Effects of Fluid Flow in a Porous Cuttings-Bed on Cuttings Transport Efficiency and Hydraulics

The study of effective cuttings transport and accurate prediction of drilling hydraulics has been a major concern for decades in the drilling industry. It is inevitable for deviated wells and long horizontal wells to have a considerable amount of cuttings-bed in the annuli. Common problems with most of the existing models are that they do not consider the drilling fluid flow through a cuttings-bed. A new mathematical model is proposed to identify the effects of fluid flow in porous cuttings-bed and the differences of relative velocities between cuttings and carrier fluid on drilling hydraulics. The carrier fluid flows through the cuttings-bed, forming a porous matrix in which porous media itself is moving or stationary depending on the force balances. This model also considers the pressure losses of carrier fluid flowing through porous media in a cuttings bed layer. This paper specifically describes the model development (including changes in axial forces in continuity and momentum equations due to changes in a deviated well angle), the solution, and simulation results. In order to ensure a comprehensive understanding of the effects of parameters affecting cuttings transport efficiency, a simulation of the hole cleaning mode is performed. This study provides a method to predict cuttings transport efficiency accurately, and to precisely estimate friction pressure losses in deviated wells (hole deviation angle: 30 to 60°), which have the most unstable cuttings bed characteristics.