Search

To help meet emission standards, hydrogen sulfide (H2S) from geothermal production may be injected back into the subsurface, where basalt offers, in theory, the capacity to mineralize H2S into pyrite. Ensuring the viability of this pollution mitigation technology requires information on how much H2S is mineralized, at what rate and where. To date, monitoring efforts of field‐scale H2S reinjection have mostly occurred via mass balance calculations, typically capturing less than 5% of the injected fluid. While these studies, along with laboratory experiments and geochemical models, conclude effective H2S mineralization, their extrapolation to quantify mineralization and its persistence over time leads to considerable uncertainty. Here, a geophysical methodology, using time‐domain induced polarization (TDIP) logging in two of the injection wells (NN3 and NN4), is developed as a complementary tool to follow the fate of H2S re‐injected at Nesjavellir geothermal site (Iceland). Results show a strong chargeability increase at +40 days, interpreted as precipitation of up to 2 vol.% based on laboratory relationships. A uniform increase is observed along NN4, whereas it is localized below 450 m in NN3. Changes are more pronounced with larger electrode spacing, indicating that pyrite precipitation takes place away from the wells. Furthermore, a chargeability decrease is observed at later monitoring rounds in both wells, suggesting that pyrite is either passivated or re‐dissolved after precipitating. These results highlight that a sequence of overlapping reactive processes (pyrite precipitation, passivation, pore clogging and possibly pyrite re‐dissolution) results from H2S injection and that TDIP monitoring is sensitive to this sequence. Plain Language Summary: High‐temperature geothermal production is responsible for air pollution due to hydrogen sulfide (H2S) present in the magmatic fluid. To help meet emission standards, H2S may be injected back into the subsurface, where basalt offers the capacity to transform H2S into pyrite. Transformation into an immobile mineral prevents further transport into the atmosphere, sea, surface streams, or lakes. However, ensuring the viability of this pollution mitigation technology requires information such as how much H2S is mineralized, at what rate and where, which are highly uncertain due to the heterogeneity and inaccessibility of subsurface processes. Here, a geophysical monitoring methodology is developed and tested during the re‐injection of H2S at Nesjavellir geothermal site in south‐west Iceland. According to laboratory studies, pyrite precipitation is expected to increase the electrical capacitance, "chargeability," of the subsurface. Using the so‐called time‐domain induced‐polarization (TDIP) method embedded in a wireline logging tool, the chargeability of a 2 m‐wide cylinder around the injection wells is measured with high spatial‐resolution before and during H2S injection. A strong chargeability increase at +40 days indicates that up to 2% pyrite is formed. A subsequent decrease at later rounds raises questions on whether pyrite is re‐dissolved or passivated by other secondary minerals. Key Points: H2S reinjection in basalt and mineralization into pyrite was monitored using TDIP logging in two of the injection wellsChargeability increases observed at +40 days (first monitoring round) correspond to 1%–2% pyrite precipitation with great spatial variabilitySubsequent monitoring rounds show a decrease in chargeability, suggesting that pyrite is either passivated or re‐dissolved [ABSTRACT FROM AUTHOR]

This study shows the usefulness of borehole geophysical logging of density in the identification of coal seams, in relation to other lithologies present in a coal deposit located in the south of Brazil. Four drillholes were studied. The geological descriptions of the core samples recovered from these holes were the main information used as a control parameter in comparison with the geophysical logs. A threshold of density (2.0 g/cm3) was established in the gamma-gamma log analysis for identifying the coal seams with economic value. Also due to the economic and operational aspects related to the coal industry, the coal seams must be at least 0.4 meters thick. Once the coal seams were identified by density logs, a verification of the accuracy in the determination of the thicknesses and densities of the coal seams was performed. The coal seam thicknesses and densities determined by borehole logging were close to the observed values in the borehole core samples. As a result of the comparison between the geological and density log data, an average value difference of 0.03 m and -0.01 g/cm3 was reached for thickness and density, respectively. Due to the results and valuable information obtained, it was also possible to indicate and determine which areas of the deposit should be mined in relation to the drillholes studied and threshold parameters established. In conclusion, the importance of this evaluation is emphasized, mainly with respect to the thickness of the coal seams, which aids in the development of effective mine planning. [ABSTRACT FROM AUTHOR]

Abstract This study shows the usefulness of borehole geophysical logging of density in the identification of coal seams, in relation to other lithologies present in a coal deposit located in the south of Brazil. Four drillholes were studied. The geological descriptions of the core samples recovered from these holes were the main information used as a control parameter in comparison with the geophysical logs. A threshold of density (2.0 g/cm3) was established in the gamma-gamma log analysis for identifying the coal seams with economic value. Also due to the economic and operational aspects related to the coal industry, the coal seams must be at least 0.4 meters thick. Once the coal seams were identified by density logs, a verification of the accuracy in the determination of the thicknesses and densities of the coal seams was performed. The coal seam thicknesses and densities determined by borehole logging were close to the observed values in the borehole core samples. As a result of the comparison between the geological and density log data, an average value difference of 0.03 m and -0.01 g/cm3 was reached for thickness and density, respectively. Due to the results and valuable information obtained, it was also possible to indicate and determine which areas of the deposit should be mined in relation to the drillholes studied and threshold parameters established. In conclusion, the importance of this evaluation is emphasized, mainly with respect to the thickness of the coal seams, which aids in the development of effective mine planning.

The grade analysis of lead-zinc ore is the basis for the optimal development and utilization of deposits. In this study, a method combining Prompt Gamma Neutron Activation Analysis (PGNAA) technology and machine learning is proposed for lead-zinc mine borehole logging, which can identify lead-zinc ores of different grades and gangue in the formation, providing real-time grade information qualitatively and semi-quantitatively. Firstly, Monte Carlo simulation is used to obtain a gamma-ray spectrum data set for training and testing machine learning classification algorithms. These spectra are broadened, normalized and separated into inelastic scattering and capture spectra, and then used to fit different classifier models. When the comprehensive grade boundary of high- and low-grade ores is set to 5%, the evaluation metrics calculated by the 5-fold cross-validation show that the SVM (Support Vector Machine), KNN (K-Nearest Neighbor), GNB (Gaussian Naive Bayes) and RF (Random Forest) models can effectively distinguish lead-zinc ore from gangue. At the same time, the GNB model has achieved the optimal accuracy of 91.45% when identifying high- and low-grade ores, and the F1 score for both types of ores is greater than 0.9.

