Lithologic Logs Research Articles

Geophysical Modeling and Hydrostratigraphic Study for Assessment of Groundwater Sustainability in Southern Part of Thal Doab, Punjab, Pakistan

ABSTRACT Groundwater resources across the country are swiftly heading towards depletion and quality deterioration. This study extensively examines the geological and hydrostratigraphic complexities in Thal Doab area, Punjab, Pakistan offering valuable insights into its subsurface lithology and groundwater quality. Data from twenty five (25) Vertical Electrical Soundings (VES) using Schlumberger electrode configuration were carefully analyzed, and calibration of resistivity models was performed by comparing them to lithological borehole logs to ensure their accuracy. The study establishes a fundamental connection between subsurface lithology and resistivity values, revealing four to six geo-electric sub-layers comprising the intermixing of clay, silt, sand, gravel, and kankar inclusions. These layers exhibit resistivity ranging from very low (<20 Ω-m) to very high (>230 Ω-m) at various depths. 2D/3D aquifer models identify the higher resistivity areas with promising good-quality groundwater primarily within sand, gravel, and kankar layers, while lower resistivity values indicate marginally suitable or saline/brackish groundwater within fine sediments like clays/silts. Groundwater quality improves significantly at depths below 75 m, suggesting sustainable water extraction potential. However, caution is advised while drawing water from depths below 50 m due to the presence of saline or brackish water, posing challenges due to limited recharge potential. The study emphasizes the importance of Indus and Chenab rivers, canal systems, and precipitation in the processes that recharge groundwater.

Revisiting the Stratigraphy and Structure of the Faroe Islands Flood Basalts for Large‐Scale CO2 Storage in Basalt Reservoirs

ABSTRACTComprehensive mapping of the stratigraphy and structures is essential when exploring basaltic reservoirs for CO2 storage. A major task in analysing the storage potential of the reservoir is to bring all relevant geological data within a single framework for integration and joint interpretation. In this study, we illustrate how data integration facilitates an improved understanding of the geological evolution of the Faroe Islands, the North Atlantic Igneous Province, and how the data integration forms a foundation for future carbon capture and storage campaigns. We have integrated new and existing data including geological field observations, digital elevation models, digital outcrop models, lithological logs, seismic profiles, and bathymetry in a single, consistent, and quality‐controlled toolbox. Two key findings are that (a) we have mapped stratigraphic markers in the central Faroe Islands across the islands, and there is no indication of large‐scale strike‐slip faults that offset the volcanic stratigraphy; (b) our analysis provides no clear onshore evidence of transfer zones in the Faroe Islands. We show that a high density of data and integration of data types across different vertical and horizontal scales is crucial for mapping the highly heterogeneous basaltic reservoir.

Seismic and geomechanical characterization of Asmari formation using well logs and simultaneous inversion in an Iranian oil field

This paper presents a case study on the application of simultaneous inversion (SI) technique and well log analysis to accurately seismic-geomechanical characterization of Asmari formation in an Iranian oil field. To achieve this goal, a one-dimensional (1D) prediction of geomechanical properties such as Young’s modulus (E), bulk modulus (K), shear modulus (), Poisson’s ratio (PR), Vp/Vs ratio and brittleness (BRI) was first generated from the analyzing the well log data. In the next step, the spatial distribution of the geomechanical parameters in the reservoir area was predicted on the basis of the results of the simultaneous inversion. Lithological facies discrimination and fluid detection of the Asmari formation were performed using simultaneous inversion of pre-stack seismic data and conventional cross-plotting analysis of well data. To accomplish this objective, elastic and geomechanical parameters were cross-plotted against conventional petrophysical logs along with BRI, water saturation (Sw), gamma ray (GR), acoustic impedance (Zp), , and lithology logs such as quartz and calcite volumes. As a result of this work, two reservoirs were identified in the Asmari formation: sandstone and carbonate. The carbonate reservoir consists predominantly of calcite and dolomite, with minimal shale content, while the sandstone reservoir is mainly composed of shale and contains less quartz. In addition, the carbonate section within the Asmari formation exhibits better reservoir quality due to lower water saturation and higher porosity compared to the sandstone zone. To determine the type of fluid in the Asmari formation of the studied oil field, LMR (lambda-mu-rho) scatterplots were employed in both well and seismic domains. The findings reveal that the sandstone reservoir in the Asmari formation is water-saturated, while the carbonate reservoir is oil-saturated. Furthermore, a gas cap is present at the top of the Asmari formation.

