Borehole Logging Data Research Articles

Enhancing groundwater potential evaluation: Integrating borehole log data with hybrid-MCDM approach

Enhancing groundwater potential evaluation: Integrating borehole log data with hybrid-MCDM approach

Investigation of orbital and sub-orbital Milankovitch cycles from borehole logging data: Examples from Cretaceous and Quaternary lake sediments

Investigation of orbital and sub-orbital Milankovitch cycles from borehole logging data: Examples from Cretaceous and Quaternary lake sediments

The role of fault pathways for modern and deep recharge to a semi-confined aquifer: revised analysis of modern water leakage pathways in the Davis wellfield, Memphis, Tennessee, USA

Hydrologic tracer, borehole log and geophysical data provide new insight into recharge sources and pathways to the semi-confined Memphis aquifer in the Davis wellfield, Memphis, Tennessee, U.S.A. New data and recent studies highlight the importance of faults as potential pathways for the migration of modern water into the Memphis aquifer, an important regional public, industrial, and agricultural water supply. Geochemical and environmental tracer data collected over the past 28 years, combined with hydrologic, stratigraphic, and structural data, were used to evaluate changes in water quality and different recharge pathways to the Memphis aquifer. Assessment of stratigraphic and structural relationships argue for the wellfield being bound by a fault along the bluff line (west) and another fault or faults along the eastern and southeastern margins. Modern water recharge (< 60 years old) occurs through the fault along the western boundary of the wellfield, whereas modern water and, seasonally, deep-seated (helium-bearing) fluids recharge along the fault on the southeastern margin. Each recharge source and pathway present different vulnerabilities, suggesting that the role of faults in wellfields within active tectonic regions needs to be assessed.

Building the fracture network model for the Okuaizu geothermal field based on microseismic data analysis

Understanding flow behavior in a geothermal reservoir is important for managing sustainable geothermal energy extraction. Fluid flow in geothermal reservoirs generally occurs in complex existing fracture systems in which the reservoirs are situated in highly fractured rocks. To simulate a discrete fracture model, the location and orientation of the fracture were computed using statistical processes and observational data. In many cases, estimating the location and orientation of fractures from 1D borehole logging data is challenging. In this study, we used microseismic data to build the fracture network systems and extract the detailed positions and dimensions of the fractures. We used the microseismic data recorded at the Okuaizu Geothermal Field, Fukushima Prefecture, Japan, from 2019 to 2021. First, we located the hypocenters, removing the effect of uncertainty in the velocity structure of the geothermal fluids. We relocated and clustered the seismic events based on waveform similarity. We analyzed each cluster to define the fracture orientation using principal component analysis (PCA) and focal mechanism (FM) analysis. We used the P polarity with the S/P ratio as a constraint for a better fault-plane solution. With PCA, we can extract the fracture dimension of each cluster. Our cluster analysis showed that the clusters were not always planar fractures, and we interpreted them as fracture zones. Based on the consistency between PCA and FM, each cluster/fracture zone was classified into three conceptual models to characterize the fracture network system in this field. This model showed variations in the orientation of small fractures within the fracture zone. We characterized the spatial variation in fracture distribution and orientations in the reservoir and demonstrated the fracture network system of this field. The fracture zone near the injection well has a N–S strike, and the dip is above 80°; however, the fracture zone in the northeastern part of the injection well has a NW–SE strike with a dip between 60° and 80°. The fracture network system estimated in this study is crucial for robust reservoir modeling because our model is more realistic, observation-orientated, and includes local anomalies of reservoir properties.Graphical

Late Pleistocene to Holocene event stratigraphy of Lake Hallstatt (Salzkammergut, Austria): revealed by the Hipercorig drilling system and borehole logging

