Fractured Basement Research Articles

GEOLOGICAL INTERPRETATION OF LANDSAT IMAGERY OF NIGERIA’S HAWAL PRECAMBRIAN BASEMENT COMPLEX TERRAIN

The Hawal Basement Complex is located in Nigeria’s NE region. Satellite imagery used in this study covers longitude 12º 00’ to 13º 30’E, and latitudes 9º 30’ to 11º 00’N. The aim of the study is to decipher the regional geologic structures based on analysis and to determine the mineralization implications from the landsat lineament data. The total land surface area covered is about 23,674.88 km2 and includes part of the north sector of Yola sedimentary Rift Basin. The data consists of LANDSAT TM and SPOT XS scenes collated as mosaics. The imagery was monoscopically studied. Classical aerial imagery interpretation techniques of mapping lineaments and tracing regional geological boundaries were used. A total of 368 lineaments were mapped and analyzed using multi-graphical analytical techniques. The results are presented as isolinear contour maps (isodensity and lineaments intersection maps). The isodensity lineament maps show two main areas of lineament concentrations, namely Shani area lying westward and Michika-Mubi area to the east. Reasons advanced for the preponderance of lineaments in parts of the study area are the combined effects of isostatic basement uplift and lithospheric stretching during the formation of Yola Rift and Chad Basin respectively, which caused large scale crustal deformations. Also, Precambrian and Cenozoic magmatic activities that caused emplacements of older granites and basaltic bodies respectively in the area contributed to fracturation of the crust. Fewer lineaments are observed over the sedimentary Rift zone and this is attributed to masking effect of the sediments on basement fractures. The lineament intersection map shows a prominent NE-SW zone of highest intersection which is parallel to the general flow direction of the Hawal River. Prominent lineament directions are N-S (0-20º), and NE-SW (40º- 60º), which are Pan African Orogenic directions. Aerogeological studies of this type are important in national economic development.

Frequency-Domain Electromagnetic and VLF Data with An Application to Modeling of Basement Structures: A Case Study Within, Ibadan Area, Southwestern Nigeria

The study area, the church camp is within Ibadan which fall within southwestern basement complex of Nigeria and it is mainly by migmatite-gneiss. The hard rocks are usually characterized by basement fracture which may serve as a conduit for groundwater passage. This has necessitated detail geological and geophysical investigation to accurately and precisely delineate this structure. Geological mapping alongside very low frequency Electromagnetic (VLF-EM) techniques were adopted in which conductivity data were acquired along Fifteen (15) VLF profiles using ABEM WADI. Thirteen (13) of these profiles were in the East-West (E-W) direction which is the dip direction of the structural elements, while the remaining two profiles were in North-South (N-S) direction. The data obtained from the field were processed, filtered and presented inform of profiles and Karous-Hjelt (K-H) filtered pseudo-section to visualise conductivity in (2-D). Pockets of conductive structures were delineated and were interpreted as fractures of various dimension and orientation. Some are single fracture and others are closely-spaced double fractures which some of them joined or fused together at depth with some suspected to contain water while some are dry base on their conductivity/resistivity signature exhibited. In conclusion, VLF-EM has proven to possess the capability to characterize and model the basement fractures and define their dimension, axial orientation and indicates their parallelism which also signifies their origin as regard stress regime that produces the fracture.

Environmental impacts of an unlined municipal solid waste landfill on groundwater and surface water quality in Ibadan, Nigeria.

