History Matched Models Can Mis-Lead the Forecasting in the Brownfield Redevelopment Projects: HM to Prediction Transition
Authors: Ranjan Rakesh , Masoudi Rahim , Karkooti Hooman , Salmi Norbashinatun , Othman Mohamad 
Published: March 2015

Abstract
Prediction of remaining oil saturation distribution is vital for any mature field re-development project. Identifying correct areas of bypassed oil pockets and remaining oil saturation is the most essential requirement for planning different activities such as production enhancement, infill, EOR etc. History matched simulation models are often used to predict remaining oil saturation at end of history and forms basis for recognizing sweet spots and production forecasting. However, transition from history to forecast, if done on unconditioned reservoir simulation model, often creates large amount of fluid rate fluctuations. This primarily results due to change in control mode from well rate in history to pressure or target rate during prediction often showing either a jump in oil rate or unrealistic oil rate plateau in forecasting.
Modifying well productivity index during prediction in typically done to get forecasted oil rate consistent with historical rate. But this corresponds to some unphysical change in model at transition and could significantly change drawdown on which well operates during forecast. As forecast period drawdown becomes unrealistically very different from history match, it downgrades the confidence in quality of history match and also the predictive capability of such models.
Although there are several options available in simulators to ensure smooth oil rate transition to forecast but each have their own limittaions and issues. Each of these methods has been evaluated and seen to result in different individual well forecast, leaving different areas of bypassed oil. In mature fields, modeling with an objective of infill candidate identification, production enhancement activities or EOR selection, the presented work explores options to ensure smooth transition from history to prediction without introducing any unphysical modeling artifact in the model.
Discussed in the paper are the reasons for erratic transition, available options to correct it, potential impact of using these options and method used to ensure smooth transition from history to reliable forecast. In this paper guideline, workflow and results is presented and discussed supported by actual field examples. In studied fields, applying various options, significant changes in individual well recovery and remaining oil saturation pattern and therby areas of un-drained oil pockets have been observed, which can potentially mis-lead further development scenarios.

Background
Many oil fields around the world are getting mature and their production rates are on decline. These fields are off their plateaueither because of increasing watercut, GOR or decreasing reservoir pressures, etc. To sustain the production level and enhancerecovery from these mature fields various brownfield redevelopment activities like production enhancement, infill drilling, pressure maintenace and EOR implementation are carried out. Estimating the remaining mobile oil and locating the bypassedoil pockets in mature reservoirs is key to any successful brownfield redevelopment activities. Computer aided reservoir simulation is the most reliable tool to predict the areas of bypassed oil and help in production forecasting for any redevelopment activity. These forecasts are used to determine the economic feasibility of project and aid in investment decisions.