fracturing process, opening the injection port to inject fracturing fluid into the model, and observing the flow path of the fracturing fluid;

[0011] Step S5: simulating the well blocking process, closing the inlet to observe the changes in oil and water distribution in different pore structures, and calculating the imbibition 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, oil and water begin to flow back, and calculate the flowback rate of fracturing fluid in different pores according to the oil and water distribution at different times;

[0013] Step S7: Analyze the influence of pore structure on imbibition and shale oil production performance based on differences in fluid distribution and flowback rate.

[0014] Optionally, in step S1, the pore structure characteristics of the core nuclear magnetic resonance test are combined, and the real bright crystal lamination pore structure model is extracted based on the high-precision scanning electron microscope image, and the nanoscale matrix, micron-scale intercrystalline fractures, and ten-micron-scale bedding fracture structures are extracted respectively, and the volume and porosity of different pores are calculated respectively by the imaging method.

[0015] Optionally, the step S1 establishes a micro-nano chip model of a spar layer pore structure, and the model has a hydrophilic wetting characteristic;

[0016] A cryptocrystalline laminar structure model consisting of matrix pores and intercrystalline cracks and a massive matrix structure model consisting of matrix pores were established to compare the effects of pores of different scales and types on imbibition.

[0017] Optionally, the pore structure of the bright crystal lamination specifically includes: matrix pores, intercrystalline cracks, and bedding cracks.

[0018] Optionally, the micro-nano chip experimental system in step S2 is similar to a conventional water injection throughput system, using a micro-flow pump to inject different fluids, and the clamp is a high temperature and high pressure resistant micro-nano chip clamp, with a microscope and a video recorder to observe the flow and distribution of the fluid in real time during the experiment.

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

[0020] Optionally, 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 injection amount of the fracturing fluid is calculated according to the injected volume, and the flow path of the fracturing fluid is recorded and observed in real time.

[0021] Optionally, in step S5, the injection port is closed to simulate the change in fluid distribution during the well blocking stage, and the change in fluid saturation before and after the well blocking is recorded by an image method to evaluate the imbibition efficiency at different scales;

[0022] Calculation of absorption efficiency:

[0023]

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

[0025] Calculation of fracturing fluid flowback rate:

[0026]

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

[0028] The present invention also provides a microfluidic experimental system for the effect of pore structure on shale oil imbibition, and the microfluidic experimental method for the effect of pore structure on shale oil imbibition described above is applied. The experimental system comprises:

[0029] The pore structure micro-nano chip model extraction module is used to select representative positions based on high-precision scanning electron microscope images of shale samples, and extract and establish pore structure micro-nano chip models of different types and scales;

[0030] Microfluidic visualization experiment system establishment module, establish a microfluidic visualization experiment system, and use microscopes and cameras to record the fluid distribution in the pore structure at different stages in real time;

[0031] The crude oil saturation injection module is used to open the injection port and the discharge port, inject crude oil into the micro-nano chip model to saturate it, and close the inlet and outlet after establishing high temperature and high pressure conditions after full saturation;

[0032] The fracturing process simulation module is used to simulate the fracturing process, open the injection port to inject fracturing fluid into the model, and observe the flow path of the fracturing fluid;

[0033] The well blocking process simulation module is used to simulate the well blocking process, close the entrance to observe the changes in oil and water distribution in different pore structures, and calculate the different pore absorption efficiency;

[0034] The elastic development process simulation module is used to simulate the elastic development process. The injection port and the discharge port are kept closed, the flowback port is opened and the outlet pressure is gradually reduced, and the oil and water begin to flow back. The flowback rate of the fracturing fluid in different pores is calculated according to the oil and water distribution at different times.

[0035] Impact analysis module, used to analyze the effect of pore structure on imbibition and shale oil production performance based on differences in fluid distribution and flowback rates.

