Core nuclear magnetic resonance measurement method and equipment based on gradient field layer selection
By dividing the core into multiple selected sections and applying a linear gradient field, the problem of poor measurement accuracy in shale reservoirs was solved, achieving high-resolution and high-precision core nuclear magnetic resonance measurements, which is suitable for rapid evaluation of shale reservoirs.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-09-23
- Publication Date
- 2026-03-24
AI Technical Summary
Existing technologies face challenges due to the strong vertical heterogeneity of shale reservoirs, which makes core sampling difficult. Traditional core nuclear magnetic resonance (NMR) instruments cannot meet the requirements for rapid, real-time, and high-precision evaluation, and also suffer from poor measurement accuracy and data distortion.
A core nuclear magnetic resonance measurement method based on gradient field selection was adopted. The core was divided into multiple selected segments, and the selected segments were measured by linear gradient field. The radio frequency coil and gradient coil output radio frequency pulse sequence and echo signal were used to invert T2 and T1T2 data to identify core fluid.
It enables high-resolution core nuclear magnetic resonance measurements, reduces fluid identification errors, and improves the flexibility and accuracy of measurements, thus meeting the measurement needs of shale reservoirs.
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Figure CN121721073A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of core analysis technology, specifically relating to a core nuclear magnetic resonance measurement method based on gradient field selection, a control device, a computer device, a machine-readable storage medium, a core nuclear magnetic resonance measurement device based on gradient field selection, and a core nuclear magnetic resonance measurement system based on gradient field selection. Background Technology
[0002] Nuclear magnetic resonance (NMR) is a rapid, efficient, and non-destructive measurement method widely used in geophysics. NMR technology can bypass the core skeleton response and directly obtain hydrogen-containing signals in pore fluids, achieving excellent results in evaluating the fluid properties of complex reservoirs such as tight sandstone, low porosity and permeability, and low resistivity. However, compared with conventional reservoirs, shale has significantly different formation characteristics. Shale exhibits strong vertical heterogeneity, making high-resolution thin-layer identification crucial for shale mining.
[0003] For conventional sandstone reservoirs, small-sample drilling is often used for testing, with measurements from small core columns used as the physical property characteristics of that section of the core. This method has two drawbacks: first, small core columns represent a point on the surface, failing to accurately describe the physical properties of the core; second, the time required to transport the small core to the laboratory is considerable, making it impossible to obtain fresh sample data. For shale reservoirs, due to their strong vertical heterogeneity and the difficulty in core sampling, the use of laboratory small core columns with nuclear magnetic resonance (NMR) measurements cannot meet the requirements for rapid, real-time, and high-precision evaluation of shale reservoirs in the field.
[0004] Uniform field full-diameter core NMR spectrometers primarily achieve high longitudinal resolution data acquisition in two ways: one is by shortening the detection range of the radio frequency (RF) coil, and the other is by using a high-resolution inversion algorithm. If the first method is used, when the maximum full-diameter core size is 115 mm, even with a single-turn RF coil, the RF excitation signal range is still approximately 80 mm, making it impossible to obtain truly high-resolution core data. If the second method is used, a high-resolution inversion algorithm is required to obtain high-resolution data. If magnetic minerals are present in the core, it can lead to accelerated relaxation and a reduced signal-to-noise ratio, and this effect accumulates with the core length, causing data distortion. Furthermore, when the core length exceeds the coil detection range during core measurement, both linear and nonlinear regions contribute to the signal. However, in two-dimensional measurements, the flip angle of the nonlinear region is inconsistent with that of the linear region, often resulting in T1 non-convergence after inversion, which introduces errors into the identification results of unconventional reservoir fluids. Summary of the Invention
[0005] The purpose of this invention is to provide a core nuclear magnetic resonance measurement method based on gradient field selection, a control device, a computer device, a machine-readable storage medium, a core nuclear magnetic resonance measurement device based on gradient field selection, and a core nuclear magnetic resonance measurement system based on gradient field selection, in order to overcome the shortcomings of poor measurement accuracy of traditional core nuclear magnetic resonance measuring instruments in the prior art.
[0006] To achieve the above objectives, a first aspect of the present invention provides a core nuclear magnetic resonance measurement method based on gradient field selection, the method comprising:
[0007] Determine the thickness of the selected layers, and divide the core into multiple selected layers based on the thickness of the selected layers;
[0008] Calculate the selected layer gradient value output by the gradient coil;
[0009] Control the conveying device so that it moves each selected section of the core to the measurement area in sequence;
[0010] For each selected layer segment, the radio frequency coil in the measurement area is controlled to output a radio frequency pulse sequence and the echo signal is collected. During the pulse opening period of all the radio frequency pulse sequences, the gradient coil in the measurement area is controlled to apply a linear gradient field with a gradient of the selected layer gradient value and a direction of the main magnetic field direction.
