Electric field assisted high-pressure oil displacement monitoring device and method compatible with nuclear magnetic resonance imaging

Abstract

The invention provides an electric field auxiliary high-voltage oil displacement monitoring device and method compatible with nuclear magnetic resonance imaging, and relates to the technical field of oil and gas exploitation monitoring. The device comprises a high-voltage clamp holder main body, a magnetic susceptibility matching electrode system and an electromagnetic compatibility filter network; the method comprises the steps of loading a rock core, collecting a baseline, performing conventional displacement to obtain a first image, applying an electric field to obtain a second image, and performing contrastive analysis to obtain an electric field utilization condition. Through electrode magnetic susceptibility matching, a hydrogen-free insulating medium and bidirectional filtering isolation, the problem of imaging interference under coexistence of a strong electric field and a strong magnetic field is solved, and high-definition in-situ monitoring of the electric field assisted oil displacement process and quantitative analysis of the remaining oil utilization degree are achieved.

Description

Technical Field

[0001] This invention relates to the field of oil and gas extraction monitoring technology, and in particular to an electric field-assisted high-pressure oil displacement monitoring device and method compatible with nuclear magnetic resonance imaging. Background Technology

[0002] In oil and gas extraction, electric field-assisted flooding (EVF) technology can effectively improve oil recovery. Combined with nuclear magnetic resonance (NMR) imaging, it can monitor the distribution and migration of fluids within the core in real time. However, NMR imaging requires a strong magnetic field, while high-pressure flooding requires high voltage. The coexistence of these two technologies presents serious electromagnetic compatibility (EMC) problems. Traditional monitoring devices typically use metal electrodes to apply the electric field. However, under the strong magnetic field of NMR, metals generate eddy currents and differences in magnetic susceptibility, leading to severe artifacts and signal black holes in the images. Simultaneously, the electromagnetic noise introduced by the high-voltage power supply can drown out the weak NMR radio frequency signal, causing a sharp drop in the signal-to-noise ratio. Furthermore, conventional insulating oil contains a large number of hydrogen atoms, generating a strong background signal in NMR imaging that masks fluid signals within the core. Therefore, current technologies cannot achieve clear, interference-free NMR imaging monitoring while applying a high-voltage electric field, making it difficult to meet the needs of in-situ visualization research during electric field-assisted flooding. Summary of the Invention

[0003] To address the technical problem of achieving clear and interference-free nuclear magnetic resonance imaging (NMR) monitoring in environments with both strong electric and magnetic fields, as described in the background, this invention provides an electric field-assisted high-pressure oil displacement monitoring device and method compatible with NMR imaging. The device employs a combined structure of a high-voltage holder body, a magnetic susceptibility matching electrode system, and an electromagnetic compatibility filter network, achieving compatibility between high-voltage electric field loading and NMR imaging during the electric field-assisted oil displacement process.

[0004] The first aspect of this invention provides an electric field-assisted high-pressure oil displacement monitoring device compatible with nuclear magnetic resonance imaging, comprising: The high-pressure clamp body is used to hold the core sample and provide a high-pressure environment. The clamp body is made of a non-metallic high-strength material that is transparent to radio frequency signals, and its confining cavity is filled with an insulating confining medium that does not contain hydrogen atoms. A magnetic susceptibility matching electrode system is disposed within the high-voltage holder body and is used to apply a high-voltage electric field to the core sample. The electrode system is made of porous conductive composite material, and its magnetic susceptibility is matched with that of the core sample and the fluid contained therein. An electromagnetic compatibility filter network is connected between the high-voltage power supply and the magnetic susceptibility matching electrode system to filter noise from the high-voltage power supply and block the leakage of radio frequency signals from the MRI scanner to the high-voltage power supply side.

[0005] Furthermore, the main body of the high-voltage clamp is made of reinforced polyetheretherketone or glass fiber composite material, and the insulating confining medium is perfluoropolyether oil.

[0006] Furthermore, the magnetic susceptibility matching electrode system employs a porous carbon fiber / aerogel composite electrode or a gold-plated graphite electrode, which has a porous structure that allows fluid to pass through.

[0007] Furthermore, the electromagnetic compatibility filter network includes a blocking unit composed of a non-magnetic inductor and a damping resistor connected in parallel, and at least one filter capacitor. The blocking unit is connected in series between the high-voltage power supply and the electrode system, and the filter capacitor is connected across the high-voltage line and ground.

[0008] Furthermore, the non-magnetic inductor is a coreless hollow inductor, the filter capacitor includes a high-voltage feedthrough capacitor, and the electromagnetic compatibility filter network is encapsulated in an electromagnetic shielding box.

[0009] A second aspect of the present invention provides a method for monitoring high-pressure oil displacement using an electric field-assisted imaging system compatible with the device described in the first aspect, comprising the following steps: A saturated oil-water core sample is loaded into the high-pressure holder body and an insulating confining pressure medium is injected. The loaded high-pressure clamp body is placed in the detection area of ​​the nuclear magnetic resonance imaging instrument, and baseline data is acquired under pressureless and electric field-free conditions to obtain the initial distribution image of the fluid inside the core. Conventional fluid displacement experiments were performed on the core samples. After the displacement stabilized, nuclear magnetic resonance imaging was performed to obtain the first distribution image. Under the condition of maintaining fluid displacement, a high-voltage electric field is applied to the core sample through the electromagnetic compatibility filter network, and nuclear magnetic resonance imaging is performed during the electric field to obtain a second distribution image; The first and second distribution images are processed and analyzed to obtain the utilization of the electric field on the remaining oil.