Identifying the Jeribe Formation Interval in the Khurmala Dome Field Using Lithology and Gamma-Ray Log Correlation Analysis

The Middle Miocene-aged Jeribe Formation is an important reservoir in many of Iraq's oilfields. This study identifies the Jeribe Formation in several drilled wells at the Khurmala Dome Field using gamma-ray log and lithology analyses, comparing gamma-ray log analysis for the Jeribe Formation of a subset of wells at Khurmala Dome Field and two wells from Jari Pika Field and Taza Field. The lithology analyses of selected wells at Khurmala Field, along with the formation’s lithology, were studied at local types and other locations, which indicates the presence of the Jeribe Formation. The analysis results denoted its lateral continuity, lithology similarity, and thickness variations over location differences for the formation at selected wells of the Khurmala Dome Field. Both gamma-ray log and lithology analyses determined the interval's top, bottom, and thickness. Future studies should include biostratigraphy, correlation with wells drilled in the north part of the Khurmala Dome, gas and hydrocarbon analyses, and reservoir modeling to evaluate the amount of hydrocarbons within the formation.

Lithology and minerals identification from well logs for Mishrif Formation in Ratawi oilfield

Lithology identification plays a crucial role in reservoir characteristics, as it directly influences petrophysical evaluations and informs decisions on permeable zone detection, hydrocarbon reserve estimation, and production optimization. This paper aims to identify lithology and minerals composition within the Mishrif Formation of the Ratawi Oilfield using well log data from five open hole logs of wells RT-2, RT-4, RT-5, RT-6, and RT-42. At this step, the logging lithology identification tasks often involve constructing a lithology identification model based on the assumption that the log data are interconnected. Lithology and minerals were identified using three empirical methods: Neutron-Density cross plots for lithology identification, M-N cross plots (also known as Litho-porosity cross plots) for mineral identification, and Matrix identification (MID) plots. Neutron-density cross plots show that the Mishrif formation consists of limestone with some data points tending to the dolomite line east of the field and to the sandstone line west of the field. The M-N and MID plots indicate that calcite is the major mineral for the Mishrif formation; however, quartz grows to the west of the area while dolomite increases to the east. These findings underscore the importance of integrating multiple well-log interpretation techniques to capture lithologic and mineralogical complexity, providing critical insights for reservoir management and targeted exploitation strategies in heterogeneous carbonate systems.

A study of geophysical techniques for identifying collapsible soil strata

ABSTRACT This study evaluates the effectiveness of four geophysical techniques—2D electrical resistivity tomography (ERT), 2D induced polarization (IP), 2D multi-channel analysis of surface waves (MASW), and downhole seismic tests—for determining the thickness of collapsible soils at two test sites. The 2D ERT survey is the most effective in accurately delineating vertical and lateral soil boundaries. This conclusion is validated by lithologic logs from boreholes and an excavated pit. The 2D MASW survey is the second most effective, followed by shear wave results from downhole seismic tests. In contrast, the 2D IP survey and compressional wave data from downhole seismic tomograms yield less distinct and more ambiguous soil boundaries. However, the 2D IP survey is useful for mapping clay content distribution within the subsurface. The non-destructive 2D ERT, 2D IP, and 2D MASW techniques provide high-resolution vertical and lateral subsurface coverage, potentially reducing the need for extensive borehole drilling.

Bacteria as paleoenvironmental proxies: the study of a cave Pleistocene profile

Abstract. Caves are well-known archives that preserve valuable information about the past, relevant for reconstructing past climates and environments. We sampled sediments from a 480 cm deep profile, and 16S ribosomal ribonucleic acid (rRNA) gene-based metabarcoding analyses were undertaken that complemented lithological logging, sedimentology, and optically stimulated luminescence (OSL) dating. These analyses revealed different sedimentation conditions along the profile with various water inputs. The OSL age of the sediments places the profile between 74.7 ± 12.3 to 56 ± 8 ka (base to top). However, the more recent Last Glacial Maximum (LGM) paleofloods might have occurred in the upper and lower passages of the cave. Bacterial compositions changed with depth, from soil bacteria (present in the upper part of the sediment profile) to thermophilic/sulfurous bacteria (abundant in the deeper samples of the profile). Considering the thermophilic bacteria, we could only assume their origin from a surface of hot sulfurous springs, old thermal springs, or sapropel sediments.

