Estimation of the petrophysical parameters of sediments from Chad basin using well logs

Abstract

Three petrophysical parameters; shaliness, porosity and thermal conductivity were estimated from well logs obtained from the Faltu-1 well, the Chad Basin. Shaliness was estimated from four independent methods, and trend lines having goodness-of-fit ranging between 0.078 and 0.6801 best describe depth - shaliness variations. The trends were interpreted to predict the lithologies in the formations. Although the shaliness estimates did all agree, the average effective shaliness appears to grow and wane in patterns consistent with geologic history of the basin. Assessment of the contributions of shaliness methods to the effective shaliness revealed dominance of the gamma ray and thorium-based methods over those based on combined bulk density-neutron porosity and self potential.
Porosity was estimated from three methods, and polynomial trends having fits ranging between 0.0604 and 0.478 describe depth - porosity variations. Interpretation of the trends revealed lithology trend that agree with the trends of shaliness. Estimates of average effective porosities of formations favorably compared with measurements, while analysis of the plots of various functions of porosity with depth allowed for the estimation of the porosities at deposition. Three independent methods were employed to estimate thermal conductivities. Trends having fits ranging
between 0.1202 and 0.7996 best describe the variations of the parameter with depth. The trends also revealed similar lithology structure as did trends of shaliness, and appear to wane and grow in patterns opposed to those of the shaliness. Variations of the well site average thermal conductivities appear to trend with the structural highs. Assessment of the methods ranked their contributions to the effective thermal conductivity.