Analytical determination of low velocity layer in 4-D hydrocarbon prospecting in parts of Imo State

Abstract

Generally, Seismic reflection surveys are done in the oil sectors to determine commercially viable hydrocarbon reservoirs but in most cases reflection records are obscured by wave behaviours in weathering layer. Hence, Up-hole refraction surveys are carried out in 3-D and 4-D prospects with a view to delineating the accurate depth or location of hydrocarbon reservoirs with least distortion by precise determination of the low velocity layer (LVL).Thus, Up-hole survey was done here using a 24-channel Seismograph OYO Mcseis 160mx which prints the seismometer responses from geological structures beneath in waveforms. These waveforms were studied and plotted to obtain the layer velocities of the waves and their corresponding layer thicknesses from fifteen randomly selected sites in the field. Analyses of results show that the field of study is basically a 3-layer zone in which the weathering layer thicknesses varied from 2.0m to 3.5m with velocity ranging from 340m/s to 1000m/s The consolidated layer velocities range from 1750m/s to 2050m/s which fall within the range used for static correction on the reflection records. Thus weathering/static corrections here may be eliminated at about 3.0 m deep and at elevation of 20m to 40m above sea level in this field and similar fields.

JONAMP Vol. 11 2007: pp. 393-402