Papers by Olawale Olatinsu
Arabian Journal of Geosciences, Sep 1, 2018
The well-established free-fluid model from NMR technique provides continuous permeability values ... more The well-established free-fluid model from NMR technique provides continuous permeability values that closely match with core permeabilities better than most theoretical models especially when it is core calibrated for field specific use. However, only few wells have NMR logs in a field while marginal fields may not have any due to economic reasons. This study explored means of achieving one of the overriding objectives of most marginal field operators, which is to reduce the overall cost of production to the attainable minimum. The free-fluid model was modified into two simple and cost-effective models in order to optimize its applicability to predict permeability in the absence of NMR data. The two new models, which were developed for the single and double porosity systems analyzed in this study, consist of calibration parameters that can be empirically determined to account for variation in reservoir quality based on the rock type profile per field. A non-matrix parameter, α, was introduced into the model derived for tight gas sandstone being regarded as a double-porosity formation. This inclusion represents the permeability contribution of natural fractures or any crack-like pores to the different flow units. By using the alternative version to the known free-fluid model, continuous permeability curves that match experimental results were predicted without NMR logs.
Ife Journal of Science, Mar 19, 2018
Porosity from log response such as density provides a continuous representation of pore volume as... more Porosity from log response such as density provides a continuous representation of pore volume as function of depth in a well, which can be calibrated with core analysis data. Obtaining a continuous log of permeability is not as straightforward as there is yet no means of logging permeability. While DST-derived permeability values are useful in calibrating dynamic models, they only represent an average value over the radius investigated by the test and will not readily correlate to permeability values derived from core especially where there are lateral and vertical permeability variations within the reservoir. It is, however, possible to obtain a depth-continuous permeability estimate by deriving a free regression algorithm known as the poroperm transform function, which defines how the permeability varies as a function of porosity. Such correlations are typically derived empirically from overburden corrected core-derived porosity and permeability data. General porosity-permeability trends are far too scattered to be of use. However, far tighter porosity-permeability trends can be obtained by use of rock typing to identify suitable analogues. The following study highlights how microstructural rock-tying can be used to improve permeability prediction in a set of tight gas sandstone wells. Scanning electron microscopy (SEM) and quantitative X-ray diffraction (QXRD) data were obtained from >200 tight gas sandstone samples from the Southern North Sea for which porosity and permeability measurements had previously been conducted. The SEM and QXRD data were used to derive microstructural and mineralogical rock types respectively. Samples from each rock-types occupy different but overlapping positions on porosity-permeability cross plots. Exponential functions were fitted to porosity-permeability data for each rock type and then applied to the porosity values from wire-line log data to derive continuous permeability estimates. The log porosity curves-being the independent variables of the respective functions, were validated by core observation to avoid error propagation. Continuous permeability curves that honour mineralogical variation were obtained by the use of microstructural rock typing.
Advances in Applied Science Research, 2013
The dielectric properties of nine rock samples [limestone (8) and sandstone (4)] collected from E... more The dielectric properties of nine rock samples [limestone (8) and sandstone (4)] collected from Ewekoro in Ogun State, Nigeria were studied in the range 10 kHz-110 MHz under ambient atmospheric conditions. It is found that dielectric constant (r ε ′) values of the dry samples decreases with increase in frequency in the range of measurement. Dielectric dispersion is relatively large in almost all the samples. Conductivity dispersions followed the opposite trend increasing in values with increase in frequency. Peaks are more pronounced in loss tangent (D) curve than in dielectric loss (r ε ′ ′) curve. This is an indication that overall electrical response of these samples is better revealed by loss tangent variation than dielectric loss variation. All the studied samples are governed by Cole-Cole dispersion which indicates a distribution of relaxation times which is common for multicomponent systems. This is confirmed by the value of the spread parameter which is below 0.5 for all the samples.
62 vertical electrical soundings (VES) were carried out to map limestone deposits of Ewekoro form... more 62 vertical electrical soundings (VES) were carried out to map limestone deposits of Ewekoro formation, southwestern Nigeria. The maximum current electrode spacing AB/2 was 1 km. The results revealed the occurrence of limestone in all the locations within the third and fourth geoelectric layers with resistivity values ranging from 10 to 100 KΩ Ω Ω Ωm and thickness range of 15 to 90 m. The resistivity values of the limestone samples collected from the study site were also analyzed by laboratory direct method. This direct method revealed that the resistivity values fall within 6 and 171 KΩ Ω Ω Ωm. The two approaches showed a good degree of correlation in the resistivity value of the limestone and their varying qualities. This research work further showed the occurrence of vast deposit of limestone, which can be of economic importance in mining and industrial purposes.