[0036] The present invention provides a microfluidic experimental method and system for the influence of pore structure on shale oil imbibition, including: a. constructing different types of pore structure micro-nano chip models based on scanning electron microscope images; b. establishing a microfluidic visualization experimental process to simulate the fracturing and elastic development pressure-suffocation-production process; c. calculating the imbibition efficiency of different pores according to the change of oil saturation in the well-suffocation stage; d. calculating the return rate of fracturing fluid of different pores according to the change of water saturation in the elastic development stage; e. analyzing the influence of pore structure on imbibition and shale oil production dynamics through the overall recovery degree and return rate. The microfluidic experimental method of the present invention realizes the influence of different pore structures on the imbibition of shale oil pressure-suffocation-production process, reveals the flow law of shale oil and fracturing fluid in different lithofacies, and clarifies the return law of fracturing fluid and the contribution rate of imbibition to oil production. The experimental method of the present invention has strong model representativeness, reasonable experimental method and high analysis accuracy, and provides a new technical method for studying the mechanism and influence of microscopic imbibition.

[0037] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention, it can be implemented according to the contents of the specification. In order to make the above and other purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0039] Figure 1 This is a scanning electron microscope image of a typical bright crystal laminar shale in a specific embodiment of the present invention;

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

[0041] Figure 3 is a research flow chart of a specific embodiment of the present invention;

[0042] Figure 4 This is a diagram of actual oil and water distribution at the end of a well being blocked in a specific embodiment of the present invention;

[0043] Figure 5 It is a diagram of actual oil-water distribution at the end of flowback in a specific embodiment of the present invention. DETAILED DESCRIPTION

[0044] The exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0045] The terms "comprises" and "having" and any variations thereof in the description embodiments, claims and drawings of the present invention are intended to cover non-exclusive inclusions, for example, including a series of steps or units.

[0046] The technical solution of the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0047] Embodiment 1:

[0048] In one embodiment 1 of the present invention, the following steps are specifically included:

[0049] Step 1) Based on the high-precision scanning electron microscope image of the shale sample, Figure 1 As shown in Figure 1, representative positions were selected to extract and establish a micro-nano chip model of the pore structure of the bright crystal layer composed of matrix, intercrystalline cracks, and bedding cracks, as shown in Figure 1. Figure 2 As shown, the model as a whole exhibits hydrophilic wetting;

[0050] Step 2) Connect the microfluidic visualization experimental system, such as Figure 3 As shown, the fluid distribution in the pore structure at different stages is recorded in real time by microscope and camera;

[0051] 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 5PV until there are no bubbles in the model, confirm that the model is fully saturated with oil, and gradually increase the temperature and pressure to 70°C and 30 MPa, then close the inlet and outlet;

[0052] Step 4) Simulating the fracturing process, opening the injection port, injecting fracturing fluid into the model with a pressure difference of 1 MPa until the pressure is balanced, and recording the flow path of the fracturing fluid in real time;

[0053] Step 5) Simulate the well blocking process, close the inlet, and record the changes in oil and water distribution in different pore structures, such as Figure 4As shown, the different pore imbibition efficiencies are calculated, see Table 1;

[0054] Table 1 Imbibition efficiency of different pores during the well blocking 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, and record the changes in oil and water distribution in different pore structures, such as Figure 5 As shown, the flowback rate of fracturing fluid in different pores after the flowback is completed is calculated, see Table 2 Flowback rate of different pores in the flowback stage;

[0058] Table 2

[0059]

[0060] Step 7) Based on the differences in fluid distribution and flowback rate, it was found that a large amount of fracturing fluid was retained in the intercrystalline cracks and matrix pores, and the bedding fractures significantly reduced the flowback rate of fracturing fluid in the matrix pores and intercrystalline cracks.

[0061] Embodiment 2:

[0062] In an embodiment 2 of the present invention, based on the embodiment 1, according to the pore structure characteristics of the cryptocrystalline laminae of shale, a cryptocrystalline laminae pore structure model is established to analyze the influence of the pore structure on the imbibition effect. Specifically, the following steps are included:

[0063] Step 1) Based on the high-precision scanning electron microscope images of shale samples and the pore structure model of bright crystal laminae, after extracting the bedding fracture structure, a cryptocrystalline laminae structure model consisting of matrix pores and intercrystalline fractures is established, such as Figure 2 As shown;

[0064] Step 2) Connect the microfluidic visualization experimental system, such as Figure 3 As shown, the fluid distribution in the pore structure at different stages is recorded in real time by 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 by 0.1 MPa, inject more than 5PV until there are no bubbles in the model, confirm that the model is fully saturated with oil, and gradually increase the temperature and pressure to 70°C and 30 MPa, then close the inlet and outlet;

