High Gamma-ray Research Articles

Gamma Ray and Radon Anomalies in Northern Taiwan as a Possible Preearthquake Indicator around the Plate Boundary

Taiwan is tectonically situated in an oblique collision zone between the Philippine Sea Plate (PSP) and the Eurasian Plate (EP). Continuous observations of gamma rays at the Yangmingshan (YMSG) station and soil radon at the Tapingti (TPT) station were recorded in the volcanic area and around a major fault zone, respectively, in Taiwan for seismic studies. A number of anomalous high gamma ray counts and radon concentrations at certain times were found. It is noted that significant increases of soil radon concentrations were observed and followed by the increase in gamma rays a few days to a few weeks before earthquakes that occurred in northeastern Taiwan. Earthquakes such as these are usually related to the subduction of the PSP beneath the EP to the north along the subduction zone in northern Taiwan (e.g., ML=6.4, April 20, 2015). It is suggested that the preseismic activity may be associated with slow geodynamic processes at the subduction interface, leading to the PSP movement triggering radon enhancements at the TPT station. Furthermore, the further movement of the PSP might be blocked by the EP, with the accumulated elastic stress resulting in the increase of gamma rays due to the increase in porosity and fractures below the YMSG station. The continuous monitoring of the multiple parameters can improve the understanding of the relationship between the observed radon and gamma ray variations and the regional crustal stress/strain in north and northeastern Taiwan.

Geological occurrence and accumulation mechanism of natural gas hydrates in the eastern Qiongdongnan Basin of the South China Sea: Insights from site GMGS5-W9-2018

Seismic and logging while drilling (LWD) data, gas hydrate samples, and hydrate gas geochemical testing results acquired during the GMGS5 expedition in 2018 have been used to explore the geological occurrence and accumulation mechanism of gas hydrates in the eastern Qiongdongnan Basin (QDNB) of the northern South China Sea (SCS). A large gas chimney with diameter of 4 km associated with the Songnan Low Uplift and the Central Channel and characterized by acoustic blanking on the seismic profile was identified at site GMGS5-W9-2018 in the deep water QDNB. Seismic indications for hydrocarbon migration and gas hydrate accumulation including low frequency features, enhanced reflections, pull-ups/downs and the bottom simulating reflector (BSR) were recognized within the chimney area. Gas hydrates were confirmed to be deposited at the depth of 7–158 mbsf based on the coring and sampling results and pilot hole LWD anomalies, which showed a high resistivity, low density, high gamma rays, and elevated acoustic velocity. Leakage type gas hydrates with multiple geomorphology occurrence, including massive, layers, nodules, fracture filling and disseminated, were recovered at the top of the gas chimney, suggesting favorable conditions for the accumulation of gas hydrates in the eastern QDNB. Although methane was the dominant hydrocarbon gas in all hydrate-bound gases, heavier hydrocarbons (C2+) were also prevalent. C2–C5 hydrocarbons made up to ~21% of the hydrocarbon gases, indicating their thermogenic origin and close relationship with deep reservoirs. Due to the presence of the C2+ hydrocarbons, structure I and structure II gas hydrates may coexist at site GMGS5-W9-2018. The base of structure II gas hydrate stability zone (BSIIGHSZ) was ~42–44 m deeper than the base of structure I gas hydrate stability zone (BSIGHSZ). The hydrocarbon migration and hydrate accumulation were closely related to the gas chimney in conjunction with the Songnan Low Uplift and the Central Channel, which transported the deep thermogenic gas to the GHSZ, forming hydrates in the fractured clay-dominated fine-grained sediments. The fractures occurred in the strata were likely driven by pneumatic forces. Overpressure in the sediments derived from gas charging and accumulation through the gas chimney may have caused the fractures in the sediments that dissipated the hydrocarbons into the GHSZ. We propose a model of gas hydrate accumulation that may aid in the future exploration of gas hydrates in the QDNB of the SCS.