Asian Journal of Earth Sciences, Aug 15, 2012
Geophysical evaluation and chemical analysis of kaolin clay deposit of Lakiri village, southwestern Nigeria
International Journal of Physical Sciences, Oct 31, 2009
African Journal of Environmental Science and Technology, Jun 30, 2010
A geophysical survey involving thirty four vertical electrical sounding (VES) was carried out at ... more A geophysical survey involving thirty four vertical electrical sounding (VES) was carried out at Federal College of Education, Osiele, Abeokuta, southwestern Nigeria using Schlumberger electrode array. The locations were selected based on the existing boreholes drilled in the past within the study area. The results revealed a maximum of five geoelectric layers, viz: topsoil, sandy clay, clayey sand, shale/clay, sandstone, fractured basement and fresh basement. Three probable aquifer units and one aquitard were delineated with clayey sand occurring in 50%, sandy clay constitutes 24%, fractured basement 24% and shale/clay 2%. VES 10, 26 and 30 with weathered layer (shale/clay) of thicknesses 14.7, 23.5 and 9.9 m respectively revealed very low yield (not productive). Borehole drilling in the study area should be executed in the peak of the dry seasons during which groundwater level is expected to be low because recharge of the existing boreholes in the study area is largely due to falling precipitation. Existing boreholes located within the study area characterized by unconfined aquifer while some are confined under pressure between relatively impermeable materials. With this, the problems of recharging and drying up of borehole can be solved.
The comparative analyses of four wells in "X" Field within the Niger Delta were carried out with ... more The comparative analyses of four wells in "X" Field within the Niger Delta were carried out with the aim of determining the hydrocarbon potential of the shaly-sand reservoirs using the Archie and Simandoux Models. The plots of effective porosity against volume of shale were used to determine the clay distribution. Composite logs comprising gamma ray, resistivity and porosity logs (density and neutron) were utilized to generate petrophysical properties in four (4) wells using Simandoux and Archie Models. Also, statistical analysis of water saturation values for both models were analysed and compared. The results of the plots of effective porosity against shale volume reveal decrease in effective porosity against increase in shale volume. The trends of the plots indicate laminated shale distribution mainly while only one hydrocarbon zone in well 3 denotes dispersed shale. Both models show very good to excellent porosity values (21-36%), and favourable hydrocarbon movability index (0.09-0.43). The statistical analyses show lower standard deviation and mean values of water saturation for Simandoux (0.008-0.2) and (0.03-0.2) when compared with that of Archie Model (0.08-0.24) and (0.15-0.5) which is indicative of higher hydrocarbon saturation than the Archie Model. At 5% error level, statistical test of difference between mean and standard deviation for both Models computed reveal t-statistics range of-20.6 to 1.8 for mean and f-statistics range of 0.005 to 11.5 for standard deviation. Their respective P (probability)-values are less than 0.05, indicating statistically significant difference between mean and standard deviation of the two models. The study reveals that the Simandoux Model has favourable petrophysical parameters indicating higher hydrocarbon potential than the Archie Model. This model could be a valuable tool in a shaly sand environment.