[0066] Step 4) Simulating the fracturing process, opening the injection port, injecting fracturing fluid into the model with a pressure difference of 1 MPa until the pressure is balanced, and recording the flow path of the fracturing fluid in real time;

[0067] Step 5) Simulate the well blocking process, close the inlet, and record the changes in oil and water distribution in different pore structures, such as Figure 4 As shown, the different pore imbibition efficiencies are calculated, see Table 1;

[0068] 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, and record the changes in oil and water distribution in different pore structures. Figure 5 As shown, the fracturing fluid flowback rate in different pores after the flowback is completed is calculated, see Table 2;

[0069] Step 7) Based on the differences in fluid distribution and flowback rate, it was found that the fracturing fluid was retained in both the intercrystalline cracks and matrix pores, but the overall flowback rate of the fracturing fluid was significantly higher than that of the bright crystal layer.

[0070] Embodiment 3:

[0071] In one embodiment 3 of the present invention, based on the examples 1 and 2, a block matrix structure model is established according to the pore structure characteristics of block matrix shale to analyze the influence of pore structure on imbibition. Specifically, the following steps are included:

[0072] Step 1) Based on the high-precision scanning electron microscope image of the shale sample and the spar laminae pore structure model, a block matrix pore structure model with only matrix pores is established, such as Figure 2 As shown;

[0073] Step 2) Connect the microfluidic visualization experimental system, such as Figure 3 As shown, the fluid distribution in the pore structure at different stages is recorded in real time by microscope and camera;

[0074] 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 5PV until there are no bubbles in the model, confirm that the model is fully saturated with oil, and gradually increase the temperature and pressure to 70°C and 30 MPa, then close the inlet and outlet;

[0075] Step 4) Simulating the fracturing process, opening the injection port, injecting fracturing fluid into the model with a pressure difference of 1 MPa until the pressure is balanced, and recording the flow path of the fracturing fluid in real time;

[0076] Step 5) Simulate the well blocking process, close the inlet, and record the changes in oil and water distribution in different pore structures, such as Figure 4 As shown, the different pore imbibition efficiencies are calculated, see Table 1;

[0077] 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, and record the changes in oil and water distribution in different pore structures, such as Figure 5 As shown, the fracturing fluid flowback rate in different pores after the flowback is completed is calculated, see Table 2;

[0078] Step 7) Based on the differences in fluid distribution and flowback rate, it was found that the retention of fracturing fluid in the matrix pores was small and the overall flowback rate of fracturing fluid was relatively the highest.

[0079] Beneficial effects: The microfluidic experimental method of the present invention realizes the influence of different pore structures on the imbibition effect of shale oil pressure-suffocation-production process, reveals the flow law of shale oil and fracturing fluid in different lithofacies, and clarifies the fracturing fluid backflow law and the imbibition contribution rate to oil production. The experimental method of the present invention has a strong model representativeness, a reasonable experimental method, and high analysis accuracy, providing a new technical method for studying the mechanism and influence of microscopic imbibition.

[0080] The above specific implementation methods further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above are only specific implementation methods of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A microfluidic experimental method for the effect of pore structure on shale oil imbibition, characterized in that: The microfluidic experimental method comprises: Step S1: Select representative positions based on high-precision scanning electron microscope images of shale samples, extract and establish micro-nano chip models of pore structures of different types and scales; Step S2: Establish a microfluidic visualization experimental system to record the fluid distribution in the pore structure at different stages in real time through a microscope and a camera; Step S3: opening the injection port and the discharge port, injecting crude oil into the micro-nano chip model to saturate it, and after complete saturation, establishing high temperature and high pressure conditions, closing the inlet and outlet; Step S4: simulating the fracturing process, opening the injection port to inject fracturing fluid into the model, and observing the flow path of the fracturing fluid; Step S5: simulating the well blocking process, closing the inlet to observe the changes in oil and water distribution in different pore structures, and calculating the imbibition efficiency of different pores; 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, oil and water begin to flow back, and calculate the flowback rate of fracturing fluid in different pores according to the oil and water distribution at different times; Step S7: Analyze the influence of pore structure on imbibition and shale oil production performance based on differences in fluid distribution and flowback rate.

