Reference Borehole Research Articles

Microtremor Full-Wavefield Modeling of Effective Phase Velocity and Horizontal-to-Vertical Spectral Ratio at Kyoto Reference Borehole Site: Comparison with Surface-Wavefield Modeling Based on a Velocity Structure with a Cap Layer

ABSTRACT Two types of data commonly used for microtremor exploration are phase-velocity dispersion curves obtained through an array measurement and horizontal-to-vertical spectral ratios (HVSRs) obtainable by a single-station measurement. Phase-velocity dispersion curves obtained by applying the spatial autocorrelation method to the array waveforms have a characteristic peaked shape in some cases. This dispersion curve shape has traditionally been explained as a consequence of the predominance of higher modes over fundamental mode in the Rayleigh waves. In this study, the effects of body waves on phase velocities and HVSRs were investigated based on both field measurements and theoretical calculations of microtremors. We used vertical-component array waveforms and single-station three-component waveforms of microtremors, obtained at and around a site where combined P-wave–S-wave (PS) and density loggings were conducted in the Kyoto basin, Japan (site KD-1), to identify phase velocities and HVSRs at frequencies in the range 0.2–2 Hz. The corresponding theoretical phase velocities and HVSRs were identified using full-wavefield synthetic data, which were generated assuming excitation points randomly distributed over the surface of a horizontally stratified velocity structure model created based on the logging data. The following key results were obtained. The measured phase-velocity dispersion curve exhibits a peaked shape with the value exceeding the S-wave velocity of the Tamba Group (Tb-Group), which is the bedrock (half-space) of the velocity structure model. Theoretical calculations based on the surface-wavefield theory were unable to reproduce this peaked shape; however, theoretical calculations based on the full-wavefield theory reproduced it with extraordinary accuracy. To reproduce the peaked shape based on the surface-wavefield theory, it was necessary to construct a model containing a cap (i.e., high-velocity layer) connected under the Tb-Group. The theoretical calculation based on the full wavefield also accurately reproduced the peak value and peak frequency of the measured HVSRs.

Local coupled Markov chain model for simulating varied stratigraphy

The coupled Markov chain (CMC) model is widely employed to simulate geological uncertainty based on sparse borehole data, owing to its simplicity, parameter efficiency, and computational effectiveness. However, the existing CMC methods exhibit limitations in accurately predicting the orientation and significant dip angle changes of soil stratigraphy. These limitations stem from their reliance on a globally constant Walther constant, resulting in generated layer boundaries converging to a fixed angle. To address these issues, this study develops a local CMC model to enhance the accuracy of predicting layer sequences and describe the geological uncertainty of complex geological structures using limited borehole and surface data. In the proposed local CMC method, the global geological profile is decomposed into interconnected fragments, guided by reference boreholes. For each CMC fragment, the likelihood of observational scenarios is determined to identify the layer orientation and optimal Walther’s constant corresponding to the local geological profile. By combining the most likely realizations from all CMC fragments, the final geological profile and stratigraphic uncertainty are obtained. Illustrative case studies demonstrate that the proposed approach effectively addresses the limitations of conventional CMC models in accurately simulating significant changes in layer orientation and dip angle variations, given the same conditions of sparse borehole data. The employed localization strategy enables the prediction of geological profiles that encompass special layers such as soil interlayers, anticlines, and synclines, which cannot be well achieved by conventional CMC models. The local CMC model significantly improves the matching accuracy of geological model in situations with limited boreholes. Therefore, it plays a crucial role in the analysis of geological structures under data-scarce conditions.