[0011] Invert the echo signal to identify the core fluid.
[0012] Optionally, for each selected layer segment, the step of controlling the radio frequency coil within the measurement area to output a radio frequency pulse sequence and acquiring echo signals, and during all pulse-on periods of the radio frequency pulse sequence, controlling the gradient coil within the measurement area to apply a linear gradient field with a gradient equal to the selected layer gradient value and a direction equal to the main magnetic field direction, includes:
[0013] For each selected layer segment, the radio frequency coil in the control measurement area outputs a first pulse sequence and acquires a first echo signal. During the 90-degree pulse and 180-degree pulse activation period of the first pulse sequence, the gradient coil in the control measurement area applies a first linear gradient field with a gradient of the selected layer gradient value and a direction of the main magnetic field direction.
[0014] For each selected layer segment, the radio frequency coil in the control measurement area outputs a second pulse sequence and acquires a second echo signal. During the inversion pulse, 90-degree pulse and 180-degree pulse activation periods of the second pulse sequence, the gradient coil in the control measurement area applies a second linear gradient field with a gradient of the selected layer gradient value and a direction of the main magnetic field direction.
[0015] In the first and second pulse sequences, the pulse width of the 90-degree pulse is equal to the pulse width of the 180-degree pulse.
[0016] Optionally, the inversion echo signal, used to identify core fluid, includes:
[0017] The first echo signal was inverted to obtain T2 data, which was used to determine the core porosity.
[0018] The T1T2 data were obtained by inverting the second echo signal to determine the oil-water saturation of the core.
[0019] Optionally, the method further includes:
[0020] Within the sampling period of each selected layer segment, while controlling the output of the first pulse sequence of the radio frequency coil, the first linear gradient field is also controlled to be in the on state during the first time period;
[0021] The first time period is the second time period after excluding the 90-degree pulse and 180-degree pulse start periods. The second time period is the period from the start of the 90-degree pulse of the first pulse sequence to the acquisition of the last echo in the sampling period.
[0022] Optionally, the method further includes:
[0023] Within the sampling period of each selected layer segment, while controlling the output of the second pulse sequence of the RF coil, the second linear gradient field is also controlled to be in the on state during the third time period;
[0024] The third time period is the fourth time period after excluding the periods when the inversion pulse, 90-degree pulse, and 180-degree pulse are activated. The fourth time period is the period from the activation of the inversion pulse of the second pulse sequence to the acquisition of the last echo in the sampling period.
[0025] Optionally, the first pulse sequence is a CPMG sequence.
[0026] Optionally, the second pulse sequence is an SR-CPMG sequence.
[0027] Optionally, the calculation of the selected layer gradient value output by the gradient coil includes:
[0028] The layer selection gradient value output by the gradient coil is calculated based on the pulse frequency bandwidth and layer selection thickness of the RF coil output.
[0029] A second aspect of the present invention provides a control device, the device comprising:
[0030] The first determining module is used to determine the selected layer thickness and divide the core into multiple selected layer segments based on the selected layer thickness.
[0031] The first calculation module is used to calculate the selected layer gradient value output by the gradient coil;
[0032] The first control module is used to control the conveying device so that the conveying device moves each selected section of the core to the measurement area in sequence.
[0033] The echo acquisition module is used to control the radio frequency coil in the measurement area to output a radio frequency pulse sequence for each selected layer segment and acquire the echo signal. During the pulse activation period of all the radio frequency pulse sequences, the gradient coil in the measurement area is controlled to apply a linear gradient field with a gradient of the selected layer gradient value and a direction of the main magnetic field direction.
[0034] The inversion module is used to invert echo signals to identify core fluids.
[0035] A third aspect of the present invention provides a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the program, it implements the core nuclear magnetic resonance measurement method based on gradient field selection as described in the first aspect of the present invention.
[0036] A fourth aspect of the present invention provides a machine-readable storage medium having a computer program stored thereon, wherein the computer program, when executed by a processor, implements the core nuclear magnetic resonance measurement method based on gradient field selection as described in the first aspect of the present invention.
[0037] A fifth aspect of the present invention provides a core nuclear magnetic resonance measurement device based on gradient field selection. The core nuclear magnetic resonance measurement device includes the control device described in the second aspect of the present invention, a main coil for generating a main magnetic field, a gradient coil for generating a linear gradient field, a radio frequency coil for generating a radio frequency pulse sequence, and an echo acquisition coil for acquiring echo signals. The control device is electrically connected to the main coil, the gradient coil, the radio frequency coil, and the echo acquisition coil, respectively. The control device is also used to connect to an external transmission device.
[0038] Optionally, the gradient coil is placed in an oil bath.
