Gamma-ray Response Research Articles

Outcrop spectral gamma-ray signals of distal arid continental basins: Facies identification and controls

Spectral gamma ray (SGR) studies can help link outcrop exposures to downhole data and provide useful case studies to reduce uncertainty in interpreting geophysical logs where core and other geological data is unavailable. However, this technique is underused in continental outcrop studies due to difficulties in determining facies comprising similarly sourced sediment, despite the fact that these deposits form prolific reservoirs for hydrocarbon and geothermal exploration, as well as carbon capture and hydrogen and storage. This work demonstrates the usefulness of spectral gamma ray measurements as an outcrop logging technique in determining quantifiable facies from the dryland continental sediments of the Cedar Mesa Sandstone Formation, Utah, USA. Complex sedimentary interactions between the aeolian, fluvial and lacustrine depositional environments are present, resulting in shared similar sedimentary characteristics within the preserved strata, such as mineralogy, grain size, sorting and provenance signals. Consequently, the geophysical signatures observed within the spectral gamma ray logs, have been suppressed, making it difficult to distinguish sedimentary facies from solely the spectral gamma ray responses. However, by combining K:Th cross-plot analysis and gamma ray log motif interpretation, this work demonstrates that individual facies within arid continental settings can be distinguished based on SGR outcrop logging, and unique spectral trends and values can be quantified and used to correlate facies across the depositional basin.

Stratigraphic architecture of the Belly River Group (Campanian, Cretaceous) in the plains of southern Alberta: Revisions and updates to an existing model and implications for correlating dinosaur-rich strata.

The Upper Cretaceous (Campanian) Belly River Group (BRG) of southern Alberta has a complex internal stratigraphic architecture derived from differential geometries of its component formations that resulted from regionalized tectonic influences and shifting source areas. A full understanding of BRG architecture has been compromised heretofore by a limited understanding of subsurface data in southwestern- and southeastern-most Alberta. In this study outcrop exposures throughout southern Alberta are tied to reference well logs and subsurface cross-sections allowing a more precise understanding of BRG architecture and how it relates to well-known vertebrate fossil producing areas. Modifications to an existing stratigraphic model of the BRG show that the Oldman and the Dinosaur Park formations have reciprocal north-to-south wedge-shaped geometries and a diachronous contact that become prominently expressed south of Twp 12. The updated model also demonstrates that the Oldman Formation thickens stratigraphically up-section to the south, and that the Foremost-Oldman contact is, essentially, a datum across much of southern Alberta. Identification of the Oldman Formation in the subsurface remains based on its relatively high gamma-ray response in mudstone successions, but it is also recognized that many of its sandstones exhibit relatively low gamma-ray responses like those in underlying and overlying formations. Nomenclature and subdivisions of the Oldman Formation are revised to accommodate this updated understanding, and modifications are also made to the definition of the Judith River-Belly River discontinuity, a newly recognized surface that marks the onset of accommodation and eustatic rise in sea-level in the northern Western Interior Basin at ~76.3 Ma.

Petrophysical properties identification and estimation of the Wufeng-Longmaxi shale gas reservoirs: a case study from South-West China

AbstractPetrophysical properties are critical for shale gas reservoir characterization and simulation. The Wufeng-Longmaxi shale, in the south-eastern margin of the Sichuan Basin, is identified as a complex reservoir due to its variability in lithification and geological mechanisms. Thus, determining its characteristics is challenging. Based on wireline logs and pressure data analysis, a shale reservoir was identified, and petrophysical properties were described to obtain parameters to build a reservoir simulation model. The properties include shale volume, sand porosity, net reservoir thickness, total and effective porosities, and water saturation. Total and effective porosities were calculated using density method. Shale volume was estimated by applying the Clavier equation to gamma-ray responses. Sand porosity and net reservoir thickness were evaluated using the Thomas–Stieber model, and the Simandoux equation was used to compute water saturation. The results indicate that the reservoir is characterized by a relatively low porosity and high shale content, with shale unequally distributed in its laminated form (approximately 75%), dispersed (about 20%), and structural form (5%). This research workflow can efficiently evaluate shale reservoir parameters and provide a reliable approach for future reservoir development and fracture identification.