Rapid groundwater assessments in gneissic settings using transient electromagnetics — Examples from Togo

Towed transient electromagnetics (tTEM) is applied in the Plateau Region of Togo for rapid and high-resolution characterization of groundwater systems surrounding six villages. Past drilling efforts in the region often resulted in unsuccessful or low-yielding boreholes, due in large part to sparse hydrogeologic data at the scale relevant for borehole siting surrounding each village. Towed transient electromagnetics systems are shown to be well suited to addressing this data sparsity issue, enabling the mapping of large regions surrounding each village in relatively short field times (two days per village in this work). Comparison with borehole lithology logs reveals that a towed electromagnetic system can accurately characterize the thickness of the weathered zone in gneissic settings, as well as delineate elevated saturation fractured zones within the gneissic bedrock in several cases. Boreholes drilled based on tTEM surveys were able to intercept fresh groundwater resources in each of the investigated villages.

Analysis of soil bearing capacity based on soil mechanics and geophysics data in Suppa, Pinrang Regency, South Sulawesi

Abstract The exposure of highly weathered rocks at the research location will affect the strength of the rock so a geological and geophysics approaches to creating subsurface lithology will make it easier to analyze the bearing capacity of soil in Suppa, Pinrang regency. The research aims to analyze subsurface lithology and soil bearing capacity based on correlations between soil mechanics and geophysics data. Data used in this research are the measurement of vertical electrical sounding (VES) Schlumberger configuration with one track, drilling, laboratory tests (test of shear strength, volume weight, specific gravity, and sieve analysis), and megascopic description of rocks. Terzaghi’s theory on the foundation (continuous, square, and circular) is used for the analysis of soil bearing capacity. Correlation of drill data with geoelectrical data and electrical logging lithology of the study area interpreted at a depth of 0-2.1 m silt sand, 2.1-7.2 m depth of clay, and 7.2-70 m depth of volcanic breccia. The results of the ultimate soil bearing capacity analysis on the first sample of silt sand (continuous, square, and circular foundations, 50-400 m wide) is 147.48 – 427.11 kg/cm2 are classified as very good condition. The second sample with the value of ultimate soil bearing capacity of 72.63 - 109.07 kg / cm2 is classified as a medium - good condition. Based on these results, the first sample has a higher soil bearing capacity than the second sample. Circular foundations have the greatest soil bearing capacity, so a circular foundation is recommended at that location.

A comparative petrophysical evaluation of the Abu Roash, Bahariya, and Kharita reservoirs using well-logging data, East El-Fayoum, Egypt

The exploration and development of hydrocarbon resources in the Western Desert require more continuous activities. The Silah is a newly discovered field in this region. Therefore, this study emphasizes the application of petrophysical evaluation to sandstone and carbonate reservoirs from the late and early Cretaceous. These formations are the most potential hydrocarbon reservoirs in the studied area as a part of the western desert. Additionally, this study involves a comparative evaluation of the Abu Roash, Bahariya, and Kharita reservoirs using well-logging data by applying different cross-plots that are used for determining different petrophysical parameters such as shale volume, porosity, fluid saturation, permeability, and net-to-gross ratio. These logs are gamma-ray (GR), calliper, resistivity (RLA5, RLA3, and RXOZ), photoelectric effect (PEFZ), neutron (APLC), and density (RHOZ). These plots agree with the results deduced from the interpretation of lithologic logs. Fourteen hydrocarbon-bearing zones are identified in the Silah field. Only two zones, namely, Zone 2 in Silah-15 and Zone 1 in South Silah-1X, are considered the best for hydrocarbon generation. These zones are characterized by low to moderate shale volume, moderate to high total porosity, good effective porosity, low water saturation, and high net-to-gross ratio. These zones lie in the Abu Roash/F member. These deduced points prove that the Abu Roash/F member can be an abundant hydrocarbon reservoir. This member in the Silah field appears to be a promising hydrocarbon reservoir because it matches the petrophysical parameters of the investigated zones and others in the northwestern Desert. This suggests that there may be reservoir continuity and similarity.

