Estimation of petrophysical parameters is an important issue of any reservoirs. Porosity, volume of shale and water saturation has been evaluated for reservoirs of Upper Assam basin, located in northeastern India from...Estimation of petrophysical parameters is an important issue of any reservoirs. Porosity, volume of shale and water saturation has been evaluated for reservoirs of Upper Assam basin, located in northeastern India from well log and seismic data. Absolute acoustic impedance(AAI) and relative acoustic impedance(RAI) are generated from model based inversion of 2-D post-stack seismic data. The top of geological formation, sand reservoirs, shale layers and discontinuities at faults are detected in RAI section under the study area. Tipam Sandstone(TS) and Barail Arenaceous Sandstone(BAS) are the main reservoirs,delineated from the logs of available wells and RAI section. Porosity section is obtained using porosity wavelet and porosity reflectivity from post-stack seismic data. Two multilayered feed forward neural network(MLFN) models are created with inputs: AAI, porosity, density and shear impedance and outputs: volume of shale and water saturation with single hidden layer. The estimated average porosity in TS and BAS reservoir varies from 30% to 36% and 18% to 30% respectively. The volume of shale and water saturation ranges from 10% to 30% and 20% to 60% in TS reservoir and 28% to 30% and 23% to 55% in BAS reservoir respectively.展开更多
We address the role of the concave and convex arcs （as observed from the subducting plate） on the deformation occurring along the Myanmar-Andaman-Sumatra margin. We categorize the pre- and post-seismic deformations ...We address the role of the concave and convex arcs （as observed from the subducting plate） on the deformation occurring along the Myanmar-Andaman-Sumatra margin. We categorize the pre- and post-seismic deformations of the lithosphere using earthquake database occurring either prior to 26th December 2004 Mw 9.3 off-Sumatra mega-event or after the incidence. Analysis under pre-seismic domain shows that area near Sumatra records highest seismicity, which largely drops in the area past the North Andaman, and further increases towards north. Shallowest depth and mini- mum dip of the subducting lithosphere is recorded at the central segment where the arc transformed into concave shape. The annual moment energy release during earthquake decreases to more than two orders of magnitude past the North Andaman towards north under post-seismic deformation phase. Higher depths of continuity of events are presumably associated with more dipping Benioff zones in both the Indo-Myanmar and Andaman-Nicobar convex arcs. These observations obviously account for tectonic subdivision of the margin near concave shape arc around the central part. Absence of vol- canism, presence of splay faults in the back-arc, sharp reduction in seismicity near central segment are interpreted to be caused by major tectonic impact of the NNE-ward converging buoyant Ninety-east Ridge against the Asian Plate. Shallowest dip, small elastic thickness, weak converging Indian litho- sphere, and evidences of series of en-echelon blocks off the eastern side of the broken northern Ninety- east Ridge might be incapable of generating great earthquake in this area.展开更多
This study is focused on the effect of vibration induced by moving trains in tunnels on the surrounding ground and structures.A three-dimensional finite element model is established for a one-track railway tunnel and ...This study is focused on the effect of vibration induced by moving trains in tunnels on the surrounding ground and structures.A three-dimensional finite element model is established for a one-track railway tunnel and an adjacent twelve-storey building frame by using commercial software Midas GTS-NX(2019)and Midas Gen.This study considered the moving load effect of a complete train,which varies with space as well as with time.The effect of factors such as train speed,overburden pressure on the tunnel and variation in soil properties are studied in the time domain.As a result,the variations in horizontal and vertical acceleration for two different sites,i.e.,the free ground surface(without structure)and the area containing the structure,are compared.Also,the displacement pattern of the raft foundation is plotted for different train velocities.At lower speeds,the heaving phenomenon is negligible,but as the speed increases,both the heaving and differential settlement increase in the foundation.This study demonstrates that the effect of moving train vibrations should be considered in the design of new nearby structures and proper ground improvement should be considered for existing structures.展开更多
Pore pressure(PP)information plays an important role in analysing the geomechanical properties of the reservoir and hydrocarbon field development.PP prediction is an essential requirement to ensure safe drilling opera...Pore pressure(PP)information plays an important role in analysing the geomechanical properties of the reservoir and hydrocarbon field development.PP prediction is an essential requirement to ensure safe drilling operations and it is a fundamental input for well design,and mud weight estimation for wellbore stability.However,the pore pressure trend prediction in complex geological provinces is challenging particularly at oceanic slope setting,where sedimentation rate is relatively high and PP can be driven by various complex geo-processes.To overcome these difficulties,an advanced machine learning(ML)tool is implemented in combination with empirical methods.The empirical method for PP prediction is comprised of data pre-processing and model establishment stage.Eaton's method and Porosity method have been used for PP calculation of the well U1517A located at Tuaheni Landslide Complex of Hikurangi Subduction zone of IODP expedition 372.Gamma-ray,sonic travel time,bulk density and sonic derived porosity are extracted from well log data for the theoretical framework construction.The normal compaction trend(NCT)curve analysis is used to check the optimum fitting of the low permeable zone data.The statistical analysis is done using the histogram analysis and Pearson correlation coefficient matrix with PP data series to identify potential input combinations for ML-based predictive model development.The dataset is prepared and divided into two parts:Training and Testing.The PP data and well log of borehole U1517A is pre-processed to scale in between[-1,+1]to fit into the input range of the non-linear activation/transfer function of the decision tree regression model.The Decision Tree Regression(DTR)algorithm is built and compared to the model performance to predict the PP and identify the overpressure zone in Hikurangi Tuaheni Zone of IODP Expedition 372.展开更多
The signal-to-noise ratio （SNR） of seismic reflection data in many areas is rather poor and conventional two-dimensional filters designed to suppress noise with different moveout from the signal tend to generate art...The signal-to-noise ratio （SNR） of seismic reflection data in many areas is rather poor and conventional two-dimensional filters designed to suppress noise with different moveout from the signal tend to generate artifacts. We have extended a method of multichannel filtering, based on the hypothesis that signals on adjacent channels are similar, for enhancing the SNR on stacked sections. Using only the mid-range frequencies where the SNR is highest, the event trend is found for overlapping windows on the section and the average signal vector is calculated. Then the data from the full bandwidth section are projected onto the spatially varying unit similarity vectors and the results are merged for the overlapping windows. Application of the method to synthetic data containing steeply dipping events and to a stacked section for a marine 2D line has produced good results. The modifications we have introduced carry a small overhead in computing time but they should enable the method to be used effectively even on sections containing steep dips.展开更多
