Method and device for detecting oil saturation by variable temperature nuclear magnetic resonance

Abstract

The present application relates to a kind of variable temperature nuclear magnetic resonance oil saturation detection method and device, the method comprises: obtaining the T2 relaxation time spectrum of the core sample to be measured when temperature gradually rises to each preset temperature;Using continuous wavelet transform to carry out multi-scale feature extraction to T2 spectrum, obtain the potential hidden peak and weak peak in T2 spectrum;Based on the feature recognition of hidden peak and weak peak at each temperature, obtain water signal peak and oil signal peak;The segmented Gaussian model of the T2 spectrum of water signal and oil signal is constructed, and the segmented Gaussian function model is iteratively optimized with the characteristics of water signal peak and oil signal peak as constraint condition, to obtain separated water signal and oil signal;Based on oil signal, the core oil saturation of the core sample to be measured is calculated;Using the huge difference in sensitivity of water and oil to temperature, oil signal peak significantly shifts with temperature change, the change amplitude of water signal peak is smaller, to realize the accurate separation of oil and water signal and the calculation of oil saturation.

Description

Technical Field

[0001] This invention relates to the field of petroleum geological experimental technology, and in particular to a method and apparatus for detecting oil saturation using variable-temperature nuclear magnetic resonance. Background Technology

[0002] In laboratory core experiments or well site trials, nuclear magnetic resonance (NMR) technology is widely used to characterize the physical properties of oil and gas reservoirs, with one of its most important applications being the identification of fluid distribution in porous media. Currently, conventional NMR detection is primarily conducted at room temperature. Because water and oil signals in the core pores often overlap in the NMR T2 spectrum, direct differentiation is difficult. To address this issue, commonly used methods are mainly based on signal shielding principles or relaxation time differences, including heavy water displacement and manganese chloride (MnCl2) solution methods.

[0003] The heavy water displacement method uses heavy water to replace the water in the core, eliminating the water signal and thus allowing for the separate measurement of the oil signal. However, this method is costly and unsuitable for large-scale deployment. The manganese chloride solution method uses manganese chloride to shorten the relaxation time of the water signal, shifting it to the left and separating it from the oil signal. However, this method disrupts the original fluid distribution in the core, making it impossible to maintain the original state for testing. For dense cores or under conventional soaking conditions, the manganese chloride solution often fails to completely soak the core, resulting in incomplete signal separation and significant measurement errors. Therefore, a non-destructive, low-cost, and high-precision method for detecting oil saturation in cores is urgently needed. Summary of the Invention

[0004] This invention addresses the technical problems existing in the prior art by providing a variable-temperature nuclear magnetic resonance (NMR) method for detecting oil saturation. By dynamically adjusting the temperature and utilizing the significant difference in temperature sensitivity between water and oil, signal processing and inversion algorithms are used to track the oil signal peaks that shift significantly with temperature changes and the water signal peaks that change less, thereby achieving accurate separation of oil and water signals and calculation of oil saturation. This enables non-destructive, high-precision oil saturation detection and solves the problem of inaccurate evaluation of oil saturation caused by the overlap of crude oil and formation water NMR relaxation signals in rock cores.

[0005] According to a first aspect of the present invention, a method for detecting oil saturation using variable-temperature nuclear magnetic resonance is provided, comprising: Step 1: Obtain the T2 relaxation time spectrum of the core sample to be tested as the temperature gradually rises to each preset temperature. Step 2: Use continuous wavelet transform to extract multi-scale features from each of the T2 relaxation time spectra to obtain potential hidden peaks and weak peaks in each of the T2 relaxation time spectra; based on the feature identification of the hidden peaks and weak peaks at each temperature, obtain the water phase signal peak and the oil phase signal peak. Step 3: Construct a piecewise Gaussian model of the T2 relaxation time spectrum of the aqueous phase signal and the oil phase signal. Iteratively optimize the piecewise Gaussian function model using the characteristics of the aqueous phase signal peak and the oil phase signal peak as constraints to obtain the separated aqueous phase signal and oil phase signal. Step 4: Calculate the oil saturation of the core sample to be tested based on the oil phase signal.

[0006] Based on the above technical solution, the present invention can also be improved as follows.

[0007] Optionally, step 1 includes: The core sample to be tested is placed in the test area, and the ambient temperature of the test area is raised to each of the preset temperatures. After the core sample to be tested reaches thermal equilibrium, nuclear magnetic resonance measurement is performed on the core sample to be tested using a CPMG pulse sequence with the same test parameters at each preset temperature. The echo attenuation signal is collected, and the T2 relaxation time spectrum is obtained by inverting the echo attenuation signal.

[0008] Optionally, after obtaining each of the T2 relaxation time spectra in step 1, a unified data preprocessing is performed on each of the T2 relaxation time spectra, including: Each of the T2 relaxation time spectra is mapped to the same logarithmic uniform sampling coordinate system to establish a unified relaxation time reference axis; a smoothing filter is used to denoise each of the T2 relaxation time spectra.