SN Applied Sciences, 2020
The task of minimizing pitfall in quantitative reservoir assessment and evaluation is an integral... more The task of minimizing pitfall in quantitative reservoir assessment and evaluation is an integral aspect of any promising petroleum exploration and evaluation project. The Niger Delta oil province in Nigeria is chiefly composed of several pay zones with many stratigraphic intervals of sand and shale formations in varying proportion. Whereas conventional seismic interpretation technique poses certain degree of uncertainty in reservoir characterization, seismic inversion constraint by log data brings significant improvement in interpretation that reduces uncertainty in the delineation of reservoir characteristics, volume and distribution. In this present study, post-stack seismic inversion and seismic attributes analysis were used to evaluate the potentials and prospects of mapped reservoirs in a field, offshore depobelt, Niger Delta. The implementation of the tasks consists of mapping of structural framework, horizon picking, log editing and correlation, wavelet extraction, building of low-frequency model, acoustic impedance inversion and crossplot analysis of reservoir properties and attributes. A hybrid approach (formulated using Greenberg-Castagna equation) specific for the Niger Delta depobelts was used to estimate and generate shear wave velocity for the wells. Results obtained from inversion depict an acoustic impedance values in the range 150-280 ft/s g/cc and V P ∕V S of 1.25-2.50 at a depth range of 9250-9280 ft within the hydrocarbon-bearing sands in the two wells. Region of low acoustic impedance (representing high reservoir porosity) coupled with a corresponding low V P ∕V S ratio (indicating hydrocarbon accumulation) is presumed to have high prospects for exploration and well development. Altogether the degree of correlation between the inverted and actual impedance was found to be about 90% across the wells. It is evident that the acoustic impedance slice at 3000 ms depicts low acoustic impedance sand within 18,500-20,000 ft/s g/cc at the northeastern and southeastern regions of the field. High reflection amplitudes (bright spots) signifying hydrocarbon accumulation are also revealed on seismic attribute maps with surrounding shale diaper as the source rock. This study has revealed the prospect (i.e., existence of active petroleum system of probable economic value) of the delineated field in the Niger Delta depobelt.
SN Applied Sciences, 2018
The occurrence of collapsible and unstable subsurface materials (clay, silt, peats etc.) in alluv... more The occurrence of collapsible and unstable subsurface materials (clay, silt, peats etc.) in alluvial deposits and other soil deposits throughout the world and the difficulties with building on them have long been recognized. Accordingly inclusive site investigation of subsurface condition is important for construction of engineering structures and buildings on land reclaimed from wetland such as marsh or swamp with soft compressible clays and peat materials. Peatlands common in most coastal areas of Lagos, Nigeria are characteristic waterlogged locations. These areas characterized by low human and economic activities in the past are now considered for building residential houses due to the surging population of the metropolis. Problem usually arises when there is uneven soil settlement which might results in disastrous collapse of structures. This study presents a subsurface geophysical mapping of a site reclaimed by sand filling in Victoria Island, Lagos, using integrated electrical resistivity techniques. The geoelectric data acquired through vertical electrical sounding (VES) and electrical resistivity imaging (ERI) techniques were processed and interpreted to provide a detailed characterization of the subsoil profile and soil parameters of the study area. VES technique employed Schlumberger configuration because of its obvious deeper current penetration, while for ERI, a combination of Werner, dipole-dipole and pole-dipole were utilized. Results from the two procedures show a maximum of four geoelectric strata, with the second and third layers consisting either sandy clay (50 Ωm < ρ < 140 Ωm) or peat/clay (ρ < 50 Ωm). These middle layers are sandwiched between the topsoil and the last layer (composed mainly of sand, ρ > 140 Ωm). Due to the lateral discontinuous and inhomogeneous nature of these sandwiched layers of high compressibility and low shear strength, the possibility of occurrence of subsidence and differential settlement is high. This might result in minor or major failure in building and engineering structures built on such soils. Sand medium encountered at shallow depth of about 0.6-0.9 m, beneath VES 7, 8, 14 and 19, could have been a suitable layer for foundation of buildings and structures except that it is directly underlain by peat/clay. Other locations with competent sand layers for which deep foundation might be required lie at depth within 9.5-30.8 m. Thus, this study has revealed both the lateral and vertical variation with depth of the subsurface strata within the study area. This would assist local structural engineers and builders in designing appropriate and adequate foundation of structures in this area.
