Comparative analysis of sonic and neutron-density logs for porosity determination in the South-eastern Niger Delta Basin, Nigeria

Abstract

A comparative analysis of porosity values computed from sonic and neutron-density logs obtained from the same well is here presented. The aim is to identify the more reliable logging tool between sonic and neutron-density in the estimation of porosity values in a formation. Two wells from different parts of Niger Delta were logged for Transit times, bulk density and hydrogen index of the formation as a function of depth. The analysis of sonic, density and neutron porosity values shows a conventional trend of decrease in porosity with depth. Sonic porosity values of well A, and well B varies from 1 to 17%, and 27 to 60% respectively while Neutron-Density Porosity values of well A, and well B varies from 24 to 45%, and 21 to 37% respectively. The Coefficient of Variation for sonic porosity data are 56%, and 23%of well A, and well B respectively , similarly the Coefficient of Variation for Neutron-Density porosity data are 15%, and 14% of well A, and well B respectively. Coefficient of variation of Neutron-density log derived porosities is less than sonic log derived porosities; therefore Neutron-density log derived porosity is more reliable tool for porosity data estimation than sonic log derived porosity. Neutron and density logging tool is here recommended for determination of a reliable porosity value of a formation.