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The identification of formations in anisotropic reservoirs using seismic reflection data and logging data may lead to misrepresentations of the actual formations. Lithofacies discrimination intrinsically has ambiguity, and the depositional sequences of the study area comprise shales, fine-grained sands, and silts. So it needs to reduce the uncertainty of the lithofacies discrimination using anisotropic parameters. This study proposes an approach involving seismic anisotropic parameters to discriminate between different lithofacies. We calculate four anisotropic parameters (ε, δ, γ, η) from logging data (V p, V s, and density) and then employ these for lithofacies discrimination. We compared our results to lithofacies discrimination based on traditional parameters such as V p/V s ratio, clay volume, and water saturation. Using field data from Muglad Basin in South Sudan, we show how the suggested parameters could be used to identify eleven zones with distinct lithofacies. According to the anisotropic parameters, the lithofacies discrimination results are similar to other logging data, and it is easier to separate the lithofacies than petrophysical data. Furthermore, we introduce a new parameter, i.e., the difference between the normalized anisotropic δ parameter and clay volume, which can be used as a possible indicator for heavy oil reservoirs. The new parameter matches well with water saturation in the field data application.

This paper describes the impacts of the M5.8(5.1) Gyeongju earthquakes on groundwater levels using data obtained from a unique coastal monitoring well. The monitoring strategy integrates conventional water level monitoring with periodic, continuous measurements of temperature and electrical conductivity (EC) within the water column of the well. Another important component of the monitoring system is a new instrument, the InterfacEGG, which is capable of dynamically tracking the freshwater‐saltwater interface. Although the system was set up to monitor seawater intrusion related to over‐pumping, as well as rainfall and tidal effects, it recorded impacts associated with a large earthquake and aftershocks approximately 241 km away. Seismic energies associated with the M5.8(5.1) Gyeongju earthquakes induced groundwater flows to the monitoring well through fractures and joints in the crystalline basement rocks. Temperature and EC logging data showed that the EC vertical profile declined from an average of approximately 5300 to 4800 μS/cm following the earthquakes. The temperature profile showed a trend toward lower temperatures as the depth increased, a feature not commonly observed in previous studies. Data from the InterfacEGG suggested that the rise in EC was not due to the saltwater intrusion, but from the tendency for brackish water entering the borehole to induce convective mixing at deeper depths as the seismic waves travel through the well‐aquifer system. The increase in groundwater levels was caused by pulse of colder, less brackish water flowing into the well because of the earthquake. This behavior reflects an enhancement in rock permeability by removing precipitates and colloidal particles from clogged fractures, which improve the hydraulic connection with a nearby unit with a higher hydraulic head. This study suggests there is value added with a more aggressive monitoring strategy., Article impact statement: This paper describes the impacts of the M5.8(5.1) earthquakes on groundwater using data obtained from a novel integrated monitoring system. The study illustrates the value added by using continuous well logging rather than single‐depth measurements of water level change. In addition, a new instrument, InterfacEGG, proved to be useful in monitoring the freshwater‐saltwater interface. This new and innovative approach provided convincing evidence of the impact of the main earthquake on the groundwater system. Although our application herein was specifically concerned with changes associated with an earthquake, it demonstrates the potential usefulness of such an integrated system for monitoring the dynamic behavior of coastal aquifers.

Understanding the physical flow mechanisms in aquifer systems is essential in effectively protecting groundwater resources and preserving subsurface environments from a wide range of contaminants. A conceptual model is a simplified representation of a groundwater system and gaining knowledge about the geological features and parameters controlling the flow and transport processes is a crucial first step towards properly constructing a site-scale conceptual model. In this study, we present a multi-step workflow that involves integrated borehole techniques to gain information concerning groundwater flow. Measurements from core-scale to field-scale enable us to better build a subsurface geological structure divided into the unconsolidated layer and the fractured bedrock. In addition, neutron logging and mercury injection capillary pressure techniques allow for the development of vertical porosity distribution in the alluvial layer. For fracture characterization, the fracture geometry is delineated using a series of borehole imaging techniques and single-hole tests to differentiate the individual permeable fractures from other hydraulically inactive fractures. Combining the hydraulic and geometric evaluations, the presence of large-scale connective fracture networks is identified. Our high-resolution three-dimensional (3D) site-scale conceptual model is expected to contribute to improving the reliability and availability of numerical groundwater models.

