A shale reservoir collapse damage visual evaluation system and method

Abstract

This invention belongs to the field of reservoir evaluation technology, specifically providing a visualization evaluation system and method for shale reservoir collapse damage. It includes a displacement unit, a testing unit, and a backpressure unit. The displacement unit includes a displacement pump and an intermediate container. The testing unit includes a shale sample, a meter, a nuclear magnetic resonance spectrometer, a sample chamber, and a microscopic image acquisition and processing device. The backpressure unit includes a confining pressure tracking pump, a backpressure container, and a backpressure pump. This invention solves the problem in existing technologies that cannot accurately depict the real-time dynamic visualization process of fluids in the reservoir, and cannot evaluate the collapse and damage level of shale reservoirs under visualization conditions. This invention can accurately depict the real-time dynamic visualization process of fluids in the reservoir, and achieve the evaluation of shale reservoir collapse and damage level under visualization conditions.

Description

Technical Field

[0001] This invention belongs to the field of reservoir evaluation technology, specifically relating to a visualization evaluation system and method for shale reservoir collapse damage. Background Technology

[0002] In recent years, shale gas has become a hot area for oil exploration and reserve enhancement in various oilfields. However, due to its unique properties, shale reservoirs are prone to collapse during drilling, significantly increasing development risks and costs. Currently, shale exploration and development in China is generally in its initial and exploratory stages. Conventional reservoir collapse and damage assessment methods are not very applicable to shale reservoirs. In recent years, domestic scholars and research institutions have made some initial theoretical understanding and practical progress by drawing on foreign theoretical models and exploration and development experience, as well as the special characteristics of unconventional shale reservoirs in my country. However, a systematic theoretical framework and evaluation method for evaluating shale reservoir collapse and damage mechanisms have not yet been formed. The understanding of the collapse and damage mechanisms of unconventional shale reservoirs is unclear, and an effective theoretical evaluation system has not been established.

[0003] In the study of wellbore instability and collapse, some domestic scholars have made some progress and applications in the research on the collapse and instability mechanism of shale gas horizontal wells by studying relevant reports from abroad. However, early studies on wellbore stability still overemphasized the effects of in-situ stress and the strength of the original rock, as well as well leakage phenomena. These studies mainly included the determination of the in-situ stress state, the measurement of rock mechanical properties, the analysis of wellbore surrounding rock stress, and stability analysis. Overall, these studies were based on mechanics and conducted on a macroscopic basis. Usually, the investigation of wellbore instability was only conducted by finally determining the reasonable drilling fluid density range for maintaining wellbore stability, while rarely considering the drilling construction technology and the physicochemical microscopic mechanism of wellbore collapse and instability. This led to the long-standing use of simple and crude methods, such as increasing the drilling fluid density, to prevent wellbore collapse and instability. However, the systematic analysis of the microscopic mechanisms of shale wellbore instability caused by different drilling methods and external fluids or drilling fluids is still in its early stages, and the overall research efforts are insufficient. Therefore, further research is needed on the microscopic collapse and instability mechanisms of shale gas horizontal wells and optimization evaluation methods. This will continuously promote the use of water-based and oil-based drilling fluids with greater adaptability in shale gas drilling, optimize drilling fluid processes, and improve the application of shale gas horizontal well technology, providing theoretical support and technical assistance for the efficient, safe, and economical development of shale gas.

[0004] Currently, high-resolution image analysis techniques are the primary means of qualitative characterization of shale porosity both domestically and internationally. Common techniques include: micron-nano CT, high-resolution field emission scanning electron microscopy (FE-SEM), focused ion beam scanning electron microscopy (FIB-SEM), wide ion beam scanning electron microscopy (BIB-SEM), atomic force microscopy (AFM), transmission electron microscopy (TEM), and nitrogen ion microscopy (HIM). While CT and FIB etching techniques can obtain a large number of high-resolution images, enabling visualization and quantitative calculation of the morphology, size, and distribution of micro- and nano-pores in shale reservoirs, these techniques primarily achieve static fluid distribution through microscopic static imaging and simulation, rather than precisely depicting the real-time dynamic process of fluid movement within the reservoir.

