Imaging with high definition video camera is an important technique to visualize the drilling conditions and to study the physics of complex multiphase flow associated with the hole cleaning process.The main advantage of visualizing multiphase flow in a drilling annulus is that the viewer can easily distinguish fluid phases,flow patterns and thicknesses of cutting beds.In this paper the hole cleaning process which involves the transportation of cuttings through a horizontal annulus was studied.The two-phase (solid-liquid) and the three-phase (solid-liquid-gas) flow conditions involved in this kind of annular transportation were experimentally simulated and images were taken using a high definition camera.Analyzing the captured images,a number of important parameters like velocities of different phases,heights of solid beds and sizes of gas bubbles were determined.Two different techniques based on an image analysis software and MATLAB coding were used for the determinations.The results were compared to validate the image analyzing methodology.The visualization technique developed in this paper has a direct application in investigating the critical conditions required for efficient hole cleaning as well as in optimizing the mud program during both planning and operational phases of drilling,Particularly,it would be useful in predicting the cuttings transport performance,estimating solid bed height,gas bubble size,and mean velocities of bubbles/particles.