NMR imaging techniques have been applied to investigate complex fluid dynamics in pipes and in annular flow conditions. In this application, aimed to simulate drilling and production operations, two lines have been set up to reproduce, at small laboratory scale, respectively, a pipe flow and an annular flow that are typical flow geometries in oilfield wells during drilling. NMR imaging measurements have been performed inside a horizontal-bore magnet with a fluid flow assured in a velocity range of 10-100 cm s(-1). The studies were dedicated to investigate the different flow regimes associated to circulating viscous polymer solutions applied in drilling mud formulations. Early transitions from laminar to turbulent regime were observed at very low Reynolds number (in a range between 300 and 500, to be compared with the theoretical transition value greater than 2100). (C) 2010 American Institute of Chemical Engineers AIChE J, 57: 1393-1401, 2011