Induced Earthquake Source Parameters, Attenuation, and Site Effects From Waveform Envelopes in the Fennoscandian Shield

AbstractWe analyze envelopes of 233 and 22 ML0.0 to ML1.8 earthquakes induced by two geothermal stimulations in the Helsinki, Finland, metropolitan area. We separate source spectra and site terms and determine intrinsic attenuation and the scattering strength of shear waves in the 3–200 Hz frequency range using radiative transfer based synthetic envelopes. Displacement spectra yield scaling relations with a general deviation from self‐similarity, with a stronger albeit more controversial signal from the weaker 2020 stimulation. The 2020 earthquakes also tend to have a smaller local magnitude compared to 2018 earthquakes with the same moment magnitude. We discuss these connections in the context of fluid effects on rupture speed or medium properties. Site terms demonstrate that the spectral amplification relative to two reference borehole sites is not neutral at the other sensors; largest variations are observed at surface stations at frequencies larger than 30 Hz. Intrinsic attenuation is exceptionally low with values down to 2.4 × 10−5 at 20 Hz, which allows the observation of a diffuse reflection at the ∼50 km deep Moho. Scattering strength is in the range of globally observed data with between 10−3 and 10−4. The application of the employed Qopen analysis program to the 2020 data in a retrospective monitoring mode demonstrates its versatility as a seismicity processing tool. The diverse results have implications for scaling relations, hazard assessment and ground motion modeling, and imaging and monitoring using ballistic and scattered wavefields in the crystalline Fennoscandian Shield environment.

Distribution of Microfossils in the Vendian Deposits of the Orsha Depression of the East European Platform, Belarus

—The complete sections of the Lower and Upper Vendian of the East European Platform were opened in the boreholes of Belarus. This allows us to consider this region as a stratotype area. In order to update the paleontological characteristics of the Vendian, organic-walled microfossils from the Bogushevsk-1, Bogushevsk-2 (Liozno), and Lepel-1 reference boreholes drilled in the north of the Orsha Depression were studied. The transitive assemblage I with Leiosphaeridia minutissima–Leiosphaeridia tenuissima was recognized in the Lower Vendian Liozno Formation of the Volyn Series and the Upper Vendian Kotlin Formation. The Redkino microfossil assemblages were identified at three stratigraphic levels in the Nizy, Selyava, and Chernitsa formations: assemblage II with Morania zinkovi, assemblage III with Morania zinkovi–Tynnia precambrica, and assemblage IV with Morania zinkovi–Tynnia precambrica–Striatella coriacea, respectively. The Kotlin assemblage V with Vendotaenia antiqua–Primoflagella speciosa was distinguished in the upper part of the Kotlin Formation (Bogushevsk-1 borehole). On the basis of the taxonomic composition, assemblages III and IV are correlated with the first Redkino biota of the Starorusskaya Formation; assemblage V is correlated with the third Kotlin biota of the Vasileostrovskaya Formation of the northwestern part of Russia. Our data show a high biostratigraphic potential of organic-walled microfossils, which should be used to substantiate regional stratigraphic units of the Upper Vendian in the updated stratigraphic scheme of the East European Platform.

Soil/rock interface profiling using a new passive seismic survey: Autocorrelation seismic interferometry

Soil/rock interface detection is an essential and critical task in geological site investigation for underground and tunnel projects. The required accuracy is within a few meters both vertically and horizontally. The required resolution poses big challenges to geophysical surveys to be applied in near-surface engineering works. This paper presents a new approach of non-invasive geophysical survey, namely autocorrelation. It is originally derived from seismic interferometry cross-correlation, which can convert a physical geophone to a virtual source. To the extreme is autocorrelation. It turns a single geophone into a self-source receiver. With this concept, the proposed approach includes two methods aiming to reduce the reliance on reference boreholes. A field testing carried out in Singapore is presented to demonstrate the concept and results step by step. The case study also demonstrates that the proposed method can fine-tune the autocorrelograms to achieve the required resolution both laterally and vertically. A by-product of realistic average Vp of the soil layers above soil/rock interface can be estimated reasonably by the proposed method. Two more case studies are followed to illustrate the proposed methods can produce reasonable 2D and 3D soil/rock interface profiles. Due to the self-source feature, this approach is convenient to implement on site. The proposed approach can be an attractive option for geotechnical and geological site investigation especially for delineating the soil/rock interface topography.