Journal of African Earth Sciences, 2017
Three representative rock types (limestone, sandstone, and shale) and glauconite samples collecte... more Three representative rock types (limestone, sandstone, and shale) and glauconite samples collected from Ewekoro Quarry, eastern Dahomey Basin in Nigeria were characterized using low field 2 MHz and 20 MHz Nuclear Magnetic Resonance (NMR) techniques. NMR T 2 relaxation time decay measurement was conducted on disc samples under partial water-saturation and full watersaturation conditions using CPMG spin-echo routine. The T 2 relaxation decay was converted into T 2 distribution in the time domain to assess and evaluate the pore size distribution of the samples. Good agreement exists between water content from T 2 NMR distributions and water imbibition porosity (WIP) technique. Results show that the most useful characteristics to discriminate the different facies come from full saturation NMR 2 MHz pore size distribution (PSD). Shale facies depict a quasi-unimodal distribution with greater than 90 % contribution from clay bound water component (T 2s) coupled to capillary bound water component (T 2i) centred on 2 ms. The other facies with well connected pore structure show either bimodal or trimodal T 2 distribution composed of the similar clay bound water component centred on 0.3 ms and quasi-capillary bound water component centred on 10 ms. But their difference depends on the movable water T 2 component (T 2l) that does not exist in the glauconite facies (bimodal distribution) while it exists in ACCEPTED MANUSCRIPT both the sandstone and limestone facies. The basic difference between the limestone and sandstone facies is related to the longer T coupling: T 2i and T 2l populations are coupled in sandstone generating a single population which convolves both populations (bimodal distribution). Limestone with a trimodal distribution attests to the fact that carbonate rocks have more complex pore system than siliclastic rocks. The degree of pore connectivity is highest in sandstone, followed by limestone and least in glauconite. Therefore a basic/quick NMR log run on samples along a geological formation can provide precise lithofacies characterization with quantitative information on pore size, structure and distributions.
Journal of Science and Technology (Ghana), 2015
Geoelectrical investigation and chemical analyses were carried out at Isheri North area of Ogun S... more Geoelectrical investigation and chemical analyses were carried out at Isheri North area of Ogun State in order to assess the groundwater quality at shallow depth and its deep potential zone for groundwater development. The study area has been selected for investigation due to infiltration of the polluted Ogun River. Forty-three (43) Schlumberger Vertical Electrical Soundings (VES) and chemical analyses of water samples from one hand dug well and two shallow boreholes in the study area were carried out. Four to five geoelectric layers which correspond to top soil, clayey sand, sandy clay, clay and sand were delineated. The longitudinal conductance values (0.02-0.106mhos) of the topsoil in the area reveal its poor to weak protective capacity, thus exposing the underlying clayey sand to contamination as reflected from its resistivity values ranging from 4.8-15.1Ωm. This low resistivity zone at shallow depth (3-26m), occasioned by infiltration, was further ascertained by high values of conductivity, turbidity, total hardness, TDS, Cl, Fe, and Mn ions in the analyzed water samples taken at depth ranges from 9-16m. The results of the analyzed water samples from this shallow zone are beyond international standards for drinking water. The underlying clay resistivity values ranged between 1.9-6.1Ωm and thickness varied from 50.8-100.5m. This acts as the seal for the underlying aquifer (sand layer). The resistivity of the sand layer varied from 91.7-159Ωm with a depth interval of 101.7-109.4m and 73.4-82.3m in VES 1 and VES 14 respectively. This constitutes the deep aquifer units in the study area. The longitudinal conductance values of the overburden above the profound aquifer units varied between 10.5-33.0 mhos and are indicative of very good to excellent protective capacity rating. Thus, the underlying deep aquifer units are well protected from being contaminated.
Current Science, Jul 25, 2017
Dielectric measurements (40 Hz-110 MHz) conducted on samples of limestone and its associated rock... more Dielectric measurements (40 Hz-110 MHz) conducted on samples of limestone and its associated rocks from Ewekoro, Eastern Dahomey Basin, Nigeria has yielded vital information for characterization. Cole-Cole plots manifest a distribution of relaxation times in the rock samples common for multicomponent systems. All the rock types show dielectric dispersion in dry and partially saturated conditions, but the frequency range differs for the rock types and depends on wettability. At partial water saturation there is: (i) enhanced polarization resulting in increase in real and imaginary permittivities; (ii) shortened region of dielectric dispersion; (iii) broadened electrode polarization plateau; and (iv) steeper and shorter dispersion region. Irrespective of the state of the rocks, dielectric parameters for shale and glauconite are at least an order greater than for limestone and sandstone. Geometric or textural effects are partly responsible for the observed differences coupled with the presence of charged clay/clay-like particles in shale and glauconite. Decrease in relaxation and critical frequencies in partial saturation for shale in contrast to the increase in these frequencies for the other three rock types is due the effect of pore geometry on overall dielectric relaxation. This study shows that dielectric measurement can complement geochemical analysis in laboratory evaluation and characterization of rock raw materials.