Core samples representing depths of hydrocarbon-bearing zones are not readily accessible for reservoir evaluations.On the other hand,wireline logs with incorporated seismic data,which can be archived over a more exten...Core samples representing depths of hydrocarbon-bearing zones are not readily accessible for reservoir evaluations.On the other hand,wireline logs with incorporated seismic data,which can be archived over a more extended period while retaining their original forms,are typically more available for research purposes.Therefore,the study relies on wireline logs with seismic data to predict the reservoirs'fluid mobility by evaluating the hydraulic(flow)units,reservoir depths,fluid saturations,and geothermal gradients.It also indicates the associated water cut(C_(w))within Ritchie oil and gas field,Niger Delta considering a three-phase(oil-gas-water-bearing)reservoir(R_(A))and an oil-saturated reservoir(R_(B))delineated across three wells(R_(W1),R_(W2) and R_(W3)).Research activities combining the presented factors to achieve the stated objectives are not quite common within the study location.It shows lower,average and upper limits of the flow unit factors and irreducible water saturation(S_(wirr))within the reservoirs.The study shows the relationship between hydraulic units/fluid saturations and fluid mobility/associated C_(w) within the sandstone reservoirs.It maximises porosity(Ф)for the theoretical flow units'prediction during qualitative and quantitative estimation based on the adopted expressions.Therefore,the study reveals that water saturation(S_(w))and hydrocarbon/water ratios substantially control C_(w),and other contributing factors include thermal gradients and S_(wirr).The flow unit factors are also significant and will encourage fluid mobility.The evaluated reservoirs(R_(A) and R_(B))are below 10400 ft(3170 m)across wells R_(W1),R_(W2) and R_(W3) within the Agbada Formation of a geothermal gradient up to 2.7℃/100 m;therefore,they have good thermal conditions to enhance hydrocarbon mobility and increase S wirr.Hence,the reservoir should feature significant hydrocarbon extraction via primary recovery.The average water cut(C_(w-avg).)(12.3%)estimated for reservoir R_(A) is within the acceptable range;therefore,the associated water production from the three-phase reservoir will not be much of a concern.In addition,simple models are presented to aid an alternative approach for predicting reservoir quality and C_(w) within sandstone res-ervoirs,especially in the absence of core samples.展开更多
The paper presents results of radiometric investigations of an area (Duku-Tarasa) near the capital city of the State of Birnin Kebbi, NW Nigeria. The area of study is about 440 m × 420 m and encloses an Escarpmen...The paper presents results of radiometric investigations of an area (Duku-Tarasa) near the capital city of the State of Birnin Kebbi, NW Nigeria. The area of study is about 440 m × 420 m and encloses an Escarpment Feature/Structure on a sedimentary rock generally referred to as the Gwandu Formation. The Gwandu Formation (though not described in the paper) consists of continental lacustrine sediments and is the youngest Palaeogene Formation present in the Sokoto sector of the larger Iullemmeden Basin. The study measured, along some selected profiles across this escarpment feature, radiometric signatures using a Sim-Max G411 portable field gamma-ray spectrometer (giving counts for U, Th and K relative to the background values over the area), the ground total-field magnetic data (using the proton precession magnetometer) along those profiles and collected some (5) rock samples for flame photometry and AAS analyses towards the target proposition. Activity concentration levels due to potassium (K), uranium (U) and thorium (Th) were measured in the area along the five established profiles spaced at 50 metres. The results from these measurements and analyses were displayed (in Tables/histograms and gray level maps/images of concentrations of Uranium, Thorium and Potassium prospects) and interpreted (dismissing the magnetic data as seemingly passive as no filter was applied to the mapped data).展开更多
This study was aimed at mapping the subsurface extent of saline water intrusions into aquifers at the eastern part of Dahomey basin, Nigeria. The study adopted geoelectric sounding methods. 108 vertical electrical sou...This study was aimed at mapping the subsurface extent of saline water intrusions into aquifers at the eastern part of Dahomey basin, Nigeria. The study adopted geoelectric sounding methods. 108 vertical electrical soundings (VES) and 9 induced polarization soundings (IPS) data were acquired using Schlumberger array technique. Three aquifer units were delineated across the study area. The resistivity of the first, second and third aquifer layers varies from 0.2 to 1569 ohm-m, 0.5 to 904 ohm-m and 0.4 to 665 ohm-m respectively, while depth to the top of first, second and third aquifer varies respectively from 0.7 to 151.5 m, 1.4 to 305.5 m and 12.9 to 452.9 m. The depth to the first aquifer layer is shallow (less than 5 m) in the coastal area which makes this area to be highly vulnerable to anthropogenic pollution while their proximity to Atlantic Ocean makes them susceptible to saline water intrusion. In all the three aquifer units, the coastal area, Agbabu and other few locations in the mainland are characterized by low resistivity values (below 60 ohm-m) indicating possible presence of brackish or saline water. IP sounding results showed that all the low resistive layers in the mainland are characterized by clayey materials. The integration of VES and IPS results enabled the delineation of the saline water lateral extent across the study area. There is a strong direct correlation (r2 = 0.8564) between location distance from the saline water source and depth to saline water in the study area. This can therefore serve as a predictive model to determine depth to saline water at any location within the saline water zone in the study area.展开更多
Aeromagnetic data for center-east Cameroon between the latitudes 3.5° to 4.5°N and longitudes 12° to 12.5°E are used to further study the subsurface area of this part of the geological Province of ...Aeromagnetic data for center-east Cameroon between the latitudes 3.5° to 4.5°N and longitudes 12° to 12.5°E are used to further study the subsurface area of this part of the geological Province of Central Africa and the Congo Craton. The GIS and GEOSOFT v6.5 softwares are used to treat the data. This analysis enabled us to explore our study area from surface right to the base. The Tilt Angle method is used to delineate geological structures and to estimate the depth. The Euler’s deconvolution method is used to estimate the specific depth of structural contacts. We estimate the northern boundary of the Congo Craton and southern boundary of the Pan-African starting from 3°7'N of West to 3°75'N of East. Its depth is estimated around 2.6 km for deep and 0.1 km for shallow while the direction is WSW-ENE and the NW slope varies from 30° to 60°. We obtain that main and minor lineaments exist throughout, from the surface to the base of the area with their principal direction being SW-NE. We also obtain the vertical gradient contact and the quasihorizontal contact. This is proof of the subduction of the Pan-African belt under the Congo Craton due to the intense collision which caused the rejuvenation of the crust. The main consequence of this collision is the formation of pudding and fold structures, beginning from the superficial part right to the base and which caused the intrusion of schistose, chlorite-schist, quartzite in the micaschist and the intrusions of gneiss and garnetiferous schist in the migmatite. In our study, we highlight the presence of 37 major and 523 minor lineaments that localize the circulation of minerals. The probable slope of the lineaments in the northern part of the region varies from 30° to 60° in a SE direction while in the southern part, and it varies from 30° to 60° in a NW direction.展开更多