During trip out of the drill string at the end of a drilling operation (logging while tripping) borehole temperatures can be measured without the need for additional operational time. A simple interpretation of the measured borehole temperatures is difficult due to the interfering influences of the drilling operations, mainly due to flushing the borehole during drilling. In this study, we present borehole temperature data from drilling campaigns with the sea floor drill rig MARUM-MeBo200 at the Danube Deep Sea Fan (Black Sea) and west of Taiwan (South China Sea). The temperature measurements were conducted with a PT1000 temperature sensor which is integrated in a memory acoustic borehole logging tool. We developed a modeling approach in order to simulate the drilling perturbations and subsequent evolution of the temperature field within the borehole. By fitting the model data to the measured time dependent temperature depth profiles, we estimated the undisturbed heat flux at the drill sites. This study shows that knowledge of the pattern of drilling operations with alternating phases of drilling/flushing and drill string handling is crucial for comparing temperatures measured during logging while tripping and simulated temperatures. [ABSTRACT FROM AUTHOR]

We conducted a vertical seismic profile (VSP) in the borehole of International Ocean Discovery Program/International Continental Scientific Drilling Program Expedition 364 Site M0077 to better understand the nature of the seismic reflectivity and the in situ seismic properties associated with the Chicxulub impact structure peak ring. Extraction of the up‐going wavefield from the VSP shows that a strong seismic reflection event imaged in seismic reflection data results from discontinuities in the elastic impedance Z (the product of density and wave speed) at the top and bottom of a zone of hydrothermally altered melt‐bearing polymict breccia (suevite) that are characterized by anomalously low Z. Below this strong carbonate/suevite reflection event, the upgoing seismic wavefield is chaotic, indicating high levels of scattering from the suevites and underlying melt rocks and shocked granitoids of the peak ring, in contrast to the clear coherent reflections throughout the overlying Cenozoic sediments. We extract shear wave speeds, which, together with those provided from the complementary sonic log and densities from core scanning, allowed determination of VP/VS and Poisson's ratio v. These values are anomalously high relative to comparable terrestrial lithologies. We also calculate a variety of damage parameters for the disrupted peak ring granitoids. These values may assist in linking seismic observations to shock levels that are necessary to calibrate current impact models and may also be useful in assessing levels of fracturing within major fault zones. Plain Language Summary: Seismic profiling over geological features reveal to us both the geometry of the structure and the speeds of the seismic waves within it. Calibrating these profiles using only data from the surface, however, remains challenging, but this can be accomplished by making direct seismic measurements in a borehole with a technique called vertical seismic profiling (VSP). Here, we describe the analysis of such a VSP acquired during drilling into the Chicxulub Impact Structure during International Ocean Discovery Program Expedition 364. Special processing of the waves confirm that the strong seismic reflection seen in surface data originates from abrupt changes in the rock properties related to the juxtaposition of hardened sediments, weak suevites, and melt rock. No seismic reflections could be found originating deeper in the uplifted and highly damaged granitoids of the structures's peak ring. As noted in earlier studies, the seismic wave speeds are anomalously low in these lower materials. These speeds were converted into damage indexes and as such this information may provide a means toward constraining advanced numerical impact modeling and in assessing levels of damage in the subsurface in advance of construction on the surfaces of the Moon and Mars. Key Points: We present analyses from a vertical seismic profile at Site M0077 on the Chicxulub peak ringReflectivity is primarily from a low velocity zone of hydrothermally altered impactites at the top of the peak ring below Cenozoic sedimentsWe derive Grady‐Kipp damage parameters and Poisson's ratios which indicate high damage levels within the peak ring [ABSTRACT FROM AUTHOR]

Abstract We conducted a vertical seismic profile (VSP) in the borehole of International Ocean Discovery Program/International Continental Scientific Drilling Program Expedition 364 Site M0077 to better understand the nature of the seismic reflectivity and the in situ seismic properties associated with the Chicxulub impact structure peak ring. Extraction of the up‐going wavefield from the VSP shows that a strong seismic reflection event imaged in seismic reflection data results from discontinuities in the elastic impedance Z (the product of density and wave speed) at the top and bottom of a zone of hydrothermally altered melt‐bearing polymict breccia (suevite) that are characterized by anomalously low Z. Below this strong carbonate/suevite reflection event, the upgoing seismic wavefield is chaotic, indicating high levels of scattering from the suevites and underlying melt rocks and shocked granitoids of the peak ring, in contrast to the clear coherent reflections throughout the overlying Cenozoic sediments. We extract shear wave speeds, which, together with those provided from the complementary sonic log and densities from core scanning, allowed determination of VP/VS and Poisson's ratio v. These values are anomalously high relative to comparable terrestrial lithologies. We also calculate a variety of damage parameters for the disrupted peak ring granitoids. These values may assist in linking seismic observations to shock levels that are necessary to calibrate current impact models and may also be useful in assessing levels of fracturing within major fault zones.

Orano Mining has relied on Nuclear Measurement Laboratories for several years to estimate calibration factors for borehole radiometric probes. The total gamma count rate recorded with a NaI(Tl) scintillation detector (NGRS probe) is converted into equivalent uranium grade using a calibration coefficient in s-1.ppmU-1 units, estimated thanks to different calibration blocks ranging from 0 to 10,000 ppm of uranium, at Orano CIME calibration facility in Bessines, France. Recently, Orano Mining embarked on an update of its measurement means by associating gamma spectrometry directly in the wellbore. Therefore, Orano Mining has recently tested a CeBr3 probe designed and developed by ALT (Advanced Logic Technology) to qualify a patented borehole spectroscopic method based on energy bands recently developed by CEA and Orano. In this context, we have implemented a fine Monte Carlo modelling of this new probe in order to correct the calibration coefficients as a function of different parameters such as the drilling diameter, the presence of a casing, the density of the mineralization, the distance of the probe with respect to the well or casing walls, etc. In the present work, we have simulated the CeBr3 probe in the concrete calibration blocks of Orano CIME. The MCNP model of the probe has been validated through a comparison with experimental data. The calibration coefficient determined by simulation is 11.6 s-1.ppm -1 > 10 % in total gamma counting, which is in good agreement with the one measured in Bessines, i.e. 10.6 s-1.ppm -1. The calculation vs. experiment agreement is also satisfactory (i.e. within 10 %) for spectroscopic energy bands used to characterize the uranium grade in case of disequilibrium in the uranium chain, when total count rate does not apply. This method recently developed for samples and boreholes will be tested in future work with this new CeBr3 probe.