[0039] A sixth aspect of the present invention provides a core nuclear magnetic resonance measurement system based on gradient field selective layering, the system comprising the core nuclear magnetic resonance measurement device and the transmission device described in the fifth aspect of the present invention, wherein the core nuclear magnetic resonance measurement device and the transmission device are electrically connected.
[0040] In the above technical solution, the core is divided into multiple selected segments based on the selected layer thickness, and each selected segment is sequentially sent to the measurement area. Each selected segment is a measurement unit. Layer selection is performed by applying a linear gradient field during echo signal acquisition, resulting in continuous slice-type core NMR signals, thus achieving core NMR measurement with a defined resolution. To achieve core NMR measurements at different resolutions, only the selected layer thickness needs to be changed, making the resolution more flexible and adjustable compared to traditional core NMR instruments. The slice-type core measurement method can meet the high-resolution measurement requirements of shale reservoirs. Simultaneously, the selected layer area is a linear region of the coil, overcoming the T1 relaxation time non-convergence problem caused by the coil nonlinearity region of traditional core NMR instruments, reducing reservoir fluid identification errors, especially for unconventional reservoirs.
[0041] Other features and advantages of the embodiments of the present invention will be described in detail in the following detailed description section. Attached Figure Description
[0042] The accompanying drawings are provided to further illustrate embodiments of the present invention and form part of the specification. They are used together with the following detailed description to explain the embodiments of the present invention, but do not constitute a limitation thereof. In the drawings:
[0043] Figure 1 A flowchart illustrating a core nuclear magnetic resonance measurement method based on gradient field selection according to an embodiment of the present invention is shown schematically.
[0044] Figure 2 A schematic diagram of a CPMG sequence with gradients is shown.
[0045] Figure 3 A schematic diagram of an SR-CPMG sequence with gradient is shown.
[0046] Figure 4 The diagram illustrates the relationship between signal quantity per unit volume and porosity.
[0047] Figure 5 The diagram illustrates layer selection at different resolutions;
[0048] Figure 6 The diagram illustrates a comparison between NMR measurement results and physical model simulation results for the calibrated sample.
[0049] Figure 7 The diagram illustrates a comparison of NMR measurement results for a calibrated sample at different resolutions.
[0050] Figure 8 This diagram illustrates the T1T2 data obtained through gradient field layer selection.
[0051] Figure 9 The diagram illustrates T1T2 data obtained by applying only a conventional uniform B0 field. Detailed Implementation
[0052] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only for illustrating and explaining the embodiments of the present invention and are not intended to limit the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.
[0053] It should be noted that if the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indicators will also change accordingly.
[0054] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. If the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.
[0055] Example 1
[0056] It should be noted that the gradient field-selective core NMR measurement method provided in this embodiment of the invention can be used for NMR measurements of full-diameter cores as well as small core columns. Preferably, in practical engineering applications, the gradient field-selective core NMR measurement is carried out at the sampling site of full-diameter cores or small core columns.
[0057] The core nuclear magnetic resonance measurement method based on gradient field selection provided by this invention includes the following implementation steps:
[0058] Step S1: Determine the selected layer thickness and divide the core into multiple selected layers based on the selected layer thickness.
[0059] Specifically, the selective layer thickness depends on the specific core sample being tested. For example, for some core samples, a 1 cm selective layer thickness is required to obtain NMR measurement results that meet the accuracy requirements for interpreting porosity and oil-water saturation. However, for unconventional shale reservoir cores, a 4 cm selective layer thickness is sufficient to meet the accuracy requirements for interpreting porosity and oil-water saturation. Therefore, the selective layer thickness must be determined based on the required measurement resolution of the specific core sample.
[0060] Step S2: Calculate the selected layer gradient value output by the gradient coil based on the selected layer thickness.
[0061] The gradient coil generates a linear gradient field, meaning that the intensity of the gradient field generated by the gradient coil changes linearly from the minimum intensity to the maximum intensity. To achieve layer selection, the application of the linear gradient field only causes the protons within the selected layer segment to resonate. In other words, the layer selection gradient value output by the gradient coil is determined by the layer thickness and the finite bandwidth of the output pulse of the RF coil (which generates RF pulses, i.e., generates B1 field) in the frequency domain. Figure 5 The diagram shows layer selection at different resolutions. Depending on the measurement resolution requirements, different layer thicknesses correspond to different layer selection gradient values.
[0062] Step S3: Control the conveying device so that it moves each selected section of the core to the measurement area in sequence.
[0063] For example, the conveying device uses a stepper motor, with the selected layer thickness as the step size of the stepper motor. The stepper motor moves the core to the measurement area according to the step size. That is, the selected layer corresponding to each step size is sequentially transported to the measurement area for nuclear magnetic resonance measurement, and one selected layer is one nuclear magnetic resonance measurement unit.