[0010] Furthermore, the baseline data acquisition includes performing T2 spectrum testing and three-dimensional MRI scanning to obtain the initial oil saturation distribution of the fluid inside the core.

[0011] Furthermore, the conventional fluid displacement experiment is a water drive experiment. After monitoring the water content at the outlet end until it reaches a stable threshold, the first distribution image obtained is a residual oil distribution map.

[0012] Furthermore, the high-voltage electric field is a DC electric field or a pulsed electric field, and the nuclear magnetic resonance imaging scan during the electric field application adopts a fast imaging sequence, acquiring images in real time at different time points of the electric field application.

[0013] Furthermore, the processing and analysis of the first distribution image and the second distribution image includes: registering the images and performing a difference operation to generate a distribution map of the remaining oil mobilized by the electric field, and combining the T2 spectrum shift to quantify the degree of mobilization of the remaining oil in different aperture channels.

[0014] Compared with the prior art, the electric field-assisted high-pressure oil displacement monitoring device and method compatible with nuclear magnetic resonance imaging provided by the present invention has the following beneficial effects: (1) This invention uses a non-metallic high-strength material that is transparent to radio frequency signals to make the main body of the clamp, and fills the confining cavity with an insulating confining medium that does not contain hydrogen atoms. This material has no shielding effect on the radio frequency field of nuclear magnetic resonance, and the hydrogen-free medium does not generate background signals in imaging, thereby eliminating the eddy current interference generated by conventional metal clamps and the background noise of hydrogen-containing insulating oil, and realizing the acquisition of high-definition nuclear magnetic resonance images without background interference during high-voltage oil displacement.

[0015] (2) This invention uses porous conductive composite materials to fabricate electrodes and matches the magnetic susceptibility of the electrodes with that of the core and the fluid contained therein. The porous structure allows the displacing fluid to pass freely, ensuring the authenticity of the flow field; the matching of magnetic susceptibility avoids local magnetic field distortion caused by metal electrodes, eliminates image artifacts and signal black holes near the electrodes, and realizes clear imaging and realistic flow simulation of the core end face under the action of an electric field.

[0016] (3) This invention sets up an electromagnetic compatibility filter network between the high-voltage power supply and the electrodes. The system consists of a blocking unit composed of a non-magnetic inductor and a damping resistor connected in parallel, and a filter capacitor. The inductor presents low impedance to DC and high impedance to radio frequency, the resistor consumes high-frequency energy to prevent resonance, and the filter capacitor provides high-frequency bypass, thereby realizing low-pass filtering of high-voltage power supply noise and bidirectional isolation of NMR radio frequency signals, effectively suppressing the interference of power supply noise on NMR signals, and ensuring the signal-to-noise ratio of imaging.

[0017] (4) This invention combines the above-mentioned devices with a phased displacement process and image comparison analysis method. First, the initial distribution is obtained, then the residual oil distribution is obtained through conventional water flooding, then an electric field is applied and real-time imaging is performed, and finally, through image difference processing and T2 spectrum analysis, the image data is converted into quantitative results of the degree of residual oil mobilization in pores of different sizes. This realizes in-situ monitoring of the entire process from baseline state to electric field-assisted displacement, providing reliable experimental data and visualization basis for the study of electric field-assisted oil displacement mechanism. Attached Figure Description

[0018] The accompanying drawings, which form part of this disclosure, are used to provide a further understanding of this disclosure. The illustrative embodiments of this disclosure and their descriptions are used to explain this disclosure and do not constitute an undue limitation of this disclosure. The spacing or dimensions between parts are exaggerated to show the position of each part, and the schematic diagrams are for illustrative purposes only.

[0019] Figure 1 This is a schematic diagram of the overall structure of the electric field-assisted high-pressure oil displacement monitoring device compatible with nuclear magnetic resonance imaging provided in Embodiment 1 of the present invention; Figure 2 This is a comparison image of the core end face artifacts of the electrode provided in Embodiment 1 of the present invention and a traditional metal electrode under the same MRI scanning parameters; Figure 3 This is a circuit schematic diagram of the electromagnetic compatibility filter network provided in Embodiment 1 of the present invention; Figure 4 This is a schematic diagram of the architecture of the electric field-assisted high-pressure oil displacement monitoring device compatible with nuclear magnetic resonance imaging provided in Embodiment 1 of the present invention; The components include: 1. First displacement fluid inlet; 2. First produced fluid outlet; 3. Second displacement fluid inlet; 4. PEEK holder cylinder; 5. NMR radio frequency coil; 6. Fluorine oil confining fluid; 7. Rubber sleeve; 8. Core sample; 9. Second produced fluid outlet; 10. Third produced fluid outlet; 11. Porous carbon fiber electrode; 12. Large-pore superconducting magnet; 13. Electromagnetic compatibility filter network; 14. Confining pressure inlet; 15. High voltage power supply. Detailed Implementation

[0020] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0021] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0022] It should be noted that the terminology used herein is for the purpose of describing specific embodiments only and is not intended to limit the exemplary embodiments of the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is intended to include the plural form as well. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof. The use of the words "upper," "lower," "left," and "right" in this invention only indicates alignment with the upper, lower, left, and right directions of the drawings themselves and does not limit the structure. They are merely for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting the invention.

[0023] Terminology Explanation: 1. Activation status: refers to the degree and characteristics of the remaining oil in the formation being activated, migrated and extracted after an electric field is applied.