Naturally occurring radioactive materials in geologic and building materials have been recommended or regulated in most countries. 226Ra, 232Th and 40K are important radionuclides for building materials. Sometimes for radiation dosimetry, the activity of the radionuclides must be determined in short time. However, samples must be stored in measurement containers for 30 days for the determination of 226Ra in traditional gamma-spectrometry. In this study, pair measurement–gamma spectrometry (PM–GS) method was studied to determine rapidly 226Ra in geologic and building materials. The samples were measured two times within 7 days after sealing. The activity concentrations of 226Ra, 232Th and 40K in geologic and building materials could be successfully determined within a week by using the PM–GS method.

We assessed the contributions of Cu smelting and Asian dust influx to metal(loid) pollution over the last century based on metal(loid) concentrations, Pb isotope ratios, and 210Pb dating of sediments from Gunsan Reservoir, South Korea. During the pre-industrial period (1827–1936), heavy metal pollutants were predominantly geogenic. Local smelting activity was dominant between 1936 and 2008. Between 1936 and 1971, Cu and Pb contamination was not significant, with contributions from smelting activities accounting for

A gravity time series slightly longer than a month acquired by using a Burris gravimeter at Daejeon, Korea has been analyzed. After removal of linear drift of the gravimeter, the observed data was found to closely match with the body tide prediction except; (i) small phase differences of each main tidal constituents and (ii) existence of long period component in the observed data. The r.m.s. observed gravity tide variation was 62.4 μGal. The overall g-factor was found as 1.165. The values of g-factor for the four main tidal constituents; M{nt2}, S2, O1, K1, were found as 1.166, 1.172, 1.168, and 1.142 respectively. The r.m.s. value of ocean tidal loading effect on gravity at Daejeon was 0.95 μGal during the time span. Both the rainfall and the atmospheric pressure change have induced gravity variations of amplitude of about 10 to 1 μGal. The long period component, which is clearly found in the observed spectrum, while not existent in the prediction, is possibly caused by the local ground water variation. It is desirable to have a few number of permanent gravity stations operating in Korean peninsula.

The Korean peninsula has three sides facing the sea, and many monitoring wells for seawater intrusion observation installed along these coasts. The electrical conductivity (EC) profiles of these monitoring wells are found to vary greatly depending on the hydrogeological characteristics of the coast. The research area is located in Seocheon, Chungnam, where two wells are about 1.5 km away, one borehole is freshwater and the other boreholes have high electrical conductivity. In the well where the high electrical conductivity is measured, the electrical conductivity increases rapidly at a depth of about 90m. The well is located about 50 meters from the coast, and the change in water level reflects tidal changes well. We conducted a variety of field surveys and laboratory tests to clarify whether seawater intrusion occurred in the freshwater-saltwater boundary at the depth of about 90 m and whether the freshwater-saltwater boundary was affected by tides. Applied methods are electrical resistivity survey, geophysical well logging and geochemistry. The geophysical survey line was located along the coast centered on the well and measured every six hours. As a result of the survey, it was difficult to identify the change of electrical resistivity due to tidal changes in the lower alluvial zone, that is, the rock formation. These result indicates that the permeable fracture zones are rarely distributed in the rock below the survey line, so the change of the formation resistivity of according to the tidal change is very small. Geophysical well logs such as optical televiewer, spectral gamma log, and water quality logs (i.e., temperature, EC, pH, DO, and ORP) were measured, and groundwater samples were collected according to depth and analyzed for T, EC, pH, DO, ORP, and 222Rn. We found it difficult to identify permeability fracture zones in the temperature gradient and optical televiewer logs. The electrical conductivity is generally around 4,000 uS/cm and increase rapidly from about 90m to 48,000 uS/cm. The water quality logs and the analysis of groundwater samples showed pH range of about 7 to 7.5, DO of 7 to 14 mg/L, and OPR of -80 to 180 mV. pH does not change with depth, DO decreases slightly, and ORP decreases rapidly around the fresh-saltwater interface. The analysis of 222Rn shows that, to the median depth of the borehole, it is similar to the intensity of natural gamma rays and decreases rapidly across the lower freshwater-saltwater interface. Finally, we measured the electrical conductivity logs repeatedly at the interval of 30 minutes in the lower borehole where the freshwater-saltwater boundary was formed, and identified that the profiles of electrical conductivity change with tides.