[0009] Optionally, in step 2, during the multi-scale feature extraction of each of the T2 relaxation time spectra using continuous wavelet transform, the mathematical expression of the continuous wavelet transform is:

[0010] in, is the wavelet transform coefficient matrix; a is the scaling factor used to control the spread width of the wavelet basis functions; b is the translation factor representing the relative position of the wavelet basis functions on the relaxation time reference axis. The input is the signal amplitude of the T2 relaxation time spectrum, and the independent variable t corresponds to the x-coordinate after uniform logarithmic mapping. ; is the complex conjugate of the selected mother wavelet function.

[0011] Optionally, step 2, which involves identifying the characteristics of the hidden and weak peaks at various temperatures to obtain the aqueous phase signal peaks and oil phase signal peaks, includes: By tracking the changes in the position, width, and amplitude of each component peak at various temperatures, component peaks with small temperature response amplitudes are identified as aqueous phase signal peaks; component peaks with significant temperature response and whose peak positions migrate towards longer relaxation times as temperature increases are identified as oil phase signal peaks.

[0012] Optionally, constructing the piecewise Gaussian model in step 3 includes: Step 301, construct a single fluid component The mathematical formula for the asymmetric Gaussian envelope is:

[0013] In the formula, x is the logarithmic x-coordinate. ; Let x be the amplitude of the T2 relaxation time spectrum of the fluid component at time x; fluid components The maximum amplitude of the T2 relaxation time spectrum; fluid components The position of the spectral peaks; and These represent the widths of the fluid spectrum peaks on the left and right sides, respectively. Step 302: Construct the piecewise Gaussian model into a composite model under multiple temperatures T. : .

[0014] Optionally, the process of obtaining the separated aqueous phase NMR signal and oil phase NMR signal in step 3 includes: Step 303, establish the nonlinear least squares objective function:

[0015] Where E is the total sum of squared residuals from the multi-temperature joint inversion; M is the total number of preset temperatures; and N is the total number of sampling points in the logarithmic uniform sampling coordinate system. This represents the logarithmic relaxation time value corresponding to the i-th sampling point in the coordinate system; The j-th preset temperature; Based on the characteristics of the aqueous phase signal peaks and oil phase signal peaks identified in step 2, the temperature at which these peaks are obtained is... The original signal amplitude of the T2 relaxation time spectrum at the i-th sampling point under the given conditions; To be at temperature Under the given conditions, the multivariate composite theoretical fitting value of the piecewise Gaussian model at the i-th sampling point; Step 304: The LM algorithm is used to iteratively optimize and solve the nonlinear least squares objective function to obtain the optimal parameters of the piecewise Gaussian model for the oil phase signal and water phase signal under various temperature conditions, thereby realizing the separation and quantitative characterization of oil and water component signals.

[0016] Optionally, in step 4, the following is calculated: Step 401: Perform full-spectrum integration on the separated oil phase signal to obtain the total NMR signal amplitude of the oil phase. Compare the total NMR signal amplitude of the oil phase with the calibration curve of the standard oil sample to calculate the crude oil volume in the pores of the core sample to be tested. ; Step 402: Calculate the total pore volume of the core sample based on its total volume and porosity parameters. ; Step 403: Calculate the oil saturation value of the core sample to be tested. .

[0017] According to a second aspect of the present invention, a variable-temperature nuclear magnetic resonance oil saturation detection device is provided, comprising: a nuclear magnetic resonance detection device, a variable-temperature cycle control device, and a data acquisition and processing system; The nuclear magnetic resonance detection device includes: a nuclear magnetic resonance main unit, a nuclear magnetic resonance probe, and a sample container; The core sample to be tested is placed in the sample container, and the sample container is placed in the sample testing area of ​​the nuclear magnetic resonance probe; The variable temperature circulation control device is connected to the inside of the sample container and provides circulating fluids at various preset temperatures to the inside of the sample container. The nuclear magnetic resonance host emits radio frequency pulses to the core sample to be tested. The data acquisition and processing system acquires echo attenuation data and performs inversion processing to obtain the T2 relaxation time spectrum of the core sample under test at various preset temperatures. It then uses continuous wavelet transform to extract multi-scale features from each T2 relaxation time spectrum to obtain the characteristics of potential hidden peaks and weak peaks. Based on the characteristics of the hidden peaks and weak peaks at various temperatures, it identifies the water phase signal peaks and oil phase signal peaks within these hidden peaks and weak peaks, and obtains the water phase signal peak characteristics and oil phase signal peak characteristics based on these characteristics. A piecewise Gaussian model of the T2 relaxation time spectrum of the aqueous phase signal and the oil phase signal is constructed. The piecewise Gaussian function model is iteratively optimized with the peak characteristics of the aqueous phase signal and the peak characteristics of the oil phase signal as constraints to obtain the separated aqueous phase NMR signal and the oil phase NMR signal. The total amplitude of the oil phase nuclear magnetic resonance signal is compared with the standard oil sample calibration curve to calculate the crude oil volume in the core pores, and the oil saturation of the core is calculated based on the crude oil volume.