[0024] 2. Flow Field Realism: In this invention, flow field realism refers to the extent to which the flow state of the displacing fluid within the experimental apparatus (including streamline direction, velocity distribution, pressure gradient, etc.) conforms to or approximates the actual displacement process of fluid in porous media under underground reservoir conditions. An experimental system with high flow field realism means that the fluid can pass through the core sample uniformly and linearly, and its flow behavior is mainly determined by the pore structure and fluid properties of the core itself, rather than by the physical obstruction or interference of external experimental equipment (such as electrodes, clamps, etc.).

[0025] 3. Flow field distortion: This concept, in contrast to "flow field realism," refers to the deviation of fluid flow within the experimental apparatus from its ideal state in the natural reservoir due to interference from external factors. For example, when the electrode lacks a porous structure or has excessively low porosity, the fluid cannot directly penetrate the electrode and is forced to flow around it through the gap between the electrode edge and the core.

[0026] Example 1 This embodiment provides an electric field-assisted high-pressure oil displacement monitoring device compatible with nuclear magnetic resonance imaging, including: a high-pressure holder body for accommodating core samples and providing a high-pressure environment. The holder body is made of a non-metallic high-strength material that is transparent to radio frequency signals, and its confining cavity is filled with an insulating confining medium that does not contain hydrogen atoms. A magnetic susceptibility matching electrode system is disposed within the high-voltage holder body and is used to apply a high-voltage electric field to the core sample. The electrode system is made of porous conductive composite material, and its magnetic susceptibility is matched with that of the core sample and the fluid contained therein. An electromagnetic compatibility filter network is connected between the high-voltage power supply and the magnetic susceptibility matching electrode system to filter noise from the high-voltage power supply and block the leakage of radio frequency signals from the MRI scanner to the high-voltage power supply side.

[0027] Specifically, such as Figure 1 As shown, the high-pressure holder body includes a PEEK holder cylinder 4, inside which is a rubber sleeve 7 for accommodating the core sample 8. A confining pressure cavity is formed between the rubber sleeve and the cylinder body, and the confining pressure cavity is filled with a fluorinated oil confining pressure fluid 6 (in one specific embodiment, perfluoropolyether oil is used). The confining pressure fluid is injected through the confining pressure inlet 14 and the pressure is controlled. The holder has a first displacement fluid inlet 1, a second displacement fluid inlet 3, and multiple product fluid outlets at both ends, including a first product fluid outlet 2, a second product fluid outlet 9, and a third product fluid outlet 10, for realizing fluid injection and production in different displacement directions. Porous carbon fiber electrodes 11 are provided at both ends of the core sample 8 as a magnetic susceptibility matching electrode system. The large-aperture superconducting magnet 12 provides the static magnetic field required for nuclear magnetic resonance imaging, and the NMR radio frequency coil 5 is placed around the holder to excite and receive nuclear magnetic resonance signals. The high-voltage power supply 15 is connected to the porous carbon fiber electrode 11 through an electromagnetic compatibility filter network 13 to apply a high-voltage electric field to the core sample.

[0028] The main body of the high-voltage clamp is made of a non-metallic, high-strength material (such as reinforced polyetheretherketone or glass fiber composite material) that is transparent to radio frequency signals. Its confining cavity is filled with an insulating confining medium (such as perfluoropolyether oil) that does not contain hydrogen atoms. This design solves the problem of conventional metal clamps generating eddy currents that shield radio frequency signals under strong nuclear magnetic fields, while eliminating strong background signal interference generated by hydrogen-containing insulating oil. This allows the nuclear magnetic resonance radio frequency field to penetrate the clamp uniformly and accurately detect fluid signals inside the core.

[0029] The magnetic susceptibility-matched electrode system, made of porous conductive composite material, has a magnetic susceptibility that matches that of the core sample and formation water. This electrode avoids the local magnetic field distortion caused by magnetic susceptibility differences in traditional metal electrodes, thus eliminating image artifacts; at the same time, its porous structure allows the displacing fluid to pass freely, ensuring the authenticity of the flow field. This feature solves the technical problems of black holes and flow field distortion in NMR imaging caused by metal electrodes.

[0030] An electromagnetic compatibility (EMC) filter network, connected between the high-voltage power supply and the electrodes, filters out the high-frequency ripple noise of the high-voltage power supply itself through filtering and isolation circuits. It also blocks the leakage of NMR radio frequency pulses along the high-voltage line, preventing radio frequency energy loss and external interference. This feature solves the technical problems of high-voltage power supply noise overwhelming the NMR signal and radio frequency energy leakage causing a decrease in signal-to-noise ratio.

[0031] Specifically, the main body of the high-voltage clamp is made of reinforced polyetheretherketone (PEEK) or glass fiber composite material, and the insulating confining medium is perfluoropolyether oil. The high-voltage clamp has a pressure resistance range of 0~40 MPa and a temperature resistance range of 0~100°C. The viscosity of the perfluoropolyether oil is preferably 0.5~2.0 cSt (25°C) to ensure that it does not generate any background signal interference in MRI imaging.

[0032] Specifically, the magnetic susceptibility matching electrode system employs a porous carbon fiber / aerogel composite electrode or a gold-plated graphite electrode, which has a porous structure that allows fluid passage. As a preferred embodiment, the magnetic susceptibility matching electrode is prepared using a porous carbon-based composite material. By adjusting the density and doping ratio of the carbon material, its magnetic susceptibility is highly matched to the rock skeleton and formation water. Its volumetric conductivity is preferably 50–150 S / m, and its porosity is preferably 20%–45%, ensuring the passage of displacing fluid while eliminating MRI image artifacts.

