Siamak Akhshik

The accurate and precise computational models in order to predict the hole cleaning process is one of the helpful assets in drilling industries. Besides the bulk properties such as the flow velocity, particles average size, cleaning fluid properties, etc., that will affect the cleaning process, there is an unanswered question about the microscopic properties of the particles, particularly those which determines the contact characteristics: Do those play a major role or not? The rudimentary answer is not. The first purpose of the present work is to answer this question via a developed computational fluid dynamics coupled with discrete element method (CFD–DEM) in which the six unknown rolling and sliding friction coefficients of particle–particle contact, particle–wall contact, and particle–drill contact are considered as the main microscopic properties of the contacts. The second purpose is to search for optimum values of these coefficients in order to calibrate the CFD–DEM model with the experimental data for a near horizontal well cleaning available in the literature. The verification of the calibrated CFD–DEM model is checked by simulation of the hole cleaning process for different inclination angles of the deviated well. The results indicate the pivotal role of the microscopic properties of the particles on the characteristics of the particle transport mechanism.

The particle shape is an important factor playing critical role in evaluation of the interactions between particles in high-concentration particle-fluid flows. In this paper, the well-known multisphere (MS) approximation approach and the novel rolling resistance approach are utilized to examine their performance in order to simplify the generalized shaped particle’s interactions within the framework of discrete element method (DEM) and computational fluid dynamics (CFD). The performance of two approaches are compared with the perfect particle’s shape geometry, for the limited cases of cubic-shaped and disk-shaped particle flows in a horizontal well drilling process as a reference scenario. Deviation of the MS approximation shape from the perfect particle geometry is evaluated by comparison of macroscopic properties of nonspherical particle. It is determined that the data on macroscopic parameters yielded by the MS model tend to converge to those of the smooth particle with the increasing number of the subspheres. Moreover, the effectiveness of rolling resistance method is investigated by comparison of macroscopic properties of nonspherical particles with approximated MS approach and approximated spherical particles subjected to the rolling friction. The results show that the updated rolling resistance model can reduce the inaccuracy in the prediction of the particles deposit originated from the spherical shape idealization fairly and can be considered where the cost of computations is a restrictive issue.

During the well drilling process, particles are produced in different shapes. The shape of particles can influence the characteristics of particles transport process. The aim of this work is to analyze the effects of particle shape on the transportation mechanism. For this purpose, a three-dimensional model is prepared for simulation of particle transportation with spherical and non-spherical shapes, during deviated well drilling. The motion of particles and the non-Newtonian fluid flow are simulated via discrete element method and CFD, respectively. The two-way coupling scheme is used to incorporate the effects of fluid–particle interactions. Three different samples of non-spherical shapes are constructed using multi-sphere method. The interactions of particle–particle/wall/drill pipe are taken into account via Hertz–Mindlin model. Simulations are carried out for some laboratory-scale configurations and fair agreements with the experimental data available in the literature are established.