Abstract. The Hipercorig Hallstatt History (H3) project aims to unravel the entire Late Glacial to Holocene sedimentary succession recording past climate, environment, natural hazard impacts, human–environment interactions, and prehistoric mining history. We successfully cored 51 m of the sedimentary succession of Lake Hallstatt, revealing a high-resolution Late Pleistocene to Holocene sediment record, overcoming the previous coring limit of 15.63 m (dated to ∼ 2.3 ka cal BP). The novel drilling platform Hipercorig allows the recovery of undisturbed long cores and the acquisition of borehole logging data of deep lakes. The sedimentary record is spliced to a composite core profile, and for the first time borehole logging data are linked to a core–log seismic correlation of an intra-mountainous lake of the Eastern Alps. The recovered sequence consists of two major lithostratigraphic units: (i) Unit 1 (Holocene, 0–41.7 m below lake floor) with 10 (up to 5.1 m thick) instantaneous deposits and (ii) Unit 2 (Late Pleistocene, &gt; 41.7 m below lake floor). The Late Pleistocene sediments comprise the Younger Dryas and the deepest recovered sediments likely date back to the Allerød interstadial. Within the Holocene, six different periods are observed in the core and borehole logging data, showing distinct physical property fluctuations and an overall increase in sedimentation rate upcore. Lake Hallstatt provides a unique prehistoric archive, being located within the UNESCO World Heritage area Hallstatt–Dachstein/Salzkammergut, a region with a rich history of human salt mining dating back to 3400 cal BP (Middle/Late Bronze Age) and one of the oldest documented cultural landscapes worldwide.

Yanovstan formation of Western Siberia: Lithology, structure, and correlation of deposits

Research subject. Yanovstan f ormation ( J3-K1jnv) of Kimmeridgian-Early Beriasian age. Aim. To identify structural features of the Yanovstan formation, to carry out a detailed correlation of its deposits, including the development of criteria for determining the boundaries of the suite. Materials and methods. The studies were carried out on the basis of borehole data, including core material from 5 boreholes and borehole logging data from 209 boreholes. The borehole logging complex comprised the following methods: gamma ray logging, neutron gamma ray logging, acoustic logging, caliper logging, as well as apparent resistivity and self-polarization logging. The borehole sections were correlated by tracing individual sections of the geological section, which are characterized by relatively stable geophysical parameters. Additionally, a sequence stratigraphic approach was used. Results. The boundaries between the Sigov and Yanovstan formations were identified based on the description of core material and its comparison with the borehole logging data. The Yanovstan formation was subdivided into three units proposed by the authors: lower (ЯНв), middle (ЯНб), and upper (ЯНa). A borehole correlation of the units of the formation was carried out, on the basis of which maps of the total thickness and net-to-gross ratio and the structural plan of each of the identified stratigraphic units were constructed. It was determined that the total thickness of the lower unit reaches 80 m and is characterized by maxima within the eastern part of the study area. The thickness of the upper unit reaches 240 m and is identified within the northeastern part of the area. This part is represented by a predominantly clay composition. The total thickness of the formation as a whole varies from 40 m in the west to 320 m in the northeast. The thicknesses of the middle unit are relatively consistent throughout the study area. The sandiness of the lower unit varies from 0 to 0.27 units; the upper ranges within 0–0.45 units. The middle unit is not characterized by the presence of sandstones. Conclusions. The theory about the supply of sedimentary material during the sedimentation of the suite from paleomounts within the eastern edge of the West Siberian Jurassic paleobasin was confirmed. An assumption was made that the increased thickness of the predominantly clayey suite within the northeastern part of the study area is associated with the redistribution and transfer of terrigenous material carried from the Siberian land by currents moving unidirectionally along the coast (counterclockwise). These currents thus seized the lightest (clayey) material and transported it to the northern part of the basin.

