During oil production, the change of production states could cause the change of pressure losses through the production facilities, and consequently result in the variations of well-boundary-conditions in time. In the de-coupled reservoir simulators, the well boundary condition (i.e. bottom hole pressure) is estimated and fixed. Therefore, when performing simulations for production prediction, the de-coupled reservoir simulator would fail to predict the behaviors of the well boundary conditions during production. In this case, a simulator that involves the effects of surface facilities is necessary when perform production prediction . The implementation of partially implicit coupling method has faced the issues due to their inaccuracies and instabilities for complex cases. In this case, the fully implicit coupling is demanded for such complex. This research explores the concept and implementation of fully coupling method. This study focuses on investigating the effects of coupling surface and subsurface model on production forecast. This production prediction is performed under simple constraints (i.e. surface production and injection pressures) and various surface facilities. The results from running the coupled model showed that the bottom hole pressures of producers are affected by both the gas-oil ratio (GOR) and water cut. Other surface facility fittings (i.e. chock or valves) and more complex reservoir description are considered in this project as well.
