Geosciences-Scholarly Publications

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Browsing Geosciences-Scholarly Publications by Author "Adesanya, O"

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    Open Access
    Application of uphole seismic refraction survey for subsurface investigation: a case study of Liso Field, Niger Delta, Nigeria
    (World Applied Sciences Journal, 2013) Adeoti, L; Ishola, K.S; Adesanya, O; Olodu, U; Bello, M.A
    In this paper, an uphole refraction survey was carried out at the location of LISO Field in Niger Delta Nigeria in order to determine/estimate the thickness and velocities of the strata with a view to ascertaining the suitability of these layers for seismic reflection data acquisition and engineering structures. A hole drilled to a depth below the weathered layer contained hydrophones positioned at specific depths and dynamite charge as source of seismic energy. The uphole data were acquired using OYO McSeis seismograph. The time- distance plot obtained using IXsexsegy software was used for picking the first breaks arrivals of the signals. The depth of the weathered layer was obtained from these plots. The upsphere software was used to obtain the velocity of the different layers. The cuttings collected during the borehole drilling reveal sand, clay and gravel in which the sand sequence vary in sizes. Analyses of well-log show that the area of study is a two-layer model and the near surface geology is comparatively stable and inhomogeneous with moderate velocity contrast. The average thickness of the weathered layer to the top of the consolidated layer is 4.8m with an average velocity of 466m/s. The weathering thickness ranges from 2.9-8.9m and the velocity ranging from 362m/s to 689m/s. The consolidated layer velocities ranges from 1642m/s to 1884m/s with an average of 1746m/s sufficient enough to support engineering structures. In order to correct for weathering or statics a datum of about 6m deep would be required as this will eliminate the effect of the weathered layer on any proposed engineering structure to be developed in the area or its environs. This will also be suitable for the acquisition of good quality seismic data in the area. Also, mathematical linear regression models were generated relating the velocities of the layers and depth of the weathered layer which could be used for the prediction of one parameter in the absence of others provided they are within the same geologic environment.
  • Item
    Open Access
    Subsurface Investigation Using Electrical Resistivity and Standard Penetration Test as Guide for Gas Pipeline Installation in Lekki Peninsula, Lagos
    (Electronic Journal of Geotechnical Engineering, 2013) Adeoti, L; Ishola, K.S; Adesanya, O
    The study focuses on the assessment of corrosives probability and cathodic protection potentials of the subsurface layers using Vertical Electrical Sounding (VES) and Standard Penetration Tests (SPT) with a view to ascertaining the suitability of the subsoil information for the installation of gas pipelines. A total of fifteen (15) VES points were carried out using Schlumberger electrode array along three traverses. NSPT -values were obtained at every 1.5m within the four boreholes drilling within the study area. The geo-electric sections produced from the interpreted data reveal three to five geo-electric layers which correspond to top soil, sand, and saline sand. A sand formation with very high resistivity indicates that this layer is not likely to cause corrosion of the buried pipelines as such it gives very good cathodic protection to the pipelines buried within this layer. The saline sand layer, a geo-material is associated with low resistivity which might be due to salt water intrusion, has very high potentiality to corrosion and very poor cathodic protection. It implies that any pipeline buried within this layer would be highly prone to corrosion. The results of the four borehole logs correspond with the depth soundings technique. The study underlines that the results of the NSPT – values of soil samples fall between 15 and 50 which are indicative of medium to dense sand. These values further reveal the competence of the soil strength for engineering purposes. However, the analysis shows the soil type in each layer within geo-electric section is not consistent because it oscillates between sand and saline sand due to their differences in resistivity. Thus, the proposed pipeline infrastructure /facilities to be installed within the study area due to systems design or other factors should be adequately supported with good cathodic protection systems. This study has shown the effectiveness of carrying out geophysical and geotechnical studies prior to burying of pipelines.