[0033] In one specific embodiment, the formulation of the high-performance magnetic susceptibility-matched carbon-based electrode is as follows: PAN-based short-cut carbon fiber (45wt%), conductive carbon black (10wt%), polytetrafluoroethylene (PTFE) emulsion (40wt%), and ammonium bicarbonate pore-forming agent (5wt%). The preparation process involves ball milling and mixing the above components, followed by molding, and then sintering at 360°C to remove the pore-forming agent. The measured physical properties of the resulting electrode are: porosity 35%, volumetric conductivity 85 S / m, and excellent charge injection capability under a high voltage of 2 kV / cm.

[0034] like Figure 2 As shown, the left image is an MRI image using the magnetic susceptibility-matched carbon-based electrode described in this invention. The edges are smooth, the signal background at the electrode is zero, the core end face is clearly visible, and there is no geometric distortion. The middle image is an MRI image of a conventional stainless steel metal electrode (Comparative Example 1), where a large signal black hole appears near the electrode, and the surrounding core image is severely distorted. The right image is an MRI image of a pure graphite non-porous electrode (Comparative Example 2). The image quality is acceptable, but the fluid accumulates at the core edge, and the central part lacks dynamics. This comparison visually demonstrates the advantages of the electrode of this invention in eliminating artifacts and maintaining the authenticity of the flow field.

[0035] As a comparative example 1, traditional stainless steel metal electrodes (such as sintered 316L stainless steel powder) have a porosity of 30% and a density of 1.4 × 10⁻⁶. 6 The high conductivity of S / m, but due to the severe mismatch between the magnetic susceptibility of the metal and the core, and the strong eddy current effect generated under the high frequency radio frequency field, huge signal loss black holes (artifacts) appear near the electrodes in the MRI image, making it impossible to monitor within 1-2 cm of the core tip.

[0036] As a comparative example 2, the porosity of the pure graphite non-porous electrode (90wt% high-purity graphite powder + 10wt% binder) is less than 5%, and the volumetric conductivity is 200S / m. Its imaging quality is acceptable, but because the fluid cannot penetrate the electrode, the displacement fluid can only flow around the edge of the electrode, which destroys the linear flow field inside the core and cannot truly simulate the underground displacement process.

[0037] The specific performance comparisons of the above schemes are shown in Table 1:

[0038] As shown in Table 1, the electrode provided by the present invention achieves perfect matching of magnetic susceptibility while ensuring good conductivity and fluid permeability, thereby obtaining clear MRI images without artifacts and solving the problem that imaging quality and flow field authenticity cannot be achieved simultaneously in the prior art.

[0039] Specifically, the electromagnetic compatibility filter network includes a blocking unit composed of a non-magnetic inductor and a damping resistor connected in parallel, and at least one filter capacitor. The blocking unit is connected in series between the high-voltage power supply and the electrode system, and the filter capacitor is connected across the high-voltage line and ground.

[0040] A blocking unit, consisting of a non-magnetic inductor and a damping resistor connected in parallel, is connected in series in the high-voltage circuit. The inductor presents low impedance to DC and high impedance to RF, while the resistor dissipates high-frequency energy to prevent resonance. A filter capacitor is connected between the high-voltage line and ground to provide high-frequency bypass. This circuit achieves bidirectional isolation, has a simple structure, and contains no magnetic components, thus avoiding interference with the nuclear magnetic field.

[0041] In one specific embodiment, such as Figure 3 As shown, the electromagnetic compatibility filter network, as a shielded isolation coupling unit, is entirely encapsulated within an external electromagnetic shielding box (dashed frame). Its specific component selection and connection relationships are as follows: Decoupling capacitor C1: Connected between the high-voltage input terminal (HV+) and ground (GND), it is the primary decoupling capacitor used to filter out low-frequency ripple and switching noise generated by the high-voltage power supply, directly guiding the subtle AC ripple at the input terminal to ground. Recommended model: CBB81-2000V-103J, capacitance 0.01μF, withstand voltage 2kV (adjust according to actual voltage).

[0042] The choke inductor L1 and the non-inductive damping resistor R connected in parallel form a choke unit: connected in series in the circuit, it is the core impedance adjustment unit. L1 is a coreless inductor with an inductance of 500μH~1mH, wound with Φ1.5mm enameled wire on a ceramic frame to ensure that the inductance is not saturated under a strong magnetic field and does not interfere with the uniformity of the magnetic field, thus blocking high frequencies and passing low frequencies, preventing radio frequency interference (RF) from entering the power supply terminal in reverse, while allowing a stable DC high voltage to pass through; R is an RI80 type oxide film resistor with a resistance of 100Ω~500Ω, connected in parallel across L1, used to reduce the Q value of the LC circuit, suppress resonance, and absorb residual RF energy.

[0043] Decoupling capacitor C2: Connected between the circuit output terminal (HV-Out) and ground, mounted on the wall of the electromagnetic shielding box. It has a capacitance of 4700pF and a withstand voltage of 2kV. As a last line of defense, it provides extremely low high-frequency grounding impedance, with a cutoff frequency of less than 1MHz.

[0044] DC blocking / filtering capacitor C3: It is connected in series with L1 to form an LC filter network. In this DC high voltage circuit, it mainly realizes the functions of energy storage filtering and smoothing electric field, and further filters out the ripple signal in the circuit, so that only extremely stable DC components flow to the output terminal. The capacitor withstand voltage is not less than 2kV, and the capacitance is preferably 0.001μF~0.01μF.