This work reports the development of a new neutron probe for mining prospection and exploitation. It allows a combined measurement of hydrogen porosity, based on the detection of neutrons backscattered by the geological formation, and of uranium concentration based on induced-fission prompt neutrons, with the Differential Die-away Technique. The probe includes a pulsed neutron generator and a single neutron counter embedded in a polyethylene block wrapped with cadmium, saving the place for a gamma-ray detector compared to usual porosity probes with two 3He counters. We first report design and feasibility studies using MCNP 6.2 simulations, showing the significant effect of hydrogen porosity on the uranium signal and the need for a combined interpretation. Then, we report laboratory experiments that validate the simulation methods of both the porosity and uranium useful signals, but also the active background due to 17O activation. Taking into account neutron absorbers in the sand of our testing system, like boron, lithium and gadolinium measured by ICP-MS, the simulated and experimental signals of prompt fission neutrons agree within +20 %. The relative effect of water, introduced in the central hole of our experimental system, is about 30 % on the backscattered neutron signal, in both simulation and experiment. Finally, the spatial sensitivity of the tool, which is maximal in front of the detector and extends to approximately 20 cm (FWHM) in the vertical axis, is well reproduced with MCNP. [ABSTRACT FROM AUTHOR]

El Moghra area, in the western desert of Egypt, is an important part of the national reclamation project (1.5 million acres—6.07 × 109 m2), which depends on the groundwater of El Moghra Formation (MF), the main aquifer in this area. Moghra Oasis and its surroundings are characterized by vast areas of good soil, which are favorable for agricultural development. In this respect, ambitious plans and successful programs are urgently required. Thirty-one vertical electrical sounding stations (VES's) were measured in El Moghra. The results of quantitative interpretation of such stations and well logging data indicate that the subsurface stratigraphy of the investigated area consists of six geo-electrical units where the main aquifer is represented by the fourth and sixth units intercalated with a clay unit (fifth unit). Thirteen boreholes of depth reaching 200 m are drilled in the study area. The hydrochemical analyses for collected samples indicate that the salinity of the groundwater in the Moghra area increases with depth. The result of the pumping test for boreholes indicates that the efficiency of the wells is ranging from 65 to 96% of the average value of 84.5%. The aquifer has transmissivity which represents a highly potential aquifer. [ABSTRACT FROM AUTHOR]

The objectives of the study is to assess the engineering competence of the subsoil and develop subsoil competence map for northern parts of Ondo State, Nigeria, using integrated remote sensing, geotechnical studies, geophysical and geological investigations, static water level measurement, and borehole logging. The generated subsoil competence map was obtained by integrating the results data of these parameters measured. Consequently, the map classified the study area into moderate competence (60%), high competence (35%), and very high competence (5%). The corrosivity map of the topsoil shows predominant moderate to mildly corrosivity, prominently in Ose and Akoko areas, and constitute about 70 %. On the basis of design, the obtained settlement values were within the 25 mm commonly recommended. Subsequently, areas characterized by moderate competence material can be improved by less expensive mechanical compaction and proper use of admixtures (lime, cement, bituminous addition, sand/gravel grading) to increase bearing capacity, compaction and shear strength, which will invariably reduce compressibility, settlement and permeability. Subsequently, shallow foundation such as pad or raft foundation of reinforced concrete can be adopted in the study area. [ABSTRACT FROM AUTHOR]

The manuscript reviews several selected applications of Activation Analysis that differ from classical laboratory measurements by the fact that they do not require sampling of the analysed object and/or measurements under analytical laboratory conditions. One of great advantages of the Activation Analysis lies in its versatility that allows it to be applied under conditions not available for other analytical techniques. [ABSTRACT FROM AUTHOR]

A new instrument for high-resolution optical logging has been built and tested in Antarctica. Its purpose is to obtain records of volcanic products and other scattering features, such as bubbles and impurities, preserved in polar ice sheets, and it achieves this by using long wavelength near-infrared light that is absorbed by the ice before many scattering events occur. Longer wavelengths ensure that the return signal is composed primarily of a single or few backscattering event(s) that limit its spatial spread. The compact optical logger features no components on its body that draw power, which minimizes its size and weight. A prototype of the logger was built and tested at Siple Dome A borehole, and the results were correlated with prior optical logging profiles and records of volcanic products from collected ice core samples.

In historical urban centres, the superimposition of excavation and deposition activities over time has resulted in an irregular spatial distribution of anthropogenic deposits, which may reach considerable thicknesses. The detection of those thicknesses requires extensive investigations. Broad borehole and geophysical campaigns cost time and money, consequently at the urban-planning level, it is usual to shift to an estimation of thicknesses, which may be performed through map-algebra operations, that is, by subtracting from the modelled ground surface the elevation of the anthropogenic-deposit basal surface. The latter is implemented through the interpolation of point elevation data, which are generally provided by borehole logs. Despite the development of advanced spatial interpolation methodologies, previous modelling results in the literature show that if the process is affected by insufficient input data, it produces imprecise interpolation outputs. This paper reports an interdisciplinary methodology aiming at enhancing elevation datasets, in order to obtain more accurate digital elevation models. The increase in number and spatial distribution of input points is achieved through past-landscape analyses mainly based on elevation data given by borehole logs, available archaeological reports and historical topographic maps, these being generally available for historical urban centres. The methodology was tested in an urban sector of Rome, where significant activities have been performed for millennia particularly during the Roman Age. A reliable model of the basal surface of the anthrostrata led to a better estimation of the spatial distribution of such deposits and, in addition, revealed the original topographic surface, as modified by human activities. [ABSTRACT FROM AUTHOR]