Cascade perovskite single crystal for gamma-ray spectroscopy

The halide lead perovskite single crystals (HLPSCs) have great potential in gamma-ray detection with high attenuation coefficient, strong defects tolerance, and large mobility-lifetime product. However, mobile halide ions would migrate under high external bias, which would both weaken the gamma-ray response and cause additional noise. Here, we report the gamma-ray PIN photodiodes made of cascade HLPSCs including both ion-formed and electron-hole-formed electrical junctions that could suppress the ions migration and improve the charges collection. Our photodiodes based on cascade HLPSCs (MAPbBr3/MAPbBr2.5Cl0.5/MAPbCl3) show a wide halide-ion-formed depletion layer of ∼52μm. The built-in potential along the wide ionic-formed junction ensures a high mobility-lifetime product of 1.1×10-2 cm2V-1. As a result, our gamma-ray PIN photodiodes exhibit compelling response to 241Am, 137Cs, and 60Co; the energy resolution can reach 9.4%@59.5keV and 5.9%@662keV, respectively. This work provides a new path toward constructing high-performance gamma-ray detectors based on HLPSCs.

Response function and photon interaction of LaBr3:Ce and BGO scintillation detectors by Monte Carlo simulation

This work aims to investigate the response function and photon interaction of the LaBr3:Ce and BGO scintillation detectors using the FLUKA Monte Carlo simulation software. To improve the realism of detectors, the DETGEB card was used to activate the gaussian energy broadening (GEB) function. The GEB parameters of both detectors were obtained by fitting a nonlinear curve to the relation between FWHM and gamma-ray energy. The energy resolution (R), peak-to-Compton ratio (PCR), peak-to-total ratio (PTR), and full-energy peak efficiency (FEPE) of both detectors were investigated by simulation and experiment at different gamma-ray energy obtained from 133Ba, 137Cs, and 60Co sources. The simulated spectra of those radioisotopes were found to agree with the actual spectra. The results found that the R, PCR, and FEPE values of the LaBr3:Ce and BGO detectors tend to decrease as energy increases. Moreover, the total atomic cross-section (σt,a), effective atomic number (Zeff) and effective electron density (Neff) of both crystals was investigated by FLUKA and compared with the XCOM theoretical program covering an energy range of 15 keV to 15 MeV. The simulated results of the σt,a, Zeff, and Neff are in excellent agreement with the theoretical ones. The GEB parameters obtained from this study will improve the simulation performance of LaBr3:Ce and BGO detectors in investigating the gamma-ray response and shielding properties of materials.

Emplacement dynamics of a complex thick mafic intrusion revealed by borehole image log facies analyses: Implications for fluid migration in the Parnaíba Basin petroleum system, Brazil

Sill intrusions may play a significant role in the development of petroleum systems in sedimentary basins by promoting maturation of source rocks, influencing fluid migration and acting as reservoirs, traps, and seals for hydrocarbon accumulations. Within this study, we present a novel approach to interpreting geophysical borehole data for a ca. 174 m thick sill from the Parnaíba Basin revealing new insights into both the emplacement mechanisms and impacts of the sill on hydrocarbon migration and trapping. High-resolution ultrasonic and microresistivity borehole image logs were integrated with conventional log data, petrography of eight side wall cores and total gas data recorded during drilling. The petrographic analysis revealed finer crystalline dolerite at the top and bottom layers of the sill while the upper central portion revealed coarser crystalline gabbroic facies, associated with anomalies in gamma ray, neutron porosity, sonic and geochemical log responses. From borehole image logs we interpreted key facies units including massive, fractured, cooling jointed and layered dolerite along with clear evidence for layers containing diverse inclusions interpreted as enclave structures. The integration and correlation of these data with analogue studies allowed the interpretation of gradational cooling with magmatic differentiation, partially melted host rock linked to sulphide production and organic matter maturation, mafic microgranular enclaves related to mingling processes of magma recharge, banding layers related to cumulate zones, and intense cooling fractures in the central sill body. An interval of ca. 44 m at the top of the sill with notably less jointing appears to be responsible for sealing the gas underneath, whilst the fractured central portion of the sill has enabled gas migration evidenced by increased gas signatures. In addition, this work also reveals for the first-time image log evidence for magma mingling and indications of assimilation and anatexis processes within the Parnaíba Basin. This study has important implications for improving the understanding of emplacement mechanisms of thick parallel layer intrusions and their implications for fluid flow in sedimentary basins worldwide.