Well cementing operation is one important factors of well completion as it provides structural support of the casing and hydraulic sealing preventing casing corrosion and groundwater contamination. A wide array of approaches have been developed and applied for leakage detection, including pressure monitoring, radioactive tracer survey, and geophysical surveys. In this work, geophysical well logging methods were adapted to the assessment of well construction and integrity. Various wireline tools yielded physical properties in each borehole environment before and after the casing installation. Several of sonic, nuclear, and mechanical methods focused on valid information to evaluate casing integrity specially after curing concrete for 28 days. Using radioactive logs such as gamma-gamma and neutron logs, we particularly tried to characterize the annular space behind casing, and these well integrity evaluations with cement bond logs corroborated the reliability of the results. Additionally, we reexamined the cement-to-casing bonding condition on the effect of perforation damage. Borehole-based analysis could contribute efficiently to in situ condition evaluation of cementing in which uncontrolled releases of fluid or gas occur.

Seismic waves caused by earthquakes can lead to the movement of fresh groundwater and saltwater in coastal aquifers. The groundwater level, temperature, and electrical conductivity in coastal monitoring wells on the volcanic island of Jeju all responded to the 2011 M 9.0 Tohoku-Oki earthquake. As a result of the earthquake, groundwater temperature and electrical conductivity patterns demonstrated freshwater outflow and saltwater inflow through the monitoring wells in multi-layered coastal aquifers. The seismicity also affected the behavior of ocean tides occurring at depth along the multi-layered coastal aquifers. These observations prove that the use of multi-depth systems for monitoring groundwater level, temperature, and electrical conductivity are more effective than single monitoring systems for understanding the exact behavior of multi-layered aquifers as well as efficiently detecting earthquake-induced or anthropogenic impacts on aquifers in coastal, karstic, or volcanic areas.

When finding the “sweet spot” of a shale gas reservoir, it is essential to estimate the brittleness index (BI) and total organic carbon (TOC) of the formation. Particularly, the BI is one of the key factors in determining the crack propagation and crushing efficiency for hydraulic fracturing. There are several methods for estimating the BI of a formation, but most of them are empirical equations that are specific to particular rock types. We estimated the mineralogical BI based on elemental capture spectroscopy (ECS) log and elastic BI based on well log data, and we propose a new method for predicting S-wave velocity (V S ) using mineralogical BI and elastic BI. The TOC is related to the gas content of shale gas reservoirs. Since it is difficult to perform core analysis for all intervals of shale gas reservoirs, we make empirical equations for the Horn River Basin, Canada, as well as TOC log using a linear relation between core-tested TOC and well log data. In addition, two empirical equations have been suggested for V S prediction based on density and gamma ray log used for TOC analysis. By applying the empirical equations proposed from the perspective of BI and TOC to another well log data and then comparing predicted V S log with real V S log, the validity of empirical equations suggested in this paper has been tested.