Abstract The paper examines the proposed approach of using T-matrix model to convert dynamic moduli (Young's modulus and Poisson's ratio) determined by sonic well logging to values equivalent to values of static moduli (called effective moduli). The chosen approach is particularly suitable for rock masses consisting of solid rocks with irregular local cracking. The proposed approach is based on the fact that for intact rock with Young's modulus values on the order of several tens of GPa and strength σ c on the order of several tens of MPa, the values of static and dynamic moduli are equivalent. Any fractures in the rock will cause the elastic behaviour to cease being linear and a difference will appear between the values of static and dynamic moduli. It is possible to approximate this difference using the T-matrix model. The starting point for creating a T-matrix model is a simplified layered geological model of a borehole profile. Added to this are values of static moduli determined by a uniaxial compression test on representative samples of the borehole core. Additional input data for calculating the T-matrix model include porosity determined from well logging measurements, and the presence of cracks as interpreted from an acoustic scan of the borehole wall. The given approach is demonstrated in the experimental measurement of a borehole in Silurian limestone. The procedure was verified by comparing the calculated effective moduli with values of static moduli, measured on control samples prepared from borehole core outside the collection intervals of samples used as input for calculation of the T-matrix model. This comparison showed that for majority of samples there was a decrease in the difference from nearly 40% (dynamic moduli) to under 10% (effective moduli). Highlights • Use of a T-matrix model made it possible to approximate static moduli from dynamic moduli. • The curves calculated by the model are significantly more detailed than the original well logging. • The calculated effective values can be used for calculations instead of the static values. [ABSTRACT FROM AUTHOR]

In this paper, we present a set of compact formulations to model the response of the electromagnetic well-logging tools in eccentric multilayered medium. Different from previous models, the coil antennas are imbedded in an insulating protection layer (IPL) rather than expose to the borehole directly, which agrees much better with some real tools, e.g., the array induction logging tool. The effects of both metal mandrel and an IPL are considered in eccentric scenarios. Our formulations are derived on the basis of the ratios of cylindrical functions, which obviate the notorious overflow issues during numerical computation. Numerical results show that the effect of IPL gradually appears with the increase of the eccentric distance. [ABSTRACT FROM AUTHOR]

Abstract Rock permeability and porosity are some of the most important features to be determined during the exploitation of a certain hydrocarbon reservoir, as these physical properties help petrophysicists understand the most likely distribution and/or presence of oil/gas reservoirs, as well as decide whether that certain field might be exploitable or not. Despite their importance, in order to obtain permeability and porosity values it is usually required to run tests on borehole core samples that are either destructives or that need to be done under very controlled conditions, which makes them very expensive and time consuming. In the last decades, some authors have been able to estimate both these properties measurements from well-logging reservoir curves –such as Gamma-Ray response (GR), Bulk Density (RHOB) or Neutron Porosity (NPHI)–. In this study, we present a novel method that can be used to estimate formation permeability and porosity from borehole image logs –instead of simple logs– using deep autoencoders. The data used in this work belongs was extracted from a Brazilian pre-salt carbonate well. First, we use a 3–level stacked autoencoder to extract internal features from both ultrasonic and microresistivity images, thus characterizing the features contained inside these images. Afterwards, we use a support vector machine regressor (SVM) to link the encoded features extracted from the autoencoders for each type of data (ultrasonic and microresistivity borehole images) to the petrophysical measurements logs. Using this method we were able to achieve a correlation coefficient between original and estimated validation samples of R 2 = 96.30 % for effective porosity logs and R 2 = 96.06 % for permeability logs, and a normalized squared mean error of N M R S E = 7.30 % and N M R S E = 5.51 % , respectively, all results in the blind test sample. Highlights • Permeability and E_ective Porosity wireline logs estimation with over 96% accuracy. • Use of Borehole Image Data Logs (Ultrasonic and Microresistivity) as only source of information for the petrophysical logs estimation. • Application of Deep Learning methods to borehole well data (Stacked Autoencoders). • The use of sliding window to extract hidden features from the Borehole Images allow us to preserve the information of the geological structures on the surroundings of each sample. • The correlation between Ultrasonic and Resistivity Image Data Logs and petrophysical logs (Porosity and Permeability) is shown to be objective in this paper, rather than something subjective or intuitive (as it used to be in the past, when petrophysicists could not quantify objectively the amount of information from these data sources that should be taken into account). [ABSTRACT FROM AUTHOR]

Spatial distribution of principal stresses in a layered elastic medium is considered in the paper. Transformations of the principal stresses across an interface between the layers are analyzed. A method for reconstructing the spatial stress distributions in layered medium from several spot measurements is proposed. The introduced approach is capable of obtaining the stable solution of the stress reconstruction problem with respect to the noise in input data. A typical layered medium is considered for which the stresses are reconstructed from few independent spot measurements of the stress state. The proposed approach may be used for solving an inverse problem of tectonic stresses reconstruction from the borehole logging data. [ABSTRACT FROM AUTHOR]

A prompt gamma neutron activation analysis logging method for formation water salinity determination is proposed. The response of formation water salinity for capture gamma ray spectrum and thermal neutron counts ratio are studied by Monte Carlo simulation method. Formation porosity and borehole fluid salinity influence on formation water salinity is corrected. A synthetical logging case is simulated to indicate the effectiveness of this logging method. The new logging method is also applied in oil field, and the formation water salinity of different depth is calculated. [ABSTRACT FROM AUTHOR]

The geothermal resources in Spain have been a source of deep research in recent years and are, in general, well-defined. However, there are some areas where the records from the National Institute for Geology and Mining show thermal activity from different sources despite no geothermal resources being registered there. This is the case of the area in the south of the Duero basin where this research was carried out. Seizing the opportunity of a deep borehole being drilled in the location, some geophysical resources were used to gather information about the geothermal properties of the area. The employed geophysical methods were time-domain electromagnetics (TDEM) and borehole logging; the first provided information about the depth of the bedrock and the general geological structure, whereas the second one gave more detail on the geological composition of the different layers and a temperature record across the whole sounding. The results allowed us to establish the geothermal gradient of the area and to discern the depth of the bedrock. Using the first 200 m of the borehole logging, the thermal conductivity of the ground for shallow geothermal systems was estimated.