[0018] Optionally, the variable temperature circulation control device includes: a liquid storage tank, a circulation pump, a heat exchanger, a temperature controller, a temperature sensor, and a fluid pipeline; The circulating pump drives the fluid in the storage tank to flow through the fluid pipeline to the heat exchanger; the heat exchanger adjusts the fluid to the target temperature according to the command of the temperature controller, and the temperature-adjusted fluid is sent through the fluid inlet into the jacket of the core holder in the sample container; after the fluid adjusts the temperature of the core sample, it flows out from the fluid outlet in the sample container and returns to the storage tank. The temperature sensor detects the temperature signal of the jacket layer in real time and transmits it back to the temperature controller. The temperature controller compares the temperature signal with the target temperature and controls the power of the heat exchanger.

[0019] The present invention provides a method and apparatus for detecting oil saturation using variable-temperature nuclear magnetic resonance, the advantages of which include: Leveraging the significant difference in temperature sensitivity between water and oil, this method dynamically controls temperature to perform nuclear magnetic resonance (NMR) scans on the same core sample at varying temperatures. Signal processing and inversion algorithms are then used to track oil signal peaks that shift significantly with temperature changes, contrasting them with relatively stable water signal peaks. This enables precise separation of oil and water signals and calculation of oil saturation, achieving non-destructive, high-precision oil saturation detection. Dynamic tracking of hidden peaks at varying temperatures based on continuous wavelet transform (CWT) and multi-constraint optimization inversion techniques based on asymmetric Gaussian function models effectively solves the challenge of distinguishing oil and water in overlapping T2 spectrum regions. A hydrogen-free fluid circulation heating system is employed to avoid the use of chemical reagents, maintain the original core structure, and prevent equipment contamination. The method is non-destructive, low-cost, and easy to operate, and can be deployed in indoor laboratories or well sites. Attached Figure Description

[0020] Figure 1 A flowchart illustrating an embodiment of a variable-temperature nuclear magnetic resonance method for detecting oil saturation provided by the present invention; Figure 2 The present invention provides a structural diagram of a variable-temperature nuclear magnetic resonance oil saturation detection device. Detailed Implementation

[0021] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0022] Figure 1 A flowchart of a variable-temperature nuclear magnetic resonance oil saturation detection method provided by the present invention is shown below. Figure 1 As shown, the oil saturation detection method includes: Step 1: Obtain the T2 relaxation time spectrum of the core sample to be tested as the temperature gradually rises to each preset temperature.

[0023] Step 2: Multi-scale feature extraction is performed on each T2 relaxation time spectrum using continuous wavelet transform to obtain potential hidden peaks and weak peaks in each T2 relaxation time spectrum; based on the feature identification of hidden peaks and weak peaks at each temperature, water phase signal peaks and oil phase signal peaks are obtained.

[0024] Step 3: Construct a piecewise Gaussian model of the T2 relaxation time spectrum of the aqueous phase signal and the oil phase signal. Use the characteristics of the aqueous phase signal peak and the oil phase signal peak as constraints to iteratively optimize the piecewise Gaussian function model to obtain the separated aqueous phase signal and oil phase signal.

[0025] Step 4: Calculate the oil saturation of the core sample to be tested based on the oil phase signal.

[0026] Water and oil exhibit vastly different sensitivities to temperature. Water signals are poorly sensitive to temperature, exhibiting highly stable relaxation characteristics in their NMR T2 spectra, with minimal shifts in peak position, essentially remaining constant. Oil signals, on the other hand, are highly sensitive to temperature, showing a significant shift in peak position with temperature changes. Generally, as temperature increases, oil signals show a significant "right shift" (longer relaxation time) in their NMR T2 spectra.

[0027] This invention provides a variable-temperature nuclear magnetic resonance (NMR) method for detecting oil saturation. Utilizing the significant difference in temperature sensitivity between water and oil, the method dynamically adjusts the temperature to perform NMR scans on the same core sample at different temperatures. Signal processing and inversion algorithms are then used to track oil signal peaks that shift significantly with temperature changes and water signal peaks that change less, thereby achieving precise separation of oil and water signals and calculation of oil saturation. This results in non-destructive, high-precision oil saturation detection, solving the problem of inaccurate oil saturation assessment caused by overlapping NMR relaxation signals of crude oil and formation water in the core sample.

[0028] Example 1

[0029] Embodiment 1 provided by this invention is an embodiment of a variable-temperature nuclear magnetic resonance method for detecting oil saturation provided by this invention, combined with... Figure 1 It can be seen that the embodiments of this oil saturation detection method include: Step 1: Obtain the T2 relaxation time spectrum of the core sample to be tested as the temperature gradually rises to each preset temperature.

