Low-field nuclear magnetic resonance (NMR) acts as an indispensable borehole logging method for the pore size characterization and formation evaluation, including the estimation of the reservoir parameters and fluid discrimination.
The YGH basin , located in the northern South China Sea, is characterized by rapid subsidence rate, high geothermal gradient, and high formation pressure coefficient. The overpressure and low-permeability reservoirs of the YGH Basin is featured with Fine-grained lithology, elevated shale content, minute pore sizes, and complex pore structures . The NMR responses are significantly affected by measurement parameters such as echo spacing. Notable discrepancies exist between the core NMR T2 spectrum and the NMR logging T2 spectrum. Key parameters derived from NMR logging, such as the T2 geometric mean and fractal dimension, fail to accurately represent the true characteristics of the rock, thereby posing substantial challenges for precise permeability evaluation.
For better estimating the reservoir permeability using the low field NMR logging data, we conducted comprehensive petrophysical measurements such as NMR, CT scanning, grain size analysis, and mercury injection capillary pressure(MICP), specifically tailored to the characteristics of overpressure and low-permeability reservoirs. Pore structure parameters were extracted from these petrophysical experiments, and the self-organizing map (SOM) unsupervised clustering method was employed to classify the pore structures of overpressure and low-permeability reservoirs. Based on the principle of phase control, multiple sets of echo spacing core NMR experiments were conducted on representative samples of different pore structure types. Systematic analysis of echo spacing 's impact on T2 spectra lead to the development of an empirical model relating T2 geometric mean, fractal dimension, and echo spacing, with a focus on the shortest echo spacing of 0.2 ms. This model provides essential data support for correcting T2 geometric mean and fractal dimension derived from NMR logging. Building on this research, the traditional Timur formula was refined by fractal dimension, significantly enhancing the accuracy of permeability calculations for overpressure and low-permeability reservoirs.
The research findings indicate that there exists a negative correlation between the T2 geometric mean value and fractal dimension, with respect to the echo interval. As the pore diameter of the rock diminishes, the porosity intensifies, accompanied by an augmentation in clay content, leading to a greater influence of echo spacing on the geometric mean of T2 and fractal dimension. By employing an enhanced permeability model, the derived permeability values demonstrate a high degree of consistency with measured data, achieving an average relative error of approximately 15%. This level of accuracy fulfills the criteria for assessing low-permeability reservoirs.
How to cite: Yang, H., Ge, X., Xu, Y., Tang, D., Wu, B., and Wu, Y.: Correction of Echo Spacing and Advanced Permeability Modeling for Key NMR Parameters in Overpressure and Low-Permeability Reservoirs of the YGH Basin, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3687, https://doi.org/10.5194/egusphere-egu25-3687, 2025.
Short T2 relaxation components are typical characteristics of porous media such as soil and rock. The ultra-short TE NMR method based on the CPMG sequence has created conditions for the overall measurement of such samples. In the evaluation of sample heterogeneity and the porous flow, in addition to the overall T2 spectrum, the 1D or multi-dimensional T2 mapping is more needed. Traditional MRI technology based on pulsed gradient field is limited by the gradient spatial encoding time and gradient eddy currents, resulting in relatively long TE, with the shortest TE being about 1.5ms, which is significantly different from the ultra-short TE required for the porous media. 1D spatially resolved T2 mapping based on constant gradient fields is a passive effect brought by the gradient magnetic field of NMR logging tools. The gradient value is not adjustable, making it difficult to regulate the layer thickness.
It is feasible to use traditional MRI gradient system combined with cooling modules to achieve 1D spatially resolved T2 mapping under constant gradient field conditions. The challenge lies in the contradiction between the Larmor frequency range in the sample selection layer direction and the -3dB bandwidth of the radio frequency coil. To address this issue, we used high Q and narrowband radio frequency coils to ensure the SNR. During 1D spatial layer selection excitation, the resonance point is tuned to match different excitation positions of the sample, or the sample position is moved to the fixed excitation frequency. Therefore, there are two technical branches, one is the radio frequency coil tuning method and the other is the sample movement method.
