Determination of Rocks Elastic constants from Compressional and Shear Waves Velocities for Western Niger Delta, Nigeria.

Abstract

The elastic properties of sedimentary rocks in the western Niger delta, Nigeria, have been computed for five oil exploratory wells. The elastic properties were obtained from the continuous borehole seismic
(compressional and shear waves) velocities and density logs. The computed Lame’s constants, ì and ë range from 0.02 x1010 to 1.0 x1010 Pa and 0.26 x1010 to 1.3 x1010 Pa respectively. The computed values of the Young’s modulus, E, range between 0.56 x1010 and 2.53 x1010 Pa. The values of the bulk modulus, K, and compressibility, â, vary from 0.64 x1010 to 2.16 x1010 Pa and from 0.11 x 10-11 to 9.4 x10-11 Pa-1 respectively. The values of the bulk modulus are the largest for all the wells. The calculated values of the Poisson’s ratio, ó, are between 0.2 and 0.41. The computed
values of the elastic properties show that the rocks encountered in the wells are soft and poorly sorted. This is a confirmation of the fact that the wells encountered two major formations (Benin and Agbada Formations). The Benin Formation is made up of sands with high porosity while the Agbada Formation is made up of alternations of sands
and shale lithologies.