We propose a discretization technique using non-fitting grids to simulate magnetic field-based resistivity logging measurements. Non-fitting grids are convenient because they are simpler to generate and handle than fitting grids when the geometry is complex. On the other side, fitting grids have been historically preferred because they offer additional accuracy for a fixed problem size in the general case. In this work, we analyse the use of non-fitting grids to simulate the response of logging instruments that are based on magnetic field resistivity measurements using 2.5D Maxwell’s equations. We provide various examples demonstrating that, for these applications, if the finite element matrix coefficients are properly integrated, the accuracy loss due to the use of non-fitting grids is negligible compared to the case where fitting grids are employed. [ABSTRACT FROM AUTHOR]

Fractured crystalline aquifers of mountain watersheds may host a significant portion of the world’s freshwater supply. To effectively utilize water resources in these environments, it is important to understand the hydraulic properties, groundwater storage, and flow processes in crystalline aquifers and field-derived insights are critically needed. Based on borehole hydraulic characterization and monitoring data, this study inferred hydraulic properties and groundwater flow of a crystalline fractured aquifer in Laramie Range, Wyoming. At three open holes completed in a fractured granite aquifer, both slug tests and FLUTe liner profiling were performed to obtain estimates of horizontal hydraulic conductivity ( K h ). Televiewer (i.e., optical and acoustic) and flowmeter logs were then jointly interpreted to identify the number of flowing fractures and fracture zones. Based on these data, hydraulic apertures were obtained for each borehole. Average groundwater velocity was then computed using K h , aperture, and water level monitoring data. Finally, based on all available data, including cores, borehole logs, LIDAR topography, and a seismic P-wave velocity model, a three dimensional geological model of the site was built. In this fractured aquifer, (1) borehole K h varies over ∼4 orders of magnitude (10 −8 –10 −5  m/s). K h is consistently higher near the top of the bedrock that is interpreted as the weathering front. Using a cutoff K h of 10 −10  m/s, the hydraulically significant zone extends to ∼40–53 m depth. (2) FLUTe-estimated hydraulic apertures of fractures vary over 1 order of magnitude, and at each borehole, the average hydraulic aperture by FLUTe is very close to that obtained from slug tests. Thus, slug test can be used to provide a reliable estimate of the average fracture hydraulic aperture. (3) Estimated average effective fracture porosity is 4.0 × 10 −4 , therefore this fractured aquifer can host significant quantity of water. (4) Natural groundwater velocity is estimated to range from 0.4 to 81.0 m/day, implying rapid pathways of fracture flow. (5) The average ambient water table position follows the boundary between saprolite and fractured bedrock. Groundwater flow at the site appears topography driven. [ABSTRACT FROM AUTHOR]

In this study, we present the prediction of permeability from time domain spectral induced polarization (IP) data, measured in boreholes on undisturbed formations using the El-log logging-while-drilling technique. We collected El-log data and hydraulic properties on unconsolidated Quaternary and Miocene deposits in boreholes at three locations at a field site in Denmark, characterized by different electrical water conductivity and chemistry. The high vertical resolution of the El-log technique matches the lithological variability at the site, minimizing ambiguity in the interpretation originating from resolution issues. The permeability values were computed from IP data using a laboratory-derived empirical relationship presented in a recent study for saturated unconsolidated sediments, without any further calibration. A very good correlation, within 1 order of magnitude, was found between the IP-derived permeability estimates and those derived using grain size analyses and slug tests, with similar depth trends and permeability contrasts. Furthermore, the effect of water conductivity on the IP-derived permeability estimations was found negligible in comparison to the permeability uncertainties estimated from the inversion and the laboratoryderived empirical relationship. [ABSTRACT FROM AUTHOR]

In the paper, a novel inversion approach is used for the solution of the problem of factor analysis. The float-encoded genetic algorithm as a global optimization method is implemented to extract factor variables using open-hole logging data. The suggested statistical workflow is used to give a reliable estimate for not only the factors but also the related petrophysical properties in hydrocarbon formations. In the first step, the factor loadings and scores are estimated by Jöreskog's fast approximate method, which are gradually improved by the genetic algorithm. The forward problem is solved to calculate wireline logs directly from the factor scores. In each generation, the observed and calculated well logs are compared to update the factor population. During the genetic algorithm run, the average fitness of factor populations is maximized to give the best fit between the observed and theoretical data. By using the empirical relation between the first factor and formation shaliness, the shale volume is estimated along the borehole. Permeability as a derived quantity also correlates with the first factor, which allows its determination from an independent source. The estimation results agree well with those of independent deterministic modeling and core measurements. Case studies from Hungary and the USA demonstrate the feasibility of the global optimization based factor analysis, which provides a useful tool for improved reservoir characterization. [ABSTRACT FROM AUTHOR]

The utilization of a microcontroller board, optimized for the simultaneous data logging of chromatographic information, the oven temperature, and remote transfer to a personal computer, is investigated, with the goal to extend the capabilities of a gas chromatograph (Shimadzu GC-14A) which does not include a built-in data logging module. An initial comparison of the chromatographic peaks obtained from solute injections, collected both by a dedicated analog-to-digital expansion card and the microcontroller board, demonstrated the latter’s ability to perform accurate analog signal digitization. Afterward, the evaporation of three organic liquids (methanol, acetone, andn-pentane) was studied by reversed-flow inverse gas chromatography. From the temperature variation of the experimentally determined rates, the respective thermodynamic functions of enthalpy and entropy changes of acetone and methanol evaporation were determined. The small deviations from the theoretical values indicate the reliability of the proposed methodology. More importantly, it was made apparent that by utilizing automatic data logging instead of the carrier gas flow reversal procedure, the monitoring of rapid physicochemical phenomena was performed with better accuracy, while the duration of the experiments was decreased with the reduced consumption of gas chromatographic consumables. [ABSTRACT FROM PUBLISHER]

Aperture, which refers to the opening size of a fracture, is a critical parameter controlling rock mass permeability. Moreover, distribution of permeability within the reservoir is commonly affected by natural fracture occurrences. In a water-based mud environment, boreholeimaging tools are able to identify both location and aperture size of the intersected fractures, whereas in oil-based environment, due to invasion of resistive mud into the fractures, this technique is impractical. Recently, some artificial intelligence techniques facilitated reliable estimations of reservoir parameters. In this paper, a teaching- learning-based optimization algorithm (TLBO) trained an initial fuzzy inference system to estimate hydraulic aperture of detected fractures using well logs responses. Comparing the results with real measurements revealed that the model can provide reliable estimations in both conductive and resistive mud environments, wherever the aperture size is unknown. TLBO, besides of its easier application, outperformed earlier optimization algorithms, which were used to evaluate the method effectiveness. [ABSTRACT FROM AUTHOR]