The disastrous Mw 9.3 （seismic moment 1.0 × 10^30 dyn/cm） earthquake that struck northwest Sumatra on 26 December 2004 and triggered -30 m high tsunami has rejuvenated the quest for identi- fying the forcing be...The disastrous Mw 9.3 （seismic moment 1.0 × 10^30 dyn/cm） earthquake that struck northwest Sumatra on 26 December 2004 and triggered -30 m high tsunami has rejuvenated the quest for identi- fying the forcing behind subduction related earthquakes around the world. Studies reveal that the stron- gest part （elastic core） of the oceanic lithosphere lie between 20 and 60 km depth beneath the upper （- 7 km thick） crustal layer, and compressive stress of GPa order is required to fail the rock-layers within the core zone. Here we present evidences in favor of an intraplate origin of mega-earthquakes right within the strong core part （at the interface of semi-brittle and brittle zone）, and propose an alternate model exploring the flexing zone of the descending lithosphere as the nodal area for major stress accumulation. We believe that at high confining pressure and elevated temperature, unidirectional cyclic compressive stress loading in the flexing zone results in an increase of material yield strength through strain hardening, which transforms the rheology of the layer from semi-brittle to near-brittle state. The increased compres- sive stress field coupled with upward migration of the neutral surface （of zero stress fields） under non- coaxial deformation triggers shear crack. The growth of the shear crack is initially confined in the near-brittle domain, and propagates later through the more brittle crustal part of the descending oceanic lithosphere in the form of cataclastic failure,展开更多
The present research work attempted to delineate and characterize the reservoir facies from the Dawson Canyon Formation in the Penobscot field,Scotian Basin.An integrated study of instantaneous frequency,P-impedance,v...The present research work attempted to delineate and characterize the reservoir facies from the Dawson Canyon Formation in the Penobscot field,Scotian Basin.An integrated study of instantaneous frequency,P-impedance,volume of clay and neutron-porosity attributes,and structural framework was done to unravel the Late Cretaceous depositional system and reservoir facies distribution patterns within the study area.Fault strikes were found in the EW and NEE-SWW directions indicating the dominant course of tectonic activities during the Late Cretaceous period in the region.P-impedance was estimated using model-based seismic inversion.Petrophysical properties such as the neutron porosity(NPHI)and volume of clay(VCL)were estimated using the multilayer perceptron neural network with high accuracy.Comparatively,a combination of low instantaneous frequency(15-30 Hz),moderate to high impedance(7000-9500 gm/cc*m/s),low neutron porosity(27%-40%)and low volume of clay(40%-60%),suggests fair-to-good sandstone development in the Dawson Canyon Formation.After calibration with the welllog data,it is found that further lowering in these attribute responses signifies the clean sandstone facies possibly containing hydrocarbons.The present study suggests that the shale lithofacies dominates the Late Cretaceous deposition(Dawson Canyon Formation)in the Penobscot field,Scotian Basin.Major faults and overlying shale facies provide structural and stratigraphic seals and act as a suitable hydrocarbon entrapment mechanism in the Dawson Canyon Formation's reservoirs.The present research advocates the integrated analysis of multi-attributes estimated using different methods to minimize the risk involved in hydrocarbon exploration.展开更多
Geoscientific evidence shows that various parameters such as compaction,buoyancy effect,hydrocarbon maturation,gas effect and tectonic activities control the pore pressure of sub-surface geology.Spatially controlled g...Geoscientific evidence shows that various parameters such as compaction,buoyancy effect,hydrocarbon maturation,gas effect and tectonic activities control the pore pressure of sub-surface geology.Spatially controlled geoscientific data in the tectonically active areas is significantly useful for robust estimation of pre-drill pore pressure.The reservoir which is tectonically complex and pore pressure is changing frequently that circumference motivated us to conduct this study.The changes in pore pressure have been captured from the fine-scale to the broad scale in the Jaisalmer sub-basin.Pore pressure variation has been distinctly observed in pre-and post-Jurassic age based on the current study.Post-stack seismic inversion study was conducted to capturing the variation of pore pressure.Analysis of low-frequency spectrum and integrated interval velocity model provided a detailed feature of pore pressure in each compartment of the study area.Pore pressure estimated from well log data was correlated with seismic inversion based result.Based on the current study one well has been proposed where pore pressure was estimated and two distinguished trends are identified in the study zone.The approaches of the current study were analysed thoroughly and it will be highly useful in complex reservoir condition where pore pressure varies frequently.展开更多
In this study, the characterization of the depth of the Mohorovicic discontinuity under the crust of Funafuti island was determined by analyzing the 3 component seismograms from 54 different earthquake events recorded...In this study, the characterization of the depth of the Mohorovicic discontinuity under the crust of Funafuti island was determined by analyzing the 3 component seismograms from 54 different earthquake events recorded by the station between 2008 and 2012. These seismograms were from teleseismic earthquakes whose epicenter lay at distances greater than 3000 km from the station. The seismograms were iteratively deconvolved in the time domain to remove the unwanted noise and then stacked to obtain better receiver functions. For analysis of the receiver functions, it was assumed that the range in which the Vp/Vs ratio would lie for the given region would be between 1.60 - 1.85 and the depth of the discontinuity was assumed to lie between 5 - 20 km. Analysis of the receiver functions showed that the Mohorovicic discontinuity was at a depth of 11 km and the Vp/Vs ratio was 1.75 for the region.展开更多
An electrical resistivity sounding investigation was carried out within the vicinity of some hand dug wells at Temidire Quarters in Akure, Ondo State, Nigeria. The aim of this study was to compare depth and thickness ...An electrical resistivity sounding investigation was carried out within the vicinity of some hand dug wells at Temidire Quarters in Akure, Ondo State, Nigeria. The aim of this study was to compare depth and thickness resolution power of Schlumberger and Wenner arrays. The investigation involved twenty-four vertical electrical soundings (VES) which consisted of twelve Schlumberger array VES and twelve Wenner array VES. The VES results delineated geoelectric layers beneath each VES locations, their layer resistivities, layer thicknesses and depth to aquifer layer(s). Depth to aquifer layer was also determined from static water level measurement and this aided the aquifer layer delineation from VES results. The geoelectric sounding results showed that the study area is dominated by a KH-curve type which consists of top soil, clay/weathered layer, fractured basement and fresh basement. Results from both Schlumberger and Wenner array data were correlated with the static water level measurement;Schlumberger array was found to have higher correlation value than Wenner array.展开更多
