The Effects of Clay Content and Porosity on Acoustic Velocity in clastic Sedimentary Formations, in parts of the Niger Delta, Nigeria.

The Variation of the speed of sound with depth is a function ofseveral formation parameters,including, compaction, density, porosity, confining pressure, temperature, and interstitial fluid. Different chemical and mineralogical compositions define different lithologies of the earth formations.Velocity variations are known to correlate well with the lithological character of earthen materials, thus providing important structural and lithological information. As pore-filling materials, clay minerals block the hydraulic paths and greatly reduce the permeability and porosity of earth formations, however, they do not substantially affect the seismic wave propagation; on the other hand, when clay minerals coat the pores of rocks, they considerably alter the seismic properties of the formations, without much effect on the porosity. This study investigates the effects of clay content on the porosity and acoustic velocities of clastic sedimentary formations in parts of the Niger Delta, Nigeria.To attain the aim of this study, two composite well-logs from two wells (JIK 1, and JIK 2) in the SouthSouth(SS) of the Niger Delta were used; from these wells the well parameters were estimated via empirical relations. Based on the estimated well formation parameters, theacoustic velocity with the influence of clay content was evaluated following after the Han et al., (1986) model.The results indicate that, an inverse relationship exists between porosity and velocity, such that an increase in velocity results in a decrease in porosity. it is evident that the linearity of porosity to velocity is more with the porosity - model velocity relationship than just the porosity - velocity relationship. The model velocity was derived from lithological function especially; clay content, which is also a cementing material. Therefore, the presence of clay content in a formation or reservoir makes it possible and easier to infiltrate pore spaces, cement formation materials and reduce porosity that in turn influences more increase in velocity values.