Large scale BN-perovskite Nanocomposite Aerogel Scintillator for Thermal Neutron Detection.

State-of-the-art thermal neutron scintillation detectors rely on rare isotopes for neutron capture, lack stability and scalability of solid-state scintillation devices, and poorly discriminate between the neutron and gamma rays. Our boron nitride (BN) - CsPbBr3 perovskite nanocomposite aerogel scintillator enables discriminative detection of thermal neutrons, features the largest known size (9cm across), the lowest density (0.17g/cm3 ) among the existing scintillation materials, high BN (50%) perovskite (1%) contents, high optical transparency (85%), and excellent radiation stability. The new detection mechanism relies on thermal neutron capture by 10 B and effective energy transfer from the charged particles to visible-range scintillation photons between the densely packed BN and CsPbBr3 nanocrystals. Low density minimizes the gamma ray response. The neutrons and gamma rays are discriminated by complete decoupling of the respective single pulses in time and intensity. These outcomes open new avenues for neutron detection in resource exploration, clean energy, environmental, aerospace, and homeland security applications. This article is protected by copyright. All rights reserved.

Environmental controls on the microfacies distribution and spectral gamma ray response of the uppermost Jurassic–Lowermost cretaceous succession (Pimienta–Lower Tamaulipas Formations) in central-eastern Mexico

Organic-rich sediments of the Pimienta Formation were deposited in the Tampico-Misantla Basin during the Late Jurassic–Earliest Cretaceous. A sedimentological, spectrometric, microfacies and geochemical analysis was performed on a stratigraphic section recording the Pimienta–Lower Tamaulipas formational transition, to gain an understanding of the depositional conditions, and to decipher the main factors that control the gamma ray signal. This latter was achieved by comparison with other records. The studied succession spans from the upper part of the lower Berriasian Calpionella Zone to the lower part of the lower Valanginian Calpionellites Zone. Moreover, the microfacies data indicate it was accumulated in an outer ramp to basinal setting influenced by high energy events and the input of grains transported from shallower areas. Oxygen levels increased during the lastest Berriasian–early Valanginian. The organic matter preserved in these sediments has a mixed marine-terrestrial origin and is immature to early mature. Several records across the basin show that from the lower part of the Pimienta Formation to the lower part of the Tamaulipas Formation sediments change from radiolarian-rich microfacies with the highest Total Organic Carbon (TOC) content and Standard Gamma Ray (SGR) values to calpionellid-rich microfacies with the lowest TOC and SGR values. This shift is interpreted as controlled by the evolution of environmental conditions from eutrophic/oxygen-depleted to oligotrophic-partially oxygenated, which caused a progressive decrease in the organic matter burial and enrichment of authigenic U.

Identification of Hydrocarbon Zones and Chimneys Using Seismic Attributes Analysis at Woda Oil Field, Western Offshore Niger Delta

This research investigated hydrocarbon zones and chimneys using seismic attributes analysis in Woda Oil Field, Western offshore Niger Delta. Seismic attributes are powerful tools in monitoring and predicting hydrocarbon zones. Detailed application of seismic attributes on the Woda seismic data aided in the extraction of important information about the geologic features on seismic profiles. Materials used in this research include well logs, seismic data and 3D Post Stack Depth Migration (PSDM) seismic volume. Methods used were seismic attribute analysis and well log interpretation. The reservoirs of interest were identified and analyzed using well log data based on gamma ray, resistivity, and Vp sonic log response. Seismic attributes such as chaos, root mean square velocity, similarity and reflection intensity were quality controlled, enhanced, and generated which assisted in identifying chimneys and hydrocarbon zones. The majority of the chimneys in this research may have nucleated in the lower part of the faulting system below the partially permeable portion of the fault planes and across a regional partially permeable barrier as revealed by thin fault likelihood attribute. Gas expulsion along the lower portion of the complex faulting system perhaps, may have preconfigured the spatial organization of the chimneys. Pockmarks formation above the chimneys as revealed by the sweetness attribute may have inherited the same linear planiform geometry, and both structures recorded the timing of hydrocarbon zones and gas expulsion within the Woda Oil Field.