A case study of petrophysical prediction using machine learning integrated with interval inversion in a tight sand reservoir in Egypt

This study presents a new algorithm for reservoir characterization using borehole logging data, which integrates unsupervised machine learning techniques and interval inversion to automatically determine layers’ boundaries and petrophysical parameters. The research aims to reduce the time and manual input required for borehole inversion to estimate petrophysical parameters. The algorithm was used to predict different layer boundaries of sand-shale intercalations for both synthetic and field wireline log data. Field well logging measurements were obtained from an oil and gas field in Egypt, specifically the Jurassic reservoir. The reservoir is composed of a dense sandstone layer with significant heterogeneity due to diagenesis, which converts kaolinite into illite. The algorithm was used to predict petrophysical parameters, resulting in a decrease in porosity and permeability. The field data from the well reveals that the reservoir is made up of varying-quality sandstone, impacting storage capacity and hydrocarbon saturation. The algorithm demonstrates consistent convergence of the data at 7.5%. Overall, the integration of the new cluster technique and interval inversion can improve the time-intensive and laborious process of borehole data inversion to estimate petrophysical parameters.

Semi-automated Rock Layer Recognition from Borehole Log Data Using Combined Wavelet and Fourier Transform: A Case Study in the KG basin, India

Abstract The accurate identification of rock layer interfaces from wireline logs is one of the crucial issue of geological interpretation as we face difficulties in traditional interpretations due to the presence of various kind of high and low frequencies in the log data. Determination of rock boundaries in shallow marine sediments is very important to understand several issues related to the exploration of conventional and non-conventional hydrocarbons. Presently a combined wavelet and Fourier transform-based approach was demonstrated to discriminate the rock layers from wireline log data in Krishna-Godavari basin, which were acquired during the India National Gas Hydrate Program Expedition 02 (NGHP-Exp.-02). Initially, we selected the suitable mother wavelets and optimum level of decomposition to perform the wavelet transform by computing the error between the original log signal(s) and approximation coefficients (cA’s) of the decomposed signal(s) at several decomposition levels. Subsequently, discrete wavelet transform (DWT) of a particular decomposition level was applied to the log signals to obtain the detail coefficients (cD’s), which contain the high-frequency components of the log signals. Further, these high-frequency components of the log signals were utilized in frequency spectrum-based filtering approaches. This approach was adapted to yield information about the abrupt changes occurring in the log signals across the studied depth interval. The combined application of Fourier and wavelet transforms to shallow marine log data demonstrates that this approach is an efficient tool for delineating rock layer boundaries.

Application of Geophysical Technique in Delineation of Marble Deposit in Ikpeshi, Edo, Nigeria

The increasing demand for mineral substances and the need to maintain the current consumption pattern require constant research for new deposits or studies to expand exploration reserves. A geophysical technique was employed in the delineation of this mineral deposit. The results obtained in each VES have three geo-electric layers, which comprise clay/clayey-sand (81.8 – 155.7 Ωm), Sand (101.8 – 380.4 Ωm) and marble (1019 – 4419 Ωm) horizon units. The geologic section was deduced from borehole log data acquired within the study area. All the surveyed locations show traces of the existence of marble deposits in the area. The study revealed occurrences of marble deposits in the study area, which will be of economic importance if exploited. The reserve tonnage was calculated to be about 1.69 x 10⁶ tons. This estimate signifies that there is a fair reserve of marble within the study portion of the location.

Shear-wave velocity imaging of weathered granite in La Campana (Chile) from Bayesian inversion of micro-tremor H/V spectral ratios