[0005] After gaining a clear understanding of the damage and collapse mechanisms and evaluation parameters of shale reservoirs, further research on reservoir or fluid adaptability assessment from a dynamic and spatiotemporal evolution perspective—including multi-dimensional / multi-scale, near-situ / in-situ, visualized, data-driven, intelligent, and smart approaches—is essential for the future development of digital, intelligent, visualized, and smart oilfields. This also represents a refined method for reducing oil and gas field development costs, efficiently developing oil and gas resources, and achieving green oil and gas fields in my country.

[0006] Chinese patent document with application number 201610390509.0 and application date of June 2, 2016 discloses an experimental method for evaluating drilling fluid damage in tight gas reservoirs. The steps are as follows: drying the core sample, marking it, and performing uniform segmentation and slicing; testing the dry sample weight of the core; immersing each segment of the core in fluid until saturated; performing a reverse centrifugation operation on the core to establish the original water saturation of each segment of the core sample; testing and judging the differences between the nuclear magnetic resonance spectra of simulated formation water and drilling fluid filtrate; performing nuclear magnetic resonance imaging tests on the internal fluid distribution of the core; placing the core in the core holder of a drilling fluid circulator for drilling fluid circulation, and then testing and calculating the water saturation and gas permeability of each segment of the core; using the test results to calculate and compare the permeability damage rate caused by drilling fluid intrusion, and evaluating the degree of damage caused by drilling fluid intrusion at different depths. The patent document requires drying, soaking, and drying of the core sample during testing. It can only test the core sample at a certain point in time. Nuclear magnetic resonance imaging and electron microscopy cannot be performed simultaneously, and real-time observation, data acquisition, and processing of the core sample are not possible. Summary of the Invention

[0007] The present invention provides a shale reservoir collapse damage visualization evaluation system and method to overcome the problems in the prior art that cannot accurately depict the real dynamic visualization process of fluid in the reservoir, and cannot evaluate the collapse and damage degree of shale reservoir under visualization conditions.

[0008] To address this, the present invention provides a visual evaluation system for shale reservoir collapse damage, comprising a displacement unit, a testing unit, and a backpressure unit. The displacement unit includes a displacement pump and an intermediate container. The testing unit includes a shale sample, a measuring instrument, an NMR spectrometer, a sample chamber, and a microscopic image acquisition and processing device. The backpressure unit includes a confining pressure tracking pump, a backpressure container, and a backpressure pump. The displacement pump is connected to the sample chamber via the intermediate container. The shale sample is connected to the sample chamber. The microscopic image acquisition and processing device is located above the sample chamber. Both the confining pressure tracking pump and the NMR spectrometer are connected to the sample chamber. One path from the sample chamber is connected to the backpressure pump via the backpressure container, and the other path from the sample chamber is connected to the measuring instrument. The confining pressure tracking pump is electrically connected to the backpressure pump.

[0009] Preferably, the intermediate container is a constant temperature and high pressure intermediate container.

[0010] Preferably, the constant temperature of the constant temperature high pressure intermediate container is 0-120℃ and the pressure is 0-65MPa.

[0011] Preferably, the intermediate container includes multiple liquid tanks, each of which is equipped with a control valve.

[0012] Preferably, the shale sample is sealed with adhesive by laser etching.

[0013] Preferably, the sample chamber is a transparent, non-magnetic sample chamber.

[0014] Preferably, the sample chamber has a temperature resistance of ≤60℃ and a pressure resistance of ≤25MPa.

[0015] Preferably, the microscopic image acquisition and processing device is a microscopic image acquisition and processing device with continuous observation, acquisition, processing and storage functions.

[0016] Preferably, the displacement unit further includes a valve, the intermediate container is connected to the sample chamber through the valve, and the back pressure unit further includes a back pressure valve, the sample chamber is connected to the back pressure container and the metering device through the back pressure valve.