Site characterization requires detailed and ideally spatially continuous information about the subsurface. Geophysical tomographic experiments allow for spatially continuous imaging of physical parameter variations, e.g., seismic wave propagation velocities. Such physical parameters are often related to typical geotechnical or hydrological target parameters, e.g. as achieved from 1D direct push or borehole logging. Here, the probabilistic inference of 2D tip resistance, sleeve friction, and relative dielectric permittivity distributions in near-surface sediments is constrained by ill-posed cross-borehole seismic P- and S-wave and radar wave traveltime tomography. In doing so, we follow a discovery science strategy employing a fully data-driven approach capable of accounting for tomographic ambiguity and differences in spatial resolution between the geophysical tomograms and the geotechnical logging data used for calibration. We compare the outcome to results achieved employing classical hypothesis-driven approaches, i.e., deterministic transfer functions derived empirically for the inference of 2D sleeve friction from S-wave velocity tomograms and theoretically for the inference of 2D dielectric permittivity from radar wave velocity tomograms. The data-driven approach offers maximal flexibility in combination with very relaxed considerations about the character of the expected links. This makes it a versatile tool applicable to almost any combination of data sets. However, error propagation may be critical and justify thinking about a hypothesis-driven pre-selection of an optimal database going along with the risk of excluding relevant information from the analyses. Results achieved by transfer function rely on information about the nature of the link and optimal calibration settings drawn as retrospective hypothesis by other authors. Applying such transfer functions at other sites turns them into a priori valid hypothesis, which can, particularly for empirically derived transfer functions, result in poor predictions. However, a mindful utilization and critical evaluation of the consequences of turning a retrospectively drawn hypothesis into an a priori valid hypothesis can also result in good results for inference and prediction problems when using classical transfer function concepts. [ABSTRACT FROM AUTHOR]

A prompt gamma neutron activation analysis borehole logging method for copper, nickel and iron grade estimation is proposed. The performance of the method was simulated by MCNP5 code. Based on the theory of neutron-gamma distribution on the borehole condition, the BGO scintillator and He neutron tube are adopted to record gamma ray spectrum and thermal neutron simultaneously, and least square method is used for the characteristic gamma ray counts calculation in the high energy range. The results of detection limit of metal grade in borehole condition indicate that the effectiveness of this logging method. [ABSTRACT FROM AUTHOR]

Geophysical methods are used increasingly for characterization and monitoring at remediation sites in fractured-rock aquifers. The complex heterogeneity of fractured rock poses enormous challenges to groundwater remediation professionals, and new methods are needed to cost-effectively infer fracture and fracture-zone locations, orientations and properties, and to develop conceptual site models for flow and transport. Despite the potential of geophysical methods to “see” between boreholes, two issues have impeded the adoption of geophysical methods by remediation professionals. First, geophysical results are commonly only indirectly related to the properties of interest (e.g., permeability) to remediation professionals, and qualitative or quantitative interpretation is required to convert geophysical results to hydrogeologic information. Additional demonstration/evaluation projects are needed in the site remediation literature to fully transfer geophysical methods from research to practice. Second, geophysical methods are commonly viewed as inherently risky by remediation professionals. Although it is widely understood that a given method may or may not work at a particular site, the reasons are not always clear to end users of geophysical products. Synthetic modeling tools are used in research to assess the potential of a particular method to successfully image a target, but these tools are not widely used in industry. Here, we seek to advance the application of geophysical methods to solve problems facing remediation professionals with respect to fractured-rock aquifers. To this end, we (1) provide an overview of geophysical methods applied to characterization and monitoring of fractured-rock aquifers; (2) review case studies showcasing different geophysical methods; and (3) discuss best practices for method selection and rejection based on synthetic modeling and decision support tools. [ABSTRACT FROM AUTHOR]

Claystones are considered as a geological barrier. However, the properties of claystone may be modified if these are cut by brittle faults and fractures. Investigations of fault rocks are therefore crucial to evaluate the barrier properties of clay rich formations. The present study is dealing with the characterization of naturally and artificially deformed Opalinus Clay of the Mont Terri rock laboratory in NW Switzerland. Complete core sections, covering the artificially excavation damaged zone (EDZ) and several tectonic fault zones, have been studied using a multidisciplinary approach consisting of geophysical, geotechnical, mineralogical/geochemical and lithological/structural data. The fault zones encountered are characterized by a high density of planar discontinuities, which often show slickenside striations. Under the microscope, the fault zones turned out to be pervasively deformed resulting in open veins and pore space, now filled with calcite and celestine. Fault zone reactivation led to very fine-grained, cohesionless fault gouge and fragmentation of the previously formed calcite veins. Packer tests in boreholes reveal excavation induced, enhanced permeabilities up to 3 m borehole depth (1.9 m ┴ to gallery floor). Seismic borehole measurements indicate that seismic attributes, which are typical for undisturbed Opalinus Clay, are not reached until 7.5 m borehole depth (4.8 m ┴ to gallery floor), which is larger than in the usual gallery configuration. We interpret the anomalies in geophysical measurements as well as the elevated permeabilities, measured in the Main Fault (3.6 m to 4.2 m ┴ to gallery floor), to result from an enlarged EDZ, influenced by the presence of the brittle fault structures. The up to two orders of magnitude higher permeability (compared to the intact claystone) most probably results from excavation induced stress and a local reactivation of fault planes. The results suggest that the presence of a fault zone can alter the extent of the EDZ significantly, and thereby affect the rock integrity, at least in the near field of a repository tunnel. [ABSTRACT FROM AUTHOR]

This paper analyzes spatially selected 286 deep borehole logs reaching up to the bedrock and the results are presented in terms of amplification factor, ground acceleration and predominant period. The peak ground acceleration (PGA) is estimated to be 0.10 and 0.50 g indicating strong influence of nonlinearity in particular areas of Kathmandu valley wherein de-amplification is observed. The peak spectral acceleration is found to be varying from 0.30 to 1.75 g for the study area and soil predominant period is estimated in the range of 0.7 to 5 sec. Preliminary microzonation maps for PGA and soil predominant period are prepared and presented in this paper. Comparisons and interpretations on the basis of 1934 and 2015 earthquakes are presented in terms of damage scenario. [ABSTRACT FROM AUTHOR]

