A Computational Study of Cuttings Transport in a Horizontal Well with an Oil-Based Drilling Fluid Modified by Multiwalled Carbon Nanotubes

We have conducted a computational study of the effect of adding multiwalled carbonnanotubes (MWCNTs) to oil-based drilling fluids on the efficiency of cuttings removal froman annular channel simulating a horizontal section of a well. To simulate the process of sludgetransport in an annular channel, a mathematical model based on the Eulerian approach ofa granular medium for a turbulent flow regime has been developed. The rheology of the drillingfluid modified with MWCNTs was described by the Herschel–Bulkley model with experimentallydetermined rheological coefficients. The base oil-based drilling fluid was an inverse emulsion witha ratio of hydrocarbon and water phases equal to 65/35. The concentration of MWCNTs insolutions varied from 0.1 to 0.5 wt %. The size of the transported sludge particles variedfrom 2 to 7 mm. The flow structure of a two-phase flow in an annular channel for variousconcentrations of MWCNTs has been studied. The dependences of the sludge removal efficiencycoefficient, the average slip speed of sludge particles, and pressure losses on the concentration ofnanotubes are obtained. It has been established that the addition of nanotubes leads to asignificant change in the flow pattern of the drilling fluid and, as a result, to a change in themodes of cuttings transport. Addition of 0.5 wt % of MWCNTs leads to an increase in theefficiency of well flushing by approximately 40%. Thus, based on the results of the computationalstudy, it has been shown that the addition of multiwalled nanotubes to oil-based drilling fluids canlead to an increase in the efficiency of cuttings transport in horizontal wells.