2. The microfluidic experimental method for the effect of pore structure on shale oil imbibition according to claim 1, characterized in that: In step S1, the pore structure characteristics of the core nuclear magnetic resonance test are combined, and the real bright crystal lamination pore structure model is extracted based on the high-precision scanning electron microscope image, and the nano-scale matrix, micron-scale intercrystalline fractures, and ten-micron-scale bedding fracture structures are extracted respectively, and the volume and porosity of different pores are calculated respectively by the image method.

3. The microfluidic experimental method for the effect of pore structure on shale oil imbibition according to claim 1, characterized in that: The step S1 establishes a micro-nano chip model with a spar layer pore structure, and the model has a hydrophilic wetting characteristic; A cryptocrystalline laminar structure model consisting of matrix pores and intercrystalline cracks and a massive matrix structure model consisting of matrix pores were established to compare the effects of pores of different scales and types on imbibition.

4. The microfluidic experimental method for the effect of pore structure on shale oil imbibition according to claim 3, characterized in that: The pore structure of the bright crystal laminae specifically includes: matrix pores, intercrystalline cracks, and bedding cracks.

5. The microfluidic experimental method for the effect of pore structure on shale oil imbibition according to claim 1, characterized in that: The micro-nano chip experimental system in step S2 is similar to a conventional water injection throughput system, using a micro-flow pump to inject different fluids, and the clamp is a high-temperature and high-pressure resistant micro-nano chip clamp, with a microscope and a video recorder to observe the flow and distribution of the fluid in real time during the experiment.

6. The microfluidic experimental method for the effect of pore structure on shale oil imbibition according to claim 1, characterized in that: During the oil saturation process in step S3, the injection port pressure is slightly higher than the discharge port pressure by 0.1 MPa, and the temperature and pressure are gradually increased. More than 5 PV is injected until the oil is completely saturated. The injection port and discharge port valves are closed to establish high temperature and high pressure conditions.

7. The microfluidic experimental method for the effect 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 injection amount of the fracturing fluid is calculated according to the injection volume, and the flow path of the fracturing fluid is recorded and observed in real time.

8. The microfluidic experimental method for the effect 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 change in fluid distribution during the well blocking stage, and the change in fluid saturation before and after the well blocking is recorded by an image method to evaluate the imbibition efficiency at different scales; Calculation of absorption efficiency:

9. The microfluidic experimental method for the effect of pore structure on shale oil imbibition according to claim 1, characterized in that: In the step 6) during the elastic development stage, the fluid is discharged from the flowback port, the pressure of the flowback port is reduced to atmospheric pressure, and the flowback rate of the fracturing fluid in different scales is statistically calculated by image processing method; Calculation of fracturing fluid flowback rate:

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

11. A microfluidic experimental system for the effect of pore structure on shale oil imbibition, using a microfluidic experimental method for the effect of pore structure on shale oil imbibition as claimed in any one of claims 1 to 10, characterized in that: The experimental system includes: The pore structure micro-nano chip model extraction module is used to select representative positions based on high-precision scanning electron microscope images of shale samples, and extract and establish pore structure micro-nano chip models of different types and scales; Microfluidic visualization experiment system establishment module, establish a microfluidic visualization experiment system, and use microscopes and cameras to record the fluid distribution in the pore structure at different stages in real time; The crude oil saturation injection module is used to open the injection port and the discharge port, inject crude oil into the micro-nano chip model to saturate it, and close the inlet and outlet after establishing high temperature and high pressure conditions after full saturation; The fracturing process simulation module is used to simulate the fracturing process, open the injection port to inject fracturing fluid into the model, and observe the flow path of the fracturing fluid; The well blocking process simulation module is used to simulate the well blocking process, close the entrance to observe the changes in oil and water distribution in different pore structures, and calculate the different pore absorption efficiency; The elastic development process simulation module is used to simulate the elastic development process. The injection port and the discharge port are kept closed, the flowback port is opened and the outlet pressure is gradually reduced, and the oil and water begin to flow back. The flowback rate of the fracturing fluid in different pores is calculated according to the oil and water distribution at different times. Impact analysis module, used to analyze the effect of pore structure on imbibition and shale oil production performance based on differences in fluid distribution and flowback rates.

Images