Since porous media have internal gradient fields, excessively high magnetic field strength will introduce internal diffusion relaxation effects. Therefore, this abstract focuses on the non-correction method which is suitable for porous media. It combines actual cases to analyze the technical features and comparison of the two branches of the non-correction method. The advantages of the tuning method are that the sample position is fixed, which is suitable for measurement conditions with peripheral accessories on the sample. The disadvantages are that the sample test length is limited, and the radio frequency hardware is complex. The advantages of the sample movement method are that the test sample length is not limited, and the radio frequency hardware is simple. The disadvantage is that sample movement is not suitable for measurement conditions with peripheral accessories. In applications, the appropriate method can be chosen according to actual needs.
How to cite: Ge, X., Wu, F., and Zhao, J.: Ultra-short TE NMR One-dimensional Spatially Resolved T2 Mapping Method for Porous Media, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3893, https://doi.org/10.5194/egusphere-egu25-3893, 2025.
Lacustrine shale oil resources are crucial for maintaining energy supply. The types and contents of fluids are key factors in estimating the resource potential and oil recovery of organic-rich shales. Accurately identifying the fluid types in shale oil reservoir successions, which are characterized by significant lithological heterogeneity, is a significant challenge. Although numerous methods for determining porosity and fluid saturation have been proposed in previous studies, many are only applicable in limited situations and have limited accuracy. In this research, an advanced logging technique, Combinable Magnetic Resonance logging (CMR-NG), is employed to evaluate fluid types. Two-dimensional Nuclear Magnetic Resonance (2D-NMR) experiments were conducted on reservoir rocks under different conditions (as received, after drying at 105℃, and after kerosene imbibition) to define the fluid types and classification criteria. In addition, the contents (proportions) of various types of fluids were estimated. Subsequently, the contributions of organic matter and mineral compositions were investigated using corresponding Rock-Eval pyrolysis parameters and various mineral contents obtained from X-ray Diffraction. Then, the contents of different fluid types were calculated using CMR-NG (Combinable Magnetic Resonance logging, also known as 2D NMR logging). Based on the fluid classification criteria under experimental conditions and production data, the most favorable model and optimal solution for logging evaluation were selected. Finally, the fluid saturations were calculated for a single well. The results indicate that six fluid types (kerogen-bitumen-Group OH, irreducible oil, movable oil, clay-bound water, irreducible water, and movable water) can be recognized through the applied 2D-NMR test. The kerogen-bitumen-Group OH is mainly affected by pyrolysis hydrocarbon (S2), and irreducible oil is influenced by soluble hydrocarbon (S1). However, due to the effects of underground environmental conditions on the instruments, kerogen-bitumen-Group OH and clay-bound water cannot be detected by CMR-NG. The Q8 and Q9 layers of the Qing 2 Member of the Cretaceous Qingshankou Formation, Gulong Sag, Songliao Basin, China are identified as the most favorable layers for shale oil. This study provides insights into the factors controlling fluid types and contents, offering guidance for the exploration and development of unconventional resources, such as geothermal and CCUS (carbon capture, utilization, and storage) reservoirs.
How to cite: Pang, X. and Wang, G.: Insights into fluid types in unconventional resources reservoirs, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6662, https://doi.org/10.5194/egusphere-egu25-6662, 2025.
The study area is located at the northwest end of Qaidam Basin. The exploration target horizon of the study area is the Paleogene Lower Ganchaigou Formation, which is a set of shore-shallow to semi-deep lacustrine sediments. The rock composition is characterized by the mixed deposition of argillaceous, carbonate and clastic particles.
The main reservoir types are micro- and nano-scale dolomite intercrystalline pores. a large number of intercrystalline pores were formed during the process of penecontemporaneous dolomization. Samples were taken from the drilling cores at a sampling depth of 3100m-4050m. The purpose of this method is to distinguish the movable fluid from the bound fluid by multiple centrifugation and NMR(nuclear magnetic resonance) tests, and to determine the lower limit of the pore throat radius of the movable fluid distribution according to the relation between the fluid and the pore throat, and to determine the lower limit of the physical property through the relation between the physical property and the pore throat radius.