Subsurface imaging of the regolith layer is an important tool for weathering zone characterization. For example, the extent of bedrock modification by weathering processes can be modelled by means of differing seismic velocities. We acquired a 360 m-long seismic profile in central Chile to characterise weathering at a semi-arid site. We used 87 3-component geophones, which continuously recorded ambient seismic noise for three days. The seismic line was centered at an 88 m deep borehole, providing core and downhole logging data for calibration. We extract Horizontal-to-Vertical Spectral Ratio (HVSR) curves along the seismic line to image the subsurface. Temporal analysis of the HVSR curves shows that the ambient noise vibrations recorded during the nighttime provide more stable HVSR curves. The trans-dimensional Bayesian Markov chain Monte Carlo (McMC) approach was used to invert the micro-tremor HVSR curves at each station to reconstruct 1D shear-wave velocity (Vs) models. The resulting individual 1D Vs models were merged to create a 2D Vs model along the linear seismic array in La Campana. The resulting Vs model shows an increase from 0.85 km/s at the surface to ca. 2.5 km/s at 100 m depth. We use the interface probability as a by-product of the Bayesian inversion to apply a more data-driven approach in identifying the different weathering layers. This method identified the boundary between saprolite and fractured bedrock at 42 m depth at the borehole, as evidenced by the interpretation of downhole logging data such as magnetic susceptibility. The resulting 2D Vs model of this site in Mediterranean climate shows a strong correlation between the interpreted weathering front at around 90-m depth and a higher precipitation rate in the study site compared to arid sites. The horizontal alignment of the weathering front indicates a correlation between the weathering front depth with topography and fractures in the bedrock.

The distributions and variations of Quaternary Thames River Terrace deposits of Greater London

A database containing c. 27 000 records of Quaternary lithostratigraphy extracted from c. 5800 boreholes drilled to a variety of depths has been compiled from information contained in logs recorded and held by the British Geological Survey (BGS) and from the Crossrail project. After ‘cleaning’ and quality assessment the raw borehole log data have been investigated for patterns in distribution, and variations in the Quaternary facies across Greater London. In particular, the analysis of Quaternary River Terrace Deposits has been focused on here and a summary of relevant published terminology and nomenclature is also included in this Technical Note, as an aid to understanding. The spatial distributions of each major Quaternary lithostratigraphic interval, as identified in the log descriptions, are also presented as point locations in map form, and in comparison with the corresponding BGS mapped outcrop patterns of the respective lithostratigraphic units. The presence of various specific clasts in the log descriptions (e.g. cobbles and chalk clasts) is also presented at stratigraphic member levels against their apparent source outcrops. For instance, cobbles recorded from the Boyne Hill Terrace intervals are concentrated in the eastern outcrops and reflect the Wealden source and former river system of the Darrent–Wid towards the Essex coast at Maldon. Similarly, the presence and distribution of shell and chalk clasts within river terrace sands and gravels reflect the geology of the underlying subcrop strata of Lower Shelly Clay and Chalk respectively. The Crossrail data also include some grain-size information from sieve analysis and some engineering in situ test values, which require careful analysis beyond the scope of this work but are potentially useful. The grain-size distributions for some of the samples from the river terrace sands and gravels show fining-up and coarsening-up sequences, and geographical grain-size trends in various stratigraphic intervals. The recorded presence of faults, fractures and fissures, as identified by the drilling contractors or logging geologists, is also extracted and mapped. Supplementary evidence, from repeated stratigraphy or improbable spatial proximity changes in subcrop depths, suggests a cause other than deposition for such changes and, on the presumption that their cause is natural, is interpreted as likely to be representative of faulting of some kind, including low-angle thrust faults. Faulting is also considered to have controlled the distribution of several interglacial silt members and is the subject of considerable research in the deeper intervals of London stratigraphy, so is only briefly dealt with here. To define the period over which tectonic structures, now known to exist within the strata of the London Basin, were active requires an analysis of Quaternary deposits that overlie them. This Technical Note provides an initial review of the data available from boreholes for such work and for any other studies requiring knowledge of these deposits. Supplementary material : Spreadsheets (and other files), and notes on the name and significance of each, are available at https://doi.org/10.6084/m9.figshare.c.6700313 Thematic collection: This article is part of the Geology of London and its implications for ground engineering collection available at: https://www.lyellcollection.org/topic/collections/geology-of-london-and-its-implications-for-ground-engineering

A novel approach for water reservoir mapping using controlled source audio‐frequency magnetotelluric in Xingning area, Hunan Province, China