Fluvial magnetic susceptibility as a proxy for long‐term variations of mountain permafrost development in the Alp‐Carpathian region

Low field magnetic susceptibility (MS) records of 13 reference boreholes representing the whole Quaternary fluvial succession of the Great Hungarian Plain were correlated to develop regional stratigraphy. Data from 12 of the boreholes were published between 2016 and 2020, the Tiszainoka borehole is newly reported in this paper. Eleven magnetic susceptibility cycles, capped by the most emergent master MS peaks (MP) and bordered by susceptibility termination surfaces, have been correlated. Supported by the already evaluated palaeomagnetic reversals and instability events, MPs have been correlated to the cold stages of the Marine Isotope Stage (MIS) records. MPs represent MIS 104, 100, 98, 82, 60, 52, 34(−36) and 26 of increased heavy oxygen isotope value, constituting the significant Early Pleistocene glaciations, and MIS 18, 16, 12, 8, 6 and 2 mostly representing the substantial Middle and Upper Pleistocene European glaciation events. The interpretation of early postglacial fluvial MS maxima, which emphasizes the escape of weathering‐sensitive magnetic minerals from the catchment area triggered by the thawing of mountain permafrost, is confirmed by the correlation of MPs to the changes of the global ice volume. As a result, fluvial MS records can be considered as a proxy for mountain permafrost development in the catchment areas. Regional correlations confirmed that the Körös and Jászság Basins and the Makó Trough are sites of almost continuous fluvial records of the past 2600 ka. Thus, the Pannonian Quaternary fluvial succession is sufficiently complete to provide a satisfactory record of mountain permafrost development of the Alp‐Carpathian region, the latter being a globally relevant European representative of mid‐latitude mountain regions. The similarity of the Pannonian fluvial MS succession as a permafrost proxy to the marine ice‐rafted detritus (IRD) and Chinese loess/palaeosol MS records promises the possibility of comparative investigations of globally relevant proxy records and mid‐latitude mountain permafrost development.

Ordovician Ostracods from the Chunya River Basin (A Right Tributary of the Podkamennaya Tunguska River, Siberian Platform)

The ostracod assemblages of the Baksian and Dolborian horizons of the Chunya River basin (a right tributary of the Podkamennaya Tunguska River) have been studied. They add essentially the paleontological characteristics of Upper Ordovician deposits of the Siberian Platform. The age of deposits was verified and the studied sections were correlated with the Gaindinskaya 3 reference borehole. Two new genera and 9 new species were described. Images for known ostracod species are given.

Conodonts of the Krevyakinian and Khamovnikian Substages of the Kasimovian Stage in the Type Region (Moscow Basin)

The Kasimovian Stage is a stage in the Pennsylvanian Subsystem, originally recognized in Russia. Its type area, despite the stage name (which is after the town of Kasimov in the Ryazan Region), is in the vicinity of the Voskresensk Region in the lower reaches of the Moscow River for the Krevyakian and Khamovnikian regional substages and the former village of Dorogomilovo (Moscow Region) for the Dorogomilovian Regional Substage. The stratotypes of the subdivisions of the Krevyakinian and Khamovnikian regional substages were established in the Voskresensk Region and no longer exist. The conodont assemblages of the Krevyakian and Khamovnikian and the lower part of the Dorogomilovian were studied in the neostratotype of the Kasimovian Stage (Afanasievo Section) and the Perkhurovo Reference Borehole drilled near the town of Voskresensk.

Archival gamma ray logs standardization by nondestructive core measurements of the low-radioactivity rocks

The present study analyzes spectral gamma ray data of low-radioactivity rock cores from Rotliegend Basin. The main goal of this research was standardization of archival gamma ray logs measured in counts per minute to American Petroleum Institute units. Selected core intervals, log data, and additional crushed samples covered three different boreholes: J-1, L-7, and K-2 from Zielona Góra Basin, localized in western Poland, where J-1 was a reference borehole. Core measurements were performed on the sandstone and conglomerate formations by Gamma Logger GT spectrometer, which uses two scintillation detectors containing bismuth germanate crystals. In the cores, real concentrations of potassium, uranium, and thorium were acquired what enabled to calculate total content of radioactive elements and total uninfluenced by uranium. Delivered new total GR_GLGT curve from cores allowed accurate standardization of archival GR curves from L-7 and K-2 boreholes. Presented results showed a very good correlation between logs, core data, and laboratory analyses. These data allow precise shale volume reinterpretation.