Karst voids at pile locations are highly adverse to the bearing capacity and construction safety of cast-in-place pile foundations. This study developed an inspection system prototype of karst voids during cast-in-place pile foundation construction. The system consists of a multifrequency borehole sonic probe, two pile hole sonar probes, an in situ computer, and a corresponding signal analysis method. Borehole and pile hole detection are conducted during the investigation and pile hole drilling to inspect karst voids around the borehole and beneath the bottom of the pile hole. The analysis of the synthetic data verifies the effectiveness of the proposed method. A field inspection of karst voids during cast-in-place pile foundation construction was conducted. Comprehensive geophysical methods, including borehole optical imaging, 3D laser scanning, and borehole logging were deployed for comparison. The results show that the system can provide detailed geological information to the design of piles and ensure the construction safety of foundations. • An inspection system of karst voids during cast-in-place pile foundation construction was developed. • Karst voids around the borehole and beneath pile holes can be identified. • The system ensure the safety of pile foundation construction in karst areas. [ABSTRACT FROM AUTHOR]

Abstract: The conventional GR (gamma ray) index model is widely used to calculate shale volume in a drilling hole. It is just based on the raw downhole GR log. However, it is found that formation porosity and density have effect on the measurement of GR log. This effect is not obvious in compacted formations, but is nonnegligible in soft formations. In this work, a new model based on the concept of matrix GR which is immune to the effect of porosity and density is proposed. We apply the new model and GR index model to two distinct wells, one is ODP Site 1173, representing soft formations, and another is a hydrocarbon exploratory borehole, representing compacted formations. The results of the new model are in better consistent with shale volumes from X-ray diffraction analysis in Site 1173 and well-log inversion in the exploratory hole. At last, we give an explanation to a long-term problem in GR index model that GR index is generally larger than the actual shale volume. [ABSTRACT FROM AUTHOR]

The current study presents an effective approach to convert well logs to music and listen to their sound. Well log data play an important role in different stages of oil and gas field's exploration and development. Several rock properties such as porosity, lithology, fluids saturation, fluid contacts and pay zones can be obtained through interpretation of well log data. Boring tabulated data or a mass of curves can be converted into joyous and pleasant sounds. For this purpose, four case studies were run to show how borehole quality logs, petrophysical evaluation results, capillary pressure data (pore size distribution) and drilling data can be converted to musical notes. The proposed approach can help in quality control or interpretation of well logs or any other reservoir data. The interpreter just needs to wear wireless headphones and listen to the music generated from reservoir data. Service companies may consider the musical interpretation of well logs as an alternative and immediate way for quality control of logging procedures at well bore site. Meanwhile, visually disabled petroleum engineers may use the aural interpretation of subsurface data. A siren can be sounded when lost circulation occurs or a kick is detected to warn well site crew about the drilling risks. The result of musical transformed well logs can be stored in MP3 files for future applications. [ABSTRACT FROM AUTHOR]

Perforated pipes are used widely in vertical and horizontal production wellbores. Understanding the fluid flow behaviour through perforated pipes by taking into consideration the wall inflow is crucial for determining the wellbore frictional characteristics. Accurate prediction of pressure drop along the perforated pipes is a key step in completion design of production wellbores. Many empirical and theoretical models have been reported in the literature to predict pressure drop and friction factor along perforated pipes. However, these models show contradictory findings which is resulted from variations in the wall inflow configuration and modelling assumptions. The fluid flow through the surrounding formation and its interactions with wellbore have been simplified in the previous models which limits their range of applicability. In this study, a three-dimensional integrated reservoir-wellbore model of fluid flow through a perforated pipe surrounded by porous media is developed via Computational Fluid Dynamics (CFD) simulation. The model is used to investigate the effect of perforation parameters including perforation density, diameter and phasing angle on the wall friction factor and the pressure drop along the perforated pipe. The simulations are carried out for pipe inlet velocities of 0.5, 2.5, and 5 m / s with inflow to pipe flow rate ratios of 0, 7.5, 15, 30%. The results from this study show that the friction factor varies linearly with the perforation density but does not change remarkably with the perforation diameter or phasing. The observed trends of wall friction factor with perforation parameters are further explained and confirmed by studying the local wall shear stress results. Increasing the number of perforations leads to a higher friction factor as well as a larger pressure drop along the pipe. It is also observed that for perforation phasing angle of 90°, the overall pressure drop has the highest value compared to other phasing angles due to intensified influence of mixing pressure drop. For turbulent flows with high Reynolds number, the accelerational pressure drop is more dominant than the frictional and mixing pressure drop for the same inflow to pipe flow rate ratios. The developed model provides an alternative solution to experimental studies of perforated pipes, while delivering more details on friction factor behaviour and overall pressure drop components. [ABSTRACT FROM AUTHOR]

The concept of cryogenic fracturing is that a sharp thermal gradient developed by applying a cryogenic fluid on a rock surface causes a strong local tensile stress that initiates fractures. Prior field tests suggest that field application with special equipment rated for cryogenic temperatures may deliver potential benefits. The tests did not, however, identify the fracture mechanisms at work in downhole conditions. In this study, we present our laboratory designs and procedures developed for studying cryogenic fracturing mechanisms in a well environment, and examine typical data indicative of the performance of the system. The experimental apparatus and procedures were specifically designed to conduct cryogenic fracturing tests in specimens under confining stress, with integrated cryogen transport, measurements, and fracture characterization. A true-triaxial loading system was built to simulate reservoir stress levels and anisotropic stress application, and was designed to avoid thermal stresses in tests involving cryogen by arranging discrete components in an open chamber. To maximize thermal shock on the wellbore surface, tubing and wellhead are configured so that liquid nitrogen enters the borehole and flow out after contributing to thermal shock. The temperature at boreholes and along flow lines, borehole pressure, and liquid nitrogen consumption are monitored throughout treatments. Acoustic transmission and pressure-decay measurements are used to characterize fractures before and after the experiments. Breakdown tests performed on un-stimulated specimens and stimulated specimens compare breakdown pressures of the two groups and thus evaluate the performance of thermal fracturing. The laboratory design was able to effectively apply cryogenic stimulations to laboratory rock specimens. The characterization methods were able to capture fracture creation and rock property changes due to cryogenic fracturing. [ABSTRACT FROM AUTHOR]