Discovery and prediction of high natural gamma sandstones in Chang 73 Submember of Triassic Yanchang Formation in Ordos Basin, China

The large scale development of high natural gamma sandstones has been discovered in the Chang 73 Submember of the Triassic Yanchang Formation in the Ordos Basin, China. High natural gamma sandstones consist of terrigenous detrital rocks with particle sizes ranging from silt to sand. They represent turbidite deposits characterized by high gamma ray values that are more than 180 American Petroleum Institute (API) units on a natural gamma ray log profile. For a long time, very high natural gamma sandstones had been identified as high-quality source rocks, such as oil shales, from conventional well log profiles, such as natural gamma ray well logs. Therefore, predicting the distribution of high natural gamma sandstones was studied. The sedimentary, lithological, and well log characteristics, as well as the genesis of the high radioactivity of high natural gamma sandstones were analyzed in the Chang 73 Submember. Thorium (Th), uranium (U) and other radioactive elements were found, carried by deep hydrothermal activity, and probably resulted in the formation of a relatively high radioactive zone in the cross-section, where high natural gamma sandstones usually develop in large quantities. This caused many turbidite sand bodies, which should have a continuous distribution in the cross-section, to appear to have a discontinuous distribution, when using conventional well log profiles, such as natural gamma ray well logs. From the above mentioned apparent discontinuous distribution of turbidite sand bodies in the cross-section, a continuous distribution can be predicted. It is obvious that the prediction of areas of continuous turbidite sand bodies in the cross-section usually corresponds with areas where high natural gamma sandstones are developed in large quantities. Exploration and development practice demonstrated that the developed method is fast and effective in predicting high natural gamma sandstones in the Chang 73 Submember.

WELL LOGGING AND ELECTROFACIES OF ZUBAIR FORMATION FOR UPPER SANDSTONE MEMBER IN ZUBAIR OIL FIELD, SOUTHERN IRAQ

The Lower Cretaceous Zubair reservoir is a main producing horizon in the Zubair oil Field, southern Iraq. The reservoir consists of a number of isolated vertical major sandstone units. Sedimentary characteristics can be determined using the well log data as one of the most fundamental methods for reservoir characterization in the oil and gas industry. The reading of high gamma-ray response indicates the presence of shale which contains clay minerals, K-feldspar, and organic material that emits natural gamma radiation. The clean sandstones emit less radiation so it has a lower gamma-ray count analysis. Five of electrofacies were identified in the upper sandstone member of Zubair formation in Zubair oil field, in more details H layer divided into three sub-units. Zubair formation delta deposited through sea regression followed by sea progression because shelf facies overlies other delta facies as shown H layer between K and C units both were shale rocks. Porosity and permeability of the upper sandstone member of Zubair Formation were identified in twenty oil-wells. The relationship between the porosity and permeability after correction with data obtained from the core analysis data showed an improvement to the north part of the field precisely in Hammar-Shuaiba domes. On the other hand the grain sizes varied from coarse to medium; medium to fine in Hammar dome while fine to medium fine to very fine with clay influence led to a decrease the porosity and permeability thus reduced oil production.

Quantum reflection above the classical radiation-reaction barrier in the quantum electro-dynamics regime

High brightness gamma rays can be generated by colliding an ultra-intense laser pulse with a high energy electron beam. This collision phenomenon also represents a powerful approach to explore new physics in the exotic strong field Quantum Electro-Dynamics (QED) regime. Here we show that in the cross-collision geometry, there exists a barrier induced by the classical radiation-reaction force that prohibits electrons of arbitrarily high energies to pass. However, such classical barrier vanishes in the QED picture, where electrons can be well reflected (transmitted) in the regimes forbidden by classical theory. This effect can be measured in the up-coming 10–100 PW laser facilities for laser intensities at 2 × 1023 W cm−2 and electron energies of ~102 MeV. The results are capable of identifying the boundaries between classical and QED approaches in the strong field regime and confirming the various models describing this fundamental process.