Gamma-Ray-Tool Characterization Avoids Traditional Limitations

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 191717, “Is API Enough for Gamma Ray Logs, or Do We Need More?” by Feyzi•Inanc, SPE, and Andreas Vogt, SPE, Baker Hughes, a GE Company, prepared for the 2018 SPE Annual Technical Conference and Exhibition, Dallas, 24–26 September. The paper has not been peer reviewed. A major issue with gamma-ray (GR) logs is that the API definition is valid only if the tool is run in a 4.89-in. borehole filled with fresh water. Although all GR tools are intended to provide the same results for such a well, in the field there is no single one-size-fits-all concept. In this paper, the authors discuss the characterization process for GR tools and how they behave in boreholes different from the one used in the University of Houston (UH) GR characterization pit. Proposals for developing correction strategies so that GR logs become quantitative logs, rather than the qualitative logs of the past, also are outlined. Introduction One of the issues inherent in ensuring repeatability of GR logs starts with tool characterization. For decades, no common industry standard existed that defined the scale for measuring radioactivity. The chaos created by different tools providing radioactivity in different units in the same environments ended with the creation of the API unit in 1959. The definition of the unit was based on work done with the UH GR characterization pit. This specific pit has a 4.89-in. borehole and a casing to ensure stability within the surrounding synthetic formation. One downside of the API definition is that different combinations of radioactive isotopes, environmental conditions, and tool designs may yield comparable count rates. UH GR pit characterizations of GR tools lose their validity as the wellbore diverges from this previously described specific borehole size and environment. Thus, environmental corrections are needed to bring readings to a reference borehole used for tool characterization. Another issue with the UH GR-pit-based characterizations became evident with the emergence of logging-while-drilling (LWD) GR tools. The LWD tools were supposed to provide natural GR values comparable with those of wireline tools. Recommended practices for wireline tools did not have a provision for calibration of LWD GR tools that did not fit into the UH GR pit. Consequently, characterizations of LWD tools to provide results comparable with those of wireline tools became a topic of interest. Background Although the UH GR characterization pit still exists, it suffers from many issues. The facility is in a state of disrepair, with significant corrosion. In addition, its activity level is decreasing because of the presence of short-lived Ra-226 as one of the main ingredients in the high-activity zone. The radionuclide distribution is not even, causing gamma readings to change with the height, and rock dimensions do not correspond to those of an infinite rock environment.

ProxInLAS, a software program for detecting coal layers and estimating parameters of layers, using geophysical well-logs

The present paper describes the algorithm and working method for detection and estimation of proximate parameters of coal beds based on digital well-log data. Designed and developed by the authors in Visual Studio using C#, ProxInLAS is used to define a threshold value on each log to distinguish between coal and non-coal layers, followed by estimating each of the coal proximate parameters by importing the data pertaining to a particular borehole: the reference borehole. Inputs of the software include the reference borehole data, target functions for accepting a layer as coal, and the methods employed to estimate the proximate parameter. The software relies mainly on two algorithms, a detection algorithm for detecting coal layers, and an estimation algorithm for estimating proximate parameters of the detected layers. Loaded by the well-log and core-sampling data, the detection algorithm calculates a set of threshold values to distinguish between the coal and non-coal layers based on the frequency distribution function of the well-log values near coal beds. ProxInLAS offers four methods for estimating proximate parameters: (1) a method based on the regression between the considered parameter and a particular log, (2) a method based on a combination of several linear relationships, (3) radial basis function (RBF) method, and (4) geostatistical interpolation method. In addition to numeric records, the software can present its outputs graphically to provide a simple and instant view of the results. The case study used to evaluate the performance of ProxInLAS.