Environmental and public health concerns grow on the interaction of municipal solid waste (MSW) leachates from unlined waste disposal sites with aquifers in many developing countries. This study investigated the environmental pollution impacts of an unlined MSW landfill at Ajakanga area, Ibadan, southwest Nigeria. Analytical studies indicated that the concentrations of NO3-, SO42-, PO43-, NH4-, Cl-, Na, Fe, Mn, Cr, and Mo in the leachate samples exceeded the WHO wastewater discharge limits. Hydrochemical parameters of the groundwater and surface water were within WHO allowable thresholds, except for EC, TDS, Fe, Mn, and Pb in the groundwater and Pb, Cd, and Cu in the surface water, indicating major geogenic and minor MSW leachate impacts on the groundwater and surface water chemistry. Bacteria found in the leachate include Enterobacter cloacae (16.67%), Pseudomonas spp. (14.28%) and Bacillus spp. (9.52%). The geoelectrical imaging data indicated substratum leachate infiltration greater than 10m deep, which is consistent with the low resistivity values of the topsoil-weathered basement layers. The health risk assessment showed high hazardous index values, indicating health risks of Mn, Cd and Pb in the surface water for the residents around Ajakanga landfill. Hydrochemical data indicated greater impact of the MSW leachates on the surface water than the groundwater, while geophysical data showed greater propensity of the surrounding aquifer to leachate interaction through fractured basement zone with increasing abstraction. Waste site closure and hydrochemical monitoring are suggested measures to mitigate environmental pollution in the study area.

Illuminating geology in areas of limited exposure using texture shading of lidar digital terrain models

Abstract Regions of sparse exposure challenge geologic mappers because of limited information available on the underlying structure and continuity of the map units. We introduce here a little-known technique for post-processing bare earth digital terrain models (DTMs) that can dramatically improve knowledge of the underlying structure in covered areas. Texture shading enhances changes in slope and does not suffer from limitations introduced by artificial illumination required in hillshade or shaded relief images. When this technique is applied to lidar DTMs, layers of rock units with variable resistance to erosion can be clearly imaged, even in areas with limited outcrop. This technique enables one to collect comprehensive orientation data in areas of deformed sedimentary strata, assess the continuity of metamorphic and igneous rock units, and depict basement fracture sets. We demonstrate the use of texture shading in the Valley and Ridge of northern Pennsylvania, metamorphic rocks in the Berkshire Hills of western Massachusetts and Green Mountains of Vermont, and glacial deposits in the Finger Lakes region of upstate New York (northeastern United States).

Analysis of the geological control on the spatial distribution of potentially toxic concentrations of As and F- in groundwater on a Pan-European scale

The distribution of the high concentrations of arsenic (As) and fluoride (F-) in groundwater on a Pan-European scale could be explained by the geological European context (lithology and structural faults). To test this hypothesis, seventeen countries and eighteen geological survey organizations (GSOs) have participated in the dataset. The methodology has used the HydroGeoToxicity (HGT) and the Baseline Concentration (BLC) index. The results prove that most of the waters considered in this study are in good conditions for drinking water consumption, in terms of As and/or F- content. A low proportion of the analysed samples present HGT≥ 1 levels (4% and 7% for As and F-, respectively). The spatial distribution of the highest As and/or F- concentrations (via BLC values) has been analysed using GIS tools. The highest values are identified associated with fissured hard rock outcrops (crystalline rocks) or Cenozoic sedimentary zones, where basement fractures seems to have an obvious control on the distribution of maximum concentrations of these elements in groundwaters.

Evaluation of Groundwater Potentials Using Dar Zarrouk Parameters in Mapeo and Environs, North-Eastern Nigeria

Groundwater is the safest and most reliable source of water in crystalline basement complex terrain especially those associated with semi-arid to arid regions. This research is aim at evaluating the groundwater potentials of Mapeo and its environs, The study area is located between latitudes 8◦ 37'and 8◦ 45' N and longitudes 12◦21'and 12◦32' E. Thirty-five Vertical Electrical Sounding (VES) points were surveyed using the Schlumberger array. The analysis of the VES conducted revealed four layered formations; Sandy clay to slightly weathered, fractured, and basement rocks. The aquifer units in the study area varied from highly weathered and fractured basement rocks. Dar-Zarrouk parameters such as the longitudinal conductance and transverse resistance revealed values that ranged from 0.0842 to 1.5926Ω with an average value of 0.5767Ω and 1107.235 to 8910.410Ωm2 with an average value of 4167.902 Ωm2 respectively. For the aquifer properties, empirical formulae based on grain size analysis were used to determine hydraulic conductivity which ranges from 1.01X 10-9 to 9.82X 10-6m/day with an average value of 2.176x10-3m/day, the hydraulic conductivity determined from geophysical method range from 1.833 to 17.525m/day with an average value of 7.2182x10-3m/day while transmissivity values range from 47.657 to 779.724 m2/day with an average of 289.113 m2/day. Groundwater potential zones were determined based on transmissivity values and classified the area into low, moderate, and high potentials.