The pore throat distribution range of the samples with carbonate intercrystalline pore in the lower Ganchaigou Formation of Yingxi area in the process of mercury injection was 11 nm to 220 nm, and the pore throat distribution range in the process of mercury ejection was 40 nm to 1500 nm.
Through saturated fluid state NMR test, it is believed that the pore throat radius of intercrystalline pore developed samples is 0-160nm, and the fluid is planar distribution, and the movable fluid accounts for 13.7%. The lower limit of pore throat containing movable fluids radius were determined to be 47nm through the separation point of accumulated curve of saturation state and centrifugal state, and it was analyzed that the lower limit of pore throat containing movable fluids were mainly affected by the median radius.The lower limit of porosity was calculated by substituting the lower limit of pore throat of movable fluid distribution into the fitting formula of the median radius of pore throat and gas porosity. There is a good correlation between permeability and test pressure. The curve of permeability and test pressure shows that when the gas permeability is less than 0.02mD, the permeability decreases rapidly with the increase of pressure, indicating that the gas flow characteristics of samples with permeability below 0.02mD and samples above 0.02mD are quite different.
How to cite: zhang, S., pan, S., wang, G., zhang, X., and fu, J.: Determination of petrophysical property cutoffs of tight lacustrine carbonate reservoir, Qaidam Basin, China, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7711, https://doi.org/10.5194/egusphere-egu25-7711, 2025.
The mineral composition of shale oil reservoirs in Jiyang Depression of Bohai Bay Basin, East China, is complex, the storage space is fine and tiny, and conventional logging methods have poor applicability. Therefore, nuclear magnetic resonance logging, which can directly obtain pore information, has been widely applied in the Shengli Jiyang shale oil reservoirs. By systematically analyzing the one-dimensional and two-dimensional nuclear magnetic resonance logging data of shale oil wells in Shengli Oilfield, combined with asymmetric Gaussian function fitting technology and clustering analysis methods, the corresponding T2 cut-off values and T1/T2 value range limits for different fluid types were respectively determined. The results indicate that the pore fluid classification results of two-dimensional nuclear magnetic resonance logging are more detailed, and the movable fluid is located in the upper right corner of the spectrum, corresponding to T1/T2 values of 3 to 20. Using this model to calculate effective porosity and movable oil porosity. By comparing the tracer results, it indicates that the effective porosity of the high-yield well sections of the actual production wells was 6% to 13%, and the movable oil porosity was 2% to 6%. In other well sections, the effective porosity was less than 6%, and the movable oil porosity was less than 2%. Based on this as the main basis, the evaluation criteria for sweet spots in Shengli shale oil were established, and the shale sweet spot level was divided.
How to cite: Li, Z., Lin, C., and Liu, P.: Application of nuclear magnetic resonance logging in Shengli shale oil reservoir, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8799, https://doi.org/10.5194/egusphere-egu25-8799, 2025.
Tight sandstone reservoirs are characterized by low porosity, low permeability and complex pore structure, and there are difficulties in the evaluating tight sandstone reservoirs. Nuclear magnetic resonance (NMR) T2 spectra can characterize the pore structure and the fluid state of the porous medium, so we combined the NMR experiments with the gas-driven water to study the influence of different gas saturation and saturation states on the T2 spectra of the tight sandstone reservoirs. It is found that the movable peaks of T2 spectra become wider in the gas-bearing state of the pores compared with the water-bearing state, and the movable peaks decrease with the increase of gas saturation, and the porosity tends to become smaller, which is due to the lower hydrogen index of the gas. Therefore, the T2 spectrum correction model of gas-bearing sandstone reservoirs is established by combining the Gaussian distribution function, and the T2 spectrum morphology and porosity components are corrected to the original state. The T2 spectra of the NMR logging data were multi-peaked and dominated by the long relaxation component, while the gas-corrected T2 spectra were mainly two-peaked and dominated by the short relaxation component. The bound water saturation obtained from the corrected T2 spectra was basically the same with the results of the core measurements. This study combines the NMR experiments to clarify the NMR response mechanism of gas-bearing sandstone reservoirs, and establishes a Gaussian distribution model for gas-corrected T2 spectra to realize the accurate characterization of pore structure.