This study is aimed at evaluating groundwater potential of Ipinsa-Okeodu area, near Akure, Southwestern Nigeria. A multi-criteria model was developed for achieving this aim;the GRT model which is based on geology of e...This study is aimed at evaluating groundwater potential of Ipinsa-Okeodu area, near Akure, Southwestern Nigeria. A multi-criteria model was developed for achieving this aim;the GRT model which is based on geology of each sounding point, resistivity, and thickness of the aquifer across the study area was successfully used to evaluate the aquifer potential of the area for future groundwater development programme in the area. Geophysical investigation involving vertical electrical sounding was carried out across the study area. A total of one hundred and two (102) vertical electrical soundings (VES) data were acquired using Schlumberger array with maximum half-current electrode separation of 150 m. Three to five geoelectric layers were delineated across the study area. The predominant curve types are KH, H, K and A. The maps of aquifer layer resistivity and aquifer layer thickness were generated and synthesized with the geology of the study area in producing the GRT model map/groundwater potential map. The groundwater potential map shows that the area is characterized by five groundwater potential zones;poor, low, moderate, good and high. The northwestern regions, north central and part of the southwestern regions are high groundwater potential zones, the northern and most part of southeastern zone are of moderate potential, while small portion in the southeastern and northern zones are of low groundwater potential.展开更多
In this study, an integrated remote sensing and geophysical (aeromagnetic and geo-electric) methods was employed to assess the potential of groundwater in a basement complex terrain of Okene and its environs, Southwes...In this study, an integrated remote sensing and geophysical (aeromagnetic and geo-electric) methods was employed to assess the potential of groundwater in a basement complex terrain of Okene and its environs, Southwestern, Nigeria. Landsat imagery acquired over the study area was processed in the Geographic Information Systems (GIS) environment to delineate the surface lineaments, drainage networks and their orientations. Aeromagnetic data over the area were analyzed and its derivative maps were interpreted to further map the structures and the geology in the subsurface;depths to magnetic sources were determined using spectral analysis. Vertical Electrical Sounding (VES) of geo-electric method was interpreted to map the subsurface geology layers. The results of the integrated data were correlated with borehole yield data of the area for effective interpretation. Delineated lineaments from the azimuth, frequency plot showed dominant trends in the NE-SW and NNE-SSW directions. Radial average power spectrum revealed the depth to magnetic sources between 100 and 2500 m and the interpreted VES data characterized the area into three to four subsurface layers. In correlating the results with borehole yield data, the zones with high lineament density and low/negative magnetic anomaly were categorized as high groundwater potential zones while areas with low lineament density and high/positive magnetic anomaly as low groundwater potential zones. This study will guide efficiently subsequent groundwater drilling program in the study area.展开更多
Geodynamics is the study of the forces and their effects on motion and physics of the processes and the phenomena attending the steady evolution of the earth and the changes that are still going on. This study reveall...Geodynamics is the study of the forces and their effects on motion and physics of the processes and the phenomena attending the steady evolution of the earth and the changes that are still going on. This study revealled the significance of electrical resistivity method on effect of geodynamic activities on an existing Dam monitoring at Ojirami Dam, Edo State, Nigeria. The electrical resistivity method involved three techniques: 2D Electrical Resistivity Tomography (ERT), Vertical Electrical Sounding (VES) and Horizontal Profiling (HP). 2D ERT using Dipole-Dipole electrode array with inter-station separation of 5 m and an expansion factor that varied from 1 to 5 with Nine (9) VES were carried out using Schlumberger array with current electrode spacing varying from 1.0 to 65.0 m and HP using Wenner array with an electrode spacing of 20 m and electrode movement at 5 meters. The 2-D imaging (Dipole-Dipole) gave information on the subsurface characteristic which section delineated five major geologic layers comprising of the topsoil, weathered basement, fractured zone, partly fractured basement and the fresh basement. The geoelectric sections identified three to four geoelectric/geologic subsurface layers along the traverse. The HP revealled the pattern of resistivity variations within the subsurface. The entire results correlate well with one another showing that all the techniques used were complemented. The combination of these techniques has proved effective and useful in geodynamic activities of the existing dam. Ojirami Dam is at a critical point of yielding to activities of geodynamic processes that may occur from the main axis, of major weak zones as observed between 75 to 95.00 m and 115 to 145.00 m. Hence, there is need to call government attention for further confirmatory test using other geophysical methods and subsequently putting in place remedial measures to prevent its future occurrence.展开更多
Well log responses can be used to delineate coal and carbonaceous shale from other non-potential litho-units by cross-plotting technique. The cross-plotting between gamma ray and density had been carried out for 15 we...Well log responses can be used to delineate coal and carbonaceous shale from other non-potential litho-units by cross-plotting technique. The cross-plotting between gamma ray and density had been carried out for 15 wells of Jharia coalfield, India. Through these different cross-plots across the study area, different litho-units like;coal, shaly coal, carbonaceous shale, shale, sand/sandstone, shaly sand, jhama and igneous intrusion (mica peridotite) have been identified. Clustering of points for different lithologies in the above cross-plots indicate that the different trends with marginal overlap between carbonaceous shale/shaly coal and shale as well as shaly sand and shale. The coal horizons are mostly overlain and underlain by shale or sandstone. Cross-plot analysis indicates the various coal lithologies which will play important role in CBM exploration and exploitation strategy.展开更多
exploitation work..The reservoir quality is a function of its petrophysical parameters.Hence the need to model these properties geostatistically in order to determine the quality away from well locations.Composite log...exploitation work..The reservoir quality is a function of its petrophysical parameters.Hence the need to model these properties geostatistically in order to determine the quality away from well locations.Composite logs for four wells and 3-D seismic data were used for the analysis.A reservoir named Sand X was mapped and correlated across wells 1 through 4.The four reservoir quality indicators-Effective porosity,permeability,volume of shale and net-to-gross-were estimated and modelled across the field.Sequential Gaussian simulation algorithm was employed to distribute these properties stochastically away from well locations and five realizations were generated.The volume of shale varied from 0.025(Well 1,second realization)to 0.18(Well 2,first realization).The net-to-gross varied from 0.81 to 0.96 in wells 3 and 4 respectively,for the third realization,while the effective porosity varied from 0.125 to 0.295 for the fifth realization in Wells 3 and 4 respectively.The permeability is above 5000mD at all the existing well locations.These realizations were ranked using Lp norm statistical tool to pick the best for further evaluation.The reservoir quality deduced from the analyzed indicators was favourably high across the reservoir.The application of geostatistics has laterally enhanced the log data resolution away from established well locations.展开更多