[0030] In one possible embodiment, step 1 includes: The core sample to be tested is placed in the test area, and the ambient temperature of the test area is raised to various preset temperatures. After the core sample reaches thermal equilibrium, nuclear magnetic resonance measurements are performed on the core sample at various preset temperatures using CPMG pulse sequences with the same test parameters. Echo attenuation signals are collected, and the T2 relaxation time spectra are obtained by inversion of the echo attenuation signals.

[0031] In the specific implementation process, the preset temperatures can be 30℃, 50℃, and 70℃. The sample temperature is gradually increased to 30℃, 50℃, and 70℃. After the sample reaches thermal equilibrium again, nuclear magnetic resonance measurements are repeated while keeping the test parameters constant, obtaining the first T2 relaxation time spectrum, the second T2 relaxation time spectrum, and the third T2 relaxation time spectrum, respectively. More temperature test points can be set as needed during the test.

[0032] In one possible embodiment, after obtaining each T2 relaxation time spectrum in step 1, a unified data preprocessing is performed on each T2 relaxation time spectrum, including: Each T2 relaxation time spectrum is mapped to the same logarithmic uniform sampling coordinate system to establish a unified relaxation time reference axis; a smoothing filter is used to denoise each T2 relaxation time spectrum to improve the comparability and stability of the spectra under different temperature conditions.

[0033] Step 2: Perform joint inversion on multiple sets of T2 relaxation time spectra, and use continuous wavelet transform to extract multi-scale features from each T2 relaxation time spectrum to obtain potential hidden peaks and weak peaks in each T2 relaxation time spectrum; based on the feature identification of hidden peaks and weak peaks at each temperature, obtain the water phase signal peak and the oil phase signal peak.

[0034] In one possible embodiment, during step 2, when performing multi-scale feature extraction on each T2 relaxation time spectrum using continuous wavelet transform, the mathematical expression for continuous wavelet transform is:

[0035] in, is the wavelet transform coefficient matrix; a is the scaling factor used to control the spread width of the wavelet basis functions; b is the translation factor representing the relative position of the wavelet basis functions on the relaxation time reference axis. The input is the signal amplitude of the T2 relaxation time spectrum, and the independent variable t corresponds to the x-axis after uniform logarithmic mapping. ; is the complex conjugate of the selected mother wavelet function.

[0036] In one possible embodiment, step 2, which involves identifying the characteristics of hidden and weak peaks at various temperatures to obtain the aqueous phase signal peaks and oil phase signal peaks, includes: By tracking the changes in the position, width, and amplitude of each component peak at various temperatures, component peaks with small temperature response amplitudes are identified as aqueous phase signal peaks; component peaks with significant temperature response and whose peak positions migrate towards longer relaxation times as temperature increases are identified as oil phase signal peaks.

[0037] Step 3: Construct a piecewise Gaussian model of the T2 relaxation time spectrum of the aqueous phase signal and the oil phase signal. Use the characteristics of the aqueous phase signal peak and the oil phase signal peak as constraints to iteratively optimize the piecewise Gaussian function model to obtain the separated aqueous phase signal and oil phase signal.

[0038] In one possible embodiment, step 3 of constructing the piecewise Gaussian model includes: Step 301: Since the confined relaxation of crude oil and water in porous media typically exhibits an asymmetric long-tail effect, in order to accurately describe their physical morphology, this embodiment of the invention constructs a single fluid component. The mathematical formula for the asymmetric Gaussian envelope is:

[0039] In the formula, x is the logarithmic x-coordinate. ; Let x be the amplitude of the T2 relaxation time spectrum of the fluid component at time x; fluid components The maximum amplitude of the T2 relaxation time spectrum; fluid components The position of the spectral peaks; and These represent the widths of the fluid spectrum peaks on the left and right sides, respectively.

[0040] Step 302: Construct a piecewise Gaussian model into a composite model under multiple temperatures T. : .

[0041] In one possible embodiment, the process of obtaining the separated oil phase NMR signal and the oil phase NMR signal in step 3 includes: Step 303, establish the nonlinear least squares objective function:

[0042] Where E is the total sum of squared residuals from the multi-temperature joint inversion; M is the total number of preset temperatures; and N is the total number of sampling points in the logarithmic uniform sampling coordinate system. This represents the logarithmic relaxation time value corresponding to the i-th sampling point in the coordinate system; The j-th preset temperature; Based on the characteristics of the aqueous phase signal peaks and oil phase signal peaks identified in step 2, the temperature at which these peaks are obtained is determined. The original signal amplitude of the T2 relaxation time spectrum at the i-th sampling point under the given conditions; For temperature Under the given conditions, the multivariate composite theoretical fitting value of the piecewise Gaussian model at the i-th sampling point.