[0064] Step S4: For each selected layer segment, control the radio frequency coil in the measurement area to output a radio frequency pulse sequence and collect the echo signal. During all pulse opening periods of the radio frequency pulse sequence, control the gradient coil in the measurement area to apply a linear gradient field with a gradient of the selected layer gradient value and a direction of the main magnetic field (uniform B0 field).
[0065] Generally, the direction of the main magnetic field is the axial direction of the core.
[0066] Step S5: Invert the echo signal to identify the core fluid.
[0067] It is known that T2 data and / or T1T2 data for core fluid identification are generally obtained by inverting the echo signal, and core fluid identification is performed using parameters such as porosity and oil-water saturation.
[0068] See Figure 1In one specific embodiment, core fluid identification is performed using porosity data and oil-water saturation data. Therefore, T2 data and T1T2 data can be retrieved from the echo signal. Based on this, the core nuclear magnetic resonance measurement method based on gradient field layer selection provided in the above embodiment includes the following steps:
[0069] Step S102: Determine the selected layer thickness and divide the core into multiple selected layers based on the selected layer thickness.
[0070] Step S104: Calculate the selected layer gradient value output by the gradient coil based on the selected layer thickness.
[0071] Step S106: Control the conveying device so that it moves each selected section of the core to the measurement area in sequence.
[0072] Step S108: For each selected layer segment, control the radio frequency coil in the measurement area to output a first pulse sequence and acquire the first echo signal. During the 90-degree pulse and 180-degree pulse activation period of the first pulse sequence, control the gradient coil in the measurement area to apply a first linear gradient field with a gradient of the selected layer gradient value and a direction of the main magnetic field (uniform B0 field).
[0073] For example, in one specific embodiment, when the radio frequency coil in the measurement area outputs the first pulse sequence, the first linear gradient field is always controlled to be on throughout the entire period from the start of the 90-degree pulse of the first pulse sequence to the acquisition of the last echo within the sampling period. Based on this, the repeated on / off switching of the first linear gradient field output of the gradient coil is avoided, reducing power consumption and improving the reliability of core nuclear magnetic resonance measurements.
[0074] Furthermore, in order to achieve layer selection, the application of the linear gradient field only causes proton resonance within the selected layer region. Therefore, it can be known that the pulse widths of each P1 pulse (90-degree pulse width) and P2 pulses (180-degree pulse width) in the first pulse sequence are equal.
[0075] For example, in one specific embodiment, the first pulse sequence is a CPMG sequence to measure the T2 relaxation time. It should be understood that, as will be known to those skilled in the art, other pulse sequences besides the CPMG sequence can also be used to measure the T2 relaxation time; that is, the applicability of other pulse sequences in the embodiments of the present invention cannot be ruled out.
[0076] Step S110: For each selected layer segment, control the radio frequency coil in the measurement area to output a second pulse sequence and acquire the second echo signal. During the inversion pulse, 90-degree pulse and 180-degree pulse activation periods of the second pulse sequence, control the gradient coil in the measurement area to apply a second linear gradient field with a gradient of the selected layer gradient value and a direction of the main magnetic field direction.
[0077] For example, in one specific embodiment, when the radio frequency coil in the measurement area outputs a second pulse sequence, the second linear gradient field is always controlled to be on during the period from the start of the inversion pulse of the second pulse sequence to the acquisition of the last echo within the sampling period. Based on this, the repeated on / off switching of the second linear gradient field output of the gradient coil is avoided, reducing power consumption and improving the reliability of core nuclear magnetic resonance measurements.
[0078] Furthermore, in order to achieve layer selection, the application of the linear gradient field only causes proton resonance within the selected layer region. Therefore, it can be known that the P1 pulse width (90-degree pulse width) and P2 pulse width (180-degree pulse width) are equal in the second pulse sequence, that is, the P1 pulse width (90-degree pulse width) and P2 pulse width (180-degree pulse width) are equal in both the first and second pulse sequences.
[0079] For example, in one specific embodiment, the second pulse sequence is an SR-CPMG sequence to measure the T1 relaxation time and the T2 relaxation time. It should be understood that, as will be known to those skilled in the art, other pulse sequences besides the SR-CPMG sequence can also be used to measure the T1 relaxation time and the T2 relaxation time; that is, the applicability of other pulse sequences in the embodiments of the present invention cannot be ruled out.
[0080] Step S112: Invert the first echo signal to obtain core T2 data to determine the core porosity.
[0081] As is known, in order to determine the core porosity, after obtaining the core T2 data, it is necessary to use the calibration curve between the unit volume signal and porosity to calculate the porosity. Therefore, it is usually necessary to first use different porosity standard samples for calibration, that is, to perform nuclear magnetic resonance measurement on the porosity standard samples at the resolution corresponding to the selected layer thickness, so as to obtain the calibration curve between the unit volume signal and porosity. For the specific calibration process, refer to the general embodiment. This embodiment will not describe this part in detail.
