scholarly journals Processing of surface-nuclear magnetic resonance data from sites with high noise levels

Geophysics ◽  
2016 ◽  
Vol 81 (4) ◽  
pp. WB75-WB83 ◽  
Author(s):  
Jakob Juul Larsen ◽  
Ahmad A. Behroozmand
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Noise Reduction ◽  
Noise Levels ◽  
Borehole Data ◽  
High Noise ◽  
Nmr Data ◽  
The Impact ◽  
Reduction Approach ◽  
Nuclear Magnetic

The applicability of surface nuclear magnetic resonance (NMR) in investigations of groundwater is often limited by high noise levels in many areas of interest. We have evaluated measurements from a high-noise-level area in Ristrup, Denmark, recorded with a Numis Poly instrument. Standard multichannel filtering techniques for noise reduction are inadequate for several data sets acquired in this area, and surface-NMR signals cannot be resolved from the acquired data. Based on a careful assessment of the frequency content of the data, we have determined how a model-based noise reduction approach can be generalized and used to subtract two harmonic noise components from the data. Reliable surface-NMR data can be extracted from the noise-reduced data. Moreover, we have determined the impact of the proposed processing approaches on our inversion results, and we have also developed an example in which the proposed methodology allowed us to reveal and avoid an otherwise overlooked contamination of the reference coil signals with a surface-NMR signal. No borehole data were available for the investigated sites, and the validity of the noise reduction approach was instead verified using a synthetic five-layer model embedded in noise-only records from Ristrup. Our results have determined that a careful processing of the recorded data made it possible to extract surface-NMR data in more places of interest.

scholarly journals Model-based subtraction of spikes from surface nuclear magnetic resonance data

Geophysics ◽  
2016 ◽  
Vol 81 (4) ◽  
pp. WB1-WB8 ◽  
Author(s):  
Jakob Juul Larsen
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Noise Reduction ◽  
Band Pass Filter ◽  
Data Set ◽  
Pass Filter ◽  
Model Based ◽  
Nmr Data ◽  
Electric Fence ◽  
Nuclear Magnetic

Surface nuclear magnetic resonance (surface NMR) has progressed significantly in recent years due to advances in instrumentation. In particular, the introduction of multichannel surface NMR instruments has been effective in improving the signal-to-noise ratio. The current methodology for noise reduction with multichannel instruments is, however, inadequate in complex noise environments, and there is a need for improved signal processing. We have evaluated a study of impulsive noise (spikes) in surface NMR data acquired with a Numis Poly instrument. We have determined how the spectral content can be used to classify spikes as originating from electric fences or sferics. Measurements of spikes from two electric fences were evaluated. The spikes were highly deterministic and can be modeled as impulsive excitations of the band-pass filter in the surface NMR receiver system. We investigated the feasibility of a model-based approach for subtraction of electric fence spikes. Model-based subtraction was shown to be possible, but it is limited by accidental fitting of the NMR signal in its current embodiment. We evaluated an example of a surface NMR data set in which subtraction of powerline harmonic noise and electric fence spike noise removed all coherence in the multichannel data, and the consequences for further noise reduction using multichannel methods were developed.

Frequency cycling for compensation of undesired off-resonance effects in surface nuclear magnetic resonance

Geophysics ◽  
2016 ◽  
Vol 81 (4) ◽  
pp. WB33-WB48 ◽  
Author(s):  
Denys Grombacher ◽  
Mike Müller-Petke ◽  
Rosemary Knight
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Larmor Frequency ◽  
Forward Model ◽  
Resonance Excitation ◽  
Entire Volume ◽  
Resonance Effects ◽  
Aquifer Properties ◽  
The Impact ◽  
Nuclear Magnetic

To produce reliable estimates of aquifer properties using surface nuclear magnetic resonance (NMR), an accurate forward model is required. The standard surface NMR forward model assumes that excitation occurs through a process called on-resonance excitation, which occurs when the transmit frequency is set to the Larmor frequency. However, this condition is often difficult to satisfy in practice due to the challenge of accurately determining the Larmor frequency within the entire volume of investigation. As such, in situations where an undesired offset is present between the assumed and true Larmor frequency, the accuracy of the forward model is degraded. This is because the undesired offset leads to a condition called off-resonance excitation, which impacts the signal amplitude, phase, and spatial distribution in the subsurface, subsequently reducing the accuracy of surface NMR estimated aquifer properties. Our aim was to reduce the impact of an undesired offset between the assumed and true Larmor frequency to ensure an accurate forward model in the presence of an uncertain Larmor frequency estimate. We have developed a methodology where data are collected using two different transmit frequencies, each an equal magnitude above and below the assumed Larmor frequency. These data are combined, through a method we refer to as frequency cycling, in a manner that allow the component well-described by our estimate of the Larmor frequency to be stacked coherently, whereas the component related to the presence of an undesired offset is combined destructively. In synthetic and field studies, we have determined that frequency cycling is able to mitigate the influence of an undesired offset providing more accurate estimates of aquifer properties. Furthermore, the frequency-cycling method stabilized the complex inversion of surface NMR data, allowing advantages associated with complex inversion to be exploited.