[0043] In the specific implementation process, step 2 identifies the aqueous phase signal peak and the oil phase signal peak, whose characteristics include: center position , Dynamic position function as a function of temperature , The nonlinear least squares objective function uses the peak position, peak width, and amplitude parameters obtained in step 2 as initial constraints to determine the parameters of the piecewise Gaussian model.

[0044] Step 304: The LM (Levenberg-Marquardt) algorithm is used to iteratively optimize the nonlinear least squares objective function to obtain the optimal parameters of the piecewise Gaussian model of the oil phase signal and water phase signal under various temperature conditions, thereby realizing the separation and quantitative characterization of oil and water component signals.

[0045] Step 4: Calculate the oil saturation of the core sample to be tested based on the oil phase signal.

[0046] In one possible embodiment, step 4 calculates: Step 401: Perform full-spectrum integration on the separated oil phase signal to obtain the total NMR signal amplitude of the oil phase. Compare the total NMR signal amplitude of the oil phase with the calibration curve of the standard oil sample to calculate the crude oil volume in the pores of the core sample to be tested. .

[0047] Step 402: Calculate the total pore volume of the core sample based on its total volume and independently measured porosity parameters. .

[0048] Step 403: Calculate the oil saturation value of the core sample to be tested. .

[0049] After the experiment, the temperature control system was turned off, and the core sample was removed after the system returned to a safe operating temperature. No chemical extractants or displacement agents were used to treat the core during the entire testing process; the fluid inside the core remained in its original state, thus achieving a non-destructive measurement of oil saturation.

[0050] Embodiment 1 of this invention provides an embodiment of a variable-temperature nuclear magnetic resonance (NMR) method for detecting oil saturation, achieving oil-water signal separation based on multi-temperature response difference constraints and nonlinear joint inversion. First, the T2 relaxation time spectra obtained under different temperature conditions are remapped using a logarithmically uniform distribution, and smoothing filtering is used to suppress noise jitter. Then, utilizing the multi-scale analysis characteristics of continuous wavelet transform, joint feature extraction and peak shape tracking are performed on the T2 spectra under different temperature conditions to identify the peak position, peak width, and amplitude variation patterns of each component. Specifically, the component peaks with smaller temperature response amplitudes are identified as water phase signal peaks (the positions are denoted as...). ), identifying component peaks with significant temperature response and whose peak positions shift towards longer relaxation times with increasing temperature as oil phase signal peaks (positions denoted as ). Finally, using the obtained peak position, peak width, and amplitude parameters as initial constraints, a multi-temperature joint inversion model was constructed. The Levenberg-Marquardt optimization algorithm was then used to iteratively fit and solve the asymmetric Gaussian function, thereby achieving the separation of oil and water component signals in the overlapping T2 spectrum.

[0051] Example 2

[0052] Embodiment 2 provided by the present invention is an embodiment of a variable-temperature nuclear magnetic resonance oil saturation detection device provided by the present invention. Figure 2 This is a structural diagram of an embodiment of a variable-temperature nuclear magnetic resonance oil saturation detection device provided by the present invention, combined with... Figure 1 and Figure 2 It is known that the embodiments of the oil saturation detection device include: a nuclear magnetic resonance detection device, a variable temperature cycle control device, and a data acquisition and processing system.

[0053] The nuclear magnetic resonance (NMR) detection device includes: the NMR main unit, the NMR probe, and the sample container.

[0054] The core sample to be tested is loaded into the sample container and placed in the sample testing area of ​​the nuclear magnetic resonance probe.

[0055] In the specific implementation process, the core sample to be tested, containing crude oil and formation water (or simulated fluid), is placed in the sample testing area of ​​the variable-temperature nuclear magnetic resonance probe, and the sample axis is kept consistent with the center position of the probe.

[0056] The variable temperature circulation control device is connected to the inside of the sample container, providing circulating fluids at various preset temperatures to the inside of the sample container, and the nuclear magnetic resonance host emits radio frequency pulses to the core sample to be tested.

[0057] During the specific testing process, the nuclear magnetic resonance (NMR) detection device employs a double-layer temperature-controlled jacket structure. A fluid-circulating temperature-controlled jacket is installed around the NMR probe's radio frequency coil or the sample testing area, using a hydrogen-free heat transfer fluid as the temperature control medium. Preferred options include perfluoropolyether fluorinated liquids, Fluorinert series fluorinated oils, or other heat transfer media that do not generate hydrogen nucleus resonance signals. Since the heat transfer medium does not contain detectable hydrogen nucleus signals, it will not interfere with NMR hydrogen nucleus testing. The continuous flow of the hydrogen-free heat transfer fluid, driven by an external circulating temperature control system, achieves uniform temperature control of the core sample, reducing the impact of local temperature gradients on the NMR test results.

[0058] The thermal equilibrium isothermal settling time at each temperature point needs to be matched according to the core size, pore structure, and fluid properties to ensure that the internal fluid temperature of the core is consistent with the external set value, thereby ensuring the accuracy of the relaxation time offset.