Hydrochemistry of Surface and Groundwater in the Vicinity of a Mine Waste Rock Dump: Assessing Impact of Acid Rock Drainage (ARD)

Acid Rock Drainage (ARD) is a well-known problem related to the mining industry due to its hazardous environmental effects. Metal-rich drainage and acid effluent transmitted from mine waste dumps compromise environmental quality of groundwater and surface water systems destroying aquatic life and increasing human health risks. This study was aimed at assessing the acid and metal drainage potential from the Subriso East Rock Dump (SERD) located in the Wassa East district of Ghana on ground and surface water quality in the catchment using a system of monitoring boreholes, reference boreholes and river samples. Water samples were collected from deep and shallow monitoring boreholes and surface water within the immediate environs of the SERD from August 2012 to February 2013 for laboratory and statistical analysis. Parameters analyzed include sulphate, alkalinity, Arsenic (As), Manganese (Mn), Iron (Fe), Zinc (Zn), Copper (Cu), Cadmium (Cd), Mercury (Hg), Aluminum (Al), Silver (Ag) and lead (Pb) and their concentrations compared with Ghana Standards Authority (GSA) GSB (2009) and WHO (2017) standards. Results indicate that surface and groundwater were not impacted by the SERD possibly because there was no generation of acid or metal-loaded effluent from the SERD into the environment. Physicochemical variables between monitoring boreholes did not differ significantly from conditions in the reference boreholes. Similarly, comparison of upstream and downstream river conditions did not yield any statistical significance (p > 0.05). Mn and Fe concentrations were above the WHO (2017)/GSB (2009) standards. Heavy metal concentrations in surface and groundwater were below detection limits except manganese and iron whose concentrations exceeded the recommended guidelines. No significant environmental impacts exist that could be attributed to the waste rock dump and may be as a result of engineering designs and mechanisms which prevent acid generated water from reaching the external environment. Furthermore, the geology of the study area potentially could be slightly inert having the potential to generate ARD under appropriate conditions. Again, the young age of the waste rock dump is a factor that may contribute to ARD generation under appropriate condition. Routine monitoring of groundwater and surface water sources is required to determine future acid generation of the SERD and its environmental impacts. The results of this study will assist decision makers and environmental managers to plan effectively to mitigate future impacts as mining waste rock dumps are known to increase in acid generation potential with age.

ИДЕНТИФИКАЦИОННЫЙ АНАЛИЗ УЛЬТРАМАФИТ-МАФИТОВЫХ ИНТРУЗИЙ МАМОНСКОГО КОМПЛЕКСА ВОРОНЕЖСКОГО КРИСТАЛЛИЧЕСКОГО МАССИВА

The paper describes the methods and results of identification analysis of the petrophysical parameters in ultramafic-mafic rocks from the Mamon intrusive complex in the Khopersky megablock of the Voronezh crystalline massif. In order to create identification models, the authors chose one of the boregoles within the Nizhnemamon deposit as the reference one. For different types of rocks, characteristic correlation equations of the relationship of density with other petrophysical parameters were obtained. The obtained identification equations of the reference borehole were applied to similar rocks from other (ordinary) boreholes located within the Khopersky megablock. The modeling showed that it is possible to apply the group method of data handling in order to solve the most important task, which is to say that is the differentiation of even-aged intrusions as ore and barren.

