Downhole optical radiometry tool

Abstract

Various methods and tools optically analyze downhole fluid properties in situ. Some disclosed downhole optical radiometry tools include a tool body having a sample cell for fluid flow. A light beam passes through the sample cell and a spectral operation unit (SOU) such as a prism, filter, interferometer, or multivariate optical element (MOE). The resulting light provides a signal indicative of one or more properties of the fluid. A sensor configuration using electrically balanced thermopiles offers a high sensitivity over a wide temperature range. Further sensitivity is achieved by modulating the light beam and/or by providing a reference light beam that does not interact with the fluid flow. To provide a wide spectral range, some embodiments include multiple filaments in the light source, each filament having a different emission spectrum. Moreover, some embodiments include a second light source, sample cell, SOU, and detector to provide increased range, flexibility, and reliability.