Mechanism of Degradation Rate on the Irradiated Double-Polysilicon Self-Aligned Bipolar Transistor

The latent enhanced low dose rate sensitivity (ELDRS) effect is observed in the double-polysilicon self-aligned (DPSA) technology PNP bipolar junction transistor (BJT) irradiated with a high and low dose rate gamma ray, which is discussed from the perspective of the three-stage degradation rate of the excess base current. The great degradation rate as a result of the high dose irradiation of the first stage is dominantly ascribed to the positive oxide trap charges accumulated during a short irradiation, and then due to the competition between the recombination of electrons and capture of the hole by the traps. It declined sharply into a degradation rate saturated region of the second stage. However, for the low dose rate, the small increase in the degradation rate in the first stage is caused by the holes escaping from the initial recombination and being transported to the interface to form the interface states. Then, the competition between the steadily increasing interfacial trap charge and the continuously annealed shallow level oxide trap charge leads to the stable increase of degradation under low dose irradiation. Finally, in stage three, the increases of the degradation rates for high and low dose irradiation result from the different amounts of the hydrogen molecules generated by the hole reactive with depassiviated Si suspended bonds, which can interact with the deep level defects and release protons, causing an increase of interfacial trap charges with prolonged irradiation.

Pile-up correction algorithm for high count rate gamma ray spectroscopy

In nuclear applications related to radiation energy measurement, digital pulse processing for fast sampling facility has great advantages compared to the traditional analog pulse processing. A distortion in energy spectrum and degradation in timing resolution take place when pulse pile-up occurs. This in turn leads to degradations of the signals used in applications such as nuclear medicine. Pile-up pulses are commonly removed in most algorithms if they are detected, but in this case, getting a clean spectrum becomes a challenge due to data loss. A proposed pile-up detection and recovery algorithm based on fitting the preamplifier data and signal extrapolation is presented. The extrapolated pulse is used for recovering (extracting) the piled-up pulse to estimate its parameters. A smoothed first derivative algorithm is used for peak tracking inside the detected events. To evaluate the proposed pile-up recovery algorithm theoretically and experimentally, it is applied on both simulated input signals generated with different time displacements between the piled-up events, and experimental preamplifier radiation signals. The obtained results prove that the proposed algorithm achieves better utilization of power and can be used for high count rate (high activity elements) spectroscopy systems.

Comparative effect of high energy electron beam and 137Cs gamma ray on survival, growth and chlorophyll content in curcuma hybrid ‘Laddawan’ and determine proper dose for mutations breeding

Curcuma alismatifolia is an ornamental plant with a beautiful flower in the curcuma genus, which is popular in Thailand and other countries. C. alismatifolia has been improved as the market needs. This research aimed to induce mutations and to study the effects of electron beam and gamma ray on tissue culture of the Curcuma hybrid ‘Laddawan.’ Eight-weeks-old plantlets were irradiated by gamma ray with a Mark I irradiator at the dose rate of 3.74 Gy/min, at the Nuclear Technology Research Center, Kasetsart University. For the electron beam irradiation, samples were exposed to a high-energy electron beam. The lowest power of this machine is 10 MeV and the lowest radiation dose per cycle is 50 Gy (240 Gy/min). The comparison between the effects of gamma ray and electron beam irradiation at doses of 0, 50, 100 and 200 Gy showed that survival percentage, growth percentage, and chlorophyll content were significantly decreased (P<0.05) when radiation dose increased. The survival percentage, growth percentage and chlorophyll content of gamma-irradiated samples were higher than the electron beam-irradiated samples in the same dose. The results indicated the optimum dose range for gamma irradiation of Curcuma hybrid ‘Laddawan’ in tissue culture is 30 – 60 Gy and for electron beams the dose should be less than 50 Gy. New characteristics (variegated leaves and light green leaves) were found in M1V2.

Commissioning the photoinjector of a gamma-ray light source

The Xian gamma-ray light source (XGLS) is a proposed novel high brightness gamma-ray source based on inverse Compton scattering (ICS) between the high brightness electron and laser beams. The photoinjector of the accelerator is one of the main components that determines the electron beam quality and related gamma-ray parameters [Phys. Rev. Accel. Beams 21, 030701 (2018); 20, 080701 (2017); 8, 100702 (2005)]. In order to reduce the risk of this project, a photoinjector including a laser-driven photocathode rf gun, two S-band tubes, and a diagnostic section was constructed and installed from 2016, serving as a pilot plant for the development of the key technologies for the projects. The injector is designed to deliver high quality electron bunches of typically 500 pC charge and $\ensuremath{\sim}120\text{ }\text{ }\mathrm{MeV}$ energy with low emittance and jitter at 10 Hz repetition. Initial system commissioning with an electron beam was finished in the end of 2017, with a goal of a stable 0.6--0.7 mm mrad emittance in a 500-pC bunch clearly demonstrated. In this paper, we report the experimental results and experience obtained in the commissioning, including rf gun, drive laser system, timing and synchronization system, and beam diagnostics.