[0082] Step S114: Invert the second echo signal to obtain core T1T2 data to determine the core oil-water saturation.
[0083] For example, in one specific embodiment, the selected layer gradient value output by the gradient coil is calculated using the following formula:
[0084]
[0085] In the above formula, h represents the selected layer thickness, P2 represents the P2 pulse width in the first and second pulse sequences, γ represents the H nucleus gyromagnetic ratio, and G... max This represents the maximum gradient output of the gradient coil. Indicates the gradient output magnitude. This represents the selected layer gradient value output by the gradient coil.
[0086] To verify the effectiveness of the above method, a series of full-diameter core calibration samples with different porosities were prepared. Continuous slice NMR measurements of each calibration sample were obtained based on gradient field layer selection. By comparing the porosity obtained from the NMR measurement results with the known porosity of the calibration sample, the error value was calculated. Furthermore, by changing the layer selection gradient value, NMR measurement results at different resolutions were obtained. By changing the layer thickness, NMR measurement results at different resolutions were obtained; see [link to details]. Figure 7 , Figure 7 The diagram shows the porosity data corresponding to selected layer thicknesses of 1 cm, 2 cm, 4 cm, and 10 cm. Comparison with the physical model simulation results of the calibrated sample revealed that the porosity data corresponding to a selected layer thickness of 1 cm showed the best match with the physical model simulation results. See [link to relevant documentation] for details. Figure 6 As shown in the figure. It can be seen that thinner selected layer thickness corresponds to higher measurement resolution, and higher measurement resolution better reflects the true physical model of the calibration sample. Furthermore, these calibration samples were tested using a traditional core nuclear magnetic resonance (NMR) instrument; that is, in the measurement area, only a uniform B0 field was applied, without a linear gradient field. In this case, the T1T2 data obtained for a certain calibration sample are as follows: Figure 9 As shown, Figure 8 The T1T2 data obtained by measuring the calibrated sample using the core nuclear magnetic resonance measurement method based on gradient field selection is shown. By comparing the two T1T2 data, it can be found that the core nuclear magnetic resonance measurement method based on gradient field selection provided in this embodiment of the invention solves the T1 non-convergence phenomenon, and the obtained porosity data and oil-water saturation data are closer to the actual situation of the formation.
[0087] Additionally, it should be noted that, Figure 1 This is a flowchart illustrating a core nuclear magnetic resonance measurement method based on gradient field layer selection in one embodiment. It should be understood that, although... Figure 1 The steps in the flowchart are shown sequentially as indicated by the arrows, but these steps are not necessarily executed in the order indicated by the arrows. Unless otherwise specified in this document, there is no strict order in which these steps are executed, and they can be performed in other orders. Furthermore, Figure 1 At least some of the steps in the process may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily completed at the same time, but can be executed at different times. The execution order of these sub-steps or stages is not necessarily sequential, but can be executed in turn or alternately with other steps or at least some of the sub-steps or stages of other steps.
[0088] Example 2
[0089] This invention provides a core nuclear magnetic resonance (NMR) measurement method based on gradient field selection, which is an application of Embodiment 1 to a specific core sample. In the following application example, the direction of the main magnetic field B0 is along the core axis, and the directions of the first and second linear gradient fields generated by the gradient coil are also along the core axis. The first pulse sequence uses the CPMG sequence. Within each sampling period, the first linear gradient field is applied only during the period from the start of the 90-degree pulse to the acquisition of the last echo within that sampling period. Figure 2 As shown. Figure 2 In this diagram, GE1 represents the gradient ramp-up time, DL10 represents the gradient settling time, RFD represents the radio frequency delay time, TE represents the echo interval, NECH represents the number of echoes, GT represents the gradient application duration, and TW represents the waiting time. The second pulse sequence uses an SR-CPMG sequence. Within each sampling period, the second linear gradient field reaches a stable output state after ramping up before the saturation pulse band begins; that is, the second linear gradient field begins earlier than the saturation pulse band. The second linear gradient field drops to 0 at the moment the last echo is acquired; that is, the second linear gradient field is turned off after the last echo is acquired. Figure 3 As shown. In both CPMG and SR-CPMG sequences, the pulse widths of P1 and P2 are fixed to be equal.
[0090] The application examples mainly include the following processes:
[0091] Step A1: Select standard samples with porosity of 1%, 5%, 10%, 20%, and 30% for calibration.
[0092] Step A2: Determine the selected layer thickness according to the measurement resolution requirements, and calculate the selected layer gradient value output by the gradient coil according to the selected layer thickness and Equation 1. Measure standard samples with different porosities to obtain the first echo signal used for T2 data inversion, establish the relationship between porosity and signal quantity per unit volume, and thus obtain the porosity calibration coefficient.