Method for calculating delayed gamma-ray response in the ACRR Central Cavity using MCNP

This document presents the process for a new method developed for the characterization of the delayed gamma-ray radiation fields in pulse reactors like the Annular Core Research Reactor (ACRR). The environments used to test this method in the ACRR Central Cavity were various standard irradiation configurations that used various amounts of moderators and shielding. All environment configurations used the same fission product gamma-ray source energy spectrum. This method required the use of fission sites recorded in the Monte Carlo N-Particle (MCNP) KCODE source tape. A FORTRAN script was written to translate and extract the coordinates for the fission sites. The fission sites were then input into an MCNP source mode input file. Using a MATLAB script, a parametric analysis was performed and determined that 10K fission sites are an appropriate number of coordinates to converge to the correct answer. The method gave excellent results as compared to previous methods. This method can be applied to other pulse research reactors as well.

Identifying and quantifying Mg-clays in well logs using new petrophysical methods: A case study from the Brazilian pre-salt

The Santos Basin, located in offshore southeast Brazil, is the site of several giant oilfields of the Pre-salt interval. The limestones from the Barra Velha Formation (Aptian in age) are complex, highly heterogeneous, and usually are associated with Mg-clays, being interpreted as deposited in an unusual alkaline lacustrine rift system that developed during the opening of the South Atlantic Ocean (Lower Cretaceous). The reservoirs of the Barra Velha Formation show exceptional reservoir quality and are sealed by marine evaporites of the Ariri Formation. Although clays traditionally present a negative impact on reservoir quality, Mg-clays (such as Mg-smectite, kerolite and talc) are prone to dissolution during diagenesis, which can increase the reservoir quality. However, in areas of the reservoir where Mg-clays are still present, they can significantly reduce it. The distribution of Mg-clays at the field, inter-field and basin scale has important implications for exploration and production. As these Mg-clays usually lack radioactive elements and therefore present a low gamma ray response, the usual petrophysical interpretation of clay-rich zones differs from the conventional method. This work proposes an algorithm to identify zones in a well with (1) presence of “pure Mg-clays” (i.e. not mixed with non-Mg-clays); (2) presence of “dirty Mg-clays” (i.e. mixed with non-Mg-clays or organic matter); and (3) absence of Mg-clays and another to quantify the Mg-clay volume in the wells. The study was carried out using well logs from 27 wells along with sidewall core samples. The occurrence of Mg-clays in the wells was confirmed by thin section description, supported by SEM- EDS and XRD analyses and allowed the understanding of the distribution of Mg-clays in the Sapinhoá Field, which are more abundant in structural lows due to better preservation whereas in higher structural positions clays were more affected by diagenetic alterations. The new algorithms proved to be reliable methods to perform both qualitative and quantitative detection of Mg-clay-rich zones using well logs and allowed the better identification of well-sections where this type of clay is present, providing a good-quality input for facies distribution. This study contributes to add new methodologies, which can be used in the improvement of petrophysical interpretations in zones with the presence of such complex clays and thus reducing the exploratory and development risks.

Reservoir lithofacies study of the Toolebuc Formation, Eromanga Basin, Australia as a potential unconventional target

