Application of uphole seismic refraction survey for subsurface investigation: a case study of Liso Field, Niger Delta, Nigeria
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World Applied Sciences Journal
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.
Uphole survey , Weathered layer , First break , Hydrophones , Dynamite , Seismic energy
Adeoti, L., Ishola, K. S., Adesanya, O., Olodu, U., & Bello, M. A. (2013). Application of uphole seismic refraction survey for subsurface investigation: a case study of Liso Field, Niger Delta, Nigeria. World Applied Sciences Journal, 26(5), 573-582.