Improved spectroscopic performance in compound semiconductor detectors for high rate X-ray and gamma-ray imaging applications: A novel depth of interaction correction technique

In this paper results are presented for a novel charge loss correction algorithm that exploits the process of charge induction within compound semiconductor detectors. By detecting the residual induced signals in the pixels neighbouring an event, it is possible to correct for variation in the charge collection efficiency that occurs when high energy photons deposit charge at different depths in the detector. Results from 500μm pitch pixel detectors produced from both GaAs:Cr and high-flux-capable CdZnTe material readout using the STFC’s PIXIE ASIC are used to demonstrate the correction process across two different detector materials. The application of this depth of interaction correction results in a significant improvement in the FWHM of the 59.5 keV γ-ray photopeak in a 0.5 mm thick GaAs:Cr sensor from 14 keV to 4.7 keV. The application of the correction at the higher energy 122 keV γ-ray photopeak in a 2 mm thick CdZnTe detector also demonstrated an improvement from 4.0 keV to 2.7 keV.

Simulation Study on the Feasibility of Current-mode SPECT for B-10 Concentration Estimation in Boron Neutron Capture Therapy

Boron neutron caputure therapy (BNCT) is a promising treatment for invasive tumors. The BNCT utilizes the energy deposition by alpha particle and 7Li created by the neutron capture reaction of 10B. One of the problem of BNCT is the imaging of 10B distribution during the treatment. The gamma rays with the energy of 0.478 MeV emitted by 7Li can be exploited for this purpose. The photon counting of the gamma rays, however, is very difficult due to the high gamma ray background caused by 2.22 MeV gamma rays originated by the neutron reactions with 1H. To overcome this difficulty, the authors propose a method to measure gamma rays as electric current by a “transXend” detector, which had been invented by them for energy-resolved X-ray computed tomography. In this paper, the feasibility study on 10B distribution imaging in a water phantom with a tumor region is shown by simulation studies. For establishing the relationship between electric currents induced in the transXend detector by gamma rays and 10B concentration, the attenuation of gamma rays by the phantom should be taken into account. For this purpose, a neural network was employed. The results showed good agreement with the training data used for the neural network.

Characteristics of latch-up current of dose rate effect by laser simulation

Due to the parasitic PNPN structure, the complementary metal oxide semiconductor (CMOS) integrated circuit may be affected by the latch-up effect, and the latching induced by the transient high dose rate Gamma ray has unique characteristics. In order to explore the complex physical mechanism of the latch-up by transient dose rate effect, in this paper we select the pulsed laser with 1064 nm wavelength as an radiation source to simulate the gamma ray radiation environment, select bulk silicon CMOS deserializer FIN1218MTDX, and use transient dose rate effect laser simulation experiments to explore its latch-up threshold and latch-up current characteristics. The test obtains that the dose rate latch-up threshold optical power density of the device at 3.3 V operating voltage is (8.5 ± 1.2) × 10<sup>4</sup> W/cm<sup>2</sup>, a latch-up voltage of the device is 2.8 V, only the device latches when the supply voltage is greater than 2.8 V. At the same time, it is found that under the working voltages of 3.3 V and 3.6 V and the optical power density between 1.9 × 10<sup>6</sup> W/cm<sup>2</sup> and 1.6 × 10<sup>7</sup> W/cm<sup>2</sup>, the latch-up current significantly decreases, the latch-up current " window phenomenon” appears. Based on the equivalent circuit model, the multi-path latching mechanism is used to construct the HSPICE model. The mechanism of the transient dose rate latching characteristics exposed by the laser test is analyzed by circuit-level simulation. The results show that the latch-up current and the latch-up voltage are related to its own latch structure when the device is latched. The phenomenon of latch-up current window in laser test is due to the multi-path latch mechanism, which will be in the specific circuit structure, and causing the multiple latch-up paths of the device to be switched. The reason of the latch-up path is switched is that the different holding voltages and trigger conditions between the latch-up paths, distributed resistance in the circuit reduces the voltage of latch-up path, so that the holding voltage of the latch-up path cannot be satisfied and the latch-up path is released. At the same time the other latch-up path is latched.

