T2 Distribution Research Articles

Interpretation of Nuclear-Magnetic-Resonance Response to Hydrocarbons: Application to Miscible Enhanced-Oil-Recovery Experiments in Shales

Summary Estimation of total reserves in shale/gas and shale/oil reservoirs is challenging but critical. Different logging tools and core-evaluation procedures are used to address this challenge. Nuclear magnetic resonance (NMR) plays a vital role in understanding fluid content, rock/fluid interaction, and determination of pore-body-size distributions. Hydrocarbon (HC)-hosting pore systems in shale includes both organic and inorganic pores. Recoverable HCs include bitumen and light HCs. Their relative fractions are strongly dependent on thermal maturity. Regardless of detailed chemical characterization, “bitumen” is simply defined on the basis of mobility in this study. The apparent mobility of HCs depends on fluid composition, solubility, and reservoir temperature. Historically, NMR laboratory-calibration measurements (nominally, 2-MHz) on core are conducted at room temperature (25–35°C). This study highlights the importance of running NMR tests at reservoir temperature. Experiments were performed for both bulk fluids and fluid-saturated rock samples. The results show that, at a specific temperature, NMR responds only to the fraction of HCs present in the liquid phase. For routine NMR measurement, at 31°C, only the relaxation signals of compounds more volatile than C17 are acquired. Thus, the C17+ fraction would be invisible to NMR at room temperature, but perhaps not at reservoir temperature. This is critical to the interpretation of NMR log response within the early oil and condensate windows, in which C17+ can be a major fraction. Thus, engineers can underestimate movable HCs by using routine core data as a basis for interpretation. On the basis of NMR experiments for several oil samples, we observed that the T1–T2 distributions depend on the overall composition of total HCs and effective mobilities. The results also show that, in the case when both light and heavy HC fractions coexist in a single phase, they do not appear as different clusters in a T1–T2 distribution map. NMR parameters were used to monitor the amount, composition, and effective mobility of remaining HCs after each injection and discharging cycle, during miscible enhanced-oil-recovery (EOR) huff ’n’ puff experiments on Eagle Ford samples.

Retained water content after nitrogen driving water on flooding saturated high volatile bituminous coal using low-field nuclear magnetic resonance

Retained water in reservoirs can result in water block damage that can lead to low productivity of coalbed methane wells. To research the water saturation increasing process during water flooding and determine the retained water content variation law after nitrogen driving water, considering that high-pressure nitrogen injection is recently regarded as an effective technology to enhance CBM well production, multiple low-field nuclear magnetic resonance methods, including T2 spectrum testing, multi-slice spin-echo sequence imaging, and spatially-resolved T2 distribution measurements, were applied during water flooding experiment and nitrogen driving water for decreasing retained water content of a high volatile bituminous coal sample. Distributions of fractures, pores and minerals were inversed based on micro-CT technology and the corresponding influences on retained water were discussed. The results showed that water saturation increasing process of total apertures, micro- and transition pores, meso-pores, macro-pores and fractures were increased by logarithmic relation with the increase of water flooding time. Nitrogen driving could basically decrease water saturation in macro-pores and fractures completely, and partly in meso-pores with a 50.11% decrease in water saturation. However, it can lead to increased water saturation by 6.89% in micro- and transition-pores. It is relatively easier to decrease retained water content when inlet pressure is increased during nitrogen driving because effective stress is decreased and connections between apertures are improved. The smaller mineral filling porosity, greater total porosity, and better connection of pores and fractures, the greater water content after water flooding. Retained water content of a sample with connected apertures is discharged effectively under nitrogen driving, while a sample that lacks connected apertures remains high in retained water content.

