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 carbon nanotubes (MWCNTs) to oil-based drilling fluids on the efficiency of cuttings removal from an annular channel simulating a horizontal section of a well. To simulate the process of sludge transport in an annular channel, a mathematical model based on the Eulerian approach of a granular medium for a turbulent flow regime has been developed. The rheology of the drilling fluid modified with MWCNTs was described by the Herschel—Bulkley model with experimentally determined rheological coefficients. The base oil-based drilling fluid was an inverse emulsion with a ratio of hydrocarbon and water phases equal to 65/35. The concentration of MWCNTs in solutions varied from 0.1 to 0.5 wt %. The size of the transported sludge particles varied from 2 to 7 mm. The flow structure of a two-phase flow in an annular channel for various concentrations of MWCNTs has been studied. The dependences of the sludge removal efficiency coefficient, the average slip speed of sludge particles, and pressure losses on the concentration of nanotubes are obtained. It has been established that the addition of nanotubes leads to a significant change in the flow pattern of the drilling fluid and, as a result, to a change in the modes of cuttings transport. Addition of 0.5 wt % of MWCNTs leads to an increase in the efficiency of well flushing by approximately 40%. Thus, based on the results of the computational study, it has been shown that the addition of multiwalled nanotubes to oil-based drilling fluids can lead to an increase in the efficiency of cuttings transport in horizontal wells.