Gas hydrate occurrence and distribution controlled by regional geological structure off eastern India: Estimates from logging-while-drilling in Area-B, National Gas Hydrate Program Expedition 02 (NGHP-02)

Abstract The National Gas Hydrate Program Expedition 02 (NGHP-02) was designed to examine gas hydrate occurrences off the eastern margin of the Indian Peninsula. Twelve holes were logged with logging-while-drilling (LWD) tools and nine holes at five sites were cored in Area-B of NGHP-02. Five logging units were defined based on the characteristics in logging data responses. Distinctive Logging Units R1 and R2 characterized by high gamma ray log values and composed of quartz and biotite-rich medium sized sand grain units that act as gas hydrate resevoirs and correlated to strong seismic reflectors. Hydrate-bearing intervals can be identified by resistivity and sonic velocity logs and classified into pore-filling type, fracture-filling type, and a mixture of pore- and fracture-filling types based on borehole image characteristics. Pore-filling type gas hydrate is typically developed in the case where the depths of R1 and/or R2 is close to the seismic inferred bottom simulating reflector (BSR). Fracture-filling type hydrates associated the R1 section occur above the BSR associated with the anticline in Area-B. The occurrence of pore-filling and fracture-filling gas hydrate represent different processes of hydrate formation related to the regional geological structure. The stratigraphic layered pore-filling gas hydrate occurrences are generated along often dipping sand layers, which are also conduits for methane-bearing fluid migrating from below the BSR in many settings. Fracture-filling type gas hydrate is an alternative mechanism for the occurrence of gas hydrate in mudstone-rich sediments above the BSR and found associated with the anticline in Area-B. This structural constraint of the hydrate-bearing fractures in the Area-B anticline suggest that the fracture dominated reservoirs possibly formed by anticlinal flexure, and the upward flow of methane-bearing fluids along porous sedimentary layers and the subsequent formation of pore-filling gas hydrate occurrences account for the range of gas hydrate accumulations discovered during NGHP-02.

Abnormal open-hole natural gamma ray (GR) log in Baikouquan Formation of Xiazijie Fan-delta, Mahu Depression, Junggar Basin, China

Abstract Based on large amounts of cores, open-hole conventional logs and mineral components analysis, abnormal natural gamma ray (GR) log showing high values in conglomerates and low values in fine-grained sediments, are described and explained in Baikouquan Formation of Xiazijie Fan-delta, Mahu Depression, Junggar Basin. After observing cores, normalizing the GR log and correcting depth errors between both, the GR log values of individual grain-sized lithology are extracted and counted. When grain-size decreases, the average GR values of different sized grains increase generally. The GR values of conglomerates are mostly between 50 and 80 API, while the values of fine-grains are mainly between 70 and 100 API. However, abnormal GR log features exist in the cores and wells of Baikouquan Formation prevalently. A great deal of high radioactive intermediate-acid volcanic minerals, such as volcanic tuff, felsite, andesite, granite, rhyolite, et al., distribute widely in the conglomerates, which results in abnormal high GR values in conglomeratic intervals. Low radioactive quartz components exit widely in high percentage in mudstones, which is the primary mineral explanation for the abnormal low GR values in reddish-brown siltstones and sandstones intervals.

