Casing correction of slimline density logs for iron ore exploration

Abstract

Slimline geophysical logs are frequently used worldwide in iron ore exploration because they provide key data for ore evaluation. Application can be limited by the fact that many formations associated with iron ore deposits are friable, increasing the occurrence of borehole collapse before geophysical logs can be obtained. A cased-hole correction scheme for density logs based on an existing technique developed for oil and gas (C–thru) has been developed. The technique enables accurate and reliable near-spaced density measurements in a cased-hole (or through-rods) environment by recharacterising the response equations of the density tool to account for the casing or rods. The method effectively treats the casing or rods as part of a 'modified' density tool. The method means that it is possible to obtain quantitative data when the logging tools are run inside the drilling rods. The application of this technique minimizes the risks associated with logging unstable open holes in iron ores, and can reduce costs and operation times.