Experimental investigations on the effects of ambient freeze-thaw cycling on dynamic properties and rock pore structure deterioration of sandstone

The issue of rock pore structure deterioration and dynamical mechanical properties has drawn much attention in recent years in the rock engineering community. In this study, a series of 140 freeze-thaw cycling tests are conducted on sandstone samples. The sandstone pore structure after freeze-thaw cycles was detected by Nuclear Magnetic Resonance (NMR), and the dynamic load test was carried out by Split Hopkinson Pressure Bar system (SHPB). The results are: with the increase of freeze-thaw cycles, the saturated mass and porosity of sandstone increase, the dynamic peak stress of sandstone decreases; while the peak strain and total strain increase gradually, and the macroscopic damages of rocks increase. The results of T2 distribution and pore size changes are that the pore sizes of sandstones increase, especially that of micro-pores and macro-pores increase obviously after 140 freeze-thaw cycles. Under the effect of freeze-thaw cycles, the sandstone pores become connected with each other, some of the micro-pores and mini-pores are changed into meso-pores and macro-pores. The number of marco-pores increases evidently, and the largest increase is 197.23%. The rock pore structures have changed, which would lead to the change of mechanic properties. As the number of freeze-thaw cycles increases, the rock dynamical peak stress gradually decreases and the peak strain and the overall strain increase gradually.

NMR logging activation sets selection and fluid relaxation characteristics analysis of tight gas reservoirs: A case study from the Sichuan Basin

With complex lithology and reservoir types, as well as high concealment and heterogeneity, tight reservoirs in the Sichuan Basin involve significant uncertainties in gas–water relationship. Since NMR logging can effectively solve problems related to the multiple results of conventional logging operations, it can be deployed for accurate assessment of the properties of formation fluids. Accordingly, different NMR logging activation sets were assessed in accordance with the specific features of tight reservoirs in the basin. With consideration to NMR logging data obtained under different activation sets and testing data of wells, the optimal NMR logging activation set was identified. Moreover, with relaxation characteristics of rocks, gas and water as theoretical foundations, the T2 gas and water relaxation characteristics were reviewed to highlight the impacts of porosity, pore sizes, fluid properties and other factors of tight reservoirs on T2 horizontal relaxation distribution. According to the research results, D9TWE3 can be seen as the most suitable NMR logging activation set for tight reservoirs in the Sichuan Basin; reservoir tightness is the key influence factor for the distribution of gas/water relaxation in tight clastic reservoirs; generally, in tight sandstone reservoirs, natural gas shows a longer T2 relaxation time than water; in fracture-vug type carbonate reservoirs, the right peak of T2 distribution spectrum of gas layers is frontal, while the right peak in T2 distribution spectrum of water layers is backward. In conclusion, the standards for gas/water relaxation in tight sandstone and carbonate reservoirs in the Sichuan Basin can help effectively determine the physical properties of fluids in tight reservoirs with porosity of 4–10%. Such standards provide reliably technical supports for gas/water identification, reserves estimation and productivity construction in tight reservoirs of the Sichuan Basin.

Dolomite cores evaluated by NMR

Nuclear Magnetic Resonance (NMR) is a very versatile technique that allows the characterization of several petrophysical properties such as porosity, pore size distribution and fluid saturation and, unlike other techniques, it is possible to be applied on field scale through well loggings and in laboratory scale on the analysis of samples. In this paper, NMR measurements were performed in several samples with different saturation conditions in order to obtain as main information that can be inferred from the application of this technique at the laboratory scale. Silurian dolomites were studied since they are common in many carbonate reservoirs. Several petrophysical properties of these rocks were evaluated from NMR T2 relaxation time distributions at different conditions and compared with common techniques used in laboratory. Three fluids pairs were used: air/brine; mineral oil/brine; and crude oil/brine. The use of different fluids was required depending on the property that was being studied. Nitrogen porosity, commonly used in the petrophysical characterization, was compared to a porosity obtained by the NMR, and an optimum correlation was obtained between the results of these two techniques. T2 relaxation time limits were defined in order to separate micro/mesopores and meso/macropores limits. Using these limit ranges, the pore size distribution was evaluated and it was compared to the pore size distribution obtained when the T2 distribution is scaled by the surface relaxivity value. It was observed that about 80% of the porous medium was composed of macropores, but the evaluation of only the T2 relaxation times provided higher fraction of macropores. The T2cutoff values obtained were in accordance to the values referenced in the literature for vuggy carbonates. From the NMR measurements performed before and after waterflooding was possible to determine the residual oil saturations, which values were similar to the values obtained by mass balance. Finally, comparing the T2 distributions before and after the aging process, it was observed that there was an increase of fluid fraction in lower relaxation times after the aging process, indicating that NMR measurements could be used to evaluate the wettability alteration of the surface. The results obtained in the quantification of the wettability from the T2 relaxation times were very different in relation to the wettability quantification provided by Amott-Harvey Wettability Index.