Effects of high dose gamma irradiation on the optical properties of Eu3+ doped zinc sodium bismuth borate glasses for red LEDs

Interaction of 10ZnO-5Na2O-10Bi2O3–74.3B2O3-0.7Eu2O3 glasses exposed to high dose gamma rays were investigated using XRD, FTIR, absorption, photoluminescence followed by thermally and optically stimulated luminescence studies. XRD analysis confirmed the amorphous nature of glasses post-irradiation. Variation in FTIR spectra revealed, structural deformation of borate groups as a result of high dose gamma irradiation. Enhanced glass absorbance and red shift in absorption edge were observed with the increase in gamma dose. Further, radiation-induced absorption coefficient confirmed the trapped charges in the forbidden energy gap supported by Tauc's plot and Urbach energy. Photoluminescence (PL) study demonstrated quenching of luminescence intensity at higher gamma doses. Lifetime of metastable 5D0 state of Eu3+ ions were estimated by the decay curves and color purity was calculated using 1931 CIE chromaticity coordinates (x,y). Thermally and optically stimulated luminescence studies reassured the existence of charges in trap centers due to irradiation. TL glow curve exhibited two broad emission peaks with the corresponding temperature being at 490 K and 625 K. Distinct TL peaks of the material and their kinetic parameters (E, S, τ and b) were determined via Computerized Glow Curve Deconvolution (CGCD) method. Linear behaviour obtained through the dose response of the glass (0.25–3 kGy) proved their suitability for dosimetric application in the food irradiation zones in addition to red LEDs (< 1 kGy).

Geophysical strata rating (GSR) as an aid in carbonate reservoir characterisation: an example from the South Pars gas field, Persian Gulf Basin

In this study, the geophysical strata rating (GSR) is calculated from petrophysical data using the equations developed for clastic rocks. The region being investigated is the South Pars gas field in the Persian Gulf Basin, where the Permian–Triassic Dalan and Kangan reservoirs host the largest accumulations of gas in the world. A 3D GSR model is estimated from 3D poststack seismic data by using a probabilistic neural network model. In this study, two methodologies are used to obtain GSR values at the different scales of wireline logs and 3D seismic data.Strong correlations between neural network predictions and actual GSR data at a blind well prove the validity of the intelligent model for estimating GSR. The GSR results are also in good agreement with porosity and elastic moduli of these carbonate rocks. Discrimination between the reservoir and non-reservoir shaly units can easily be obtained by comparing GSR and well logs. Very low GSR values with high gamma ray log responses indicate shaly intervals. These can cause washouts, casing collapse and other related drilling problems. Intervals with low GSR values and low gamma ray log responses indicate the presence of good reservoir units.

Organic matter network in post-mature Marcellus Shale: Effects on petrophysical properties

Shale samples of the Marcellus Shale from a well drilled in northeastern Pennsylvania were used to study diagenetic effects on the mineral and organic matter and their impact on petrophysical response. We analyzed an interval of high gamma ray and anomalously low electrical resistivity from a high thermal maturity (mean maximum vitrinite reflectance > 4%) part of the shalehgas play. A suite of microanalytical techniques was used to study features of the shale down to the nanoscale and assess the level of thermal alteration of the mineral and organic phases. The samples are organic rich, with total organic carbon contents of 3–7 wt. %; the vast majority of the organic matter was identified as highly porous pyrobitumen. Matrix porosity is also present, especially within the clay aggregates and at the interface between rigid clasts and clay minerals. Mineral- and organic-based thermal maturity indices suggest that during burial the sediment had been exposed to temperatures as high as 285°C (545°F). Under these conditions, the residual, migrated organic matter assumed a partially crystalline habit as confirmed by the identification of turbostratic structures via electron microscopy imaging. Experimental dielectric measurements on organic matter–rich samples confirm that the anomalous electrical properties observed in the wire-line logs can be ascribed to the presence of an electrically conductive interconnected network of partially graphitized organic matter. The preservation of porosity suggests that this organic network can contribute not only to the electrical properties but also to the gas flow properties within the Marcellus Shale.