A geophysical survey involving the electrical resistivity method utilizing the Vertical Electrical Sounding (VES) and Electrical Imaging Techniques was conducted around the premises of an area within south-western Nig...A geophysical survey involving the electrical resistivity method utilizing the Vertical Electrical Sounding (VES) and Electrical Imaging Techniques was conducted around the premises of an area within south-western Nigeria with the aim of studying structural defects which may be responsible for future problems and characterizing the soil conditions of the site. A total of 15 VES stations were occupied using Schlumberger Configuration with AB/2 varying from 1 to 65 m. In the electrical imaging, dipole-dipole array was adopted and the two traverses were occupied in the S-N and E-W directions close to where wall cracks and subsurface problems were manifested. Five main geoelectric sequences were delineated within the study area;these include the topsoil (clay and sandy clay), lateritic clay, weathered bedrock (clay, sandy clay and clayey sand), fractured bedrock and fresh basement. A major discontinuity (fracture zone) was discovered along the S-N direction, while a weak zone was also discovered along E-W direction. The result of this research has shown that the causes of the cracks and distress on the walls within the site may have been influenced by the differential settlement resulting from the incompetent subsoil materials and the fractured bedrock on which the foundation of the building was laid.展开更多
基金funding the project (MoES/P.O. (Seismo)/1(273)/2015)
文摘Estimation of petrophysical parameters is an important issue of any reservoirs. Porosity, volume of shale and water saturation has been evaluated for reservoirs of Upper Assam basin, located in northeastern India from well log and seismic data. Absolute acoustic impedance(AAI) and relative acoustic impedance(RAI) are generated from model based inversion of 2-D post-stack seismic data. The top of geological formation, sand reservoirs, shale layers and discontinuities at faults are detected in RAI section under the study area. Tipam Sandstone(TS) and Barail Arenaceous Sandstone(BAS) are the main reservoirs,delineated from the logs of available wells and RAI section. Porosity section is obtained using porosity wavelet and porosity reflectivity from post-stack seismic data. Two multilayered feed forward neural network(MLFN) models are created with inputs: AAI, porosity, density and shear impedance and outputs: volume of shale and water saturation with single hidden layer. The estimated average porosity in TS and BAS reservoir varies from 30% to 36% and 18% to 30% respectively. The volume of shale and water saturation ranges from 10% to 30% and 20% to 60% in TS reservoir and 28% to 30% and 23% to 55% in BAS reservoir respectively.
基金supported by the grant of the Department of Science and Technology,Govt.of India,New Delhi
文摘We address the role of the concave and convex arcs （as observed from the subducting plate） on the deformation occurring along the Myanmar-Andaman-Sumatra margin. We categorize the pre- and post-seismic deformations of the lithosphere using earthquake database occurring either prior to 26th December 2004 Mw 9.3 off-Sumatra mega-event or after the incidence. Analysis under pre-seismic domain shows that area near Sumatra records highest seismicity, which largely drops in the area past the North Andaman, and further increases towards north. Shallowest depth and mini- mum dip of the subducting lithosphere is recorded at the central segment where the arc transformed into concave shape. The annual moment energy release during earthquake decreases to more than two orders of magnitude past the North Andaman towards north under post-seismic deformation phase. Higher depths of continuity of events are presumably associated with more dipping Benioff zones in both the Indo-Myanmar and Andaman-Nicobar convex arcs. These observations obviously account for tectonic subdivision of the margin near concave shape arc around the central part. Absence of vol- canism, presence of splay faults in the back-arc, sharp reduction in seismicity near central segment are interpreted to be caused by major tectonic impact of the NNE-ward converging buoyant Ninety-east Ridge against the Asian Plate. Shallowest dip, small elastic thickness, weak converging Indian litho- sphere, and evidences of series of en-echelon blocks off the eastern side of the broken northern Ninety- east Ridge might be incapable of generating great earthquake in this area.
文摘This study is focused on the effect of vibration induced by moving trains in tunnels on the surrounding ground and structures.A three-dimensional finite element model is established for a one-track railway tunnel and an adjacent twelve-storey building frame by using commercial software Midas GTS-NX(2019)and Midas Gen.This study considered the moving load effect of a complete train,which varies with space as well as with time.The effect of factors such as train speed,overburden pressure on the tunnel and variation in soil properties are studied in the time domain.As a result,the variations in horizontal and vertical acceleration for two different sites,i.e.,the free ground surface(without structure)and the area containing the structure,are compared.Also,the displacement pattern of the raft foundation is plotted for different train velocities.At lower speeds,the heaving phenomenon is negligible,but as the speed increases,both the heaving and differential settlement increase in the foundation.This study demonstrates that the effect of moving train vibrations should be considered in the design of new nearby structures and proper ground improvement should be considered for existing structures.
文摘Pore pressure(PP)information plays an important role in analysing the geomechanical properties of the reservoir and hydrocarbon field development.PP prediction is an essential requirement to ensure safe drilling operations and it is a fundamental input for well design,and mud weight estimation for wellbore stability.However,the pore pressure trend prediction in complex geological provinces is challenging particularly at oceanic slope setting,where sedimentation rate is relatively high and PP can be driven by various complex geo-processes.To overcome these difficulties,an advanced machine learning(ML)tool is implemented in combination with empirical methods.The empirical method for PP prediction is comprised of data pre-processing and model establishment stage.Eaton's method and Porosity method have been used for PP calculation of the well U1517A located at Tuaheni Landslide Complex of Hikurangi Subduction zone of IODP expedition 372.Gamma-ray,sonic travel time,bulk density and sonic derived porosity are extracted from well log data for the theoretical framework construction.The normal compaction trend(NCT)curve analysis is used to check the optimum fitting of the low permeable zone data.The statistical analysis is done using the histogram analysis and Pearson correlation coefficient matrix with PP data series to identify potential input combinations for ML-based predictive model development.The dataset is prepared and divided into two parts:Training and Testing.The PP data and well log of borehole U1517A is pre-processed to scale in between[-1,+1]to fit into the input range of the non-linear activation/transfer function of the decision tree regression model.The Decision Tree Regression(DTR)algorithm is built and compared to the model performance to predict the PP and identify the overpressure zone in Hikurangi Tuaheni Zone of IODP Expedition 372.