Open file data and new laboratory data were integrated with different lithofacies from gamma-ray (GR) response and core to interpret reservoir properties that would lead to a hydrocarbon potential targeting model for the Toolebuc Formation (Fm). The Toolebuc Fm is divided into an upward deepening cycle (UDC) followed by an upward shallowing cycle (USC), in which silica-rich argillaceous mudstone (Facies 1), mixed argillaceous mudstone (Facies 2) and interbedded calcareous mudstone and shelly thin beds/horizons (Facies 3) occur. Facies 1 is enriched in clay and silica component with relatively low Total Organic Carbon (TOC). Facies 2 has a mixed mineralogical composition with high TOC. Facies 3 is enriched in carbonates (coccoliths and shelly debris). The TOC value is high and shows large variation. The organic matter (OM) in the Toolebuc Fm corresponds to Type II kerogen and exhibits variability in maturity indicators but has arguably entered the early oil window. The dominant pore types of the Toolebuc Fm are intraparticle mineral pores and interparticle mineral pores while OM pores are rare. Samples collected from the basin centre show evidence of hydrocarbon generation.Vertically, the three lithofacies show a cyclic stacking pattern that corresponds to deepening and shallowing in a marine environment. Facies 1 is the transitional interval between the Toolebuc Fm and its adjacent units, the Wallumbilla Fm below and the Allaru Fm above. Facies 2 dominates the upward deepening cycle while Facies 3 dominates the upward shallowing cycle. The stacking of lithofacies corresponds to an upward increase and a following decrease in GR response, TOC, Brittleness Index (BI), and an upward decrease and a following increase in clay content.Facies 3 in the Toolebuc Fm shows the greatest unconventional potential due to the coincidence of the high TOC and BI. Facies 2 shows moderate potential with the high TOC and moderate BI, while Facies 1 is less favourable with the lower TOC and low BI. The target zone is located at the basin centre due to the higher thermal maturity relative to the marginal areas.

Coal seam gas reservoir characterisation based on high-resolution image logs from vertical and horizontal wells: A case study

Drilling horizontal surface-to-inseam (SIS) wells along low permeability coal seams, e.g. <10 mD, is a crucial technology to increase the drainage area for this type of unconventional reservoir. For the first time in the Bowen Basin, a continuous 1900 m long formation resistivity-based high-resolution image log from a SIS well is used to investigate key coal reservoir characteristics including faults, fractures, coal plies, porosity and permeability. This study presents a workflow from image log interpretation to discrete fracture network (DFN) modelling and then to well performance analysis. The interpreted faults from the image logs were used to analyse the uncertainty of fault interpretation from 3D seismic data. The image log was also used in analysing the variation of fracture distribution vertically and horizontally and compared to similar data obtained from vertical wells. All these data were used to understand the variation in productions from three nearby chevron well groups. Results show that the fracture density decreases with increasing Gamma-ray response from the in-seam section, including the intra-seam partings. Regionally, the orientation of fractures and cleats is parallel, sub-parallel or even perpendicular to the regional maximum stress orientation; however, in the study area, the majority of fractures are generally parallel or near parallel to the maximum stress orientation. This study confirmed the trend that the orientation of fractures/cleats rotated from NE to NW from the study area to the north. Because the maximum stress orientation is NNE, this cleat orientation will yield a decrease in coal permeability from south to north. This can explain at least partially the decrease in well performance from south to north. Based on the modelled fractures and their apertures, the upscaled fracture porosity ranged from 0% to 0.01%, with fracture permeability in the x-direction (easting direction) ranging mainly from 1 mD to 10 mD, and with the ratio of permeability in the x-direction to y-direction (northing direction) ranging from 5 to 20.

Experimental and Simulated Spectral Gamma-Ray Response of a NaI(Tl) Scintillation Detector used in Airborne Gamma-Ray Spectrometry

Abstract. The objective of this work is to simulate the spectral gamma-ray response of NaI(Tl) scintillation detectors for airborne gamma-ray spectrometry (AGRS) using the state-of-the-art multi-purpose Monte Carlo code FLUKA. The study is based on a commercial airborne gamma-ray spectrometry detector system with four individual NaI(Tl) scintillation crystals and a total volume of 16.8 L. To validate the developed model, radiation measurements were conducted using 57Co, 60Co, 88Y, 109Cd, 133Ba, 137Cs and 152Eu calibration point sources with known activities and source-detector geometries under laboratory conditions. In addition, empirical calibration and resolution functions were derived from these measurements combined with additional radiation measurements adopting natural uranium, thorium and potassium volume sources. The simulation results show superior accuracy and precision compared to previous AGRS simulation models with a median relative spectral error &lt; 10 % for most of the radiation sources. Moreover, the implementation of a lower level discriminator model and detailed modelling of the laboratory result in a significant improvement in model accuracy for spectral energies &lt; 100 keV compared to previous studies. Yet thorough statistical analysis incorporating statistical and systematic uncertainty estimates revealed statistically significant deviations between the simulated and measured spectra in the spectral region around the Compton edge, which could be attributed to the scintillator non-proportionality. These findings imply that the linear energy deposition model applied in this and previously developed AGRS simulation models should be revised and considered to be replaced by more accurate non-proportional models.