How to cite: Xie, B., Tang, Q., Zhu, X., Wang, Y., and Han, B.: Characterization of pore structure in tight sandstone reservoirs based on NMR, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9846, https://doi.org/10.5194/egusphere-egu25-9846, 2025.
Nuclear Magnetic Resonance (NMR) technology plays a key role in many fields such as medical imaging, chemical analysis and the petroleum industry. In chemical analysis and industrial testing, the ability to measure multiple nuclides quickly and accurately is essential for productivity and quality control. Especially in key areas such as petrochemicals, materials science and environmental monitoring, there is a growing demand for equipment that can measure multiple nuclides simultaneously. However, conventional high-field NMR devices are bulky and costly, limiting their widespread use in specific application scenarios. To address these challenges, a low-field NMR-based multinuclide measurement instrument has been successfully developed in this study, which is capable of accurately measuring four nuclides, namely hydrogen (H), sodium (Na), lithium (Li), and fluorine (F), in low-field environments, and is highly integrated and suitable for a wide range of practical applications such as laboratories, on-site inspections, and industrial production lines, and supports automated data acquisition, analysis, and remote monitoring. It supports automated data acquisition, analysis and remote monitoring.
In the field of petroleum energy and civil construction materials, low-field NMR technology equipment can quickly and accurately measure and characterise the hydrogen signal, which is widely used in the structural analysis and water content determination of porous media materials, especially in pore permeability saturation testing, which supports the optimisation of the performance of petroleum extraction and civil construction materials by detecting the pore structure and permeability of the materials [1][2]. In the field of oil drilling fluids, accurate measurement of sodium (Na) ion concentration is essential to ensure drilling fluid performance. This method utilises low-field NMR technology for the non-destructive detection of Na ions in drilling fluids to safeguard the stability and efficiency of drilling fluids. In addition, during the optimisation of cement formulations, the device is able to accurately determine the change in concentration of Na ions in seawater-configured cementitious materials, thereby improving the strength and durability of the cement [3][4][5][6]. For lithium (Li), a key component in battery materials, the device is able to effectively detect lithium ion signals under low-field conditions, supporting battery R&D and materials science research to ensure continued improvement in battery performance and lifetime [7]. Fluoride (F) content is also important in the toothpaste, pharmaceutical and materials industries, and the device can quickly determine fluoride content to help optimise product formulations and ensure product quality and safety.
The electronic spectrometer system uses multiple independent RF transmitter channels, each capable of transmitting RF pulse signals with different frequencies, amplitudes or phases to suit different sample characteristics and measurement needs. The system integrates MRF (Magnetic Resonance Fingerprinting) technology and intelligent multi-classification algorithms into the host computer, which automatically captures the sample's magnetic resonance signal patterns, such as T1 and T2 relaxation times, and applies them to different field strengths and pulse sequences. With the multi-classification algorithm, the system is able to recognise and differentiate between different signal patterns, each representing a group of samples with similar properties.
How to cite: huaxue, L., jiapeng, Z., huabing, L., and baxin, G.: Application of low-field nuclear magnetic resonance technology in multinuclide measurements and equipment development, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14149, https://doi.org/10.5194/egusphere-egu25-14149, 2025.
A new method for permeability estimation in tight sandstone formations based on the BSS algorithm and NMR data is proposed. BSS algorithm is introduced into the data processing of laboratory and downhole NMR data, and relaxation components with different NMR responses and pore size distributions can be obtained. The influence of pore structure on the percolation capacity is also discussed. The new method achieves great results in tight sandstone formations.
BSS algorithm refers to the process of separating various source signals from the observed signal when the theoretical model of the source signal is unknown and obtaining the best estimation of the source signal model and signal amplitude. When applying the BSS algorithm to NMR data processing, the laboratory and downhole NMR data can be considered as the observed signal, the relaxation components with specific NMR response can be considered as the source signal, and the proportions of different relaxation components can be considered as the signal amplitude. Based on the BSS algorithm, NMR responses and proportions of different components can be obtained.