[0017] A method for visually evaluating shale reservoir collapse damage includes the following steps: loading a target liquid into an intermediate container, loading a shale sample into a sample chamber, using a displacement pump to drive the target liquid from the intermediate container into the sample chamber to displace the shale sample, using a confining pressure tracking pump to provide confining pressure to the shale sample, using a backpressure pump to provide pressurized gas to the shale sample through a backpressure container based on feedback data from the confining pressure tracking pump, using a nuclear magnetic resonance spectrometer to perform nuclear magnetic resonance scanning on the shale sample, and using a microscopic image acquisition and processing device to acquire, process, and store images of the shale sample in real time.

[0018] The beneficial effects of this invention are:

[0019] 1. The shale reservoir collapse damage visualization evaluation system and method provided by this invention involves loading a target liquid into an intermediate container, loading a shale sample into a sample chamber, using a displacement pump to drive the target liquid from the intermediate container into the sample chamber to displace the shale sample, using a confining pressure tracking pump to provide confining pressure to the shale sample, using a back pressure pump to provide pressurized gas to the shale sample through a back pressure container based on feedback data from the confining pressure tracking pump, using a nuclear magnetic resonance spectrometer to perform nuclear magnetic resonance scanning on the shale sample, and using a microscopic image acquisition and processing device to acquire, process, and store images of the shale sample in real time; it can provide real-time... By photographing or observing changes in the microscopic pore throats and fractures of shale micro-regions, the state of oil and gas enrichment, reservoir pore space, microscopic controlling factors, oil, gas and water distribution and interface conditions, and the changes in the contact process between pore clay and fluids, this method can also extract parameters from the changes that occur in stages. This further enhances the sensory understanding of shale reservoir collapse and damage mechanisms, thereby effectively and realistically understanding changes in the internal mineral or pore throat structure of the reservoir. It can also more effectively improve traditional shale reservoir evaluation methods and parameter indicators, and provide a more reliable method for further optimizing drilling fluids, completion fluids, fracturing fluids, etc.

[0020] 2. The shale reservoir collapse damage visualization evaluation system and method provided by the present invention connects to the sample chamber through a confining pressure tracking pump to provide confining pressure to the sample chamber, realistically simulating the formation confining pressure on shale. The confining pressure tracking pump can automatically track the displacement pressure to prevent the displacement fluid pressure from exceeding the confining pressure, thus allowing the displacement fluid to enter the confining pressure tracking pump.

[0021] 3. The shale reservoir collapse damage visualization evaluation system and method provided by this invention uses a backpressure pump to ensure a stable supply of pressurized gas to the shale sample through a backpressure container. The backpressure container is adjusted according to the feedback data from the confining pressure tracking pump, thus realistically simulating the actual pressure changes in the shale formation.

[0022] 4. The shale reservoir collapse damage visualization evaluation system and method provided by the present invention includes an intermediate container comprising multiple liquid tanks, which can simultaneously provide a variety of different displacement liquids. Each of the multiple liquid tanks is equipped with a control valve to control the opening and closing of each liquid tank.

[0023] 5. The shale reservoir collapse damage visualization evaluation system and method provided by the present invention adopts a transparent and non-magnetic sample chamber, which facilitates the acquisition of images by the microscopic image acquisition and processing device, and avoids interference with the operation of the nuclear magnetic resonance spectrometer and the microscopic image acquisition and processing device. Attached Figure Description

[0024] The present invention will now be described in further detail with reference to the accompanying drawings.

[0025] Figure 1 A schematic diagram of the structure of a visual evaluation system for shale reservoir collapse damage;

[0026] Figure 2 This is a diagram showing the displacement effect of the water-based drilling fluid filtrate in Example 1;

[0027] Figure 3 This is a pseudo-color image of the water-based drilling fluid in Example 1, visualized simultaneously using nuclear magnetic resonance imaging and microscopy.

[0028] Figure 4 The PV number and permeability spectrum of the water-based drilling fluid injected into the core in Example 1;

[0029] Figure 5 This is a graph showing the ratio of PV number to permeability in the core sample injected with the water-based drilling fluid in Example 1.

[0030] Figure 6 The T2 nuclear magnetic resonance spectra of cores under different fluid displacement conditions in Example 1;

[0031] Figure 7 The displacement effect of water-based drilling fluid filtrate in Example 2 (Note: the blue part is a microscopic image of water-based drilling fluid ingress).

