Improved in situ mineral and petrophysical interpretation with neutron-induced gamma-ray spectroscopy elemental logs

2016 ◽  
Vol 4 (2) ◽  
pp. SF31-SF53 ◽  
Author(s):  
Oyinkansola Ajayi ◽  
Carlos Torres-Verdín
Keyword(s):  
Gamma Ray ◽  
Water Saturation ◽  
Matrix Effects ◽  
Rock Formations ◽  
Wide Range ◽  
Gamma Ray Spectroscopy ◽  
New Interpretation ◽  
Mineral Concentrations ◽  
Interpretation Method

Neutron logs are routinely expressed as apparent neutron porosity based on the assumption of a freshwater-saturated homogeneous formation with solid composition equal to either sandstone, limestone, or dolomite. Rock formations are often extremely heterogeneous and consist of different minerals and fluids in varying proportions, which cause simultaneous matrix and fluid effects on neutron logs. Detailed quantification of formation mineral composition enables the correction of matrix effects on measured neutron logs to unmask fluid effects; this in turn enables accurate quantification of porosity and water saturation. Neutron-induced gamma-ray spectroscopy is one of the most direct means available to quantify in situ formation mineralogy but available spectroscopy-based interpretation methods are usually tool dependent and incorporate empirical correlations. We have developed a new interpretation method to quantify mineral concentrations through the joint nonlinear matrix inversion of measured spectroscopy elemental weight concentrations and matrix-sensitive logs, such as gamma ray, matrix photoelectric factor, matrix sigma (neutron capture cross section), and matrix density. The estimated mineralogy was used in the correction of matrix effects on porosity logs and subsequent calculation of true formation porosity. The water saturation was quantified through joint petrophysical interpretation of matrix-corrected porosities and resistivity measurements using an appropriate saturation model. The developed inversion-based interpretation method is applicable to a wide range of formation lithologies, well trajectories, and borehole environments (including open and cased hole environments), and it is independent of tool and neutron source type. Verification results with synthetic and field cases confirm that the spectroscopy-based algorithm is reliable and accurate in the quantification of mineral concentrations, matrix properties, porosity, and hydrocarbon saturation.

Interpretation of porosity and fluid constituents from well logs using an interactive neutron-density matrix scale

2013 ◽  
Vol 1 (2) ◽  
pp. T143-T155 ◽  
Author(s):  
Olabode Ijasan ◽  
Carlos Torres-Verdín ◽  
William E. Preeg
Keyword(s):  
Gamma Ray ◽  
Water Saturation ◽  
Matrix Effects ◽  
Neutron Density ◽  
Reservoir Capacity ◽  
Constant Matrix ◽  
Light Oil ◽  
Saturated Formations ◽  
Neutron Porosity ◽  
Interactive Variable

Neutron and density logs are important borehole measurements for estimating reservoir capacity and inferring saturating fluids. The neutron log, measuring the hydrogen index, is commonly expressed in apparent water-filled porosity units assuming a constant matrix lithology whereby it is not always representative of actual pore fluid. By contrast, a lithology-independent porosity calculation from nuclear magnetic resonance (NMR) and/or core measurements provides reliable evaluations of reservoir capacity. In practice, not all wells include core or NMR measurements. We discovered an interpretation workflow wherein formation porosity and hydrocarbon constituents can be estimated from density and neutron logs using an interactive, variable matrix scale specifically suited for the precalculated matrix density. First, we estimated matrix components from combinations of nuclear logs (photoelectric factor, spontaneous gamma ray, neutron, and density) using Schlumberger’s nuclear parameter calculator (SNUPAR) as a matrix compositional solver while assuming freshwater-filled formations. The combined effects of grain density, volumetric concentration of shale, matrix hydrogen, and neutron lithology units define an interactive matrix scale for correction of neutron porosity. Under updated matrix conditions, the resulting neutron-density crossover can only be attributed to pore volume and saturating fluid effects. Second, porosity, connate-water saturation, and hydrocarbon density are calculated from the discrepancy between corrected neutron and density logs using SNUPAR and Archie’s water saturation equation, thereby eliminating the assumption of freshwater saturation. With matrix effects eliminated from the neutron-density overlay, gas- or light-oil-saturated formations exhibiting the characteristic gas neutron-density crossover become representative of saturating hydrocarbons. This behavior gives a clear qualitative distinction between hydrocarbon-saturated and nonviable depth zones.