文摘The signal-to-noise ratio （SNR） of seismic reflection data in many areas is rather poor and conventional two-dimensional filters designed to suppress noise with different moveout from the signal tend to generate artifacts. We have extended a method of multichannel filtering, based on the hypothesis that signals on adjacent channels are similar, for enhancing the SNR on stacked sections. Using only the mid-range frequencies where the SNR is highest, the event trend is found for overlapping windows on the section and the average signal vector is calculated. Then the data from the full bandwidth section are projected onto the spatially varying unit similarity vectors and the results are merged for the overlapping windows. Application of the method to synthetic data containing steeply dipping events and to a stacked section for a marine 2D line has produced good results. The modifications we have introduced carry a small overhead in computing time but they should enable the method to be used effectively even on sections containing steep dips.
文摘Core samples representing depths of hydrocarbon-bearing zones are not readily accessible for reservoir evaluations.On the other hand,wireline logs with incorporated seismic data,which can be archived over a more extended period while retaining their original forms,are typically more available for research purposes.Therefore,the study relies on wireline logs with seismic data to predict the reservoirs'fluid mobility by evaluating the hydraulic(flow)units,reservoir depths,fluid saturations,and geothermal gradients.It also indicates the associated water cut(C_(w))within Ritchie oil and gas field,Niger Delta considering a three-phase(oil-gas-water-bearing)reservoir(R_(A))and an oil-saturated reservoir(R_(B))delineated across three wells(R_(W1),R_(W2) and R_(W3)).Research activities combining the presented factors to achieve the stated objectives are not quite common within the study location.It shows lower,average and upper limits of the flow unit factors and irreducible water saturation(S_(wirr))within the reservoirs.The study shows the relationship between hydraulic units/fluid saturations and fluid mobility/associated C_(w) within the sandstone reservoirs.It maximises porosity(Ф)for the theoretical flow units'prediction during qualitative and quantitative estimation based on the adopted expressions.Therefore,the study reveals that water saturation(S_(w))and hydrocarbon/water ratios substantially control C_(w),and other contributing factors include thermal gradients and S_(wirr).The flow unit factors are also significant and will encourage fluid mobility.The evaluated reservoirs(R_(A) and R_(B))are below 10400 ft(3170 m)across wells R_(W1),R_(W2) and R_(W3) within the Agbada Formation of a geothermal gradient up to 2.7℃/100 m;therefore,they have good thermal conditions to enhance hydrocarbon mobility and increase S wirr.Hence,the reservoir should feature significant hydrocarbon extraction via primary recovery.The average water cut(C_(w-avg).)(12.3%)estimated for reservoir R_(A) is within the acceptable range;therefore,the associated water production from the three-phase reservoir will not be much of a concern.In addition,simple models are presented to aid an alternative approach for predicting reservoir quality and C_(w) within sandstone res-ervoirs,especially in the absence of core samples.
文摘The paper presents results of radiometric investigations of an area (Duku-Tarasa) near the capital city of the State of Birnin Kebbi, NW Nigeria. The area of study is about 440 m × 420 m and encloses an Escarpment Feature/Structure on a sedimentary rock generally referred to as the Gwandu Formation. The Gwandu Formation (though not described in the paper) consists of continental lacustrine sediments and is the youngest Palaeogene Formation present in the Sokoto sector of the larger Iullemmeden Basin. The study measured, along some selected profiles across this escarpment feature, radiometric signatures using a Sim-Max G411 portable field gamma-ray spectrometer (giving counts for U, Th and K relative to the background values over the area), the ground total-field magnetic data (using the proton precession magnetometer) along those profiles and collected some (5) rock samples for flame photometry and AAS analyses towards the target proposition. Activity concentration levels due to potassium (K), uranium (U) and thorium (Th) were measured in the area along the five established profiles spaced at 50 metres. The results from these measurements and analyses were displayed (in Tables/histograms and gray level maps/images of concentrations of Uranium, Thorium and Potassium prospects) and interpreted (dismissing the magnetic data as seemingly passive as no filter was applied to the mapped data).
文摘This study was aimed at mapping the subsurface extent of saline water intrusions into aquifers at the eastern part of Dahomey basin, Nigeria. The study adopted geoelectric sounding methods. 108 vertical electrical soundings (VES) and 9 induced polarization soundings (IPS) data were acquired using Schlumberger array technique. Three aquifer units were delineated across the study area. The resistivity of the first, second and third aquifer layers varies from 0.2 to 1569 ohm-m, 0.5 to 904 ohm-m and 0.4 to 665 ohm-m respectively, while depth to the top of first, second and third aquifer varies respectively from 0.7 to 151.5 m, 1.4 to 305.5 m and 12.9 to 452.9 m. The depth to the first aquifer layer is shallow (less than 5 m) in the coastal area which makes this area to be highly vulnerable to anthropogenic pollution while their proximity to Atlantic Ocean makes them susceptible to saline water intrusion. In all the three aquifer units, the coastal area, Agbabu and other few locations in the mainland are characterized by low resistivity values (below 60 ohm-m) indicating possible presence of brackish or saline water. IP sounding results showed that all the low resistive layers in the mainland are characterized by clayey materials. The integration of VES and IPS results enabled the delineation of the saline water lateral extent across the study area. There is a strong direct correlation (r2 = 0.8564) between location distance from the saline water source and depth to saline water in the study area. This can therefore serve as a predictive model to determine depth to saline water at any location within the saline water zone in the study area.
文摘Aeromagnetic data for center-east Cameroon between the latitudes 3.5° to 4.5°N and longitudes 12° to 12.5°E are used to further study the subsurface area of this part of the geological Province of Central Africa and the Congo Craton. The GIS and GEOSOFT v6.5 softwares are used to treat the data. This analysis enabled us to explore our study area from surface right to the base. The Tilt Angle method is used to delineate geological structures and to estimate the depth. The Euler’s deconvolution method is used to estimate the specific depth of structural contacts. We estimate the northern boundary of the Congo Craton and southern boundary of the Pan-African starting from 3°7'N of West to 3°75'N of East. Its depth is estimated around 2.6 km for deep and 0.1 km for shallow while the direction is WSW-ENE and the NW slope varies from 30° to 60°. We obtain that main and minor lineaments exist throughout, from the surface to the base of the area with their principal direction being SW-NE. We also obtain the vertical gradient contact and the quasihorizontal contact. This is proof of the subduction of the Pan-African belt under the Congo Craton due to the intense collision which caused the rejuvenation of the crust. The main consequence of this collision is the formation of pudding and fold structures, beginning from the superficial part right to the base and which caused the intrusion of schistose, chlorite-schist, quartzite in the micaschist and the intrusions of gneiss and garnetiferous schist in the migmatite. In our study, we highlight the presence of 37 major and 523 minor lineaments that localize the circulation of minerals. The probable slope of the lineaments in the northern part of the region varies from 30° to 60° in a SE direction while in the southern part, and it varies from 30° to 60° in a NW direction.