We applied the BSS algorithm to the laboratory and downhole NMR data. Four pore types with different pore radius can be discriminated and their proportion can be extracted from the laboratory and downhole NMR data. The permeability of tight sandstone formation is affected by many factors and has poor correlations with the porosity. Based on the thin section observation, MICP and NMR analysis, the pore space of tight sandstone formation is complex and can be divided into micropore, mesopore, macropore and megapore. Pore structure is one of the main influential factors of permeability in tight sandstone formations. Relaxation components with the same NMR response and their proportions can be extracted from the BSS algorithm. Four relaxation components referring to different pore types can be obtained from laboratory and downhole NMR data. The permeability of tight sandstone formation is positively correlated with proportions of macropore and megapore, while negatively correlated with proportions of micropore and mesopore. A new permeability estimation method is established based on porosity, geometrical T2 value, the sum proportion of macropore and megapore, and the sum proportion of micropore and mesopore. The new model achieves great results compared with the conventional models. The new method can be easily extended in other tight sandstone formations where the main influential factors of permeability are porosity and pore structure. Besides, laboratory experiments and core calibration can significantly improve the accuracy of permeability estimation.
How to cite: Liu, J.: A new permeability estimation method based on blind source separation and NMR data, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18330, https://doi.org/10.5194/egusphere-egu25-18330, 2025.
Low-field nuclear magnetic resonance (LF-NMR) has emerged as a critical tool in geophysical prospecting, particularly for reservoir rocks exploration and their pore space characterization. However, accurate assessment of pore size distribution (PSD) in unconventional reservoirs, such as tight sandstone and shale formations, remains challenging due to their complex pore structures, high clay mineral content, low porosity, and nanometer-scale pore sizes. Additionally, these challenges can be further amplified by the presence of internal gradients (G), induced by differences in magnetic susceptibility of the rock matrix and saturating fluid, which can distort PSD estimates obtained under traditional assumptions of their negligibility.
In the fast diffusion regime, as demonstrated by Brownstein and Tarr, NMR transverse relaxation time (T2) is proportional to pore size, with the proportionality factor governed solely by surface relaxivity (ρ2). However, conventional approaches assume negligible internal gradients which often lead to unrealistic PSD results, especially in nanometer-scale pores where the induced gradient effect can be significant. Internal gradient is inversely proportional to the pore size and can cause substantial distortions even when applying low field and CPMG sequence with low echo times (TE) in rocks of minimal paramagnetic mineral content.
This work presents a novel methodology integrating differential LF-NMR with mercury injection capillary pressure (MICP) for simultaneous estimation of PSD, ρ2, and internal gradients in siliciclastic reservoir rocks. This approach enables comprehensive evaluation of pore space, accounting for both ρ2 and internal gradients without requiring additional magnetic susceptibility measurements. LF-NMR relaxometry was conducted on rock core samples saturated with kerosene having a bulk self-diffusion coefficient almost three times lower compared to water to minimize the effects of diffusion in nanopores and stay within detection limits for this pore size range, as well as to preserve samples from dissolving. ρ2 and G were estimated based on the specific conversion framework established using physical characteristics of the kerosene molecule, percolation theory and non-linear PSD–T2 transformation.
The methodology was applied to core samples from various lithologies, including sandstones, heteroliths, and mudstones of wide pore size ranges, offering insights into the interplay of ρ2 and internal gradient influence over PSD across diverse siliciclastic rock matrices.
Preliminary findings demonstrate that the differential LF-NMR protocol effectively identifies open-pore space systems while mitigating the influence of clay minerals and organic matter on PSD estimates. Furthermore, by incorporating ρ2 and internal gradient effects on T2 relaxation, our approach provides realistic PSD values, covering the open-pore size range down to 0.6 nm, the smallest particle diameter of kerosene. Validation of obtained PSD was additionally conducted through nitrogen (N2) adsorption measurements. Importantly, it is planned to develop empirical LF-NMR PSD models that can overcome the limitations of traditional destructive MICP and nitrogen adsorption methods in detecting pores in siliciclastic rocks with diameters below 3 and 1.78 nm, respectively.