Studying groundwater inflow and quantifying its flux into aquatic systems remain challenging because of geological and topographical heterogeneities. In this study, we measured the 222Rn activities in the surface water and porewater of a shallow wetland, the Baekseok Reservoir Wetland, to investigate the groundwater flow system and quantify the groundwater inflow rate. Three field campaigns were carried out in April 2018, September 2018, and February 2019 to determine the spatial and temporal variations in the 222Rn activity. The 222Rn activities were significantly higher along the western boundary of the wetland than the eastern boundary, suggesting a significant difference in the groundwater inflow rate, which reflects different hydrological characteristics on the two boundaries of the wetland. The results of hydrogeological investigations (electrical resistivity survey and monitoring of groundwater and surface water levels) and microbiological analyses were consistent with the 222Rn distribution results, supporting our hypothesis that the groundwater inflow qualitatively and quantitatively exhibits a spatial difference. Based on the mass balances of water and 222Rn under a steady-state condition, the groundwater inflow rates were estimated to be 3.2 × 102, 1.7 × 103, and 7.6 × 102 m3 day−1 in April, September, and February, respectively. The highest groundwater inflow rate in September may be due to the relatively high hydraulic gradient resulting from intense rainfall events. The water residence time of the wetland estimated from the 222Rn mass balance results was approximately one month regardless of the seasons. In addition, the groundwater-derived dissolved silica flux accounted for ~60% of the total dissolved silica input flux of the wetland, highlighting the importance of groundwater-derived dissolved silica. Our multidisciplinary approach to identify and quantify groundwater inflow has important implications in determining groundwater sources in aquatic systems and the behaviors of other substances, such as dissolved nutrients.

For efficiently designing neutron induced gamma spectroscopy sonde, Monte Carlo simulation is employed to understand a dominant location of thermal neutron and classify the formation elements from the energy peak of capture gamma spectrum. A pulsed neutron generator emitting 14 MeV neutron particles was used as a source, and flux of thermal neutron was calculated from the twelve detectors arranged at each 10 cm intervals from the source. Design for reducing borehole effects using shielding materials was also applied to numerical sonde model. Moreover, principal elements and quantities of numerical earth models were verified through the energy spectrum analysis of capture gamma detected from a gamma detector. These results can help to enhance the signal-to-noise ratio, and determine an optimal placement of capture gamma detectors of neutron induced gamma spectroscopy sonde.

Understanding the basaltic aquifer system and seawater intrusion on the volcanic island of Jeju, Korea, has received significant attention over the years, and various methodologies have been suggested in the contributions. Nevertheless, it is still difficult to effectively characterize groundwater systems due to the long period of volcanic activity and the lithological variability of basalt. In this study, geophysical well logging in seawater intrusion monitoring boreholes detected a sudden decrease of electrical conductivity within the saltwater zone in the eastern part of Jeju Island. This anomalous condition cannot be explained by the Ghyben-Herzberg model, which has historically been considered as the basic groundwater model of Jeju Island. This paper focuses on fine-scale temporal and spatial variability of groundwater flow using electrical conductivity and temperature logs and borehole temperature monitoring by a thermal line sensor. On the basis of the results, we evaluate an alternative model to replace the traditional conceptual model in the eastern part of Jeju Island. It is revealed that the area consists of heterogeneous aquifer systems, and the behavior of freshwater and saltwater is understood by temperature monitoring over the entire depth of boreholes. Coastal aquifers flow through two or more independent channels with weak vertical connections. In addition, seawater intrusion does not occur continuously in the vertical direction from the bottom depth, but instead occurs through these multilayered aquifers. In particular, the multilayered aquifers that are responsible for flow pathway, as well as the freshwater&ndash, saltwater interface form mainly at lithological boundaries. Our preliminary conceptual model is expected to be improved and revised by various measurements of hydrodynamic parameters such as flowmeter or packer test.