Fractures have a significant impact on rock mass mechanical and hydraulic properties, which is a concern for rock engineering applications like excavation or repository design, support design, slope stability and caving in mines. To address this issue, a sound description of the fracturing pattern is required. DFN models are statistical models which define the density of fractures having given geometrical properties (size and orientation) and which include an intrinsic variability term. One of the main challenging task is to combine all available data. Data remain sparse and scarce and are acquired at different scales and from different support shapes and dimension (1D, 2D). We present a 3D modelling approach combining data from borehole logs, outcrop trace maps and tunnel walls mapping. It is applied to the Äspö site in Sweden, for which a large database is available, containing tens of thousands of records. Using stereological rules and assumptions about the underlying DFN scaling model, we are able to integrate all data to define the fracturing properties from the borehole scale (ten centimeters) to the repository scale (several kilometers). An advanced DFN modeling framework is applied, accounting for fractures mechanical interactions. This model has proved to be almost universal in crystalline rocks and reproduces, with very few parameters, the scaling properties of fractures. We show that this modelling framework better reproduces observations at all available scales and yields DFN, which structure and associated properties have a better consistency with natural cases than for simple DFN approaches. [ABSTRACT FROM AUTHOR]

Hydrofracturing of low-yielding boreholes in hard rocks is a widely used technique in Africa for improvement of yield, thus making them qualified for installation of a hand-pump for domestic water supply. However, the success rate of the hydrofracturing campaigns seems not to be that high as generally claimed by contractors. One reason amongst others might be that the selection of zones for hydrofracturing in the individual borehole is based on pre-hydrofracturing investigation using conventional electrical logs only. Thereby, the zones selected are the occurring resistivity minima interpreted as weak zones with some fracturing. However, resistivity minima can also be caused solely by lithological reasons, which then in most cases could have been seen on a gamma log as corresponding increased gamma radiation. The advantages of using gamma logging in combination with conventional electrical logging technique for prediction of fractured zones in basement rocks is illustrated by investigations of three low-yielding boreholes located in different geological environments in crystalline basement rocks in Ghana. [ABSTRACT FROM AUTHOR]

The risk of coal and gas outbursts can be predicted using a method that is linear and continuous and based on the initial gas flow in the borehole (IGFB); this method is significantly superior to the traditional point prediction method. Acquiring accurate critical values is the key to ensuring accurate predictions. Based on ideal rock cross-cut coal uncovering model, the IGFB measurement device was developed. The present study measured the data of the initial gas flow over 3 min in a 1 m long borehole with a diameter of 42 mm in the laboratory. A total of 48 sets of data were obtained. These data were fuzzy and chaotic. Fisher’s discrimination method was able to transform these spatial data, which were multidimensional due to the factors influencing the IGFB, into a one-dimensional function and determine its critical value. Then, by processing the data into a normal distribution, the critical values of the outbursts were analyzed using linear discriminant analysis with Fisher’s criterion. The weak and strong outbursts had critical values of 36.63 L and 80.85 L, respectively, and the accuracy of the back-discriminant analysis for the weak and strong outbursts was 94.74% and 92.86%, respectively. Eight outburst tests were simulated in the laboratory, the reverse verification accuracy was 100%, and the accuracy of the critical value was verified. [ABSTRACT FROM AUTHOR]

The Deccan trap basalt, laid down by multiple lava flows during upper Cretaceous to Paleocene times forms the basement of current study in Cambay basin. As such, there is great interest and value in fracture detection and evaluation of fractured basement reservoirs in the Cambay basin. The procedure for identification and evaluation of natural as well as induced fractures in basaltic basement of the Cambay basin is presented in this work. In this study formation micro-imager (FMI) and extended range micro-imager (XRMI) log data for fracture identification is used. The Deccan trap basaltic basement of the study area, comprising five wells in the Tarapur-Cambay block, has potential for holding commercial hydrocarbon due to the presence of fractures and weathered basement. Both image logs (FMI, XRMI) identify three types of fracture including open (conductive), partially open and closed (resistive) fractures, of which open and partially open fractures are important for hydrocarbon accumulation. Fracture dip ranges from 10° to 80°. Image logs have also identified washout, breakout and drilling-induced fracture zones. The strike direction of the open natural fractures for four wells varies from N60°E to N30°E whereas the strike direction of most natural fracture in the fifth well is oriented towards N20°W. The orientations of drilling-induced fractures and breakouts may be interpreted for the in-situ stress direction over the logged interval. Drilling-induced tensile fractures, identified over the depth interval of 1969-1972 m, and borehole breakouts over the interval of 1953-1955 m in one well, suggest an orientation of maximum in-situ horizontal compressive stress (S) lies in the north-south direction. The azimuths of open natural fractures in the same well vary from north-south to N30°E. It is expected that the direction of fluid flow will be controlled by open natural fractures and therefore would be in a direction parallel to the S direction, which is orthogonal to the minimum horizontal stress (S) direction. The orientations observed are consistent with the present day S direction in the study area of Cambay basin. [ABSTRACT FROM AUTHOR]

Several factors influence the stress state in subsurface rocks. In addition to pore pressure and far-field in-situ stresses, thermal and chemical gradients have substantial bearings on the in-situ stress state during and after drilling operations. Drilling inclined boreholes through laminated formations such as shaley sands presents several challenges. Due to their laminated nature, shales demonstrate high degree of elastic anisotropy, and are often chemically-reactive to drilling fluid. The majority of models utilized in the industry assume a homogeneous isotropic elastic static model that fails to give an accurate depiction of the observed borehole failure. In this work, governing equations for anisotropic porochemothermoelasticity are developed to simulate the drilling of an inclined borehole problem in a transversely isotropic rock. Using the developed constitutive and transport equations, a finite element method based numerical model is constructed to estimate the pore pressure, temperature, solute concentration and stress distribution. Nonlinear conductive-convective heat transfer and diffusive-advective solute transfer models are considered in this work to address both high and low permeability formations. Finally, the model is used to assess time-dependent wellbore stability during and after drilling. The novel pseudo-3D analysis developed in this work is advantageous for real-time operations due to its computational speed and stability. [ABSTRACT FROM AUTHOR]

Copyright of Hydrogeology Journal is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)