AbstractControlled source audio‐frequency magnetotelluric is frequently used in association with other geophysical methods, especially in complex geological areas to highlight geological structures such as water reservoir rock. Although it gives satisfactory results, combining several methods requires time and expense. In addition, despite this combination, several drilling locations proposed after geophysical investigations were inaccurate, resulting in many unsuccessful drillings. The latter occurs due to the difficulty to emphasize the fracture zones properly. To work around this problem, we proposed a novel approach called pseudostratigraphic to reduce the repercussion of unsuccessful drilled boreholes and to demarcate the water reservoir rock. The technique consists to discretize the resistivity of the inverted OCCAM2D model based on the true layer resistivities collected from the borehole log data (observed layers). The discrete resistivity model is known as the new resistivity model. It is used to generate the pseudostratigraphic log at each station by pseudo‐demarcating the thicknesses of the observed layers with a low margin of error. Moreover, the combination of multiple new resistivity models from different survey lines creates a three‐dimensional pseudostratigraphic map useful to emphasize the water reservoir rock. The pseudostratigraphic implementation is carried out in the Xingning area as a real‐world case study. The results show that the intersection of the main fault (F1) and the conductive zones (≤100 Ω m) indicates the potential water reservoir rock. Its thickness is estimated around 150–600 with an error equal to ± 7°m. Based on the three‐dimensional pseudostratigraphic map, the water found in the fracture zone located under the reservoir rock is considered much hotter due to the intense geothermal activity along F1, thereby making it a better place for hot water exploitation. Finally, the pseudostratigraphic technique could be an innovative and cheap strategy to find groundwater reservoirs in complex geological areas.

Hydraulic conductivity of the crystalline crust: Insights from hydraulic stimulation and induced seismicity of an enhanced geothermal system pilot reservoir at 6 km depth, Espoo, southern Finland

We analyze hydraulic stimulation data from the St1 Deep Heat Project, which comprised drilling wells to >6 km depth in crystalline rock in southern Finland with an aim to study the conditions for an Enhanced Geothermal System. Combining the stimulation and borehole logging data with induced seismicity results allows for a comprehensive analysis of hydraulic conductivity at rarely tested depths of 5 – 6 km. Hydraulic conductivity was observed to be pressure-dependent, heterogeneously distributed and affected by pre-existing fractures and lithological variation. The pre-stimulation formation fracture frequency is in the range of 0 – 8 m−1 with an average of 1.9 m−1. Only a small fraction of the fractures were open and conductive implying a hydraulically heterogeneous medium. The average natural hydraulic conductivity derived from leak-off tests and well tests before stimulation and from cross-hole pressure data is of the order of 5 0·10−10 - 5 0·10−9 m/s (permeability 1· 10−17 – 1·10−16 m2), which is in agreement with permeability models for the brittle crystalline crust at this depth. Hydraulic stimulation increased conductivity to 10−8 – 10−7 m/s, but it gradually decreased back to the natural level after pressure release. Stimulation generated five micro-earthquake clusters at 4.8 – 6.3 km TVD depth. Hydraulic connections between clusters were apparently not attained. The project generated extensive experience and data sets regarding deep drilling, hydrogeological properties, and seismic response to stimulation of crystalline rock in the upper continental crust. Hydraulic conductivity turned out to be the most challenging issue for the St1 EGS development and the EGS project is not continued at the moment.

Delineating the main structural outlines and the petrophysical properties of the Albian-upper Cretaceous Reservoirs using seismic and well log data, Shushan Basin, north Western Desert, Egypt