[0059] The data acquisition and processing system collects echo attenuation data and performs inversion processing to obtain the T2 relaxation time spectrum of the core sample under test at various preset temperatures. Continuous wavelet transform is used to extract multi-scale features from each T2 relaxation time spectrum to obtain the characteristics of potential hidden peaks and weak peaks in each T2 relaxation time spectrum. Based on the characteristics of hidden peaks and weak peaks at various temperatures, water phase signal peaks and oil phase signal peaks are identified in the hidden peaks and weak peaks. Based on the water phase signal peaks and oil phase signal peaks, the characteristics of water phase signal peaks and oil phase signal peaks are obtained.

[0060] A piecewise Gaussian model of the T2 relaxation time spectrum of the aqueous phase signal and the oil phase signal was constructed. The piecewise Gaussian function model was iteratively optimized with the peak characteristics of the aqueous phase signal and the peak characteristics of the oil phase signal as constraints to obtain the separated oil phase NMR signal and oil phase NMR signal.

[0061] The total amplitude of the oil phase nuclear magnetic resonance signal is compared with the calibration curve of the standard oil sample to calculate the crude oil volume in the core pores, and the oil saturation of the core is calculated based on the crude oil volume.

[0062] In one possible embodiment, combining Figure 2 It is known that the variable temperature circulation control device includes: a liquid storage tank, a circulation pump, a heat exchanger, a temperature controller, a temperature sensor, and fluid pipelines. In actual implementation, the various components are connected by fluid pipelines that transmit hydrogen-free fluid.

[0063] The circulating pump drives the fluid in the storage tank to flow through the fluid pipeline to the heat exchanger; the heat exchanger adjusts the fluid to the target temperature according to the instructions of the temperature controller, and the temperature-adjusted fluid is sent through the fluid inlet into the jacket of the core holder in the sample container; after the fluid regulates the temperature of the core sample, it flows out from the fluid outlet in the sample container and returns to the storage tank.

[0064] The temperature sensor detects the temperature signal of the jacket layer in real time and sends it back to the temperature controller. The temperature controller compares the temperature signal with the target temperature and controls the power of the heat exchanger.

[0065] In one possible embodiment, the process of performing oil saturation detection using a variable-temperature nuclear magnetic resonance oil saturation detection device provided in this invention includes: Select a clean, intact, and regularly shaped cylindrical core sample in its original oil-water coexistence state (or after a simulated crude oil saturation displacement experiment). Record the core's basic parameters, such as size, weight, and porosity. Place the core sample into the sample container provided with the NMR instrument, and position the container within the NMR probe's testing area, ensuring the core is within the effective detection range of the radio frequency coil. Connect the variable temperature circulation control device.

[0066] The target temperature of the external circulating temperature control system was set to 30℃. The circulation pump was started, allowing the hydrogen-free heat transfer fluid to continuously circulate within the probe's temperature control interlayer, controlling the temperature of the sample testing area. Temperature changes in the testing area were monitored in real time by a temperature monitoring unit installed in the temperature control system. Once the temperature in the testing area stabilized at 30℃, it was maintained at this preset temperature for 0.5 hours to allow the core sample to reach a stable thermal equilibrium. After thermal equilibrium was achieved, nuclear magnetic resonance (NMR) measurements were performed using a CPMG pulse sequence while maintaining consistent test parameters, and echo attenuation data were acquired. Subsequently, the first set of T2 relaxation time spectrum data under 30℃ conditions was obtained using an inversion algorithm.

[0067] After completing the 30℃ test, the target temperature of the circulating temperature control system was adjusted to 50℃. With continuous circulation of the hydrogen-free heat transfer fluid, the temperature in the sample test area gradually increased. Once the temperature monitoring unit indicated that the test area temperature had stabilized at 50℃, the system was kept at this preset temperature for 0.5 hours to allow the core to return to thermal equilibrium. Subsequently, under the same CPMG pulse sequence parameters and data acquisition parameters as the 30℃ test, nuclear magnetic resonance measurements were performed again to obtain a second set of T2 relaxation time spectrum data under the 50℃ condition.

[0068] Using the same method, the target temperature of the circulating temperature control system was further increased to 70℃. The temperature of the test area was stabilized at 70℃ and maintained at a preset constant temperature for 0.5 hours. A third nuclear magnetic resonance (NMR) measurement was then performed under the same instrument parameters as the previous two tests. Echo attenuation data were collected and inversion processing was completed to obtain the third set of T2 relaxation time spectrum data under 70℃ conditions. Depending on actual testing needs, more temperature test points can be set to obtain multiple sets of T2 relaxation time spectrum data under different temperature conditions, providing a data foundation for subsequent oil-water signal separation and oil saturation calculation.

[0069] The T2 relaxation time spectrum data obtained at 30℃, 50℃ and 70℃ are input into the data processing module, and the oil-water signal is separated by a multi-temperature inversion algorithm based on the joint constraints of continuous wavelet transform (CWT) and asymmetric Gaussian function model.

