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Home  >  Volume 26 (March 2014)

37. Uphole Seismic Refraction Survey for Low Velocity Layer Determination Over Oga Field, South West of Niger Delta, Nigeria by Alile O.M., Airen J.O., Okunzuwa I.S., Ebomwonyi O. and Olague G. Volume26, (March, 2014), pp277 – 288.
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Uphole seismic refraction shooting experiment aimed at investigating the subsurface layers, was carried out using a three dimensional (3D) approach, to evaluate the weathering parameters in prospect areas, such as weathering thickness or Depth (Dw); weathering velocity (Vw) of the low velocity layer (LVL) and Velocity of sub-weathering or consolidated layer (Vc) in OGA field located South West of Niger Delta. Six uphole locations were drilled using a rotatory (hand operated) drilling machine in the study area. The time-offset curve of the first arrivals for shots from different charge depth inside the borehole was used and time-intercept techniques of seismic refraction interpretation were employed for the different locations (A – F). The weathering thickness was found to vary from 6.0m to 10.0m.The P-wave velocity of the LVL ranges from 328msec-1 to 444msec-1, with an average value of374.3msec-1. Sub-weathering was found in all locations. The velocity of the consolidated zone was found to vary from 1666msec-1 to 1785msec-1 with an average velocity of 1714msec-1.Using the result, the effect of weathering on refraction data was eliminated during seismic data processing .The record playback has a good signal quality with distinct first break times. An Interpretation Software designed by Integrated Data Service Limited (IDSL) a subsidiary of Nigeria National Petroleum Cooperation (NNPC) was employed. A two-layered case was displayed from the graph of each uphole point analysis and the sub-weathering parameters were obtained. Therefore, the weathering velocity and thickness on the prospect area are in correlation with what is obtainable in the Niger Delta weathering statistics.

Keywords:Uphole, Seismic, Refraction Survey, Low Velocity, Layer Media