[0093] Assuming the porosity calibration factor is denoted as k, the relationship between porosity and signal quantity per unit volume can be expressed by the following formula:
[0094] por = k * S (Equation 2);
[0095] In the above formula, por represents porosity and S represents signal quantity per unit volume.
[0096] Figure 4 The relationship curves between porosity and signal intensity per unit volume obtained through different standard sample calibrations are shown. Specifically, the relationship curves can be expressed by the following formula:
[0097] y = 120x + 1E - 12 (Equation 3);
[0098] In the above formula, y represents the signal quantity per unit volume, and x represents the porosity.
[0099] Step A3: Move the core sample to the measurement area using a stepper motor with the selected layer thickness as the step size. At this time, for each selected layer, control the RF coil in the measurement area to output a CPMG sequence and acquire the first echo signal. During the entire period from the start of the 90-degree pulse of the CPMG sequence to the acquisition of the last echo in the sampling period, control the gradient coil in the measurement area to apply a first linear gradient field with a gradient equal to the selected layer gradient value and a direction equal to the main magnetic field direction. Then, control the RF coil in the measurement area to output an SR-CPMG sequence and acquire the second echo signal. During the period from the start of the inversion pulse of the second pulse sequence to the acquisition of the last echo in the sampling period, control the gradient coil in the measurement area to apply a second linear gradient field with a gradient equal to the selected layer gradient value and a direction equal to the main magnetic field direction, until the first echo signal and the second echo signal are measured in each selected layer of the core sample.
[0100] Step A4: Invert the first echo signal to obtain T2 data, and calculate the porosity of the core sample using Equation 2.
[0101] Step A5: Invert the second echo signal to obtain T1T2 data, and combine it with the porosity of the tested core to determine the oil-water saturation of the tested core.
[0102] Example 3
[0103] An embodiment of the present invention provides a control device comprising a first determining module, a first calculating module, a first controlling module, an echo acquisition module, and an inversion module, wherein:
[0104] The first determining module is used to determine the selected layer thickness and divide the core into multiple selected layer segments based on the selected layer thickness.
[0105] The first calculation module is used to calculate the selected layer gradient value output by the gradient coil;
[0106] The first control module is used to control the conveying device so that the conveying device moves each selected section of the core to the measurement area in sequence.
[0107] The echo acquisition module is used to control the radio frequency coil in the measurement area to output a radio frequency pulse sequence for each selected layer segment and acquire the echo signal. During the pulse activation period of all the radio frequency pulse sequences, the gradient coil in the measurement area is controlled to apply a linear gradient field with a gradient of the selected layer gradient value and a direction of the main magnetic field direction.
[0108] The inversion module is used to invert echo signals to identify core fluids.
[0109] Optionally, the echo acquisition module includes a first echo module and a second echo module. The first echo module is used to control the radio frequency coil in the measurement area to output a first pulse sequence for each selected layer segment and acquire the first echo signal. During the 90-degree pulse and 180-degree pulse activation periods of the first pulse sequence, the gradient coil in the measurement area is controlled to apply a first linear gradient field with a gradient equal to the selected layer gradient value and a direction equal to the direction of the main magnetic field. The second echo acquisition module is used to control the radio frequency coil in the measurement area to output a second pulse sequence for each selected layer segment and acquire the second echo signal. During the inversion pulse, 90-degree pulse, and 180-degree pulse activation periods of the second pulse sequence, the gradient coil in the measurement area is controlled to apply a second linear gradient field with a gradient equal to the selected layer gradient value and a direction equal to the direction of the main magnetic field.
[0110] In the first and second pulse sequences, the pulse width of the 90-degree pulse is equal to the pulse width of the 180-degree pulse.
[0111] Optionally, the inversion module includes a first inversion module and a second inversion module;
[0112] The first inversion module is used to invert the first echo signal to obtain T2 data in order to determine the core porosity; the second inversion module is used to invert the second echo signal to obtain T1T2 data in order to determine the core oil-water saturation.
[0113] In one specific embodiment, the control device further includes a second control module, which is used to control the first linear gradient field to be in an on state during the first time period when controlling the RF coil to output the first pulse sequence during the sampling period of each selected layer segment.
[0114] The first time period is the second time period after excluding the 90-degree pulse and 180-degree pulse start periods. The second time period is the period from the start of the 90-degree pulse of the first pulse sequence to the acquisition of the last echo in the sampling period.
[0115] In one specific embodiment, the control device further includes a third control module, which is used to control the second linear gradient field to be in an on state during a third time period when controlling the output of the second pulse sequence of the radio frequency coil during the sampling period of each selected layer segment.
[0116] The third time period is the fourth time period after excluding the periods when the inversion pulse, 90-degree pulse, and 180-degree pulse are activated. The fourth time period is the period from the activation of the inversion pulse of the second pulse sequence to the acquisition of the last echo in the sampling period.
[0117] In one specific embodiment, the first pulse sequence is a CPMG sequence.