This study concerns with delineating and analyzing the subsurface structural setting of Khalda Oil Field at Shushan Basin as a key factor for evaluating the petrophysical properties and the deliverability of the Bahariya Formation. Shushan Basin is considered one of the most prospective basins in the Western Desert. The oil is trapped within a gentle seismically defined anticline that contains a series of coastal sandstone reservoirs interbedded with a neritic and tidal flat mudstone and a few carbonate interbeds of the Albian-Cenomanian Bahariya Formation forming multiple oil-bearing sandstone reservoirs. A set of borehole logging and seismic data were available, tied, processed, and mapped to delineate the predominant structures in the study area. Results show the implication of the NW–SE, NE–SW, and E–W gravity faulting on the Bahariya and the overlying Abu Roash formations. This set of gravity faults is attributed to the Mesozoic tensional stresses. The depth structure contour maps on the upper surfaces of the Lower and Upper Bahariya members reveal the presence of some NE–SW gravity faults that dissected the Khalda Field into some slightly tilted blocks, shallowing in depth to the south as deepening to the north. Besides, the study area has been affected later in the Jurassic by E–W gravity faults during the Atlantic Ocean opening. This faulting trend was changed later into the NE–SW direction as a result of the movement of North Africa against Laurasia. The petrophysical analysis indicated that the Lower Bahariya sandstone reservoir has a good reservoir quality (16 ≤ ∅ ≤ 25%, 53 ≤ Sw ≤ 59%, 6.0 ≤ Vsh ≤ 32.2%, and good net-pay thickness 18.0–38.0 ft). It is revealed that the drilled wells penetrating the crest of the anticline are prospective while that located in the anticline flanks are water-bearing recommending exploration away from the anticline flanks. By applying this workflow, it is possible to explore for the similar subsurface hydrocarbons-bearing sequences in the Western Desert and North Africa in future exploitation plans.

Characterization Of Lojing Hot Springs, Gua Musang, Kelantan From Geosciences Aspects

The study was conducted to identify and determine the relationship between geology, geophysics and geochemistry of the study area. Geophysical surveys were conducted to obtain the sub-surface profile and to relate it with lineament analysis. Based on gravity method analysis, it is interpreted that the study area consists of granite bedrock close to the surface which exhibits high gravity anomalies whereas low density rock areas with high fractures and lineaments exhibit low gravity anomaly values. The electrical resistivity survey shows that the study area is underlain by granite bedrocks which also proves that the origin of the hot springs are non-volcanic as no volcanic activity or rocks can be found around the study area. Resistivity values recorded for granite bedrock exceeded 900 Ωm. Based on the resistivity profile, it is also possible to determine the reservoir zone and fractured zone which shows the resistivity values between 0 Ωm to 250 Ωm. The direction of the lineaments on the resistivity profile together with gravity survey are parallel to the lineament analysis, which is Northeast-Southwest, Northwest-Southeast and North-South. The borehole log data also shows that the study area is underlain by granite bedrock and the hot water source in this area is from confined aquifer. Geochemical and geothermometry analysis were performed on 14 hot water samples. The results of geochemical analysis show that the average elements concentration is as follows; silica 277 ppm, calcium 2.00 ppm, magnesium 0.14 ppm, potassium 2.3 ppm, sodium 29 ppm, iron 0.12 ppm, bicarbonate 41 ppm, sulphate 18 ppm, chloride 1.5 ppm and fluoride 2.9 ppm. The calculation results of quartz geothermometry shows an average temperature of 203°C, while chalcedony geothermometry shows an average temperature of 177°C. The enthalpy for heating water calculated from quartz geothermometry using the Steam Table shows an average of 864 kJ/kg which can be interpreted as a mid-level enthalpy. The geology of the hot springs area shown in the geological map and lineament analysis map proves the relationship with the geophysical survey and borehole log data.

The effects of planar structures on reservoir quality of Triassic Kangan formation in the central Persian Gulf, an integrated approach