Joint geophysical and hydrogeochemical assessment of groundwater quality degradation in coastal aquifer systems at a suburb of Kosofe, Lagos, southwest Nigeria
Sustainable Water Resources Management
Earth sciences Malaysia : ESMY
Very low frequency electromagnetic (VLF-EM) survey was conducted along failed segments of some ro... more Very low frequency electromagnetic (VLF-EM) survey was conducted along failed segments of some roads in Ota, southwest Nigeria to reveal the geologic dispositions of subsurface material underlying the road pavements. Geonics EM-16 VLF was employed for data acquisition across a total distance of about 2.6 km. Fourteen traverses were positioned along failed road segments with one control traverse arranged along stable road segments. Real and quadrature field data components were processed via Fraser and Karous-Hjelt filtering to suppress noise and enhance signal strength. Positive peaks of filtered real component on Fraser plots depict the presence of conductive subsurface materials. Good correlation exists between positive peaks on Fraser plots and conductive zones on 2-D current density at several lateral distances and depths across all the traverses. Delineated VLF anomalies represent weak zones that might pose serious threat to road stability. These conductive anomalies are presumably composed of clayey bodies (laterite/lateritic soil) in the subgrade soil used for road construction or unexcavated host materials in the subsurface. Changing volume of clayey materials under varying climatic conditions is a major cause of distress to engineering structures. Clayey materials by virtue of their pore characteristics (high porosity and low permeability) tends to undergo alternating series of expansion and contraction under different climatic conditions. These seasonal dispositions would eventually manifest as cracks and potholes on road pavements. Uneven distribution of different adjacent subsurface lithologies contributes to differential settlement, which is a possible catalyst of road failure.
Copyright © 2014 Lukumon Adeoti et al. This is an open access article distributed under the Creat... more Copyright © 2014 Lukumon Adeoti et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. In accor-dance of the Creative Commons Attribution License all Copyrights © 2014 are reserved for SCIRP and the owner of the intellectual property Lukumon Adeoti et al. All Copyright © 2014 are guarded by law and by SCIRP as a guardian. This study focuses on the application of 3D static model using 3-D seismic and well log data for proper optimiza-tion and development of hydrocarbon potential in KN field of Niger Delta Province. 3D Seismic data were used to generate the input interpreted horizon grids and fault polygons. The horizon which cut across the six wells was used for the analysis and detailed petrophysical analysis was carried out. Structural and property modeling (net to gross, porosity, permeability, water saturation and f...
Geophysical Evaluation of Subsurface Protective Capacity and Groundwater Prospect in a Typical Sedimentary Zone, Eastern Dahomey Basin Using Electrical Resistivity Technique
MALAYSIAN JOURNAL OF GEOSCIENCES
Subsurface protective capacity evaluation is important in groundwater prospecting. With the aid o... more Subsurface protective capacity evaluation is important in groundwater prospecting. With the aid of Dar-Zarrouk parameters which show direct relationship with contaminants infiltration time and transmissivity, joint interpretation of vertical electrical sounding (VES) and 2-D resistivity imaging were employed to evaluate overburden protective capacity and groundwater potentials at Mowe in Obafemi-Owode LGA, southwest Nigeria. Total longitudinal conductance S, total transverse resistance T, longitudinal resistivity ρL and transverse resistivity ρT were computed. Sand/clayey sand was delineated at 70% of the area either as confined aquifers (78%) or unconfined aquifers (22%). S values in 87% of locations has moderate protective rating (0.2071 – 0.5630), one location has good protective rating (0.7736), others have weak protective ratings (0.1053 – 0.1814). The entire area is characterized by low overburden thickness H (7.9 – 25.6 m), which agrees with a correlation coefficient of 0.58 ...
Integrated geophysical investigation of groundwater potential and bedrock structure in Precambrian basement rocks of Ife, southwest Nigeria
Groundwater for Sustainable Development, 2021
Industrial Rock Characterization using Nuclear Magnetic Resonance (NMR): A Case Study of Ewekoro Quarry
Investigating and modelling ground settlement response to groundwater dynamic variation in parts of Lagos using space-based retrievals
Solid Earth Sciences
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Papers by Olawale Olatinsu