Application of electrical resistivity tomography for groundwater evaluation in Yirgacheffe Town and its environs, Main Ethiopian Rift

Application of electrical resistivity tomography for groundwater evaluation in Yirgacheffe Town and its environs, Main Ethiopian Rift

Helium in Rocks of Vindhyan Super Group around Sagar, South Ganga Basin, Bundelkhand Region M.P India

Studies on the exploration of the Helium gasin the rocks of the Vindhyan Super Group around Sagar, South Ganga Basin, Bundel khand region, M.P. is carried out in the detail with joint collaboration of Deptt. of Applied Geology and ONGC Energy Centre, Ahmadabad. As Author has already reported the Discovery og Helium has leakages through more than 50 tube wells/e wells excavated in agriculture fields various Villages in Sagar Distt. The geochemical analysis of the soil, gas and water indicates remarkable amount of Helium gas in these tube wells, containing about 0.45 to 0.735 and methane varying from 72 % to 99%. These investigations were done in the long research work (more then 25 years) dedication carried out in this area and research finding published in the Journal of National and International repute, which has attracted the officers/ Scientists of ONGC, Dehradun, CGWB, Faridbad, Atomic Mineral Directorate Hyderabad and Bhabha Atomic Research Centre Mumbai. The Result of the stable isotopic analysis of Ethane gas in these samples δ C13 value are ranging from -24.9 per mill w.r.t. PDB and -26.9 per mill w.r.t. PDB and the Methane gas are ranging from Isotopic Values -54.0- per mill w.r.t. PDB to -61.5 per mill w.r.t. PDB are indicative that this gas is of thermogenic origin, which must have been formed at very high temperature & pressure condition in the deeper horizon of the great Vindhyan sedimentary basin of late Proterozoic (>500m.y.) period. A reporting of leakages of above mentioned gas from 50 tubewells in the inliers of Vindhyan rocks and even in the Deccan trap rocks ensures that this area must be having a big gas reservoir within Vindhayn rocks around Sagar - Distt. in M.P. The ONGC energy Centre Ahmadabad has started the detail collaborative geophysical work on the drilling exploration upto the depth of 600 m has been carried out and to be carried out in various location from where the leakages of has been earlier reported earlier. In these 600 m deepdrill holes detail geophysical logging including the gama ray logging and Neutron logging, lithological and structural logging will be carried out to know the probable gas reserve and at what depth the, we can get the gas for the exploration and utilization of these ases for industrial purpose and other uses etc. The detail geophysical studies will be very much helpful in the gas reserve calculation and the depth of the gas pockes in the South Ganga Basin in Bundelkhand region in M.P

Inversion of induced polarization-affected electrical-source transient electromagnetic data observed in the groundwater survey from eastern Tibet, China

Recent advancements in the signal-to-noise ratio of transient electromagnetic (TEM) devices have highlighted the significance of induced polarization (IP) effects in areas containing polarizable materials such as clays or sulfide minerals. These effects are characterized by an abnormally rapid decay followed by late-time negative values in the voltage response, which often lead to unsatisfactory outcomes in conventional resistivity-only inversion workflows. Previous research demonstrates that incorporating the Cole-Cole complex resistivity model into an inversion workflow enhances the characterization of this phenomenon. In a recent hydrologic survey in eastern Tibet, China, significant TEM-IP-affected phenomena are observed during the implementation of an electrical-source TEM system to map the distribution of groundwater. In this instance, data from two representative survey lines are inverted using a modified quasi-2D regularized Newton inversion scheme that simultaneously extracted the direct current resistivity and three IP parameters: chargeability, time constant, and frequency dependence. The results reveal clear conductive polarization distributions against the resistive host, correlating well with groundwater-enriched weathered layers, as confirmed by borehole lithologic logs. Consequently, conductive polarization signatures are identified as potential key indicators of groundwater presence considering potential associations with clay and shale. This case study emphasizes the significance of accounting for potential IP effects in TEM surveys and highlights the advantages of multiparametric inversion for achieving more accurate results and enhancing the interpretation of subsurface properties.