Planar structures including stylolites, solution seams, dense streaks, bedding and cross-bedding surfaces, and fractures of carbonate Early Triassic Kangan Formation were evaluated in the central Persian Gulf. Core X-ray computed tomography (CT), Fullbore Formation Micro-Imager (FMI) log, and cores were used to detect the structures. Furthermore, conventional borehole logging data, routine core analysis, and petrographic thin sections were employed to assess the reservoir properties. Stereographic projections demonstrated that the reservoir has two sets of planar structures. The first group contains shallowly-dipping structures, consisting of stylolites, solution seams, dense streaks, bedding and cross-bedding surfaces. These structures have been created by sedimentary and diagenetic processes. The other set includes deformation-related structures that are steeply-dipping and occurred scarcely, like fractures. Spearman correlation coefficients between the frequency of each planar structure and reservoir characteristics (porosity and permeability) were calculated to reveal the numerical relationship between the parameters. The significant correlation coefficients indicate that stylolites, solution seams, and filled tension gashes diminish reservoir quality while bedding and cross-bedding surfaces have enhanced reservoir characteristics. The strongest correlation was observed as a strong negative relationship between the frequency of stylolites and permeability in K2 reservoir unit. This study implies that sedimentary and diagenetic factors are more effective in controlling the reservoir quality than deformation factors in the studied formation. The present work also indicates that each used method has unique advantages and disadvantages. Therefore, simultaneous utilization of the methods to investigate planar structures would have the best efficiency.

Lithofacies discrimination of the Ordovician unconventional gas-bearing tight sandstone reservoirs using a subtractive fuzzy clustering algorithm applied on the well log data: Illizi Basin, the Algerian Sahara

The main objective of this paper is to prove the capability of the fuzzy clustering algorithm for discriminating between lithofacies that are derived from the borehole log data of Ordovician tight sandstone reservoirs in the Illizi Basin of the Algerian South-Eastern Sahara. The technique is based on applying an unsupervised machine learning fuzzy algorithm on the natural gamma-ray, the photoelectric factor, the sonic log, the neutron porosity, and the bulk density well log data as an input to discriminate lithology into four lithofacies types: clay, sand, clayey sand, and sandy clay. The primary advantage of the fuzzy algorithms is that they can handle uncertainties and errors associated with the inaccurate or incomplete data of any measurements. Furthermore, it has a broader scope and a higher level of generality than the binary logic, which means that the results and interpretations that are based on this approach can be more appropriate and probable than other possible interpretations. A comparison between our algorithm's results and the results from the Kohonen Self-organizing Maps (SOM) and the Multilayer Perceptron (MPL) has also been carried out which proved that our approach provides better results than the other commonly applied neural networks. The obtained lithofacies types are highly comparable with that obtained from the core description data with minimal estimated errors. Therefore, this fuzzy algorithm can be applied as an alternative, fast, and low-cost technique for adequate lithofacies discrimination in case of lacking the core data.

An astronomical age-depth model and reconstruction of moisture availability in the sediments of Lake Chalco, central Mexico, using borehole logging data

Understanding the moisture history of low latitudes from the most recent glacial period of the latest Pleistocene to post-glacial warmth in continental tropical regions is hampered by the lack of continuous time series. We conducted downhole spectral gamma (γ) ray and magnetic susceptibility logs over 300 m of lacustrine deposits of Lake Chalco (Mexico City) to reconstruct an age-depth model using an astronomical and correlative approach, and to reconstruct long-term moisture availability. Our results suggest that the Lake Chalco sediments contain several rhythmic alternations with a quasi-cyclic pattern comparable to the Pleistocene benthic stack. This allows us to calculate a time span of about 500,000 years for this sediment deposition. We developed proxies for moisture, detrital input, and salinity, all based on the physical properties of γ-ray spectroscopy and magnetic susceptibility. Our results indicate that Lake Chalco formed during Marine Isotope Stage 13 (MIS13) and the lake level gradually increased over time until the interglacial MIS9. Moisture content is generally higher during interglacials than during glacials. However, two periods, namely MIS6 and MIS4, have higher moisture contents. We developed a model by comparing the obtained moisture proxy with climatic drivers, to understand how different climate systems drove effective moisture availability in the Chalco sub-basin over the past 500,000 years. Carbon dioxide, eccentricity, and precession are all key drivers of the moisture content of Lake Chalco over the past 500,000 years.