[0045] High-voltage feedthrough capacitor: for Figure 3 The component marked in the right box is installed on the wall of the electromagnetic shielding box, that is, where the wires pass through the physical holes of the shielding box. As a secondary shielding component, it is connected between the final output terminal of the circuit and ground (GND) to completely filter out conducted interference, prevent electromagnetic wave leakage, and provide extremely low high-frequency grounding impedance. The cutoff frequency is less than 1MHz, the capacitance is 4700pF, and the withstand voltage is 2kV.

[0046] Electromagnetic shielding box: Made of oxygen-free copper or pure copper with a wall thickness of 2mm, serving as the system common ground (GND) to achieve electrostatic shielding, physically isolating external electromagnetic stray signals from interfering with internal circuits and weak nuclear magnetic resonance signals, and blocking space radiation.

[0047] This filtering network achieves bidirectional isolation and suppression: during downlink blocking, high-voltage DC enters the MRI cavity through L1, while high-frequency ripple noise is intercepted by the low-pass filter network composed of C1 and L1 and guided to the shielding ground; during uplink isolation, the MRI radio frequency pulse signal (10MHz~128MHz) encounters the high-impedance wall of L1 when leaking along the conductor, the parallel resistor R dissipates the high-frequency oscillation energy, and finally the residual signal is grounded by the feedthrough capacitor C2. Test results show that when the high-voltage power supply is turned on to 2kV, the background noise of MRI imaging without this filtering system increases by about 240%, and obvious stripe artifacts appear in the image; after connecting the electromagnetic compatibility filtering network described in this invention, the imaging noise fluctuation is less than 1.2%, the signal-to-noise ratio is almost unaffected, and the application of the DC high-voltage electric field does not generate induced noise in the MRI coil, realizing in-situ high-definition imaging under strong electric field environment.

[0048] Specifically, the functions of each component in the electromagnetic compatibility filter network are explained in detail below: HV+ (High Voltage Input): Function: Connects to an external high voltage regulated power supply, inputting the required DC energy. The DC current generated by the external high voltage power supply enters the circuit from here, and this current may carry power fluctuations or environmental noise.

[0049] C1 (Decoupling Capacitor): Location: After the input terminal, connected across HV+ and ground (GND). Function: Primary decoupling and noise bypass, directly guiding the small AC ripple and switching noise from the high-voltage power input terminal to ground, completing primary filtering and ensuring the initial stability of the power entering subsequent circuits.

[0050] L1 & R (Damping Choke - Core Component): Structure: Inductor L1 and resistor R are connected in parallel and in series with C1 in the subsequent stage circuit. Function: Bidirectional barrier and impedance regulation. L1 (non-magnetic inductor) provides almost no obstruction to direct current (DC), allowing stable high voltage DC to pass smoothly. However, it has extremely high impedance to radio frequency (RF) pulses generated by nuclear magnetic resonance, preventing RF interference from entering the power supply in reverse. R (damping resistor) is used to dissipate high-frequency energy in the circuit, preventing the circuit from resonating due to inductance and capacitance (once resonance occurs, large bright spots will appear in the image), and also absorbing residual RF energy.

[0051] C2 (Decoupling Capacitor): Location: After the LC filter network and before the feedthrough capacitor, connected across the circuit and ground (GND). Function: Secondary decoupling, bypassing noise, further filtering out AC ripple in the circuit and directing it to ground, thus ensuring the purity of the voltage transmitted to the output.

[0052] C3 (DC blocking / filter capacitor): Location: Connected in series with L1 to form an LC filter network. Function: Stores energy, filters, smooths the electric field, further filters out ripple signals in the circuit, and is in an open-circuit state for stable DC, so that only extremely stable DC components flow to the output terminal, thereby improving the stability of DC voltage.

[0053] Electromagnetic shielding box (outer dashed frame): Functions: electrostatic shielding, spatial radiation isolation, physically isolating external electromagnetic stray signals (such as mobile phone signals, Wi-Fi signals) from interfering with the internal circuits, while preventing internal interference signals from radiating outwards and affecting the MRI scanner, and blocking spatial radiation coupling.

[0054] Specifically, the principles of current flow and noise interception in the electromagnetic compatibility filter network are explained in detail below: 1. DC high voltage forward flow (forward: from left to right, the dynamic flow of applying an electric field to the core) Route: External high voltage power supply → HV + input terminal → C1 decoupling capacitor → L1 / R damping choke circuit → C3 DC blocking / filtering capacitor → C2 decoupling capacitor → feedthrough capacitor → output to nuclear magnetic resonance electrode (core electrode).

[0055] 2. RF / Noise Reverse Interception (Reverse: from right to left, intercepting MRI RF and circuit noise) Background: During nuclear magnetic resonance imaging, there are extremely strong radio frequency (RF) signals around the core, and there are a small amount of residual AC ripple in the circuit. If such signals flow back into the power supply or radiate outward, they will seriously interfere with nuclear magnetic resonance imaging.

[0056] Interception process: First, when the nuclear magnetic resonance radio frequency (RF) signal attempts to flow back into the circuit from the output, it first encounters the feedthrough capacitor, and most of the RF signal is directly guided to the ground wire, achieving the initial interception of conducted interference. Second, a small amount of residual RF signal continues to flow to the left, encountering the high impedance wall formed by L1, and cannot continue to move towards the power supply. Because L1 is connected in parallel with a damping resistor R, the high-frequency energy of the residual noise is quickly consumed by R as a small amount of heat, and cannot form an echo. At the same time, the LC filter network of C3 and L1 will further filter out the residual ripple. If there is still a very small amount of noise reaching the input, C1 will bypass it again and guide it to the ground wire, completing the final interception.