[0032] Figure 8 This is a pseudo-color image of the water-based drilling fluid in Example 2, visualized simultaneously using nuclear magnetic resonance imaging and microscopy.

[0033] Figure 9 The graph shows the PV number and permeability of the water-based drilling fluid injected in Example 2.

[0034] Figure 10 This is a graph showing the ratio of PV number to permeability in the water-based drilling fluid experimental injection in Example 2;

[0035] Figure 11 The images are T2 nuclear magnetic resonance spectra under different fluid displacement conditions in Example 2.

[0036] Explanation of reference numerals in the attached figures: 1. Displacement pump; 2. Intermediate container; 3. Valve; 4. Shale sample; 5. Back pressure valve; 6. Measuring instrument; 7. Confining pressure tracking pump; 8. Nuclear magnetic resonance spectrometer; 9. Sample chamber; 10. Microscopic image acquisition and processing device; 11. Back pressure container; 12. Back pressure pump. Detailed Implementation

[0037] Example 1:

[0038] like Figure 1As shown, a shale reservoir collapse damage visualization evaluation system includes a displacement unit, a testing unit, and a backpressure unit. The displacement unit includes a displacement pump 1 and an intermediate container 2. The testing unit includes a shale sample 4, a meter 6, an nuclear magnetic resonance spectrometer 8, a sample chamber 9, and a microscopic image acquisition and processing device 10. The backpressure unit includes a confining pressure tracking pump 7, a backpressure container 11, and a backpressure pump 12. The displacement pump 1 is connected to the sample chamber 9 through the intermediate container 2. The shale sample 4 is connected inside the sample chamber 9. The microscopic image acquisition and processing device 10 is located above the sample chamber 9. The confining pressure tracking pump 7 and the nuclear magnetic resonance spectrometer 8 are both connected to the sample chamber 9. One path of the sample chamber 9 is connected to the backpressure pump 12 through the backpressure container 11, and the other path of the sample chamber 9 is connected to the meter 6. The confining pressure tracking pump 7 is electrically connected to the backpressure pump 12.

[0039] The process involves loading the target liquid into intermediate container 2, placing shale sample 4 into sample chamber 9, and using displacement pump 1 to drive the target liquid from intermediate container 2 into sample chamber 9 to displace shale sample 4. Confining pressure tracking pump 7 provides confining pressure to shale sample 4, realistically simulating the formation confining pressure experienced by shale. Confining pressure tracking pump 7 automatically tracks the displacement pressure to prevent the displacement fluid pressure from exceeding the confining pressure, thus preventing the displacement fluid from entering the confining pressure tracking pump. Backpressure pump 12, based on feedback data from confining pressure tracking pump 7, provides pressurized gas to shale sample 4 through backpressure container 11, ensuring a stable supply of pressurized gas. Backpressure container 11 adjusts according to feedback data from confining pressure tracking pump 7, realistically simulating the actual pressure changes in shale formations. Nuclear magnetic resonance spectrometer 8... Nuclear magnetic resonance scanning was performed on shale sample 4, and the microscopic image acquisition and processing device 10 acquired, processed, and stored images of shale sample 4 in real time. It can capture or observe changes in microscopic pore throats and fractures in shale micro-regions in real time, as well as the oil and gas enrichment state, reservoir pore space, microscopic control factors, oil, gas, and water distribution and interface state, and changes in the contact process between pore clay and fluids. At the same time, it can also extract parameters of changes that occur in stages, further improving the sensory understanding of shale reservoir collapse and damage mechanisms. This allows for an effective and realistic understanding of changes in the internal mineral or pore throat structure of the reservoir, and more effectively improves traditional shale reservoir evaluation methods and parameter indicators, providing a more reliable method for further optimizing drilling fluids, completion fluids, fracturing fluids, etc.

[0040] Example 2:

[0041] Based on Example 1, the intermediate container 2 is a constant-temperature, high-pressure intermediate container. The constant-temperature, high-pressure intermediate container provides a displacement fluid with stable temperature and pressure, realistically simulating formation temperature and pressure, thus ensuring the authenticity and accuracy of the experiment.