The pore structure of tight limestone—Jurassic Ziliujing Formation, Central Sichuan Basin, China

The pore structure of the tight limestone in the Daanzhai Member of the Ziliujing Formation, Jurassic System, in central Sichuan Basin, China, is complex but essential to the exploration and development of tight oil. The pore structure of the tight limestone is studied by using scanning electron microscopy (SEM), nitrogen adsorption, high-pressure mercury intrusion, and nuclear magnetic resonance (NMR). The experimental results suggest that the pores are mainly slit pores and mesopores and macropores contribute to the pore volume and specific surface. The displacement pressure, average pore size, and homogeneity coefficient correlate with porosity and permeability and can be used to evaluate the pore structure. The full pore-size distribution was obtained by combining nitrogen adsorption and high-pressure mercury intrusion. We find that the limestone mainly contains mesopores with diameter of 2−50 nm. The T2 distribution was converted into pore-size distribution, well matching the full pore-size distribution. The relation between T2 and pore size obeys a power law and the geometric mean of T2 correlates with the pore structure and can be used in the pore structure evaluation.

A New Method for Predicting Capillary Pressure Curves Based on NMR Logging in Tight Sandstone Reservoirs

The accurate prediction of capillary pressure curves is of great significance for the evaluation of pore structure in tight sandstone reservoirs. In this paper, a hybrid model is proposed to predict the mercury injection capillary pressure (MICP) curve using multiple characteristic parameters of the nuclear magnetic resonance (NMR) transverse relaxation (T2) distribution; models based on the capillary pressure point and on the non-wetting phase saturation point are combined. Because of the high level of multicollinearity among the characteristic parameters of the NMR T2 distribution, the partial least squares method is used to solve the model coefficients. The leave-one-out cross-validation (LOOCV) method is used to determine the optimal combination of parameters of the hybrid model, i.e., the number of latent variables of the model based on the capillary pressure point, the number of latent variables of the model based on the non-wetting phase saturation point, and the location of the splicing point. The result of model self-testing, the result of the LOOCV, and the analysis of the generalization ability all indicate that the hybrid model has high accuracy and strong stability for MICP curves prediction. The prediction results in tight sandstone reservoirs further verify the effectiveness of this method.

Dynamics and spatial distribution of water in Nafion 117 membrane investigated by NMR spin-spin relaxation

The dynamics and spatial distribution of water molecules in Nafion 117 membrane has been investigated by 1H NMR. To this end, 1D and 2D spin-spin (T2) relaxometry experiments were carried out as a function of the relative humidity ranging from 9 to 100%. The inverse Laplace transform was successfully applied to obtain the 1D T2 distributions and 2D relaxation maps. The 1D T2 distributions show two peaks at low RH and mainly one at high water content, which can be associated with the rearrangement of the exchange sites inside the polymeric channels with the amount of water. From the T2 distribution at 70% RH three types of water were identified corresponding to different degree of molecular mobility. The 2D T2-T2 maps show molecular exchange between the two water populations found at low RH, while at 70% the exchange between only the two more mobile water populations takes place.

Impact of Annealing Prior to Solution Treatment on Aging Precipitates and Intergranular Corrosion Behavior of Al-Cu-Li Alloy 2050

The influences of annealing prior to solution treatment on the grain structure, subsequent aging precipitates, and intergranular corrosion (IGC) of Al-Cu-Li alloy (AA2050) sheet with T6 aging at 448 K (175 °C) were investigated. Annealing impedes the full recrystallization during solution treatment, increasing the population density of T1 (Al2CuLi) precipitates, but decreasing that of θ′ (Al2Cu) precipitates, of the aged alloy. Meanwhile, annealing leads to the heterogeneous distribution of T1 precipitates, increasing the alloy hardness, and decreasing the open-circuit potential of the aged alloy. With prolonged aging time, the corrosion mode of the aged AA2050 samples with and without annealing evolved in a similar manner. The corrosion mode as a function of aging may be summarized as local IGC with pitting and general IGC with pitting (following initial aging and under the underaged condition), pitting corrosion (later in the under-aging stage), pitting with slight IGC (near the peak-aged condition), and pitting with local IGC (under the overaging condition). The annealing treatment hinders IGC propagation on the rolling surface while accelerating the IGC on transverse surfaces.