[0118] In one specific embodiment, the second pulse sequence is an SR-CPMG sequence.
[0119] In one specific embodiment, calculating the selected layer gradient value output by the gradient coil includes:
[0120] The layer selection gradient value output by the gradient coil is calculated based on the pulse frequency bandwidth and layer selection thickness of the RF coil output.
[0121] In one specific embodiment, the selected layer gradient value output by the gradient coil is calculated using the following formula:
[0122]
[0123] Where h represents the selected layer thickness, P2 represents the P2 pulse width within the first and second pulse sequences, γ represents the H nucleus gyromagnetic ratio, and G... max This represents the maximum gradient output of the gradient coil. Indicates the gradient output magnitude. This represents the selected layer gradient value output by the gradient coil.
[0124] Example 4
[0125] This invention provides a core nuclear magnetic resonance (NMR) measurement device based on gradient field selection. The device includes a control device as described in the above embodiment, a main coil for generating a main magnetic field, a gradient coil for generating a linear gradient field, a radio frequency (RF) coil for generating an RF pulse sequence, and an echo acquisition coil for acquiring echo signals. The control device is electrically connected to the main coil, gradient coil, RF coil, and echo acquisition coil, respectively. The control device is also used to connect to an external transmission device.
[0126] For example, the gradient coil is placed in an oil bath.
[0127] In a comparative example, the gradient coil was cooled using a coil-type water cooling method. Compared to the coil-type water cooling method, placing the gradient coil in an oil bath resulted in better cooling, thus ensuring that it remained in a stable working state during core NMR measurements.
[0128] Example 5
[0129] This invention provides a mobile core nuclear magnetic resonance (NMR) measurement device based on gradient field selection, used to conduct NMR measurements on the core sample at the sampling site. Specifically, it includes a device body containing a control device as described in the previous embodiment, a main coil for generating a main magnetic field, a gradient coil for generating a linear gradient field, a radio frequency (RF) coil for generating a radio frequency pulse sequence, and an echo acquisition coil for acquiring echo signals. The control device is electrically connected to the main coil, gradient coil, RF coil, and echo acquisition coil, and is also used to connect to an external transmission device.
[0130] For example, the gradient coil is placed in an oil bath.
[0131] In the above embodiments, the mobile core nuclear magnetic resonance measurement equipment can conduct tests on the core samples at the core sampling site, which improves the real-time performance of nuclear magnetic resonance measurements. By testing fresh rock samples on site, the accuracy of nuclear magnetic resonance measurement results is improved.
[0132] Example 6
[0133] This invention provides a core nuclear magnetic resonance measurement system based on gradient field selection, specifically including a core nuclear magnetic resonance measurement device and a transmission device as described in the above embodiment, wherein the core nuclear magnetic resonance measurement device and the transmission device are electrically connected.
[0134] Example 7
[0135] This invention provides a mobile core nuclear magnetic resonance measurement system based on gradient field selection, used to conduct nuclear magnetic resonance measurements on the core sample at the sampling site. Specifically, it includes a mobile core nuclear magnetic resonance measurement device based on gradient field selection and a transmission device as described in the above embodiment. The mobile core nuclear magnetic resonance measurement device based on gradient field selection is electrically connected to the transmission device.
[0136] On the other hand, embodiments of the present invention also provide a machine-readable storage medium storing a computer program thereon, which, when executed by a processor, implements the above-described core nuclear magnetic resonance measurement method based on gradient field selection.
[0137] In another aspect, embodiments of the present invention also provide a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement the above-described core nuclear magnetic resonance measurement method based on gradient field selection.
[0138] This invention also provides a computer program product that, when executed on a data processing device, is suitable for executing a program that initializes the following method steps:
[0139] Determine the thickness of the selected layers, and divide the core into multiple selected layers based on the thickness of the selected layers;
[0140] Calculate the selected layer gradient value output by the gradient coil;
[0141] Control the conveying device so that it moves each selected section of the core to the measurement area in sequence;
[0142] For each selected layer segment, the radio frequency coil in the measurement area is controlled to output a radio frequency pulse sequence and the echo signal is collected. During the pulse opening period of all the radio frequency pulse sequences, the gradient coil in the measurement area is controlled to apply a linear gradient field with a gradient of the selected layer gradient value and a direction of the main magnetic field direction.
[0143] Invert the echo signal to identify the core fluid.
[0144] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs. Those skilled in the art can understand and implement this without any creative effort.
[0145] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.
[0146] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.
[0147] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.
