Computer simulation of turbulent electrocoalescence

Offshore wells produce some water, and the ratio of water increases during the lifetime of a well, in particular when water is injected to increase the extraction rate. Hence, oil companies demand techniques that enhance the separation of oil and water. A speed-up of the separation process is achieved by applying electric fields to turbulent-flow water-in-oil emulsions. The electric field gives rise to attractive forces between close droplets and increases the probability of coalescence at contact, while the turbulence enhances the frequency of droplet collisions. To improve the understanding of the mutual interaction between the turbulence and the electric field, this thesis presents a framework for computer simulation of turbulent electrocoalescence. The framework is based on the Eulerian-Lagrangian approach where each droplet is tracked and the electric and the hydrodynamic interactions between the droplets are handled. The forces working between two droplets in stagnant oil are modelled and compared with experimental data. It was found that the electric dipole-dipole forces and the filmthinning forces dominate at small droplet spacings. The turbulence felt by the droplets is modelled by a stochastic differential-equation model. A new model is proposed to correlate the fluid velocities seen by close droplets, and this is important for the prediction of the collision velocity, the collision frequency, and the clustering of droplets. Two algorithmic improvements are made: An adaptive cell structure and the cluster integration method. The proposed adaptive cell structure adapts to the number density of droplets and ensures an efficient computation without any input from the user regarding the cell structure. The cluster integration method assembles clusters of droplets that interact and integrates each cluster separately using a variable step-size Runge-Kutta method. A significant speed-up compared to traditional approaches is reported. Finally, the results obtained by computer simulations of turbulent electrocoalescence agree qualitatively with experimental observations in the literature.Paper III reprinted with kind permission of Elsevier, Sciencedirect.co

CO2pipehaz : quantitative hazard assessment for next generation CO2 pipelines

International audienceThis paper presents an overview of the recently commenced CO(2)PipeHaz project focused on the hazard assessment of CO2 pipelines to be employed as an integral part of the Carbon Capture and Storage (CCS) chain. Funded by the European Commission FP7 Energy programme, the project's objective is to address the fundamentally important and urgent issue regarding the accurate predictions of fluid phase, discharge rate and subsequent atmospheric dispersion during accidental releases from pressurised CO2 pipelines. This information is pivotal to quantifying all the hazard consequences associated with failure of CO2 transportation pipelines forming the basis for emergency response planning and determining minimum safe distances to populated areas. The developments of the state of the art multi-phase heterogeneous discharge and dispersion models for predicting the correct fluid phase during the discharge process will be given special consideration given the very different hazard profiles of CO2 in the gas and solid states. Model validations are based on both small scale controlled laboratory conditions as well as large scale field trials using a unique CCS facility in China, the world's largest CO2 emitter. A cost/benefit analysis will be performed to determine the optimum level of impurities in the captured CO2 stream based on safety and economic considerations. The project will embody the understanding gained within safety and risk assessment tools that can be used for evaluating the adequacy of controls in CO2 pipelines, with best practice guidelines also being developed