A method to determine nuclear magnetic resonance (NMR) T2cutoff based on normal distribution simulation in tight sandstone reservoirs

The T2cutoff is an important input parameter in nuclear magnetic resonance (NMR) applications. The accuracy of the T2cutoff affects the prediction reliability of parameters associated with the identification and evaluation of formations. Current methods are based on regional statistics; they have limited applications and the predicted values are not always reliable. In this study, a total of 36 core samples, drilled from Triassic tight sandstone reservoirs of the southwest Ordos Basin in China, were used for laboratory NMR measurements under fully brine saturated and irreducible water conditions. Based on the morphological character analysis of experimental NMR T2 spectra, we demonstrate that NMR T2 spectra can be fully simulated using the normal distribution function. In addition, a new method was proposed, which can predict various T2cutoffs based on the morphological differences of NMR T2 spectra, and the irreducible water saturation (Swirr) was calculated, which represents the ratio of the sum volume of clay bound water and capillary bound water to total pore volume. The reliability of this method was verified by comparing the predicted T2cutoff and Swirr values with those of core NMR experimental results. Finally, we extended this method into field applications in several tight sandstone reservoirs in China. The results show that total T2 distributions of the formation were fully simulated by the normal distribution function, and various T2cutoff and Swirr values were precisely predicted. Meanwhile, tight sands permeability curves, predicted based on the Timur-Coates model, were also accurately estimated. The results of our study may be applied to improve tight sandstone reservoir identification and evaluation using NMR logs.

A new method for mechanical damage characterization in proppant packs using nuclear magnetic resonance measurements

Proppant performance can significantly affect the success of hydraulic fracturing treatments and production in unconventional plays. Performance of proppants can decrease rapidly by mechanical damage. Quantifying the impact of mechanical damage on proppant performance can be challenging either in the laboratory or in-situ condition. This paper introduces a new method based on Nuclear Magnetic Resonance (NMR) Transverse relaxation (T2) measurements to characterize pore-size distribution in proppant packs. Quantifying the pore-size distribution in proppant packs enables enhanced evaluation of porosity and conductivity of proppant packs and possible mechanical damage to the packs. The objectives of this paper are (a) to evaluate the performance of this new NMR-based method for characterizing pore structure of the proppant packs, and (b) to isolate and quantify the mechanical damage in proppant packs due to generating of fines in the laboratory using this new NMR-based method.First, we prepared proppant pack test samples in three categories including (a) different types of proppants with different surface relaxivity, (b) mixture of proppants with different sizes, and (c) proppants undergone different levels of mechanical damage. We measured NMR response in proppant packs and quantified the impacts of proppant type, size, and mechanical damage on NMR T2 distribution. Next, we used the fractional packing model to quantify the efficiency of packing of proppant mixture and to quantify the changes in porosity of proppant packs caused by variation in size and fraction of fines. Finally, we used Kozeny-Carman (KC) equation and modified Schlumberger Doll Research (SDR) equation to correlate the variation in T2 distribution to the decrease in proppant pack permeability.Results showed that NMR T2 distribution is sensitive to pore-size distribution in the proppant packs. The variable pore-size distribution was either a consequence of having a mixture of proppants with different sizes or different levels of mechanical damage. The impacts of fines on the pore-size distribution of the proppant packs was measureable, which is promising for the successful application of the introduced method for time-lapse quantification of generated fines. We also observed a measurable sensitivity of T2 distribution to mechanical damage in the proppant packs, which enables quantifying the level of damage in proppants through quantifying pore structure in the proppant packs. The NMR T2 measurements were, however, sensitive to the presence of paramagnetic materials such as iron in proppants. This sensitivity was more significant in cases where paramagnetic materials were distributed on the proppant surface. The proposed method is considered as an indirect measurement of pore structure and could potentially provide a quantitative assessment of the proppant pack conductivity both in the lab-scale and in-situ conditions. Improved assessment of proppant conductivity can help in enhancing the design and execution of fracture treatments for successful development of unconventional plays.