[0057] Based on the above process, the radio frequency signal of the MRI scanner cannot leak back to the power supply, the ripple noise of the circuit itself is completely filtered out, the imaging no longer has artifacts, and the image clarity is greatly improved.

[0058] Specifically, the non-magnetic inductor is a coreless hollow inductor, the filter capacitor includes a high-voltage feedthrough capacitor, and the electromagnetic compatibility filter network is encapsulated in an electromagnetic shielding box.

[0059] The hollow inductor avoids the saturation failure of the magnetic core under strong magnetic fields, the feedthrough capacitor provides extremely low high-frequency grounding impedance, and the shielding box prevents spatial radiation coupling, further improving electromagnetic compatibility performance.

[0060] Example 2 This embodiment provides a field-assisted high-pressure oil displacement monitoring method based on the device described in Embodiment 1, compatible with nuclear magnetic resonance imaging, including the following steps: A saturated oil-water core sample is loaded into the high-pressure holder body and an insulating confining pressure medium is injected. The loaded high-pressure clamp body is placed in the detection area of ​​the nuclear magnetic resonance imaging instrument, and baseline data is acquired under pressureless and electric field-free conditions to obtain the initial distribution image of the fluid inside the core. Conventional fluid displacement experiments were performed on the core samples. After the displacement stabilized, nuclear magnetic resonance imaging was performed to obtain the first distribution image. Under the condition of maintaining fluid displacement, a high-voltage electric field is applied to the core sample through the electromagnetic compatibility filter network, and nuclear magnetic resonance imaging is performed during the electric field to obtain a second distribution image; The first and second distribution images are processed and analyzed to obtain the utilization of the electric field on the remaining oil.

[0061] The method provided in this embodiment first obtains the initial state through baseline acquisition, then performs conventional displacement to obtain the residual oil distribution (first distribution image), followed by applying an electric field and imaging in real time (second distribution image), and finally obtains the electric field mobilization effect through comparative analysis. This method solves the problem that existing technologies cannot dynamically and quantitatively monitor changes in residual oil under the action of an electric field.

[0062] Specifically, the baseline data acquisition includes performing T2 spectrum testing and three-dimensional MRI scanning to obtain the initial oil saturation distribution of fluids inside the core, providing a benchmark for subsequent comparisons.

[0063] Specifically, the conventional fluid displacement experiment is a water drive experiment. After monitoring the water content at the outlet until it reaches a stable threshold, the first distribution image obtained is a residual oil distribution map.

[0064] Specifically, the high-voltage electric field is a DC electric field or a pulsed electric field. The nuclear magnetic resonance imaging scan during the electric field operation adopts a fast imaging sequence, and images are acquired in real time at different time points of the electric field operation. This can capture the transient transport characteristics of the fluid under the electric field operation and solve the problem of difficult monitoring of dynamic processes.

[0065] Specifically, the processing and analysis of the first and second distribution images includes: registering the images and performing a difference operation to generate a distribution map of the residual oil mobilized by the electric field, and combining this with T2 spectral shift to quantify the degree of mobilization of residual oil in channels of different pore sizes. This method transforms qualitative images into quantitative data, providing a reliable means to analyze the mechanism of the effect of the electric field on residual oil in micropores.

[0066] In one specific embodiment, the monitoring method includes: S1: Pretreatment and loading of core samples; Sandstone cores are washed and dried, and basic physical parameters are measured. They are then placed in a vacuum pressurization saturation device to saturate formation water and simulated oil, preparing a saturated oil-water core. This saturated oil-water core is then loaded into a PEEK high-voltage holder equipped with a magnetic susceptibility matching electrode, and perfluoropolyether oil is injected as the insulating confining pressure medium. Core specifications: preferably a diameter of 25mm or 38mm and a length of 50mm~80mm. Vacuum saturation parameters: the vacuum level must reach below 0.1kPa, and the vacuuming time must be no less than 24 hours; the pressurization saturation pressure is preferably 10MPa~30MPa, and the duration must be no less than 48 hours to ensure uniform saturation.

[0067] Furthermore, the magnetic susceptibility matching electrode is made of porous carbon-based composite material with a volume conductivity of 50~150 S / m and a porosity of 20%~45%, which ensures the permeability of the displacing fluid while eliminating MRI image artifacts.

[0068] S2: Baseline data acquisition and initial state assessment; The assembled holder is placed at the center of the effective measurement area of ​​the nuclear magnetic resonance imaging (MRI) instrument. T2 spectral analysis and 3D MRI scanning are performed under pressureless and electric field-free conditions to obtain the initial oil saturation distribution map of the fluid inside the core. Main magnetic field strength: preferably 0.5T, 1.5T, or 3.0T (low-field MRI is more suitable for porous media; a frequency of approximately 12MHz or 23MHz is recommended). T2 spectral parameters: Echo interval (TE): 0.1ms~0.3ms (short TE is crucial for capturing micropore signals). Number of echoes: 4096~8192. Waiting time (TW): 3000ms~5000ms (to ensure complete proton relaxation).