[0070] It is understood that the variable-temperature nuclear magnetic resonance oil saturation detection device provided by the present invention corresponds to the variable-temperature nuclear magnetic resonance oil saturation detection method provided in the foregoing embodiments. The relevant technical features of the variable-temperature nuclear magnetic resonance oil saturation detection device can be referred to the relevant technical features of the variable-temperature nuclear magnetic resonance oil saturation detection method, and will not be repeated here.

[0071] The present invention provides a method and apparatus for detecting oil saturation using variable-temperature nuclear magnetic resonance, the advantages of which include: Leveraging the significant difference in temperature sensitivity between water and oil, this method dynamically controls temperature to perform nuclear magnetic resonance (NMR) scans on the same core sample at varying temperatures. Signal processing and inversion algorithms are then used to track oil signal peaks that shift significantly with temperature changes and water signal peaks that change less dramatically, enabling precise separation of oil and water signals and calculation of oil saturation. This achieves non-destructive, high-precision oil saturation detection. Dynamic tracking of hidden peaks at varying temperatures based on continuous wavelet transform (CWT) and multi-constraint optimization inversion techniques based on asymmetric Gaussian function models effectively solves the challenge of distinguishing oil and water in overlapping T2 spectrum regions. A hydrogen-free fluid circulation heating system is employed to avoid the use of chemical reagents, maintain the original core structure, and prevent equipment contamination. The method is non-destructive, low-cost, and easy to operate, and can be deployed in indoor laboratories or well sites.

[0072] It should be noted that the descriptions of each embodiment in the above embodiments have different focuses. For parts that are not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0073] 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.

[0074] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations. Figure 1 One or more processes and / or boxes Figure 1A device that provides the functions specified in one or more boxes.

[0075] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0076] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0077] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0078] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for detecting oil saturation using variable-temperature nuclear magnetic resonance, characterized in that, The oil saturation detection method includes: Step 1: Obtain the T2 relaxation time spectrum of the core sample to be tested as the temperature gradually rises to each preset temperature. Step 2: Use continuous wavelet transform to extract multi-scale features from each of the T2 relaxation time spectra to obtain potential hidden peaks and weak peaks in each of the T2 relaxation time spectra; based on the feature identification of the hidden peaks and weak peaks at each temperature, obtain the water phase signal peak and the oil phase signal peak. Step 3: Construct a piecewise Gaussian model of the T2 relaxation time spectrum of the aqueous phase signal and the oil phase signal. Iteratively optimize the piecewise Gaussian function model using the characteristics of the aqueous phase signal peak and the oil phase signal peak as constraints to obtain the separated aqueous phase signal and oil phase signal. Step 4: Calculate the oil saturation of the core sample to be tested based on the oil phase signal.

2. The oil saturation detection method according to claim 1, characterized in that, Step 1 includes: The core sample to be tested is placed in the test area, and the ambient temperature of the test area is raised to each of the preset temperatures. After the core sample to be tested reaches thermal equilibrium, nuclear magnetic resonance measurement is performed on the core sample to be tested using a CPMG pulse sequence with the same test parameters at each preset temperature. The echo attenuation signal is collected, and the T2 relaxation time spectrum is obtained by inverting the echo attenuation signal.

3. The oil saturation detection method according to claim 1, characterized in that, After obtaining each T2 relaxation time spectrum in step 1, a unified data preprocessing is performed on each T2 relaxation time spectrum, including: Each of the T2 relaxation time spectra is mapped to the same logarithmic uniform sampling coordinate system to establish a unified relaxation time reference axis; a smoothing filter is used to denoise each of the T2 relaxation time spectra.

4. The oil saturation detection method according to claim 3, characterized in that, In step 2, during the multi-scale feature extraction of each of the T2 relaxation time spectra using continuous wavelet transform, the mathematical expression of the continuous wavelet transform is: in, is the wavelet transform coefficient matrix; a is the scaling factor used to control the spread width of the wavelet basis functions; b is the translation factor representing the relative position of the wavelet basis functions on the relaxation time reference axis. The input is the signal amplitude of the T2 relaxation time spectrum, and the independent variable t corresponds to the x-coordinate after uniform logarithmic mapping. ; is the complex conjugate of the selected mother wavelet function.

5. The method for detecting oil saturation according to claim 1, characterized in that, Step 2, which involves identifying the characteristics of the hidden and weak peaks at various temperatures to obtain the aqueous phase signal peaks and oil phase signal peaks, includes the following: By tracking the changes in the position, width, and amplitude of each component peak at various temperatures, component peaks with small temperature response amplitudes are identified as aqueous phase signal peaks; component peaks with significant temperature response and whose peak positions migrate towards longer relaxation times as temperature increases are identified as oil phase signal peaks.

