IMPROVED LOG EVALUATION IN A LITHOLOGICALLY COMPLEX, GLAUCONITIC RESERVOIR—A CASE STUDY

Abstract

This paper describes a case study of the application of an improved method of formation evaluation from well logs in a pilot area of the Mardie Greensand reservoirs in the Carnarvon Basin of Western Australia. They are lithologically complex reservoirs with a high and highly variable content of glauconite and extensive micro- porosity. These facts, in addition to the presence of other lithological components, make traditional log analysis, in particular the estimation of log-derived values of permeability, difficult if not impossible. The aim of this project was mainly to determine electrofacies and evaluate porosity and permeability from conventional well logs in this area. The sequential steps in the log evaluation of these glauconite-rich reservoirs were as follows: log quality control (borehole environmental corrections and depth matching); analysis of the log response characteristics; determination of litho- parameters used to identify the electrofacies; identification of the so-called hard streaks and their subsequent elimination for the purpose of reading log responses largely unaffected by these horizons; electrofacies identification and classification; porosity and permeability evaluation. The paper presents examples from several wells in the pilot area of the Mardie Greensand to illustrate this study.