[0042] Preferably, the constant temperature of the constant-temperature high-pressure intermediate container is 0-120℃, and the pressure is 0-65MPa. This provides a displacement liquid with a wide temperature range, good pressure resistance, broad applicability, and strong practicality.

[0043] Preferably, the intermediate container 2 includes multiple liquid tanks, each of which is equipped with a control valve. The multiple liquid tanks can simultaneously provide various displacing liquids, and the control valve allows for the opening and closing of each tank as needed, providing good independence and operability.

[0044] Example 3:

[0045] Based on Example 2, the shale sample 4 was sealed using laser etching. Laser etching of the sealed shale sample 4 resulted in a high yield rate, high stability, and good flexibility. It allows for one-time molding of different shapes and angles, and is free of consumables, pollution, and has low cost.

[0046] Example 4:

[0047] Based on Example 3, the sample chamber 9 is a transparent, non-magnetic sample chamber. This facilitates image acquisition by the microscopic image acquisition and processing device 10 and avoids interference with the operation of the nuclear magnetic resonance spectrometer 8 and the microscopic image acquisition and processing device 10.

[0048] Preferably, the sample chamber 9 has a temperature resistance of ≤60℃ and a pressure resistance of ≤25MPa. This range ensures that the actual shale formation conditions can be fully simulated.

[0049] Example 5:

[0050] Preferably, the microscopic image acquisition and processing device 10 is a microscopic image acquisition and processing device with continuous observation, acquisition, processing and storage functions. This microscopic image acquisition and processing device 10 has the functions of continuous observation, acquisition, processing and storage of images and automatic stitching, with a magnification of 0 to 500 times, and can accurately and in real time depict the real dynamic visualization process of fluid in the reservoir.

[0051] Preferably, the displacement unit further includes a valve 3, through which the intermediate container 2 is connected to the sample chamber 9. The backpressure unit further includes a backpressure valve 5, through which the sample chamber 9 is connected to the backpressure container 11 and the metering device 6. In actual use, the valve 3 and the backpressure valve 5 are opened and closed as needed to realistically simulate the fluid dynamics of the formation.

[0052] Preferably, the back pressure valve 5 has a pressure resistance of ≤25MPa and an accuracy of 0.005; the back pressure pump 12 has a pressure resistance of ≤45MPa; the confining pressure tracking pump 7 has a pressure resistance of ≤45MPa; and the displacement pump 1 has an output pressure range of 0~45MPa, an output flow rate of 0~15mL / min, and an accuracy of 0.00001. It exhibits good pressure resistance, strong adaptability, and high measurement accuracy.

[0053] Preferably, the measuring instrument 6 has a measurement accuracy of 0.1 mm; the measurement accuracy is high.

[0054] Preferably, the measuring instrument 6 can be a measuring tool such as a graduated cylinder; the specific choice is made according to the actual situation to achieve the measuring function.

[0055] Preferably, the nuclear magnetic resonance spectrometer 8 has the function of scanning and simultaneously realizing pseudo-color. Pseudo-color is mainly based on Matalabe technology, which uses an array algorithm to scan and arrange points on the two-dimensional rock core. At the same time, the microscopic image acquisition and processing device 10 is activated to scan and compare the features of the two synchronously, thereby extracting synchronous and identical feature data for coupling, and finally realizing the consistency of pseudo-color image and microscopic image features. This technology will provide a more reliable technical means for studying the micro-light damage collapse mechanism of shale gas reservoirs.

[0056] Example 6:

[0057] A method for visually evaluating shale reservoir collapse damage includes the following steps: a target liquid is loaded into an intermediate container 2; a shale sample 4 is loaded into a sample chamber 9; a displacement pump 1 drives the target liquid from the intermediate container 2 into the sample chamber 9 to displace the shale sample 4; a confining pressure tracking pump 7 provides confining pressure to the shale sample 4; a backpressure pump 12 provides pressurized gas to the shale sample 4 through a backpressure container 11 based on feedback data from the confining pressure tracking pump 7; a nuclear magnetic resonance spectrometer 8 performs nuclear magnetic resonance scanning on the shale sample 4; and a microscopic image acquisition and processing device 10 acquires, processes, and stores images of the shale sample 4 in real time.