基金the Ministry of Earth Seiences,Govt.of India for the finaneial support
文摘The disastrous Mw 9.3 （seismic moment 1.0 × 10^30 dyn/cm） earthquake that struck northwest Sumatra on 26 December 2004 and triggered -30 m high tsunami has rejuvenated the quest for identi- fying the forcing behind subduction related earthquakes around the world. Studies reveal that the stron- gest part （elastic core） of the oceanic lithosphere lie between 20 and 60 km depth beneath the upper （- 7 km thick） crustal layer, and compressive stress of GPa order is required to fail the rock-layers within the core zone. Here we present evidences in favor of an intraplate origin of mega-earthquakes right within the strong core part （at the interface of semi-brittle and brittle zone）, and propose an alternate model exploring the flexing zone of the descending lithosphere as the nodal area for major stress accumulation. We believe that at high confining pressure and elevated temperature, unidirectional cyclic compressive stress loading in the flexing zone results in an increase of material yield strength through strain hardening, which transforms the rheology of the layer from semi-brittle to near-brittle state. The increased compres- sive stress field coupled with upward migration of the neutral surface （of zero stress fields） under non- coaxial deformation triggers shear crack. The growth of the shear crack is initially confined in the near-brittle domain, and propagates later through the more brittle crustal part of the descending oceanic lithosphere in the form of cataclastic failure,
文摘The present research work attempted to delineate and characterize the reservoir facies from the Dawson Canyon Formation in the Penobscot field,Scotian Basin.An integrated study of instantaneous frequency,P-impedance,volume of clay and neutron-porosity attributes,and structural framework was done to unravel the Late Cretaceous depositional system and reservoir facies distribution patterns within the study area.Fault strikes were found in the EW and NEE-SWW directions indicating the dominant course of tectonic activities during the Late Cretaceous period in the region.P-impedance was estimated using model-based seismic inversion.Petrophysical properties such as the neutron porosity(NPHI)and volume of clay(VCL)were estimated using the multilayer perceptron neural network with high accuracy.Comparatively,a combination of low instantaneous frequency(15-30 Hz),moderate to high impedance(7000-9500 gm/cc*m/s),low neutron porosity(27%-40%)and low volume of clay(40%-60%),suggests fair-to-good sandstone development in the Dawson Canyon Formation.After calibration with the welllog data,it is found that further lowering in these attribute responses signifies the clean sandstone facies possibly containing hydrocarbons.The present study suggests that the shale lithofacies dominates the Late Cretaceous deposition(Dawson Canyon Formation)in the Penobscot field,Scotian Basin.Major faults and overlying shale facies provide structural and stratigraphic seals and act as a suitable hydrocarbon entrapment mechanism in the Dawson Canyon Formation's reservoirs.The present research advocates the integrated analysis of multi-attributes estimated using different methods to minimize the risk involved in hydrocarbon exploration.
文摘Geoscientific evidence shows that various parameters such as compaction,buoyancy effect,hydrocarbon maturation,gas effect and tectonic activities control the pore pressure of sub-surface geology.Spatially controlled geoscientific data in the tectonically active areas is significantly useful for robust estimation of pre-drill pore pressure.The reservoir which is tectonically complex and pore pressure is changing frequently that circumference motivated us to conduct this study.The changes in pore pressure have been captured from the fine-scale to the broad scale in the Jaisalmer sub-basin.Pore pressure variation has been distinctly observed in pre-and post-Jurassic age based on the current study.Post-stack seismic inversion study was conducted to capturing the variation of pore pressure.Analysis of low-frequency spectrum and integrated interval velocity model provided a detailed feature of pore pressure in each compartment of the study area.Pore pressure estimated from well log data was correlated with seismic inversion based result.Based on the current study one well has been proposed where pore pressure was estimated and two distinguished trends are identified in the study zone.The approaches of the current study were analysed thoroughly and it will be highly useful in complex reservoir condition where pore pressure varies frequently.
文摘In this study, the characterization of the depth of the Mohorovicic discontinuity under the crust of Funafuti island was determined by analyzing the 3 component seismograms from 54 different earthquake events recorded by the station between 2008 and 2012. These seismograms were from teleseismic earthquakes whose epicenter lay at distances greater than 3000 km from the station. The seismograms were iteratively deconvolved in the time domain to remove the unwanted noise and then stacked to obtain better receiver functions. For analysis of the receiver functions, it was assumed that the range in which the Vp/Vs ratio would lie for the given region would be between 1.60 - 1.85 and the depth of the discontinuity was assumed to lie between 5 - 20 km. Analysis of the receiver functions showed that the Mohorovicic discontinuity was at a depth of 11 km and the Vp/Vs ratio was 1.75 for the region.
文摘An electrical resistivity sounding investigation was carried out within the vicinity of some hand dug wells at Temidire Quarters in Akure, Ondo State, Nigeria. The aim of this study was to compare depth and thickness resolution power of Schlumberger and Wenner arrays. The investigation involved twenty-four vertical electrical soundings (VES) which consisted of twelve Schlumberger array VES and twelve Wenner array VES. The VES results delineated geoelectric layers beneath each VES locations, their layer resistivities, layer thicknesses and depth to aquifer layer(s). Depth to aquifer layer was also determined from static water level measurement and this aided the aquifer layer delineation from VES results. The geoelectric sounding results showed that the study area is dominated by a KH-curve type which consists of top soil, clay/weathered layer, fractured basement and fresh basement. Results from both Schlumberger and Wenner array data were correlated with the static water level measurement;Schlumberger array was found to have higher correlation value than Wenner array.