Claims
1. A method for core NMR measurement based on gradient field selected layer, characterized in that, The method comprises: determining a selected layer thickness, and dividing the core into a plurality of selected layer sections according to the selected layer thickness; calculating a selected layer gradient value output by the gradient coil; controlling the conveying device to move each selected layer section of the core to the measurement region in sequence; for each selected layer section, controlling the radio frequency coil in the measurement region to output a radio frequency pulse sequence, and collecting echo signals, and controlling the gradient coil in the measurement region to apply a linear gradient field with a gradient of the selected layer gradient value and a direction of the main magnetic field during all pulse-on periods of the radio frequency pulse sequence; inverting the echo signals to identify the core fluid.
2. The method of claim 1, wherein, The method further comprises: for each selected layer section, controlling the radio frequency coil in the measurement region to output a first pulse sequence, and collecting first echo signals, and controlling the gradient coil in the measurement region to apply a first linear gradient field with a gradient of the selected layer gradient value and a direction of the main magnetic field during 90-degree pulse and 180-degree pulse-on periods of the first pulse sequence; for each selected layer section, controlling the radio frequency coil in the measurement region to output a second pulse sequence, and collecting second echo signals, and controlling the gradient coil in the measurement region to apply a second linear gradient field with a gradient of the selected layer gradient value and a direction of the main magnetic field during inversion pulse, 90-degree pulse and 180-degree pulse-on periods of the second pulse sequence; wherein the pulse width of the 90-degree pulse and the pulse width of the 180-degree pulse in the first pulse sequence and the second pulse sequence are equal.
3. The method of claim 2, wherein, The method further comprises: inverting the first echo signals to obtain T2 data to determine the core porosity; inverting the second echo signals to obtain T1T2 data to determine the core oil-water saturation.
4. The method of claim 2, wherein, The method further comprises: during the control of the radio frequency coil to output the first pulse sequence, the first linear gradient field is further controlled to be in an on state for a first time period in the sampling period of each selected layer section; wherein the first time period is a second time period after the 90-degree pulse and 180-degree pulse-on periods, and the second time period is a time period from the 90-degree pulse-on of the first pulse sequence to the collection of the last echo in the sampling period.
5. The method of claim 2, wherein, The method further comprises: during the control of the radio frequency coil to output the second pulse sequence, the second linear gradient field is further controlled to be in an on state for a third time period in the sampling period of each selected layer section; wherein the third time period is a fourth time period after the inversion pulse, 90-degree pulse and 180-degree pulse-on periods, and the fourth time period is a time period from the inversion pulse-on of the second pulse sequence to the collection of the last echo in the sampling period.
6. The method of claim 2, wherein, The first pulse sequence is a CPMG sequence.
7. The method of claim 2, wherein, The second pulse sequence is an SR-CPMG sequence.
8. The method of claim 1, wherein, The method further comprises: calculating the selected layer gradient value output by the gradient coil according to the pulse frequency bandwidth output by the radio frequency coil and the selected layer thickness.
9. A control device characterized by comprising: The device comprises: The first determination module is configured to determine a selected layer thickness, and divide the core into a plurality of selected layer sections according to the selected layer thickness. The first calculation module is configured to calculate a selected layer gradient value output by the gradient coil. The first control module is configured to control the conveying device to sequentially move each selected layer section of the core to the measurement region. The echo acquisition module is configured to, for each selected layer section, control the radio frequency coil in the measurement region to output a radio frequency pulse sequence, and acquire an echo signal, and control the gradient coil in the measurement region to apply a linear gradient field with a gradient of the selected layer gradient value and a direction of the main magnetic field direction during all pulse-on periods of the radio frequency pulse sequence. The inversion module is configured to invert the echo signal to identify the core fluid.
10. A computer device comprising a memory, a processor, and a computer program stored on the memory and executable on the processor, characterized in that, The processor implements the gradient field selected layer based core nuclear magnetic resonance measurement method in any one of claims 1 to 8 when executing the program.
11. A machine-readable storage medium having stored thereon a computer program, characterized in that The computer program implements the gradient field selected layer based core nuclear magnetic resonance measurement method in any one of claims 1 to 8 when executed by the processor.
12. A core NMR measuring apparatus based on gradient field selective layer, characterized by, The core nuclear magnetic resonance measurement device comprises the control device in claim 9, a main coil for generating a main magnetic field, a gradient coil for generating a linear gradient field, a radio frequency coil for generating a radio frequency pulse sequence, and an echo acquisition coil for acquiring an echo signal, the control device is electrically connected with the main coil, the gradient coil, the radio frequency coil, and the echo acquisition coil respectively, and the control device is further configured to be connected with an external conveying device.
13. The gradient field selected layer imaging core nuclear magnetic resonance measuring device according to any one of claims 12, characterized in that, The gradient coil is placed in an oil bath.
14. A core NMR measurement system based on gradient field selected layer, characterized in that, The system comprises the gradient field selected layer based core nuclear magnetic resonance measurement device in any one of claims 12 to 13 and the conveying device, and the core nuclear magnetic resonance measurement device and the conveying device are electrically connected.