Use of sector models with fine grids that preserve the boundary conditions of the full field model has been of particular benefit to studying well coning behaviour for the different well geometries while allowing detail studies of the physics of flow and to optimize production rate by different well designs. The objective of this project was to carry out simulation studies to investigate the pattern of gas coning and water encroachment for a bilateral well with the primary aim of producing oil from a reservoir overlain by a large gas cap in Field A. High precision local refinement studies in the simulation model were undertaken to help place the wells and optimize the completion design at the same time capturing the global field behaviour. This methodology was also used to properly simulate multilateral wells containing inflow control devices, allowing for pressure losses along the wellbore to be equalized and to minimize gas and water coning. Prior to undertaking the simulation studies, several sensitivities were carried out to determine how other parameters such as boundary conditions and grid refinements could affect the output of near well bore models. By taking advantage of the time savings resulting from the generation of reduced fine grid models, several simulations were run to investigate the impact of different well configurations and operations due for instance to close/opening of valves or laterals. The simulation studies resulted in the determination of the pattern of gas coning, water encroachment, optimum vertical placement of the oil lateral and the orientation of the gas lateral as they affect total recovery. The use of Inflow Control Device (ICD) was determined to be of benefit especially in controlling water and gas influx while providing a uniform production profile along the wellbore that delay gas and water coning and this is being incorporated now in the plan of development. Introduction These simulation studies are part of an ongoing reservoir development project for a gas/oil field with an oil rim about 40m thick and large gas cap. The objective of this study was to carry out several sensitivity studies so as to optimize the production of oil using multilateral well and smart completions, while accounting for the uncertainties in developing the model. The main uncertainties that have been identified while developing the static model include determination of the exact fluid contacts GOC and GWC, depth conversion methods, porosity and permeability distribution, which are directly related to facies distribution. Uncertainties in the dynamic model include permeability distribution, relative permeability data, impact of fractures, direction and density, aquifer size and connectivity, and the transmissibility in the z-direction. The main focus of this project was to try to model capture the effects of some of these uncertainties and how they impact the production of oil from the well. The multilateral wells are bilateral with the top lateral drilled through the gas cap with the primary aim of producing gas which will serve as the means for meeting the gas requirements for a natural gas lift system and gas producers when oil production finishes. The well completion is such as to make the gas available at the main bore and at the appropriate depth to lighten the liquid column with the adequate adjustment of the inlet control valves if water breakthrough fractures.