15N and 13C nuclear magnetic resonance of deoxydinucleotide monophosphates. II. Protonation of the homo dimers deoxycytidylyl-(3′,5′)-deoxycytidine, thymidylyl-(3′,5′)-thymidine, and deoxyadenylyl-(3′,5′)-deoxyadenosine in dimethyl sulfoxide

1990 ◽  
Vol 68 (11) ◽  
pp. 2033-2038 ◽  
Author(s):  
Giovanna Barbarella ◽  
Massimo Luigi Capobianco ◽  
Luisa Tondelli ◽  
Vitaliano Tugnoli
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Chemical Shift ◽  
Dimethyl Sulfoxide ◽  
Phosphate Group ◽  
Nmr Data ◽  
13C Nuclear Magnetic Resonance ◽  
C Nmr ◽  
Nuclear Magnetic

The preferential protonation sites of the homo dimers deoxycytidylyl-(3′,5′)-deoxycytidine, thymidylyl-(3′,5′)-thymidine, and deoxyadenylyl-(3′,5′)-deoxyadenosine were established by nitrogen-15 and carbon-13 NMR in dimethyl sulfoxide, in the presence of varying amounts of CF3COOH. The nitrogen-15 NMR data show that in d(CpC) the capability of the two N3 nitrogens to accept the proton is slightly different. In d(TpT) and d(ApA) the protonation of the phosphate group leads to significant variations of the chemical shift of the carbons adjacent to phosphorus. Keywords: deoxydinucleotides, protonation, 15N and 13C NMR.

Perfluoroalkyl- and fluoroalkyl- complexes of rhodium(III)

1976 ◽  
Vol 54 (13) ◽  
pp. 2077-2084 ◽  
Author(s):  
Howard C. Clark ◽  
Kenneth J. Reimer
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Infrared Spectra ◽  
Oxidative Addition ◽  
Far Infrared ◽  
Addition Reactions ◽  
Nmr Data ◽  
Far Infrared Spectra ◽  
Nuclear Magnetic

A series of perfluoroalkyl (Rf—) and fluoroalkyl (RfCH2—) complexes of rhodium(III) have been prepared by oxidative addition reactions of RfI and RfCH2I (Rf = CF3, C2F5 and C3F7) with trans-RhClCO(PMe2Ph)2. The reaction of CF3I with trans-RhClCO(PMePH2)2 gave RhClI(CF3)CO(PMePh2)2 but no reaction was observed with CF3CH2I. The trans stereochemistry of addition has been assigned to all complexes by nuclear magnetic resonance measurements and the comparison of the far-infrared spectra to those of some bromo compounds: RhBrI(CF3)CO(PMe2Ph)2 and RhBrI(C3F7CH2)CO(PMe2Ph)2. Both 1H and 19F nmr data are presented and discussed.

scholarly journals Exploring the impact of maternal nutritional status on the compositional profile of mid-trimester biofluids

2017 ◽  
Author(s):  
Μαρία Φωτίου
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Nutritional Status ◽  
Compositional Profile ◽  
Maternal Nutritional Status ◽  
The Impact ◽  
Nuclear Magnetic