Assessment of natural radioactivity levels in the Ajali Formation, Enugu, South Eastern Nigeria

Activity concentrations of the radionuclides (238U, 232Th and 40K) were analysed using high resolution co-axial HPGe gamma ray spectrometer system to know the implication where groundwater is sourced from Enugu, South-East Nigeria. The activity concentration of 238U ranges from 37 ± 4 to 74 ± 6 Bq kg−1 with the highest value of 74 ± 6 Bq kg−1 noted in the thin coal sample. The 232Th activity level in the rock samples ranges from 58 ±5 to 85 ± 7 Bq kg−1 with the higher value of 89 ± 7 Bq kg−1 reported in the coal sample. For 40K, the activity concentration varies from 140 ± 19 to 293 ± 25 Bq kg−1 with the highest value of 293 ± 25 Bq kg−1 reported in coal samples whereas lowest value of 140 ± 19 Bq kg−1 was noted in Ajali sandstone in the study area (Enugu State). The higher activity levels of 238U, 232Th and 40K reported in coal samples may be due to the closer clusters of weathered surface of Ajali sandstone that overlays the thin coal layer with an escarpment being spread out, implying higher permeability towards deeper direction. All the values are within the recommended level when compared with United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR, 2000). Further research on groundwater activity concentration and rock geochemistry is required within the study area. This will allow for a comprehensive conclusion to be drawn on the level of exposures to the inhabitants relying on groundwater for consumption.

Field gamma-ray patterns and stratigraphic reinterpretation of offshore well-log data from Lower Jurassic organic-rich units of the Lusitanian Basin (Portugal)

Abstract Lower Jurassic (Sinemurian–Pliensbachian) successions cropping out in onshore areas of the Lusitanian Basin provide detailed information of three well characterized organic-rich intervals: i) the Unit F from the Coimbra Formation, ii) the Polvoeira Member of the Agua de Madeiros Formation, and the iii) Marly Limestones with Organic-rich Facies (MLOF) Member of the Vale das Fontes Formation. Despite decades of research, these source rocks have not yet been properly identified and characterized in terms of extension and thickness in the basin's offshore. This paper compares detailed gamma-ray (GR) profiles from onshore outcrops (Coimbra, Montemor-o-Velho, Figueira da Foz, Monte Real, Sao Pedro de Moel and Peniche regions) with seven offshore wells. Our objective is to recognise Lower Jurassic organic-rich intervals in offshore areas of the basin, highlighting their lateral extension and improving the overall stratigraphic definition of the Lower Jurassic in the Lusitanian Basin. GR field measurements indicate that the highest GR values and U contents are consistently observed in the organic-rich intervals, reaching up to 134 API and 9.0 ppm of U. In contrast, the lowest API and U contents were determined in dominantly calcareous units, ranging between 5-34 API and 0.1-1.4 ppm, respectively. Wireline gamma-ray logs show a good correspondence between field patterns and offshore well logs, recognizing the organic-rich intervals in offshore areas. The highest GR values are interpreted to be linked with the 2nd- and 3rd-order maximum flooding intervals previously recognised in the Sinemurian–Pliensbachian successions in the western Iberian margin. Detailed GR maps linked to maximum flooding intervals highlight the variation of the vertical and lateral distributions of the organic-rich units in offshore areas of the Lusitanian Basin.

Formation evaluation of a clastic gas reservoir: presentation of a solution to a fundamentally difficult problem

Formation evaluation of clastic reservoirs has always had some difficulties. This issue for a clastic gas reservoir from North-East Iran has already made some problems for petrophysicists. Therefore, this paper presents a basic and consequential strategy for (1) solving the problem regarding the petrophysical evaluation, (2) evaluating the petrophysical parameters as precisely as possible, and (3) presenting a general framework for formation evaluation of clastic reservoirs with complex mineralogy. The applied strategy had three main steps. At the first step, using some conventional methods like petrographical analysis and some petrophysical cross plots, all the minerals in the rock structure were identified as precisely as possible. At the second step, having sufficient logs for a key well, all the identified minerals were modeled to distinguish the main minerals. At the final step, all the main minerals were then used for modeling of the other wells. The evaluation of the formation was basically improved using the applied procedure. Alongside the clay minerals, the results showed an important contribution of other high gamma ray minerals in the mineralogy, such as the mica and feldspars. The results also showed important effects of the precise mineralogy on some petrophysical parameters, such as the porosity, grain density, and water saturation.