Granitic Basement Fracture Analogue by Using Integrated Digital Outcrop Model and Fieldwork, at Muaro Silokek, West Sumatra

The study aims to determine fracture characteristics such as orientation, fracture attributes, fracture density distribution, and mineral composition of quartz and feldspar. The study used photogrammetry data to know the distribution and geometry of macro-scale fracture, linear scanline and windows scan data to understand the characteristics of mesoscale fracture attribute, and thin section rocks data from oriented samples to determine petrographic analysis and micro-scale fracture. After analyzing each of these data, analog basement fractured reservoir modeling could be built from integrating the data and modeling parameters based on available fieldwork data. The fault in the research area is represented as a Riedel shear with the orientation direction of NNW-SSE, NE-SW, and ENE-WSW. The fracture density is influenced by its position on the fault and increases in the fault damage zone. The granite type in the study area was divided into three types, namely alkali feldspar granite, syeno granite, and monzogranite. Each granite type has a different response to fractures and shows that the fracture density will increase with the greater quartz and k-feldspar in the fault damage zone. Fracture permeability values are strongly influenced by the geometry of fracture position, fracture aperture, and fracture length. This study produced a new perspective for fractured basement reservoirs, especially for granitic rocks, generally the primary target for basement fracture reservoirs along Sumatra.

Application of gas-assisted gravity drainage (GAGD) to improve oil recovery of Rang Dong basement reservoir

As an option to improve the ultimate oil recovery factor of the Rang Dong field, a feasibility study of gas-assisted gravity drainage (GAGD) application was carried out for the fractured basement reservoir with a single-well Huff ‘n’ Puff pilot test applied on a high water-cut producer. This paper aims to provide an in-depth understanding about such case study, which includes details on candidate selection, gas injection scheme, on-site execution, results of flow-back, post-job review and lessons learned. 
 The pilot test of GAGD was recorded with a good oil rate and low water-cut during flowing back after gas injection and shut-in for gas segregation, which suggests the positive effectiveness of GAGD to some degree. The expansion of the GAGD application to other wells and areas in the field would be encouraged in any similar situation. On the other hand, the results of this pilot test shed a light into further optimisation of the candidate selection and gas injection scheme by material balance analysis and reservoir simulation respectively.

Detection of groundwater level and heavy metal contamination: A case study of Olubunku dumpsite and environs, Ede North, Southwestern Nigeria

This research presents the result of the application of the PQWT Electromagnetic Groundwater Detector and analysis of heavy metal contamination around an open dumpsite in Olubunku, Ede North, Southwestern Nigeria, which has been in operation for the past fifty years. A PQWT-300S 300 m was used to acquire 8 profiles at the site. The quantitative analysis of heavy metals was conducted for seven available well water samples and five surface soil samples. The water and soil samples (digested) were read on BuckScientific Atomic Absorption Spectrophotometer model 210/211 vap to determine the concentration of Pb,Cd,Cr, Co, and Ni in the samples. As and Hg in the samples were read colorimetrically using a Niesa Spectrophotometer. From the PQWT results, profiles 1,4,5,6,7, and 8 indicate a shallow level of groundwater at a depth of around 30m, which is prone to contamination as most water in the study area is obtained from hand dug wells less than 20m deep. Profile 2 and 3 show contacts that indicate a boundary between fresh basement and well fractured basement, which serves as the water-bearing rock. The HPI scale indicates a high presence of Cd, Hg, Pb, As, and Co in all the samples, which is above the maximum allowable concentration for water. The low scale of Ni and Cr indicates the water is free from Ni and Cr contamination. In the soil, the Igeo scale of Co, Ni, Cd, Pb, and Hg are higher than the maximum allowable concentration, while As and Cr are very low and therefore pose no threat. Chromium is generally low in both the soil and water samples analyzed, while Co, Cd, Hg, and Pb are high above the prescribed scale in both soil and water samples.The groundwater depth in the study area is predominantly at a shallow level of around 30m. The high conductivity of the top shallow level is suspected to be due to contamination by leachates from the dumpsite. The soil and groundwater in and around the investigated dumpsite may be polluted. The study has indicated the vulnerability of the unconfined shallow aquifer underlying the predominantly clayey sand and the effectiveness of PQWT EM in delineating groundwater zones in the basement complex.