Rock-Type Definition and Pore Characterization of Tight Carbonate Rocks Based on Thin Sections and MICP and NMR Experiments

Thick tight Ordovician carbonate rocks are present at depths exceeding 5300 m in the Tahe oilfield and their matrix is considered to contain no storage space. An integrated petrographical and petrophysical study was conducted on a set of 25 tight carbonate core samples from Ordovician strata, covering a wide range of lithologies and textures. Six carbonate rock types were characterized by integrating both petrographical and petrophysical data, including thin-section observations and porosity, permeability, mercury injection capillary pressure and nuclear magnetic resonance (NMR) measurements. We found that thick grainstone and limestone with half-filled fractures exhibited good reservoir properties. NMR testing is an invaluable tool for characterizing pore structures in tight carbonate rocks. For example, six rock types can be identified from the NMR T2 distributions and the changes in pore volume under different pressures (up to 20 MPa) can be calculated. NMR technology can be used to perform rapid and accurate rock-type identification and pore network evaluation in tight carbonate rocks. The results provide an experimental foundation for NMR logging interpretations and advance the understanding of geological and geophysical characteristics of ultra-deep carbonate reservoirs.

An improved method of characterizing the pore structure in tight oil reservoirs: Integrated NMR and constant-rate-controlled porosimetry data

Tight oil reservoirs have an ultrafine pore structure with a large heterogeneity, which requires the integration of multiple techniques to characterize pore structure characteristics systematically and, therefore, to gain a better understanding of reservoir quality. Tight oil sandstone samples from the Upper Triassic Yanchang Formation in the Ordos basin were measured by nuclear magnetic resonance (NMR), constant-rate-controlled mercury porosimetry (CMP) and field emission scanning electron microscopy (FE-SEM) to investigate the pore structure characteristics and their control on petrophysical properties. Various types of pores from intergranular pores, dissolution pores, and intercrystalline pores to small microfractures occurred in the studied tight sandstones, which indicates that the NMR T2 distributions may be unimodal or bimodal in behaviour with a wide range. The short components of the T2 distributions match the CMP-derived throat size distributions regarding the dimensions, width and shape of the curves. We combined CMP and NMR to uncover the total pore size distribution; the size distributions of the throat and pore body range from 0.01 to 1 μm and from 0.1 μm to tens of microns respectively, which match the FE-SEM results. The pore body-to-throat ratio may be the important factor affecting the free water saturation in the pore body, which, in turn, is probably associated with the mineralogy of tight sandstones, in particular, the quartz, feldspar and clay mineral contents. The pore radius of 0.3–0.5 μm is the percolation threshold. The seepage porosity rather than total porosity overwhelmingly dominates the permeability, which, in turn, relates to the pore types, i.e., mesopores and macropores. An improved permeability prediction model is presented for tight oil reservoirs based on the contribution from different pore size intervals to the permeability. This model has a distinctly better performance than the classic models such as the Timur-Coates and SDR models and may be generalized to other similar reservoirs with ultrafine pore structures and significant volumes of clay minerals.

Kα emission by the electrons with bi-Maxwellian distribution in a Cu foil

In our previous research [J. C. Zhao et al., Laser Part. Beams 35, 483 (2017)], we studied the influence of the electron refluxing on the electron transport and Kα emission in a solid target. In this work, the electrons with the bi-Maxwellian distribution of low temperature T1 and high temperature T2 interacting with Cu foil to produce Kα emission are investigated when the electron refluxing effect is included or excluded. Simulation results show that including the refluxing effect, high temperature T2 plays a more significant role in the Kα photon yield, while in the absence of the refluxing effect, the low temperature T1 has a dominant effect. In addition, at the target thickness d ≈ 20 μm, the maximum Kα yield is achieved when the electrons with bi-Maxwellian distribution interact with the Cu target including the refluxing effect. As emitted electrons have the bi-Maxwellian distribution of T1 = 0.1 MeV and T2 = 1.4 MeV, the Kα photon yield is always higher than that in other bi-Maxwellian distributions. Therefore, when the low temperature T1 tends towards a larger value and the high temperature T2 tends towards a smaller one, the maximum Kα photon yield will be obtained whether the electron refluxing effect is considered or not.