[0058] This invention can capture or observe in real time changes in microscopic pore throats and fractures in shale micro-regions through pseudo-color synchronization, as well as the oil and gas enrichment state, reservoir pore space, microscopic control factors, oil, gas and water distribution and interface state, and changes in the contact process between porous clay and fluids. It can also extract parameters in real time based on phased changes, thereby further improving the sensory understanding of shale reservoir collapse and damage mechanisms. This allows for an effective and realistic understanding of changes in the internal mineral or pore throat structure of the reservoir, and more effectively improves traditional evaluation methods and parameter indicators, providing a more reliable method for optimizing drilling fluids, completion fluids, fracturing fluids, etc.

[0059] Example 7:

[0060] This study utilized the CNRM-900 shale reservoir collapse damage visualization assessment system, with a confining pressure of 17 MPa, a displacement pressure of 15 MPa, and a flow rate of 0.05 ml / min, to conduct a water-based drilling fluid filtrate flooding damage experiment on core sample 6-1.

[0061] Experimental steps:

[0062] 1. Check the instrument and place the standard etched glass sample in the sample chamber 9, and use the standard etched glass sample for synchronous calibration to synchronize the data acquisition, microscopic images, and pseudocolor of the nuclear magnetic resonance spectrometer 8 and the microscopic image acquisition and processing device 10.

[0063] 2. Place the target liquid (drilling fluid filtrate) into intermediate container 2;

[0064] 3. Close valve 3, purge sample chamber 9 with nitrogen, and simultaneously drive shale sample with nitrogen to ensure pore connectivity of shale sample. After the gas drive is completed, evacuate shale sample. Pressurize sample chamber 9 with confining pressure tracking pump 7 and argon gas to a confining pressure of 17 MPa, and perform dry sample nuclear magnetic resonance scanning on shale sample.

[0065] 4. Fill the intermediate container 2 with simulated formation water, close valve 3, vacuum saturate the shale sample with simulated formation water, and perform nuclear magnetic resonance scanning on the shale sample again.

[0066] 5. Fill the intermediate container 2 with simulated formation water, open valve 3, adjust the injection flow rate of displacement pump 1 to 0.05 ml / min, and perform simulated formation water flooding on the shale sample, and then perform nuclear magnetic resonance scanning on the shale sample again.

[0067] 6. Fill the intermediate container 2 with drilling fluid filtrate, close the control valve in the intermediate container 2, adjust the injection flow rate of the displacement pump 1 to 0.05 ml / min, open the control valve containing the drilling fluid filtrate to displace the shale sample with drilling fluid, perform nuclear magnetic resonance scanning at the same time, and turn on the microscopic image acquisition and processing device 10 to take pictures and observe the changes in its pore space or the fluid inrush law.

[0068] 7. Close the control valve for drilling fluid filtrate in intermediate container 2, open the valve for simulated formation water in intermediate container 2, adjust the injection flow rate of displacement pump 1 to 0.05 ml / min, and perform simulated formation water flooding on the shale sample. Perform nuclear magnetic resonance scanning on the shale sample again.

[0069] 8. Close the entire shale reservoir collapse damage visualization evaluation system; the experiment is now complete.

[0070] The experimental results are as follows:

[0071] Table 1. Experimental data on the damage of water-based drilling fluid to core sample #1.

[0072]

[0073] Table 2. Nuclear Magnetic Resonance Experimental Data on Damage to Core No. 1 Caused by Water-Based Drilling Fluid

[0074]

[0075] After the core sample was injected with water-based drilling fluid and penetrated the reservoir ( Figure 2 and Figure 3 The process of changes in reservoir space is analyzed, and the change in permeability is measured. Figure 4 and Figure 5 Analysis of experimental data revealed that, under the same injection rate, when water-based drilling fluid penetrated the shale reservoir, the seepage space changed, and the maximum core damage rate was 241.94%.