Application of machine learning algorithm to forecast production for fracture basement formation, Central arch, Bach Ho field

Oil production forecast is a big challenge in the oil and gas industry. Simulation model and prediction results play an important role in field operation and management. Currently, dynamic simulation model, decline curve analysis are popular tools applied to forecast production. The dynamic simulation model shows a remarkable effect for sedimentary objects. However, production forecasting by this method for fracture basement formation sometimes gives unreliable results because the fracture basement formation is a complex of geological objects, which causes difficulties in predicting the geological characteristics. The decline curve analysis (DCA) method uses simple extrapolated mathematical functions to forecast oil production, therefore the results do not reflect the production operations such as opening/closing production interval.To avoid the disadvantages of these traditional methods, Vietnam Petroleum Institute (VPI) has studied the applicability of machine learning to forecast oil production for fracture basement formation of Bach Ho field. The study results show that the random forest model has improved the production forecast with low relative error (4%).

Tectonic Regime as a Control Factor for Crustal Fault Zone (CFZ) Geothermal Reservoir in an Amagmatic System: A 3D Dynamic Numerical Modeling Approach

Crustal fault zones provide interesting geological targets for high-temperature geothermal energy source in naturally deep-fractured basement areas. Field and laboratory studies have shown the ability of these systems to let fluid flow down to the brittle–ductile transition. However, several key questions about exploration still exist, in particular the fundamental effect of tectonic regimes on fluid flow in fractured basement domains. Based on poro-elasticity assumption, we considered an idealized 3D geometry and realistic physical properties. We examined a model with no tectonic regime (benchmark experiment) and a model with different tectonic regimes, namely a compressional, an extensional and a strike-slip tectonic regime. Compared to the benchmark experiment, the results demonstrate that different tectonic regimes cause pressure changes in the fault/basement system. The tectonic-induced pressure changes affect convective patterns, onset of convection as well as the spatial extent of thermal plumes and the intensity of temperature anomalies. Driven by poro-elastic forces, temperature anomalies around vertical faults in a strike-slip tectonic regime have a spatial extent that should be considered in preliminary exploratory phases.

Mapping and Delineation of Hard Rock Aquifers in Parts of the South-western Nigeria Basement Complex Using Integrated Geophysical Techniques

Abstract: An integrated geophysical survey involving three different techniques; namely, VLF-EM, Seismic Refraction and Vertical Electrical Sounding (VES) has been carried out in parts of Eruwa, Ibarapa East LGA, Oyo State with a view of determining the structural characteristics of the subsurface geology and identifying suitable sites where viable borehole could be sited to reduce the problem associated with acute shortage of groundwater in the area. The area lies within the crystalline basement rock terrain of South-Western Nigeria and bounded by Latitude 7° 32' 59"N and Longitude 3° 25' 59"E. The VES results reveal that the area is made up of four major lithologic layers with the topmost layer being majorly laterites, the second layer being sandy clay, the third is weathered basement, while the fourth layer is fractured basement. The aquifer in the study area is mostly confined with curve responses of HA- and HKH-types. The 2-D pseudosection also showed that the fresh basement is very extensive laterally with undulating topography. The result of VLF-EM revealed high-amplitude anomalies. These anomalies are indicative of high conductive zones within the basement bedrock of the study area. The results of the seismic inversion reveals three lithologic layers; namely, the topmost layer / topsoil which is sandy (moderately loose) with an average velocity of 500 m/s, the middle layer can be sandy clay/laterite/caked clay with an average velocity of 1,149.33 m/s and the third layer can be said to be the beginning of the weathered/fresh basement with a velocity of 2,719 m/s. In conclusion, the three geophysical techniques have shown that the area is a hard-rock terrain with complicated geology with aquifers confined and the water bearing formation with low total longitudinal conductance. Keywords: Basement terrain, Granitic masses, Aquifer, Topography, Curve types.

