Tills r('~arch explored a few opportunIties of Improving the simulations available to reservoir engineers In the 011 and gas Industry. Three very speclflc simu latlon models were used In thIs thesis. Firstly, Improvements were made to an InHow model for a horizontal well by making it possible to run the model for different fluids easily. Se(ondly. a vertical flow model was developed by comb ining a wellknown. multi-phase flow correlation with a multi-phase temperature model. A novel approach was developed to solve these two models In seq uence. Thirdly, this thesis scoped out the application of two different wax crystallization models.[t was the first time that these wax models were tested using a flow simulator.The results obtained from all three simulation models were In par with theory and expectations. It was concluded that these models together would be a very useful tool for both the Industry and for fu rther research work. ACKNOWLEDGEMENTS

There is a lack of comprehensive simulation tools that (a) accommodates the complexities of advanced completions together with near wellbore behaviour, and (b) has reliable wax precipitation models for production planning. In this work, these issues are tackled by combining three specific models. Firstly, a steady-state, three-phase, non-isothermal flow model in advanced horizontal completions was implemented to run fluid specific simulations, thereby calculating field specific flow conditions. This is useful in situations when fluid specific temperature calculations are important, such as wax crystallization. Secondly, a non-isothermal vertical flow model was developed by combining Hagedorn and Brown's multi-phase flow correlation with Ramey's multi-phase temperature model by solving them in sequence (iteratively). The advanced horizontal well model and vertical flow model were coupled iteratively at the bottom hole where the two models meet. Thirdly, two different analytical wax crystallization models were incorporated in the above coupled flow simulator to calculate the location of wax precipitation along the vertical section of the well. These three simulation models, individually and in combination, were tested and found to be in par with theory, expectations and published results. Additionally, significant difference was noted between Ramey's analytical temperature profile (which is a widely used approximation) and the complete Ramey's model integrated with the simulator developed in this work.