Enhancing Characterization of Reservoirs Within the Niger Delta Basin Using Integration of Seismic and Well Logs

This research utilized well logs and seismic to unravel the reservoir architecture of a field within the offshore depolbelt of Niger Delta. Gamma ray and resistivity log responses were used for lithology and hydrocarbon reservoirs identifications. The principle of similarity in log signatures was used for correlation across the three studied wells. Pertinent reservoir parameters such as shale volume, effective porosity, permeability, hydrocarbon saturation and water saturation were calculated using well-established equations consistent with the geology. Seismic structural interpretation that will give insight to deformation of the field involves the identification and mapping of faults and horizons from seismic sections. By integrating information from seismic and wells, 3D geological modelling was done using geostatistical methods of Sequential Gaussian Simulation and Indicator. The general stratigraphy of the studied field comprises of intercalation of sands and shales which is typical of Agbada formation. Three reservoirs designated as AA, BB and CC were identified and mapped. Only reservoir CC was laterally continuous across the three wells. Reservoir AA has average shale volume of 13%, effective porosity 26%, hydrocarbon saturation 46% and permeability 1328 mD. Reservoir BB has shale volume of 10%, effective porosity 28%, hydrocarbon saturation 43% and permeability 1616 mD. Reservoir CC has shale volume of 21%, effective porosity 20%, hydrocarbon saturation 89% and permeability 580 mD. Twenty faults comprising of both major and minor faults were mapped. The faults mapped were majorly normal faults. The result of the seismic structural interpretation shows that the probable structures harboring oil and gas are a combination of four-way closure and fault assisted anticlinal structures. The modelling of facies and petrophysical parameters into maps aided the understanding of parameter’s influence on oil and gas production. Reservoir CC has oil and gas in commercial quantities with 2520 MMcf and 622Mbbls respectively. The result shows the reservoir has high performance system and is therefore recommended for development and production. The resulting models will aid placement of production wells and monitoring of future performance of the reservoirs.

Feasibility study of β-ray detection system for small leakage from reactor coolant system

Because existing reactant coolant system (RCS) leakage detection mechanisms are insensitive to small leaks, a real-time, direct detection system with a detection threshold below 0.5 gpm∙hr−1 was studied. A beta-ray detection system using a silicon detector with good energy resolution for beta rays and a low gamma-ray response was proposed. The detection performance in the leakage condition was evaluated through experiments and simulations. The concentration of 16N in the coolant corresponding to a coolant leakage of 0.5 gpm was calculated using the analytic method and ORIGEN-ARP. Based on the concentration of 16N and the measurement of the silicon detector with 90Sr/90Y, the beta-ray count rate was estimated using MCNPX. To evaluate the effect of gamma rays inside the containment building, the signal-to-noise ratio (SNR) was calculated. To evaluate the count rate ratio, the radiation field inside the containment building was simulated using MCNPX, and response evaluation experiments were performed using beta and gamma rays on the silicon detector. The expected beta-ray count rate at 0.5 gpm leakage was 7.26 × 105 counts/sec, and the signal-to-background count rate ratio exceeded 88 for a transport time of 10 s, demonstrating its suitability for operation inside a reactor containment building.