Analysis of high-resolution airborne-magnetic data for hydrocarbon generation and preservation potential evaluation of Yola sub-basins, northern Benue Trough, northeastern Nigeria

High-resolution airborne-magnetic data acquired over the Yola extension of the northern Benue Trough, northeastern Nigeria, were analyzed to delineate rock distribution, define basement geometry, determine sedimentary thicknesses, and highlight structural framework among others for the hydrocarbon prospect evaluation of sub-basins in the extension. Filtered and refined magnetic intensity data were subjected to Analytic Signal, Horizontal and Vertical Tilt Derivatives and Euler deconvolution depth weighting analyses to enhance various geological features requisite for petroleum prospect evaluation. Sedimentary rock units flanked the northeast and south widely occur in the central part with volcanic rock intrusions delineated within the sedimentary terrain. Extracted lineaments (less than 5 km and up to 45 km) were observed to dominantly follow the established Benue Trough and Yola sub-basin evolutionary trend along the NE–SW and ESE–WNW directions, respectively. Three prominent sub-basins with sedimentary thicknesses in excess of 3 km and width of more than 60 km, separated by basement highs of mostly volcanic intrusions origin, were identified. The occurrence of relatively thick and extensive sub-basins which are underlain by structurally active basement rocks suggests relatively high geothermal gradient for generation of hydrocarbon from organic matter rich source rocks while the generated oil and gas are preserved within intra-sedimentary structural traps created when the basement fractures were reactivated.

Integrated Geophysical Assessment of Groundwater Potential in Southwestern Saudi Arabia

Saudi Arabia is seeking fresh groundwater resources to face the increase in anthropogenic activities. The groundwater storage variations and occurrence were investigated and the surface and subsurface structures influencing the groundwater resources in the research area were defined using a combined study of Gravity Recovery and Climate Experiment, aeromagnetic data, and electrical resistivity data with other relevant datasets. Results are: The groundwater storage fluctuation is calculated at −0.34 ± 0.01 mm/yr during the period 04/2002-12/2021. The area is receiving an average annual rainfall rate of 117.6 mm during the period 2002 to 2019. Three structural trends, defined in the directions of NS, NNW, and NNE are cutting the sedimentary cover and the basement rocks. The sedimentary cover ranges from 0 to 1.2 km thick. Vertical electrical sounding results indicate three main geoelectric layers: the surface geoelectrical layer of higher resistivity values (428-9626 Ω. m) is made up of unconsolidated Quaternary sediments; the water-bearing layer of saturated sands with a resistivity range between 5.1 and 153 Ω. m and with depths vary from 1 to 94 m, and highly fractured basement rocks with resistivity values ranging from 813 to 6030 Ω. m. The integrated results are useful in providing a comprehensive image of the study area’s surface and subsurface structures, as well as groundwater potential in the southwestern part of Saudi Arabia. Our integrated approach provides a reproducible model for assessing groundwater potential in arid and semiarid areas.

Identification of hydrogeological features using remote sensing and electromagnetic methods in the hard- rock formations of the Cameroon coastal plain (Central Africa): implications for water borehole location