Sciatic Nerve Regeneration in Wistar Albino Rats Evaluated by in vivo Conductivity and in vitro 1H NMR Relaxometry

Abstract Objective: The aim of this study was to evaluate and quantify functional and structural nerve regeneration after reconstruction using either direct suture or silicon graft. Methods: Thirty-two adult Wistar Albino rats were divided in two equal groups. The left sciatic nerve was cross-sectioned and reconstructed using either direct suture (DS group) or a silicone graft (SG group). At 4, 6, 8 and 10 weeks two rats were randomly chosen from each group for in vivo measurement of nerve electric conductivity and subsequently sacrificed together with other two rats from the same group for in vitro 1H NMR relaxometry measurements. The T2 distributions were assigned to 1H located in different pools corresponding to the nerve structure. Results: In the injured nerve we observed a significant increase in the stimulation threshold and a decrease in conduction velocity when compared with the healthy nerve in both groups. Whereas the conduction velocity increased progressively from 4 to 10 weeks in the DS group, the opposite evolution was observed in the SG group. In both groups, the first two peaks corresponding to water bound to collagen and epineurium had smaller transverse relaxation times in the injured nerves, while there was no change in the peaks corresponding to perineurium and free water between healthy and injured nerves. Conclusions: Significant differences were observed between direct suture and nerve graft reconstructions from both a functional and structural point of view. In the case of direct suture reconstruction, the nerve was functionally healed at 10 weeks after injury.

Fractal Analysis of Donghetang Sandstones Using NMR Measurements

Routine core analysis, thin section epifluorescence and scanning electron microscopy (SEM) analyses were performed to delineate the reservoir qualities, pore systems, and pore network characteristics of the Devonian Donghetang sandstone samples. Nuclear magnetic resonance (NMR) measurements were used to gain insight into pore size distributions of these sandstones. Fractal analysis was performed on the NMR T2 spectrum measured at echo spacings of 0.6 and 1.2 ms. Then the relationships between NMR parameters and fractal dimension were investigated. The results show that the pore systems are dominated by primary intergranular pores with a combination of secondary dissolution pores, micropores, and microfractures. Samples with the highest reservoir quality are characterized by a coexistence of primary intergranular and secondary dissolution pores. The parameter T2gm (the geometric mean of the T2 distribution) is a sensitive one for characterizing the pore size distribution and microscopic pore structure sinc...

Fractal analysis of tight shaly sandstones using nuclear magnetic resonance measurements

Assessing quantitatively the microscopic pore structures of porous rocks, including irregularities of pore shapes and pore size distributions, is becoming one of the most challenging efforts. Nuclear magnetic resonance (NMR) measurements were used to provide insights into the pore geometry (pore size and shape) and pore connectivity of the Chang 7 tight shaly sandstones (in situ permeability <0.1 md) in Ordos basin. The incremental transverse relaxation time (T2) distributions for the 100% brine-saturated samples display unimodal and bimodal behaviors, presenting a geometrical arrangement composed of small to large pore size domains. The NMR parameters such as bulk volume irreducible (BVI) (capillary and clay-bound water), free fluid index (FFI) (movable water), the value of T2 separating the BVI from FFI, the amplitude weighted mean on a logarithmic scale (T2gm), and the value of T2 that shows the highest frequency on the T2 spectrum (T2peak) for each sample were determined. Then the fractal theory was adopted to quantitatively express the complexity and heterogeneity of the sandstones. The results show that only minor primary intergranular porosity remains, and variable amounts of micropores and secondary intragranular porosity with poor connectivity occur in the Chang 7 tight shaly sandstones. Assuming spherical pores, a new model to calculate the fractal dimension of pore structure from the NMR T2 distributions is proposed. The fractal dimensions of all the samples are calculated, and the accuracy of the proposed model is verified by the regression coefficients. The microscopic pore structures are heterogeneous in these tight sandstones according to the high value of fractal dimensions. Micropores are the primary causes of heterogeneity in tight sandstones, and samples with unimodal T2 distribution behaviors and high content of short components have the highest fractal dimension and heterogeneity. The calculated fractal dimension is strongly correlated with T2peak and T2gm; therefore, the fractal model proposed in this study can be used to calculate the fractal dimensions and evaluate the heterogeneities of the porous rocks satisfactorily. The fractal model proposed in this study helps to quantitatively assess the pore structures of tight sandstones using NMR measurements.