Evaluating the productivity of basement rock aquifers for sustainable groundwater development in sub-Sahara Africa using borehole pumping experiments and geophysical data

Evaluating the productivity of basement rock aquifers for sustainable groundwater development in sub-Sahara Africa using borehole pumping experiments and geophysical data

Attention mechanism‐assisted recurrent neural network for well log lithology classification

AbstractLithology classification is a fundamental aspect of reservoir classification. Due to the limited availability of core samples, computational modelling methods for lithology classification based on indirect measurements are required. The main challenge for standard clustering methods is the complex vertical dependency of sedimentological sequences as well as the spatial coupling of well logs. Machine learning methods, such as recurrent neural networks, long short‐term memory and bidirectional long short‐term memory, can account for the spatial correlation of the measured data and the predicted model. Based on these developments, we propose a novel approach using two distinct models: a self‐attention‐assisted bidirectional long short‐term memory model and a multi‐head attention‐based bidirectional long short‐term memory model. These models consider spatial continuity and adaptively adjust the weight in each step to improve the classification using the attention mechanism. The proposed method is tested on a set of real well logs with limited training data obtained from core samples. The prediction results from the proposed models and the benchmark one are compared in terms of the accuracy of lithology classification. Additionally, the weight matrices from both attention mechanisms are visualized to elucidate the correlations between depth steps and to help analyse how these mechanisms contribute to improved prediction accuracy. The study shows that the proposed multi‐head attention‐based bidirectional long short‐term memory model improves classification, especially for thin layers.

Pattern recognition approach (PRA) for identifying oil reservoir lithology of Camaal oil field, Yemen

The accurate determination of reservoir lithology remains a challenge in petroleum engineering. There are some conventional techniques available to determine the lithology. However, the application of those techniques has been long and complex. So, the main goal of this study is to simplify the identification of reservoir lithology. This paper presents a Pattern Recognition Approach (PRA) to identify the reservoir lithology simply and accurately. It is type of artificial neural network. Four wells from the Camaal Field were chosen to develop this approach. Around 32400 data points from the previous wells were digitized. The PRA approach used depth, gamma ray, lithology, sonic, neutron, and density logs as inputs. The model classifies lithology into permeable and impermeable rocks, further categorizing them into clastic and carbonate rocks, and subsequently into specific types into sand, sandstone, dolomite and limestone. The results show that the proposed approach provides a suitable prediction of lithology with higher accuracy compared with actual lithology. The model demonstrates high accuracy rates in identifying various lithologies, with overall accuracies of 76.2% for permeable/impermeable rocks, 94.9 for clastic/carbonate rocks, 86.2% for sand/sandstone, and 92.8% for dolomite/limestone.

Evaluation of specific retention, specific yield, and storage-dependent drainability efficiency in a coastal milieu via geo-electrical technology

ABSTRACT The aim of this research was the application of geo-electrical technology in the determination of specific retention, specific yield, and storage-dependent drainability efficiency within a major coastal milieu in Nigeria. This improves on past work where expensive and time-intensive pumping tests were employed to determine specific retention and specific yield. In addition to the determination of these key aquifer geo-kinetic properties, other important aquifer characteristics such as aquifer potentiality, protectivity, and vulnerability to contamination within this major coastal system were determined. Geo-electrical technology employed Wenner and Schlumberger arrays to undertake Vertical Electrical Soundings (VES) and Electrical Resistivity Tomography (ERT) surveys and results obtained were constrained by ground truth from lithological logs. Results from the electrical resistivity surveys indicated that the lithological strata comprised motley topsoil, coarse sand, fine sand, and sandy clay. Measures of specific yield and specific retention were generated as secondary geo-electrical indices. Specific yield intersected with specific retention at 73% storage-dependent drainability efficiency (SDE), indicating that this percentage must be exceeded for optimal groundwater extraction from the rock matrix's pore spaces during pumping. Aquifer transmissivity measures indicated high aquifer potentiality; longitudinal conductance measures indicated poor aquifer protectivity implying increased vulnerability of the aquifer to contamination.