Sustainable access to groundwater in rural areas such as the coastal plain of Cameroon (Sub-Saharan Africa) is an ongoing challenge due to the lack of knowledge on hydrogeological features favorable to the identification of potential groundwater targets. In this study, remote sensing imagery and electromagnetic surveys were used to assess the hydrogeological potential of the Ngwei locality hard-rock. Automatic extraction of lineaments from Landsat-8 images indicated 200 lineaments with a total length of 293 km corresponding to 0.6 km of lineament per square km, suggesting a median groundwater potential. The main directions are NNW-SSE, N-S and NNE-SSW while the secondary directions are NW-SE; NE-SW and E-W. Surface geophysical investigations showed an electromagnetic field of 0 to 0.57 mV. These surface and borehole investigations confirmed basement fracturing and spatial variations in weathering profiles whose aquifer structure and yields (4.4 m3/h on average) are similar to what is commonly observed in the hard rock aquifer. The correlation between borehole productivity and the nearest lineament suggests that these lineaments are not (at least not all) surface traces of regional discontinuities that may act as major groundwater flow paths. This implies that the productivity of the Ngwei aquifers appears to be dependent on the fissured/fractured horizon, so exploration should be based on a contextual rather than general approach.Analysis of the consistency of the results with the field data allowed to propose a preliminary electromagnetic log model and also shows the value of using this approach to assess the availability of potential groundwater zones in hard rock areas. However, the methods used should be supported by further investigations to allow a better understanding of the hydrogeological characteristics of this part of the Central African basement so that no one is left behind in the achievement of the SDGs.

EVALUATION OF AQUIFER PROTECTIVE CAPACITY USING ELECTRICAL RESISTIVITY METHOD IN LAMBATA, KWALI AREA COUNCIL, ABUJA

This study evaluated the aquifer protective capacity of Lambata in Kwali area council of Abuja, using electrical resistivity method. The obtained data were interpreted manually by partial curve matching and the obtained results were iterated using WINREIST software. The first layer is the topsoil whose resistivity range from 127.7 to 562.4 Ωm and its thickness range from 0.7 to 1.6 m. The second layer is laterite and its resistivity range from 302.3 to 937.6 Ωm, the thickness of the second layer range from 3.7 to 13.3 m. The third layer is a clay formation whose resistivity range from 46.7 to 88.8 Ωm and its thickness range from 6.6 to 27.9 m. The fourth layer is a weather/ fractured basement, this layer is the aquifer and it is confined by the overlying clay formation. Its resistivity range from 59.0 to 870.2 Ωm, while its thickness range from 6.0 to 28.5 m. The fifth layer is the fresh basement whose resistivity range from 1038.5 to 4992.5 Ωm. The total longitudinal conductance values of the overburden in the study area range from 0.00143 to 0.410334 mΩ-1. The average aquifer thickness in the study area is 16.60 m. The aquifer protective capacity is about 93.3% moderate and 6.7% weak. The aquifer protective capacity of the study area is fairly good but not sufficient to protect the groundwater in the area from pollution. We therefore strongly suggest that there should be proper environmental and waste monitoring management in the study area to safeguard the groundwater

Causes of Variability in Groundwater Salinity of the Lower Jurassic Sediments in the Talinskoye Oilfield of West Siberia

This study aimed to identify the nature of variable groundwater salinity from the standpoint of whether natural or man-caused factors have a dominant impact on the modern salinity range of the Lower Jurassic sediments in the Talinskoye oilfield of West Siberia in Russia. As of now, the salinity values of reservoir waters vary from 3.7 to 15.3 g/dm3, with an average of 8.9 g/dm3. Petroleum hydrocarbons are extracted at the oilfield from the Lower Jurassic sediments. The volume of overlying sediments’ waters injected into the pay zones to maintain the formation pressure was more than 8960.3 thousand m3 between 2014 and 2021. In this regard, it is necessary to establish whether anthropogenic factors are critical for the variability in groundwater salinity of the Lower Jurassic sediments, or the complex geologic and hydrogeologic conditions are determinant factors affecting the salinity variability. To achieve this objective, we evaluated the genetic coefficients of various types of waters (inclusive of injected waters) which could contribute to the variability in groundwaters with varying quantities and ratios. The resultant genetic coefficients were compared with those of reservoir waters of the Lower Jurassic hydrogeological complex. This allowed for the conclusion that the major factors currently affecting the variable salinity of the reservoir waters of the Lower Jurassic complex are natural ones. We also assessed the relationship between the groundwater salinity values of the complex under study and basic parameters of the geologic setting, such as porosity, formation pressure, modern temperature and paleotemperature of the basement, and basement depth of burial. A tight association was found between the salinity values and porosity of the sediments (R = 0.87), and a very tight connection between the salinity and formation pressure (R = 0.91), which, we believe, also evidences that natural factors have a dominant effect on the variability in groundwater salinity. The variability in the modern salinity values of the reservoir waters of the complex in question ensues from the continental conditions of the groundwater genesis, expelled-water exchange processes (ingress of the pore waters expelled from argillaceous deposits as geostatic pressure rises), and the intrusion of abyssal fluids along the basement fractures.