[0069] S3: Conventional water drive control experiment and residual oil calibration; Start the constant flow and constant pressure pump and perform conventional water displacement at the preset flow rate, and monitor the water content at the outlet in real time. When the water content reaches the limit threshold (95%~98%) and the NMR signal tends to stabilize, perform MRI scan again to obtain the first distribution image of residual oil. It is recommended to set the flow rate to a constant 0.01~0.5 mL / min.

[0070] S4: Dynamic in-situ monitoring under electro-assisted displacement; On the basis of maintaining the fluid displacement pressure, start a high-voltage direct current or pulsed electric field through an electromagnetic compatibility (EMC) filtering injection system, and adjust the field strength to 0.5 - 5 kV / cm; use a fast scanning imaging sequence (such as RARE or EPI sequence) to take real-time snapshots at different time points under the action of the electric field, obtain the dynamic image of the fluid migration in the core driven by the electric field until the signal stabilizes again, and obtain the second distribution image after electric drive; Electric field strength control: DC voltage range: 0 - 10 kV (corresponding field strength 0 - 2 kV / cm). Pulse parameters (if using a pulsed electric field): duty cycle 20% - 50%, frequency 10 Hz - 1000 Hz. Performance of the EMC filtering injection system: Radio frequency suppression ratio: suppression ratio > 60 dB in the frequency band of 10 MHz - 100 MHz. Leakage current control: The system leakage current should be less than 10 μA to prevent the thermal effect from interfering with the fluid rheology. The repetition time (TR) of the fast imaging sequence is 500 - 2000 ms, the echo time (TE) is 5 - 15 ms, and the single imaging time is controlled within 2 minutes to capture the transient migration characteristics of the fluid under the action of the electric field force.

[0071] Further, the electromagnetic compatibility (EMC) filtering injection system includes a blocking unit composed of a non-magnetic inductor and a damping resistor connected in parallel, which is connected in series between the high-voltage power supply and the clamp to block the feedback leakage of the nuclear magnetic resonance radio frequency signal to the power supply end.

[0072] S5: Image difference processing and mobilization mechanism analysis; Perform pixel-level matrix subtraction on the first distribution image and the second distribution image to generate an electric field mobilized remaining oil distribution map; combine the T2 spectrum shift situation to quantitatively calculate the mobilization degree of the remaining oil in different pore size channels. Image registration: Before performing image subtraction, rigid registration is required to ensure that the pixel points completely coincide, and the error is controlled within 0.5 pixels. Signal normalization: Use a reference standard tube (usually placed beside the clamp, filled with a known liquid of a constant volume) to normalize the MRI signals at different time points to eliminate the influence of magnetic field drift. Pore mobilization threshold: Micro pores (T2 < 10 ms), medium pores (10 ms < T2 < 100 ms), large pores (T2 > 100 ms), and calculate the displacement efficiency of each level of pores by comparing the spectral coverage areas before and after electric drive.

[0073] Such as Figure 4 , the working principle of the present invention is based on two mechanisms of frequency domain isolation and physical field compatibility, and three functional units work together to achieve the compatibility of high-voltage electric field and nuclear magnetic resonance imaging.

[0074] On the left is the high-voltage power supply and filtering unit. This unit includes an HV high-voltage power supply and an EMI / RF filter network. The high-voltage power supply generates the DC or pulsed high voltage required for oil displacement. The filter network connects the high-voltage power supply to the internal components of the magnet. The filter network performs low-pass filtering on the high-frequency ripple noise generated by the high-voltage power supply itself, directing this noise to ground. Simultaneously, the filter network exhibits high impedance characteristics for the radio frequency signals generated during NMR imaging. This high impedance prevents the radio frequency signal from leaking outward along the high-voltage line. Through this bidirectional isolation mechanism, the electric field applied to the core sample is a pure DC or low-frequency pulse. This mechanism avoids interference from power supply noise on the NMR signal and also prevents the loss of NMR radio frequency signals.

[0075] The central component is the core clamping assembly within the superconducting magnet cavity. This assembly comprises a PEEK clamping cylinder, susceptibility-matched carbon-based electrodes, a core sample, and a hydrofluoric acid-free confining medium. The PEEK clamping cylinder is made of a non-metallic, high-strength material transparent to radio frequency signals. This material provides no shielding against the NMR radio frequency field, allowing the field to penetrate the clamping cylinder uniformly. The susceptibility-matched carbon-based electrodes are positioned at both ends of the core sample. These electrodes are made of a porous carbon-based composite material, with a susceptibility matched to that of the core and formation water. These electrodes do not produce localized magnetic field distortion in NMR imaging, eliminating image artifacts near the electrodes. The porous structure of these electrodes allows the displacing fluid to pass freely, ensuring the authenticity of the flow field. The confining cavity is filled with hydrofluoric acid-free oil as an insulating confining medium. Hydrofluoric acid-free oil contains no hydrogen atoms and does not produce any background signal in NMR imaging, highlighting the true distribution of fluid within the core. The displacing fluid is injected through the inlet, flows through the core sample, and exits through the produced fluid outlet. The confining pressure system maintains the pressure environment inside the clamp through the confining pressure inlet, simulating formation confining pressure conditions.

[0076] The right side shows the NMR signal acquisition and fluid control unit. This unit includes a T / R switch and preamplifier, a high-pressure advection pump, and a confining pressure tracking pump. The T / R switch controls the transmission of NMR radio frequency pulses and the reception of NMR signals. The preamplifier amplifies the weak NMR signals and sends them to the imaging system for processing. The high-pressure advection pump injects displacement fluid into the core at a constant flow rate or pressure. The confining pressure tracking pump adjusts the confining pressure in real time to ensure that the experimental process is consistent with the formation conditions.