How to cite: Fajt, M., Machowski, G., Puzio, B., and Krzyżak, A. T.: A holistic approach to low-field NMR and MICP data integration for the accurate determination of the absolute pore size distribution in siliciclastic rocks, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19812, https://doi.org/10.5194/egusphere-egu25-19812, 2025.
The launch of the GRACE (Gravity Recovery and Climate Experiment) polar-orbiting gravity satellite in 2002 opened a new perspective on the mass distribution and redistribution in the Earth system, together with its successor launched in 2018, providing valuable gravity data for more than two decades. Taking its value, two established GRACE-like missions are expected to be launched and operated before 2030. Nonetheless, the high cost and insufficient spatial resolution for a GRACE-like mission continue to limit current geophysical applications, requiring an investigation into gravity satellite constellation optimization. To do so, we propose a novel gravity star network covering mid-low latitudes and put a comparison in a closed-loop simulation with the Bender constellation, showing that the new low-cost constellation may have the potential to improve the accuracy and spatiotemporal resolution of gravity field observation, opening up a new way for satellite gravity observation.
How to cite: Jian, G. and Zhong, M.: A new gravity satellite constellation plan for enhancement in mid-low latitude regions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14615, https://doi.org/10.5194/egusphere-egu25-14615, 2025.
Since the successful development of the improved magnetic resonance logging tool（iMRT）, it has been well applied in complex well conditions of salinity mud and unconventional oil and gas exploration. However, the logging speed has always been the subject of discussion and research. The operation engineer expects high logging speed to improve logging efficiency, while the interpretation engineer expects lower logging speed to improve formation resolution and data quality. This article analyzes the influence of probe structure of iMRT, logging time of different observation modes, and the quality of nuclear magnetic echo signal under different mud resistivity conditions on logging speed, and establishes a calculation method. It is suitable for different geological conditions, meets the requirements of stratigraphic layering ability and high-quality data quality.
How to cite: wanli, Z., guangzhi, L., wenhui, C., xueli, H., xianjun, C., dandan, H., and tao, B.: Method for determining the logging speed of Improved magnetic resonance logging tool, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7679, https://doi.org/10.5194/egusphere-egu25-7679, 2025.
Posters virtual: Tue, 29 Apr, 14:00–15:45 | vPoster spot 4
EGU25-121 | ECS | Posters virtual | VPS19 | Highlight
A Novel Q-Switch Technique for Borehole NMR MeasurementTue, 29 Apr, 14:00–15:45 (CEST) | vP4.6
Nuclear Magnetic Resonance (NMR) is a crucial logging technique for the unconventional and complex reservoir evaluation. However, the echo spacing is always an issue of borehole NMR measurement, which limits the performance of NMR tools to acquire the short relaxation components.
In this abstract, we proposed a novel Q-Switch technique aiming at breaking through the limitation of dead-time of borehole NMR logging tool, and to achieve much shorter echo spacing. Instead of using resistors of larger resistance in parallel with the radio-frequency (RF) coil to reduce the active dead-time, an inductive coupling circuit was introduced to decrease the ringing-down time significantly after transmitting the RF pulses with high voltage. The Q-Switch circuit consists of inductive coupling coil, capacitors, resistors and active high-voltage MOSFETs. The ringing-down time of RF system was decreased by at least 10 times compared to the system without using proposed Q-switch scheme, leading to echo spacing lower to 0.3 ms under the condition with resonant frequency lower to 500 kHz.
Both simulations and experiments were in great agreements, validating the feasibility and efficiency of proposed Q-switch scheme, and proved to be promising in the borehole NMR applications.
How to cite: Luo, S., Li, X., Yu, H., Wang, Z., Xing, T., Long, Z., Che, C., Liao, G., and Xiao, L.: A Novel Q-Switch Technique for Borehole NMR Measurement, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-121, https://doi.org/10.5194/egusphere-egu25-121, 2025.
Additional speaker
- Gong Zhang, Yangtze University, China