Digital Position and Depth of Interaction Measurement of the PET Detector Through the Signal Ratio

A new detector was designed to improve the spatial resolution of positron emission tomography (PET) and acquire digital coordinates of the detector"s scintillation pixels. In order to solve the spatial resolution deterioration phenomenon due to parallax error occurring outside the field of view (FOV), a method of measuring the depth of interaction was developed, and this was accomplished with the acquisition of digital coordinates. A detector using a 4 × 4 × 2 GAGG scintillator was designed using the DETECT2000 simulation tool to acquire digital coordinates of the scintillation pixels and measure the depth of interaction of the two layers. A gamma-ray reaction was generated in all the scintillation pixels, and the signals were obtained from SiPM pixels in a 4 × 4 array. The 16-channels of optical sensor signals were reduced to signals of 4 channels, and these were calculated as a ratio of each signal. The ratio of the signal was obtained from all the flash pixels, and the position was obtained as digital coordinates by comparing it with the ratio of the signal by the gamma ray response generated at the new position. In order to evaluate the accuracy of acquiring the digital coordinates and the accuracy of the layer where the scintillation pixel in which the scintillator and the gamma ray reacted, a signal was obtained by generating a gamma ray response for the entire length of each scintillation pixel. Gamma-ray reactions were generated at intervals of 0.2 mm from 0.1 mm to 19.9 mm. The obtained signals through these reactions were compared with the signals of each scintillation pixel obtained in advance. Then, the accuracy of measured positions on the X, Y, and Z axes were evaluated. The accuracy of both the X and Y axis showed perfect results, and the accuracy of the Z axis was 91.46 %.

Evaluation of the thermal neutron sensitivity, output linearity, and gamma-ray response of optical fiber-based neutron detectors using Li-glass scintillator

An optical fiber-based neutron detector can be used as a real-time neutron monitor for an intense neutron field. In this study, optical fiber-based neutron detectors were fabricated using Li-glass scintillator. The thermal neutron sensitivity, upper limit of the output linearity, and response to gamma rays from 60Co and Cd were evaluated. The thermal neutron sensitivity was proportional to the mass of the Li-glass scintillator, and the calibration factor was 2.06 × 10−6 and 3.18 × 10−6 cps/(n/cm 2/s)/μg for the lower-level discrimination of the peak and valley channel, respectively. The detector output linearity was confirmed to be up to nearly 2 Mcps. While evaluating the response to gamma rays, for both 60Co and Cd, the gamma-ray counting rate was found to be smaller than the uncertainty associated with counting statistics in most expected applications where the neutron counting rate was >1 kcps.

Characterization of reservoirs and depositional study of J-P Field, shallow offshore of Niger Delta Basin, Nigeria

Well log data interpretation was carried out over J-P Field in the Niger Delta, Nigeria. This was done with a view to characterizing the reservoirs based on the estimation of petrophysical parameters and to assessing the environment of deposition in J-P Field. Seven reservoirs were mapped and correlated across the four drilled wells in J-P Field. Petrophysical parameters such as porosity, volume of shale, water saturation and hydrocarbon saturation were estimated. In addition, depositional environments of each reservoir in J-P Field were determined based on the gamma ray responses. This study reveals that the range of petrophysical parameters across the delineated reservoirs; for porosity varies from 19 to 21%, thickness varies from 24 to 122 m, volume of shale varies from 15 to 29%, water saturation varies from 22 to 60% and hydrocarbon saturation varies from 40 to 78%. The depositional environment was interpreted as comprised of prograding deltas, transgressive marine sands, fluvial channels and deltaic settings. It is concluded that J-P Field has a porosity range varying from good to very good in quality and high hydrocarbon saturation of oil. Furthermore, the study revealed that J-P Field falls within the marginal marine depositional environment.

Analysis of situ elemental concentration log data for lithology and mineralogy exploration— A case study

Metamorphic rocks are diverse with more compositions, structures, and textures that are complex. Rock type identification and prediction from metamorphic rocks using well log data are difficult tasks. This study shows the use of cross plot technique, Pearson correlation, and factor analysis in metamorphic rocks interpretation using borehole geochemical data from the 4390–5089 m interval depth of the Chinese Continental Scientific Drilling Main hole. Lithological identification abilities, correlation between geochemical and geophysical logs, and build a factor model which link in situ chemical element to minerals were studied. The results show that Potassium and Thorium logs are the most discriminating logs in metamorphic rocks. Pearson correlation shows that Potassium and Thorium are the largest contributors to the gamma ray responses. Factor analysis results show a 2 factor model-where factor 1 (amphibole mineral) and factor 2 (K-feldspar mineral) described 76.261% of the variation in log responses. These statistical methods can be a very helpful tool in helping the task of geoscientists in the context of research drillings.