Μελέτες υποδεικνύουν ότι ακόμη και ήπιες αποκλίσεις από ένα θρεπτικά-ισορροπημένο ενδομήτριο περιβάλλον, οι οποίες οφείλονται στη διατροφική κατάσταση και το μεταβολισμό της μητέρας, μπορεί να προκαλούν σοβαρές επιπτώσεις στην υγεία του απογόνου κατά την ενήλικη ζωή. Ο προσδιορισμός/ταυτοποίηση μεταβολιτών στο αμνιακό υγρό (ΑΥ) θα συνέβαλε στη διαλεύκανση των μηχανισμών, μέσω των οποίων η μητρική διατροφή επηρεάζει το ενδομήτριο περιβάλλον. Πράγματι, μελέτες σε ζώα έχουν δείξει ότι παρεμβάσεις στη μητρική διατροφή μεταβάλουν τη σύσταση του ΑΥ. Ωστόσο, τα δεδομένα που αφορούν στη συσχέτιση της διατροφής έγκυων γυναικών με τη συγκέντρωση μεταβολιτών στο ΑΥ είναι περιορισμένα. Σκοπός της διατριβής ήταν η διερεύνηση της επίδρασης της μητρικής διατροφικής κατάστασης στη σύσταση του ΑΥ έγκυων γυναικών. Το δείγμα αποτέλεσαν έγκυες που υποβλήθηκαν σε αμνιοπαρακέντηση για προγεννητικό έλεγχο. Η συλλογή δημογραφικών/ανθρωπομετρικών χαρακτηριστικών πραγματοποιήθηκε με χρήση ερωτηματολογίων, η καταγραφή της μητρικής διατροφικής πρόσληψης με ημιποσοτικό-ερωτηματολόγιο-συχνότητας-κατανάλωσης-τροφίμων, ενώ δεδομένα για την εξέλιξη/έκβαση της κύησης ελήφθησαν από ιατρικά αρχεία. Για την ανάλυση του ΑΥ χρησιμοποιήθηκαν συμβατικά αναλυτικά εργαλεία και πυρηνικός μαγνητικός συντονισμός (Nuclear Magnetic Resonance, NMR). Η διατριβή αποτελείται από 3 μελέτες. Στην 1η μελέτη διερευνήθηκε η συσχέτιση των συγκεντρώσεων γλυκόζης, ουρικού οξέος, και ιόντων φωσφόρου, καλίου και νατρίου στο ΑΥ με α. την ηλικία κύησης, β. δημογραφικά/ανθρωπομετρικά χαρακτηριστικά των εγκύων και γ. παραμέτρους νεογνικής ανάπτυξης. Από τα σημαντικότερα ευρήματα ήταν η συσχέτιση μεταξύ εβδομάδας κύησης και ιόντων φωσφόρου, η οποία αναδεικνύει το ρόλο του φωσφόρου στην εμβρυική ανάπτυξη/ωρίμανση. Επίσης, ο δείκτης-σωματικής-μάζας των εγκύων πριν την εγκυμοσύνη παρουσίασε στατιστικά σημαντική συσχέτιση με τη συγκέντρωση του ουρικού οξέος, ενώ η εκατοστιαία-θέση-βάρους των νεογνών με τη συγκέντρωση του ουρικού οξέος και των ιόντων φωσφόρου. Η 2η μελέτη περιγράφει την περίπτωση εγκύου της οποίας το ΑΥ κατά την 222/7 εβδομάδα κύησης παρουσίασε υπερβολικά υψηλή συγκέντρωση ουρικού οξέoς και καλίου, και υψηλή αναλογία κυστεΐνης/μεθειονίνη, σε σχέση με τις μέσες τιμές που αναφέρονται στη βιβλιογραφία για τη συγκεκριμένη εβδομάδα κύησης. Τη χρονική στιγμή της αμνιοπαρακέντησης, η έγκυος ήταν κλινικά υγιής. Ωστόσο, την 280/7 εβδομάδα, διαγνώστηκε προεκλαμψία. Το σημαντικότερο εύρημα αφορά στον υψηλό λόγο κυστεΐνης/μεθειονίνη που πιθανότατα απορρέει από τη μη κάλυψη των συστάσεων σε συγκεκριμένα μη-ενεργοφόρα θρεπτικά συστατικά που δρουν ως ρυθμιστές του μεταβολισμού στον κύκλο της μεθειονίνης (π.χ. φυλλικό οξύ). Στην 3η μελέτη διερευνήθηκε η υπόθεση ότι οι διατροφικές συνήθειες της μητέρας αντικατοπτρίζονται στο μεταβολομικό αποτύπωμα του ΑΥ. Μελετήθηκαν 2 διατροφικά-πρότυπα εγκύων, τα οποία διέφεραν στατιστικά σημαντικά ως προς το %ποσοστό της συνολικής ημερήσιας ενεργειακής πρόσληψης 10 ομάδων τροφίμων. Οι διατροφικές προτιμήσεις αποτυπώθηκαν και στην πρόσληψη ενεργοφόρων και μη-ενεργοφόρων θρεπτικών συστατικών. Με την εφαρμογή της μεταβολομικής (NMR) φάνηκε ότι οι διατροφικές συνήθειες της μητέρας αντικατοπτρίζονται στο ΑΥ, καθώς τα δύο διατροφικά πρότυπα διέφεραν στις συγκεντρώσεις γλυκόζης, αμινοξέων, ενδιάμεσων μεταβολιτών του κύκλου του κιτρικού οξέος, και μυρμηκικού οξέος. Η μελέτη ανέδειξε τη δυνατότητα εφαρμογής της μεταβολομικής-ανάλυσης σε συνδυασμό με τα διατροφικά-πρότυπα με στόχο τη διερεύνηση της επίδρασης της μητρικής διατροφής στην εξέλιξη της κύησης. Τα αποτελέσματα της διατριβής θα μπορούσαν να συμβάλουν στην αποσαφήνιση των μηχανισμών μέσω των οποίων η μητρική διατροφική κατάσταση επηρεάζει την έκβαση της κύησης, καθώς και στη διαμόρφωση διατροφικών συστάσεων.

