Steady-State Gamma-Gamma Density Well Logging for Density Measurement in Friable Rocks

Abstract

This paper presents a new proposal for the application of the gamma-gamma geophysical well logging to determine densities in friable lithology, denominated Steady-State Gamma-Gamma Density in Friable rocks. We detailed calibration and standardization measurement steps for the gamma-gamma well logging tool, as well as the validation steps for density data acquired in the field, specifically, in a mining operation environment.  In order to measure density in friable lithology/materials, a gamma-gamma well logging tool is positioned at the bottom of a borehole at approximately 1 meter depth, measuring density in stationary mode, over a data acquisition period of around five minutes. The final density value is defined based on the average of the accumulated measurements per borehole.  This methodology was developed to overcome the scarcity of density measurements in friable rocks at Vale's operational mining areas. In addition to operational mine areas, the methodology has been successfully applied to acquire density measurements in waste. Using the proposed methodology, it is possible to acquire approximately 15 density values per day, which would not be possible using conventional methodologies that obtain only 2 or 3 values.