Experimental study of drainage radius considering borehole interaction based on 3D monitoring of gas pressure in coal

In practical engineering, borehole drainage is the most effective and widely used method of extracting coalbed methane (CBM). The drainage radius of a borehole is a key parameter in determining the design and layout of drainage boreholes, and the interaction among boreholes in multiple-borehole system significantly influences the drainage radius of each individual borehole. Therefore, the physical simulation experiments of gas drainage with single, double, and multiple boreholes were carried out using a self-developed device. This paper discusses the drainage radius considering borehole interaction based on 3D monitoring of gas pressure in coal, which can provide reference data for numerical simulation and offer practical guidance for engineering. The results show that multiple boreholes lead to a faster drop in gas pressure along the monitoring line and require less time to reach the safety line, with two distinct propagation patterns observed in the effective drainage zones. Besides, a calculation model was proposed for obtaining the drainage radius of a borehole. The drainage radius can be fitted using a power function with respect to drainage time, with larger values giving an increase in the drainage radius. Meanwhile, a benchmark borehole was selected from which the gas pressure decrease coefficients at different monitoring points are calculated; these coefficients reflect the degree of borehole interaction. The relationship between the pressure decrease coefficient and drainage time is approximated by a negative exponential function, with multiple boreholes exhibiting more intense interaction. Finally, it is found that the influence of other boreholes on monitoring points near the reference borehole is relatively small and subject to a time lag.

COALINLAS, a software for detecting coal beds in well-logs

In this paper, the algorithm and working method of the software are described, which allows the detection of depth and thickness of coal beds by digital information in well-logs. The software known as COALINLAS is designed and developed in Visual Studio using C# by the authors. In this software, a boundary value of each log is defined for detection of coal and non-coal layers, by importing the data of a borehole, called the reference borehole. Inputs of the software are the reference borehole data including digital files of values ​​of well logs in “.las” format, and core-sampling data; and target functions for accepting a layer as coal. The main engine of software is an algorithm called the detection algorithm. Importing the well-logging and core-sampling data, this algorithm calculates the boundary values ​​to separate the coal bed from the other by the frequency distribution function for values ​​of well logs near coal beds. The frequency distribution of well logs ​​follows the generalized extreme value (GEV) function. The location of distribution depends on the mode and the scale depends on the standard deviation and the software calculates three boundary values ​​in conditions where the cumulative density function (CDF) is equal to 50%, 70 and 90%. The case study used to test the performance of software shows that the boundary limit calculated for CDF of 70% separates the layers more precisely. In this case study, it is concluded that the software has the ability to detect all coal beds in the boring path using well-logs data. Moreover, COALINLAS can identify fine-scale changes in the characteristics of layers and detect dispersed thin layers neglected in core-sampling.

Ordovician Ostracods from the Core of the Gaindinskaya-3 Reference Borehole (Tunguska Syneclise, Siberian Platform)

The core of the Gaindinskaya-3 reference borehole disclosing a complete section of Ordovician deposits in the basin of the middle reaches of the Podkamennaya Tunguska River has yielded a diverse ostracod assemblage, which supplements the paleontological characteristics of the Upper Ordovician of the Siberian Platform. Three new genera and 14 new species are described; the previously known taxa are provided with photographs. The characteristics of stratigraphic distribution of ostracod assemblages in the section of the core are considered and boundaries between some regional stages and ostracod biozones are revised.

Jurassic continental deposits in the sections of the Irkutsk Coal Basin stratoregion

This paper presents bed-by-bed description and paleofloristic characterization (on the basis of plant macroremains) of the Jurassic continental deposits of the Irkutsk Coal Basin, in the sections of the stratotype region where the lithostrata now widely used for the geological mapping works were established for the first time. The characteristics of these units are refined along with their age and occurrences. Newly obtained taphofloras are comparatively analyzed and established to be synchronous. The spatial distribution of Jurassic deposits from different outcrops is correlated with sections of the reference boreholes. Two successive phytostratigraphic assemblages, Cheremkhovo and Prisayan, are recognized. These assemblages are correlated based on the taxonomic composition of the dominant plant groups, with the assemblages of the end of the Early Jurassic and the beginning of the Middle Jurassic of Western Siberia, which are dated using coastal marine fauna.