Diffraction Imaging of the Fractured Crystalline Basement, Lancaster Field, UK

In this paper, we demonstrate the application of seismic diffraction imaging technology to map the distribution of faults within Hurricane Energy’s operated, fractured basement fields, offshore West of Shetland. After the reprocessing of legacy 3D seismic data in 2018, it became apparent that the reflection seismic image had limited ability to image the intra-basement structure. Intra-basement imaging is crucial for understanding the distribution, frequency and geometry of intra-basement structures which directly influence production trends in fractured basement reservoirs. Diffraction imaging is a novel seismic processing technique that can produce high-resolution images of small-scale scattering subsurface events by extracting and focusing the diffractive component of the total wavefield to its subsurface origin. Analysis of the diffraction imaging seismic volume alongside well data and other seismic products can complement conventional seismic attributes and enhance the interpretational value of the seismic data. This paper shows how the intensity of the diffraction image varies from location to location across the Rona Ridge and is seen to have a strong, positive correlation with observed well productivity. As such, the application of this technology shows great promise to provide additional information for detailed analysis of Hurricane Energy’s fractured basement reservoirs and can facilitate new well placement and trajectory design.

Subsurface Investigation for Road Construction Using Electrical Resistivity Method along Oloko road, Apatapiti, Akure, Ondo State, Nigeria

Abstract Evaluation of the shallow geologic materials in terms of types, nature, and bedrock structure as possible causes of pavement failure was carried out along Oloko road Apatatpiti, Akure, Nigeria, using Schlumberger vertical electrical sounding and 2-D imaging dipole-dipole techniques. Three lithological layers, namely thin top soil, weathered layer and weathered basement, were revealed by the 2-D resistivity structure. Vertical electrical soundings were made at locations with a very low resistive medium typical of linear features such as fractures/faults at some distances on the 2-D resistivity structure. Four geologic layers, namely the top soil, clay/sandy clay, fractured basement, weathered/fresh basement, were identified by the geoelectric section. The geoelectric section and the 2-D resistivity structure revealed that the upper 0-6m, which constitutes the subgrade, has a low resistivity (36 Ωm to 108 Ωm) characterised to be clayey materials and suggestive of weak zones that might impair the stability of the road. A relatively shallow depth, ranging from 3.7 m to 4.29 m, was the depth to the water table of the four wells close to the road. Therefore, the possible causes of pavement failure are the thick and low resistive layer, the near-surface linear features suspected to be fractures/faults, and the water table’s shallow depth.

Characterization Of Naturally Fractured Basement Reservoir And Its Play Concept, South Pattani Basin, Gulf Of Thailand

Structural development and complex basin forming mechanism in Pattani Basin may have formed naturally fractured basement reservoirs. The basement of the South Pattani Basin is poorly understood, as a result of low seismic resolution in its deeper part and lack of wells that reach the basement. Hence, seismic interpretation may improve the understanding of South Pattani Basin basement fracture systems. This paper aims to investigate the geological and seismic characteristics of the fractured basement reservoir, identify the relation between basin evolution and fracture network and development, and proposed a play concept for naturally fractured basement reservoir. Seismic attributes exhibit prominent N-S fault and fracture trends in the study area. Three basement high areas revealed that open fractures distribution identified using seismic ant-tracking technology has good correlation with regional maximum horizontal stress direction (N-S), but the intra-basement (central) area exhibits strong alignment with pre-existing fabrics (NW-SE). Open fracture networks in Zone A and B developed around major fault swarm features. Integrated qualitative and quantitative seismic analysis suggests that the three basement high areas have the potential for fractured basement reservoirs, with a complex fracture configuration and development due to poly-phase deformations.