Application of NMRT2to Pore Size Distribution and Movable Fluid Distribution in Tight Sandstones

This paper explores the applicability of nuclear magnetic resonance (NMR) technology on pore size distribution (PSD) and movable fluid distribution (MFD) in tight sandstones. Centrifugation experiments and NMR tests are performed on saturated samples. The fluid changes in pores corresponding with three different types of NMR T2 distribution after each centrifugation is then analyzed. In addition, a new method to determine the conversion factor from NMR T2 distribution to PSD is developed. In comparison with the PSD obtained by mercury intrusion porosimetry, the new method is more suitable for PSD calculation in tight sandstones. Afterward, the optimum centrifugal force to determine the threshold radius for fluid flow is obtained. On the basis of this, we analyze MFD in tight formation. Through study, the following results are arrived at: patterns of NMR T2 distributions of outcrop and subsurface cores at water saturation condition can be classified into three types (I, II, and III). Among which, type I an...

Interpretation of NMR Relaxation in Bitumen and Organic Shale Using Polymer–Heptane Mixes

One of the much debated mysteries in 1H NMR relaxation measurements of bitumen and heavy crude oils is the departure from expected theoretical trends at high viscosities, where traditional theories of 1H–1H dipole–dipole interactions predict an increase in T1 with increasing viscosity. However, previous experiments on bitumen and heavy crude oils clearly show that T1LM (i.e., log-mean of the T1 distribution) becomes independent of viscosity at high viscosities; in other words, T1LM versus viscosity approaches a plateau. We report 1H NMR data at ambient conditions on a set of pure polymers and polymer–heptane mixes spanning a wide range of viscosities (η = 0.39 cP ↔ 334 000 cP) and NMR frequencies (ω0/2π = f0 = 2.3 MHz ↔ 400 MHz) and find that at high viscosities (i.e., in the slow-motion regime) T1LM plateaus to a value T1LM> ∝ ω0 independent of viscosity, similar to bitumen. More specifically, on a frequency-normalized scale, we find that T1LM> × 2.3/f0 ≃ 3 ms (i.e., normalized relative to 2.3 MHz), in g...

Water Dynamics and Physicochemical Analysis of Two Different Varieties of Apple Jam (Fuji) and (Yinduqing) by LF- NMR and MRI

Abstract Apple jam is one of the favorite foods consumed worldwide. This study investigated the effect of storage time and sugar concentration on water dynamics in Fuji and Yinduqing, using low-field nuclear magnetic resonance (LF-NMR) and magnetic resonance imaging (MRI) techniques. The samples were taken for jam preparation with various concentrations of sugar solution (0, 25, 50 and 75-oBrix) and stored at a room temperature of 20 °C for 16 days. The LF-NMR relaxation time T 2 distribution displayed bound, intermediate and free water, respectively. The lowest T 2 range reflected lowest sugar hydrogen mobility depending on total soluble solids (TSS) and water content. A significant correlation (r &gt; 0.9) existed between LF-NMR analysis and physicochemical parameters (water content, color, pH and TSS). MRI displayed uniform water distributions in samples with low sugar concentration. Fluorescence microscopy was used to evaluate sugar crystals and microstructural changes during processing. The study demonstrated the viability of LF-NMR method in determining water dynamics in the apple jams upon processing and storage that may be implemented for quality analysis in other jam products.