Estimation of Groundwater Potential and Aquifer Protective Capacity Within Old Ikenga Hotel, Nsukka, Enugu State, Nigeria

A geophysical survey using electrical resistivity method was conducted around Old Ikenga Hotel, Nsukka in Enugu State, Nigeria to investigate the groundwater potential and aquifer protective capacity of the area. The project area lies within latitudes 6°50'4.0''N – 6°57'52.0"N and longitudes 7°21'6.3"E – 7°28'12.0"E, and covers an area of about 89.6 km2. Vertical Electrical Soundings (VES) were carried out with a digital read out resistivity meter (ABEM SAS 1000). The VES points were marked at 25 m and 75 m along a 100 m line. A total of eight soundings were carried out in the area. The VES data collected were interpreted using INTERPEX software and the results presented in terms of resistivity, thickness, depth and lithology. The lithology was inferred by correlating the result to the lithology log of the borehole drilled in the hotel and the geology of the study area. The VES result shows lithologic layers varying from 4 to 5. Aquiferous sand and Aquiferous sandy shale constitute the aquifer units in the area at depth of 30.26 m to 188.20 m, with their thickness ranging from 30 m to 74 m as shown by their isopach map. The aquifer protective capacity was determined by calculating for longitudinal conductance and matching the values to known standards. The calculated longitudinal conductance varies from 0.0409 to 3.1235 mhos. The interpreted VES results reveal poor, moderate, good and very good aquifer protective capacities of the overburden layers.

PALYNOLOGICAL, PALEOENVIRONMENTAL AND PALEOCLIMATE ANALYSES OF EMI-5-WELL, OFFSHORE NIGER DELTA, NIGERIA

Palynological, Paleoenvironmental and Paleoclimatic investigations of Emi-5 well Offshore, Niger Delta, Nigeria was conducted to established palynozones, determine age, reconstruct paleoenvironmental conditions and paleoclimatic conditions to permit stratigraphic correlation, provide insights into the depositional settings and changes overtime within the basin. Fifty one (51) shaly ditch cutting samples were subjected to standard palynological method involving sample maceration with 10 % HCl and 40 % HF acids to remove carbonates and siliceous components, neutralization with distilled water and sieving through 5-micron sieve, followed by separation of palynomorphs from residue prior to mounting of the grains on glass slides for further analysis. The palynological composition is marked by dorminance of pollen and spores over dinoflagellate cysts. The intercalation of the sandy and shaly intervals across the section evidenced from lithologic, textural, and wire line log data suggested that the entire studied interval belong to the Agbada Formation. Three interval range zones were delineated using the international stratigraphic guide for the establishment of biozones, they are Stereisporites sp – Verrutricolporites rotundiporus; Verrutricolporites rotundiporus – Gemmemonoporites sp. and Retistephanocolpites gracilis – Pachydermites diederixi Zones and based on the aforementioned zones the interval is assigned middle Miocene to late Miocene. Coastal-deltaic environment of deposition is inferred for the studied interval on the basis of occurrence and dominance of diagnostic forms such as Zonocostites ramonae,Rhizophora, Psilatricoloporites crasssus and Acrostichum aureum while good representation of these forms and the identified palyno-ecological groups placed the interval on a wet climatic zone.

Correlation of the Coniacian and Santonian stages of the Upper Cretaceous in the Anglo-Paris Basin

The correlation of the Coniacian and Santonian chalks of the Anglo-Paris Basin is described on the basis of detailed lithological logs and extensive records of macrofossils and microcrinoids. In the almost complete absence of ammonites, inoceramid bivalves afford the highest resolution correlation of these stages in chalks, but their value here is limited by the absence of key genera and species, most notably in the Upper Coniacian and middle and Upper Santonian. Echinoids and other macrofossils (brachiopods, stalked crinoids, belemnites) have proved useful, but many are long-ranging or uncommon. Some marker beds, including flints and marl seams, provide useful correlations across the basin, but are locally absent. For the Upper Santonian, the stemless benthonic crinoids Uintacrinus and Marsupites provide high-resolution correlation, both within the basin and to other regions. The successions on the basin margins, in the far north of France (Nord, Pas de Calais) and the southwest (Touraine) are condensed and yield ammonites in association with important inoceramid species. The controls on sedimentation caused by sea-level changes are evaluated on a basinal and global scale, most especially for the Upper Santonian.