Results of operational verification of vertical ground heat exchangers

This article is devoted to verification of VGHEs (Vertical Ground Heat Exchangers) used as a low-temperature energy source for heat pumps. The aim and objective of the study was to obtain practical knowledge of temperatures of rock mass and heat transfer fluids which affect the life cycle of the low temperature sources and the effectiveness of heat pump systems. The objective was also to gain knowledge of specific thermal energy and power extracted by these exchangers which are relevant to the evaluation of frequently used configurations of VGHEs. The results of the operational tests of two active boreholes with different arrangements, namely a single U exchanger (A), a double U exchanger (B) – and the reference (inactive) borehole (R). The tests were performed in the years 2012–2014 and involved 2 heating seasons and 2 exchanger stagnation periods. Results of the tests showed that exchanger B is more effective than exchanger A in terms of temperatures and particularly specific heat power and energies. The average specific thermal power in the heating periods were 23.11Wm−1 and 26.57Wm−1 for exchanger B and 16.88Wm−1 and 20.66Wm−1 for exchanger A. Total specific energies transferred from the massif during the heating periods were higher by 6.05kWhm−1 and 6.94kWhm−1 at exchanger B than at exchanger A.

The use of geoelectrics in the study of a shallow quaternary alluvial aquifer in Yenagoa, southern Nigeria

Fifteen (15) electrical surveys (VES) were carried out and results used to delineate the shallow lithostratigraphic units and evaluate the electrical and hydrogeological characteristics of the aquifer zone of the alluvial deposits in Yenagoa metropolis and environs. The Schlumberger electrode configuration was adopted and maximum current electrode halfspacings (AB/2) ranged from 100 to 200m. The VES data were interpreted using 1D inversion technique software (1X1D, Interpex, USA). A maximum of four geoelectric layers were delineated and the aquifer is characterised by loose sand with resistivity ranging from 136.1 – 828.69m and thickness of 8.3-97.6m. The hydraulic conductivity (K = 41.3m/day) value measured in a reference borehole was combined with the normalized electrical conductivity (σ1) from a nearby vertical electrical sounding data. The resulting relation was interpreted with Dar Zarrouk parameters to infer the transmissivity variations at other vertical electrical sounding locations, where K values are unknown. The results showed that the transmissivity is linearly related to the normalized transverse resistance and hydraulic conductivity is also linearly related with normalized aquifer resistivity. Transmissivity values in the aquifer vary from 342.8 to 4030.9 m2/day, and hydraulic conductivity K varies from 12.0 – 88.0m/day throughout the study area.KEYWORDS: Porosity, hydraulic conductivity, transmissivity, transverse resistance, Yenagoa

Estimation of aquifer hydraulic parameters from geoelectrical method—a case study of Yenagoa and environs, Southern Nigeria

Knowledge of water transmitting properties of an aquifer is crucial for successful groundwater development and management practices in an area. In this study, the determination of aquifer hydraulic characteristics at Yenagoa and environs from Dar Zarrouk parameters was carried out using 14 vertical electrical sounding data (VES) and information from existing boreholes. The Schlumberger electrode configuration was employed for the field data acquisition with a maximum half electrode separation (AB/2) ranging between 100 and 350 m. The VES data were interpreted using 1D inversion technique software (1X1D, Interpex, USA). A maximum of four geoelectric layers were delineated and the aquifer is characterized by loose sand with resistivity ranging from 136.1 to 828.6 Ωm and thickness of 8.3–97.6 m. Using the VES results and water resistivity, porosity was determined using modified Archie’s equation. The hydraulic conductivity (K) values obtained from three reference boreholes were combined with the electrical resistivity obtained from the respective nearby VES stations to determine a diagnostic constant (Kρ). The resulting relation was interpreted with Dar Zarrouk parameters to infer the hydraulic conductivity (K) and transmissivity (T) variations at vertical electrical sounding locations, where K values are unknown. The results indicate that porosity varies between 0.09 and 0.32. The hydraulic conductivities range from 0.8 × 10−4 to 6.6 × 10−4 m/s while the transmissivity values vary between 1.1 × 10−3 and 29.6 × 10−3 m2/s. The high transmissivity values are consistent with the aquifer being unconsolidated with fine–medium–coarse sands.