요약: MCNP를 이용한 밀도검층에 대한 수치모델링을 수행하였고, 인공 모형 시추공에 대한 교정곡선과의 비교를 통하여 MCNP 수치모델링의 신뢰성을 검토하였다. 이를 바탕으로 케이싱의 유무와 종류, 공내수의 유무, 존데와 공벽과의 거리 변화 등 국내 물리검층 자료 취득 현장에서 쉽게 접하는 3인치 시추공 환경에 대한 밀도검층 수치모델링을 수행하였다. 수치모델링 결과는 케이싱과 공내수의 영향을 정량적으로 반영하고 있으며 공벽으로부터의 간격 변화에 따른 일정한양상을 보여준다. 본 연구를 통하여 MCNP를 이용한 수치모델링의 적용성을 파악할 수 있었으며 이를 활용하여 효과적인 검층 보정이 가능할 것으로 판단된다.주요어: MCNP, 밀도검층, 수치모델링, 교정곡선, 물리검층Abstract: We performed MCNP modeling for density log, and examined its reliability and validity comparing thecorrection curves from physical borehole model. Based on the constructed numerical model, numerical modelings ofdensity sonde in three-inch borehole were carried out under the various conditions such as the existence and type ofcasing or fluid, and also the stand-off between the sonde and borehole wall. These results of numerical modelingquantitatively reflect effects of casing and fluid in borehole, and moreover, demonstrate constant patterns with intervalchange from borehole wall. From this study, numerical modeling using MCNP shows a good applicability for welllogging, and therefore, can be efficiently used for the calibration of well logging data under the various boreholeconditions. Keywords: MCNP, Density log, Numerical modeling, Correction curve, Well logging

According to the forecast of the International Energy Agency (IEA), CCS has the potential to reduce carbon dioxide emissions and could contribute to 19% of global carbon dioxide mitigation by 2050. Korean government recently announced that Korea has set its voluntary 2020 emissions reduction target to a 30% reduction from its forecast under a ”business as usual” scenario, which is equivalent to 4% less than the 594 million tons of carbon that was emitted in 2005. CCS is included to achieve this target. This paper first explains the CO 2 storage potential both in onshore and offshore areas in Korea. While onshore sedimentary basins seem to have unfavorable physical properties such as porosity and permeability, offshore sedimentary basins exhibit very good physical properties in sand thickness and porosity. In order to implement CCS project at the scale needed to achieve a meaningful reduction of carbon dioxide emissions, the knowledge of the available CO 2 storage capacity obtained by detailed matching of large stationary CO 2 sources with geological storage sites is required. Most CCS programs in Korea, however, are not integrated with capture and storage projects. This paper considers the feasibility of CO 2 capture and storage in Korea and shows several conceptual business models for CCS projects with the recent E&P activities in the continental shelf.

Resistivity logging instruments are designed to measure the electrical resistivity of a formation, and this can be directly interpreted to provide a water-saturation profile. However, resistivity logs are sensitive to borehole and shoulder- bed effects, which often result in misinterpretation of the results. These effects are emphasised more in the presence of tool eccentricity. For precise interpretation of short- and long-normal logging measurements in the presence of tool eccentricity, we simulate and analyse eccentricity effects by combining the use of a Fourier series expansion in a new system of coordinates with a 2D goal-oriented high-order self-adaptive hp finite-element refinement strategy, where h denotes the element size and p the polynomial order of approximation within each element. The algorithm automatically performs local mesh refinement to construct an optimal grid for the problem under consideration. In addition, the proper combination of h and p refinements produces highly accurate simulations even in the presence of high electrical resistivity contrasts. Numerical results demonstrate that our algorithm provides highly accurate and reliable simulation results. Eccentricity effects are more noticeable when the borehole is large or resistive, or when the formation is highly conductive.