Case study of quantification of oil viscosity and saturation in complex reservoirs using advanced nuclear magnetic resonance log interpretation techniques

2011 ◽  
Vol 51 (2) ◽  
pp. 725
Author(s):  
Adrian Manescu ◽  
Keith Boyle
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Clay Content ◽  
Hydrocarbon Exploration ◽  
Fluid Viscosity ◽  
Oil Viscosity ◽  
Porosity Distribution ◽  
Nmr Data ◽  
Log Interpretation ◽  
Nuclear Magnetic

In the hydrocarbon exploration process, after a prospect has been identified and an exploration well has been drilled, a critical piece of information is the oil type. Earlier wireline or while-drilling well-logging technologies provided rock properties and saturation information, but relied on expensive sampling and testing to determine oil properties. This weakness was overcome through the introduction of nuclear magnetic resonance (NMR) logs that can provide formation properties—lithology-independent porosity, porosity distribution, permeability, etcetera—and information about the reservoir fluid viscosity. NMR data were recently acquired in complex, high-clay content, low-salinity oil reservoirs. Traditional petrophysical interpretations throughout these reservoirs were confronted with a complex lithology—comprising feldspathic litharenites and volcanic lithic components—high clay content and low formation water salinity, of 3-4 Kppm NaCl eq. This extended abstract shows how acquisition and interpretation of NMR data not only provided porosity and porosity distribution, but also identified oil viscosity across the logged intervals. Advanced NMR log interpretation techniques (2D-NMR maps of diffusion (D) versus T2, int) were used to identify oil NMR signal. This technique produced a continuous profile of diffusion and intrinsic T2 distribution maps. Once the oil NMR signal was identified, an estimation of the oil viscosity was also possible because D and T2, int are related with viscosity. Several available correlations have been used and results were comparable with production data.

Using the temporal distribution of noise for reference noise cancelation in sNMR surveys

2020 ◽  
Author(s):  
Thomas Kremer
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Noise Reduction ◽  
Field Survey ◽  
Coherence Function ◽  
Noise Cancellation ◽  
Nuclear Magnetic Resonance Method ◽  
Primary Loop ◽  
Secondary Loop ◽  
Nuclear Magnetic

<p>The surface Nuclear Magnetic Resonance method is gaining momentum as an efficient geophysical method for the detection and characterization of groundwater. However, the method still suffers from a low signal to noise ratio mostly due to electromagnetic noise of anthropic origin.</p><p>To solve this problem, signal processing in surface nuclear magnetic resonance surveys often relies on the reference-based noise cancellation technique. This method consists of capturing the main characteristics of the noise through a secondary loop ideally located and obtaining an estimate of the noise affecting the primary loop which can be subtracted from the noisy sNMR signal.</p><p>The main problem associated with the method occurs when the spatial distribution of the noise is heterogeneous, which can result in a low correlation between the reference loop and the primary loop, and hence in a poor noise reduction. Difficulties may also arise when the field survey location prevents the display of a reference loop for logistics or physical reasons.</p><p>To remediate these situations we have investigated the possibility of recording noise-only signals through the primary loop, prior to the sNMR measurement, and use those signals as references for subsequent calculation of the local transfer function. The correlation between a series of noise-only signal recorded on a primary loop was analyzed through the computation of the magnitude squared coherence function, and comparison was made with noise records from a secondary loop. The analysis demonstrates that temporal reference noise cancellation (TRNC) can provide more efficient noise reduction results than the classical spatial reference noise cancellation if the temporal noise-only database is large enough.</p><p>Such a technique would be particularly suited for the development of long-term sNMR monitoring systems, where noise records could be acquired for long periods without any difficulty. In addition to two field survey examples, we present a synthetic statistical analysis to estimate the minimal volume of the signal database required for optimal noise reduction.</p>

Sign in / Sign up

Export Citation Format

Share Document