[0077] The workflow of this invention is as follows: First, baseline data is acquired under pressureless and electric field-free conditions to obtain an initial distribution image of the fluid inside the core. Then, a high-pressure advection pump is started for conventional water flooding. After the displacement stabilizes, nuclear magnetic resonance imaging (NMR) scanning is performed to obtain a first distribution image, which is a residual oil distribution map. Next, an electric field is applied through a high-voltage power supply. The electric field is applied to the core sample after passing through a filter network. During the application of the electric field, images are acquired in real time using a fast imaging sequence to obtain a second distribution image, which is a distribution map after electric flooding. Finally, the first and second distribution images are processed by difference. During processing, the images are first registered to ensure pixel overlap. Then, a subtraction operation is performed to generate a distribution map of the residual oil mobilized by the electric field. Combined with T2 spectral shift, the degree of mobilization of residual oil in different pore size channels is quantified.

[0078] Through the coordinated work of the above three units, this invention realizes in-situ, real-time, and high-definition imaging monitoring in an environment where strong electric and magnetic fields coexist, providing a reliable experimental platform for the study of electric field-assisted oil displacement mechanism.

[0079] In the description of this specification, the terms "connection", "installation", "fixing", "setting", etc. are interpreted broadly. For example, "connection" can be a fixed connection or an indirect connection through an intermediate component without affecting the relationship between components and the technical effect. It can also be an integral connection or a partial connection. In such cases, those skilled in the art can understand the specific meaning of the above terms in this invention or invention according to the specific circumstances.

[0080] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A field-assisted high-pressure oil displacement monitoring device compatible with nuclear magnetic resonance imaging, characterized in that, include: The high-pressure clamp body is used to hold the core sample and provide a high-pressure environment. The clamp body is made of a non-metallic high-strength material that is transparent to radio frequency signals, and its confining cavity is filled with an insulating confining medium that does not contain hydrogen atoms. A magnetic susceptibility matching electrode system is disposed within the high-voltage holder body and is used to apply a high-voltage electric field to the core sample. The electrode system is made of porous conductive composite material, and its magnetic susceptibility is matched with that of the core sample and the fluid contained therein. An electromagnetic compatibility filter network is connected between the high-voltage power supply and the magnetic susceptibility matching electrode system to filter noise from the high-voltage power supply and block the leakage of radio frequency signals from the MRI scanner to the high-voltage power supply side.

2. The apparatus as claimed in claim 1, characterized in that, The main body of the high-voltage clamp is made of reinforced polyetheretherketone or glass fiber composite material, and the insulating confining medium is perfluoropolyether oil.

3. The apparatus as described in claim 1, characterized in that, The magnetic susceptibility matching electrode system employs a porous carbon fiber / aerogel composite electrode or a gold-plated graphite electrode, which has a porous structure that allows fluid to pass through.

4. The apparatus as claimed in claim 1, characterized in that, The electromagnetic compatibility filter network includes a blocking unit consisting of a non-magnetic inductor and a damping resistor connected in parallel, and at least one filter capacitor. The blocking unit is connected in series between the high-voltage power supply and the electrode system, and the filter capacitor is connected across the high-voltage line and ground.

5. The apparatus as described in claim 4, characterized in that, The non-magnetic inductor is a coreless hollow inductor, the filter capacitor includes a high-voltage feedthrough capacitor, and the electromagnetic compatibility filter network is encapsulated in an electromagnetic shielding box.

6. A method for monitoring electric field-assisted high-pressure oil displacement compatible with nuclear magnetic resonance imaging using the apparatus described in any one of claims 1-5, characterized in that, Includes the following steps: A saturated oil-water core sample is loaded into the high-pressure holder body and an insulating confining pressure medium is injected. The loaded high-pressure clamp body is placed in the detection area of ​​the nuclear magnetic resonance imaging instrument, and baseline data is acquired under pressureless and electric field-free conditions to obtain the initial distribution image of the fluid inside the core. Conventional fluid displacement experiments were performed on the core samples. After the displacement stabilized, nuclear magnetic resonance imaging was performed to obtain the first distribution image. Under the condition of maintaining fluid displacement, a high-voltage electric field is applied to the core sample through the electromagnetic compatibility filter network, and nuclear magnetic resonance imaging is performed during the electric field to obtain a second distribution image; The first and second distribution images are processed and analyzed to obtain the utilization of the electric field on the remaining oil.

7. The method as described in claim 6, characterized in that, The baseline data acquisition includes T2 spectrum testing and three-dimensional MRI scanning to obtain the initial oil saturation distribution of the fluid inside the core.

8. The method as described in claim 6, characterized in that, The conventional fluid displacement experiment is a water drive experiment. After monitoring the water content at the outlet until it reaches a stable threshold, the first distribution image is obtained as a residual oil distribution map.

9. The method as described in claim 6, characterized in that, The high-voltage electric field is a DC electric field or a pulsed electric field. During the application of the electric field, the nuclear magnetic resonance imaging scan adopts a fast imaging sequence, and images are acquired in real time at different time points of the electric field application.

10. The method as described in claim 6, characterized in that, The processing and analysis of the first distribution image and the second distribution image includes: registering the images and performing a difference operation to generate a distribution map of the remaining oil mobilized by the electric field, and combining the T2 spectrum shift to quantify the degree of mobilization of the remaining oil in the channels with different aperture sizes.

Images