文摘This study is aimed at evaluating groundwater potential of Ipinsa-Okeodu area, near Akure, Southwestern Nigeria. A multi-criteria model was developed for achieving this aim;the GRT model which is based on geology of each sounding point, resistivity, and thickness of the aquifer across the study area was successfully used to evaluate the aquifer potential of the area for future groundwater development programme in the area. Geophysical investigation involving vertical electrical sounding was carried out across the study area. A total of one hundred and two (102) vertical electrical soundings (VES) data were acquired using Schlumberger array with maximum half-current electrode separation of 150 m. Three to five geoelectric layers were delineated across the study area. The predominant curve types are KH, H, K and A. The maps of aquifer layer resistivity and aquifer layer thickness were generated and synthesized with the geology of the study area in producing the GRT model map/groundwater potential map. The groundwater potential map shows that the area is characterized by five groundwater potential zones;poor, low, moderate, good and high. The northwestern regions, north central and part of the southwestern regions are high groundwater potential zones, the northern and most part of southeastern zone are of moderate potential, while small portion in the southeastern and northern zones are of low groundwater potential.
文摘In this study, an integrated remote sensing and geophysical (aeromagnetic and geo-electric) methods was employed to assess the potential of groundwater in a basement complex terrain of Okene and its environs, Southwestern, Nigeria. Landsat imagery acquired over the study area was processed in the Geographic Information Systems (GIS) environment to delineate the surface lineaments, drainage networks and their orientations. Aeromagnetic data over the area were analyzed and its derivative maps were interpreted to further map the structures and the geology in the subsurface;depths to magnetic sources were determined using spectral analysis. Vertical Electrical Sounding (VES) of geo-electric method was interpreted to map the subsurface geology layers. The results of the integrated data were correlated with borehole yield data of the area for effective interpretation. Delineated lineaments from the azimuth, frequency plot showed dominant trends in the NE-SW and NNE-SSW directions. Radial average power spectrum revealed the depth to magnetic sources between 100 and 2500 m and the interpreted VES data characterized the area into three to four subsurface layers. In correlating the results with borehole yield data, the zones with high lineament density and low/negative magnetic anomaly were categorized as high groundwater potential zones while areas with low lineament density and high/positive magnetic anomaly as low groundwater potential zones. This study will guide efficiently subsequent groundwater drilling program in the study area.
文摘Geodynamics is the study of the forces and their effects on motion and physics of the processes and the phenomena attending the steady evolution of the earth and the changes that are still going on. This study revealled the significance of electrical resistivity method on effect of geodynamic activities on an existing Dam monitoring at Ojirami Dam, Edo State, Nigeria. The electrical resistivity method involved three techniques: 2D Electrical Resistivity Tomography (ERT), Vertical Electrical Sounding (VES) and Horizontal Profiling (HP). 2D ERT using Dipole-Dipole electrode array with inter-station separation of 5 m and an expansion factor that varied from 1 to 5 with Nine (9) VES were carried out using Schlumberger array with current electrode spacing varying from 1.0 to 65.0 m and HP using Wenner array with an electrode spacing of 20 m and electrode movement at 5 meters. The 2-D imaging (Dipole-Dipole) gave information on the subsurface characteristic which section delineated five major geologic layers comprising of the topsoil, weathered basement, fractured zone, partly fractured basement and the fresh basement. The geoelectric sections identified three to four geoelectric/geologic subsurface layers along the traverse. The HP revealled the pattern of resistivity variations within the subsurface. The entire results correlate well with one another showing that all the techniques used were complemented. The combination of these techniques has proved effective and useful in geodynamic activities of the existing dam. Ojirami Dam is at a critical point of yielding to activities of geodynamic processes that may occur from the main axis, of major weak zones as observed between 75 to 95.00 m and 115 to 145.00 m. Hence, there is need to call government attention for further confirmatory test using other geophysical methods and subsequently putting in place remedial measures to prevent its future occurrence.
文摘Well log responses can be used to delineate coal and carbonaceous shale from other non-potential litho-units by cross-plotting technique. The cross-plotting between gamma ray and density had been carried out for 15 wells of Jharia coalfield, India. Through these different cross-plots across the study area, different litho-units like;coal, shaly coal, carbonaceous shale, shale, sand/sandstone, shaly sand, jhama and igneous intrusion (mica peridotite) have been identified. Clustering of points for different lithologies in the above cross-plots indicate that the different trends with marginal overlap between carbonaceous shale/shaly coal and shale as well as shaly sand and shale. The coal horizons are mostly overlain and underlain by shale or sandstone. Cross-plot analysis indicates the various coal lithologies which will play important role in CBM exploration and exploitation strategy.
文摘exploitation work..The reservoir quality is a function of its petrophysical parameters.Hence the need to model these properties geostatistically in order to determine the quality away from well locations.Composite logs for four wells and 3-D seismic data were used for the analysis.A reservoir named Sand X was mapped and correlated across wells 1 through 4.The four reservoir quality indicators-Effective porosity,permeability,volume of shale and net-to-gross-were estimated and modelled across the field.Sequential Gaussian simulation algorithm was employed to distribute these properties stochastically away from well locations and five realizations were generated.The volume of shale varied from 0.025(Well 1,second realization)to 0.18(Well 2,first realization).The net-to-gross varied from 0.81 to 0.96 in wells 3 and 4 respectively,for the third realization,while the effective porosity varied from 0.125 to 0.295 for the fifth realization in Wells 3 and 4 respectively.The permeability is above 5000mD at all the existing well locations.These realizations were ranked using Lp norm statistical tool to pick the best for further evaluation.The reservoir quality deduced from the analyzed indicators was favourably high across the reservoir.The application of geostatistics has laterally enhanced the log data resolution away from established well locations.
文摘A geophysical survey involving the electrical resistivity method utilizing the Vertical Electrical Sounding (VES) and Electrical Imaging Techniques was conducted around the premises of an area within south-western Nigeria with the aim of studying structural defects which may be responsible for future problems and characterizing the soil conditions of the site. A total of 15 VES stations were occupied using Schlumberger Configuration with AB/2 varying from 1 to 65 m. In the electrical imaging, dipole-dipole array was adopted and the two traverses were occupied in the S-N and E-W directions close to where wall cracks and subsurface problems were manifested. Five main geoelectric sequences were delineated within the study area;these include the topsoil (clay and sandy clay), lateritic clay, weathered bedrock (clay, sandy clay and clayey sand), fractured bedrock and fresh basement. A major discontinuity (fracture zone) was discovered along the S-N direction, while a weak zone was also discovered along E-W direction. The result of this research has shown that the causes of the cracks and distress on the walls within the site may have been influenced by the differential settlement resulting from the incompetent subsoil materials and the fractured bedrock on which the foundation of the building was laid.