[0076] Analysis of nuclear magnetic resonance (NMR) scanning data from different stages of core #1 revealed that core #1 was saturated with simulated formation water during the pre-intrusion displacement stage of water-based drilling fluid. Figure 6 The maximum signal value and overall area of ​​the T2 spectrum increased, and the spectrum shifted to the right. The nuclear magnetic porosity ranged from 2.40% to 3.11%, mainly due to the displacement pressure and the migration of mineral particles out of the pore throat, leading to pore connectivity. After the injection of water-based drilling fluid, the signal value of the spectrum decreased compared to the displacement stage before the water-based drilling fluid invasion, but the overall pore structure did not change significantly. However, the water-based drilling fluid invaded the surface layer under the displacement pressure difference, causing the saturated water in the clay minerals of the shale surface to have a seepage potential difference under the effect of concentration difference. Water on the core surface precipitated into the water-based drilling fluid, ultimately leading to a decrease in the pore signal. However, in the original reservoir state, due to the combined effect of capillary force and clay, the water-based drilling fluid invaded the reservoir and underwent water absorption and expansion, both of which tended to form fractures, damaging the seepage space of the shale reservoir.

[0077] Example 8

[0078] This study utilized the CNRM-900 shale reservoir collapse damage visualization evaluation system, with a confining pressure of 17 MPa, a displacement pressure of 15 MPa, and a flow rate of 0.05 ml / min, to conduct a water-based drilling fluid filtrate flooding damage experiment on core sample #2. The experimental procedures are as shown in Example 1, and the experimental results are as follows:

[0079] Table 3. Experimental data on the damage of water-based drilling fluid to core sample #2.

[0080]

[0081] Table 4. Nuclear Magnetic Resonance Experimental Data on Damage to Core No. 2 by Water-Based Drilling Fluid

[0082]

[0083] For core #2, after injecting water-based drilling fluid to penetrate the reservoir ( Figure 7 and Figure 8 The process of changes in reservoir space is analyzed, and the change in permeability is measured. Figure 9 and Figure 10Analysis of experimental data revealed that, under the same injection rate, the water-based drilling fluid intruded into the shale reservoir, causing changes in the seepage space. The maximum damage rate of core #2 was 98.38%.

[0084] Analysis of nuclear magnetic resonance scanning data from different stages of core #2 revealed the displacement stage from saturated simulated formation water to water-based drilling fluid intrusion in core #2. Figure 11 The maximum signal value and overall area of ​​the T2 spectrum increased, and the spectrum shifted to the right. The nuclear magnetic resonance porosity was between 2.23% and 2.68%, mainly due to the displacement pressure and the migration of mineral particles out of the pore throat, leading to pore connectivity. After the injection of water-based drilling fluid, the signal value of the spectrum decreased compared to the displacement stage before the water-based drilling fluid invasion, but the overall pore structure did not change significantly. However, the water-based drilling fluid invaded the surface layer under the displacement pressure difference, causing the saturated water in the clay minerals of the shale surface to have a seepage potential difference under the effect of concentration difference. Water on the core surface precipitated into the water-based drilling fluid, ultimately leading to a decrease in the pore signal. However, in the original reservoir state, due to the combined effect of capillary force and clay, the water-based drilling fluid invaded the reservoir and underwent water absorption and expansion, both of which tended to form fractures, damaging the seepage space of the shale reservoir.

[0085] As shown in Examples 7 and 8 above, this further promotes the exploration of shale reservoir seepage space damage mechanisms under visualized conditions, truly achieving a subjective and objective understanding of shale reservoir collapse and damage mechanisms. This provides a more powerful technical means to promote shale gas development and further realizes a truly digital visualized oilfield indoor evaluation system. This platform has the advantages of high efficiency, simplicity, low cost, and reliable parameters, achieving an effective combination of visualization and parameter quantification research, and making a more favorable contribution to the future development of smart oilfields.

[0086] In the description of this invention, it should be understood that if terms such as "inner" or "upper" indicate a location or positional relationship based on the location or positional relationship shown in the drawings, it does not indicate or imply that the device or element referred to must have a specific location, or be constructed and operated in a specific location. Therefore, the terms used to describe positional relationships in the drawings are for illustrative purposes only and should not be construed as limiting the invention.