Determination of the Aquifer and Its Hydraulic Parameters Using Vertical Electrical Sounding, Borehole Log Data and Borehole Water Conductivity: A Case Study of Olbanita Menengai Area, Nakuru, Kenya

Development of groundwater needs the capabilities to distinguish the different aquifer layers found in a region, and thereafter the parameters which can be used expressly to define the aquifer type. The past studies in the Olbanita sub-basin have accorded the area as having one aquifer, which has resulted into generalization of the aquifer parameters. The objective in this study is to map the main aquifer layer and determine its parameters. The use of modeled geoelectric layers from Vertical Electrical Sounding (VES) data has been used in the study area to distinguish the major aquifer from the minor ones. There is noted an excellent correlation between the geoelectric layers and the lithologies as outlined by the driller’s log clearly delineating four aquifer stratums. The main aquifer is identified to be geoelectric layer 11 and 12, defined by a thickness of 30.18 m mainly of tuffs, and 17.39 m mainly of weathered phonolites. Hydraulic conductivity of the main aquifer averages value of 17.16389314 m/day, in consideration of the ranges 0.248690465 m/day to 74.62681942 m/day for the 31 VES points. For the aquifer breadth of 30.18 m, the Transmissivity values vary from a minimum of 57.32119 Ωm2 to 53365.49 Ωm2 and for 47.57 m breadth, the range is between 11.83021 Ωm2 and 1390.921 Ωm2. The variance of longitudinal unit conductance shows that 63.15 percent of the aquifer represented by one lithology is having lowest values of S (-1), an indication that the resistivity values of these points are relatively high when compared to their corresponding breadths. Notably, where the geoelectric layer is represented by more than one lithologic layer, the longitudinal unit conductance has high values of S (~1.1 - 5.3 Ω-1) at about 83.33 percent of the aquifer, thus giving a manifestation that a change in lithology has an implication in the aquifer characteristics. The transverse resistance values have a direct proportionality to both the aquifer layer thickness and the geoelectric layer resistivities. Evidently, using the close range of resistivities record indicates that indeed transverse resistance increases with increase in aquifer thickness. For example, for resistivities 52.677 Ω, 54.78 Ω, 54.297 Ω, 57.819 Ω, and 51.85 Ω, for 30.18 m, 47.57 m, 136.35 m, 190.84 m, 277.93 m thicknesses respectively, have their correlated transverse resistances values notably rising incrementally, from 1589.7919 Ωm2, 2605.8846 Ωm2, 7403.396 Ωm2, and 11034.178 Ωm2 correspondingly. There is confirmation that the modeled VES data can help map aquifers despite the limited resources of borehole logs that can used as control points.

Borehole logging and seismic data from Lake Ohrid (North Macedonia/Albania) as a basis for age-depth modelling over the last one million years

Robust age-depth models are essential for developing sophisticated interpretations of the sedimentological history in lake basins. In most cases, such models are created using an integrated geoscientific approach, including biostratigraphy, magnetostratigraphy and radiometric dating. In this study, we present an approach to construct age-depth models based on integrating downhole logging and seismic survey data when there are no samples available for dating. An example of this method is shown using data from Lake Ohrid (North Macedonia/Albania).First, we interpret seismic data and correlate downhole logging data from three sites - DEEP, Pestani and Cerava - to the LR04 benthic stack. We cross-check the resulting age-depth models using cyclostratigraphic methods, which deliver sedimentation rates that are on the same order of magnitude. The maximum age of the investigated sediments is based on lacustrine seismic marker horizons and is approximately 1 million years at DEEP/Pestani and 0.6 million years at Cerava.In the second step, we construct an artificial lithological log based on cluster analysis using the physical properties of the sediments and integrate it with the age-depth model. This allows an initial interpretation of the sedimentological history at Cerava and Pestani.Our methodological approach cannot substitute classical sediment core investigations, but we suggest that this two-step approach be applied to future projects of the International Continental Scientific Drilling Program. It can rapidly provide preliminary results on age and sediment type and is particularly useful when datable material is not available.