The micro-sonde well logging system is a concept for obtaining along-well measurements of temperature, changes in fluid velocity and pressure while drilling. The micro-sondes are encapsulated, self-contained measurement devices designed to follow the flow from the bottom hole assembly to surface. Once retrieved at surface, the measurements can provide information about well conditions such as the presence of cuttings beds, washed out zones and gain/loss zones. Post-processing of the data requires knowledge of the forces acting on the micro-sonde and the resulting trajectories from the release point at the bottom hole assembly and to surface. The main objectives of the studies presented in this work are to understand the micro-sonde motion in the mud flow and to design and construct a demonstration device. We have performed a literature study, CFD-modelling and experiments to better understand the behavior of a micro-sonde in a typical annular flow domain. The trajectory of a single micro-sonde has been investigated as it passes tool-joints under the influence of inner string rotation. Further, the experiments investigated the likelihood of transporting the micro-sonde intact to surface for a drilling application. For the experimental studies, two annular flow loops, one vertical without rotation of the drill-string and one horizontal with a rotating drill-string, including tool-joints and a model bottom hole assembly have been constructed and utilized.