[0087] The above examples are merely illustrative of the present invention and do not constitute a limitation on the scope of protection of the present invention. All designs that are the same as or similar to the present invention are within the scope of protection of the present invention.

Claims

1. A shale reservoir collapse damage visualization evaluation system, characterized in that: The system includes a displacement unit, a testing unit, and a backpressure unit. The displacement unit includes a displacement pump (1) and an intermediate container (2). The testing unit includes a shale sample (4), a meter (6), an NMR spectrometer (8), a sample chamber (9), and a microscopic image acquisition and processing device (10). The backpressure unit includes a confining pressure tracking pump (7), a backpressure container (11), and a backpressure pump (12). The displacement pump (1) is connected to the sample chamber (9) through the intermediate container (2). The shale sample (4) is connected inside the sample chamber (9). The microscopic image acquisition and processing device (10) is located above the sample chamber (9). The confining pressure tracking pump (7) and the NMR spectrometer (8) are both connected to the sample chamber (4). 9), the sample chamber (9) is connected to the back pressure pump (12) through the back pressure container (11) and the other part of the sample chamber (9) is connected to the meter (6). The confining pressure tracking pump (7) is electrically connected to the back pressure pump (12); the shale sample (4) is sealed by laser etching; the nuclear magnetic resonance instrument (8) has the function of scanning and simultaneously realizing pseudo-color; the pseudo-color is mainly based on Matalabe technology, using array algorithm to scan the two-dimensional core, and simultaneously starting the microscopic image acquisition and processing device (10) to scan and compare the features of both synchronously, thereby extracting synchronous and identical feature data for coupling, and finally realizing the consistency of pseudo-color image and microscopic image features.

2. The shale reservoir collapse damage visualization evaluation system of claim 1, wherein: The intermediate container (2) is a constant temperature and high pressure intermediate container.

3. The shale reservoir collapse damage visualization evaluation system as described in claim 2, characterized in that: The constant temperature of the constant temperature and pressure of the constant pressure intermediate container is 0-120℃ and 0-65 MPa.

4. The shale reservoir collapse damage visualization assessment system as described in claim 1, characterized in that: The intermediate container (2) includes multiple liquid tanks, each of which is equipped with a control valve.

5. The shale reservoir collapse damage visualization evaluation system as described in claim 1, characterized in that: The sample chamber (9) is a transparent, non-magnetic sample chamber.

6. The shale reservoir collapse damage visualization assessment system as described in claim 5, characterized in that: The temperature resistance of the sample chamber (9) is ≤60℃ and the pressure resistance is ≤25MPa.

7. The shale reservoir collapse damage visualization assessment system as described in claim 1, characterized in that: The microscopic image acquisition and processing device (10) is a microscopic image acquisition and processing device with continuous observation, acquisition, processing and storage functions.

8. The shale reservoir collapse damage visualization evaluation system as described in claim 1, characterized in that: The displacement unit also includes a valve (3), the intermediate container (2) is connected to the sample chamber (9) through the valve (3), and the back pressure unit also includes a back pressure valve (5), the sample chamber (9) is connected to the back pressure container (11) and the meter (6) through the back pressure valve (5).

9. A method for visual evaluation of shale reservoir collapse damage based on any one of claims 1-8, characterized in that: The process includes the following steps: the target liquid is loaded into the intermediate container (2), the shale sample (4) is loaded into the sample chamber (9), the displacement pump (1) drives the target liquid in the intermediate container (2) into the sample chamber (9) to displace the shale sample (4), the confining pressure tracking pump (7) provides confining pressure to the shale sample (4), the back pressure pump (12) provides pressurized gas to the shale sample (4) through the back pressure container (11) according to the feedback data of the confining pressure tracking pump (7), the nuclear magnetic resonance spectrometer (8) performs nuclear magnetic resonance scanning on the shale sample (4), and the microscopic image acquisition and processing device (10) acquires, processes and stores images of the shale sample (4) in real time.

Images