-In this work, a study on the modeling of sedimentation and transport of barite particles in drilling fluids was developed. The goal of this study was to evaluate the feasibility of using a simplified two-phase model based on conservation equations to describe the sedimentation of particulate material in drilling fluids. The model was evaluated in three different case studies, where the transport and the sedimentation of solid particles in a carrying fluid were simulated. The simulation results included a two-dimensional flow of liquid in the absence of particles; the axial flow of fluid and particles to investigate the existence of the slip velocity; and the one-dimensional particle settling in drilling fluids. The resulting model used to predict the barite sag is based on the conservation equations and uses the Eulerian approach to take into account the two-phase flow. The model was able to predict the barite sedimentation as well as the formation and properties of the bed of particles. Moreover, the proposed model can be used to evaluate the influence of the particle size, the liquid viscosity, and the solids concentration on the sedimentation process of particles in drilling fluids. Experimental work was also conducted in order to estimate the parameters of the proposed model related to the solid-solid force interaction due to solid particles, and the contribution of the pressure gradient. The results were analyzed by using the one-way ANOVA test for a 95% confidence level, and showed significant reproducibility. Therefore, despite to the simplicity of the proposed model, it could be used as a first approach to the modeling of the barite sag in drilling fluids.
Relative permeability curves obtained in laboratory are used in reservoir simulators to predict production and establish the best strategies for an oil field. Therefore, researchers study several procedures to obtain relative permeability curves. Among these procedures are the multiple flow rates injection methods. Thus, this work proposes to develop an experimental procedure with multiple increasing flows. To make this feasible, simulations were initially carried out at CYDAR, aiming to establish flow rates and time necessary to achieve system stabilization, within the limits of the equipment. After that, tests were carried out establishing the minimum time of 5 hours to stabilize the oil production, and the differential pressure at each flow rate. The accounting and minimization of the capillary end effect in these tests were also evaluated. Capillary pressure constraints contributed to minimize the number of possible solutions to the optimization problem improving the fit of solutions for a specific case.
The characteristics of the fluid flows in tool joints were studied experimentally and theoretically in a laboratory scale. The goal of this study was to evaluate the pressure drop in accessories such as tool joints, placed along the drilling columns. The experimental fluid flow loop consisted of a 25-hp positive displacement pump, a 500-liter tank, a 3-HP mixer and a series of circular and annular pipes where the tool joints were installed. Based on the Reynolds number, the fluid flow loop was set to have dynamic similarity with respect to the real hydraulics of oil well fields. CFD simulations were implemented to aid in the design of the fluid flow loop. Pressure drop and fluid flow rate data were experimentally determined in a set of tool joints using water-based muds with non-Newtonian behavior. The CFD simulations showed a good performance on the tool joint simulations. Finally, the literature's correlations originally employed by Petrobras were used to estimate the friction factor, and new parameters for these correlations were established. The evaluation of the parameters improved the predictive capacity mostly in the laminar regime.
The settling of barite, or any other weighting material, causes undesirable fluctuations in the density of drilling fluids. Problems such as stuck pipe, pressure control difficulties and lost circulation are caused by the settling of barite particles. In this work, we studied a biphasic model to describe the settling and transport of barite particles in oil based drilling fluids. The model is based on the conservation equations and uses the Eulerian approach. The model studied was able to predict the settling and the formation of the particles bed, qualitatively the influence of particle size and liquid viscosity and initial solids concentration. We conducted sedimentation experiments to evaluate parameter of the model. The experimental data was analyzed in terms of the one-way ANOVA test for a 95% confidence level and showed significant reproducibility. The simulation results are qualitatively in accordance with the experimental results.
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