In situ subterranean gamma-ray spectroscopy

1977 ◽  
Vol 143 (2) ◽  
pp. 385-389 ◽  
Author(s):  
H.L. Nielson ◽  
N.A. Wogman ◽  
R.L. Brodzinski
Keyword(s):  
Gamma Ray ◽  
Gamma Ray Spectroscopy

Geostatistical Mapping of Cs-137 Contamination Depth in Building Structures by Integrating ISOCS Measurements of Different Spatial Supports

2013 ◽  
Author(s):  
B. Rogiers ◽  
S. Boden ◽  
D. Jacques
Keyword(s):  
Radioactive Waste ◽  
Gamma Ray ◽  
Future Application ◽  
Building Structures ◽  
Gamma Ray Spectroscopy ◽  
Reliable Methods

Reliable methods to determine the contamination depth in nuclear building structures are very much needed for minimizing the radioactive waste volume and the decontamination workload. This paper investigates the geostatistical integration of in situ gamma-ray spectroscopy measurements of different spatial supports. A case study is presented from the BR3 decommissioning project, yielding an estimated reduction of waste volume of ∼35%, and recommendations are made for future application of the proposed methodology.

Inversion-based interpretation of logging-while-drilling gamma-ray spectroscopy measurements

Geophysics ◽  
2016 ◽  
Vol 81 (1) ◽  
pp. D9-D34 ◽  
Author(s):  
Oyinkansola Ajayi ◽  
Carlos Torres-Verdín ◽  
William E. Preeg
Keyword(s):  
Gamma Ray ◽  
Chemical Elements ◽  
Weight Fraction ◽  
Layer By Layer ◽  
Elemental Compositions ◽  
Gamma Ray Spectroscopy ◽  
Measurement Mode ◽  
Logging While Drilling ◽  
Pulsed Neutron ◽  
Interpretation Method

Neutron-induced spectroscopy measurements are commonly used to quantify in situ elemental compositions of rocks from the processing of measured gamma-ray energy spectra. However, geometric effects on the measured spectroscopy logs, such as thin beds, dipping beds, and deviated well trajectories, can cause shoulder-bed averaging that compromises the assessment of the true layer elemental composition. We have developed an inversion-based interpretation method to evaluate layer elemental compositions from spectroscopy measurements acquired with a commercial 14-MeV pulsed-neutron logging-while-drilling spectroscopy tool. The algorithm is based on a new spectroscopy fast-forward simulation technique, and it estimates layer-by-layer elemental relative yields, weight concentrations, and their uncertainties. Calculations are performed with inelastic and capture gamma-ray spectroscopy measurements that arose from high- and low-energy neutron interactions, respectively. This strategy provides two sets of data that independently validate estimated elemental compositions and can ascertain chemical elements present in only one measurement mode. In laminated formations in which layer thicknesses are appreciably below the vertical resolution of the tool, it is impossible to quantify layer properties with inversion methods. We have therefore developed an additional interpretation method based on a spectroscopy mixing law to estimate elemental compositions within individual laminae. The new inversion-based interpretation methods were successfully verified with two challenging synthetic cases and implemented in two field cases with varying lithology and well trajectories. Our results found that the developed methods reduced shoulder-bed averaging effects on the measured spectroscopy logs by as much as a 0.4 yield fraction and a 0.17 weight fraction. Estimated elemental compositions with reduced shoulder-bed averaging effects improved the calculations in subsequent spectroscopy-based petrophysical interpretation.

scholarly journals Gamma-ray and X-ray constraints on non-thermal processes in η Carinae

2020 ◽  
Vol 635 ◽  
pp. A144 ◽  
Author(s):  
R. White ◽  
M. Breuhaus ◽  
R. Konno ◽  
S. Ohm ◽  
B. Reville ◽  
...  
Keyword(s):  
Gamma Ray ◽  
Pion Decay ◽  
Single Population ◽  
Data Set ◽  
X Ray ◽  
Wide Range ◽  
Inverse Compton ◽  
Accelerated Protons ◽  
Important System

The binary system η Carinae is a unique laboratory that facilitates the study of particle acceleration to high energies under a wide range of conditions, including extremely high densities around periastron. To date, no consensus has emerged as to the origin of the gigaelectronvolt γ-ray emission in this important system. With a re-analysis of the full Fermi-LAT data set for η Carinae, we show that the spectrum is consistent with a pion decay origin. A single population leptonic model connecting X-ray to γ-ray emission can be ruled out. We revisit our physical model from 2015, based on two acceleration zones associated with the termination shocks in the winds of both stars. We conclude that inverse Compton emission from in-situ accelerated electrons dominates the hard X-ray emission detected with NuSTAR at all phases away from periastron and that pion-decay from shock accelerated protons is the source of γ-ray emission. Very close to periastron there is a pronounced dip in hard X-ray emission, concomitant with the repeated disappearance of the thermal X-ray emission, which we interpret as due to the suppression of significant electron acceleration in the system. Within our model, the residual emission seen by NuSTAR at this phase can be accounted for with secondary electrons produced in interactions of accelerated protons, which agrees with the variation in pion-decay γ-ray emission. Future observations with H.E.S.S., CTA, and NuSTAR should confirm or refute this scenario.