6. The method for detecting oil saturation according to claim 1, characterized in that, Step 3, which involves constructing the piecewise Gaussian model, includes: Step 301, construct a single fluid component The mathematical formula for the asymmetric Gaussian envelope is: In the formula, x is the logarithmic x-coordinate ; Let x be the amplitude of the T2 relaxation time spectrum of the fluid component at time x; fluid components The maximum amplitude of the T2 relaxation time spectrum; fluid components The position of the spectral peaks; and These represent the widths of the fluid spectrum peaks on the left and right sides, respectively. Step 302: Construct the piecewise Gaussian model into a composite model under multiple temperatures T. : 。 7. The method for detecting oil saturation according to claim 1, characterized in that, The process of obtaining the separated oil phase NMR signal and aqueous phase NMR signal in step 3 includes: Step 303, establish the nonlinear least squares objective function: Where E is the total sum of squared residuals from the multi-temperature joint inversion; M is the total number of preset temperatures; and N is the total number of sampling points in the logarithmic uniform sampling coordinate system. This represents the logarithmic relaxation time value corresponding to the i-th sampling point in the coordinate system; The j-th preset temperature; Based on the characteristics of the aqueous phase signal peaks and oil phase signal peaks identified in step 2, the temperature at which these peaks are obtained is... The original signal amplitude of the T2 relaxation time spectrum at the i-th sampling point under the given conditions; To be at temperature Under the given conditions, the multivariate composite theoretical fitting value of the piecewise Gaussian model at the i-th sampling point; Step 304: The LM algorithm is used to iteratively optimize and solve the nonlinear least squares objective function to obtain the optimal parameters of the piecewise Gaussian model for the oil phase signal and water phase signal under various temperature conditions, thereby realizing the separation and quantitative characterization of oil and water component signals.

8. The method for detecting oil saturation according to claim 1, characterized in that, The calculation in step 4 is as follows: Step 401: Perform full-spectrum integration on the separated oil phase signal to obtain the total NMR signal amplitude of the oil phase. Compare the total NMR signal amplitude of the oil phase with the calibration curve of the standard oil sample to calculate the crude oil volume in the pores of the core sample to be tested. ; Step 402: Calculate the total pore volume of the core sample based on its total volume and porosity parameters. ; Step 403: Calculate the oil saturation value of the core sample to be tested. .

9. A variable-temperature nuclear magnetic resonance oil saturation detection device, characterized in that, The oil saturation detection device includes: a nuclear magnetic resonance detection device, a variable temperature cycle control device, and a data acquisition and processing system; The nuclear magnetic resonance detection device includes: a nuclear magnetic resonance main unit, a nuclear magnetic resonance probe, and a sample container; The core sample to be tested is placed in the sample container, and the sample container is placed in the sample testing area of ​​the nuclear magnetic resonance probe; The variable temperature circulation control device is connected to the inside of the sample container and provides circulating fluids at various preset temperatures to the inside of the sample container. The nuclear magnetic resonance host emits radio frequency pulses to the core sample to be tested. The data acquisition and processing system acquires echo attenuation data and performs inversion processing to obtain the T2 relaxation time spectrum of the core sample under test at various preset temperatures. It then uses continuous wavelet transform to extract multi-scale features from each T2 relaxation time spectrum to obtain the characteristics of potential hidden peaks and weak peaks. Based on the characteristics of the hidden peaks and weak peaks at various temperatures, it identifies the water phase signal peaks and oil phase signal peaks within these hidden peaks and weak peaks, and obtains the water phase signal peak characteristics and oil phase signal peak characteristics based on these characteristics. A piecewise Gaussian model of the T2 relaxation time spectrum of the aqueous phase signal and the oil phase signal is constructed. The piecewise Gaussian function model is iteratively optimized with the peak characteristics of the aqueous phase signal and the peak characteristics of the oil phase signal as constraints to obtain the separated aqueous phase NMR signal and the oil phase NMR signal. The total amplitude of the oil phase nuclear magnetic resonance signal is compared with the standard oil sample calibration curve to calculate the crude oil volume in the core pores, and the oil saturation of the core is calculated based on the crude oil volume.

10. The oil saturation detection device according to claim 9, characterized in that, The variable temperature circulation control device includes: a liquid storage tank, a circulation pump, a heat exchanger, a temperature controller, a temperature sensor, and fluid pipelines; The circulating pump drives the fluid in the storage tank to flow through the fluid pipeline to the heat exchanger; the heat exchanger adjusts the fluid to the target temperature according to the command of the temperature controller, and the temperature-adjusted fluid is sent through the fluid inlet into the jacket of the core holder in the sample container; after the fluid adjusts the temperature of the core sample, it flows out from the fluid outlet in the sample container and returns to the storage tank. The temperature sensor detects the temperature signal of the jacket layer in real time and transmits it back to the temperature controller. The temperature controller compares the temperature signal with the target temperature and controls the power of the heat exchanger.

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