A combination of drilling, hydrogeochemical survey, geophysical survey, and the numerical modeling for the flow and transport of groundwater was performed to evaluate seawater intrusion in Baeksu-eup, Yeonggwang-gun, Korea. Twelve wells were drilled for the collection of geologic, hydrogeochemical, hydrologic, and geophysical logging data to characterize seawater intrusion. To evaluate the salinity distribution of a coastal aquifer, drilling, geophysical data such as vertical electrical soundings (VES), well logging, and hydrogeochemical results were used. Hydrogeochemical results were used to understand the origin of salt and the seawater mixing ratio of groundwater. Spatial layer interfaces derived from VES data, various in situ physical properties from geophysical well loggings, the estimated equivalent NaCl concentration, and aquifer test such as slug test and so on were used as useful input parameters for the numerical simulation with density-dependent flow. Our multidisciplinary approach fo...

Korea Institute of Geoscience and Mineral Resources (KIGAM) launched a new project to develop the low-enthalpy geothermal water in the area showing high geothermal anomaly, north of Pohang city, for large-scale space heating from Korea Research Council of Public Science & Technology(KORP) funding. Surface geologic and geophysical surveys including Landsat TM image analysis, gravity, magnetic, magnetotelluric (MT) and controlled-source audio-frequency MT (CSAMT) and self-potential (SP) methods have been conducted and the possible fracture zone was found that would serve as deeply connected geothermal water conduit. By the end of 2003, two test wells of 1 km depth were drilled, various kinds of borehole survey along with additional MT measurements and sample analysis will follow and then the detailed subsurface condition is to be characterized. Next step would be drilling the production well of 2 km depth and all further steps remain to be determined depending upon the results of the test well studies.

Density log is widely applied for a variety of fields such as the petroleum exploration, mineral exploration, and geotechnical survey. The logging condition of density log is normally open holes but there are frequently cased boreholes. The primary calibration curve by slim hole logging manufacturer is normally the calibration curves for the variation of borehole diameter. In this study, we have performed the correction of steel casing effects using numerical and experimental methods. We have performed numerical modeling using the Monte Carlo N-Particle (MCNP) code based on Monte Carlo method, and field experimental method from open and cased hole log. In this study, we used the FDGS (Formation Density Gamma Sonde) for slim borehole with a 100 mCi 137Cs source, three inch borehole and steel casing. The casing effect between numerical and experimental method is well matched.

This article discusses experimental approaches for the development of gamma spectroscopy well logging system. Considering the size of borehole sonde, we customize 2 x 2 inches inorganic scintillators and the system including high voltage, preamplifier, amplifier and multichannel analyzer (MCA). The calibration chart is made by test using standard radioactive sources so that the measured count rates are expressed by energy spectrum. Optimum high-voltage supplies and the measurement parameters of each detector are set up by experimental investigation. Also, the responses of scintillation detectors have been examined by analysis according to the distance between source and detector. Because gamma spectroscopy well logging needs broad spectrum, high sensitivity and resolution, the energy resolution and sensitivity as a function of gamma ray energy are investigated by analyzing the gamma ray activities of the radioactive sources.

Geophysical well logging is frequently applied to the geotechnical investigation of the subsurface for the construction of tunnel and bridges. The advantage of geophysical well logging lies in that the measurements of in situ physical properties of rocks along the borehole are made in a continuous way. The correlation between the rock mass classification and the in situ physical properties may be found. We analyzed the relationship between the physical properties estimated by well logs and the rock mass classification as well as the dynamic elastic constants using the data gathered at a tunnel construction site of gneiss formation in Korea. The full waveform sonic logs acquired at the seven boreholes showed a fairly good correlation between the velocities of S- and P-wave. We could, further, find a good relation between the rock mass classification, Rock Mass Rating (RMR) and Q system, and apparent resistivity out of short normal logs as well as P-wave velocity. Especially, the apparent resistivity from short normal logs showed an excellent correlation both" with RMR and Q to make the application of the short normal logs to the rock mass classification quite acceptable at the site. Although our analyses are based on the data set acquired at a site that consists of only gneiss, the result can be a useful ease in relating the in situ geophysical data with the rock mass classification that is indeed the required quantity in geoteehnical engineering.