scholarly journals Rapid in situ assessment of radiocesium wood contamination using field gamma-ray spectroscopy to optimise felling

2020 ◽  
Vol 218 ◽  
pp. 106259
Author(s):  
Adam Varley ◽  
Andrew Tyler ◽  
Maksim Kudzin ◽  
Viachaslau Zabrotski ◽  
Justin Brown ◽  
...  
Keyword(s):  
Gamma Ray ◽  
In Situ Assessment ◽  
Gamma Ray Spectroscopy

Mobile underwater in situ gamma-ray spectroscopy to localize groundwater emanation from pockmarks in the Eckernförde bay, Germany

2018 ◽  
Vol 140 ◽  
pp. 305-313 ◽  
Author(s):  
Dionisis L. Patiris ◽  
Christos Tsabaris ◽  
Mark Schmidt ◽  
Aristomenis P. Karageorgis ◽  
Aristides M. Prospathopoulos ◽  
...  
Keyword(s):  
Gamma Ray ◽  
Gamma Ray Spectroscopy

Neutron-Induced Gamma Ray Spectroscopy for Reservoir Analysis

1983 ◽  
Vol 23 (03) ◽  
pp. 553-564 ◽  
Author(s):  
Peter Westaway ◽  
Russel Hertzog ◽  
Ronald E. Plasek
Keyword(s):  
Gamma Rays ◽  
Gamma Ray ◽  
Gamma Spectroscopy ◽  
Spectral Response ◽  
Weighted Least Squares ◽  
Well Logging ◽  
High Energy ◽  
Detailed Measurement ◽  
Wide Range ◽  
Gamma Ray Spectroscopy

The weighted least-squares (WLS) approach to spectral analysis has enabled more information to be extracted from the downhole recorded induced gamma ray spectra than was previously possible. GST (gamma ray spectroscopy tool), with its optimized inelastic and capture spectral modes, permits analysis of most and often all significant elements present in the formation and provides the possibility of evaluating hydrocarbons, salinity, lithology, porosity, and shaliness. Data have been obtained in a wide range of conditions in open and cased holes with the GST tool both in its present and experimental versions. This paper presents field examples to demonstrate the versatility and potential of the technique, not only as an effective oil-finder independent of water salinity conditions but as a valuable input to a more complete interpretation of well logs. Introduction Nuclear well logging has been long established as a means of evaluating reservoir porosity and hydrocarbons in open hole and behind casing. The count rates of neutrons or gamma rays returning to one or more detectors are measured and related to the formation rock characteristics according to the physics of the neutron inter-actions that have occurred. For example, high-energy neutrons interact with the surrounding formation nuclei and can induce gamma ray emission. Most conventional neutron/gamma spectroscopy techniques for well logging that have been developed to date are based on integral counts in rather broad energy windows. In this paper, we discuss an alternate technique that allows an accurate and detailed formation evaluation. Gamma rays emitted from the formation nuclei are limited to specific and well-defined energies governed by the laws of quantum mechanics. Each element (isotope) has a characteristic spectrum of gamma rays that can be emitted from a given neutron interaction. Therefore, an element may be identified by its gamma my spectral shape or signature whose emission intensity is related to the elemental concentration. The GST tool measures the relative yields of gamma rays resulting from the interactions of neutrons with different elements present in the formation. The measurements are based on a WLS shape analysis of the observed gamma ray spectral distribution. This is a recently introduced approach to induced nuclear logging. Neutron induced gamma rays are analyzed downhole in terms of intensity in each of more than 200 discrete, narrow energy increments. From this detailed measurement of formation spectral response to neutron bombardment, eight constituent elements can be identified and their proportions estimated. These elements, C, 0, C1, H. Si, Ca, Fe. and S, are significant in formation mineralogical and fluid analysis. A considerable amount of new information is thus made available in the form of a continuous or quasicontinuous well log for a more comprehensive evaluation of the formation. Because of its immediate commercial interest, emphasis in a previous publications was placed on the application of the carbon and oxygen measurements in estimating hydrocarbon saturation. This approach has the advantage of being unaffected by the presence of salts (particularly NACl) in the pore fluid, and has had encouraging success in the monitoring of reservoirs where salinities were either unknown, variable, or too low for conventional neutron logging. SPEJ P. 553^

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